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Nanostructured Functional Materials

Research Groups:

  • Nanostructured Materials and Microstructure  (web)
  • Nanotechnologies on Surfaces and Plasma (web)
  • Materials for Bioengineering and Tissue Regeneration
  • Tribology and Protection of Surfaces

Profesores de Investigación

Espinós Manzorro, Juan Pedro

954 48 95 30

Grupo de Investigación:
Nanotecnología en Superficies

Fernández Camacho, Asunción

954 48 95 31

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Rodríguez González-Elipe, Agustín

954 48 95 28

Grupo de Investigación:
Nanotecnología en Superficies


Cotrino Bautista, José

954 48 95 77

Grupo de Investigación:
Nanotecnología en Superficies

Investigadores Científicos

Barranco Quero, Angel

954 48 95 00 + ext. 909596

Grupo de Investigación:
Nanotecnología en Superficies

Sánchez López, Juan Carlos

954 48 95 79

Grupo de Investigación:
Tribología y Protección de Superficies

Yubero Valencia, Francisco

954 48 95 97

Grupo de Investigación:
Nanotecnología en Superficies

Científicos Titulares

Borrás Martos, Ana Isabel

954 48 95 92

Grupo de Investigación:
Nanotecnología en Superficies

Díaz Cuenca, María Aránzazu

954 48 95 42

Grupo de Investigación:
Materiales para la Bioingeniería y Regeneración Tisular

Palmero Acebedo, Alberto

954 48 95 00 + ext. 909620

Grupo de Investigación:
Nanotecnología en Superficies

Rojas Ruiz, Cristina

954 48 95 00 + ext. 909625

Grupo de Investigación:
Tribología y Protección de Superficies

Investigadores/Doctores Contratados

Alvarez Molina, Rafael

954 48 95 76

Grupo de Investigación:
Nanotecnología en Superficies

Gómez Ramírez, Ana María

954 48 95 00 + ext. 90 92 48

Grupo de Investigación:
Nanotecnología en Superficies

López Santos, Mª Carmen

954 48 95 00 + ext. 90 92 48

Grupo de Investigación:
Nanotecnología en Superficies

Sánchez Valencia, Juan Ramón

954 48 95 00 + ext. 90 92 49

Grupo de Investigación:
Nanotecnología en Superficies

Becarios Predoctorales

Obrero Pérez, José Manuel

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Personal Técnico

Rico Gavira, Victor Joaquín

954 48 95 00 + ext. 909677

Grupo de Investigación:
Nanotecnología en Superficies

Personal Contratado

Contreras Bernal, Lidia

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

De Navascués Garvin, Paula

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Fortio Godinho, Vanda Cristina

954 48 95 76

Grupo de Investigación:
Nanotecnología en Superficies

García Casas, Xabier

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

García Valenzuela, Aurelio

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Gil Rostra, Jorge

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Hufschmidt, Dirk

954 48 95 00 + ext. 90 92 45

Grupo de Investigación:
Materiales Nanoestructurados y Microestructura

Orozco Corrales, Noel

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Perea Brenes, Alvaro

954 48 95 00 + ext. 90 92 41

Grupo de Investigación:
Nanotecnología en Superficies

Development of catalysts and supports for CO2 neutral chemical energy storage processes based on liquid organic hydrogen carriers

Research head: María Asunción Fernández Camacho
Period: 1-1-2019 / 31-12-2021
Financial source: Ministerio de Ciencia, Innovación y Universidades
Code: RTI2018-093871-B-I00
Research group: María del Carmen Jiménez de Haro

Abstract [+]

TIle depletion of fossil fuels (in short and long term) and the global warming derived from greenhouse eHect are consequences of the extensive use of these fuels. It is therefore highly desirable to use and develop renewable energies and so eliminate our dependence on fossil tuels. This makes the storage of energy produced by renewable sources (which are ¡ntermittent) an important target. In previous projects we have been working in the study of nanomaterials and catalysts for the storage of hydrogen as a vector of energy transport and storage (H2 cycle). In this new project the research group propose to move into the implementatlon of the liquid organic hydrogen carriers (LOHC) as a promising way of comblning the C02 and de H2 cycles leading to a sustainable energy storage in a carbon neutral cycle.
Small organic molecules, IIke formic acid or methanol, can be used to store the H2 (and energy) coming from renewable sources. These alternative fuels can be combusted themselves or be used to generate H2 directly feeding a fuel cell.
Research will be conducted in this project to the implementation of two processes related to the LOHC technologies:
i) The selective low temperature decomposition of formic acid by heterogeneous catalysis to the on-demand production of carbon monoxide free hydrogen.
ii) The hydrogen production by reforming of alcohols (i.e. biomethanol) in heterogeneous photocatalytic processes.
Catalysis is playing the key role in the implementation of these Iwo processes. Therefore the main objectives and activities in the project are the rational design and preparation of catalysts and supports to study composition-structure-performance relationships for the two aboye mentioned processes. The innovative approach is the application of plasma assisted techniques, like the magnetron sputtering for
thin film growth, as well as plasma treatments of oxidation, reduction and etchlng for the development of nanostructured catalytic coatings and supported nanoparticles. Porous carbon foams supports and Pd based catalysts including Pd, Pd-C, Pd-B or Pd-Cu will be developed for the study of the formic acid decomposition reaction. Ti02-TiOx photocatalytic films with Pt (and/or gold) as co-catalysts will be
investlgated for the photo-reforming 01 methanol.

Nanostructured multilayered architectures for the development of optofluidic responsive devices, smart labels, and advanced surface functionalization (NANOFLOW)

Research head: Angel Barranco Quero y Francisco Yubero Valencia
Period: 31-12-2016 / 31-12-2019
Financial source: Agencia Estatal de Investigación (AEI) y Fondo Europeo de Desarrollo Regional (FEDRE)
Code: MAT2016-79866-R
Research group: Agustín R. González-Elipe, José Cotrino Bautista, Juan Pedro Espinós Manzorro, Fabián Frutos (US), Ana I. Borrás Martos, Alberto Palmero Acebedo, Victor Rico Gavira, Ricardo Molina (IQAC-CSIC), Fernando Lahoz (ULL), Xerman de la Fuente (ICMA-CSIC), Jesús Cuevas (US), M. Fe Laguna (UPM), Antonio Rodero (UCO), M. Carmen García (UCO)

Abstract [+]

NANOFlow is a multidisciplinary Project that aims the development of novel optofluidics sensing devices integrating advanced multifunctional nanostructured materials. The project is solidly grounded in the research group experience in the synthesis of nanoestructured functional thin films, advance surface treatments and development of planar photonic structures The main objective of the project is to combine and integrate the available synthetic and processing methodologies in the fabrication of optofluidic components capable of modifying their physical behavior when they are exposed to liquids. The integration of these optofluidic components together with accessory technologies based on new principles of photonic detection, large surface area microplasmas discharge as light sources or flexible substrates for the fabrication of sensing tags define an ambitious landscape of applications that will be explored in the project. Besides, the modeling of thin film growth in combination with advanced deposition diagnosis methodologies will be combined to adjust the thin film deposition processes to the desired functionalities.Therefore, NANOFlow aims to cover all the scientific-technological chain from the materials development to the final applications including advanced characterization, flexible synthetic routes, alternative low-cost and high throughput process (e.g. atmospheric plasma synthesis), device integration and testing of devices in real conditions.

The NANOFlow research activities will culminate in the development of three innovative devices, namely smart labels for sensing, traceability and anticounterfeiting applications (e.g. smart labels incorporated in food-packaging), a versatile optofluidic multisensing device and an optofluidic photocatalytic cleaning system that will integrate a large area microplasma source, liquid actuated UV/Visible optical switches and a photocatalytic nanostructured surface. All of these devices will operate under the basis of an optofluidic actuation and/or response and are designed to present clear potentialities for direct application in liquid sensing, manipulation and monitoring.

The NANOFlow research activities in the different work-packages and, particularly, the final devices are intended to have a direct impact in the Theme 2 (Seguridad and Calidad Alimentaria) of the “RETOS” defined in the call covering this project proposal.. Besides, some of the activities proposed, in particular the third device are also connected with the Theme 3 (Energía segura eficiente y limpia) of the call. It is very interesting to stress that these activities are of particular relevance in the geographical context of Andalucia where Agriculture,  Food production and Energy are three of the most relevant strategic sectors. 

Super-IcePhobic Surfaces to Prevent Ice Formation on Aircraft

Research head: Agustín R. González-Elipe
Period: 01-02-2016 / 31-01-2019
Financial source: Union Europea
Code: H2020-TRANSPORT/0149
Research group:

Abstract [+]

The accretion of ice represents a severe problem for aircraft, as the presence of even a scarcely visible layer can severely limit the function of wings, propellers, windshields, antennas, vents, intakes and cowlings. The PHOBIC2ICE Project aims at developing technologies and predictive simulation tools for avoiding or mitigating this phenomenon.
The PHOBIC2ICE project, by applying an innovative approach to simulation and modelling, will enable the design and fabrication of icephobic surfaces with improved functionalities. Several types of polymeric, metallic and hybrid coatings using different deposition methods will be developed. Laser treated and anodized surfaces will be prepared. Consequently, the Project focuses on collecting fundamental knowledge of phenomena associated with icephobicity issues. This knowledge will give better understanding of the ice accretion process on different coatings and modified surfaces. Certified research infrastructure (ice wind tunnel) and flight tests planned will aid in developing comprehensive solutions to address ice formation issue and will raise the Project’s innovation level.
The proposed solution will be environment-friendly, will contribute to the reduction of energy consumption, and will help eliminate the need for frequent on-ground de-icing procedures. This in turn will contribute to the reduction of cost, pollution and flight delay.

A full plasma and vacuum integrated process for the synthesis of high efficiency planar and 1D conformal perovskite solar cells

Research head: Angel Barranco Quero
Period: 01-01-2016 / 31-12-2017
Financial source: Union Europea
Code: EU144338_01 Marie Curie Actions
Research group: Juan Ramón Sánchez Valencia

Abstract [+]

Photovoltaic or solar cells (SC) devices –that transform light into electricity- have been extensively studied in the last decades since they represent a promising way to exploit the sun energy. Currently, perovskite-based solar cells(SC) are receiving increasing attention due to their low cost and high efficiency. They are very promising as an alternative for the existing ones, but still need to advance to reach higher efficiency and durability and require synthesis methods compatible with the industrial production of CMOS devices at wafer scale. These recent SC are mostly fabricated via wet methods in planar architecture. Inherent to the nature of the wet approaches, usually appear several drawbacks as contaminations and chemical reactions on the interfaces that might result deterioration of the SC performance.
PlasmaPerovSol main objective is the fabrication of a complete perovskite solar cell device by a full plasma and vacuum integrated process carried out under the premises of the “one reactor concept”. Thus, the different components of the solar cell will be deposited sequentially within a vacuum reactor avoiding exposition of the materials and interfaces to air or solvents. The technology developed by the hosting group combine vacuum deposition assisted by plasma that permits the fabrication of conformal layers over a large variety of templates. This approach is also proposed here to fabricate conformal multilayers over 1D scaffold that will demonstrate the advantages of 1D-SC. Plasma and vacuum processes present as advantage the high purity and stoichiometric control on the deposition within an ample range of materials compositions. The synthesis approach is compatible with large scale industrial production and allows the fabrication of SC on processable and flexible substrates. At the same time, the low temperatures used make the approach compatible with current CMOS technology and by using masks permits their integration on preformed devices.


Development of supported catalysts on porous structures for hydrogen generation and catalytic combustion applications in the framework of renewable energies

Research head: Asunción Fernández Camacho
Period: 01-01-2016 / 31-12-2018
Financial source: Ministerio de Economía y Competitividad
Code: CTQ2015-65918-R
Research group: Asunción Fernández, Mª Carmen Jiménez de Haro, Vanda Godinho, Gisela Arzac, Dirk Hufschmidt, Rocio García

Abstract [+]

The depletion of fossil fuels (in a short and long term) and the global warming derived from greenhouse effect are consequences of the extensive use of these fuels. In this context, hydrogen appears as an attractive, clean and abundant energy carrier in the context of a wider use of clean and removable energies. For the implementation of the “hydrogen economy” many technological challenges regarding hydrogen production (free from CO2), transport, storage (in a safe manner) and combustion (to produce heat or electricity) should be met first. New research will be conducted in this project on the basis of our previous results regarding the study of complex hydrides for hydrogen storage and the development of catalysts and processes for hydrogen generation and use in portable applications. In particular, new catalysts will be developed on porous structures such as polymeric, metallic and ceramic membranes and/or foams with high actual interest.  Catalysts will we developed and studied for hydrogen generation and combustion reactions according to the following research lines:

1) Development of new materials (catalysts and supports) with a high added value of the complete system catalyst + support. Porous Ni and SiC foams together with PTFE membranes will be selected as supports for the studies. The main objective is to design new catalysts on technologically interesting supports such as separating membranes, electrolytes, electrodes and/or hydrogen combustors. These new catalysts will be developed following the objective of reducing the amount of noble metals by combining or replacing with another non-noble metals (e.g. Pt-Cu and Ni-Fe) and/or with metalloids (e.g carbides, borides, etc). Wet impregnation methods will be used and special emphasis will be put on the use of the PVD methodology (magnetron sputtering) recently employed in our laboratory for the fabrication of Co thin films with very good results. The latter methodology opens a highly interesting research field because permits to tune microstructure and composition (i.e. Co, Co-B, Co-C) on demand.

2) Characterization of the prepared materials from a microstructural and chemical point of view. Modern nanoscopies will play a key role in the characterization, comprehension and further improvement of these highly nanostructured catalysts.

3) Catalytic studies on the prepared materials will be carried out in three catalytic tests: i) the hydrogen generation through hydrolysis reactions, ii) the photocatalytic water splitting, and iii) the catalytic hydrogen combustion. These reactions are of high interest in the context of the hydrogen economy.

--The interaction of these three research lines as proposed in this project will permit to achieve basic knowledge on the rational design of nanocatalysts supported on porous materials. Structure-composition-activity relationships will be established through catalytic and photo-catalytic studies in combination with characterization techniques based on high resolution analytical TEM and additional spectroscopic techniques.

High temperature energy application coatings

Research head: Juan Carlos Sánchez López
Period: 01-01-2016 / 31-12-2018
Financial source: Ministerio de Economía y Competitividad
Code: MAT2015-65539-P
Research group: Iñigo Braceras Izaguirre (INASMET), Teresa Cristina Rojas Ruiz, Maria Belinda Sigüenza Carballo

Abstract [+]

The protection of surfaces from thermal, wear and oxidation phenomena has reached a substantial progress by developing new materials and coatings with improved properties as extreme hardness, low friction and wear rates, increased thermal and oxidation resistance. These improvements suppose a huge energy-saving and cost reduction due to the increased life-time of mechanical components without needs of replacement as well as a reduction in the environmental impact. This field of research has a deep impact in a large variety of industrial sectors (energy, machining tools, automotive, aeronautic, metallurgy, etc.). The challenge for most of these surface functionalization procedures is to get a strict control of the micro and nanostructure of the surface and interfaces that make possible the advent of new properties and applications that nanotechnology concept offers.

In this project, tailored nanostructured coatings for protection of components submitted to high temperature and aggressive environments are prepared seeking for an improved performance. This goal will be explored for three different applications that would contribute to an energy efficiency, renewable energies and solutions to decrease environmental impact. Based on the Cr-Al-N system, different coatings will be prepared by reactive magnetron sputtering technology changing chemical composition (metal content, incorporation of dopants like Y or Si); microstructure; phase distribution; architecture (multilayer/ nanocomposite) or more complex structures (tandem, multilayer gradient) on appropriated substrates depending on the foreseen application: a) oxidation resistance at high temperature (up to 1000ºC) for tool components; b) thermal stable solar selective absorber coating for mid (300-500ºC) and high temperature (>600ºC); c) corrosion resistant coating for supercritical turbine components (650ºC and 100% steam atmosphere).

The investigation of the oxidation mechanisms, phase transformations, structural modifications, etc. will be object of a careful study directly over the defined substrates for these applications to get fundamental knowledge on the degradation phenomena and protective effects. The establishment of the relationships between the initial properties and observed functional performance will enable the better understanding of the protection mechanisms and the optimization of such nanostructured coating systems for the selected application.


Keywords: Coating, high-temperature, oxidation-resistant, corrosion, nanostructured, energy, solar absorber, multilayer

Purely organic and hybrid organic-inorganic spin valves on supported nanowires produced by advanced vacuum and plasma-assisted deposition techniques

Research head: Víctor López-Flores
Period: 01-10-2015 / 30-09-2017
Financial source: Junta de Andalucia
Code: TAPOST-234
Research group: Supervisor: Ana Borrás Martos. Cmponentes: Angel Barranco Quero, Francisco Aparicio, Juan Ramón Sánchez Valencia

Abstract [+]

The transition to organic electronics requires new devices on the nanometer scale composed only by organic materials, providing small, flexible, transparent and cheap devices. Among electronic devices, the spin valves have stood out for their rapid transfer from the experimental phase to the general public products, but a reliable organic spin valve nanometric device is yet to be developed.
The scientific objective of this project is to fill that gap. By using advanced, industrially scalable nanotechnology methods, we intend to produce a hybrid organic-inorganic and a fully organic spin valve in the form of a supported nanowire of ~200 nm width and several microns length, with a concentric spin valve stack. Three main fabrication techniques will be used: organic Physical Vapor Deposition (O-PVD), plasma-enhanced Chemical Vapour Deposition (PE-CVD) and remote plasma assisted vacuum deposition (RPAVD). Magnetoresistance measurements will be performed on single nanowires by conducting-probe atomic force microscopy (CP-AFM), and will give the definite measurement of quality of the samples produced.
This project will be developed within the Nanotechnology on Surfaces research group (NanoOnSurf), at the Institute of Materials Science of Seville (CSIC – University of Seville), located in the multidisciplinary CicCartuja research centre (Seville, Spain). State-of-the-art synthesis and characterisation techniques developed in the host research group will be the key for the success of this proposal..
This project is directly related with Horizon 2020 Work Programme 2014-2015, chapter 5.i, action ICT 3 – 2014: Advanced Thin, Organic and Large Area Electronics (TOLAE) technologies, and thus is expected to have a strong impact in the future European electronic industry.

Application of advanced electron microscopy techniques to the characterization of nanostructured coatings for clean energy applications

Research head: Ana María Beltrán Custodio
Period: 01-03-2015 / 28-02-2017
Financial source: Junta de Andalucía
Code: TAHUB-050. Programa Talent HUB
Research group:

Abstract [+]

This project is focus on the hydrogen generation and storage with the aim of producing hydrogen for clean and sustainable energies. It happens due to an exothermic reaction where a catalyst is required to do so safety. Catalysts based on noble metals are good candidates for this purpose such as, cobalt, cupper… Here, the complete catalysts systems and different supports are studied. They have been grown by magnetron sputtering technology. The structure and composition are studied, up to nano-scale, by advanced scanning-transmission electron microscopy techniques, (S)TEM, such as high-resolution (HRTEM), high-angle annular dark field (HAADF), energy dispersive X‑Ray (EDX), electron energy loss spectroscopy (EELS), for chemical analysis. Furthermore, the use of the three-dimensional characterization technique electron-tomography provides a full understanding of the analysed material. The combination of structural and compositional analytical microscope techniques, in both STEM and TEM mode, allows a full nano-characterization of the systems. The (S)TEM analyses are the essential tool to determine the relationship among the microstructure, the growth conditions and the final behaviour and properties of the systems which will help to improve them and, therefore, to contribute to the production of clean energy.

This project has four main strategic objectives:

1. Nano-materials for sustainable energy applications. Materials for the production, use and storage of Hydrogen.
2. Development of sputtering technology for the fabrication of nanostructures (thin films, coatings and controlled microstructure multilayers).
3. Development of the potential capabilities of the Laboratory for Nanoscopies and Spectroscopies (LANE).
4. Use of advanced structural and analytical techniques for the nano-analysis of new nanomaterials.

Synthesis and properties of luminescent nanoparticles for biomedical applications

Research head: Alberto Escudero Belmonte
Period: 01-10-2014 / 30-09-2016
Financial source: Junta de Andalucia
Code: TAPOST-234
Research group:

Abstract [+]

Luminescent nanoparticles are currently attracting wide research interest in Nanobiomedicine due to their applications, ranging from optical biolabels for imaging of tissues or intracellular structures to sensors to detect biological molecules, and as tracking devices. This project is focused on the design of new, cheaper, and environmentally friendly synthesis methods of uniform luminescent nanoparticles, such as rare earth doped fluorides, phosphates, molybdates, and vanadates. It also evaluates their biomedical applications, with especial attention to their sensing properties and their ability to detect tumour cells. This scientific work includes the characterization of the resulting materials, the optimization of their optical and magnetic properties, and the development of different functionalization processes. The final step of this research project deals with the study of the interaction of the functionalised nanoparticles with cells of different nature, and includes cytotoxicity studies, with special attention to the role played by the morphology and chemistry of the particles.

Development of processes for the catalytic combustion of hydrogen and study of the integration in devices for portable applications

Research head: Asunción Fernández Camacho
Period: 16-05-2014 / 15-05-2016
Financial source: Junta de Andalucía
Code: P12-TEp-862
Research group: Julián Martínez, Gisela Arzac, Dirk Hufschmidt, Joaquín Ramírez, M.Carmen Vera, Vanda Godinho, Lionel Cervera, T.Cristina Rojas, Olga Montes, Mariana Paladini, Jaime Caballero-Hernández

Abstract [+]

Hydrogen is an attractive candidate as a vector for storage and transport of energy in the context of an increased use of renewable and clean energies. The production and use of energy based on hydrogen technology is particularly important for small-scale portable (and potentially scalable for stationary) applications. In this project the process of catalytic (controlled) combustion of hydrogen will be investigated in the various aspects that could lead to a final integrated configuration with a H2 generation system for portable applications. For that the project will take advantage of the synergy of integrating two researcher groups from the PAI: i) The TEP217 group, specialists in storage and generation of hydrogen based on metal hydrides, complex hydrides and hydride composites reactive systems; and in the use of catalysts and additives to control and improve the kinetics of these processes. ii) The FQM342, specialist group for the fabrication of porous ceramics of high interest as catalyst supports for harsh combustion environments. Further collaboration is completed with the participation of the company Abengoa Hidrógeno SA that will be involved as sub-contractor as specialist in systems for the production and storage of hydrogen.
In particular we will work on this project in the following lines:
1.- Development of catalysts and supports for catalytic combustion. Typically porous biomorphic silicon carbide ceramics and classic noble metal catalysts, as well as new low cost catalysts to be developed in the project.
2.- Development of reactors needed for the study of the catalytic combustion. Typically hydrogen flows from a few ml/min to the scale of a H2 generator already available in the range 0.5 to 1.5 L/min.
3.- Coupling the catalytic combustion system with a portable hydrogen generation systems that we have developed in previous projects.
4.- Application of the sputtering technology in an exploratory manner in this project to deposit the catalyst materials for the H2 catalytic combustion on porous substrates.
5.- Microstructural and chemical characterization of the supports and catalysts in the nanoscale to follow the procedures of synthesis and evolution in operation.


Dielectric Barrier Discharge plasma for the developing of industrial process at atmospheric pressure (DBD-Tech)

Research head: José Cotrino Bautista
Period: 30-01-2014 / 29-01-2017
Financial source: Junta de Andalucía
Code: P12-FQM-2265 (Proyecto de Excelencia)
Research group: Francisco José García García, Jorge Gil Rostra, Richard M. Lambert, Manuel Macías Montero, Alberto Palmero Acebedo, Victor Rico Gavira

Abstract [+]

This research project aims first the study of different unknown basic aspects of the construction of the dielectric barrier discharge, better design conditions for: barrier electrodes, the design of the metallic electrodes and dielectrics and to know the best working conditions (size and operation frequency) for the plasma. One goal is to control the lateral functionalization of advanced materials and other objective, is the discovering of new plasma catalysis processes that can increase selectivity and the reduction of energy consumption by plasma chemical reactions in controlled industrial processes of high added value and/or impact. It is expected for both applications, a clear advance in optimization of the industrial process.

Environmental and process monitoring with responsive devices integrating nanostructured thin films grown by innovative vacuum and plasma technologies

Research head: Agustín R. González-Elipe
Period: 01-01-2014 / 31-12-2017
Financial source: Ministerio de Economía y Competitividad
Code: MAT2013-40852-R
Research group: José Cotrino Bautista, Ricardo Molina Mansilla, Victor Rico Gavira, Francisco Yubero Valencia, Juan Pedro Espinós Manzorro, Alberto Palmero Acebedo, Angel Barranco Quero, Fernando Lahoz Zamarro

Abstract [+]

This project aims at the development of a new generation of low dimensional responsive systems and sensors that integrate nanostructured layers with well-controlled electrical and optical properties which, prepared by innovative vacuum and plasma methods, present a tunable and high porosity and are able to actively interact with the environment. The basic principles of the oblique angle approach (OAD) during the physical vapor  deposition (PVD) of evaporated thin films will be extended to the fabrication of similar layers by plasma and magnetron sputtering techniques. Combination of these techniques along with other innovative plasma technologies, including atmospheric pressure plasma deposition or plasma-evaporation polymerization will be employed to achieve a strict control over the nanostructure and properties of  final films and complex systems . Supported metal and oxide  nanostructured thin films, stacked multilayers and hybrid and composite suported nanostructures will be prepared and thereafter characterized by advanced electron and proximity microscopies and other techniques. Process-control strategies will be implemented in order to understand the fundamental mechanisms governing the film structurations and to propose new synthetic routes scalable to industrial production so as to achieve tailored morphologies and properties for these porous thin film materials. Highly ordered and homogenous arrays of these nanostructures will be used  as ambient temperature gas and liquid sensors, microfluidic responsive devices and intelligent labelling tags. For these applications the supported porous thin films will be suitably functionalized with metal nanoparticles, grafted molecular chains or layers of other polymeric materials. They will be also stacked in the form of vertically ordered photonic structures. Innovative device integration approaches including the water removal of evaporated sacrificial layers of NaCl and their integration in the form of microdevices will be carried out to fabricate advanced sensors, microreactors  and responsive systems. Photonic, electrical and/or electrochemical principles of transduction will be implemented into the devices for detecting and/or fabricating  i) oxygen and chlorine in solutions, ii) glucose and organic matter in water  iii) gas and vapor sensors or iv)  inteligent labels. Specific applications are foressen for the control of the outside environment (air and waters), industrial and greenhouse locations, agroindustrial processes such as fermentation and the tracking and trazability of different kinds of goods and foods.

It is expected that the combination of scientific breakthroughs in thin film technology and new film engineering principles at the micro- and nano-scales will open new areas of research with a high impact in key enabling technologies such as photonics, nanotechnology, advanced materials and in other fields like plasma technology and microfluidics.

New multifunctional 1D hybrid nanostructures for selfpowered nanosystems

Research head: Ana Isabel Borrás Martos
Period: 1-01-2014 / 31-12-2016
Financial source: Ministerio de Economía y Competitividad
Code: MAT2013-42900-P
Research group: José Cotrino Bautista, Ricardo Molina Mansilla, Juan Pedro Espinós Manzorro, Ana Isabel Borrás Martos, Angel Barranco Quero

Abstract [+]

HYBR(1)D is a multidisciplinary Project that aims the development of novel multifunctional nanostructured materials for applications as renewable energy devices, photonics and device miniaturization. The main objective of the project is the development of original synthetic strategies for nanostructured 1D materials like organic and inorganic nanowires and other hybrid hetero-structured systems. Special attention will be paid to the development of coaxial “core@shell/multi-shell” structures integrating organic, metallic and oxide nanostructured components. These materials will be synthesized using an innovative methodology compatible with processable substrates of different nature that will be fully scalable to industrial production. In addition, the project also included exploratory studies about self-supported composite membranes where the nanostructured 1D materials will be embedded.

A second project objective is to probe the functionality of the novel 1D nanostructures in different applications under the global strategy that we defined as development of “selfpowered nanosystems”. These applications are: energy power generation devices (solar cells and piezoelectric nanogenerators) and nanosensors. It is worthy to notice that although the materials under study are relatively diverse, from semiconducting inorganic nanotubes (TiO2, ZnO) to organic single-crystal nanowires (“small molecules”) or hybrid heterostructures, the synthetic vacuum methodologies are, in all the cases, very similar and easily adaptable. These methodologies are physical vapor deposition (organic molecules), plasma assisted vacuum deposition (organic molecules and inorganic oxides), metal dc-sputtering and oxygen plasma etching. All of them can be used sequentially or in combination and are integrated in the same reactors. The project PI and the Nanotechnology on Surface group from the ICMS-CSIC have a solid background in the use of plasma and vacuum technology for the study of functional thin films and devices that is being extended to the field of 1D supported nanostructures in the recent years. HYBR(1)D project intend to cover all the scientific-technological chain from the materials development to the final applications including advanced characterization, flexible synthetic routes, device integration and testing at laboratory scale.

Microfluidic integrated sensors for the control of fermentation

Research head: Agustín R. González-Elipe
Period: 2-12-2013 / 31-12-2015
Financial source: Ministerio de Economía y Competitividad
Code: RECUPERA2020 - 1.4.1
Research group: Juan Pedro Espinós Manzorro, José Cotrnio Bautista, Francisco Yubero Valencia, Alberto Palmero Acebedo, Angel Barranco Quero, Ana I. Borrás Martos, Victor J. Rico Gavira, Rafael Alvarez Molina, Pedro Angel Salazar Carballo

Abstract [+]

The objective of this Project is the development of new integrated and robust micro/nano- fluidic systems that enable the reliable incorporation of control tests, sensorization and rapid analysis of agrofood products, mainly liquids or soluble. The technology to be developed should be applied to final products, as well as during their different elaboration steps. IN particular, a niche of application that will be directly addressed in the project is the control of fermentation process with the development of new integrated fluidic transductors that permit the quantitative detection of glucose and/or other sugars by means of electrochemical and photonic developments integrated in microfluidic and similar devices.

New materials for advanced packaging, intelligent label-ing, anti-counterfeiting and monitoring of agricultural and livestock products

Research head: Angel Barranco Quero
Period: 02-12-2013 / 31-12-2015
Financial source: Ministerio de Economía y Competitividad
Code: RECUPERA2020 - 1.4.2
Research group: Ana Isabel Borrás, Francisco Yubero, José Co-trino, Juan Pedro Espinós, Juan Ramón Sánchez Valencia, Francisco Javier Aparicio Rebollo

Abstract [+]

This Project intends the development of novel materials and processes for intelligent labeling of agricultural and livestock products to improve their traceability. The project is based on the development of active optical structures, laser processing strategies and the fabrication of practical testing prototypes.

Purification of air in greenhouses and food processing centers

Research head: José Cotrino Bautista
Period: 2-12-2013 / 31-12-2015
Financial source: Ministerio de Economía y Competitividad
Code: RECUPERA2020 - 2.2.3
Research group: Ana María Gómez Ramírez, Antonio Méndez Montoro de Damas

Abstract [+]

This project is related with a technology to generate a cold plasma at atmospheric pressure with air flowing through a reactor. The specific objective of this activity is the development of a prototype air purification system for greenhouses, food processing centers, livestock enclosures, or other similar types of markets or enclosures where the concentration of gases harmful to the health of the workers can be very significant by the use of insecticides, fungicides, disinfectants or other compounds. The developed system should be able to purify the air in closed installations and where a large number of chemicals, mainly volatile organic compounds, accumulate in the air that is handled. The cold plasma reactor technology design follows the characteristics of packed-bed dielectric barrier discharge by using ferroelectric dielectric.

New materials for advanced packaging, intelligent labeling, anti-counterfeiting and monitoring of agricultural and livestock products

Research head: Angel Barranco Quero
Period: 01-12-2013 / 31-12-2015
Financial source: Ministerio de Economía y Competitividad
Code: RECUPERA2020 - 1.4.2
Research group: Ana Isabel Borrás, Francisco Yubero, José Cotrino, Juan Pedro Espinós, Juan Ramón Sánchez Valencia, Francisco Javier Aparicio Rebollo

Abstract [+]

This Project intends the development of novel materials and processes for intelligent labeling of agricultural and livestock products to improve their traceability. The project is based on the development of active optical structures, laser processing strategies and the fabrication of practical testing prototypes.

Luminescent devices based on rare earth containing thin films deposited by plasma technology (LUMEN)

Research head: Angel Barranco Quero
Period: 16-05-2013 / 15-05-2016
Financial source: Junta de Andalucía
Code: P11-TEP-8067 (Proyecto de Excelencia Motriz)
Research group: Agustín R. González-Elipe, Juan Pedro Espinós, Richard Lambert, Juan Carlos González-González, Francisco J. García García, Victor J. Rico Gavira, Jorge Gil Rostra, Lola González García, F. Javier Ferrer (CNA), Fabián Frutos Rayego

Abstract [+]

The objective of the LUMEN project is the development of luminescent devices incorporating as active layers rare earth containing thin films deposited by plasma CVD.  The thin films will be deposited by novel synthetic approaches that combined classic approaches as magnetron sputtering and plasma CVD with the sublimation of functional molecules. This methodology is very effective to introduce a controlled amount of functional elements (i.e., rare earth cations of functional organic groups) in the growing film. Due to the full compatibility of the proposed methodology with optoelectronics processes the active layers will be directly incorporated in photonic structures as Bragg reflectors and photonic crystals to fabricate prototype devices. Thus, the LUMEN projects start with the development of new materials but also intend to study the functionality of devices that integrates these novel materials in real life conditions. These devices are intelligent label structures, up-converters and ion detectors.

Development of novel materials and processes for the generation and use of hydrogen mainly in portable applications

Research head: Asunción Fernández Camacho
Period: 01-01-2013 / 31-12-2015
Financial source: Ministerio de Economía y Competitividad
Code: CTQ2012-32519
Research group: Gisela Arzac, Jaime Caballero, Lionel Cervera, Vanda Fortio, Carlos Negrete, Dirk Hufschmidt, Cristina Rojas Ruiz, Roland Schierholz

Abstract [+]

Hydrogen as a vector of transport and storage of energy is a very attractive candidate in the context of increased use of renewable and clean energies. This project will address the study of the different processes that lead to the final configuration of an integrated systems for hydrogen generation and use mainly in portable applications (and potentially scalable for stationary applications). In particular, work will be carried out in this project in the following lines:
a) Research on new lightweight compounds for use in hydrogen generation processes on a small scale by chemical routes (hydrolysis). Typically hydrolysis reactions of borohydrides (i.e. NaBH4) and compounds like ammonia borane, hydrazine borane or hydrazine. This line includes the development of catalysts at the nanoscale using wet chemical methods for their synthesis: Metal-metalloid nanostructures (i.e. Co-B, Co-B-P and similar ones) and bimetallic catalysts (including or not metalloid) of low cost which potentiate synergistic effects (i.e. CoRu, NiPt or Co-Ru-B). The topic also includes the development of portable reactors for these processes and the development of new substrates and monoliths, studies of adherence and durability of the catalyst.
b) Research on new host-guest systems containing hydrogen for reversible storage (loading / unloading). Mainly porous supports (host) like the so called "nanoscaffolds" (based on C or BN) infiltrated with borohydrides materials (guest) (i.e. titanium borohydride) typically used for reversible hydrogen storage. These new materials must present improved charging and de-charging kinetics.
c) Studies of coupling a hydrogen generator system with a low cost fuel cell. Typically a continuous reactor for the hydrolysis of NaBH4 with Co-B catalyst for providing H2 at constant flow rate conditions to directly feed a PEM fuel cell of 60 W.
d) Fundamental studies for the development of catalysts and supports for the controlled combustion of hydrogen. It's a new line in the research group based on wet chemical preparation of noble metal nanoparticle catalysts on commercial porous ceramic supports (i.e. SiC). The line also includes the design of a reactor for laboratory-scale study of heat production by controlled combustion of hydrogen.
e) Development of sputtering technology ("magnetron sputtering") for the preparation of catalysts and nano-structures on various substrates for use in the processes developed in the previous sections. The group has extensive experience in this technology to be applied in novel ways in this project leading to a great versatility regarding nanostructure, composition and addition of additives to improve catalytic activity, durability and selectivity of catalysts.
f) Microstructural and chemical characterization of new materials and catalysts developed in the project. We are dealing typically with materials of controlled nanostructure where modern nanoscopic techniques will play a key role in the custom manufacturing of these materials


Innovative SOFC Architecture based on Triode Operation

Research head: Agustín R. González-Elipe
Period: 01-09-2012 / 29-02-2016
Financial source: Unión Europea
Code: FCH-JU-2011-1
Research group: Francisco Yubero Valencia, Juan Pedro Espinós Manzorro, Angel Barranco Quero, Richard Lambert, Victor J. Rico, Ana Borrás Martos, José Cotrino, Jorge Gil, Pedro Castillero, Fran J. García, Alberto Palmero

Abstract [+]

The development of Solid Oxide Fuel Cells (SOFCs) operating on hydrocarbon fuels (natural gas, biofuel,LPG) is the key to their short to medium term broad commercialization. The development of direct HC SOFCs still meets lot of challenges and problems arising from the fact that the anode materials operate under severe conditions leading to low activity towards reforming and oxidation reactions, fast deactivation due to carbon formation and instability due to the presence of sulphur compounds. Although research on these issues is intensive, no major technological breakthroughs have been so far with respect to robust operation, sufficient lifetime and competitive cost.

T-CELL proposes a novel electrochemical approach aiming at tackling these problems by a comprehensive effort to define, explore, characterize, develop and realize a radically new triode approach to SOFC technology means of an integrated approach based both on materials development and on the deployment of an innovative cell design that permits the effective control of electrocatalytic activity under steam or dry reforming conditions.
The novelty of the proposed work lies in the pioneering effort to apply Ni-modified materials electrodes of proven advanced tolerance, as anodic electrodes in SOFCs and in the exploitation of our novel triode SOFC concept which introduces a new controllable variable into fuel cell operation.
In order to provide a proof of concept of the stackability of triode cells, a triode SOFC stack consisting of at least 4 repeating units will be developed and its performance will be evaluated under methane and steam co-feed, in presence of a small concentration of sulphur compound.

Development of nanostructured protective coatings for extreme environmental conditions (NANOPROTEXT)

Research head: Juan Carlos Sánchez López
Period: 01-01-2012 / 31-12-2014
Financial source: Ministerio de Ciencia e Innovación
Code: MAT2011-29074-C02-01
Research group: T. Cristina Rojas Ruiz; Francisco Javier Pérez Trujillo;Maria del Pilar Hierro de Bengoa;Germán Alcalá Penades; Maria Sonia Mato Díaz; Marta Brizuela; Pablo Corengia; José Luis Viviente; Alberto García;Daniel González

Abstract [+]

In many industrial operations, the machines or tool components in contact are submitted to severe conditions of load, friction, temperature or variable atmosphere. The research efforts are directed towards the development of new multiphase coatings capable to increase their performance by protection of the surface against wear and oxidation that cause failure mechanisms. By appropriate control of the size and distribution of phases, chemical composition and microstructure in the nanometric regime it is possible to obtain multifunctionality as low friction, hardness and thermal stability. To achieve excel in this purpose it is necessary to correlate the macroscopic properties of these coated surfaces (mechanical, tribological, oxidation resistance) with these basic phenomena.

In this project, three types of nanostructured coatings will be prepared using a magnetron sputtering process for protection in running operations under extreme or singular conditions (pressure, temperature, oxidant atmospheres, vacuum, etc.). The chosen systems are constituted by crystals of hard materials (nitrides or carbides) in combination with a second element or phase that improves the practical performance. Thus, nanocomposite coatings consisting of WC nanocrystals dispersed in an amorphous dichalcogenide phase (WS2 or WSe2) are proposed as solid lubricant coatings to run under high vacuum conditions useful for spatial applications or inert environments. In the second case, Y or Zr will be tested as dopant elements in CrAlN coatings with the aim of increasing the corrosion and oxidation resistance and tribological behaviour useful for many industrial fields (machining tools, metallurgy, aeronautic, automotive, etc…). Finally, hard and transparent nanocomposite coatings based on the Al-Si-N system are suggested as protective coatings for optical systems.

In all cases, the project comprises their synthesis, chemical and structural characterization, and validation in tribological and oxidation under extreme condition tests that simulate the final operation conditions. In the case of the hard and transparent coatings, their optical properties will be also analysed. The establishment of the relationships between microstructure and measured properties will be an essential objective, since it enables the better understanding of the action mechanisms, and thus, the optimisation of such nanostructured multifunctional systems for an improved technological benefit.


Advanced laboratory for the nano-analysis of novel functional materials (AL-NANOFUNC)

Research head: María Asunción Fernández Camacho
Period: 01-10-2011 / 30-03-2015
Financial source: Unión Europea
Code: REGPOT-CT-2011-285895
Research group: T. Cristina Rojas, M.Carmen Jiménez, Gisela Arzac, Olga Montes, Inmaculada Rosa, Rafael Alvarez, Vanda Godinho, Juan Carlos Sánchez-López, Hernán Míguez, Agustín R. González-Elipe, Manuel Ocaña, M. Jesús Sayagués, Lionel Cervera, Roland Schierholz, Salah Rouillon, Lucia Castillo, Rocío García, Carlos García-Negrete, Jaime Caballero

Abstract [+]

The AL-NANOFUNC project has been designed to install and fully develop at the Materials Science Institute of Seville (ICMS, CSIC-Univ.Seville, Spain) an advanced laboratory for the Nano-analysis of novel functional materials. Advanced Nanoscopy facilities, based on latest generation electron microscopy equipments, will be devoted to breakthrough research in specific topics of high interest: i) Nanomaterials for sustainable energy applications; ii) protective and multifunctional thin film and nanostructured coatings; iii) nanostructured photonic materials and sensors. To take the ICMS laboratories to a leading position that is competitive in a world-wide scenario, the AL-NANOFUNC project is contemplated to up-grade the actual research potential in several directions: i) improve equipment capabilities regarding the Analytical High Resolution Electron Microscopy facilities; ii) improve the impact and excellence of basic research through hiring of experienced researchers and transnational exchange with the reference centers in Europe; iii) develop and improve the innovation potential of the ICMS’s research by opening the new facilities to companies and stakeholders; iv) organize workshops and conferences, dissemination and take-up activities to improve research visibility. Close collaborations with reference centers and companies in Liège (Belgium), Graz (Austria), Jülich (Germany), Oxford (England), Cambridge (England), Dübendorf (Switzerland) and Rabat (Morocco), as well as with laboratories at Andalucian Universities, are foreseen in this project. Five companies in Andalusia will also collaborate in close synergies to promote the long-term strategic lines of interest for the region in the natural and artificial stone products and solar and renowable energy sectors.

Nanostructured films for operating under vacuum

Research head: Juan Carlos Sánchez López
Period: 01-10-2011 / 31-12-2011
Financial source: Ministerio de Ciencia e Innovación
Code: MAT2010-21597-C02-01
Research group: T. Cristina Rojas Ruiz, Santiago Domínguez Meister

Abstract [+]

In this project, nanostructured coatings will be prepared using a magnetron sputtering process for lubrication of mechanical components used in aerospace applications. These materials must provide wear protection and low friction when operating in ambient air or vacuum environment. The chosen systems to obtain this compromise are constituted by WC nanocrystals dispersed in an amorphous dichalchogenide phase (WS2 or WSe2). These solid lubricant coatings are proposed to enhance the wear resistance, mechanical strength and oxidation resistance in comparison to their conventional MoS2 or DLC coatings for this kind of applications.

Development of Nanostructured Ceramic Coatings and Scaffolds for Bone Regeneration (BIOCEREG)

Research head: María Aránzazu Díaz Cuenca
Period: 06-07-2011 / 05-06-2016
Financial source: Junta de Andalucía
Code: CTS-661
Research group: M. Lourdes Ramiro Gutiérrez, Sara Borrego González

Abstract [+]

The aim of this Project is to advance in the development of new biomaterials with im-proved bioactivity for their application in bone repair and regeneration. The goal is the prepa-ration of new coatings and scaffolds of ceramic materials using laser processing techniques from nanostructured ceramic particulates in the SiO2-CaO-P2O5 system which will be synthe-sised at the ICMS. The hypothesis is the compositional properties and the textural parameters of the particulates in combination with the laser source have potential for processing depositions with controlled macro-nanostructure. It is programmed to prepare two types of prototype pieces: i) Titanium metallic substrates with bioactive ceramic coatings and ii) monolith scaffolds of bioactive ceramic with controlled geometry. There are two milestones to highlight. The first one is the fabrication of prototype pieces (coatings and scaffolds) with reproducibility, homogeneity, micro-nanostructural features, and surface and mechanical properties requirements. A second milestone will be the evaluation of their in vitro an in vivo biological properties. The achievement of both mentioned milestones will lead to the final biomaterial prototype. Bone regeneration biologists and orthopaedic surgeons will study the bioactivity and biocompatibility of the coatings on titanium substrates provided by Synthes which is a leader Company in orthopaedic trauma devices for internal and external fixation and is included in the proposal as EPO. The application of the laser processing to the SiO2-CaO-P2O5 nanostructured ceramic materials is completely new and we believe that it could be optimised for obtaining coatings and reticulated scaffolds while keeping their nanostructural features. The Project integrates material scientist, laser engineers, biologists and orthopaedic surgeons. We believe that this multidisciplinary approach with work in the i) synthesis, processing and characterisation of materials, ii) regeneration biology and tissue engineering and iii) medical practise could achieve results with potential to be transferred to the industry to promote the orthopaedic products to improve Andalusian bone repair and regeneration therapies.

Sun and vision for the present thermal energy. SOLVENTA

Research head: Agustín R. González-Elipe
Period: 4-05-2011 / 31-12-2014
Financial source: Ministerio de Ciencia e Innovación
Code: Proyecto INNPACTO - IPT-2011-1425-920000
Research group: Francisco Yubero Valencia, Juan Pedro Espinós Manzorro, Angel Barranco Quero, Victor J. Rico, Ana Borrás Martos, José Cotrino, Jorge Gil, Pedro Castillero, Fran J. García

Abstract [+]

This Project aims at the development of a series of equipment and devices to monitor the working conditions of solar thermal plants based on light concentration with cylindrical parabolic mirrors. The role of ICMSE in this project focusses on the application of plasma technology systems and the development of thin films able to determine the working conditions of these facilities.

Development of carbon-based composites for biomedical applications

Research head: Juan Carlos Sánchez López
Period: 15-03-2011 / 15-03-2014
Financial source: Junta de Andalucía
Code: P10-TEP 06782
Research group: T. Cristina Rojas, Carlos López Cartes, David Abad, Vanda Godinho, Santiago Domínguez, Inmaculada Rosa

Abstract [+]

This project pursues the development of carbon-based coatings including the tailored synthesis, characterization, evaluation in wear tests and biocompatibility study for the application in artificial implants. The control of the carbon chemical bonding (sp2/sp3) and the chemical composition, including metals as (Ag, Ti) or other elements (B, N, O) will enable to tune the mechanical and tribological properties (hardness, friction and wear resistance) with the aim of improving the final performance. To achieve this goal, the use of magnetron sputtering technique is envisaged to deposit advanced coatings under different synthesis conditions. Next, these carbon composites will be evaluated comparatively in friction and wear tests that simulate the conditions that these materials will face in the final application. In this way, it will be possible to establish the correlation between the observed behavior and chemical and structural characteristics of the prepared layers in cell adhesion tests, cytotoxicity and antibacterial activity. This complete characterization will provide an excellent overview of the possibilities of technological transfer of these advanced materials to the biomedicine.

Process-control in plasmas for the synthesis of nanostructured thin films (PLASMATER)

Research head: Alberto Palmero Acebedo
Period: 15-03-2011 / 14-03-2014
Financial source: Junta de Andalucía
Code: P09-FQM-6900
Research group: José Cotrino Bautista, Ana Borrás Martos, Francisco Yubero Valencia, Rafael Alvarez Molina, Juan Carlos González González, Carmen López Santos

Abstract [+]

Project PLASMATER aims at developing new plasma-based procedures to control the nanostructure, porosity and morphology of deposited thin films, and optimize the material functionalities and applications. From an experimental point of view, plasma-assisted thin film deposition techniques make use of various quantities to define the deposition conditions, such as the electromagnetic power, pressure in the reactor, etc. These quantities controls the plasma properties, which at the same time conditions the growth mechanism of the films. The complexity of the relation between experimentally controllable quantities and growth processes has produced the existence of empirical relations between experimental conditions and final film structure and composition, whose justification from a fundamental point of view is unclear. In PLASMATER we propose to analyze three related aspects of the deposition of TiO2 and ZnO thin films assisted by plasmas: i) complete diagnosis of the plasma bulk and sheath in connection with the material microstructure, ii) functionality of the material, and iii) the de-velopment of predictive numerical codes that calculate the final film microstructure as a func-tion of experimentally controllable quantities. This last part is of relevance because to our knowledge, i) it is the first time in the literature the deposition is fully characterized from a fundamental point of view, ii) this knowledge can be applied to suggest modifications in the deposition reactor in order to enhance different structural properties of the films. In order to carry out the PLASMATER project, we aim at following at mixed theoretical and experimental strategy in order to interactively develop numerical codes of the thin film growth in multiple conditions. All the spatial scales involved in the description must be studied, from the plasma bulk itself (typically of few tens cm), the plasma sheath (below 1 mm), and the surface of the material (tens nm). Advanced diagnosis techniques will be employed to understand the plasma behavior and the film growth. Finally, PLASMATER will focus on the experimental conditions that lead to an optimized performance of the studied materials for advance applications in technology and industry.

Environmentally friendly processing of ceramics and glass (CERAMGLASS)

Research head: Xermán F. de la Fuente Leis
Period: 1-01-2011 / 31-12-2014
Financial source: Ministerio de Economía y Competitividad
Code: LIFE11 ENV/ES/560
Research group: ICMS: Agustín R. González-Elipe, Victor J. Rico, Angel Barranco Quero, Juan Pedro Espinós Manzorro, Jorge Gil, Francisco Yubero Valencia

Abstract [+]

The general objective of the 'CERAMGLASS' project is to reduce the environment impact of thermal treatment of ceramics by the successful application of an innovative laser-furnace technology on planar ceramics and glass. The project plans to construct a pilot plant based on the innovative combination of a continuous furnace and a scanning laser. It aims at demonstrating a considerable reduction in energy consumption and the industrial scalability of the process.
The project primarily aims at showing that it is feasible to produce robust ceramic tile of only 4 mm thick. This would represent a 50% reduction in tile thickness, with consequent reduction in consumption of raw source materials. The project will adapt decoration compositions with more environmentally friendly materials by using the laser processing. Specifically it will adapt screen printing decorations to third-fire products with lustre and metallic effects and decoration inks for planar glass. The replacement of toxic starting materials will allow a minimisation of CO2 and other gas emissions, toxic residues and a reduction of the energy consumption of the process.


Functional porous thin films and 1D supported oxide nanostructures for the development of thin film microfluidics, photonic, valves, and microplasmas (POROUSFILMS)

Research head: Francisco Yubero Valencia
Period: 01-01-2011 / 31-12-2013
Financial source: Ministerio de Ciencia e Innovación
Code: MAT2010-18447
Research group: Agustín R. González-Elipe, Juan Pedro Espinós Manzorro, Alberto Palmero Acebedo, Rafael Alvarez Molina, Juan Carlos González González, Victor J. Rico Gavira, Jorge Gil Rostra, Ana Isabel Borrás Martos, Lola González García, José Cotrino Bautista

Abstract [+]

Functional TiO2, ZnO, SiO2 and doped SnO2 in the form of porous thin films and other supported fiber-like nanostructures will be prepared by plasma deposition and evaporation at glancing angles (GLAD). Precise control of the nano and microstructure of the films and fibers will be attained by selecting appropriate GLAD deposition conditions and, in the case of plasma deposition, by adjusting the principal plasma parameters after modelling the plasma processes and sheath-related phenomena that control the development of the film/fibers nanostructure. The primary objective of the project is to successfully tailor the porosity and other key properties (optical, electrical conductivity, wetting behaviour etc.) of the synthetized materials to enable novel methods of fluid handling (liquids and gases) at the micro and, possibly, nanoscales so as to invent and develop applications in the fields of microfluidic and microplasmas. A further objective is the processing of these structures in both 2D (i.e., lithographic processsing) and 3D by use of laser-based techniques, multilayer stacking of different porous thin film structures and/or selected plasma deposition of hydrophobic patches of other materials such as polymers, silicones, etc. Microfluidic thin film-based devices controlled by light (i.e., photonic valves) will then be developed by employing appropriately designed TiO2 and ZnO porous structures. These materials become superhydrophilic when illuminated with light of <390 nm which will be used to selectively illuminate very small areas (channels, micrometer circuits, etc.) by either a suitable lamp or a laser. Light-controlled microfiltration is envisaged as another new application in this field, whereby preferential diffusion/filtration of polar liquids through the illuminated zones may be induced (i.e. valve open). Achieving prompt reversal of this process (i.e. valve closed) is another challenge that will be addressed by the project. A final, exploratory objective is the modelling, design and development of microplas-mas based on the most promising thin film porous structures developed during the earlier phases of the work. These prototype microplasma devices will consist of porous doped SnO2 thin film electrodes permeable to gases with porous insulator layers (SiO2) acting as separation barriers. Evaluation of the plasma characteristics of these prototype devices will be another distinct task undertaken by the project.

Plasma CVD synthesis of novel organic nanostructured materials integrated in planar devices for photonic sensing and security applications NANOPLASMA

Research head: Angel Barranco Quero
Period: 01-01-2011 / 31-12-2013
Financial source: Ministerio de Ciencia e Innovación. Programa  FEDER Unión Europea
Code: MAT2010-21228
Research group: Ana Borrás Martos, Agustín R. González-Elipe, Carmen Ruiz, M. Carmen López-Santos

Abstract [+]

NANOPLASMA proposes the development of novel techniques based on plasma for the synthesis and processing of new organic functional materials. In contrast with the established plasma technology used in plasma enhanced CVD and plasma polymerization that implies the complete fragmentation of volatile precursor molecules, NANOPLASMA processes achieve the synthesis of new families of fluorescent thin films and supported 1D nanomaterials by controlling the chemistry and fragmentation degree at the boundaries of plasma discharge. The research focuses in the synthesis of organic matrices with a well controlled nanometric microstructure incorporating luminescent dye molecules (i.e. perylenes, rhodamines, phtalocyanines y porphirins) and 1D luminescent organic nanowires formed by similar molecules. The project also contemplates the development of methodologies based on the plas-ma etching and laser ablation for the production of 2D lithographic patterns of the lumines-cent thin films and nanostructures. The research in this line will be completed with basic stud-ies aiming the development of a “chemical patterning” process based on the plasma surface functionalization and chemical derivatization of self-assembled monolayers. Both the synthetic methodologies and the patterning strategies of NANOPLASMA are fully compatible with the present optoelectronic and silicon technologies and can be adapted to wafer scale integration for mass scale production. These materials and processes will be used for the fabrication of two types of proto-type devices: photonic gas sensors and luminescent microstructures for intelligent labelling applications. The gas sensing devices consist of a luminescence film and/or structure integrat-ed onto a 1D photonic crystal with a stacking defect designed and constructed to couple the luminescent signal of the sensor layer. The intelligent labelling devices are patterned litho-graphic structures made on single or multilayer structures of luminescence films with specific functionalities and environmental responses not achieved by any available technology.

Systems for the detection of explosives in publlic infrastructures

Research head: Angel Barranco Quero
Period: 1-09-2010 / 31-10-2011
Financial source: Ministerio de Industria (Contrato: ARQUIMEA)
Code: Centro para el Desarrollo Tecnológico Industrial (Programa CENIT)
Research group: Francisco Javier Aparicio, Agustín R. González-Elipe, Ana Isabel Borrás Martos, Juan Pedro Espinós

Abstract [+]

The objective of the project is the development of thin films with adequate optical properties for their use as active elements in optical gas sensors capable of responding to the presence of gases and/or volatile products produced by the partial decomposition of explosives.

Development of bones regeneration membranes modified at nanometric scale (OSTEOMEM)

Research head: Agustín R. González-Elipe
Period: 03-02-2010 / 02-02-2013
Financial source: Junta de Andalucía
Code: P09-CTS-5189 (Proyecto de Excelencia)
Research group: José Cotrino Bautista, Rafael Alvarez Molina, Carmen López Santos, Jorge Gil Rostra, Antonia Terriza Fernández

Abstract [+]

OSTEOMEM aims at developing disposable and biodegradable membranes for bone regeneration to be use in chirurgic oral and maxillofacial implants for the treatment of defects. During the healing of the bone defects, membranes must simultaneously preserve the formation of soft tissues and promote the filling of the hole by the new bone, so that, after the reabsorption of the membrane, the structure of tissues would be similar to that prior to the chirurgical intervention. To achieve that, the membranes should degrade within the body in a period of four-six months, thus avoiding the need of a second intervention required to remove non-biodegradable membranes. It is expected that the membranes developed in the project are comparable to that of animal membranes and avoid the problems associated with the use of these latter.

Functionalized for hypethermia applications and evaluation of ecotoxicity

Research head: Asunción Fernández Camacho
Period: 03-02-2010 / 02-02-2013
Financial source: Junta de Andalucía
Code: P09-FQM-4554
Research group: J. Blasco, M. Hampel, Carlos López, L.M. Lubián, I. Moreno, Miguel Angel Muñoz, David Philippon, T. Cristina Rojas, Inmaculada Rosa, Carlos García-Negrete

Abstract [+]

This Excellence project is taking profit of the previous experience of the group TEP-217 in the development and characterization of functionalized biocompatible nanoparticles and potentially trying to advance in four directions. a) Continue with the development of nanoparticle based mainly on Au, Ag and magnetic oxides with different functionalizations and microstructure. b) To deepen the physical-chemical interaction with electromagnetic fields (in a wide range of frequencies from kHz to GHz) to produce local heating. Currently, various mechanisms have been proposed (Eddy current, hysteresis, relaxation of magnetic moments and Brownian motion) without enough data yet existing to understand and interpret the experimental results. c) Establish a multidisciplinary collaboration with the group RNM-306, a specialist in ecotoxicity testing, to improve the knowledge of the environmental impact of nanoparticles (mainly gold and silver) in marine ecosystems, which are the ultimate sink for a good part of nanomaterials currently produced. d) Conduct preliminary studies of the toxicity of nanoparticles as a function of applied magnetic field. In any project dedicated to nanotechnology is extremely valuable to introduce studies to determine the toxicological and environmental impact of new materials being developed at present. A key objective of this project is the training of research personnel through the implementation of one doctoral thesis at the Institute of Materials Science of Seville.

Mesoporous materials (HA-SBA-15) functionalized with a collagen-targeted rhBMP-2 and their related collagen hybrid composites for bone tissue engineering

Research head: M. Aránzazu Díaz Cuenca
Period: 01-01-2010 / 31-12- 2012
Financial source: Ministerio de Ciencia e Innovación
Code: BIO2009-13903-C02-02
Research group: M. Lourdes Ramiro Gutiérrez

Abstract [+]

A key component in tissue engineered materials for bone repair and regeneration is the scaffold that serves as a template for cell interactions and the formation on bone-extracellular matrix. This scaffold material also provides structural support to the newly formed tissue. Materials in the ternary system SiO2-CaO-P2O5 have demostrated excellent bioactivity for their use in orthopaedic repair and regeneration. The development of new synthesis routes which combine sol-gel chemistry and Block Copolymer (BCPs) self-assembly procedures have potential to be used as interesting methods to produce mesoporous organised SiO2-CaO-P2O5 materials with improved surface area and reactivity. Previous work carried out by the PI of this application has resulted in the synthesis of a biocompatible material (HA-SBA-15) consisting of calcium phosphate hydroxyapatite (HA) nanoparticles growth within a mesoporous (nano-sized-pore-organised) silica SBA-15 structure. Among their biocompatibility, the high surface area and the ordered distribution of pores with very homogeneous size confers to this material very interesting properties for their application as a matrix material for the adsorption of therapeutic agents, drugs or growth factors with requires their application in a controlled and prolonged release. The bone morphogenetic proteins (BMPs) have been widely used because their potent osteinductive properties and certain recombinant proteins BMP-2 and BMP-7 have been approved by the FDA for their use in orthopaedic surgery. Nevertheless, the use of these growth factors is not very extended due to the very high costs of these treatments and the fear to possible undesired side effects due to the use of high concentrations without any controlled delivery system. On the other hand, recent achievements of the team coordinator of this project application (Subproject 2) has produced and patented a recombinant BMP (rhBMP-2) with an additional decapeptidic collagen type I binding domain (CBD) which has shown that this fusion protein has advantages over native BMP-2, and that its combination with collagen may be better and safer alternative for bone repair. In this SubProject application we propose to work in new synthesis routes to produce a nanostructured composite material (HA-SBA-15) with variations in the textural and HA nanoparticle parameters to optimise improved collagen targeted BMP-2 protein adsorption capacities and delivery properties capacities and kinetics. A related objective will be to find and asses the experimental conditions and variables to incorporate successfully a collagen targeted BMP-2 protein to the nano-organised material. The study will cover the analysis of the biomolecule loading, desorption kinetics and final integrity. A second task of the proposed project will be the consolidation of the nano organised powder precursors in 3D ceramic-collagen hybrids composite scaffolds structures which fulfil requirements of biocompatibility, macroporosity and minimal mechanical stability for be using in the in the vivo experimental models which will be carried out as part of the working plan of the other SubProject (Subproyect 2). Work will be carried out to develop fabrication methods of the nanostructured materials into 3D scaffolds while retaining their nanostructural features. The integration of both the protein free HA-SBA-15 and also the fuctionalised collagen targeted BMP-2 material will be considered.

Polymeric and hybrid nanocomposite thin films for photonic and photovoltaic applications (NANOPHOTON)

Research head: Angel Barranco Quero
Period: 01-01-2010 / 02-02-2013
Financial source: Junta de Andalucía
Code: P09-TEP-5283 (Proyecto de Excelencia)
Research group: Ana Borrás, Fabián Frutos, Lola González-García, Said Hamad, S. Lago, Alberto Palmero, Carmen Ruiz-Herrero, Juan R. Sánchez-Valencia, Johan Toudert

Abstract [+]

The Nanophoton project aims the development of a novel family of materials, struc-tures and device prototypes for application in solar energy, environmental sensing and space communication technology. The starting point of the project is the research in the photonic properties of hybrid nanometric films. These functional thin films will be processed and inte-grated in optical structures. The project encompasses fundamental molecular simulation studies, the development of novel nanometric functional structures, the study of suitable processing/integration procedures and the validation of prototype devices. These devices will be of three kinds: photonic gas sensors, detectors insensitive to the angle of detection for diffuse optical communications and photovoltaic cells. An interesting characteristic of the Nanophoton technology will be its fully compatibility with the current optoelectronic and microelectronic industrial manufacturing processes.

Role of additives in the reactive hydride composite systems for hydrogen storage

Research head: Asunción Fernández Camacho
Period: 01/01/2010 - 31/12/2012
Financial source: Ministerio de Educación y Ciencia
Code: CTQ2009-13440
Research group: Carlos López, Cristina Rojas Ruiz, Gisela Arzac, Dirk Hufschmidt, Raimondo Ceccini, Emilie Deprez

Abstract [+]

Due to the expected short-medium term exhaustion of fossil fuels and due to clime changes produced by the green house effect, it is necessary to reconsider a new global energy policy. Hydrogen, as a vector for energy storage and transport, is an attractive candidate for a clean handling of energy. In the present project it is proposed the study of the so called reactive hydride composite systems (RHC) for hydrogen storage. These systems are based in the coupling of a single metal hydride (i.e. MgH2) with a complex hydride (typically a borohydride compound, i.e LiBH4) to give a reversible reaction that is producing or consuming hydrogen. The system can so be used as a hydrogen storage material according to following reaction: MgH2+2LiBH4 ↔ MgB2+LiH+4H2 (11.4 wt% hydrogen storage capacity). The reaction is improving the heat transfer handling, as compared to pure MgH2, by reducing heat release during the charging process. To improve the kinetic aspects (reduction of operation temperatures and times) it has been proposed the use of catalysts a/o additives. The main objective of the project is to understand the role of these additives to improve the hydrogen sorption kinetics. In particular commercial Ti-Isopropoxide (TiO4C12H28) , TiO2 and VCl3 have been selected as additives for this study. Also other catalysts like Co3B, Ni3B or RuCo will be prepared in our laboratory and also tested. The systems will be prepared and activated by high energy ball milling of the two hy-dride materials milled together with or without the additives (5-10 mol%). Kinetic studies will be carried out by gravimetric and volumetric hydrogen sorption measurements (hydrogen desorption or adsorption vs. time at constant T) and differential scanning calorymetry (DSC) analysis. An exhaustive microstructural and chemical analysis of the systems at the different step (as prepared, desorbed and re-absorbed) will be undertaken by following techniques: X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) coupled to EDX (energy dispersive X-Ray) and EELS (Electron Energy Loss Spectroscopy) analysis, X-Ray Photoelectrton Spectroscopy (XPS) and X-Ray absorption Spectroscopy (XAS). The comparative study of the samples, with and without additives, and the correlation between the kinetic studies and the microstructural and chemical analysis, should clarify the mechanisms of the kinetic improvements produced by the additives. These mechanisms are today far from being understood. On basis of the acquired knowledge we expect to significantly improve the systems with respect to hydrogen storage applications.

Study of Surface modified materials and coatings by ReflEXAFS SURCOXAFS

Research head: Adela Muñoz Páez
Period: 01-01-2009 / 31-12-2011
Financial source: Ministerio de Ciencia e Innovación
Code: MAT2008-06652
Research group: Stuart Ansell, Regla Ayala Espinar, Sofía Díaz Moreno, Lola González García, José Manuel Martínez Fernández, Víctor López Flores

Abstract [+]

X-ray Absorption spectroscopy in reflection mode, ReflEXAFS, is a novel technique yielding the typical information from EXAFS, local structure around de absorbing atom, together with that obtained from reflectometry, such as roughness, layer thickness or density within the near surface region. The technique has also the capability of controlling the thickness of the region probed simply by changing the incidence angle, within a rather interesting range, 20-200 Ǻ. Moreover, in contrast with other surface spectroscopic techniques, such as XPS, it allows the study of buried layers. For all these reasons, it is a useful tool to provide structural information of surface materials, such as those with thin layer structure, coatings and surface modified bulk materials. In previous projects we developed measurement protocols for this technique at using model sample. Herewith we propose to apply the technique to real systems of two types: surface modified steels by nitriding treatments and materials made of mixed thin layers with optic and magnetic properties. Apart form the intrinsic interest of the technique itself and the systems which are going to be prepared and studied, this project is relevant in the framework of the development of XAS-based techniques of potential application in the Spanish beamline at the ESRF, SPLINE, as well as in the new Spanish synchrotron source, ALBA.

Surface functionalisation of materials for high added value applications (FUNCOAT)

Research head: Agustín R. González-Elipe
Period: 15-12-2008 / 15-12-2013
Financial source: Ministerio de Ciencia e Innovación
Code: CSD2008- 00023 (Consolider)
Research group: Fernández Camacho, A., Espinós, J.P., Yubero, F., Cotrino, J., Sánchez López, J.C., Barranco, A., Palmero, A., Rojas, C.

Abstract [+]

FUNCOAT is an integrated project within the application call CONSOLIDER-INGENIO 2010 aiming at the exploitation of synergies existing in the Spanish scientific community, with the general objective of developing principles, processes and devices related to the surface functionalisation of materials. The project integrates 14 well-accredited research centres covering from fundamental and theoretical aspects to final applications. This large effort of integration is critical to achieve substantial advances in this broad field, which go beyond the mere accumulation of results. The research teams belong to different institutions: University, CSIC (responsible for the management of the project) and Technological centres. They maintain scientific relationships among them that extend over the last 15 years. Specific scientific and technological objectives are: understanding of fundamental phenomena driving the modification of surfaces and interfaces, control of the micro- and nano- structure of surfaces and thin films, optimization of thin film deposition methods, process development of multifunctional surfaces for novel applications (mechanical and metallurgical, optical, magnetic, energy, biomaterials, etc) and, finally, the production of new devices based on functionalised surfaces. Other important objectives include the technological transfer of the scientific results to the productive sectors as well as the education and training of scientists, young researchers and engineers. Strategic sectors of our modern society where the activities of FUNCOAT find a direct impact are material processing, energy, environment, health care, agriculture, etc. In order to accomplish an efficient coordination of efforts and the integration of the activities of all the groups, the project is structured around six workpackages: A) Fundamental phenomena in surfaces, interfaces and thin films, B) New processes for the control of the micro- and nano- structure of films and surfaces, C) Mechanical and metallurgical coatings for surface protection, D) Chemical functionalisation and biomedical applications, E) Coatings for optical control, photonic applications and solar energy collection and F) Novel magnetic phenomena in surfaces/interfaces.

Creating and disseminating novel nano-mechanical characterization techniques and standars (NANOINDENT)

Research head: Asunción Fernández Camacho
Period: 01-09-2008 / 31-08-2011
Financial source: Unión Europea
Code: NMP3-CA-2008-218659
Research group: Godinho, V., Philippon, D.

Abstract [+]

Our project aims to gather, improve, catalogue and present characterisation tech-niques, methods and equipment for nanomechanical testing. European-wide activities coordinated by a new virtual centre will improve existing nanoindentation metrology to reveal structure-properties relationship at the nano-scale. These methods are the only tools to characterise nanocomposite, nanolayer and interface mechanical behaviours in the nanometre range. This work will also lay down a solid base for subsequent efforts for defining and preparing new standards to support measurement technology in the field of nanomaterials characterisation. Steps include development of the classical and the dynamic nanoindentation method and its application to new fields, application of modified nano-indenters to new fields as scratching and wear measurement, firm and uniform determination of instrumental parameters and defining new standard samples for the new applications. The virtual centre will disseminate information based on a new “Nanocharacterisation database” built on two definite levels: on a broader level partners will inventory and process all novel nanocharacterisation techniques and, in narrower terms, they will concentrate on nanomechanical characterisation. This will be achieved through the synchronisation of efforts set around a core of round robins but the database will include data of other channels as parallel research work and literature recherché.

Nitrogen Plasmas for the superficial functionalization of materials

Research head: José Cotrino Bautista
Period: 01-02-2008 / 31-01- 2011
Financial source: Junta de Andalucía
Code: P07-FQM-03298 (Proyecto de Excelencia)
Research group: Agustín R. González-Elipe, Francisco Yubero Valencia

Abstract [+]

The project PlasNitro discusses the characterization of nitrogen plasmas in various technological related applications with techniques of deposition and functionalization of materials, reforming and processes of sterilization. Different procedures to measure properties of plasmas will go down to point, plasma that can be used in doping, deposition, functionalization and modification of materials and that contain nitrogen. In all cases by using techniques of diagnosis based in the detection of nitrogen species. Nitrogen is a usual component nowadays, only or in mixtures with other gases, in a lot of processes used in technology of plasma. Its experimental characterization and/or the modeling will allow getting fundamental properties from plasma (electron density, electron temperature, temperature of the gas, reactive species, etc.) and knowing the contribution to the homogenous (in phase plasma) and heterogeneous (in the surface-material interaction) reactions of the appropriate components of nitrogen. Numerical codes to get out the electron energy distribution function in plasma will become elaborate in the project. To this end the evaluation of the vibrational distribution of nitrogen will be necessary previously. This step implies taking into account multiple vibrational-vibrational processes, vibrational-translactional and vibrational-rotational processes. In the project we will be able to obtain models of fluid of the nitrogen plasma with the contributions of the most important species of the plasma. The theoretical calculations will be complemented with experimental measurements using electrostatic Langmuir's probe, this will allow measuring the electron energy distribution function, as well as density and temperature of the electrons. The partial nitrogen pressure in each application and the plasma's neutral components will be controlled by means of an analysis of residual gases. The kinetic modeling of the nitrogen plasma will enable the interpretation of measurements in the plasma out of the thermodynamic equilibrium and by using the Monte Carlo technique of simulation that enable the control of deposition/modification and the nano/microstructure of the materials. We will have, in this way, techniques that they will enable to control themselves and improving the procedures of work and the properties desired in the materials.

Multifunctional nanostructured coatings for mechanical and tribological applications (NANOMETRIB)

Research head: Juan Carlos Sánchez López
Period: 01-10-2007 / 30-09-2011
Financial source: Ministerio de Ciencia e Innovación
Code: MAT2007-66881-C02-01
Research group: Asunción Fernández Camacho, Cristina Fernández, Miguel Angel Muñoz-Márquez, Said El Mrabet, Vanda Godinho, M. David Abad

Abstract [+]

In this In the field of mechanical and tribological applications, the investigations are oriented towards the development of new systems capable to increase the performance of industrial operations, machines or tools by increasing the hardness and diminution of the friction and wear rate of materials under contact or increasing the oxidation resistance. These improvements suppose an energy-saving and cost reduction due to increase of tool life-time without needs of reparation as well as a reduction in the employment of lubricant emulsions with oils and greases. This project goal is to develop bew multifunctional nanostructured sys-tems by the Magnetron Sputtering PVD technique for mechanical and tribological applications where an adequate balance among the above-mentioned properties as friction, hardness and thermal stability are searched. The combination of multiple functions into a materials increase noticeably the material added value. To achieve this general objective, different coatings will be prepared by confinement of size and distribution of phases, chemical composition and microstructure in the nanometric regime. The chosen systems are constituted by crystals of hard materials (nitrides, carbides and borides of transition metals: Cr, Ti, W) that can be surrounded by a second phase that acts as lubricant based on C or dichalcogenides of W and doped with certain metals to increase their thermal resistance (V or Nb). In all cases, the project comprises their synthesis, chemical and structural characterization, and their practical validation in tribological tests of friction and wear. The establishment of the relationships between microstructure and measured properties will be an essential objective, since it enables the better understanding of the action mechanisms, and thus, the optimisation of such nanostructured multifunctional systems for an improved technological benefit.


Chemistry and Electrocatalytic Activity of Nanostructured Nickel Electrodes for Water Electrolysis

Lopez-Fernandez, E; Gil-Rostra, J; Espinos, JP; Gonzalez-Elipe, AR; Consuegra, AD; Yubero, F
ACS Catalysis, 10 (2020) 6159-6170


Herein we have developed nanostructured nickel-based electrode films for anion exchange membrane water electrolysis (AEMWE). The electrodes were prepared by magnetron sputtering (MS) in an oblique angle configuration and under various conditions aimed at preparing metallic, oxide, or oxyhydroxide films. Their electrochemical analysis has been complemented with a thorough physicochemical characterization to determine the effect of microstructure, chemical state, bilayer structure, and film thickness on the oxygen evolution reaction (OER). The maximum electrocatalytic activity was found for the metallic electrode, where analysis by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) demonstrated that the active catalytic phase at the surface after its electrochemical conditioning is a kind of oxidized nickel oxide/hydroxide layer with the thickness of a few nanometers. Electrochemical impedance spectroscopy analysis of these steady-state working electrodes supports that the enhanced performance of the metallic nickel anode vs other chemical states resides in the easier electron transfer through the electrode films and the various interlayers built up during their fabrication and activation. The long-term steady-state operation of the anodes and their efficiency for water splitting was proved in a full-cell AEMWE setup incorporating magnetron-sputtered metallic nickel as the cathode. This work proves that MS is a suitable technique to prepare active, stable, and low-cost electrodes for AEMWE and the capacity of this technique to control the chemical state of the electrocatalytically active layers involved in the OER.

June, 2020 | DOI: 10.1021/acscatal.0c00856

Optical properties of molybdenum in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy

Pauly, N; Yubero, F; Tougaard, S
Applied Optics, 59 (2020) 4527-4532


Optical properties of polycrystalline molybdenum are determined from ultraviolet up to extreme ultraviolet by reflection electron energy loss spectroscopy (REELS). Calculations are performed within the dielectric response theory by means of the quantitative analysis of electron energy losses at surfaces QUEELS-epsilon (k, omega)-REELS software [Surf. Interface Anal. 36, 824 (2004)] that allows the simulation of inelastic scattering cross sections, using a parametric energy loss function describing the optical response of the material. From this energy loss function, the real and imaginary parts of the dielectric function, the refractive index, and the extinction coefficient are deduced and compared with previously published results.

May, 2020 | DOI: 10.1364/AO.391014

Advanced Strategies in Thin Films Engineering by Magnetron Sputtering

Palmero, A; Martin, N
Coatings, 10 (2020) 419


This Special Issue contains a series of reviews and papers representing some recent results and some exciting perspectives focused on advanced strategies in thin films growth, thin films engineering by magnetron sputtering and related techniques. Innovative fundamental and applied research studies are then reported, emphasizing correlations between structuration process parameters, new ideas and approaches for thin films engineering and resulting properties of as-deposited coatings.

April, 2020 | DOI: 10.3390/coatings10040419

A 4-view imaging to reveal microstructural differences in obliquely sputter-deposited tungsten films

El Beainou, R; Garcia-Valenzuela, A; Raschetti, M; Cote, JM; Alvarez, R; Palmero, A; Potin, V; Martin, N
Materials Letters, 264 (2020) 127381


We report on the morphological disparity of the columnar growth in W thin films sputter-deposited by oblique angle deposition. Oriented tungsten thin films (400 +/- 50 nm thick) are prepared using a tilt angle alpha of 80 degrees and a sputtering pressure of 0.25 Pa. Inclined columns (beta = 38 +/- 2 degrees) are produced and the microstructure is observed by scanning electron microscopy. A 4-view imaging is performed in order to show inhomogeneous growing evolutions in the columns. Morphological features vs. viewing direction are also investigated from a growth simulation of these tilted W columns. Experimental and theoretical approaches are successfully compared and allow understanding how the direction of the W particle flux leads to dense or fibrous morphologies, as the column apexes are in front of the flux or in the shadowing zone. 

April, 2020 | DOI: 10.1016/j.matlet.2020.127381

Study of the influence of the precursors on the sensing properties of ZnO:Cu system

Ramos, A; Urbieta, A; Escalante, G; Hidalgo, P; Espinos, JP; Fernandez, P
Ceramics International, 46 (2020) 8358-8367


The properties of ZnO based materials for ethanol detection have been studied. Cu doped samples obtained from different precursors have been investigated. ZnO and ZnS have been used as host and Cu and CuO as dopant sources.

The sensing measurements have been mostly performed at room temperature. To monitor the effect of the presence of gas, resistivity and photoluminescence experiments with and without sensing gas have been carried out. The sensing behaviour is affected by the nature of the precursors used. For ZnO:Cu and ZnO:CuO series, a higher sensitivity is obtained at the lower gas concentrations, the better response is obtained for the sample ZnO:Cu with wt.1% of metallic copper. Strong segregation effects observed in these samples could be deleterious for the sensing properties. In the series ZnS:CuO, no segregation is observed, however the sensing behaviour is erratic and attributed to the reduction of Cu ions to the metallic state.

April, 2020 | DOI: 10.1016/j.ceramint.2019.12.068

A Microstructure Insight of MTA Repair HP of Rapid Setting Capacity and Bioactive Response

Jimenez-Sanchez, MC; Segura-Egea, JJ; Diaz-Cuenca, A
Materials, 13 (2020)


Mineral trioxide aggregate (MTA) is considered a bioactive endodontic material, which promotes natural mineralization at the material-tooth tissue interface. MTA Repair HP stands out because of the short setting time and the quick and effective bioactive response in vitro. The bioactivity, depens on material composition and microstructure. This work is devoted to analyze MTA Repair HP microstructural features, of both the powder precursor and set material, to get insights into the material physicochemical parameters-functionality performance relationships. Transmission electron microscopy (TEM), and field emission gun scanning electron microscopy (FEG-SEM) coupled with energy-dispersive X-ray (EDX) analyses were performed. X-ray diffraction (XRD) measurements were carried out at different times to investigate setting process. Bioactivity evaluation in vitro was carried out by soaking the processed cement disk in simulated body fluid (SBF). The presented results point out those MTA Repair HP precursor material characteristics of tricalcium silicate particles of nanometric size and high aspect ratio, which provide an elevated surface area and maximized components dispersion of calcium silicate and very reactive calcium aluminate. The MTA Repair HP precursor powder nanostructure and formulation, allows a hydration process comprising silicate hydrate structures, which are very effective to achieve both fast setting and efficient bioactive response.

April, 2020 | DOI: 10.3390/ma13071641

In Vitro and In Vivo Study of Titanium Grade IV and Titanium Grade V Implants with Different Surface Treatments

Diaz-Sanchez, RM; de-Paz-Carrion, A; Serrera-Figallo, MA; Torres-Lagares, D; Barranco, A; Leon-Ramos, JR; Gutierrez-Perez, JL
Metals, 10 (2020) 449


The aim of our study is to evaluate different implant surface treatments using TiIV and TiV in in vitro and in vivo studies. An in vitro study was established comprising four study groups with treated and untreated TiIV titanium discs (TiIVT and TiIVNT) and treated and untreated TiV titanium discs (TiVT and TiVNT). The surface treatment consisted in a grit blasting treatment with alumina and double acid passivation to modify surface roughness. The surface chemical composition and the surface microstructure of the samples were analyzed. The titanium discs were subjected to cell cultures to determine cell adhesion and proliferation of osteoblasts on them. The in vivo study was carried out on the tibia of three New Zealand rabbits in which 18 implants divided into three experimental groups were placed (TiIVT, TiIVNT, and TiVT). Micro-computed tomography (micro-CT) was performed to determine bone density around the implants. The results showed that cell culture had minor adhesion and cell proliferation in TiIVT and TiVT within the first 6 and 24 h. However, no differences were found after 48 h. No statistically significant differences were found in the in vivo micro-CT and histological study; however, there was a positive trend in bone formation in the groups with a treated surface. Conclusions: All groups showed a similar response to in vitro cell proliferation cultures after 48 h. No statistically significant differences were found in the in vivo micro-CT and histological study

April, 2020 | DOI: 10.3390/met10040449

Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO2 and SiO2 thin films and multilayers

Garcia-Valenzuela, A; Butterling, M; Liedke, MO; Hirschmann, E; Trinh, TT; Attallah, AG; Wagner, A; Alvarez, R; Gil-Rostra, J; Rico, V; Palmero, A; Gonzalez-Elipe, AR
Microporous and Mesoporous Materials, 295 (2020) 109968


The nano-porosity embedded into the tilted and separated nanocolumns characteristic of the microstructure of evaporated thin films at oblique angles has been critically assessed by various variants of the positron annihilation spectroscopy. This technique represents a powerful tool for the analysis of porosity, defects and internal interfaces of materials, and has been applied to different as-deposited SiO2 and TiO2 thin films as well as SiO2/TiO2 multilayers prepared by electron beam evaporation at 70 and 85 zenithal angles. It is shown that, under same deposition conditions, the concentration of internal nano-pores in SiO2 is higher than in TiO2 nanocolumns, while the situation is closer to this latter in TiO2/SiO2 multilayers. These features have been compared with the predictions of a Monte Carlo simulation of the film growth and explained by considering the influence of the chemical composition on the growth mechanism and, ultimately, on the structure of the films.

March, 2020 | DOI: 10.1016/j.micromeso.2019.109968

Optofluidic liquid sensing on electromicrofluidic devices

Oliva-Ramirez, M; Wang, SL; Rico-Gavira, V; Lopez-Santos, C; Fan, SK; Gonzalez-Elipe, AR
Materials Research Express, 7 (2020) 036407


Electromicrofluidic (EMF) devices are used to handle and move tiny amounts of liquids by electrical actuation, including electrowetting-on-dielectric (EWOD) and dielectrophoresis (DEP). Monitoring the liquid characteristics in one of these devices requires suitable sensing transducers incorporated within the microfluidic structure. In the present work, we describe the incorporation of an optofluidic photonic transducer in an EMF device to monitor the refractive index of a liquid during its manipulation. The incorporated transducer consists of a responsive porous Bragg Microcavity (BM) deposited via physical vapor oblique angle deposition. Besides reporting the manufacturing procedure of the sensing-EMF device combining liquid handling and monitoring, the performance of the BM is verified by infiltrating several liquids dripped on its surface and comparing the responses with those of liquid droplets electrically moved from the delivery part of the chip to the BM location. This study proved that modified EMF devices can incorporate photonic structures to analyze very low liquid volumes (similar to 0.2 mu L) during its handling.

March, 2020 | DOI: 10.1088/2053-1591/ab7fdf

Robust label-free CuxCoyOz electrochemical sensors for hexose detection during fermentation process monitoring

Lopez-Fernandez, E; Gil-Rostra, J; Espinos, JP; Gonzalez, R; Yubero, F; de Lucas-Consuegra, A; Gonzalez-Elipe, AR
Sensors and Actuators B-Chemical, 304 (2020) 127360


Label free electrochemical sensors of glucose are used whenever long-term operation and stable response are required. For this purpose, various metals and oxides of the first transition series have been proposed as alternative to more expensive noble metal electrochemical sensors. In this work we propose a new formulation consisting of copper-cobalt mixed oxides which, in the form of porous and nanostructured thin films with well controlled Co/Cu ratio, are prepared at room temperature in one step by a modification of the magnetron sputtering oblique angle deposition procedure. Films with various compositions were electrochemically characterized by cyclic voltammetry to determine their amperometric response to glucose as a function of voltage and NaOH electrolyte concentration. This analysis showed that films with a Co/Cu atomic ratio equal 3.4 presented a maximum sensitivity (0.710 A M−1 cm−2), a small limit of detection (0.105 μM) and a resilient behaviour upon cycling operation and long storage periods that clearly overpassed the performance of copper and cobalt single oxides. The CuxCoyO electrocatalysts also presented a good selectivity towards glucose and fructose in the presence of common interference compounds found in biological fluids (e.g., ascorbic acid, acetaminophen and uric acid), sucrose and ethanol, this latter present in many agrofood liquids. The possibilities of this sensor electrocatalyst have been tested for the analysis of a wine synthetic fermentation process. The comparison of the electrochemical results with conventional analytical methods showed a lineal amperometric response with respect hexose contents in a must at different stages of its transformation into wine.

February, 2020 | DOI: 10.1016/j.snb.2019.127360

Low gas consumption fabrication of He-3 solid targets for nuclear reactions

Fernandez, A; Hufschmidt, D; Colaux, JL; Valiente-Dobon, JJ; Godinho, V; de Haro, MCJ; Feria, D; Gadea, A; Lucas, S
Materials & Design, 186 (2020) 108337


Nanoporous solids that stabilize trapped gas nanobubbles open new possibilities to fabricate solid targets for nuclear reactions. A methodology is described based on the magnetron sputtering (MS) technique operated under quasistatic flux conditions to produce such nanocomposites films with He-3 contents of up to 16 at.% in an amorphous-silicon matrix. In addition to the characteristic low pressure (3-6 Pa) needed for the gas discharge, the method ensures almost complete reduction of the process gas flow during film fabrication. The method could produce similar materials to those obtained under classical dynamic flux conditions for MS. The drastic reduction (>99.5%) of the gas consumption is fundamental for the fabrication of targets with scarce and expensive gases. Si:He-3 and W:He-3 targets are presented together with their microstructural (scanning and transmission electron microscopy, SEM and TEM respectively) and compositional (Ion Beam Analysis, IBA) characterization. The He-3 content achieved was over 1 x 10(18) at/cm(2) for film thicknesses between 1.5 and 3 mu m for both Si and W matrices. First experiments to probe the stability of the targets for nuclear reaction studies in inverse kinematics configurations are presented. 

January, 2020 | DOI: 10.1016/j.matdes.2019.108337

Tribomechanical properties of hard Cr-doped DLC coatings deposited by low-frequency HiPIMS

Santiago, JA; Fernandez-Martinez, I; Sanchez-Lopez, JC; Rojas, TC; Wennberg, A; Bellido-Gonzalez, V; Molina-Aldareguia, JM; Monclus, MA; Gonzalez-Arrabal, R
Surface & Coatings Technology, 382 (2020) 124899


Cr-doped diamond-like carbon (Cr-DLC) films with Cr contents ranging from 3 up to 20 at. % were synthesised in a codeposition process with HiPIMS (Cr deposition) and DC-pulsed technology (C deposition). The application of HiPIMS at low frequencies was observed to significantly enhance the energy density during the Cr plasma discharge due to the interaction of Cr-C species. The higher energy bombardment at low HiPIMS frequencies allowed doping with Cr the DLC structure avoiding the graphitization of the carbon structure. EELS spectroscopy was used to evaluate sp(3) content and Raman was used for sp(2) structural characterization of the films. Enhanced mechanical properties (hardness up to 30 GPa) were observed with nanoindentation for Cr-doped DLC at low frequencies. High temperature nanoindentation tests were also performed from room temperature to 425 degrees C in order to evaluate the evolution of hardness and Young Modulus with temperature. The results showed that the mechanical properties at high temperature mainly depend on the initial sp(3)-sp(2) structure. Tribological tests were carried out in air from room temperature to 250 degrees C. Cr-doped DLC coatings deposited by low-frequency HiPIMS showed lower friction and wear compared to undoped DLC.

January, 2020 | DOI: 10.1016/j.surfcoat.2019.124899

Enhanced Stability of Perovskite Solar Cells Incorporating Dopant-Free Crystalline Spiro-OMeTAD Layers by Vacuum Sublimation

Barranco, A; Lopez-Santos, MC; Idigoras, J; Aparicio, FJ; Obrero-Perez, J; Lopez-Flores, V; Contreras-Bernal, L; Rico, V; Ferrer, J; Espinos, JP; Borras, A; Anta, JA; Sanchez-Valencia, JR
Advanced Energy Materials, (2020) 1901524


The main handicap still hindering the eventual exploitation of organometal halide perovskite-based solar cells is their poor stability under prolonged illumination, ambient conditions, and increased temperatures. This article shows for the first time the vacuum processing of the most widely used solid-state hole conductor (SSHC), i.e., the Spiro-OMeTAD [2,2 ',7,7 '-tetrakis (N,N-di-p-methoxyphenyl-amine) 9,9 '-spirobifluorene], and how its dopant-free crystalline formation unprecedently improves perovskite solar cell (PSC) stability under continuous illumination by about two orders of magnitude with respect to the solution-processed reference and after annealing in air up to 200 degrees C. It is demonstrated that the control over the temperature of the samples during the vacuum deposition enhances the crystallinity of the SSHC, obtaining a preferential orientation along the pi-pi stacking direction. These results may represent a milestone toward the full vacuum processing of hybrid organic halide PSCs as well as light-emitting diodes, with promising impacts on the development of durable devices. The microstructure, purity, and crystallinity of the vacuum sublimated Spiro-OMeTAD layers are fully elucidated by applying an unparalleled set of complementary characterization techniques, including scanning electron microscopy, X-ray diffraction, grazing-incidence small-angle X-ray scattering and grazing-incidence wide-angle X-ray scattering, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy.

January, 2020 | DOI: 10.1002/aenm.201901524


Graphene Formation Mechanism by the Electrochemical Promotion of a Ni Catalyst

Espinos, JP; Rico, VJ; Gonzalez-Cobos, J; Sanchez-Valencia, JR; Perez-Dieste, V; Escudero, C; de Lucas-Consuegra, A; Gonzalez-Elipe, AR
ACS Catalysis, 9 (2019) 11447-11454


In this work, we show that multilayer graphene forms by methanol decomposition at 280 degrees C on an electrochemically promoted nickel catalyst film supported on a K-beta Al2O3 solid electrolyte. In operando near ambient pressure photoemission spectroscopy and electrochemical measurements have shown that polarizing negatively the Ni electrode induces the electrochemical reduction and migration of potassium to the nickel surface. This elemental potassium promotes the catalytic decomposition of methanol into graphene and also stabilizes the graphene formed via diffusion and direct K-C interaction. Experiments reveal that adsorbed methoxy radicals are intermediate species in this process and that, once formed, multilayer graphene remains stable after electrochemical oxidation and back migration of potassium to the solid electrolyte upon positive polarization. The reversible diffusion of ca. 100 equivalent monolayers of potassium through the carbon layers and the unprecedented low-temperature formation of graphene and other carbon forms are mechanistic pathways of high potential impact for applications where mild synthesis and operation conditions are required.

December, 2019 | DOI: 10.1021/acscatal.9b03820

Silver effect on the tribological and antibacterial properties of a-C:Ag coatings

Dominguez-Meister, S; Rojas, TC; Frias, JE; Sanchez-Lopez, JC
Tribology International, 140 (2019) UNSP 105837


a-C:Ag coatings (1.2-23.4 at.% of Ag) were deposited using magnetron sputtering. Ag nanoparticles appear embedded in the carbon matrix or segregated to the column boundaries or surface. The silver doping has not promoted significant changes of the sp(2)/sp(3) ratio although a decrease of the hardness is observed (from 17 to 7 GPa). The tribological behavior did not show a clear dependence on the silver concentration in unlubricated or lubricated conditions (fetal bovinum serum) against alumina or UHMWPE balls. Ag nanoparticle dispersion enhanced the bactericide behavior as determined by the released Ag+ ion in the fluid media. There is no clear effect of friction rubbing on the released silver indicating that diffusion and top segregation are prevalent mechanisms for its dissolution.

December, 2019 | DOI: 10.1016/j.triboint.2019.06.030

3D Organic Nanofabrics: Plasma-Assisted Synthesis and Antifreezing Behavior of Superhydrophobic and Lubricant-Infused Slippery Surfaces

Alcaire, M; Lopez-Santos, C; Aparicio, FJ; Sanchez-Valencia, JR; Obrero, JM; Saghi, Z; Rico, VJ; de la Fuente, G; Gonzalez-Elipe, AR; Barranco, A; Borras, A
Langmuir, 35 (2019) 16876-16885


Herein, we present the development of supported organic nanofabrics formed by a conformal polymer-like interconnection of small-molecule organic nanowires and nanotrees. These organic nanostructures are fabricated by a combination of vacuum and plasma-assisted deposition techniques to generate step by step, single-crystalline organic nanowires forming one-dimensional building blocks, organic nanotrees applied as three-dimensional templates, and the polymer-like shell that produces the final fabric. The complete procedure is carried out at low temperatures and is compatible with an ample variety of substrates (polymers, metal, ceramics; either planar or in the form of meshes) yielding flexible and low solid-fraction three-dimensional nanostructures. The systematic investigation of this progressively complex organic nanomaterial delivers key clues relating their wetting, nonwetting, and anti-icing properties with their specific morphology and outer surface composition. Water contact angles higher than 150° are attainable as a function of the nanofabric shell thickness with outstanding freezing-delay times (FDT) longer than 2 h at −5 °C. The role of the extremely low roughness of the shell surface is settled as a critical feature for such an achievement. In addition, the characteristic interconnected microstructure of the nanofabrics is demonstrated as ideal for the fabrication of slippery liquid-infused porous surfaces (SLIPS). We present the straightforward deposition of the nanofabric on laser patterns and the knowledge of how this approach provides SLIPS with FDTs longer than 5 h at −5 °C and 1 h at −15 °C.

December, 2019 | DOI: 10.1021/acs.langmuir.9b03116

Hydrophobic and Icephobic Behaviour of Polyurethane-Based Nanocomposite Coatings

Przybyszewski, B; Boczkowska, A; Kozera, R; Mora, J; Garcia, P; Aguero, A; Borras, A
Coatings, 9 (2019) 811


In this paper, hydrophobic nanocomposite coatings based on polyurethane (PUR) modified by nano-silica and silane-based compounds were manufactured by spraying. The main challenge was to assess and improve the hydrophobic as well as anti-icing properties of initially hydrophilic polymer coatings. The prepared nanocomposite coatings were characterized by means of scanning electron microscopy (SEM), optical profilometry and X-ray photoelectron spectroscopy (XPS). The results obtained showed that in order to achieve hydrophobicity, appropriate amounts of nano-silica must be incorporated in the coating, and complete coverage by nano-silica particles is necessary for achieving hydrophobicity. Coating adhesion and the durability of the hydrophobic behaviour were also studied by scratch test and frosting/defrosting cycles, respectively. The results show that use of both nano-silica and silane-based compounds improve the hydrophobic and anti-icing properties of the coating as compared to a non-modified PUR topcoat. A synergistic effect of both additives was observed. It was also found that the anti-icing behaviour does not necessarily correlate with surface roughness and the materials' wetting properties.

December, 2019 | DOI: 10.3390/coatings9120811

Morphological effects on the photocatalytic properties of SnO2 nanostructures

Kar, A; Olszowka, J; Sain, S; Sloman, SRI; Montes, O; Fernandez, A; Pradhan, SK; Wheatley, AEH
Journal of Alloys and Compounds, 810 (2019) UNSP 151718


The photocatalytic properties of SnO2 nanocrystals are tuned by varying their morphology and microstructure. SnO2 nanoparticles and nanowedges have been synthesized using hydrothermal methods, while microwave irradiation techniques have given nanospheres. Detailed structural and chemical characterization of these different morphologies has been accomplished. The influence of SnO2 morphology on photocatalytic activity has been examined by monitoring the degradation of aqueous methylene blue dye. Results demonstrate that changing the morphology of the SnO2 modulates both surface area and levels of surface defects and that these alterations are reflected in the photocatalytic properties of the materials. The degradation of methylene blue dye (98%) in the presence of SnO2 nanoparticles under simulated solar irradiation is superior to previously reported photocatalyst performance and is comparable to that of standard TiO2 (Degussa P-25). The SnO2 nanoparticles perform better than both the nanowedges and nanospheres and this is attributed to the number of surface defects available to the high surface area material. They also reveal outstanding recyclability and stability. 

November, 2019 | DOI: 10.1016/j.jallcom.2019.151718

Ultrastable CoxSiyOz Nanowires by Glancing Angle Deposition with Magnetron Sputtering as Novel Electrocatalyst for Water Oxidation

Cano, M; Garcia-Garcia, FJ; Rodriguez-Padron, D; Gonzalez-Elipe, AR; Giner-Casares, JJ; Luque, R


Cobalt is one of the most promising non-noble metal as electrocatalyst for water oxidation. Herein, a highly stable silicon-cobalt mixed oxide thin film with a porous columnar nanostructure is proposed as electrocatalyst for oxygen evolution reaction (OER). CoOx and CoxSiyOz layers with similar thickness were fabricated at room temperature by magnetron sputtering in a glancing angle configuration (MS-GLAD) on tin-doped indium oxide (ITO) substrates. After characterization, a comparative study of the electrocatalytic performance for OER of both layers was carried out. The excellent long-term stability as electrocatalyst for OER of the porous CoxSiyOz thin film demonstrates that the presence of silicon on the mixed oxide network increases the mechanical stability of the Si/Co layer, whilst maintaining a considerable electrocatalytic response.

November, 2019 | DOI: 10.1002/cctc.201901730

Highly selective few-ppm NO gas-sensing based on necklace-like nanofibers of ZnO/CdO n-n type I heterojunction

Naderi, H; Hajati, S; Ghaedi, M; Espinos, JP
Sensors and Actuators B-Chemical, 297 (2019) 126774


Electrospinning method followed by calcination is applied to synthesize ZnO/CdO nanofibers. Characterization is performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and reflection electron energy loss spectroscopy (REELS), which resulted in detailed analysis of the sensing material. For instance, it was found that the ZnO/CdO is n-n type I heterojunction which possesses straddling energy band gap, which could affect the mechanism of gas sensing. An electroless gold-plated interdigitated electrode with spacing 200 mu m is fabricated on alumina substrate to host the designed nanofibers being used as gas sensor. Gas-sensing activity of the heterojunction is investigated against NO, NO2, H2S, CH4, SO2 and CO in addition to VOCs such as ethanol, acetone, ammonia, methanol, and chloroform with high selectivity and response to NO gas by monitoring resistance changes. Detailed discussion on the mechanism of sensing is presented. The ZnO/CdO nanofibers are found to be highly sensitive to very low concentration range of NO gas (1.2-33 ppm) at optimal operating temperature of 215 degrees C. The influence of humidity (20-96%) on the sensor response was found to be ignorable. Additionally, good repeatability and long-term stability (45 days, every 5 days, SD = 0.7) was obtained for this sensor. Typically, short response times of 47 and 35 s are obtained versus 3 and 33 ppm of NO, respectively, making our sensor promisingly applicable for monitoring this toxic gas in polluting industries, metropolises and maybe in exhaled breath.

October, 2019 | DOI: 10.1016/j.snb.2019.126774

Sodium ion storage performance of magnetron sputtered WO3 thin films

Garcia-Garcia, FJ; Mosa, J; Gonzalez-Elipe, AR; Aparicio, M
Electrochimica Acta, 321 (2019) 134669


WO3 thin film electrodes were successfully prepared by magnetron sputtering (MS) deposition under an oblique angle configuration (OAD). Intercalation of Na ions in the tungsten oxide layers has been studied using electrochemical techniques. Sample characterization before and after sodium intercalation has been carried out by Raman, XPS and XRD measurements. ToF-SIMS analysis has been also performed in order to analyze the element depth profiles along the electrode thickness. Electron microscopy evaluation of the cross section confirms the porous structure of the coatings. Batteries integrating these WO3 electrodes have a discharge capacity of 120 mA h g(-1) at the initial cycles and show an adequate capacity retention upon 300 cycles. The WO3-OAD thin-films are proposed as promising electrodes for Na-ion batteries.

October, 2019 | DOI: 10.1016/j.electacta.2019.134669

Influence of Titanium Oxide Pillar Array Nanometric Structures and Ultraviolet Irradiation on the Properties of the Surface of Dental Implants-A Pilot Study

Leon-Ramos, JR; Diosdado-Cano, JM; Lopez-Santos, C; Barranco, A; Torres-Lagares, D; Serrera-Figallo, MA
Nanomaterials, 9 (2019) 1458


Aim: Titanium implants are commonly used as replacement therapy for lost teeth and much current research is focusing on the improvement of the chemical and physical properties of their surfaces in order to improve the osseointegration process. TiO2, when it is deposited in the form of pillar array nanometric structures, has photocatalytic properties and wet surface control, which, together with UV irradiation, provide it with superhydrophilic surfaces, which may be of interest for improving cell adhesion on the peri-implant surface. In this article, we address the influence of this type of surface treatment on type IV and type V titanium discs on their surface energy and cell growth on them. Materials and methods: Samples from titanium rods used for making dental implants were used. There were two types of samples: grade IV and grade V. In turn, within each grade, two types of samples were differentiated: untreated and treated with sand blasting and subjected to double acid etching. Synthesis of the film consisting of titanium oxide pillar array structures was carried out using plasma-enhanced chemical vapor deposition equipment. The plasma was generated in a quartz vessel by an external SLAN-1 microwave source with a frequency of 2.45 GHz. Five specimens from each group were used (40 discs in total). On the surfaces to be studied, the following determinations were carried out: (a) X-ray photoelectron spectroscopy, (b) scanning electron microscopy, (c) energy dispersive X-ray spectroscopy, (d) profilometry, (e) contact angle measurement or surface wettability, (f) progression of contact angle on applying ultraviolet irradiation, and (g) a biocompatibility test and cytotoxicity with cell cultures. Results: The application of ultraviolet light decreased the hydrophobicity of all the surfaces studied, although it did so to a greater extent on the surfaces with the studied modification applied, this being more evident in samples manufactured in grade V titanium. In samples made in grade IV titanium, this difference was less evident, and even in the sample manufactured with grade IV and SLA treatment, the application of the nanometric modification of the surface made the surface optically less active. Regarding cell growth, all the surfaces studied, grouped in relation to the presence or not of the nanometric treatment, showed similar growth. Conclusions. Treatment of titanium oxide surfaces with ultraviolet irradiation made them change temporarily into superhydrophilic ones, which confirms that their biocompatibility could be improved in this way, or at least be maintained.

October, 2019 | DOI: 10.3390/nano9101458

Antibacterial Nanostructured Ti Coatings by Magnetron Sputtering: From Laboratory Scales to Industrial Reactors

Alvarez, R; Munoz-Pina, S; Gonzalez, MU; Izquierdo-Barba, I; Fernandez-Martinez, I; Rico, V; Arcos, D; Garcia-Valenzuela, A; Palmero, A; Vallet-Regi, M; Gonzalez-Elipe, AR; Garcia-Martin, JM
Nanomaterials, 9 (2019) art. 1217


Based on an already tested laboratory procedure, a new magnetron sputtering methodology to simultaneously coat two-sides of large area implants (up to similar to 15 cm(2)) with Ti nanocolumns in industrial reactors has been developed. By analyzing the required growth conditions in a laboratory setup, a new geometry and methodology have been proposed and tested in a semi-industrial scale reactor. A bone plate (DePuy Synthes) and a pseudo-rectangular bone plate extracted from a patient were coated following the new methodology, obtaining that their osteoblast proliferation efficiency and antibacterial functionality were equivalent to the coatings grown in the laboratory reactor on small areas. In particular, two kinds of experiments were performed: Analysis of bacterial adhesion and biofilm formation, and osteoblasts-bacteria competitive in vitro growth scenarios. In all these cases, the coatings show an opposite behavior toward osteoblast and bacterial proliferation, demonstrating that the proposed methodology represents a valid approach for industrial production and practical application of nanostructured titanium coatings.

September, 2019 | DOI: 10.3390/nano9091217

SiOx by magnetron sputtered revisited: Tailoring the photonic properties of multilayers

Garcia-Valenzuela, A; Alvarez, R; Espinos, JP; Rico, V; Gil-Rostra, J; Palmero, A; Gonzalez-Elipe, AR
Applied Surface Science, 488 (2019) 791-800


Traditionally porous silicon based photonic structures have been prepared by electrochemically etching of silicon. In this work, porous multilayers of nanocolumnar SiOx and SiO2 thin films acting as near infrared (NIR) 1D-photonic nanostructures are prepared by magnetron sputtering deposition at oblique angles (MS-OA). Simultaneous control of porosity and stoichiometry of the stacked films is achieved by adjusting the deposition angle and oxygen partial pressure according to a parametric formula. This new methodologoy is proved for the synthesis of SiOx thin films with x close to 0.4, 0.8, 1.2, 1.6 and nanostructures varying from compact (at 0 degrees deposition angle) to highly porous and nanocolumnar (at 70 degrees and 85 degrees deposition angles). The strict control of composition, structure and nanostructure provided by this technique permits a fine tuning of the absorption edge and refraction index at 1500 nm of the porous films and their manufacturing in the form of SiOx-SiO2 porous multilayers acting as near infrared (NIR) 1D-photonic structures with well-defined optofluidic responses. Liquid tunable NIR Bragg mirrors and Bragg microcavities for liquid sensing applications are presented as proof of concept of the possibilities of this MS-OA manufacturing method as an alternative to the conventional electrochemical fabrication of silicon based photonic structures.

September, 2019 | DOI: 10.1016/j.apsusc.2019.05.273

Higher hydration performance and bioactive response of the new endodontic bioactive cement MTA HP repair compared with ProRoot MTA white and NeoMTA plus

Jimenez-Sanchez, Maria Del Carmen; Segura-Egea, Juan Jose; Diaz-Cuenca, Aranzazu
Journal of biomedical materials research. Part B, Applied biomaterials, 107 (2019) 2109-2120


The aim of this study was to characterize the hydration performance and the bioactive response of the new bioactive endodontic cement MTA HP repair (HP), comparing its physicochemical parameters with those of ProRoot MTA White (Pro) and NeoMTA Plus (Neo). Un-hydrated precursor materials were characterized by X-ray fluorescence, laser diffraction, N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated materials were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR) and (FEG-SEM). Bioactivity evaluation in vitro was carried out, by soaking processed cement disk in simulated body fluid (SBF) during 168 h. The cements surface was studied by FT-IR, FEG-SEM, and energy dispersive X-ray. Release to the SBF media of ionic degradation products was monitored using inductively coupled plasma atomic emission spectroscopy. HP showed shorter initial setting time compared to Pro and Neo and produce a quick and effective bioactive response in vitro in terms of phosphate phase surface coating formation. This higher bioactive response for HP is correlated with increasing calcium aluminate content, increasing surface area of un-hydrated powder precursor and the increasing release capacity of Si ionic products of the final hydrated product. The higher bioactive response of MTA HP repair highlights this material, as very interesting to further investigate its performance to improve the outcome of vital pulp therapy procedures. 

August, 2019 | DOI: 10.1002/jbm.b.34304

MTA HP Repair stimulates in vitro an homogeneous calcium phosphate phase coating deposition

Jiménez-Sánchez, M.D.C.; Segura-Egea, J.J.; Díaz-Cuenca, A.
Journal of Clinical and Experimental Dentistry, 11 (2019) e322-e326


Background: To study the mineralization capacity in vitro of the bioceramic endodontic material MTA HP Repair. Material and Methods: Bioactivity evaluation in vitro was carried out, by soaking processed cement disk in simulated body fluid (SBF) during 168 h. The cement surface was studied by Fourier transform infrared spectroscopy (FTIR), field emission gun scanning electron microscopy (FEG-SEM) and energy dispersive X-ray analysis (EDX). Release to the SBF media of ionic degradation products was monitored using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Results: FT-IR showed increasing formation of phosphate phase bands at 1097, 960, 607 and 570 cm -1 with prolonged SBF soaking. FEG-SEM analysis reveals that HP produces a effectively surface covering consisting in homogeneous spherical phosphate phase aggregates with an average diameter of 0.5 -1 .0 μm. EDX analysis comparing un-treated (hydrated), 24 h and 72 h SBF treated surfaces of MTA HP Repair revealed phosphate deposition after 24 h, with high phosphorous/silicon element ratio signal measured after 24 h, indicating a very high phosphate phase deposition for this material. Conclusions: The study shows that MTA HP Repair produces a quick and effective bioactive response in vitro in terms of crystalline calcium phosphate surface coating formation. The high bioactive response of MTA HP Repair makes it an interesting candidate for endodontic use as repair cement. 

August, 2019 | DOI: 10.4317/jced.55661

Physicochemical parameters - hydration performance relationship of the new endodontic cement MTA Repair HP

Jiménez-Sánchez, M.D.C.; Segura-Egea, J.J.; Díaz-Cuenca, A.
Journal of Clinical and Experimental Dentistry, 11 (2019) e739-e744


Background: To characterize the chemical composition and textural parameters of the MTA Repair HP precursor powder and their influence to hydration performance. Material and Methods: Un-hydrated precursor material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF), laser diffraction (LD), N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated material was analysed by XRD, FT-IR, energy dispersive X-ray (EDX) analysis and FEG-SEM. Results: Ca3SiO5 and Ca2SiO4, in addition to CaWO4 as radiopacifier are the main compositional phases. Other measured parameters indicate high specific surface area of 4.8 m2 g-1, high aluminium content of 1.7 wt.% and low initial and final setting times of 12 and 199 min, respectively. Singular microstructural features consisting of high aspect ratio nanoparticles are main constituents of un-hydrated precursor. Besides, FEM-SEM observation shows notably growth of hexagonal shaped plate-like morphologies homogeneously distributed along the sample during hydration process. Conclusions: The short setting time measured for HP Repair, is correlated with high surface area of precursor powder, high Al content and the absence of compositional sulphate phases. 

August, 2019 | DOI: 10.4317/jced.56013

Plasma Enabled Conformal and Damage Free Encapsulation of Fragile Molecular Matter: from Surface-Supported to On-Device Nanostructures

Alcaire, M; Aparicio, FJ; Obrero, J; Lopez-Santos, C; Garcia-Garcia, FJ; Sanchez-Valencia, JR; Frutos, F; Ostrikov, K; Borras, A; Barranco, A
Advanced Functional Materials, (2019) art. 1903535


Damage-free encapsulation of molecular structures with functional nanolayers is crucial to protect nanodevices from environmental exposure. With nanoscale electronic, optoelectronic, photonic, sensing, and other nanodevices based on atomically thin and fragile organic matter shrinking in size, it becomes increasingly challenging to develop nanoencapsulation that is simultaneously conformal at atomic scale and does not damage fragile molecular networks, while delivering added device functionality. This work presents an effective, plasma-enabled, potentially universal approach to produce highly conformal multifunctional organic films to encapsulate atomically thin graphene layers and metalorganic nanowires, without affecting their molecular structure and atomic bonding. Deposition of adamantane precursor and gentle remote plasma chemical vapor deposition are synergized to assemble molecular fragments and cage-like building blocks and completely encapsulate not only the molecular structures, but also the growth substrates and device elements upon nanowire integration. The films are insulating, transparent, and conformal at sub-nanometer scale even on near-tip high-curvature areas of high-aspect-ratio nanowires. The encapsulated structures are multifunctional and provide effective electric isolation, chemical and environmental protection, and transparency in the near-UV-visible-near-infrared range. This single-step, solvent-free remote-plasma approach preserves and guides molecular building blocks thus opening new avenues for precise, atomically conformal nanofabrication of fragile nanoscale matter with multiple functionalities.

July, 2019 | DOI: 10.1002/adfm.201903535

Large gap atmospheric pressure barrier discharges using ferroelectric materials

Navascues, P.; Gonzalez-Elipe, A. R.; Cotrino, J.; Gomez-Ramirez, A.
Plasma Sources Sciences & Tecnology, 28 (2019) 075002


This work reports a phenomenological comparative study of atmospheric pressure barrier plasmas using ferroelectric (ferroelectric barrier discharge (FBD)) and dielectric (dielectric barrier discharge (DBD)) plates to moderate the discharge. For FBD operation and large inter-electrode distances, experiments with helium carried out in a parallel plate reactor as a function of applied voltage have shown an enhancement of one order of magnitude in the charge transferred through the circuit. In a similar way to DBDs, FBDs rendered a laterally localized arrangement of discrete columnar discharges with a pattern distribution and an overall current intensity that depended on operation conditions. However, unlike the regular columnar pattern found for DBD operation, discharge columns in the FBD mode appear randomly and inhomogeneously distributed on the ferroelectric surface. This geometrical behavior of FBD plasma columns, as well as the singular variation of current with applied voltage and the particular shape characteristics of the current discharge curves have been accounted for by the high capacity of ferroelectric surfaces to randomly accumulate charge and to promote the emission of secondary electrons in the presence of a plasma.

July, 2019 | DOI: 10.1088/1361-6595/ab28ce

On‐Surface Synthesis and Characterization of Acene‐Based Nanoribbons Incorporating Four‐Membered Rings

Sanchez-Sanchez, C; Dienel, T; Nicolai, A; Kharche, N; Liang, LB; Daniels, C; Meunier, V; Liu, JZ; Feng, XL; Mullen, K; Sanchez-Valencia, JR; Groning, O; Ruffieux, P; Fasel, R
Chemistry-A European Journal


A bottom up method for the synthesis of unique tetracene-based nanoribbons, which incorporate cyclobutadiene moieties as linkers between the acene segments, is reported. These structures were achieved through the formal [2+2] cycloaddition reaction of ortho-functionalized tetracene precursor monomers. The formation mechanism and the electronic and magnetic properties of these nanoribbons were comprehensively studied by means of a multitechnique approach. Ultra-high vacuum scanning tunneling microscopy showed the occurrence of metal-coordinated nanostructures at room temperature and their evolution into nanoribbons through formal [2+2] cycloaddition at 475 K. Frequency-shift non-contact atomic force microscopy images clearly proved the presence of bridging cyclobutadiene moieties upon covalent coupling of activated tetracene molecules. Insight into the electronic and vibrational properties of the so-formed ribbons was obtained by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Magnetic properties were addressed from a computational point of view, allowing us to propose promising candidates to magnetic acene-based ribbons incorporating four-membered rings. The reported findings will increase the understanding and availability of new graphene-based nanoribbons with high potential in future spintronics.

July, 2019 | DOI: 10.1002/chem.201901410

Multifunctional antimicrobial chlorhexidine polymers by remote plasma assisted vacuum deposition

Mora-Boza, A; Aparicio, FJ; Alcaire, M; Lopez-Santos, C; Espinos, JP; Torres-Lagares, D; Borras, A; Barranco, A
Frontiers of chemical science and engineering, 13 (2019) 330-339


Novel antibacterial materials for implants and medical instruments are essential to develop practical strategies to stop the spread of healthcare associated infections. This study presents the synthesis of multifunctional antibacterial nanocoatings on polydimethylsiloxane (PDMS) by remote plasma assisted deposition of sublimated chlorhexidine powders at low pressure and room temperature. The obtained materials present effective antibacterial activity against Escherichia coli K12, either by contact killing and antibacterial adhesion or by biocide agents release depending on the synthetic parameters. In addition, these multifunctional coatings allow the endure hydrophilization of the hydrophobic PDMS surface, thereby improving their biocompatibility. Importantly, cell-viability tests conducted on these materials also prove their non-cytotoxicity, opening a way for the integration of this type of functional plasma films in biomedical devices.

June, 2019 | DOI: 10.1007/s11705-019-1803-6

2D compositional self-patterning in magnetron sputtered thin films

Garcia-Valenzuela, A; Alvarez, R; Rico, V; Espinos, JP; Lopez-Santos, MC; Solis, J; Siegel, J; del Campo, A; Palmero, A; Gonzalez-Elipe, AR
Applied Surface Science, 480 (2019) 115-121


Unlike topography patterning, widely used for numerous applications and produced by means of different technologies, there are no simple procedures to achieve surface compositional patterning at nanometric scales. In this work we have developed a simple method for 2D patterning the composition of thin films. The method relies on the magnetron sputtering deposition at oblique angles onto patterned substrates made by laser induced periodic surface structures (LIPSS). The method feasibility has been demonstrated by depositing SiOx thin films onto LIPSS structures generated in Cr layers. A heterogeneous and aligned distribution of O/Si ratios (and different Sin+ chemical states) along the LIPSS structure in length scales of some hundreds nm's has been proven by angle resolved X-ray photoelectron spectroscopy and a patterned arrangement of composition monitored by atomic force microscopy-Raman analysis. The obtained results are explained by the predictions of a Monte Carlo simulation of this deposition process and open the way for the tailored one-step fabrication of surface devices with patterned compositions.

June, 2019 | DOI: 10.1016/j.apsusc.2019.02.206

Exchange bias and two steps magnetization reversal in porous Co/CoO layer

Ovejero, JG; Godinho, V; Lacroix, B; Garcia, MA; Hernando, A; Fernandez, A
Materials & Design, 171 (2019) 107691


In this paper Co/CoO thick layers (hundreds of nanometers) of different porosity and oxidation degree were prepared in a magnetron sputtering deposition processby tailoring the DC sputtering power, as well as the process gas and target composition. The control of the synthesis parameters allowed the nanostructuration of the films with a singular distribution of closed pores and a controlled amount of CoO. We observed an exchange bias field of 2.8 KOe for porous Co/CoO composites, similar to Co/CoO bilayers but for coatings thicker than 300 nm. Besides, it was observed that the coating presents bistable magnetic features when cooled under zero field conditions as a result of the unusual exchange coupling.

June, 2019 | DOI: 10.1016/j.matdes.2019.107691

Hydrophobicity, Freezing Delay, and Morphology of Laser-Treated Aluminum Surfaces

Rico, VJ; Lopez-Santos, C; Villagra, M; Espinos, JP; de la Fuente, GF; Angurel, LA; Borras, A; Gonzalez-Elipe, AR
Langmuir, 35 (2019) 6483-6491


Until recently, superhydrophobicity was considered as a hint to predict surface icephobicity, an association of concepts that is by no means universal and that has been proven to depend on different experimental factors and material properties, including the actual morphology and chemical state of surfaces. This work presents a systematic study of the wetting and freezing properties of aluminum Al6061, a common material widely used in aviation, after being subjected to nanosecond pulsed IR laser treatments to modify its surface roughness and morphology. All treated samples, independent of their surface finishing state, presented initially an unstable hydrophilic wetting behavior that naturally evolved with time to reach hydrophobicity or even superhydrophobicity. To stabilize the surface state and to bestow the samples with a permanent and stable hydrophobic character, laser-treated surfaces were covered with a thin layer of CFx prepared by plasma-enhanced chemical vapor deposition. A systematic comparison between freezing delay (FD) and wetting properties of water droplets onto these plasma-/polymer-modified laser-treated surfaces that, under conditions where a heterogeneous nucleation mechanism prevails, surface morphology rather than the actual value of the surface roughness parameter the key feature for long FD times. In particular, it is found that surface morphologies rendering a Cassie-Baxter wetting regime longer FDs than those characterized by a Wenzel-like wetting state. It is that laser treatment, with or without additional coverage with thin CFx coatings, affects wetting and ice formation behaviors and might be an efficient procedure to mitigate icing problems on metal surfaces.

May, 2019 | DOI: 10.1021/acs.langmuir.9b00457

Liquid switchable radial polarization converters made of sculptured thin films

Oliva-Ramirez, M; Rico, VJ; Gil-Rostra, J; Arteaga, O; Bertran, E; Serna, R; Gonzalez-Elip, AR; Yubero, F
Applied Surface Science, 475 (2019) 230-236


A radial polarization converter is a super-structured optical retarder that converts a conventional linearly polarized light beam into a structured beam with radial or azimuthal polarization. We present a new type of these sophisticated optical elements, which is made of porous nanostructured sculptured single thin films or multilayers prepared by physical vapor deposition at an oblique angle. They are bestowed with an axisymmetric retardation activity (with the fast axis in a radial configuration). In particular, a Bragg microcavity multilayer that exhibits a tunable transmission peak in the visible range with a retardance of up to 0.35 rad has been fabricated using this methodology. Owing to the highly porous structure of this type of thin films and multilayers, their retardance could be switched off by liquid infiltration. These results prove the possibility of developing wavelength dependent (through multilayer optical design) and switchable (through vapor condensation or liquid infiltration within the pore structure) radial polarization converters by means of oblique angle physical vapor deposition.

May, 2019 | DOI: 10.1016/j.apsusc.2018.12.200

Surface nickel particles generated by exsolution from a perovskite structure

Aguero, FN; Beltran, AM; Fernandez, MA; Cadus, LE
Journal of Solid State Chemistry, 273 (2019) 75-80


LaAl1-xNixO3 (with x = 0.05 and 0.2) perovskite oxides were successfully synthesized and its behavior under reduction atmosphere was studied. HRTEM and STEM studies, coupled to HAADF and EDX detection, allowed to evidence the Ni exsolution process to the surface of the solid and to build nano-catalytic centers. The size of these centers is independent of the reduction conditions in the range studied. The high specific surface of the raw material, its porosity and the structure defects could be responsible of the low temperature at which the exsolution process starts. The content of Ni dopants allows the control of Ni centers size on the surface and the synthesis method provides Ni-nanoparticles strongly anchored to the resultant support.

May, 2019 | DOI: 10.1016/j.jssc.2019.02.036

Laser-induced coloration of ceramic tiles covered with magnetron sputtered precursor layers

Rico, VJ; Lahoz, R; Rey-Garcia, F; de Francisco, I; Gil-Rostra, J; Espinos, JP; de la Fuente, GF; Gonzalez-Elipe, AR
Journal of the American Ceramic Society, 102 (2019) 1589-1598


This paper reports a new methodology for the coloring of glazed ceramic tiles consisting of the near infrared pulsed laser processing of copper containing oxide coatings prepared by magnetron sputtering. As a second approach, the employ for the same purpose of a novel laser furnace technique is also described. Changing the laser parameters and using the laser furnace to treat the tiles at high temperature during irradiation has resulted in a wide color palette. The optical characterization of the modified tiles by UV-Vis spectroscopy has been complemented with their microstructural and compositional analysis by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Time Of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The chemical composition of the surface was obtained by X-ray Photoemission Spectroscopy (XPS) and its structure determined by X?ray diffraction (XRD). The chemical resistance was characterized by several tests following the norm ISO 10545-13. Color changes have been attributed to surface microstructural and chemical transformations that have been accounted for by simple models involving different ablation, melting, diffusion, and segregation/agglomeration phenomena depending on the laser treatments employed.

April, 2019 | DOI: 10.1111/jace.16022

3D core-multishell piezoelectric nanogenerators

A. Nicolas Filippin; Juan R.Sanchez-Valencia; Xabier Garcia-Casas; Victor Lopez-Flores; Manuel Macias-Montero; Fabian Frutos; Angel Barranco; Ana Borras
Nano Energy, 58 (2019) 476-483


The thin film configuration presents obvious practical advantages over the 1D implementation in energy harvesting systems such as easily manufacturing and processing, and long-lasting and stable devices. However, ZnO-based piezoelectric nanogenerators (PENGs) generally rely on the exploitation of single-crystalline nanowires because of their self-orientation in the c-axis direction and ability to accommodate long deformations resulting in high piezoelectric performance. Herein, we show an innovative approach to produce PENGs by combining polycrystalline ZnO layers fabricated at room temperature by plasma-assisted deposition with supported small-molecule organic nanowires (ONWs) acting as 1D scaffolds. Such hybrid nanostructures present convoluted core-shell morphology, formed by a single-crystalline organic nanowire conformally surrounded by a poly-crystalline ZnO shell and combine the organic core mechanical properties with the ZnO layer piezoelectric response. In a step forward towards the integration of multiple functions within a single wire, we have also developed ONW-Au-ZnO nanoarchitectures including a gold shell acting as inner electrode achieving output piezo-voltages up to 170 mV. The synergistic combination of functionalities in the ONW-Au-ZnO devices promotes an enhanced performance generating piezo-currents one order of magnitude larger than the ONW-ZnO nanowires and superior to the thin film nanogenerators for equivalent and higher thicknesses.

April, 2019 | DOI: 10.1016/j.nanoen.2019.01.047

CuxCo3-xO4 ultra-thin film as efficient anodic catalysts for anion exchange membrane water electrolysers

Lopez-Fernandez, E; Gil-Rostra, J; Espinos, JP; Gonzalez-Elipe, AR; Yubero, F; de Lucas-Consuegra, A
Journal of Power Sources, 415 (2019) 136-144


CuxCo3-xO4 ultra-thin films, deposited by magnetron sputtering at oblique angles have been used as anodic catalysts in anion exchange membrane water electrolysers. It has been demonstrated that the used deposition procedure provides porous and amorphous samples with a strict control of the total catalyst load and Co/Cu ratio. Electrocatalytic tests showed a maximum performance for the oxygen evolution reaction at Co/Cu atomic ratio around 1.8. The optimized anodic catalyst presented a long-term stability confirmed by accelerated lifetime tests together with the chemical surface analysis of the used samples. The effect of the crystallization of a single layer CuxCo3-xO4 and a multilayer (CuO/Co3O4)(n) anodic catalyst samples was also investigated. The observed loss of catalytic performance found in both cases may prove that a particular local chemical environment around the Co and Cu sites acts as an efficient catalytic site for the oxygen evolution reaction. A catalyst film with the optimum Co/Cu atomic ratio was incorporated into a Membrane Electrode Assembly, using a sputtered Ni film as cathode. Current density values up to 100 mA cm(-2) at 2.0 V were obtained in 1.0 M KOH electrolyte. Upon normalization by the amount of catalyst, this performance is one of the highest reported in literature.

March, 2019 | DOI: 10.1016/j.jpowsour.2019.01.056

Microstructure, interfaces and properties of 3YTZP ceramic composites with 10 and 20 vol% different graphene-based nanostructures as fillers

Munoz-Ferreiro, C; Morales-Rodriguez, A; Rojas, TC; Jimenez-Pique, E; Lopez-Pernia, C; Poyato, R; Gallardo-Lopez, A
Journal of Alloys and Compounds, 777 (2019) 213-224


The graphene family comprises not only single layer graphene but also graphene-based nanomaterials (GBN), with remarkably different number of layers, lateral dimension and price. In this work, two of these GBN, namely graphene nanoplatelets (GNP) with n similar to 15-30 layers and few-layer graphene (FLG) with n < 3 layers have been evaluated as fillers in 3 mol% yttria stabilized tetragonal zirconia (3YTZP) ceramic composites. Composites with 10 and 20 vol% GNP or FLG have been fabricated by wet powder processing and spark plasma sintering (SPS) and the influence of the content and number of layers of the graphene-based filler has been assessed. For both graphene-based fillers, an intermediate zirconia oxycarbide has been detected in the grain boundaries. The lower stacking degree and much more homogeneous distribution of the FLG, revealed by transmission electron microscopy (TEM), can improve load transfer between the GBNs and the ceramic matrix. However, high FLG contents lower densification of the composites, due partly to the larger FLG interplanar spacing also estimated by TEM. The hardness (both Vickers and nanoindentation) and the elastic modulus decrease with increased GBN content and with improved graphene dispersion. The FLG greatly inhibit the crack propagation that occur perpendicular to their preferential orientation plane. The composites with thinner FLG have higher electrical conductivity than those with GNP. The highest electrical conductivity is achieved by composites with 20 vol% FLG in the direction perpendicular to the compression axis during sintering, sigma(perpendicular to) = 3400 +/- 500 Sm-1. 

March, 2019 | DOI: 10.1016/j.jallcom.2018.10.336

Controlled thermolysis of MIL-101(Fe, Cr) for synthesis of FexOy/porous carbon as negative electrode and Cr2O3/porous carbon as positive electrode of supercapacitor

Farisabadi, A; Moradi, M; Hajati, S; Kiani, MA; Espinos, JP
Applied Surface Science, 469 (2019) 192-203


In the present study, two kinds of metal oxide/carbon nanocomposite were prepared through calcination of MIL-101(Fe, Cr). The morphological and structural properties of the specimens were investigated using X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer, Emmett, and Teller analysis, energy dispersive Xray spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The electrode materials were also electrochemically investigated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy techniques in 6 M KOH electrolyte. Because of synergistic effect of metal oxides and carbon, the obtained samples showed excellent performance; in a way that Cr2O3/C and Fe Oy/C showed high specific capacitance of 420 F g(-1) and 114 F g(-1) at current density of 2 A g(-1), respectively. The Cr2O3/C electrode also displayed high rate capability even at scan rate of 1500 mV s(-1). Moreover, we successfully developed an asymmetric supercapacitor in which Cr2O3/C served as positive electrode and Fe Oy/C served as negative electrode. The asymmetric device can deliver an energy density of 9.6 W h kg(-1) and power density of 8000 W kg(-1), with 93% capacitance retention after 3000 charge-discharge cycles. These outcomes show that the MOF-derived metal oxide/carbon composite can be regarded as a promising development for advanced electrode materials for applying in supercapacitors.

March, 2019 | DOI: 10.1016/j.apsusc.2018.11.053

XPS primary excitation spectra of Zn 2p, Fe 2p, and Ce 3d from ZnO, α‐Fe2O3, and CeO2

Pauly, N.; Yubero, F.; Espinós, J.P.; Tougaard, S.
Surface and Interface Analysis, 51 (2019) 353-360


Metal oxides are important for current development in nanotechnology. X‐ray photoelectron spectroscopy(XPS) is a widely used technique to study the oxidation states of metals, and a basic understanding of the photoexcitation process is important to obtain the full information from XPS. We have studied core level excitations of Zn 2p, Fe 2p, and Ce 3d photoelectron emissions from ZnO, α‐Fe2O3, and CeO2. Using an effective energy‐differential XPS inelastic‐scattering cross section evaluated within the semiclassical dielectric response model for XPS, we analysed the experimental spectra to determine the corresponding primary excitation spectra, ie, the initial excitation processes. We find that simple emission (Zn 2p) as well as complex multiplet photoemission spectra (Fe 2p and Ce 3d) can be quantitatively analysed with our procedure. Moreover, for α‐Fe2O3, it is possible to use the software package CTM4XAS (Charge Transfer Multiplet program for X‐ray Absorption Spectroscopy) to calculate its primary excitation spectrum within a quantum mechanical model, and it was found to be in good agreement with the spectrum determined by analysis of the experiment.

March, 2019 | DOI: 10.1002/sia.6587

The impact of photocatalytic Ag/TiO2 and Ag/N-TiO2 nanoparticles on human keratinocytes and epithelial lung cells

Rebleanu, D; Gaidau, C; Voicu, G; Constantinescu, CA; Sanchez, CM; Rojas, TC; Carvalho, S; Calin, M
Toxicology, 416 (2019) 30-43


The potential human health risks following the exposure to inorganic nanoparticles (NPs) is a very important issue for their application in leather finishing industry. The aim of our study was to investigate the cytotoxic effect of silver (Ag)/titanium dioxide (TiO2) NPs on human cells. Photocatalytic NPs were prepared by electrochemical deposition of Ag on the surface of TiO2 and nitrogen (N)-TiO2 NPs and, subsequently, physicochemical characterized. Then, a set of experiments have been performed to study the cytotoxicity and cell death mechanisms involved, the changes in cell morphology and the production of ROS induced in human keratinocytes (HaCaT) and human lung epithelial cells (A549) by exposure to NPs. Moreover, the changes in major signaling pathways and the inflammatory response induced by Ag/N-TiO2 NPs in A549 cells were investigated. The data showed that cell death by late apoptosis/necrosis is induced in cells as function of the dose and the type of NPs and is characterized by morphological changes and cytoskeletal disorganization and an increase in reactive oxygen species (ROS) production. The exposure of A549 cells to Ag/N-TiO2 NPs determine the activation of ERK1/2 MAP-kinase pathway and the release of pro-inflammatory mediators CXCL1, GM-CSF and MIF, known to be involved in the recruitment of circulating neutrophils and monocytes.

March, 2019 | DOI: 10.1016/j.tox.2019.01.013

Test of a He-3 target for transfer reactions in inverse kinematics

Carozzi, G; Valiente-Dobon, JJ; Gadea, A; Siciliano, M; Mengoni, D; Fernandez, A; Godinho, V; Hufschmidt, D; Di Nitto, A
Nuovo cimento c-colloquia and communications in physics, 42 (2019) 94


With the aim of studying exotic nuclei close to the proton dripline, an innovative He-3 target was produced and tested in a collaboration between the Materials Science Institute of Seville (Spain) and the Legnaro National Laboratories (Italy). The target was manufactured with a new technique that aims to reduce the costs while providing high quality targets. The target was tested at the Legnaro National Laboratories. The results of this test are presented in this contribution.

March, 2019 | DOI: 10.1393/ncc/i2019-19094-9

Comparative studies on electrochemical energy storage of NiFe-S nanoflake and NiFe-OH towards aqueous supercapacitor

Naseri, M; Moradi, M; Hajati, S; Espinos, JP; Kiani, MA
Journal of Materials Science-Materials in Electronics, 30 (2019) 4499-4510


In this study, electrochemical energy storage performances of an efficient Ni-Fe sulfide and hydroxide supported on porous nickel foam are compared. X-ray diffraction (XRD), X-rayphotoelectron spectroscopy (XPS) and energy-dispersive X-ray spectrometer (EDS) results confirmed the formation of Ni-Fe-S and Ni-Fe-OH electrodes. In addition, Brunauer-Emmett Teller (BET) was used to determine the specific surface area of the prepared materials. Moreover, the morphologies were observed by scanning electron microscopy (SEM). The brilliant characteristics of Ni-Fe-S could be attributed to transport acceleration in electrolyte ions and electrons, occurrence of redox reactions as well as the higher conductivity of the sample. From stand point of comparison, the capacitance of Ni-Fe-S is more than that of Ni-Fe-OH. Therefore, the exchange of O2- with S2- in Ni-Fe-OH lattice obviously improves the electrochemical performance. The as-fabricated Ni-Fe sulfide electrode exhibits a tremendous specific capacitance of 884.9Fg(-1) at 1A g(-1). Furthermore, an assembled asymmetric supercapacitor device using the activated carbon as negative electrode and this smart configuration (Ni-Fe-S) as positive electrode also provided a maximum specific power and specific energy of 8000Wkg(-1), 37.9 Whkg(-1), respectively. Also, it shows cycling stability with 88.8% capacitance retention after 1700 cycles in aqueous electrolyte, demonstrating its potential application in the next-generation high-performance supercapacitors used for energy storage.

March, 2019 | DOI: 10.1007/s10854-019-00738-x

Mechanism of Photoluminescence Intermittency in Organic-Inorganic Perovskite Nanocrystals

Galisteo-Lopez, JF; Calvo, ME; Rojas, TC; Miguez, H
ACS Applied Materials & Interfaces, 11 (4) (2019) 6344-6349


Lead halide perovskite nanocrystals have demonstrated their potential as active materials for optoelectronic applications over the past few years. Nevertheless, one issue that hampers their applicability has to do with the observation of photoluminescence intermittency, commonly referred to as "blinking", as in their inorganic counterparts. Such behavior, reported for structures well above the quantum confinement regime, has been discussed to be strongly related to the presence of charge carrier traps. In this work, we analyze the characteristics of this intermittency and explore the dependence on the surrounding atmosphere, showing evidence for the critical role played by the presence of oxygen. We discuss a possible mechanism in which a constant creation/annihilation of halide-related carrier traps takes place under light irradiation, with the dominant rate being determined by the atmosphere.

February, 2019 | DOI: 10.1021/acsami.8b17122

An innovative approach for micro/nano structuring plasma polymer films

Thiry, D; Vinx, N; Aparicio, FJ; Moerman, D; Lazzaroni, R; Cossement, D; Snyders, R
Thin Solid Films, 672 (2019) 26-32


This work aims at presenting an innovative method for tailoring the morphology of functionalized plasma polymer films (PPF). The approach is based on the formation of a plasma polymer bilayer system in which the two layers differ by their chemical composition and cross-linking degree. As a case study, propanethiol-based plasma polymer films have been investigated. As revealed by a much higher S/C ratio than in the propanethiol precursor (i.e. 0.83 vs 0.33), it has been demonstrated that the bottom layer contains a large fraction of trapped sulfur-based molecules (e.g. H2S). When further covered by a denser PPF formed at higher energetic conditions, a three-dimensional morphological reorganization takes place giving rise to the micro/nano structuration of the organic material. The shape, the dimensions as well as the density of the generated structures are found to depend on the thickness of both coatings involved in the bilayer structure, offering a great flexibility for surface engineering. Annealing experiments unambiguously confirm the major role played by the sulfur-based trapped molecules for inducing the reshaping process. The whole set of data clearly paves the way for the development of an innovative approach for finely tailoring the morphology of functionalized PPF at the micro/nano scale.

February, 2019 | DOI: 10.1016/j.tsf.2018.12.050

Holmium doped fiber thermal sensing based on an optofluidic Fabry-Perot microresonator

Lahoz, F; Martin, IR; Soler-Carracedo, K; Caceres, JM; Gil-Rostra, J; Yubero, F
Journal of Luminescence, 206 (2019) 492-497


An optical temperature sensor suitable for label free liquid sensing has been designed and characterized. The sensor combines the photochemical stability of rare earth doped glasses and the high sensitivity of interferometric resonators. It is formed by a planar Eabry-Perot (FP) microcavity filled with the liquid to be monitored. A Ho3+ doped tapered optical fiber has been placed inside the microcavity surrounded by the fluid medium. An external laser is focused on the optical fiber inside the cavity to induce the luminescence of the Ho3+ ions, which couples to the FP optical resonances. The spectral position of the FP resonances is highly sensitive to the refractive index of the cavity medium. A second laser is co-aligned with the first one to locally heat the liquid medium around the optical fiber. An average blue shift of the FP resonances around 32 pm/degrees C is measured. The limit of detection of the laser induced heating of the liquid medium is about 0.3 degrees C in the biological temperature range. Alternatively, a hot-plate is used to heat the system. Interestingly, a red shift of the FP modes is observed with 75 pm/degrees C dependence and 0.12 degrees C limit of detection features.

February, 2019 | DOI: 10.1016/j.jlumin.2018.10.103

Growth of nanocolumnar thin films on patterned substrates at oblique angles

Garcia-Valenzuela, A; Munoz-Pina, S; Alcala, G; Alvarez, R; Lacroix, B; Santos, AJ; Cuevas-Maraver, J; Rico, V; Gago, R; Vazquez, L; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Plasma Processes and Polymers, 16 (2019) e1800135


The influence of one dimensional substrate patterns on the nanocolumnar growth of thin films deposited by magnetron sputtering at oblique angles is theoretically and experimentally studied. A well-established growth model has been used to study the interplay between the substrate topography and the thin film morphology. A critical thickness has been defined, below which the columnar growth is modulated by the substrate topography, while for thicknesses above, the impact of substrate features is progressively lost in two stages; first columns grown on taller features take over neighboring ones, and later the film morphology evolves independently of substrate features. These results have been experimentally tested by analyzing the nanocolumnar growth of SiO2 thin films on ion-induced patterned substrates.

February, 2019 | DOI: 10.1002/ppap.201800135

Study of the Interface of the Early Stages of Growth under Quasi-Equilibrium Conditions of ZnO on Graphene/Cu and Graphite

Morales, C; Black, A; Urbanos, FJ; Granados, D; Mendez, J; del Campo, A; Yubero, F; Soriano, L
Advanced Materials Interfaces, 6 (2019) art. 1801689


The study of the early stages of growth of ZnO on graphene supported on Cu and on highly oriented pyrolytic graphite by means of reactive thermal evaporation of metallic Zn at room temperature is presented. This growth method allows to go in depth in the study of the fundamental interaction between ZnO and graphene at the interface in quasi-equilibrium conditions. Quantitative, chemical, and morphological analysis is performed using photoemission spectroscopy, atomic force, and scanning microscopies as experimental characterization techniques and factor analysis and inelastic peak shape analysis as modeling techniques. The growth of ZnO on a highly oriented pyrolytic graphite substrate is also studied using the same growth method for comparison. The results show that, in spite that the first atomic layer of both substrates is identical, the growth kinetics and morphology of the deposits are completely different. A model for the kinetics of the growth of ZnO on both substrates is proposed.

February, 2019 | DOI: 10.1002/admi.201801689

Environmentally Tight TiO2-SiO2 Porous 1D-Photonic Structures

Garcia-Valenzuela, A; Lopez-Santos, C; Rico, V; Alvarez, R; Palmero, A; Gonzalez-Elipe, AR
Advanced Materials Interfaces, 6 (2019) art. 1801212


Although thin film porosity is the basis of many optical sensors, it can be deleterious for a stable optical behavior of passive optical elements due to the condensation of water and other vapors in their pores. This paper proposes a new strategy for the magnetron sputtering (MS) fabrication of environmentally tight SiO2-TiO2 porous multilayers. Thin films of these two oxides deposited in an oblique angle configuration (MS-OAD) present a nanocolumnar and highly porous nanostructure and, as a consequence, experience significant changes in their optical properties when exposed to water vapor. Similarly, the optical properties of Bragg reflectors and Bragg microcavities made of the stacking of porous and compact SiO2 and TiO2 thin films experience reversible changes when these 1D-photonic structures are exposed to water pressure. A key finding of this work is that a very thin capping layer of SiO2 deposited on the surface of porous SiO2 films in the stack, at the interlayer between the two oxides, efficiently seals the pores making the photonic structures environmentally tight. This capping layer approach is a useful strategy to incorporate porosity as an additional parameter to design the optical behavior of planar photonic structures while preserving optical and environmental stability.

February, 2019 | DOI: 10.1002/admi.201801212

Isotope Labelling for Reaction Mechanism Analysis in DBD Plasma Processes

Navascues, P; Obrero-Perez, JM; Cotrino, J; Gonzalez-Elipe, AR; Gomez-Ramirez, A
Catalysts, 9(1) (2019) 45


Dielectric barrier discharge (DBD) plasmas and plasma catalysis are becoming an alternative procedure to activate various gas phase reactions. A low-temperature and normal operating pressure are the main advantages of these processes, but a limited energy efficiency and little selectivity control hinder their practical implementation. In this work, we propose the use of isotope labelling to retrieve information about the intermediate reactions that may intervene during the DBD processes contributing to a decrease in their energy efficiency. The results are shown for the wet reforming reaction of methane, using D2O instead of H2O as reactant, and for the ammonia synthesis, using NH3/D-2/N-2 mixtures. In the two cases, it was found that a significant amount of outlet gas molecules, either reactants or products, have deuterium in their structure (e.g., HD for hydrogen, CDxHy for methane, or NDxHy for ammonia). From the analysis of the evolution of the labelled molecules as a function of power, useful information has been obtained about the exchange events of H by D atoms (or vice versa) between the plasma intermediate species. An evaluation of the number of these events revealed a significant progression with the plasma power, a tendency that is recognized to be detrimental for the energy efficiency of reactant to product transformation. The labelling technique is proposed as a useful approach for the analysis of plasma reaction mechanisms.

January, 2019 | DOI: 10.3390/catal9010045

Influence of Al and Y content on the oxidation resistance of CrAlYN protective coatings for high temperature applications: New insights about the Y role

Rojas, TC; Dominguez-Meister, S; Brizuela, M; Sanchez-Lopez, JC
Journal of Alloys and Compounds, 777 (2019) 1172-1181


CrAlYN hard coatings with two different average Al contents: similar to 16 at.% and similar to 25 at.%, and Y concentration varying between 1.2 and 5.7 at.% were deposited by direct current reactive magnetron co-sputtering of mixed Cr-Al and Y targets on commercial M2 steel substrates. The samples were heated to 1000 degrees C in air during 2 h to study their oxidation resistance and thermal stability. The Y content is critical and the coatings present different behaviour depending on the Al content. The best oxidation resistance and thermal stability are obtained for the coating with similar to 16 at.% Al and 3.4 at.% Y. The initial film microstructure and the cubic phase (fcc-CrAlN) were retained, and a thin (Cr,Al)(2)O-3 oxide protective scale was formed. At lower Y content (1.2 at.%) iron, from the substrate crosses the coating, while a higher content (4.6 at.%) avoided the iron diffusion at the expense of a thicker oxide scale with new oxide phases. The coatings with higher Al content (similar to 25 at. %) were not thermally stable at 1000 degrees C. A good oxidation resistance was obtained for 2.6 at.% of Y although new phases (hcp-AlN and Cr-Fe) were formed. Higher amount of yttrium (similar to 5.7 at. %) led to the complete oxidation of the coating. 

January, 2019 | DOI: 10.1016/j.jallcom.2018.09.280


Influence of irrigation conditions in the germination of plasma treated Nasturtium seeds

Molina, R; Lopez-Santos, C; Gomez-Ramirez, A; Vilchez, A; Espinos, JP; Gonzalez-Elipe, AR
Scientific Reports, 8 (2018) art. 16442


Plasma treatments had emerged as a useful technique to improve seed germination. In this work we investigate the influence of different irrigation conditions and plasma treatments on the germination of nasturtium seeds. During plasma treatment, seeds experience a progressive weight loss as a function of treatment time that has been associated to water release, a process that is more pronounced after longer plasma treatment times. Seeds treated for short times (<30 s) are able to germinate more efficiently than untreated specimen under hydric stress (drought conditions), while plasma treatments for longer times (up to 300 s) impaired germination independently on irrigation conditions. Characterization analysis of plasma treated seeds by FTIR-ATR, SEM/EDX and XPS showed that plasma treatment affected the chemical state of pericarp while, simultaneously, induced a considerable increase in the seeds water uptake capacity. The decrease in germination efficiency found after plasma treatment for long times, or for short times under optimum irrigation conditions, has been attributed to that the excess of water accumulated in the pericarp hampers the diffusion up to the embryo of other agents like oxygen which are deemed essential for germination.

November, 2018 | DOI: 10.1038/s41598-018-34801-0

Nanoporous Pt-based catalysts prepared by chemical dealloying of magnetron-sputtered Pt-Cu thin films for the catalytic combustion of hydrogen

Giarratano, F; Arzac, GM; Godinho, V; Hufschmidt, D; de Haro, MCJ; Montes, O; Fernandez, A
Applied Catalysis B-Environmental, 235 (2018) 168-176


In this work, we prepared SiC-supported Pt-Cu thin films by magnetron sputtering for use as catalysts for the combustion of hydrogen under oxidizing conditions. We tested the catalysts as prepared and after chemical dealloying. A methodology is presented to fabricate catalytic thin films of a desired composition with tailored magnetron targets with lower Pt consumption. The deposition gas was changed to prepare columnar (Ar-deposited) and closed-porous (He-deposited) films to study the effect of the microstructure on the activity. The effect of composition was also studied for the columnar samples. The as-prepared Pt-Cu thin films showed significant activity only at temperatures higher than 100 °C. Dealloying permitted an increase in the activity to achieve near room-temperature activity. The dealloyed closed-porous He-deposited sample was the most active, being able to convert as much as 13.15 LH2·min−1 gPt−1 at 70 °C (Ea = 1 kJ mol−1). This sample was preferentially dealloyed on the surface, yielding an almost pure Pt shell (96% at. Pt) and a Cu-depleted interior (71% at. Pt). This compositional inhomogeneity enabled the sample to achieve enhanced activity compared to the Ar-deposited columnar sample (with similar initial composition, but uniformly dealloyed), probably due to the compressive surface lattice strain. The dealloyed closed-porous He-deposited sample was shown to be durable over five cycles.

November, 2018 | DOI: 10.1016/j.apcatb.2018.04.064

Quantitative analysis of Yb 4d photoelectron spectrum of metallic Yb

Pauly, N; Yubero, F; Tougaard, S
Surface & Coatings Technology, 50 (2018) 1168-1173


The measured Yb 4d(3/2) intensity is larger than the Yb 4d(5/2) in X-ray photoelectron (XPS) emission of metallic Yb, which is unexpected. The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. To quantitatively extract from experimental XPS the primary excitation spectrum (ie, the initial excitation process) of the considered transition, these effects must be included within the theoretical description. The combined effect of both extrinsic and intrinsic excitations can be described by an effective energy-differential inelastic electron scattering cross section for XPS evaluated by a dielectric response model with the dielectric function as only input. Then, using this cross section, a direct evaluation of the primary excitation spectrum is performed by standard peak shape analysis for thick homogeneous samples. We use this approach in the present paper to determine the Yb 4d photoemission spectrum for metallic Yb. We show that the unexpected larger intensity of Yb 4d(3/2) compared to 4d(5/2) can be fully accounted for by our model and that the total spectrum consists of a sum of symmetric primary excitation peaks.

November, 2018 | DOI: 10.1002/sia.6402

The Role of Surface Recombination on the Performance of Perovskite Solar Cells: Effect of Morphology and Crystalline Phase of TiO2 Contact

Idigoras, J; Contreras-Bernal, L; Cave, JM; Courtier, NE; Barranco, A; Borras, A; Sanchez-Valencia, JR; Anta, JA; Walker, AB
Advanced Materials Interfaces, 5 (2018) art. 1801076


Herein, the preparation of 1D TiO2 nanocolumnar films grown by plasma-enhanced chemical vapor deposition is reported as the electron selective layer (ESL) for perovskite solar devices. The impact of the ESL architecture (1D and 3D morphologies) and the nanocrystalline phase (anatase and amorphous) is analyzed. For anatase structures, similar power conversion efficiencies are achieved using an ESL either the 1D nanocolumns or the classical 3D nanoparticle film. However, lower power conversion efficiencies and different optoelectronic properties are found for perovskite devices based on amorphous 1D films. The use of amorphous TiO2 as electron selective contact produces a bump in the reverse scan of the current-voltage curve as well as an additional electronic signal, detected by impedance spectroscopy measurements. The dependence of this additional signal on the optical excitation wavelength used in the IS experiments suggests that it stems from an interfacial process. Calculations using a drift-diffusion model which explicitly considers the selective contacts reproduces qualitatively the main features observed experimentally. These results demonstrate that for a solar cell in which the contact is working properly the open-circuit photovoltage is mainly determined by bulk recombination, whereas the introduction of a "bad contact" shifts the balance to surface recombination.

November, 2018 | DOI: 10.1002/admi.201801076

High-temperature oxidation of CrAlYN coatings: Implications of the presence of Y and type of steel

Rojas, TC; Dominguez-Meister, S; Brizuela, M; Sanchez-Lopez, JC
Surface & Coatings Technology, 354 (2018) 203-2013


Nanolayered CrAIN and CrAIYN/CrAIN (average contents of Al approximate to 25 at.% and Y approximate to 1.6 at. %) coatings are deposited on M2 and 316 steel substrates and heated to 1000 degrees C in air for 2 h to study their oxidation mechanism, the thermal stability and the reactive element (RE) effect of yttrium. CrAIN on M2 develops a Cr2O3/Al2O3 passivation layer that preserves in high degree the fcc-CrAIN structure however iron ions leave the substrate and travel to the surface along the column boundaries. The CrAIYN/CrAIN coatings deposited on steels are not stable at 1000 degrees C, and the initial fcc-CrAIN phase is partially transformed to hcp-Al(O)N and Cr-Fe phases (M2) and Cr2N and Al2O3 (316). The addition of Y changes the predominant scale growth direction. Inward oxygen diffusion becomes dominant but a reduction of the oxide scale thickness as compared to CrAIN is not observed. The advanced microstructural analysis made by transmission electron microscopy combined with electron energy loss spectroscopy determined that yttrium migrates mainly to the oxide scale (forming mixed oxides with substrate elements - V and Mo, either as dispersed particles or segregated at the grain boundaries) in M2, and to the oxide interface and column boundaries (forming Al-Y oxides and YN, respectively) in 316 steel. The benefits of addition of Y in improving the oxidation resistance are discussed comparatively with literature data. The RE effect of yttrium is thus observed to be dependent on the substrate, film architecture and composition.

October, 2018 | DOI: 10.1016/j.surfcoat.2018.09.020

Adhesion enhancement of DLC hard coatings by HiPIMS metal ion etching pretreatment

Santiago, JA; Fernandez-Martinez, I; Wennberg, A; Molina-Aldareguia, JM; Castillo-Rodriguez, M; Rojas, TC; Sanchez-Lopez, JC; Gonzalez, MU; Garcia-Martin, JM; Li, H; Bellido-Gonzalez, V; Monclus, MA; Gonzalez-Arrabal, R
Surface & Coatings Technology, 349 (2018) 787-796


Poor adhesion is a recurrent problem for the wider use of diamond-like carbon (DLC) coatings in industrial applications. In this work, we investigate the effectiveness of high-power impulse magnetron sputtering (HiPIMS) metal ion etching to improve the adhesion of DLC coatings on high speed steel substrates. The influence of HiPIMS pretreatment parameters, the metal ion selection for the process and the addition of bonding layers on the adhesion properties were studied. Daimler-Benz and nanoscratch test methods were used to evaluate the adhesion. The elemental composition, morphology and microstructure of the samples were evaluated by EELS, SEM, AFM and HRTEM. In general, samples pretreated with HiPIMS metal ion etching withstand larger critical loads than those pretreated by conventional Ar + glow discharge and bonding layers. The pretreatment is proven to be very effective at removing surface contaminants and providing a gradual interface. The selection of Cr over Ti contributes to a significant improvement on the adhesion due to the reduction of the oxygen level at the interface thus ensuring an optimal coating-substrate contact and a more compliant structure, which prevents the delamination failure.

September, 2018 | DOI: 10.1016/j.surfcoat.2018.04.090

Sensing and biosensing with screen printed electrodes modified with nanostructured nickel oxide thin films prepared by magnetron sputtering at oblique angles

Salazar, P; Garcia-Garcia, FJ; Gonzalez-Elipe, AR
Electrochemistry Communications, 94 (2018) 5-8


This work reports about the sensing and biosensing applications of a novel screen printed electrode (SPE) modified by nanostructured nickel oxide thin films obtained by reactive magnetron sputtering under an oblique angle configuration. Using these films as electrodes we demonstrate their ability to detect hydrogen peroxide under neutral pH conditions. Furthermore, as a proof-of-concept, NiO-modified SPEs have been developed and their cholesterol biosensing properties determined by cyclic voltammetry and chronoamperometry.

September, 2018 | DOI: 10.1016/j.elecom.2018.07.020

Nanostructural Analysis of Porous Oblique Angle Deposited (OAD) Multilayer Systems by Grazing-Incidence Small-Angle X-Ray Scattering

Oliva-Ramirez, M; Lopez-Santos, C; Yubero, F; Gonzalez-Elipe, AR
Advanced Optical Materials, 5 (2018) 1800530


This work reports a thorough characterization analysis of various porous thin film multilayers by means of grazing-incidence small-angle X-ray scattering (GISAXS). Alternated TiO2/SiO2 nanocolumnar layers deposited at oblique angles are fabricated in slanted, chiral, and zig-zag configurations by rotating azimuthally the substrate from one layer to the next. Multilayer systems formed by the stacking of 3 and 15 alternant thin films of these two oxides are morphologically characterized by scanning electron microscopy (SEM) and structurally by GISAXS. This technique has provided a means to determine various vertical and lateral correlation lengths and to assess the anisotropic electron density distribution along the structural elements existing in the multilayers. This information can be systematically used to account for the actual arrangement of nanostructural elements in multilayer systems.

September, 2018 | DOI: 10.1002/admi.201800530

Origin of Light-Induced Photophysical Effects in Organic Metal Halide Perovskites in the Presence of Oxygen

Anaya, M; Galisteo-Lopez, JF; Calvo, ME; Espinos, JP; Miguez, H
Journal of Physical Chemistry Letters, 9 (2018) 3891-3896


Herein we present a combined study of the evolution of both the photoluminescence (PL) and the surface chemical structure of organic metal halide perovskites as the environmental oxygen pressure rises from ultrahigh vacuum up to a few thousandths of an atmosphere. Analyzing the changes occurring at the semiconductor surface upon photoexcitation under a controlled oxygen atmosphere in an X-ray photoelectron spectroscopy (XPS) chamber, we can rationalize the rich variety of photophysical phenomena observed and provide a plausible explanation for light-induced ion migration, one of the most conspicuous and debated concomitant effects detected during photoexcitation. We find direct evidence of the formation of a superficial layer of negatively charged oxygen species capable of repelling the halide anions away from the surface and toward the bulk. The reported PL transient dynamics, the partial recovery of the initial state when photoexcitation stops, and the eventual degradation after intense exposure times can thus be rationalized.

July, 2018 | DOI: 10.1021/acs.jpclett.8b01830

Strong activation effect on a ru-co-c thin film catalyst for the hydrolysis of sodium borohydride

Arzac, GM; Paladini, M; Godinho, V; Beltran, AM; de Haro, MCJ; Fernandez, A
Scientific Reports, 8 (2018) art. 9755


In this work, we prepared a series of Ni foam supported Ru-Co, Ru-Co-B and Ru-Co-C catalysts in the form of columnar thin films by magnetron sputtering for the hydrolysis of sodium borohydride. We studied the activity and durability upon cycling. We found a strong activation effect for the Ru-Co-C sample which was the highest ever reported. This catalyst reached in the second cycle an activity 5 times higher than the initial (maximum activity 9310 ml.min(-1).g(CoRu)(-1) at 25 degrees C). Catalytic studies and characterization of the fresh and used samples permitted to attribute the strong activation effect to the following factors: (i) small column width and amorphous character (ii) the presence of Ru and (iii) dry state before each cycle. The presence of boron in the initial composition is detrimental to the durability. Our studies point out to the idea that after the first cycle the activity is controlled by surface Ru, which is the most active of the two metals. Apart from the activation effect, we found that catalysts deactivated in further cycles. We ascribed this effect to the loss of cobalt in the form of hydroxides, showing that deactivation was controlled by the chemistry of Co, the major surface metal component of the alloy. Alloying with Ru is beneficial for the activity but not for the durability, and this should be improved.

June, 2018 | DOI: 10.1038/s41598-018-28032-6

Growth of nanocolumnar porous TiO2 thin films by magnetron sputtering using particle collimators

Garcia-Valenzuela, A; Alvarez, R; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Surface & Coatings Technology, 343 (2018) 172-177


The selective incorporation of deposition species with preferential directionality is analyzed during the growth of TiO2 thin films by magnetron sputtering. Using wisely-designed collimators, tilted nanocolumnar morphologies are grown in a ballistic deposition regime, i.e. when most deposition species arrive at the film surface along well-defined preferential directions, and also in a thermalized deposition regime, when these species follow an isotropic momentum distribution in the plasma gas. The obtained results suggest that the use of particle collimators may promote the growth of porous thin films even in the classical magnetron sputtering configuration, when the target and the substrate are parallel. General insights are given on this approach and, as a proof of concept, its principles applied for the synthesis of nanostructured films in a laboratory-size reactor.

June, 2018 | DOI: 10.1016/j.surfcoat.2017.09.039

Room temperature synthesis of water-dispersible Ln(3+):CeF3 (Ln = Nd, Tb) nanoparticles with different morphology as bimodal probes for fluorescence and CT imaging

Gonzalez-Mancebo, D; Becerro, AI; Rojas, TC; Olivencia, A; Corral, A; Balcerzyk, M; Cantelar, E; Cusso, F; Ocana, M
Journal of Colloid and Interface Science, 520 (2018) 134-144


The singular properties of lanthanide-based inorganic nanoparticles (NPs) has raised the attention of the scientific community in biotechnological applications. In particular, those systems with two or more functionalities are especially interesting. In this work, an effective and commercially attractive procedure has been developed that renders uniform, water-dispersible Ln(3+):CeF3 (Ln = Tb, Nd) NPs with different shapes and size. The method consists of the homogeneous precipitation, in a mixture of polyol and water, of cations and anions using precursors that allow the controlled release of the latter. The advantages of the reported method are related to the absence of surfactants, dispersing agents or corrosive precursors as well as to the room temperature of the process. The obtained Tb:CeF3 NPs produce an intense emission after excitation through the Ce-Tb energy transfer band located in the UV spectral region, thus being potentially useful as phosphors for in-vitro imaging purposes. On the other hand, the synthesized Nd:CeF3 NPs are good candidates for in-vivo imaging because their excitation and emission wavelengths lie in the biological windows. Finally, the excellent X-ray attenuation efficacy of the Nd:CeF(3)NPs is shown, which confers double functionality to this material as both luminescence bioprobe and contrast agent for X-ray computed-tomography. 

June, 2018 | DOI: 10.1016/j.jcis.2018.03.007

Tribological properties of TiC/a-C:H nanocomposite coatings prepared via HiPIMS

Sanchez-Lopez, JC; Dominguez-Meister, S; Rojas, TC; Colasuonno, M; Bazzan, M; Patelli, A
Applied Surface Science, 440 (2018) 458-466


High power impulse magnetron sputtering (HiPIMS) technology has been employed to prepare TiC/a-C:H nanocomposite coatings from a titanium target in acetylene (C2H2) reactive atmospheres. Gas fluxes were varied from 1.3 to 4.4 sccm to obtain C/Ti ratios from 2 to 15 as measured by electron probe microanalysis (EPMA). X-ray diffraction and transmission electron microscopy demonstrate the presence of TiC nanocrystals embedded in an amorphous carbon-based matrix. The hardness properties decrease from 17 to 10 GPa as the carbon content increases. The tribological properties were measured using a pinon-disk tribometer in ambient air (RH = 30-40%) at 10 cm/s with 5 N of applied load against 6-mm 100Cr6 balls. The friction coefficient and the film wear rates are gradually improved from 0.3 and 7 x 10(-6) mm(3)/N m to 0.15 and 2 x 10(-7) mm(3)/N m, respectively, by increasing the C2H2 flux. To understand the tribological processes appearing at the interface and to elucidate the wear mechanism, microstructural and chemical investigations of the coatings were performed before and after the friction test. EPMA, X-ray photoelectron and electron energy-loss spectroscopies were employed to obtain an estimation of the fraction of the a-C:H phase, which can be correlated with the tribological behavior. Examination of the friction counterfaces (ball and track) by Raman microanalysis reveals an increased ordering of the amorphous carbon phase concomitant with friction reduction. The tribological results were compared with similar TiC/a-C(:H) composites prepared by the conventional direct current process. 

May, 2018 | DOI: 10.1016/j.apsusc.2018.01.135

The nanostructure of porous cobalt coatings deposited by magnetron sputtering in helium atmosphere

Lacroix, B; Godinho, V; Fernandez, A
Micron, 108 (2018) 49-54


In this work, (scanning) transmission electron microscopy has been used to study the nanostructure of porous cobalt coatings obtained by magnetron sputtering using helium as process gas. This nanostructure consists of closed pores of different nanometric size (about 4-20 nm) that are distributed all over a nanocrystalline Co matrix and filled with the deposition gas. Spatially resolved electron energy-loss spectroscopy analysis was applied to measure and map, with high lateral resolution, the relevant physical properties (density, pressure and He-K edge shift) of helium trapped inside these individual nanopores, in order to provide new insights about the growth mechanism involved in such systems. In particular, a coefficient of proportionality, C = 0.039 eV nm(3), between the blue shift of the He K-edge and the He density has been found. In addition, very high He densities (10-100 at./nm(3)) and pressures in the gigapascal range (0.05-5.0 GPa) have been measured. The linear dependence of these parameters as a function of the inverse radii obeying to the Laplace-Young law for most of the pores suggests that their formation during the coating's growth takes place in regime of elastic deformation of the Co matrix.

May, 2018 | DOI: 10.1016/j.micron.2018.02.004

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

Manuel, JM; Jimenez, JJ; Morales, FM; Lacroix, B; Santos, AJ; Garcia, R; Blanco, E; Dominguez, M; Ramirez, M; Beltran, AM; Alexandrov, D; Tot, J; Dubreuil, R; Videkov, V; Andreev, S; Tzaneva, B; Bartsch, H; Breiling, J; Pezoldt, J; Fischer, M; Muller, J
Scientific Reports, 8 (2018) art. 6879


This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

May, 2018 | DOI: 10.1038/s41598-018-25416-6

Microemulsion Assisted Sol-Gel Method as Approach to Load a Model Anticancer Drug inside Silica Nanoparticles for Controlled Release Applications

Jaramillo, N; Paucar, C; Fernandez, A; Negrete, CG; Garcia, C
Collid and Interface Science Communications, 24 (2018) 13-17


Silica nanoparticles are attractive carriers due to their improved safety and effectiveness in drug delivery. Silica nanoparticles were synthesized by using microemulsion assisted sol-gel method, and a model anticancer drug 5-fluorouracil (5-FU) was added to the silica precursor before hydrolysis and condensation reactions start. The obtained materials were characterized by Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). Drug encapsulation within silica nanoparticles causes an increase in particle size. However, particle morphology is not affected. The drug release profile was obtained through high performance liquid chromatography (HPLC). The encapsulation approach showed to be effective for sustaining a continuous and increasing release during testing time (98 h). Further studies were performed to evaluate the cytotoxic effects of silica nanoparticles with loaded 5-FU on Chinese hamster ovary cells (CHO-K1). Materials are non-cytotoxic for all concentration tested (5-200 mu g/mL).

May, 2018 | DOI: 10.1016/j.colcom.2018.03.002

In Vitro Comparative Study of Oxygen Plasma Treated Poly(Lactic-Co-Glycolic) (PLGA) Membranes and Supported Nanostructured Oxides for Guided Bone Regeneration Processes

Torres-Lagares, D; Castellanos-Cosano, L; Serrera-Figallo, MA; Lopez-Santos, C; Barranco, A; Rodriguez-Gonzalez-Elipe, A; Gutierrez-Perez, JL
Materials, 11 (2018) art. 752


(1) Background: The use of physical barriers to prevent the invasion of gingival and connective tissue cells into bone cavities during the healing process is called guided bone regeneration. The objective of this in-vitro study was to compare the growth of human osteoblasts on Poly(Lactic-co-Glycolic) (PLGA) membranes modified with oxygen plasma and Hydroxyapatite (HA), silicon dioxide (SiO2), and titanium dioxide (TiO2) composite nanoparticles, respectively. (2) Methods: All the membranes received a common treatment with oxygen plasma and were subsequently treated with HA nanostructured coatings (n = 10), SiO2 (n = 10) and TiO2 (n = 10), respectively and a PLGA control membrane (n = 10). The assays were performed using the human osteoblast line MG-63 acquired from the Center for Scientific Instrumentation (CIC) from the University of Granada. The cell adhesion and the viability of the osteoblasts were analyzed by means of light-field microphotographs of each condition with the inverted microscope Axio Observer A1 (Carl Zeiss). For the determination of the mitochondrial energy balance, the MitoProbe (TM) JC-1 Assay Kit was employed. For the determination of cell growth and the morphology of adherent osteoblasts, two techniques were employed: staining with phalloidin-TRITC and staining with DAPI. (3) Results: The modified membranes that show osteoblasts with a morphology more similar to the control osteoblasts follow the order: PLGA/PO2/HA > PLGA/PO2/SiO2 > PLGA/PO2/TiO2 > PLGA (p < 0.05). When analysing the cell viability, a higher percentage of viable cells bound to the membranes was observed as follows: PLGA/PO2/SiO2 > PLGA/PO2/HA > PLGA/PO2/TiO2 > PLGA (p < 0.05), with a better energy balance of the cells adhered to the membranes PLGA/PO2/HA and PLGA/PO2/SiO2. (4) Conclusion: The membrane in which osteoblasts show characteristics more similar to the control osteoblasts is the PLGA/PO2/HA, followed by the PLGA/PO2/SiO2.

May, 2018 | DOI: 10.3390/ma11050752

Electrophoretic deposition of mixed copper oxide/GO as cathode and N-doped GO as anode for electrochemical energy storage

Jafari, EA; Moradi, M; Hajati, S; Kiani, MA; Espinos, JP
Electrochimica Acta, 268 (2018) 392-402


In this work, energy storage properties of mixed copper oxide wrapped by reduced graphene oxide and nitrogen-doped reduced graphene oxide were investigated. First, co-electrophoretic deposition technique was used to coat GO@CuO on nickel foam; followed by electrochemical phase transformation to rGO@CuxO. Electron spectroscopy analyses (XPS, REELS and UPS) confirm the phase transformation and electrochemical reduction. Then, an electrophoretic deposition was carried out for coating nitrogen-doped graphene oxide on nickel foam coupled to its electrochemical reduction to the NrGO. The cathode and anode performances were studied by galvanostatic charge-discharge, cyclic voltammetry and impedance spectroscopy. The rGO@CuxO and NrGO exhibit a favorable specific capacity of 267.2 and 332.6 C g(-1) at 2 A g(-1), respectively. High electrochemical activity and elimination of polymer binders with a maximum potential of 1.6 V are among the advantages of rGO@CuxO//NrGO electrochemical charge storage device. Furthermore, fabricated device provided a maximum specific power and specific energy of 11917.24 W kg(-1) and 14.15 Wh kg(-1), respectively, with 86% capacity retention after 2000 cycles.

April, 2018 | DOI: 10.1016/j.electacta.2018.02.122

Colorimetric energy sensitive scintillator detectors based on luminescent multilayer designs

Ferrer, FJ; Gil-Rostra, J; Gonzalez-Elipe, AR; Yubero, F
Sensors and Actuators A-Physical, 272 (2018) 217-222


In this work we present a new concept for energy sensitive radiation-beam scintillator detectors based on a luminescent multilayer design, where each layer within the stack consists of a rare-earth-doped highly transparent oxide. For a given type of particle beam (i.e., protons, a particles, etc.), its penetration depth, and therefore its energy loss at a particular buried layer, depends on its initial kinetic energy. Relying on this principle and since the intensity of the luminescent response of each layer and substrate should be proportional to the energy deposited by the radiation beam, we prove that a characteristic energy dependent color emission is obtained depending on both the phosphors integrated in the luminescent stack and on the primary energy and type of particle beam. Phosphor doping, emission efficiency, layer thickness, and multilayer structure design are key parameters to achieve a broad gamut in colorimetric response. The developed scintillators are designed to operate in a transmission geometry (light detection from the opposite side of the incident radiation) which is well suited for high energy particle detection in fields such as oncotherapy, space radiation, or of fusion studies. The principles of the method are illustrated with a case example typical of ion beam accelerators devoted to materials analysis. It is obtained that the kinetic energy of protons/alpha particle beams can be distinguished and evaluated with a sensitivity of 0.06/0.25 chromaticity units per MeV in the 0.7-2.0 MeV range. 

April, 2018 | DOI: 10.1016/j.sna.2018.01.062

Enhancing Moisture and Water Resistance in Perovskite Solar Cells by Encapsulation with Ultrathin Plasma Polymers

Idigoras, J; Aparicio, FJ; Contreras-Bemal, L; Ramos-Terron, S; Alcaire, M; Sanchez-Valencia, JR; Borras, A; Barranco, A; Anta, JA
ACS Applied Materials & Interfaces, 10 (2018) 11587-11594


A compromise between high power conversion efficiency and long-term stability of hybrid organic inorganic metal halide perovskite solar cells is necessary for their outdoor photovoltaic application and commercialization. Herein, a method to improve the stability of perovskite solar cells under water and moisture exposure consisting of the encapsulation of the cell with an ultrathin plasma polymer is reported. The deposition of the polymer is carried out at room temperature by the remote plasma vacuum deposition of adamantane powder. This encapsulation method does not affect the photovoltaic performance of the tested devices and is virtually compatible with any device configuration independent of the chemical composition. After 30 days under ambient conditions with a relative humidity (RH) in the range of 35-60%, the absorbance of encapsulated perovskite films remains practically unaltered. The deterioration in the photovoltaic performance of the corresponding encapsulated devices also becomes significantly delayed with respect to devices without encapsulation when vented continuously with very humid air (RH > 85%). More impressively, when encapsulated solar devices were immersed in liquid water, the photovoltaic performance was not affected at least within the first 60 s. In fact, it has been possible to measure the power conversion efficiency of encapsulated devices under operation in water. The proposed method opens up a new promising strategy to develop stable photovoltaic and photocatalytic perovskite devices.

April, 2018 | DOI: 10.1021/acsami.7b17824

Dye Giant Absorption and Light Confinement Effects in Porous Bragg Microcavities

Oliva-Ramirez, M; Gil-Rostra, J; Simonsen, AC; Yubero, F; Gonzalez-Elipe, AR
ACS Photonics, 5 (2018) 984-991


This work presents a simple experimental procedure to probe light confinement effects in photonic structures. Two types of porous 1D Bragg microcavities with two resonant peaks in the reflection gap were prepared by physical vapor deposition at oblique angle configurations and then infiltrated with dye solutions of increasing concentrations. The unusual position shift and intensity drop of the transmitted resonant peak observed when it was scanned through the dye absorption band have been accounted for by the effect of the light trapped at their optical defect layer. An experimentally observed giant absorption of the dye molecules and a strong anomalous dispersion in the refractive index of the solution are claimed as the reasons for the observed variations in the Bragg microcavity resonant feature. Determining the giant absorption of infiltrated dye solutions is proposed as a general and simple methodology to experimentally assess light trapping effects in porous photonic structures.

March, 2018 | DOI: 10.1021/acsphotonics.7b01283

Copper-containing mesoporous bioactive glass promotes angiogenesis in an in vivo zebrafish model

Romero-Sanchez, LB; Mari-Beffa, M; Carrillo, P; Medina, MA; Diaz-Cuenca, A
Acta Biomaterialia, 68 (2018) 272-285


The osteogenic and angiogenic responses of organisms to the ionic products of degradation of bioactive glasses (BGs) are being intensively investigated. The promotion of angiogenesis by copper (Cu) has been known for more than three decades. This element can be incorporated to delivery carriers, such as BGs, and the materials used in biological assays. In this work, Cu-containing mesoporous bioactive glass (MBG) in the SiO2-CaO-P2O5compositional system was prepared incorporating 5% mol Cu (MBG-5Cu) by replacement of the corresponding amount of Ca. The biological effects of the ionic products of MBG biodegradation were evaluated on a well-known endothelial cell line, the bovine aorta endothelial cells (BAEC), as well as in an in vivo zebrafish (Danio rerio) embryo assay. The results suggest that ionic products of both MBG (Cu free) and MBG-5Cu materials promote angiogenesis. In vitro cell cultures show that the ionic dissolution products of these materials are not toxic and promote BAEC viability and migration. In addition, the in vivo assay indicates that both exposition and microinjection of zebrafish embryos with Cu free MBG material increase vessel number and thickness of the subintestinal venous plexus (SIVP), whereas assays using MBG-5Cu enhance this effect.

March, 2018 | DOI: 10.1016/j.actbio.2017.12.032

Robust polarization active nanostructured 1D Bragg Microcavities as optofluidic label-free refractive index sensor

Oliva-Ramirez, M; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Sensors and Actuators B-Chemical, 256 (2018) 590-599


In this work we report the use of polarization active porous 1D Bragg microcavities (BM) prepared by physical vapor deposition at oblique angles for the optofluidic analysis of liquid solutions. These photonic structures consist of a series of stacked highly porous layers of two materials with different refractive indices and high birefringence. Their operational principle implies filling the pores with the analyzed liquid while monitoring with linearly polarized light the associated changes in optical response as a function of the solution refractive index. The response of both polarization active and inactive BMs as optofluidic sensors for the determination of glucose concentration in water solutions has been systematically compared. Different methods of detection, including monitoring the BM wave retarder behavior, are critically compared for both low and high glucose concentrations. Data are taken in transmission and reflection modes and different options explored to prove the incorporation of these nanostructured transducers into microfluidic systems and/or onto the tip of an optical fiber. This analysis has proven the advantages of the polarization active transducer sensors for the optofluidic analysis of liquids and their robustness even in the presence of light source instabilities or misalignments of the optical system used for detection.

March, 2018 | DOI: 10.1016/j.snb.2017.10.060

Biodegradabiliy of spherical mesoporous silica particles (MCM-41) in simulated body fluid (SBF)

Boccardi, E; Philippart, A; Beltran, AM; Schmidt, J; Liverani, L; Peukert, W; Boccaccini, AR
American Mineralogist, 103 (2018) 350-354


Mesoporous silica particles of type MCM-41 (Mobile Composition of Matter No. 41), exhibiting highly ordered mesoporosity (pores with diameter between 2 and 50 nm) and surface roughness, are developed and used as a functional coating on bioactive glass-based scaffolds for bone tissue engineering. The degradability and the mesostructure stability of these novel MCM-41 particles were evaluated. The particles are immersed in simulated body fluid (SBF) for up to 28 days at 37 degrees C, and the variation of the ordered porosity, surface characteristics, and chemical composition of the particles are assessed by SEM-EDX, HRTEM, FTIR, ICP-OES, and pH measurements. The results indicate that the MCM-41 particles are affected by immersion in SBF only during the first few days; however, the surface and the mesopore structure of the particles do not change further with increasing time in SBF. The pore channel diameter increased slightly, confirming the stability of the developed material. The release of dissolved Si-species, which reached a maximum of 260 mg SiO2 per gram of material, could play a key role in gene activation of osteoblast cells and in inducing new bone matrix formation. 

March, 2018 | DOI: 10.2138/am-2018-6281

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires

Filippin, AN; Lopez-Flores, V; Rojas, TC; Saghi, Z; Rico, VJ; Sanchez-Valencia, JR; Espinos, JP; Zitolo, A; Viret, M; Midgley, PA; Barranco, A; Borras, A
Chemistry of Materials, 30 (2018) 879-887


In this article we show for the first time the formation of magnetic supported organic nanowires (ONWs) driven by self-assembly of a nonplanar Fe(III) phthalocyanine chloride (FePcCl) molecule. The ONWs grow by a crystallization mechanism on roughness-tailored substrates. The growth methodology consists of a vapor deposition under low vacuum and mild temperature conditions. The structure, microstructure, and chemical composition of the FePcCl NWs are thoroughly elucidated and compared with those of Fe(II) phthalocyanine NWs by a consistent and complementary combination of advanced electron microscopies and X-ray spectroscopies. In a further step, we vertically align the NWs by conformal deposition of a SiO2 shell. Such orientation is critical to analyze the magnetic properties of the FePcCl and FePc supported NWs. A ferromagnetic behavior below 30 K with an easy axis perpendicular to the phthalocyanine plane was observed in the two cases with the FePcCl nanowires presenting a wider hysteresis. These results open the path to the fabrication of nanostructured one-dimensional small-molecule spintronic devices.

February, 2018 | DOI: 10.1021/acs.chemmater.7b04515

In situ monitoring of the phenomenon of electrochemical promotion of catalysis

Espinos, JP; Rico, VJ; Gonzalez-Cobos, J; Sanchez-Valencia, JR; Perez-Dieste, V; Escudero, C; de Lucas-Consuegra, A; Gonzalez-Elipe, AR
Journal of Catalysis, 358 (2018) 27-34


In this work we investigate by in-situ near-ambient pressure photoemission (NAPP) spectroscopy the phenomenon of Electrochemical Promotion of Catalysis (EPOC). We studied the reduction and diffusion kinetics of alkaline ions in a solid electrolyte cell formed by a nickel electrode supported on K+-beta-alumina electrolyte. Experiments in ultra-high vacuum and in the presence of steam showed that the amount of potassium atoms supplied to the surface is probably affected by nickel electronic modifications induced by adsorbed OH- groups. It was also deduced that part of the segregated potassium would be adsorbed at inner interfaces where it would be inaccessible to the photoelectron analyzer. A migration mechanism of the promoter is proposed consisting in: (i) the electrochemical reduction of the alkali ions (potassium) at the Ni/solid electrolyte/gas interface; (ii) the spillover of potassium atoms onto the Ni gas-exposed surface; and (iii) the diffusion of potassium atoms to Ni inner grain boundary interfaces.

February, 2018 | DOI: 10.1016/j.jcat.2017.11.027

Microstructural engineering and use of efficient poison resistant Au-doped Ni-GDC ultrathin anodes in methane-fed solid oxide fuel cells

Garcia-Garcia, FJ; Yubero, F; Gonzalez-Elipe, AR; Lambert, RM
International Journal of Refractory Metals & Hard Materials, 43 (2018) 885-893


Ultrathin porous solid oxide fuel cell (SOFC) anodes consisting of nickel-gadolinia-dopedceria (Ni-GDC) cermets with a unique porous micro-columnar architecture with intimate contact between the GDC and the Ni phases were made by magnetron sputtering at an oblique deposition angle and characterised in detail by a variety of methods prior to use in hydrogen or methane-fuelled SOFCs. These Ni-GDC anodes exhibited excellent transport properties, were robust under thermal cycling and resistant to delamination from the underlying yttria-stabilised zirconia electrolyte. Similarly prepared Au-doped Ni-GDC anodes exhibited the same morphology, porosity and durability. The gold associated exclusively with the Ni component in which it was present as a surface alloy. Strikingly, whatever their treatment, a substantial amount of Ce3+ persisted in the anodes, even after operation at 800 degrees C under fuel cell conditions. With hydrogen as fuel, the un-doped and Au doped Ni-GDC anodes exhibited identical electrochemical performances, comparable to that of much thicker commercial state-of-the-art Ni-GDC anodes. However, under steam reforming conditions with CH4/H(2)0 mixtures the behaviour of the Au-doped Ni-GDC anodes were far superior, exhibiting retention of good power density and dramatically improved resistance to deactivation by carbon deposition. Thus two distinct beneficial effects contributed to overall performance: persistence of Ce3+ in the working anodes could induce a strong metal-support interaction with Ni that enhanced the catalytic oxidation of methane, while formation of a Ni Au surface alloy that inhibited carbonisation and poisoning of the active nickel surface. 

January, 2018 | DOI: 10.1016/j.ijhydene.2017.11.020

Nanostructured hybrid device mimicking bone extracellular matrix as local and sustained antibiotic delivery system

Borrego-Gonzalez, S; Romero-Sanchez, LB; Blazquez, J; Diaz-Cuenca, A
Microporous and Mesoporous Materials, 256 (2018) 165-176


A fluidic permeable and stable in wet media, MBG-NfGel, device consisting of a mesoporous ceramic embodied in a nanofibrillar biodegradable polymer has been processed using appropriate thermally induced phase separation (TIPS) processing variables of 5.4% (wt/v) gelatin in 50/50 water/ethanol (v/v) ratio. The device comprises high surface area mesoporous bioactive glass (MBG) microparticles within a fibrous matrix of 170 nm average diameter nanofibers gelatin, forming a meshwork of 0.2-1.6 mu m range voids. Gentamicin sulphate (GS) antibiotic high loading capacity and sustained release ability, as well as in vitro bioactivity and osteoprogenitor cells biocompatibility supports long-term antibacterial and bone growth stimulation properties. Antibiotic local delivery functionality in vitro of this device has been analysed and discussed in relation to other systems previously reported. The presented device properties as well as its industrial scalability potential, in terms of process reliability and absence of toxic chemical agents, low raw material biopolymer cost and immunogenicity, are other important advantages. These advantages rank MBG-NfGel device as a potential candidate to further development for application as local antibiotic device in bone surgery and therapy.

January, 2018 | DOI: 10.1016/j.micromeso.2017.08.010

Nickel/Copper Bilayer-modified Screen Printed Electrode for Glucose Determination in Flow Injection Analysis

Salazar, P.; Rico, V.; Gonzalez-Elipe, Agustin R.
Electroanalysis, 30 (2018) 187-193


This work reports about the performance of a Ni/Cu-modified screen printed electrodes (SPE/Ni/Cu), prepared by physical vapor deposition (PVD) in an oblique angle configuration (OAD), for non-enzymatic glucose sensing applications. SPE/Ni/Cu electrodes showed an excellent reversibility and a catalytic behavior for detection of glucose that were controlled by the diffusion of reactants up to the active sites at the electrode surface. The study with a flow injection analysis (FIA) setup of the main experimental variables affecting the detection process has shown that the developed electrode system had an excellent glucose sensitivity of 1.04AM(-1)cm(-2) (R-2:0.999), a linear response up to 1mM, a limit of detection of 0.33M and a time of analysis of ca. 30s per sample. The selectivity of the sensor was checked against various interferences, including ascorbic acid, uric acid, acetaminophen and other sugars, in all cases with excellent results. The feasibility of using this sensor for practical applications was successfully confirmed by determining the glucose concentration in different commercial beverages.

January, 2018 | DOI: 10.1002/elan.201700592


Silver and gold nanoparticles in nanometric confined templates: synthesis and alloying within the anisotropic pores of oblique angle deposited films

Parra-Barranco, J., Sánchez-Valencia, J.R., Barranco, A., González-Elipe, A.R.
Nanotechnology, 28 (2017) 485602


In this work we have developed an infiltration methodology to incorporate metal nanoparticles (NPs) of controlled size and shape into the open voids available in oblique angle deposited thin films. These NPs exhibited well-defined surface plasmon resonances (SPRs). The nanometric confined space provided by their porous microstructure has been used as a template for the growth of anisotropic NPs with interesting SPR properties. The fabrication methodology has been applied for the preparation of films with embedded Ag and Au NPs with two associated plasmon resonance features that developed a dichroic behaviour when examined with linearly polarized light. A confined alloying process was induced by near IR nanosecond laser irradiation yielding bimetallic NPs with SPR features covering a large zone of the electromagnetic spectrum. The possibilities of the method for the tailored fabrication of a wide range colour palette based on SPR features are highlighted.

December, 2017 | DOI: 10.1088/1361-6528/aa92af

Micron-scale wedge thin films prepared by plasma enhanced chemical vapor deposition

Lopez-Santos, MC; Alvarez, R; Palmero, A; Borras, A; del Campo, RC; Holgado, M; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 14 (2017) e1700043


Wedge-shaped materials are currently employed for optical analyses and sensing applications. In this paper, we present an easy to implement plasma enhanced chemical vapor deposition procedure to grow wedge-shaped thin films with controlled slope at the scale of few hundred microns. The method relies on the use of few tenths micron height obstacles to alter the laminar flow of precursor gas during deposition and is applied for the fabrication of wedge-shaped ZnO thin films. Local interference patterns, refractive index, and birefringence of the films have been measured with one micron resolution using a specially designed optical set-up. Their micro- and nano-structures have been characterized by means of scanning electron microscopy and theoretically reproduced by Monte Carlo calculations.

December, 2017 | DOI: 10.1002/ppap.201700043

Structural control in porous/compact multilayer systems grown by magnetron sputtering

Garcia-Valenzuela, A; Lopez-Santos, C; Alvarez, R; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Nanotechnology, 28 (2017) 46


In this work we analyze a phenomenon that takes place when growing magnetron sputtered porous/compact multilayer systems by alternating the oblique angle and the classical configuration geometries. We show that the compact layers develop numerous fissures rooted in the porous structures of the film below, in a phenomenon that amplifies when increasing the number of stacked layers. We demonstrate that these fissures emerge during growth due to the high roughness of the porous layers and the coarsening of a discontinuous interfacial region. To minimize this phenomenon, we have grown thin interlayers between porous and compact films under the impingement of energetic plasma ions, responsible for smoothing out the interfaces and inhibiting the formation of structural fissures. This method has been tested in practical situations for compact TiO2/porous SiO2 multilayer systems, although it can be extrapolated to other materials and conditions.

November, 2017 | DOI: 10.1088/1361-6528/aa8cf4

Determination of the thickness of the embedding phase in 0D nanocomposites

Martinez-Martinez, D; Sanchez-Lopez, JC
Applied Surface Science, 421 (2017) 179-184


0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting systems which may show properties that are beyond those observed in the original constituents alone. One of the main parameters to understand the behavior of such nanocomposites is the determination of the separation between two adjacent nanoparticles, in other words, the thickness of the embedding phase. However, its experimental measurement is extremely complicated. Therefore, its evaluation is performed by an indirect approach using geometrical models. The ones typically used represent the nanoparticles by cubes or spheres. 
In this paper the used geometrical models are revised, and additional geometrical models based in other parallelohedra (hexagonal prism, rhombic and elongated dodecahedron and truncated octahedron) are presented. Additionally, a hybrid model that shows a transition between the spherical and tessellated models is proposed. Finally, the different approaches are tested on a set of titanium carbide/amorphous carbon (TiC/a-C) nanocomposite films to estimate the thickness of the a-C phase and explain the observed hardness properties. 

November, 2017 | DOI: 10.1016/j.apsusc.2016.12.081

Incorporation of Calcium Containing Mesoporous (MCM-41-Type) Particles in Electrospun PCL Fibers by Using Benign Solvents

Liverani, L.;Boccardi, E.; Beltrán, A.M.; Boccaccini, A.R.
Polymers, 9 (2017) 487


The electrospinning technique is a versatile method for the production of fibrous scaffolds able to resemble the morphology of the native extra cellular matrix. In the present paper, electrospinning is used to fabricate novel SiO2particles (type MCM-41) containing poly(epsilon-caprolactone) (PCL) fibers. The main aims of the present work are both the optimization of the particle synthesis and the fabrication of composite fibers, obtained using benign solvents, suitable as drug delivery systems and scaffolds for soft tissue engineering applications. The optimized synthesis and characterization of calcium-containing MCM-41 particles are reported. Homogeneous bead-free composite electrospun mats were obtained by using acetic acid and formic acid as solvents; neat PCL electrospun mats were used as control. Initially, an optimization of the electrospinning environmental parameters, like relative humidity, was performed. The obtained composite nanofibers were characterized from the morphological, chemical and mechanical points of view, the acellular bioactivity of the composite nanofibers was also investigated. Positive results were obtained in terms of mesoporous particle incorporation in the fibers and no significant differences in terms of average fiber diameter were detected between the neat and composite electrospun fibers. Even if the Ca-containing MCM-41 particles are bioactive, this property is not preserved in the composite fibers. In fact, during the bioactivity assessment, the particles were released confirming the potential application of the composite fibers as a drug delivery system. Preliminary in vitro tests with bone marrow stromal cells were performed to investigate cell adhesion on the fabricated composite mats, the positive obtained results confirmed the suitability of the composite fibers as scaffolds for soft tissue engineering.

October, 2017 | DOI: 10.3390/polym9100487

Vapor and liquid optical monitoring with sculptured Bragg microcavities

Oliva-Ramirez, M; Gil-Rostra, J; Lopez-Santos, MC; Gonzalez-Elipe, AR; Yubero, F
Journal of Nanophotonics, 11 (2017) 046009


Sculptured porous Bragg microcavities (BMs) formed by the successive stacking of columnar SiO2 and TiO2 thin films with a zig-zag columnar microstructure are prepared by glancing angle deposition. These BMs act as wavelength-dependent optical retarders. This optical behavior is attributed to a self-structuration of the stacked layers involving the lateral association of nanocolumns in the direction perpendicular to the main flux of particles during the multilayer film growth, as observed by focused ion beam scanning electron microscopy. The retardance of these optically active BMs can be modulated by dynamic infiltration of their open porosity with vapors, liquids, or solutions with different refractive indices. The tunable birefringence of these nanostructured photonic systems has been successfully simulated with a simple model that assumes that each layer within the BMs stack has uniaxial birefringence. The sculptured BMs have been incorporated as microfluidic chips for optical transduction for label-free vapor and liquid sensing. Several examples of the detection performance of these chips, working either in reflection or transmission configuration, for the optical monitoring of vapor and liquids of different refractive indices and aqueous solutions of glucose flowing through the microfluidic chips are described.

October, 2017 | DOI: 10.1117/1.JNP.11.046009

Towards Extending Solar Cell Lifetimes: Addition of a Fluorous Cation to Triple Cation-Based Perovskite Films

Salado, M; Fernandez, MA; Holgado, JP; Kazim, S; Nazeeruddin, MK; Dyson, PJ; Ahmad, S
Chemsuschem, 10 (2017) 3846-3853


Organohalide perovskites have emerged as highly promising replacements for thin-film solar cells. However, their poor stability under ambient conditions remains problematic, hindering commercial exploitation. The addition of a fluorous-functionalized imidazolium cation during the preparation of a highly stable cesium-based mixed perovskite material Cs-0.05(MA(0.15)FA(0.85))(0.95)Pb(I0.85Br0.15)(3) (MA= methylammonium; FA= formamidinium) has been shown to influence its stability. The resulting materials, which vary according to the amount of the fluorous-functionalized imidazolium cation present during fabrication, display a prolonged tolerance to atmospheric humidity (> 100 days) along with power conversion efficiencies exceeding 16%. This work provides a general route that can be implemented in a variety of perovskites and highlights a promising way to increase perovskite solar cell stability.

October, 2017 | DOI: 10.1002/cssc.201700797

HoF3 and DyF3 Nanoparticles as Contrast Agents for High-Field Magnetic Resonance Imaging

Gonzalez-Mancebo, Daniel; Becerro, Ana I.; Rojas, T. Cristina; Garcia-Martin, Maria L.; de la Fuente, Jesus M.; Ocana, Manuel
Particle & particle systems characterization, 34 (2017) art. 1700116


Clinical contrast agents (CAs) currently used in magnetic resonance imaging (MRI) at low fields are less effective at high magnetic fields. The development of new CAs is mandatory to improve diagnostic capabilities of the new generation of high field MRI scanners. The purpose of this study is to synthesize uniform, water dispersible LnF3 (Ln = Ho, Dy) nanoparticles (NPs) and to evaluate their relaxivity at high magnetic field (9.4 T) as a function of size and composition. Two different types of HoF3 NPs are obtained by homogeneous precipitation in ethylene glycol at 120 °C. The use of holmium acetate as holmium precursor leads to rhombus-like nanoparticles, while smaller, ellipsoid-like nanoparticles are obtained when nitrate is used as the holmium salt. To explain this behavior, the mechanism of formation of both kinds of particles is analyzed in detail. Likewise, rhombus-like DyF3 nanoparticles are prepared following the same method as for the rhombus-like HoF3 nanoparticles. We have found, to the best of knowledge, the highest transverse relaxivity values at 9.4 T described in the literature for this kind of CAs. Finally, the LnF3 NPs have shown negligible cytotoxicity for C6 rat glioma cells for concentrations up to 0.1 mg mL−1.

October, 2017 | DOI: 10.1002/ppsc.201700116

Enhanced green fluorescent protein in optofluidic Fabry-Perot microcavity to detect laser induced temperature changes in a bacterial culture

Lahoz, F; Martin, IR; Walo, D; Freire, R; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Applied Physics Letters, 111 (2017) 111103


Thermal therapy using laser sources can be used in combination with other cancer therapies to eliminate tumors. However, high precision temperature control is required to avoid damage in healthy surrounding tissues. Therefore, in order to detect laser induced temperature changes, we have used the fluorescence signal of the enhanced Green Fluorescent Protein (eGFP) over-expressed in an E. coli bacterial culture. For that purpose, the bacteria expressing eGFP are injected in a Fabry-Perot (FP) optofluidic planar microcavity. In order to locally heat the bacterial culture, external infrared or ultraviolet lasers were used. Shifts in the wavelengths of the resonant FP modes are used to determine the temperature increase as a function of the heating laser pump power. Laser induced local temperature increments up to 6-7 degrees C were measured. These results show a relatively easy way to measure laser induced local temperature changes using a FP microcavity and using eGFP as a molecular probe instead of external nanoparticles, which could damage/alter the cell. Therefore, we believe that this approach can be of interest for the study of thermal effects in laser induced thermal therapies. 

September, 2017 | DOI: 10.1063/1.4990870

High performance novel gadolinium doped ceria/yttria stabilized zirconia/nickel layered and hybrid thin film anodes for application in solid oxide fuel cells

Garcia-Garcia, FJ; Beltran, AM; Yubero, E; Gonzalez-Elipe, AR; Lambert, RM
Journal of Power Sources, 363 (2017) 251-259


Magnetron sputtering under oblique angle deposition was used to produce Ni-containing ultra thin film anodes comprising alternating layers of,gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) of either 200 nm or 1000 nm thickness. The evolution of film structure from initial deposition, through calcination and final reduction was examined by XRD, SEM, TEM and TOF-SIMS. After subsequent fuel cell usage, the porous columnar architecture of the two-component layered thin film anodes was maintained and their resistance to delamination from the underlying YSZ electrolyte was superior to that of corresponding single component Ni-YSZ and Ni-GDC thin films. Moreover, the fuel cell performance of the 200 nm layered anodes compared favorably with conventional commercially available thick anodes. The observed dependence of fuel cell performance on individual layer thicknesses prompted study of equivalent but more easily fabricated hybrid anodes consisting of simultaneously deposited Ni-GDC and Ni-YSZ, which procedure resulted in exceptionally intimate mixing and interaction of the components. The hybrids exhibited very unusual and favorable I-V characteristics, along with exceptionally high power densities at high currents. Their discovery is the principal contribution of the present work. 

September, 2017 | DOI: 10.1016/j.jpowsour.2017.07.085

In Vitro and in Vivo Study of Poly(Lactic-co-Glycolic) (PLGA) Membranes Treated with Oxygen Plasma and Coated with Nanostructured Hydroxyapatite Ultrathin Films for Guided Bone Regeneration Processes

Torres-Lagares, D; Castellanos-Cosano, L; Serrera-Figallo, MA; Garcia-Garcia, FJ; Lopez-Santos, C; Barranco, A; Elipe, ARG; Rivera-Jimenez, C; Gutierrez-Perez, JL
Polymers, 9 (2017) art. 410


The novelty of this study is the addition of an ultrathin layer of nanostructured hydroxyapatite (HA) on oxygen plasmamodified poly(lactic-co-glycolic) (PLGA) membranes (PO2) in order to evaluate the efficiency of this novel material in bone regeneration. Methods: Two groups of regenerative membranes were prepared: PLGA (control) and PLGA/PO2/HA (experimental). These membranes were subjected to cell cultures and then used to cover bone defects prepared on the skulls of eight experimental rabbits. Results: Cell morphology and adhesion of the osteoblasts to the membranes showed that the osteoblasts bound to PLGA were smaller and with a lower number of adhered cells than the osteoblasts bound to the PLGA/PO2/HA membrane (p < 0.05). The PLGA/PO2/HA membrane had a higher percentage of viable cells bound than the control membrane (p < 0.05). Both micro-CT and histological evaluation confirmed that PLGA/PO2/HA membranes enhance bone regeneration. A statistically significant difference in the percentage of osteoid area in relation to the total area between both groups was found. Conclusions: The incorporation of nanometric layers of nanostructured HA into PLGA membranes modified with PO2 might be considered for the regeneration of bone defects. PLGA/PO2/HA membranes promote higher osteosynthetic activity, new bone formation, and mineralisation than the PLGA control group.

September, 2017 | DOI: 10.3390/polym9090410

One-reactor plasma assisted fabrication of ZnO@TiO2 multishell nanotubes: assessing the impact of a full coverage on the photovoltaic performance

Filippin, Alejandro Nicolas; Macias-Montero, Manuel; Saghi, Zineb; Idigoras, Jesus; Burdet, Pierre; Sanchez-Valencia, Juan R.; Barranco, Angel; Migdley, Paul A.; Anta, Juan A.; Borras, Ana
Scientific Reports, 7 (2017) art 9621


This paper addresses the fabrication of vertically aligned ZnO@TiO2multishell nanotubes by a combined full vacuum-plasma approach at mild temperatures. The growth is carried out within the premises of a one-reactor approach, i.e. minimizing the number of vacuum chambers and sample transferences. In this way, the interface between ZnO and TiO2 is fully preserved from humidity thus increasing ZnO durability and stability. These nanostructures are studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy in STEM (EDX-STEM). High density one-dimensional arrays of these nanotubes formed on FTO substrates are applied as photoanode in a dye-sensitized solar cell (DSC). The evolution of the dye adsorption capacity and solar cells parameters are explored as a function of the crystallinity and thickness of the TiO2 shell. The results show the critical effect of a full coverage by TiO2 of ZnO core to explain the mixed results found in the literature.

August, 2017 | DOI: 10.1038/s41598-017-09601-7

Optical properties and electronic transitions of zinc oxide, ferric oxide, cerium oxide, and samarium oxide in the ultraviolet and extreme ultraviolet

Pauly, N; Yubero, F; Espinos, JP; Tougaard, S
Applied Optics, 56 (2017) 6611-6621


Optical properties and electronic transitions of four oxides, namely zinc oxide, ferric oxide, cerium oxide, and samarium oxide, are determined in the ultraviolet and extreme ultraviolet by reflection electron energy loss spectroscopy using primary electron energies in the range 0.3 - 2.0 keV. This technique allows the evaluation of the optical response in these ultraviolet spectral regions of a thin layer of material, and the analysis is straightforward. It is performed within the dielectric response theory by means of the QUEELS-epsilon(k,omega)-REELS software developed by Tougaard and Yubero [Surf. Interface Anal. 36, 824 ( 2004)]. The method consists basically in the fitting of experimentally determined single-scattering electron energy loss cross sections with a parametric energy loss function of the corresponding material, to the one calculated within a dielectric response formalism. The obtained refractive index and extinction coefficients, as well as the identified electronic transitions are compared, when available, with previously published results. 

August, 2017 | DOI: 10.1364/AO.56.006611

The role of cobalt hydroxide in deactivation of thin film Co-based catalysts for sodium borohydride hydrolysis

Paladini, M; Arzac, GM; Godinho, V; Hufschmidt, D; de Haro, MCJ; Beltran, AM; Fernandez, A
Applied Catalysis B-Environmental, 210 (2017) 342-351


Deactivation of a Co catalyst prepared as thin film by magnetron sputtering was studied for the sodium borohydride (SB) hydrolysis reaction under different conditions. Under high SB concentration in single run experiments, the formation of a B-O passivating layer was observed after 1.5 and 24 h use. This layer was not responsible for the catalyst deactivation. Instead, a peeling-off mechanism produced the loss of cobalt. This peeling-off mechanism was further studied in cycling experiments (14 cycles) under low SB concentrations. Ex-situ study of catalyst surface after use and solid reaction products (precipitates) was performed by X-Ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The presence of cobalt hydroxide and oxyhydroxide was detected as major components on the catalyst surface after use and as precipitates in the supernatant solutions after washing. Cobalt borate, cobalt carbonate and oxycarbonate were also formed but in lesser amounts. These oxidized cobalt species were formed and further detached from the catalyst at the end of the reaction and/or during catalyst washing by decomposition of the unstable in-situ formed cobalt boride. Leaching of cobalt soluble species was negligible. Thin film mechanical detachment was also found but in a smaller extent. To study the influence of catalyst composition on deactivation processes, cycling experiments were performed with Co-B and Co-C catalysts, also prepared as thin films. We found that the deactivation mechanism proposed by us for the pure Co catalyst also occurred for a different pure Co (prepared at higher pressure) and the Co-B and Co-C samples in our experimental conditions. 

August, 2017 | DOI: 10.1016/j.apcatb.2017.04.005

Low-Temperature Plasma Processing of Platinum Porphyrins for the Development of Metal Nanostructured Layers

Filippin, AN; Sanchez-Valencia, JR; Idigoras, J; Macias-Montero, M; Alcaire, M; Aparicio, FJ; Espinos, JP; Lopez-Santos, C; Frutos, F; Barranco, A; Anta, JA; Borras, A
Advanced Materials Interfaces, 4 (2017) 1601233


This article establishes the bases for a vacuum and plasma supported methodology for the fabrication at mild temperatures of nanostructured platinum in the form of porous layers and nanocolumns using platinum octaethylporphyrin as precursor. In addition, the application of these materials as tunable optical filters and nano-counterelectrodes is proved. On one hand, the transparency in the ultraviolet-visible-near infrared range can be adjusted precisely between 70% and 1% by tuning the deposition and processing conditions, obtaining a high spectral planarity. Deviations of the spectra from an ideal flat filter are below 4%, paving the way to the fabrication of neutral density filters. The transparency limit values yield a sheet resistivity of approximate to 1350 and 120 Omega square(-1), respectively. On the other hand, the catalytic properties of the nanostructures are further demonstrated by their implementation as counterelectrodes of excitonic solar cells surpassing the performance of commercial platinum as counterelectrode in a 20% of the overall cell efficiency due to simultaneous enhancement of short-circuit photocurrent and open-circuit photovoltage. One of the most interesting features of the developed methodology is its straightforward application to other metal porphyrins and phthalocyanines readily sublimable under mild vacuum and temperature conditions.

July, 2017 | DOI: 10.1002/admi.201601233

Formation of Subsurface W5+ Species in Gasochromic Pt/WO3 Thin Films Exposed to Hydrogen

Castillero, Pedro; Rico-Gavira, Victor; Lopez-Santos, Carmen; Barranco, Angel; Perez-Dieste, Virginia; Escudero, Carlos; Espinos, Juan P.; Gonzalez-Elipe, Agustin R.
Journal of Physical Chemistry C, 121 (2017) 15719-15727


M/WO3 (M = Pt, Pd) systems formed by a porous WO3 thin film decorated by metal nanoparticles are known for their reversible coloring upon exposure to H2 at room temperature. In this work, this gasochromic behavior is investigated in situ by means of near-ambient photoemission (NAPP). Pt/WO3 systems formed by very small Pt nanoparticles (10 ± 1 nm average size) incorporated in the pores of nanocolumnar WO3 thin films prepared by magnetron sputtering at an oblique angle have been exposed to a small pressure of hydrogen at ambient temperature. The recorded UV–vis transmission spectra showed the reversible appearance of a very intense absorption band responsible for the blue coloration of these gasochromic films. In an equivalent experiment carried out in the NAPP spectrometer, W 4f, O 1s, Pt 4f, and valence band photoemission spectra have been recorded at various photon energies to follow the evolution of the reduced tungsten species and hydroxyl groups formed upon film exposure to hydrogen. The obtained results are compared with those of a conventional X-ray photoemission study after hydrogen exposure between 298 and 573 K. As investigated by NAPP, the gasochromic behavior at 298 K is accounted for by a reaction scheme in which hydrogen atoms resulting from the dissociation of H2 onto the Pt nanoparticles are spilt over to the WO3 substrate where they form surface OH–/H2O species and subsurface W5+ cations preferentially located in buried layers of the oxide network.

July, 2017 | DOI: 10.1021/acs.jpcc.7b03385

Surface chemistry and germination improvement of Quinoa seeds subjected to plasma activation

Gomez-Ramierez, A.; Lopez-Santos, C.; Cantos, M.; Garcia, J. L.; Molina, R.; Cotrino, J.; Espinos, J. P.; Gonzalez-Elipe, A. R.
Scientific Reports, 7 (2017) art. 5924


Plasma treatment is recognized as a suitable technology to improve germination efficiency of numerous seeds. In this work Quinoa seeds have been subjected to air plasma treatments both at atmospheric and low pressure and improvements found in germination rate and percentage of success. Seed water uptake by exposure to water vapor, although slightly greater for plasma treated seeds, did not justify the observed germination improvement. To identify other possible factors contributing to germination, the chemical changes experienced by outer parts of the seed upon plasma exposure have been investigated by X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM-EDX). XPS revealed that the outer layers of the Quinoa plasma treated seeds were highly oxidized and appeared enriched in potassium ions and adsorbed nitrate species. Simultaneously, SEM-EDX showed that the enrichment in potassium and other mineral elements extended to the seed pericarp and closer zones. The disappearance from the surface of both potassium ions and nitrate species upon exposure of the plasma treated seeds to water vapor is proposed as a factor favoring germination. The use of XPS to study chemical changes at seed surfaces induced by plasma treatments is deemed very important to unravel the mechanisms contributing to germination improvement.

July, 2017 | DOI: 10.1038/s41598-017-06164-5

Plasma assisted deposition of single and multistacked TiO2 hierarchical nanotube photoanodes

Filippin, AN; Sanchez-Valencia, JR; Idigoras, J; Rojas, TC; Barranco, A; Anta, JA; Borras, A
Nanoscale, 9 (2017) 8133-8141


We present herein an evolved methodology for the growth of nanocrystalline hierarchical nanotubes combining physical vapor deposition of organic nanowires (ONWs) and plasma enhanced chemical vacuum deposition of anatase TiO2 layers. The ONWs act as vacuum removable 1D and 3D templates, with the whole process occurring at temperatures ranging from RT to 250 degrees C. As a result, a high density of hierarchical nanotubes with tunable diameter, length and tailored wall microstructures are formed on a variety of processable substrates as metal and metal oxide films or nanoparticles including transparent conductive oxides. The reiteration of the process leads to the development of an unprecedented 3D nanoarchitecture formed by stacking the layers of hierarchical TiO2 nanotubes. As a proof of concept, we present the superior performance of the 3D nanoarchitecture as a photoanode within an excitonic solar cell with efficiencies as high as 4.69% for a nominal thickness of the anatase layer below 2.75 mu m. Mechanical stability and straightforward implementation in devices are demonstrated at the same time. The process is extendable to other functional oxides fabricated by plasma-assisted methods with readily available applications in energy harvesting and storage, catalysis and nanosensing.

July, 2017 | DOI: 10.1039/c7nr00923b

High surface area biopolymeric-ceramic scaffolds for hard tissue engineering

Romero-Sanchez, LB; Borrego-Gonzalez, S; Diaz-Cuenca, A
Biomedical Physics & Engineering Express, 3 (2017) art UNSP 035012


The development of scaffolds mimicking native bone tissue composition and structure is a challenge in bone tissue engineering. 3D scaffolds with both an interconnected macropore structure and nanotextured surfaces are required. However, 3D scaffolds processed by microfabrication usually lack of nanotextured surface, while nanotextured materials generated by bottom-up nanofabrication are difficult to process conforming scaffolds having well interconnected microsized cavities. In this work, the processing of reticulated (macropore interconnected) structures using nanostructured precursors has been performed to improve the mechanical properties of the scaffolds. The application of a fibrillar collagen coating, using less than 1 wt% collagen per scaffold, has allow a significant increase of the compressive strength while preserving a high surface area and nanopore accessibility. Besides, the fibrillar nanostructured collagen coating promotes hydroxyapatite mineralization. Two different collagen-coating procedures are applied showing interesting differences in terms of mechanical performance.

June, 2017 | DOI: 10.1088/2057-1976/aa7001

A compact and portable optofluidic device for detection of liquid properties and label-free sensing

Lahoz, F; Martin, IR; Walo, D; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Journal of Physics D: Applied Physics, 50 (2017) 21


Optofluidic lasers have been widely investigated over the last few years mainly because they can be easily integrated in sensor devices. However, high power pulse lasers arc required as excitation sources, which, in practice, limit the portability of the system. Trying to overcome some of these limitations, in this paper we propose the combined use of a small CW laser with a Fabry-Perot optofluidic planar microcavity showing high sensitivity and versatility for detection of liquid properties and label-free sensing. Firstly, a fluorescein solution in ethanol is used to demonstrate the high performances of the FP microcavity as a temperature sensor both in the laser (high pump power above laser threshold) and in the fluorescence (low pump power) regimes. A shift in the wavelength of the resonant cavity modes is used to detect changes in the temperature and our results show that high sensitivities could be already obtained using cheap and portable CW diode lasers. In the second part of the paper, the demonstration of this portable device for label-free sensing is illustrated under low CW pumping. The wavelength positions of the optolluidic resonant modes are used to detect glucose concentrations in water solutions using a protein labelled with a fluorescent dye as the active medium.

June, 2017 | DOI: 10.1088/1361-6463/aa6cdd

Impact of moisture on efficiency-determining electronic processes in perovskite solar cells

Salado, Manuel; Contreras-Bernal, Lidia; Calio, Laura; Todinova, Anna; Lopez-Santos, Carmen; Ahmad, Shahzada; Borras, Ana; Idigoras, Jesus; Anta, Juan A.
Journal of Materials Chemistry A, 5 (2017) 10917-10927


Moisture-induced degradation in perovskite solar cells was thoroughly investigated by structural (SEM, EDS, XRD and XPS) and device characterization (impedance and intensity modulated photocurrent spectroscopy) techniques. Both the influence of the perovskite composition and the nature of the hole selective material were analyzed. The degradation rate was found to be significantly slower for mixed perovskites and P3HT-based devices. However, for a fixed degradation degree (defined as a 50% drop from the initial photocurrent), all configurations show similar features in small-perturbation analysis. Thus, a new mid-frequency signal appears in the impedance response, which seems to be related to charge accumulation at the interfaces. In addition, faster recombination, with a more important surface contribution, and slower transport were clearly inferred from our results. Both features can be associated with the deterioration of the contacts and the formation of a higher number of grain boundaries.

June, 2017 | DOI: 10.1039/c7ta02264f

In Situ Determination of the Water Condensation Mechanisms on Superhydrophobic and Superhydrophilic Titanium Dioxide Nanotubes

Macias-Montero, Manuel; Lopez-Santos, Carmen; Nicolas Filippin, A.; Rico, Victor J.; Espinos, Juan P.; Fraxedas, Jordi; Perez-Dieste, Virginia; Escudero, Carlos; Gonzalez-Elipe, Agustin R.; Borras, Ana
Langmuir, 33 (2017) 6449-6456


One-dimensional (1D) nanostructured surfaces based on high-density arrays of nanowires and nanotubes of photoactive titanium dioxide (TiO2) present a tunable wetting behavior from superhydrophobic to superhydrophilic states. These situations are depicted in a reversible way by simply irradiating with ultraviolet light (superhydrophobic to superhydrophilic) and storage in dark. In this article, we combine in situ environmental scanning electron microscopy (ESEM) and near ambient pressure photoemission analysis (NAPP) to understand this transition. These experiments reveal complementary information at microscopic and atomic level reflecting the surface wettability and chemical state modifications experienced by these 1D surfaces upon irradiation. We pay special attention to the role of the water condensation mechanisms and try to elucidate the relationship between apparent water contact angles of sessile drops under ambient conditions at the macroscale with the formation of droplets by water condensation at low temperature and increasing humidity on the nanotubes surfaces. Thus, for the as-grown nanotubes, we reveal a metastable and superhydrophobic Cassie state for sessile drops that tunes toward water dropwise condensation at the microscale compatible with a partial hydrophobic Wenzel state. For the UV-irradiated surfaces, a filmwise wetting behavior is observed for both condensed water and sessile droplets. NAPP analyses show a hydroxyl accumulation on the as-grown nanotubes surfaces during the exposure to water condensation conditions, whereas the water filmwise condensation on a previously hydroxyl enriched surface is proved for the superhydrophilic counterpart.

June, 2017 | DOI: 10.1021/acs.langmuir.7b00156

About the enhancement of chemical yield during the atmospheric plasma synthesis of ammonia in a ferroelectric packed bed reactor

Gomez-Ramirez, Ana; Montoro-Damas, Antonio M.; Cotrino, Jose; Lambert, Richard M.; Gonzalez-Elipe, Agustin R.
Plasma Processes and Polymers, 14 (2017) e1600081


Plasma reactions offer an attractive alternative route for the synthesis of a variety of valuable chemical compounds. Here we investigate the parameters that determine the efficiency of ammonia synthesis in a ferroelectric packed bed dielectric barrier discharge (DBD) reactor. The effects of varying the operating frequency, the size of the ferroelectric pellets and the inter-electrode distance have been systematically studied. Under optimised conditions nitrogen conversions in excess of 7% were achieved, higher than those previously obtained using DBD reactors. These findings are discussed with respect to variations in the electrical characteristics of the reactor under operating conditions and in the light of emission spectra obtained as a function of reactant flow rates. These encouraging results signpost future developments that could very substantially improve the efficiency of ammonia synthesis by means of DBD technology.

June, 2017 | DOI: 10.1002/ppap.201600081

1-dimensional TiO2 nano-forests as photoanodes for efficient and stable perovskite solar cells fabrication

Salado, M; Oliva-Ramirez, M; Kazim, S; Gonzalez-Elipe, AR; Ahmad, S
Nano Energy, 35 (2017) 215-222


During the last years, perovskite solar cells have gained increasing interest among the photovoltaic community, in particularly after reaching performances at par with mature thin film based PV. This rapid evolution has been fostered by the compositional engineering of perovskite and new device architectures. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional vertically oriented TiO2 nano-forests. These vertically oriented porous TiO2 photoanodes were deposited by physical vapor deposition in an oblique angle configuration, a method which is scalable to fabricate large area devices. Mixed (MA0.15FA0.85)Pb(I0.85Br0.15)3 or triple cation Cs0.05(MA0.15FA0.85)0.95Pb(I0.85Br0.15)3 based perovskites were then infiltrated into these 1-dimensional nanostructures and power conversion efficiencies of 16.8% along with improved stability was obtained. The devices fabricated using 1D-TiO2 were found to be more stable compare to the classical 3-dimensional TiO2 photoanodes prepared by wet chemistry. These 1-D photoanodes will be of interest for scaling up the technology and in other opto-electrical devices as they can be easily fabricated utilizing industrially adapted methodologies.

May, 2017 | DOI: 10.1016/j.nanoen.2017.03.034

Critical Role of Oxygen in Silver-Catalyzed Glaser-Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles

Orozco, N; Kyriakou, G; Beaumont, SK; Sanz, JF; Holgado, JP; Taylor, MJ; Espinos, JP; Marquez, AM; Watson, DJ; Gonzalez-Elipe, AR; Lambert, RM
ACS Catalysis, 7 (2017) 3113-3120


The essential role of oxygen in enabling heterogeneously catalyzed Glaser–Hay coupling of phenylacetylene on Ag(100) was elucidated by STM, laboratory and synchrotron photoemission, and DFT calculations. In the absence of coadsorbed oxygen, phenylacetylene formed well-ordered dense overlayers which, with increasing temperature, desorbed without reaction. In striking contrast, even at 120 K, the presence of oxygen led to immediate and complete disruption of the organic layer due to abstraction of acetylenic hydrogen with formation of a disordered mixed layer containing immobile adsorbed phenylacetylide. At higher temperatures phenylacetylide underwent Glaser–Hay coupling to form highly ordered domains of diphenyldiacetylene that eventually desorbed without decomposition, leaving the bare metal surface. DFT calculations showed that, while acetylenic H abstraction was otherwise an endothermic process, oxygen adatoms triggered a reaction-initiating exothermic pathway leading to OH(a) + phenylacetylide, consistent with the experimental observations. Moreover, it was found that, with a solution of phenylacetylene in nonane and in the presence of O2, Ag particles catalyzed Glaser–Hay coupling with high selectivity. Rigorous exclusion of oxygen from the reactor strongly suppressed the catalytic reaction. Interestingly, too much oxygen lowers the selectivity toward diphenyldiacetylene. Thus, vacuum studies and theoretical calculations revealed the key role of oxygen in the reaction mechanism, subsequently borne out by catalytic studies with Ag particles that confirmed the presence of oxygen as a necessary and sufficient condition for the coupling reaction to occur. The direct relevance of model studies to a mechanistic understanding of coupling reactions under conditions of practical catalysis was reaffirmed.

May, 2017 | DOI: 10.1021/acscatal.7b00431

Non-enzymatic hydrogen peroxide detection at NiO nanoporous thin film-electrodes prepared by physical vapor deposition at oblique angles

Salazar, Pedro; Rico, Victor; Gonzalez-Elipe, Agustin R.
Electrochimica Acta, 235 (2017) 534-542


In this work we report a non-enzymatic sensor for hydrogen peroxide (H2O2) detection based on nanostructured nickel thin films prepared by physical vapor deposition at oblique angles. Porous thin films deposited on ITO substrates were characterized by X-ray diffraction analysis, scanning electron microcopy (SEMs), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques such as Cyclic Voltammetry (CV) and Constant Potential Amperometry (CPA). The microstructure of the thin films consisted of inclined and separated Ni nanocolumns forming a porous thin layer of about 500 nm thickness. Prior to their use, the films surface was electrochemically modified and the chemical state studied by CV and XPS analysis. These techniques also showed that Ni2+/Ni3+ species were involved in the electrochemical oxidation and detection of H2O2 in alkaline medium. Main analytical parameters such as sensitivity (807 mA M(-1)cm(-2)), limit of detection (3.22 mu M) and linear range (0.011-2.4 mM) were obtained under optimal operation conditions. Sensors depicted an outstanding selectivity and a high stability and they were successfully used to determine H2O2 concentration in commercial antiseptic solutions.

May, 2017 | DOI: 10.1016/j.electacta.2017.03.087

Energy-Sensitive Ion- and Cathode-Luminescent Radiation-Beam Monitors Based on Multilayer Thin-Film Designs

Gil-Rostra, Jorge; Ferrer, Francisco J.; Pedro Espinos, Juan; Gonzalez-Elipe, Agustin R.; Yubero, Francisco
ACS Applied Materials & Interfaces, 9 (2017) 16313-16320


A multilayer luminescent design concept is presented to develop energy sensitive radiation-beam monitors on the basis of colorimetric analysis. Each luminescent layer within the stack consists of rare-earth-doped transparent oxides of optical quality and a characteristic luminescent emission under excitation with electron or ion beams. For a given type of particle beam (electron, protons, alpha particles, etc.), its penetration depth and therefore its energy loss at a particular buried layer within the multilayer stack depend on the energy of the initial beam. The intensity of the luminescent response of each layer is proportional to the energy deposited by the radiation beam within the layer, so characteristic color emission will be achieved if different phosphors are considered in the layers of the luminescent stack. Phosphor doping, emission efficiency, layer thickness, and multilayer structure design are key parameters relevant to achieving a broad colorimetric response. Two case examples are designed and fabricated to illustrate the capabilities of these new types of detector to evaluate the kinetic energy of either electron beams of a few kilo-electron volts or a particles of alpha few mega-electron volts.

May, 2017 | DOI: 10.1021/acsami.7b01175

Formation of nitrile species on Ag nanostructures supported on a-Al2O3: a new corrosion route for silver exposed to the atmosphere

Pelaez, RJ; Espinos, JP; Afonso, CN
Nanotechnology, 28 (2017) 175709


The aging of supported Ag nanostructures upon storage in ambient conditions (air and room temperature) for 20 months has been studied. The samples are produced on glass substrates by pulsed laser deposition (PLD); first a 15 nm thick buffer layer of amorphous aluminum oxide (a-Al2O3) is deposited, followed by PLD of Ag. The amount of deposited Ag ranges from that leading to a discontinuous layer up to an almost-percolated layer with a thickness of <6 nm. Some regions of the as-grown silver layers are converted, by laser induced dewetting, into round isolated nanoparticles (NPs) with diameters of up to ~25 nm. The plasmonic, structural and chemical properties of both as-grown and laser exposed regions upon aging have been followed using extinction spectroscopy, scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. The results show that the discontinuous as-grown regions are optically and chemically unstable and that the metal becomes oxidized faster, the smaller the amount of Ag. The corrosion leads to the formation of nitrile species due to the reaction between NO x species from the atmosphere adsorbed at the surface of Ag, and hydrocarbons adsorbed in defects at the surface of the a-Al2O3 layer during the deposition of the Ag nanostructures by PLD that migrate to the surface of the metal with time. The nitrile formation thus results in the main oxidation mechanism and inhibits almost completely the formation of sulphate/sulphide. Finally, the optical changes upon aging offer an easy-to-use tool for following the aging process. They are dominated by an enhanced absorption in the UV side of the spectrum and a blue-shift of the surface plasmon resonance that are, respectively, related to the formation of a dielectric overlayer on the Ag nanostructure and changes in the dimensions/features of the nanostructures, both due to the oxidation process.

April, 2017 | DOI: 10.1088/1361-6528/aa65c0

Improving the pollutant removal efficiency of packed-bed plasma reactors incorporating ferroelectric components

Gomez-Ramirez, Ana; Montoro-Damas, Antonio M.; Rodriguez, Miguel A.; Gonzalez-Elipe, Agustin R.; Cotrino, Jose
Chemical Engineering Journal, 314 (2017) 311-319


In this work we have studied the plasma removal of air contaminants such as methane, chloroform, toluene and acetone in two parallel plate packed-bed dielectric barrier discharge (DBD) reactors of different sizes. Removal and energy efficiencies have been determined as a function of the residence time of the contaminated air within the reactor, the kind of packed-bed material (ferroelectrics or classical dielectric materials), the frequency and the incorporation of a ferroelectric plate onto the active electrode together with the inter-electrode ferroelectric pellets filling the gap. Results at low frequency with the small reactor and the ferroelectric plate showed an enhancement in energy efficiency (e.g., it was multiplied by a factor of six and three for toluene and chloroform, respectively) and in removal yield (e.g., it increased from 22% to 52% for chloroform and from 15% to 21% for methane). Such enhancements have been attributed to the higher energy of plasma electrons and a lower reactor capacitance found for this plate-modified configuration. A careful analysis of reaction efficiencies and electron energy distributions for the different investigated conditions and the simulation of the electric field at the necks between ferroelectric/dielectric pellets complete the present study. Overall, the obtained results prove the critical role of the barrier architecture and operating conditions for an enhanced performance of pollution removal processes using DBD systems.

April, 2017 | DOI: 10.1016/j.cej.2016.11.065

Reliability of new poly (lactic-co-glycolic acid) membranes treated with oxygen plasma plus silicon dioxide layers for pre-prosthetic guided bone regeneration processes

Castillo-Dali, G; Castillo-Oyague, R; Batista-Cruzado, A; Lopez-Santos, C; Rodriguez-Gonzalez-Elipe, A; Saffar, JL; Lynch, CD; Gutierrez-Perez, JL; Torres-Lagares, D
Medicina Oral Patología Oral y Cirugia Oral, 22 (2017) E242-E250


Background: The use of cold plasmas may improve the surface roughness of poly(lactic-co-glycolic) acid (PLGA) membranes, which may stimulate the adhesion of osteogenic mediators and cells, thus accelerating the biodegradation of the barriers. Moreover, the incorporation of metallic-oxide particles to the surface of these membranes may enhance their osteoinductive capacity. Therefore, the aim of this paper was to evaluate the reliability of a new PLGA membrane after being treated with oxygen plasma (PO2) plus silicon dioxide (SiO2) layers for guided bone regeneration (GBR) processes. 
Material and Methods: Circumferential bone defects (diameter: 11 mm; depth: 3 mm) were created on the top of eight experimentation rabbits' skulls and were randomly covered with: (1) PLGA membranes (control), or (2) PLGA/ PO2/SiO2 barriers. The animals were euthanized two months afterwards. A micromorphologic study was then performed using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone, concentration of osteoclasts, and intensity of ostheosynthetic activity were assessed and compared with those of the original bone tissue. The Kruskal-Wallis test was applied for between-group com asignificance level of a=0.05 was considered. 
Results: The PLGA/ PO2/SiO2 membranes achieved the significantly highest new bone formation, length of miner-alised bone, concentration of osteoclasts, and ostheosynthetic activity. The percentage of regenerated bone supplied by the new membranes was similar to that of the original bone tissue. Unlike what happened in the control group, PLGA/PO2/SiO2 membranes predominantly showed bone layers in advanced stages of formation. Conclusions: The addition of SiO2 layers to PLGA membranes pre-treated with PO2 improves their bone-regeneration potential. Although further research is necessary to corroborate these conclusions in humans, this could be a promising strategy to rebuild the bone architecture prior to rehabilitate edentulous areas.

March, 2017 | DOI: 10.4317/medoral.21512

Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings

Dominguez-Meister, S; Rojas, TC; Brizuela, M; Sanchez-Lopez, JC
Science and Tecnology of Advances Materials, 18 (2017) 1


Tribological coatings made of MoS2 and WSe2 phases and their corresponding combinations with tungsten carbide (WC) were prepared by non-reactive magnetron sputtering of individual targets of similar composition. A comparative tribological analysis of these multiphase coatings was done in both ambient air (30-40% relative humidity, RH) and dry nitrogen (RH<7%) environments using the same tribometer and testing conditions. A nanostructural study using advanced transmission electron microscopy of the initial coatings and examination of the counterfaces after the friction test using different analytical tools helped to elucidate what governs the tribological behavior for each type of environment. This allowed conclusions to be made about the influence of the coating microstructure and composition on the tribological response. The best performance obtained with a WSe x film (specific wear rate of 2 x 10(-8) mm(3) N(-1)m(-1) and a friction coefficient of 0.03-0.05) was compared with that of the well-established MoS2 lubricant material.

March, 2017 | DOI: 10.1080/14686996.2016.1275784

On the effect of wall slip on the determination of the yield stress of magnetorheological fluids

Caballero-Hernandez, J; Gomez-Ramirez, A; Duran, JDG; Gonzalez-Caballero, F; Zubarev, AY; Lopez-Lopez, MT
Applied Rheology, 27 (2017) 15001 (8 pages)


We study the effect of wall slip on the measured values of the yield stress of magnetorheological (MR) fluids. For this aim we used a rheometer provided with parallel-plate geometries of two types, distinguished by having smooth or rough surfaces. We found that wall slip led to the underestimation of the yield stress when measuring geometries with smooth surfaces were used, and that this underestimation was more pronounced for the static than for the dynamic yield stress. Furthermore, we analysed the effect that both irreversible particle aggregation due to colloidal interactions and reversible magnetic fieldinduced particle aggregation had on the underestimation provoked by wall slip. We found that the higher the degree of aggregation the stronger the underestimation of the yield stress. At low intensity of the applied magnetic field irreversible particle aggregation was dominant and, thus, the underestimation of the yield stress was almost negligible for well-dispersed MR fluids, whereas it was rather pronounced for MR fluids suffering from irreversible aggregation. As the magnetic field was increased the underestimation of the yield stress became significant even for the best dispersed MR fluid.

March, 2017 | DOI: 10.3933/ApplRheol-27-15001

Antibacterial response of titanium oxide coatings doped by nitrogen plasma immersion ion implantation

Esparza, J; Fuentes, GF; Bueno, R; Rodriguez, R; Garcia, JA; Vitas, AI; Rico, V; Gonzalez-Elipe, AR
Surface and Coatings Technology, 314 (2017) 67-71


Plasma immersion ion implantation technology has been utilized to enhance the photocatalytic activity of the anatase phase of TiO2 thin films deposited by cathodic arc evaporation PVD. The main objective of this study is to shift the light absorbance of the titania in order to obtain antibacterial activity under visible light irradiation. TiO2 thin films, deposited on polished stainless steel AISI 304 and silicon wafers, were implanted with nitrogen ions (N+/N2+) at 20 kV energy and different temperatures between 250 and 350 °C. The antibacterial activity of nitrogen implanted titania coatings has been monitored for Escherichia coli under visible light irradiation. Additionally ultra violet/visible spectrophotometry tests have been carried out to measure the changes in the light absorbance of the doped films. Further characterization has been performed, including X-ray photoelectron spectroscopy, X-ray diffraction and glow discharge optical emission spectrometry. As a result of Nitrogen implantation, the light absorption peak shifted from ultra violet region (UV-A) to visible wavelength range, which led to an increase of the antibacterial efficacy under visible light irradiation.

March, 2017 | DOI: 10.1016/j.surfcoat.2016.11.002

Multicolored Emission and Lasing in DCM-Adamantane Plasma Nanocomposite Optical Films

Alcaire, M; Cerdan, L; Zamarro, FL; Aparicio, FJ; Gonzalez, JC; Ferrer, FJ; Borras, A; Espinos, JP; Barranco, A
ACS Applied Materials & Interfaces, 9 (2017) 8948-8959


We present a low-temperature versatile protocol for the fabrication of plasma nanocomposite thin films to act as tunable emitters and optical gain media. The films are obtained by the remote plasma-assisted deposition of a 4-(dicyano-methylene)-2-methy1-6-(4-dimethylamino-styry1)-4Hpyran (DCM) laser dye alongside adamantane. The experimental parameters that determine the concentration of the dye in the films and their optical properties, including light absorption, the refractive index, and luminescence, are evaluated. Amplified spontaneous emission experiments in the DCM/adamantane nano composite waveguides show the improvement of the copolymerized nano composites' properties compared to films that were deposited with DCM as the sole precursor. Moreover, one-dimensional distributed feed-back laser emission is demonstrated and characterized in some of the nanocomposite films that are studied. These results open new paths for the optimization of the optical and lasing properties of plasma nanocomposite polymers, which can be straightforwardly integrated as active components in optoelectronic devices.

March, 2017 | DOI: 10.1021/acsami.7b01534

Strong Quantum Confinement and Fast Photoemission Activation in CH3NH3PbI3 Perovskite Nanocrystals Grown within Periodically Mesostructured Films

Miguel Anaya; Andrea Rubino; Teresa Cristina Rojas; Juan Francisco Galisteo-López; Mauricio Ernesto Calvo; Hernán Míguez
Advanced Optical Materials, 5 (2017) 1601087


In this Communication, a synthetic route is demonstrated to obtain stabilized MAPbI3 nanocrystals embedded in thin metal oxide films that display well-defined and adjustable quantum confinement effects over a wide range of 0.34 eV. Mesostructured TiO2 and SiO2 films displaying an ordered 3D pore network are prepared by evaporation-induced self-assembly of a series of organic supramolecular templates in the presence of metal oxide precursors. The pores in the inorganic films obtained after thermal annealing are then used as nanoreactors to synthesize MAPbI3crystallites with narrow size distribution and average radius comprised between 1 and 4 nm, depending on the template of choice. Both the static and dynamic photoemission properties of the ensemble display features distinctive of the regime of strong quantum confinement. Photoemission maps demonstrate that the spectral and intensity properties of the luminescence extracted from the perovskite quantum dot loaded films are homogeneous over squared centimeters areas. At variance with their bulk counterparts, constant emission intensity is reached in time scales at least four orders of magnitude shorter.

March, 2017 | DOI: 10.1002/adom.201601087

High vacuum synthesis and ambient stability of bottom-up graphene nanoribbons

Fairbrother, A; Sanchez-Valencia, JR; Lauber, B; Shorubalko, I; Ruffieux, P; Hintermann, T; Fasel, R
Nanoscale, 9 (2017) 2785-2792


Carbon-based nanomaterials such as graphene are at a crucial point in application development, and their promising potential, which has been demonstrated at the laboratory scale, must be translated to an industrial setting for commercialization. Graphene nanoribbons in particular overcome one limitation of graphene in some electronic applications because they exhibit a sizeable bandgap. However, synthesis of bottom-up graphene nanoribbons is most commonly performed under ultra-high vacuum conditions, which are costly and difficult to maintain in a manufacturing environment. Additionally, little is known about the stability of graphene nanoribbons under ambient conditions or during transfer to technologically relevant substrates and subsequent device processing. This work addresses some of these challenges, first by synthesizing bottom-up graphene nanoribbons under easily obtained high vacuum conditions and identifying water and oxygen as the residual gases responsible for interfering with proper coupling during the polymerization step. And second, by using Raman spectroscopy to probe the stability of nanoribbons during storage under ambient conditions, after transfer to arbitrary substrates, and after fabrication of field-effect transistor devices, which shows structurally intact nanoribbons even several months after synthesis. These findings demonstrate the potential of graphene nanoribbon technologies by addressing some limitations which might arise in their commercialization.

February, 2017 | DOI: 10.1039/C6NR08975E

Fabrication of black-gold coatings by glancing angle deposition with sputtering

Vitrey, A; Alvarez, R; Palmero, A; Gonzalez, MU; Garcia-Martin, JM
Beilstein Journal of Nanotechnology, 8 (2017) 434–439


The fabrication of black-gold coatings using sputtering is reported here. Glancing angle deposition with a rotating substrate is needed to obtain vertical nanostructures. Enhanced light absorption is obtained in the samples prepared in the ballistic regime with high tilt angles. Under these conditions the diameter distribution of the nanostructures is centered at about 60 nm and the standard deviation is large enough to obtain black-metal behavior in the visible range.

February, 2017 | DOI: 10.3762/bjnano.8.46

Preparation and Optimization of Fluorescent Thin Films of Rosamine-SiO2/TiO2 Composites for NO2 Sensing

Guillen, MG; Gamez, F; Suarez, B; Queiros, C; Silva, AMG; Barranco, A; Sanchez-Valencia, JR; Pedrosa, JM; Lopes-Costa, T
Materials, 10 (2017) art 124


The incorporation of a prototypical rosamine fluorescent dye from organic solutions into transparent and microstructured columnar TiO2 and SiO2 (MO2) thin films, prepared by evaporation at glancing angles (GAPVD), was evaluated. The aggregation of the adsorbed molecules, the infiltration efficiency and the adsorption kinetics were studied by means of UV-Vis absorption and fluorescence spectroscopies. Specifically, the infiltration equilibrium as well as the kinetic of adsorption of the emitting dye has been described by a Langmuir type adsorption isotherm and a pseudosecond order kinetic model, respectively. The anchoring mechanism of the rosamine to the MO2 matrix has been revealed by specular reflectance Fourier transform infrared spectroscopy and infiltration from aqueous solutions at different pH values. Finally, the sensing performance towards NO2 gas of optimized films has been assessed by following the changes of its fluorescence intensity revealing that the so-selected device exhibited improved sensing response compared to similar hybrid films reported in the literature.

February, 2017 | DOI: 10.3390/ma10020124

Cholesterol biosensing with a polydopamine-modified nanostructured platinum electrode prepared by oblique angle physical vacuum deposition

Martin, M; Salazar, P; Alvarez, R; Palmero, A; Lopez-Santos, C; Gonzalez-Mora, JL; Gonzalez-Elipe, AR
Sensors and Actuators B-Chemical, 240 (2017) 37-45


This paper reports a novel cholesterol biosensor based on nanostructured platinum (Pt) thin films prepared by Magnetron Sputtering (MS) in an oblique angle (OAD) configuration. Pt thin films were deposited onto a gold screen-printed electrode and characterized using Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Cyclic Voltammetry (CV), X-ray Photo-electron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and wetting analysis. Our results confirmed that the film is highly porous and formed by tilted nanocolumns, with an inclination of around 40 degrees and a total thickness of 280 nm. XRD and CV analysis confirmed the polycrystalline nature of the Pt thin film. Cholesterol oxidase (ChOx) was covalently immobilized using a bioinspired polymer, polydopamine (PDA), via Schiff base formation and Michael-type addition. After being immobilized, ChOx displayed apparent activation energy of 34.09 kJ mol(-1) and Michaelis constant (K-M) values of 34.09 kJ mol(-1) and 3.65 mM, respectively, confirming the high affinity between ChOx and cholesterol and the excellent ability of the PDA film for immobilizing biological material without degradation. Under optimized working conditions the developed biosensor presented a sensitivity of 14.3 mA M(-1)cm(-2) (R-2:0.999) with a linear range up to 0.5 mM and a limit of detection of 10.5 mu M (S/N= 3). Furthermore, the biosensor exhibited a fast response (<8 s), good anti-interference properties and high stability after relatively long-term storage (2 months). 

February, 2017 | DOI: 10.1016/j.snb.2016.08.092

Optical Gas Sensing of Ammonia and Amines Based on Protonated Porphyrin/TiO2 Composite Thin Films

Castillero, Pedro; Roales, Javier; Lopes-Costa, Tania; Sanchez-Valencia, Juan R.; Barranco, Angel; Gonzalez-Elipe, Agustin R.; Pedrosa, Jose M.
Sensors, 17 (2017) 24


Open porous and transparent microcolumnar structures of TiO2 prepared by physical vapour deposition in glancing angle configuration (GLAD-PVD) have been used as host matrices for two different fluorescent cationic porphyrins, 5-(N-methyl 4-pyridyl)-10,15,20-triphenyl porphine chloride (MMPyP) and meso-tetra (N-methyl 4-pyridyl) porphine tetrachloride (TMPyP). The porphyrins have been anchored by electrostatic interactions to the microcolumns by self-assembly through the dip-coating method. These porphyrin/TiO2 composites have been used as gas sensors for ammonia and amines through previous protonation of the porphyrin with HCl followed by subsequent exposure to the basic analyte. UV-vis absorption, emission, and time-resolved spectroscopies have been used to confirm the protonation-deprotonation of the two porphyrins and to follow their spectral changes in the presence of the analytes. The monocationic porphyrin has been found to be more sensible (up to 10 times) than its tetracationic counterpart. This result has been attributed to the different anchoring arrangements of the two porphyrins to the TiO2 surface and their different states of aggregation within the film. Finally, there was an observed decrease of the emission fluorescence intensity in consecutive cycles of exposure and recovery due to the formation of ammonium chloride inside the film.

January, 2017 | DOI: 10.3390/s17010024

Regenerative Endodontic Procedures: A Perspective from Stem Cell Niche Biology

M. Marí-Beffa, J.J. Segura-Egea, A. Díaz-Cuenca
Journal of Endodontics, 43 (2017) 52-62



Endodontics uses cell therapy strategies to treat pulpal and periapical diseases. During these therapies, surgeons aim to reconstruct the natural microenvironments that regulate the activity of dental stem cells.


We searched for more than 400 articles in PubMed using key words from regenerative endodontics and dental stem cell biology. In 268 articles, we reviewed what factors may influence histologic results after preclinical dental treatments that use regenerative endodontic procedures after pulpectomy.


Several factors, such as the origin of stem cells, the biomimicry of scaffolds used, and the size of lesions, are considered to influence the histologic appearance of the regenerated pulp-dentin complex after treatments. Information is accumulating on transcription factors that generate the pulp-dentin complex and survival/trophic factors that would benefit niche recovery and histologic results.


In this article, we discuss the noninterchangeability of stem cells, the influence of dentin-entrapped molecule release on pulp regeneration and survival of stem cells, and the need of positional markers to assess treatments histologically. The ex vivo amplification of appropriate dental stem cells, the search for scaffolds storing the molecular diversity entrapped in the dentin, and the use of positional transcription factors as histologic markers are necessary to improve future preclinical experiments.

January, 2017 | DOI: 10.1016/j.joen.2016.09.011

Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions

Arzac, G. M.; Montes, O.; Fernandez, A.
Applied Catalysis B-Envionmental, 201 (2017) 391-399


We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H2PtCl6 as precursor. The reaction was conducted in excess of oxygen. beta-SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5 nm for 0.5 wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO2 and Al2O3 commercial supports (Pt particles very small in size, average particle diameter of 1 nm for 0.5 wt% Pt in both cases). The case of a SiO2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt, indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7 nm for 0.5 wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalystsi surface.

January, 2017 | DOI: 10.1016/j.apcatb.2016.08.042


Stoichiometric Control of SiOx Thin Films Grown by Reactive Magnetron Sputtering at Oblique Angles

Garcia-Valenzuela, A; Alvarez, R; Lopez-Santos, C; Ferrer, FJ; Rico, V; Guillen, E; Alcon-Camas, M; Escobar-Galindo, R; Gonzalez-Elipe, AR; Palmero, A
Plasma Processes and Polymers, 13 (2016) 1242-1248


The deposition of SiOx (x <= 2) compound thin films by the reactive magnetron sputtering technique at oblique angles is studied from both theoretical and experimental points of view. A simple mathematical formula that links the film stoichiometry and the deposition conditions is deduced. Numerous experiments have been carried out to test this formula at different deposition pressures and oblique angle geometries obtaining a fairly good agreement in all studied conditions. It is found that, at low deposition pressures, the proportion of oxygen with respect to silicon in the film increases a factor of similar to 5 when solely tilting the film substrate with respect to the target, whereas at high pressures the film stoichiometry depends very weakly on the tilt angle. This behavior is explained by considering the fundamental processes mediating the growth of the film by this technique.

December, 2016 | DOI: 10.1002/ppap.201600077

Non-Enzymatic Glucose Sensors Based on Nickel Nanoporous Thin Films Prepared by Physical Vapor Deposition at Oblique Angles for Beverage Industry Applications

Salazar, P; Rico, V; Gonzalez-Elipe, AR
Journal of the Electrochemical Society, 163 (14) (2016) B704-B709


Nickel nanoporous thin films deposited on Indium tin oxide conductive plates have been prepared by physical vapor deposition in an oblique angle configuration. The scanning electron microscopy characterization of these films revealed a microstructure formed by tilted nanocolumns of ca. 40-60 nm of diameter inclined by ca. 26 degrees with respect to the normal. These highly porous films had ca. 30% of void space and provided a large exposed area and outstanding diffusion properties for sensor applications. X-ray diffraction analysis confirmed the deposition of metallic nickel, while Raman and X-ray photoelectron spectroscopies demonstrated that electrochemically treated films presented an oxi/hydroxide outer layer that is the active phase for glucose sensing. The activated electrodes had a high sensitivity (2.05 A M-1 cm(-2)), an excellent coefficient of determination (R-2: 0.999), an outstanding reproducibility (3.2%) and a detection limit of 0.34 mu M. Their glucose selectivity was excellent with regard to common electroactive interferences and other sugars found in agro-alimentary products. Tests carried out with commercial beverages proved the reliability of these electrodes for glucose analysis in real conditions.

December, 2016 | DOI: 10.1149/2.1241614jes

Tailor-made preparation of Co-C, Co-B, and Co catalytic thin films using magnetron sputtering: insights into structure-composition and activation effects for catalyzed NaBH4 hydrolysis

Paladini, M; Godinho, V; Arzac, GM; de Haro, MCJ; Beltran, AM; Fernandez, A
RSC Advances, 6 (2016) 108611-108620


The magnetron sputtering (MS) methodology is a powerful tool for tailor-made fabrication of Co-based thin film catalysts with controlled microstructures and compositions for sodium borohydride (SBH) hydrolysis. In particular, Co-C catalysts were tested in this reaction and compared to Co-B and Co catalyst coatings. The microstructural and chemical analyses by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy (XPS) were used to characterize a complete library of thin film catalysts. Pure Co materials were characterized by their nanocrystalline microstructure, and grain refinement was achieved via an increase in the deposition pressure. The incorporation of boron or carbon via co-deposition results in amorphization and dispersion of the active metallic Co phase. The composition can be tuned while keeping a controlled microstructure, and a comparison of activity at 25 degrees C was performed on catalysts deposited on Ni foam substrates. A comparison of the initial activities showed that the Co-B samples were more active than the Co-C samples because of electronic effects. However, a strong activation was found for the Co-C catalysts after the first use. This effect was dependent upon the incorporation of cobalt boride (CoxB) species on the catalysts' surface, as shown by XPS. After the first several uses, the activity of the Co-C samples (values up to 2495 mL min(-1) g(catalyst)(-1)) were as high as that of fresh Co-B, and the surface composition of both the catalysts was similar. This activation was not observed for the pure Co and was very weak for the Co-B catalysts. The use of polymeric (PTFE) substrates (flexible membranes) illustrated the versatility of the methodology to obtain catalytic membranes and allowed for a TEM microstructural analysis at the nanoscale. Catalytic activities at 60 degrees C were as high as 16.7 and 20 L min(-1) g(Co)(-1) for the Co-C and Co-B membranes, respectively. We determined the optimized conditions to increase the catalytic activity of Co-based coatings prepared via magnetron sputtering.

November, 2016 | DOI: 10.1039/c6ra23171c

Glutamate microbiosensors based on Prussian Blue modified carbon fiber electrodes for neuroscience applications: In-vitro characterization

Salazar, P; Martin, M; O'Neill, RD; Gonzalez-Mora, JL
Sensors and Actuators B: Chemical, 235 (2016) 117-125


Herein we report a Prussian Blue modified carbon fiber electrode (CFE/PB) to be used in microbiosensors for glutamate monitoring in physiological applications as an alternative to the classical Pt and Pt-Ir transducers. Their low dimensions (∼250 μm CFE length and ∼10 μm diameter) are advantageous for measuring in living tissues. In addition, PB-modified microelectrodes allow the detection of enzyme-generated hydrogen peroxide at a low applied potential (∼0.0 V against SCE), contrasting the high potential used in many previous designs (∼0.7 V), decreasing the endogenous interference contributions. Moreover, the electrosynthesized polymer, poly-o-phenylenediamine (PoPD), was used to improve biosensor stability and selectivity. CFE/PB was conveniently characterized using impedance, Raman and XPS spectroscopies. Optimization of the fabrication procedure and analytical conditions is described, including activation of CFE/PB, enzyme enrichment, cross-linking, stabilization and anti-interference. A range of analytical parameters were also characterized such as sensitivity, limit of detection, linear range, and enzymatic loading. Finally, an optimized biosensor displaying a linear sensitivity of 135 ± 2 nA μM−1 cm−2 (n = 3), LOD of <2 μM, linear range up to 150 μM and effectively free of interference, is proposed as a suitable candidate for in-vivo glutamate monitoring in the central nervous system.

November, 2016 | DOI: 10.1016/j.snb.2016.05.057

Characterization and Validation of a-Si Magnetron-Sputtered Thin Films as Solid He Targets with High Stability for Nuclear Reactions

Godinho, V; Ferrer, FJ; Fernandez, B; Caballero-Hernandez, J; Gomez-Camacho, J; Fernandez, A
ACS Omega, 1 (2016) 1229-1238


In this work, we present our magnetron sputtering based methodology to produce amorphous silicon coatings with closed porosity, as a strategy to fabricate solid helium targets, in the form of supported or self-supported thin films, for nuclear reactions. We show how by changing the He working pressure it is possible to obtain highly porous homogeneous structures incorporating different He amounts. These porous coatings (a-Si: He) are very reproducible from run to run, and the high He amount incorporated makes them excellent candidates for solid He targets. The possibility of producing self-supported films is illustrated here, and its potential use in inverse kinematics experiments with radioactive beams is shown through the dispersion in forward geometry of a stable Li-6 beam. Also the elastic scattering cross-sections for proton from helium were determined using an a-Si: He coating. The results agree well with the ones reported in the literature. These two examples validate our coatings as good candidates to be used as solid He targets in nuclear reactions. The stability of He inside the coatings, fundamental for its use as solid He targets, was investigated, both over time and after irradiation. The coatings proved to be very stable, and the amount of He inside the pores remains unaltered at least 2 years after deposition and after high irradiation fluence (5 x 10(17) particles/cm(2); with a dose rate of 5 x 10(12) particles/(cm(2) s)).

November, 2016 | DOI: 10.1021/acsomega.6b00270

Cathode and ion-luminescence of Eu:ZnO thin films prepared by reactive magnetron sputtering and plasma decomposition of non-volatile precursors

Gil-Rostra, J; Ferrer, FJ; Martin, IR; Gonzalez-Elipe, AR; Yubero, F
Journal of Luminescence, 178 (2016) 139-146


This paper reports the luminescent behavior of Eu:ZnO thin films prepared by an one-step procedure that combines reactive magnetron sputtering deposition of ZnO with the plasma activated decomposition of a non-volatile acetylacetonate precursor of Eu sublimated in an effusion cell. Chemical composition and microstructure of the Eu:ZnO thin films have been characterized by several methods and their photo-, cathode- and ion-luminescent properties studied as a function of Eu concentration. The high transparency and well controlled optical properties of the films have demonstrated to be ideal for the development of cathode- and ion- luminescence sensors.

October, 2016 | DOI: 10.1016/j.jlumin.2016.01.034

High-Rate Deposition of Stoichiometric Compounds by Reactive Magnetron Sputtering at Oblique Angles

Rafael Alvarez, Aurelio Garcia-Valenzuela, Carmen Lopez-Santos, Francisco J. Ferrer, Victor Rico, Elena Guillen, Mercedes Alcon-Camas, Ramon Escobar-Galindo, Agustin R. Gonzalez-Elipe, Alberto Palmero
Plasma Processes and Polymers, 13 (2016) 571-576


Target poisoning in reactive magnetron sputtering deposition of thin films is an undesired phenomenon, well known for causing a drastic fall of the process efficiency. We demonstrate that when this technique is operated at oblique angles, films with composition raging from pure metallic to stoichiometric compound can be grown in non-poisoned conditions, thus avoiding most of the associated drawbacks. We have employed amorphous TiOx, although the presented results can be easily extrapolated to other materials and conditions. It is found that the proposed method improves 400% the growth rate of TiO2 thin films.

October, 2016 | DOI: 10.1002/ppap.201600019

Laser Treatment of Nanoparticulated Metal Thin Films for Ceramic Tile Decoration

Rico, VJ; Lahoz, R; Rey-Garcia, F; Yubero, F; Espinos, JP; de la Fuente, GF; Gonzalez-Elipe, AR
Applied Materials & Interfaces, 8 (2016) 24880-24886


This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of Cu thin films prepared by electron-beam evaporation at glancing angles. A thin film of discontinuous Cu nanoparticles was electron-beam-evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy along with UV–vis–near-IR spectroscopy and time-of-flight secondary ion mass spectrometry analysis were used to characterize the differently colored layers. On the basis of these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of the samples.

September, 2016 | DOI: 10.1021/acsami.6b07469

Metallization of ceramic substrates by laser induced decomposition of coordination complexes

Rico, V; Lopez-Gascon, C; Espinos, JP; Lahoz, R; Laguna, M; Gonzalez-Elipe, AR; de la Fuente, GF
Journal of the European Ceramic Society, 36 (2016) 2831-2836


This work describes an in-situ Nd:YAG laser-assisted coating method to modify industrial glazed ceramic surfaces. The method makes use of a Cu polymer coordination complex, transformed via 1064 nm continuos wave (cw) laser irradiation, into a lustre-type glassy coating covering the ceramic substrate. The obtained coatings, with typical thicknesses ranging between 4 and 14 μm, become integrated onto the ceramic glaze via a sharp interface, as found by SEM observation. Diffuse Reflectance UV-vis spectroscopy shows that the lustre effect arises from surface plasmon resonant effects associated to the formation of nanometric size Cu particles dispersed throughout the glaze coating. This was confirmed by XPS analysis and other techniques showing that the laser decomposition treatment induces the redox transformation of the Cu (II) complexes, present in the original precursor, into reduced Cu (0) nanoparticles.

September, 2016 | DOI: 10.1016/j.jeurceramsoc.2016.04.016

Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen

Arzac, G. M.; Ramirez-Rico, J.; Gutierrez-Pardo, A.; Jimenez de Haro, M. C.; Hufschmidt, D.; Martinez-Fernandez, J.; Fernandez, A.
RSC Advances, 6 (2016) 66373-66384


Catalytic hydrogen combustion was studied with H-2/air mixtures in conditions that simulate the H-2 concentration of the exhaust gases from fuel cells (3-4% v/v H-2 in air). Pt-impregnated monoliths based on porous biomorphic SiC (bio-SiC) substrates were employed for the first time for this reaction. Capillary forces were exploited for the incipient impregnation of supports with H2PtCl6 solutions. Freeze drying permitted us to obtain a homogeneous distribution of the active phase reducing accumulation at the monolith's outer shell. The supports and catalysts were characterized from a structural and thermal point of view. Catalytic tests were performed in a homemade reactor fed with up to 1000 ml min(-1) H-2/air mixtures and a diffusional regime (non-isothermal) was achieved in the selected conditions. Catalyst loading was tested in the range of 0.25-1.5 wt% Pt and 100% conversion was achieved in all cases. Temperatures were recorded at different points of the monoliths during the reaction showing anisotropic thermal behavior for selected bio-SiC substrates. These effects are of interest for heat management applications and were explained in correlation with thermal conductivity measurements performed on the supports. Pt-impregnated monoliths were also tested in less than 100% conversion conditions (1% v/v H-2 in air) and in powder form in kinetic conditions for comparative purposes.

September, 2016 | DOI: 10.1039/c6ra09127j

Timing of calcium nitrate addition affects morphology, dispersity and composition of bioactive glass nanoparticles

Zheng, K; Taccardi, N; Beltran, AM; Sui, BY; Zhou, T; Marthala, VRR; Hartmann, M; Boccaccini, AR
RSC Advances, 6 (2016) 95101-95111


Bioactive glass nanoparticles (BGN) are promising materials for a number of biomedical applications. Many parameters related to the synthesis of BGN using sol–gel methods can affect their characteristics. In this study, the influence of timing of calcium nitrate (calcium precursor) addition during processing on BGN characteristics was investigated. The results showed that the addition timing could affect the morphology, dispersity and composition of BGN. With delayed addition of calcium nitrate, larger, more regular and better dispersed BGN could be synthesized while the gap between nominal and actual compositions of BGN was widened. However, the addition timing had no significant influence on structural characteristics, as BGN with different addition-timing of calcium nitrate exhibited similar infrared spectra and amorphous nature. The results also suggested that monodispersed BGN could be synthesized by carefully controlling the addition of calcium nitrate. The synthesized monodispersed BGN could release Si and Ca ions continuously for up to at least 14 days. They also showed in vitro bioactivity and non-cytotoxicity towards rat bone marrow-derived mesenchymal stem cells (rBMSCs). In conclusion, the timing of calcium precursor addition is an essential parameter to be considered when producing BGN which should exhibit monodisperse characteristics for biomedical applications.

September, 2016 | DOI: 10.1039/C6RA05548F

Effect of Nickel and Magnesium on the Electrochemical Behavior of AA 1050 Alloys in Nitric Acid Solution

Garcia-Garcia, FJ; Skeldon, P; Thompson, GE
Journal of the Electrochemical Society, 163 (9) (2016) C593-C601


The study investigates the influence of nickel and magnesium additions to AA 1050 aluminum alloy on the electrochemical behavior of the alloy in nitric acid solution under conditions relevant to the lithographic and electronic industries. Magnesium and nickel additions are of interest, since they can improve the alloy properties for the printing process by improving reverse bending fatigue strength and thermal softening resistance, while nickel may provide uniform pitting during electrograining. Scanning electron microscopy was used to characterize the resulting surface morphologies. The addition of nickel led to an increase in the pitting and corrosion potentials; additionally, it reduced the rate of dissolution of intermetallic particles during anodic polarization and increased the rate of aluminum dissolution during cathodic polarization. In contrast, the addition of magnesium had negligible influence on the open circuit and pitting behaviors, since the magnesium is retained in solid solution and has negligible influence on the cathodic behavior of intermetallic particles, which dominate the corrosion behavior.

September, 2016 | DOI: 10.1149/2.1181609jes

Isotope labelling to study molecular fragmentation during the dielectric barrier discharge wet reforming of methane

Montoro-Damas, AM; Gomez-Ramirez, A; Gonzalez-Elipe, AR; Cotrino, J
Journal of Power Sources, 325 (2016) 501-505


Isotope labelling is used to study the wet plasma reforming of methane in a dielectric barrier discharge reactor using D2O and CH4 as reactants. Besides the formation of CO and hydrogen as main products, different partitions of H and D atoms are found in the hydrogen (i.e., Hz, HD, D-2), methane (i.e., CH4, CH3D and CH2D2) and water (D2O, DHO) molecules detected by mass spectrometry as outlet gases of the plasma process. The effect of operating parameters such as applied current, residence time and the addition of oxygen to the reaction mixture is correlated with the H/D distribution in these molecules, the overall reaction yield and the energetic efficiency of the process. The results prove the plasma formation of intermediate excited species that rendering water and methane instead of CO and hydrogen greatly contribute to decrease the overall energy efficiency of the reforming process.

September, 2016 | DOI: 10.1016/j.jpowsour.2016.06.028

Stabilization of catalyst particles against sintering on oxide supports with high oxygen ion lability exemplified by Ir-catalyzed decomposition of N2O

Yentekakis, IV; Goula, G; Panagiotopoulou, P; Kampouri, S; Taylor, MJ; Kyriakou, G; Lambert, RM
Applied Catalysis B-Environmental, 192 (2016) 357-364


Iridium nanoparticles deposited on a variety of surfaces exhibited thermal sintering characteristics that were very strongly correlated with the lability of lattice oxygen in the supporting oxide materials. Specifically, the higher the lability of oxygen ions in the support, the greater the resistance of the nanoparticles to sintering in an oxidative environment. Thus with gamma-Al2O3 as the support, rapid and extensive sintering occurred. In striking contrast, when supported on gadolinia-ceria and alumina-ceria-zirconia composite, the Ir nanoparticles underwent negligible sintering. In keeping with this trend, the behavior found with yttria-stabilized zirconia was an intermediate between the two extremes. This resistance, or lack of resistance, to sintering is considered in terms of oxygen spillover from support to nanoparticles and discussed with respect to the alternative mechanisms of Ostwald ripening versus nanoparticle diffusion. Activity towards the decomposition of N2O, a reaction that displays pronounced sensitivity to catalyst particle size (large particles more active than small particles), was used to confirm that catalytic behavior was consistent with the independently measured sintering characteristics. It was found that the nanoparticle active phase was Ir oxide, which is metallic, possibly present as a capping layer. Moreover, observed turnover frequencies indicated that catalyst-support interactions were important in the cases of the sinter-resistant systems, an effect that may itself be linked to the phenomena that gave rise to materials with a strong resistance to nanoparticle sintering. 

September, 2016 | DOI: 10.1016/j.apcatb.2016.04.011

Reduced graphene oxide-carboxymethylcellulose layered with platinum nanoparticles/PAMAM dendrimer/magnetic nanoparticles hybrids. Application to the preparation of enzyme electrochemical biosensors

Borisova, B; Sanchez, A; Jimenez-Falcao, S; Martin, M; Salazar, P; Parrado, C; Pingarron, JM; Villalonga, R
Sensors and Actuators B-Chemical, 232 (2016) 84-90


The assembly of a novel layer-by-layer biosensor architecture using hybrid nanomaterials is explored for the construction of an amperometric enzyme biosensors. The nanostructured sensing interface was prepared with poly(dopamine)-modified magnetic nanoparticles which were covalently coated with four-generation ethylenediamine core polyamidoamine G-4 dendrimers and further decorated with platinum nanoparticles. This nanohybrid was fully characterized and further layered on glassy carbon electrodes coated with a graphene oxide-carboxymethylcellulose hybrid nanomaterial through electrostatic interactions. The nanostructured surface was then employed as scaffold for the covalent immobilization of the enzyme xanthine oxidase through a glutaraldehyde-mediated cross-linking. The enzyme electrode allowed the amperometric detection of xanthine in the 50 nM-12 mu M range, with a high sensitivity of 140 mA/M cm(2) and low detection limit of 13 nM. The biosensor exhibited high reproducibility and repeatability, and was successfully tested for the quantification of xanthine in fish samples. 

September, 2016 | DOI: 10.1016/j.snb.2016.02.106

Nanocolumnar association and domain formation in porous thin films grown by evaporation at oblique angles

Lopez-Santos, C; Alvarez, R; Garcia-Valenzuela, A; Rico, V; Loeffler, M; Gonzalez-Elipe, AR; Palmero, A
Nanotechnology, 27 (2016) 395702


Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO2 and TiO2.

September, 2016 | DOI: 10.1088/0957-4484/27/39/395702

Effects of electronic and nuclear stopping power on disorder induced in GaN under swift heavy ion irradiation

Moisy, F; Sall, M; Grygiel, C; Balanzat, E; Boisserie, M; Lacroix, B; Simon, P; Monnet, I
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 381 (2016) 39-44


Wurtzite GaN epilayers, grown on the c-plane of sapphire substrate, have been irradiated with swift heavy ions at different energies and fluences, and thereafter studied by Raman scattering spectroscopy, UV–visible spectroscopy and transmission electron microscopy. Raman spectra show strong structural modifications in the GaN layer. Indeed, in addition to the broadening of the allowed modes, a large continuum and three new modes at approximately 200 cm−1, 300 cm−1 and 670 cm−1 appear after irradiation attributed to disorder-activated Raman scattering. In this case, spectra are driven by the phonon density of states of the material due to the loss of translation symmetry of the lattice induced by defects. It was shown qualitatively that both electronic excitations and elastic collisions play an important role in the disorder induced by irradiation. UV–visible spectra reveal an absorption band at 2.8 eV which is linked to the new mode at 300 cm−1observed in irradiated Raman spectra and comes from Ga-vacancies. These color centers are produced by elastic collisions (without any visible effect of electronic excitations).

August, 2016 | DOI: 10.1016/j.nimb.2016.05.024

Effect of TiO2-Pd and TiO2-Ag on the photocatalytic oxidation of diclofenac, isoproturon and phenol

Espino-Estevez, MR; Fernandez-Rodriguez, C; Gonzalez-Diaz, OM; Arana, J; Espinos, JP; Ortega-Mendez, JA; Dona-Rodriguez, JM
Chemical Engineering Journal, 298 (2016) 82-95


The effects of silver and palladium metals on the photocatalytic degradation of diclofenac sodium salt (DCF), isoproturon (IP) and phenol (PHL) in water over lab-made TiO2 synthesized following a sol-gel method were investigated. Silver and palladium catalysts were prepared by photodeposition at 1 wt.% of loading metal. The resulting materials were characterized through BET, XRD, TEM, SEM, XPS and DRS-UV-Vis. The photodeposition test conditions of both metals determined their final oxidation state, with reduced particles of palladium and silver as well as silver oxides found on the catalysts. The results showed that the type of metal had different effects on the photodegradation mechanism depending on the nature of the pollutants. Accordingly, the highest degradation rate for IP and DCF was obtained when using the catalyst photodeposited with palladium and for PHL the catalyst photodeposited with silver. The photodegradation intermediates of PHL, DCF and IP were also identified.

August, 2016 | DOI: 10.1016/j.cej.2016.04.016

Synthesis, characterization and performance of robust poison resistant ultrathin film yttria stabilized zirconia nickel anodes for application in solid electrolyte fuel cells

Garcia-Garcia, FJ; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR; Lambert, RM
Journal of Power Sources, 324 (2016) 679-686


We report on the synthesis of undoped ∼5 μm YSZ-Ni porous thin films prepared by reactive pulsed DC magnetron sputtering at an oblique angle of incidence. Pre-calcination of the amorphous unmodified precursor layers followed by reduction produces a film consisting of uniformly distributed tilted columnar aggregates having extensive three-phase boundaries and favorable gas diffusion characteristics. Similarly prepared films doped with 1.2 at.% Au are also porous and contain highly dispersed gold present as Ni-Au alloy particles whose surfaces are strongly enriched with Au. With hydrogen as fuel, the performance of the undoped thin film anodes is comparable to that of 10–20 times thicker typical commercial anodes. With a 1:1 steam/carbon feed, the un-doped anode cell current rapidly falls to zero after 60 h. In striking contrast, the initial performance of the Au-doped anode is much higher and remains unaffected after 170 h. Under deliberately harsh conditions the performance of the Au-doped anodes decreases progressively, almost certainly due to carbon deposition. Even so, the cell maintains some activity after 3 days operation in dramatic contrast with the un-doped anode, which stops working after only three hours of use. The implications and possible practical application of these findings are discussed.

July, 2016 | DOI: 10.1016/j.jpowsour.2016.05.124

In vitro stimulation of MC3T3-E1cells and sustained drug delivery by a hierarchical nanostructured SiO2-CaO-P2O5 scaffold

Ramiro-Gutierrez, ML; Santos-Ruiz, L; Borrego-Gonzalez, S; Becerra, J; Diaz-Cuenca, A
Microporous and Mesoporous Materials, 229 (2016) 31-43


A hierarchical scaffold, SP1_h_HA, consisting of a biomimetic nano-hydroxyapatite surface coating growth onto a reticulated structure having a nano-organized porous texture was fabricated and functionally studied in vitro using osteoprogenitor cells. Three scaffold materials (designated as SP0_l, SP0_h and SP1_h) were also prepared through modifications of the processing variables as control materials. The scaffolds were characterized showing well-interconnected micron-sized voids and a nano (4–6 nm)-organized porosity. In order to evaluate potential local risks and performance over mammalian cells the scaffolds were studied in comparison with a commercial clinical grade scaffold material, ProOsteon® 500R. MC3T3-E1 pre-osteoblast viability was evaluated using the resazurin assay and field emission gun scanning electron microscopy (FEG-SEM), showing in all cases good proliferative response. Alkaline phosphatase (ALP) production and analysis of the differentiation marker osteocalcin (OC), both in non-osteoinductive and osteoinductive media, were assessed using colorimetric and RT-PCR methods. The implementation of the new scaffold processing variables enhanced ALP activity with respect to the SP0_l control material. The cell proliferation, ALP activity, and mRNA OC expression response to SP1_h_HA scaffold were higher than those observed after the use of ProOsteon® 500R. In addition, SP1_h_HA scaffold showed a two stage sustained release of gentamicin sulfate (GS) instead of the quick release shown by ProOsteon® 500R. These results suggest that our synthesized scaffold could be effective for antibiotic delivery and bone regeneration and a better option than ProOsteon® 500R.

July, 2016 | DOI: 10.1016/j.micromeso.2016.04.018

A Full Vacuum Approach for the Fabrication of Hybrid White-Light-Emitting Thin Films and Wide-Range In Situ Tunable Luminescent Microcavities

Y. Oulad-Zian, J.R. Sánchez-Valencia, M. Oliva, J. Parra-Barranco, M. Alcaire, F.J. Aparicio, A. Mora-Boza, J.P. Espinós, F. Yubero, A.R. González-Elipe, A. Barranco, A. Borras
Advanced Optical Materials, 4 (2016) 1134


A wide-range in situ tunable 1D Bragg microcavity including a hybrid layer as white light emitter defect is shown by J. R. Sanchez-Valencia, A. Borras, and co-workers on page 1124. White emission is obtained by Förster resonance energy transfer between blue (1,3,5-triphenyl-2-pyrazoline) and orange (rubrene) dyes homogeneously infiltrated within the host nanocolumnar SiO2film, which is formed by glancing angle deposition. Sequential physical vapor deposition at low temperatures provides the organic dyes localization within the porous nanostructure of the defect layer.

June, 2016 | DOI: 10.1002/adom.201670041

The 16th European Conference on Applications of Surface and Interface Analysis

Yubero, F
Surface and Interface Analysis


Portable IR dye laser optofluidic microresonator as a temperature and chemical sensor

Lahoz, F; Martin, IR; Gil-Rostra, J; Oliva-Ramirez, M; Yubero, F; Gonzalez-Elipe, AR
Optics Express, 24 (2016) 14383-14392


A compact and portable optofluidic microresonator has been fabricated and characterized. It is based on a Fabry-Perot microcavity consisting essentially of two tailored dichroic Bragg mirrors prepared by reactive magnetron sputtering deposition. The microresonator has been filled with an ethanol solution of Nile-Blue dye. Infrared laser emission has been measured with a pump threshold as low as 0.12 MW/cm2 and an external energy conversion efficiency of 41%. The application of the device as a temperature and a chemical sensor is demonstrated. Small temperature variations as well as small amount of water concentrations in the liquid laser medium are detected as a shift of the resonant laser modes.

June, 2016 | DOI: 10.1364/OE.24.014383

Dye-based photonic sensing systems

Aparicio, FJ; Alcaire, M; Gonzalez-Elipe, AR; Barranco, A; Holgado, M; Casquel, R; Sanza, FJ; Griol, A; Bernier, D; Dortu, F; Caceres, S; Antelius, M; Lapisa, M; Sohlstrom, H; Niklaus, F
Sensors and Actuators B: Chemical, 228 (2016) 649-657


We report on dye-based photonic sensing systems which are fabricated and packaged at wafer scale. For the first time luminescent organic nanocomposite thin-films deposited by plasma technology are integrated in photonic sensing systems as active sensing elements. The realized dye-based photonic sensors include an environmental NO2 sensor and a sunlight ultraviolet light (UV) A+B sensor. The luminescent signal from the nanocomposite thin-films responds to changes in the environment and is selectively filtered by a photonic structure consisting of a Fabry-Perot cavity. The sensors are fabricated and packaged at wafer-scale, which makes the technology viable for volume manufacturing. Prototype photonic sensor systems have been tested in real-world scenarios. 

June, 2016 | DOI: 10.1016/j.snb.2016.01.092

Non-enzymatic Glucose electrochemical sensor made of porous NiO thin films prepared by reactive magnetron sputtering at oblique angles

Garcia-Garcia, FJ; Salazar, P; Yubero, F; Gonzalez-Elipe, AR
Electrochimica Acta, 201 (2016) 38-44


Porous nanostructured NiO thin films have been prepared in one step by magnetron sputtering in an oblique angle configuration (MS-OAD) and used as electrodes for the non-enzymatic detection of glucose. The films have been thoroughly characterized by different complementary techniques and their performance for the analysis of glucose in basic solutions determined by electrochemical methods. These electrodes presented four times higher sensitivity that equivalent compact thin films prepared by MS in a normal configuration and were superior in terms of sensitivity than majority of nickel based electrodes prepared by other methods. Finally, a high sensitivity towards detection of glucose in blood, insensitivity to common interferences, a long term stability and high reproducibility confirmed the good performance and reliability of these electrodes for practical analytical purposes.

May, 2016 | DOI: 10.1016/j.electacta.2016.03.193

The interaction between hybrid organic-inorganic halide perovskite and selective contacts in perovskite solar cells: an infrared spectroscopy study

Idigoras, J; Todinova, A; Sanchez-Valencia, JR; Barranco, A; Borras, A; Anta, JA
Physical Chemistry Chemical Physics, 18 (2016) 13583-13590


The interaction of hybrid organic-inorganic halide perovskite and selective contacts is crucial to get efficient, stable and hysteresis-free perovskite-based solar cells. In this report, we analyze the vibrational properties of methylammonium lead halide perovskites deposited on different substrates by infrared absorption (IR) measurements (4000-500 cm(-1)). The materials employed as substrates are not only characterized by different chemical natures (TiO2, ZnO and Al2O3), but also by different morphologies. For all of them, we have investigated the influence of these substrate properties on perovskite formation and its degradation by humidity. The effect of selective-hole contact (Spiro-OmeTad and P3HT) layers on the degradation rate by moisture has also been studied. Our IR results reveal the existence of a strong interaction between perovskite and all ZnO materials considered, evidenced by a shift of the peaks related to the N-H vibrational modes. The interaction even induces a morphological change in ZnO nanoparticles after perovskite deposition, pointing to an acid-base reaction that takes place through the NH3+ groups of the methylammonium cation. Our IR and X-ray diffraction results also indicate that this specific interaction favors perovskite decomposition and PbI2 formation for ZnO/perovskite films subjected to humid conditions. Although no interaction is observed for TiO2, Al2O3, and the hole selective contact, the morphology and chemical nature of both contacts appear to play an important role in the rate of degradation upon exposure to moisture.

May, 2016 | DOI: 10.1039/c6cp01265e

Nickel-copper bilayer nanoporous electrode prepared by physical vapor deposition at oblique angles for the non-enzymatic determination of glucose

Salazar, P; Rico, V; Gonzalez-Elipe, AR
Sensors and Actuators B: Chemical, 226 (2016) 436-443


This work presents a novel bilayer Ni/Cu porous nanostructured film electrode prepared by physical vapor deposition (PVD) in an oblique angle configuration. Scanning electron microscopy (SEM) data revealed that the film, with an approximate thickness of 200 nm, is formed by tilted nanocolumns of around 50 nm of diameter and an inclination of 30° with respect to the surface normal. X ray photoelectron spectroscopy (XPS) data confirmed a bilayer configuration with Cu and Ni located at the top and bottom parts of the film, respectively. A porosity of ca. 45–35% as determined by Rutherford back scattering (RBS) offered a large exposed area and excellent diffusion properties that, combined with a very good catalytic activity, rendered these films excellent electrodes for the quantitative determination of glucose. Under optimized working conditions of detection these electrodes presented a high sensitivity of 2.53 A M−1 cm−2 (R2: 0.999), a limit of detection of 0.23 μM and a time response of ca. 2 s. The sensors did not show any loss of response during a period of 4 months. The selectivity of the sensor was checked against various interferences, including physiological compounds, different sugars and ethanol, in all cases with excellent results. The feasibility of using of this sensor for practical applications was confirmed by successfully determining the glucose content in different commercial beverages.

April, 2016 | DOI: 10.1016/j.snb.2015.12.003

Light management: porous 1-dimensional nanocolumnar structures as effective photonic crystals for perovskite solar cells

Ramos, FJ; Oliva-Ramirez, M; Nazeeruddin, MK; Graetzel, M; Gonzalez-Elipe, AR; Ahmad, S
Journal of Materials Chemistry A, 4 (2016) 4962-4970


Hybrid organic-inorganic perovskite solar cells are a topic of increasing interest, as in a short time span they are able to lead in the third generation photovoltaics. Organohalide perovskites possess exceptional optoelectronic and physical properties, thus making their implementation possible in many diverse configurations of photovoltaic devices. In this work, we present three different configurations of porous 1-dimensional photonic crystals (1-DPCs) based on alternated nanocolumnar layers of oxides with different refractive indices (n) that were deposited by Physical Vapor Deposition at Oblique Angle Deposition (PVD-OAD). They are then implemented as the photoanode in CH3NH3PbI3 solar cells to improve the management of light into the device. These configurations improved the performance of the photovoltaic system by designing a light interference structure capable of enhancing the absorption capability of the perovskite. A device fabricated using these photonic crystal structures presented an efficiency >12% in contrast with only 10.22% for a reference device based on non-photonic crystal TiO2 layers deposited under analogous conditions.

April, 2016 | DOI: 10.1039/c5ta08743k

Growth Assisted by Glancing Angle Deposition: A New Technique to Fabricate Highly Porous Anisotropic Thin Films

Sanchez-Valencia, JR; Longtin, R; Rossell, MD; Groning, P
ACS Applied Materials & Interfaces, 8 (2016) 8686-8693


We report a new methodology based on glancing angle deposition (GLAD) of an organic molecule in combination with perpendicular growth of a second inorganic material. The resulting thin films retain a very well-defined tilted columnar microstructure characteristic of GLAD with the inorganic material embedded inside the columns. We refer to this new methodology as growth assisted by glancing angle deposition or GAGLAD, since the material of interest (here, the inorganic) grows in the form of tilted columns, though it is deposited under a nonglancing configuration. As a “proof of concept”, we have used silver and zinc oxide as the perpendicularly deposited material since they usually form ill-defined columnar microstructures at room temperature by GLAD. By means of our GAGLAD methodology, the typical tilted columnar microstructure can be developed for materials that otherwise do not form ordered structures under conventional GLAD. This simple methodology broadens significantly the range of materials where control of the microstructure can be achieved by tuning the geometrical deposition parameters. The two examples presented here, Ag/Alq3 and ZnO/Alq3, have been deposited by physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), respectively: two different vacuum techniques that illustrate the generality of the proposed technique. The two type of hybrid samples present very interesting properties that demonstrate the potentiality of GAGLAD. On one hand, the Ag/Alq3 samples present highly optical anisotropic properties when they are analyzed with linearly polarized light. To our knowledge, these Ag/Alq3 samples present the highest angular selectivity reported in the visible range. On the other hand, ZnO/Alq3 samples are used to develop highly porous ZnO thin films by using Alq3 as sacrificial material. In this way, antireflective ZnO samples with very low refractive index and extinction coefficient have been obtained.

April, 2016 | DOI: 10.1021/acsami.6b00232

Pre-prosthetic use of poly(lactic-co-glycolic acid) membranes treated with oxygen plasma and TiO2 nanocomposite particles for guided bone regeneration processes

Castillo-Dali, G; Castillo-Oyague, R; Terriza, A; Saffar, JL; Batista-Cruzado, A; Lynch, CD; Sloan, AJ; Gutierrez-Perez, JL; Torres-Lagares, D
Journal of Dentistry, 47 (2016) 71-79


Objectives: Guided bone regeneration (GBR) processes are frequently necessary to achieve appropriate substrates before the restoration of edentulous areas. This study aimed to evaluate the bone regeneration reliability of a new poly-lactic-co-glycolic acid (PLGA) membrane after treatment with oxygen plasma (PO2) and titanium dioxide (TiO2) composite nanoparticles. 

Methods: Circumferential bone defects (diameter: 10 mm; depth: 3 mm) were created on the parietal bones of eight experimentation rabbits and were randomly covered with control membranes (Group 1: PLGA) or experimental membranes (Group 2: PLGA/PO2/TiO2). The animals were euthanized two months afterwards, and a morphologic study was then performed under microscope using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone formed in the grown defects, concentration of osteoclasts, and intensity of osteosynthetic activity were assessed. Comparisons among the groups and with the original bone tissue were made using the Kruskal-Wallis test. The level of significance was set in advance at a = 0.05. 

Results: The experimental group recorded higher values for new bone formation, mineralised bone length, and osteoclast concentration; this group also registered the highest osteosynthetic activity. Bone layers in advanced formation stages and low proportions of immature tissue were observed in the study group. 

April, 2016 | DOI: 10.1016/j.jdent.2016.01.015

Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation

Maddi, C; Bourquard, F; Tite, T; Loir, AS; Donnet, C; Garrelie, F; Barnier, V; Wolski, K; Fortgang, P; Zehani, N; Braiek, M; Lagarde, F; Chaix, C; Jaffrezic-Renault, N; Rojas, TC; Sanchez-Lopez, JC
Diamond and Related Materials,65 (2016) 17-25


Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to -350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at%. Nitrogen content increase induces a higher sp(2) character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor. 

April, 2016 | DOI: 10.1016/j.diamond.2016.01.001

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Barranco, A; Borras, A; Gonzalez-Elipe, AR; Palmero, A
Progress in Materials Science, 78 (2016) 59-153


The oblique angle configuration has emerged as an invaluable tool for the deposition of nanostructured thin films. This review develops an up to date description of its principles, including the atomistic mechanisms governing film growth and nanostructuration possibilities, as well as a comprehensive description of the applications benefiting from its incorporation in actual devices. In contrast with other reviews on the subject, the electron beam assisted evaporation technique is analyzed along with other methods operating at oblique angles, including, among others, magnetron sputtering and pulsed laser or ion beam-assisted deposition techniques. To account for the existing differences between deposition in vacuum or in the presence of a plasma, mechanistic simulations are critically revised, discussing well-established paradigms such as the tangent or cosine rules, and proposing new models that explain the growth of tilted porous nanostructures. In the second part, we present an extensive description of applications wherein oblique-angle-deposited thin films are of relevance. From there, we proceed by considering the requirements of a large number of functional devices in which these films are currently being utilized (e.g., solar cells, Li batteries, electrochromic glasses, biomaterials, sensors, etc.), and subsequently describe how and why these nanostructured materials meet with these needs. 

March, 2016 | DOI: 10.1016/j.pmatsci.2015.06.003

Nitrogen Nanobubbles in a-SiOxNy Coatings: Evaluation of Its Physical Properties and Chemical Bonding State by Spatially Resolved Electron Energy-Loss Spectroscopy

Lacroix, B.; Godinho, V.; Fernández, A.
Journal of Physical Chemistry C, 120 (2016) 5651-5658


Nanoporous silicon-based materials with closed porosity filled with the sputtering gas have been recently developed by magnetron sputtering. In this work the physical properties (density and pressure) of molecular nitrogen inside closed pores in a SiOxNy coating are investigated for the first time using spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope. The paper offers a detailed methodology to record and process multiple EELS spectrum images (SIs) acquired at different energy ranges and with different dwell times. An adequate extraction and quantification of the N–K edge contribution due to the molecular nitrogen inside nanopores is demonstrated. Core-loss intensity and N chemical bond state were evaluated to retrieve 2D maps revealing the stable high density of molecular nitrogen (from 40 to 70 at./nm3) in nanopores of different size (20–11 nm). This work provides new insights into the quantification of molecular N2 trapped in porous nitride matrices that could also be applied to other systems.

March, 2016 | DOI: 10.1021/acs.jpcc.5b09036

Electrocatalytic System for the Simultaneous Hydrogen Production and Storage from Methanol

Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, A
ACS Catalysis, 6 (2016) 1942-1951


This paper reports a groundbreaking approach for simultaneous hydrogen production and storage that entails catalysis, electrochemistry, surface science, and materials synthesis. A novel electrocatalytic system is developed based on nickel nanocolumnar films of controlled microstructure prepared on K-βAl2O3 solid electrolyte supports by oblique angle physical vapor deposition. The outstanding characteristics of this system are a hydrogen storage capacity of up to 19 g of H2 (100 g of Ni)−1, which is unparalleled in the literature and the possibility of controlling its release electrochemically, under fixed mild conditions (280 °C and normal pressure). H2 is produced in situ by methanol steam re-forming on the Ni catalyst, and it spills over onto graphene oxide aggregates formed during the catalytic process, as confirmed by SEM, FTIR, and Raman spectroscopy. The proposed storage mechanism considers a synergetic contribution of both Ni and graphene oxide, promoted by K+ ions, in enhancing the hydrogen storage capacity of the system.

March, 2016 | DOI: 10.1021/acscatal.5b02844

Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique angles

Salazar, P; Garcia-Garcia, FJ; Yubero, F; Gil-Rostra, J; Gonzalez-Elipe, AR
Electrochimica Acta, 193 (2016) 24-31


In this communication we report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto indium tin oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behaviour, i.e. a linear working range from pH 1 to 12 with a slope of about -57.7 mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 months. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal reference electrode. This full solid state pH sensor presented a Nernstian behaviour with a slope of about -59 mV/pH and offered important analytical and operation advantages for decentralized pH measurements in different applications. 

March, 2016 | DOI: 10.1016/j.electacta.2016.02.040

Nanoindentation and scratch resistance of multilayered TiO2-SiO2 coatings with different nanocolumnar structures deposited by PV-OAD

Roa, JJ; Rico, V; Oliva-Ramirez, M; Gonzalez-Elipe, AR; Jimenez-Pique, E
Journal of Physics D-Applied Physics, 49 (2016) 13


This paper presents a study of the mechanical properties and an evaluation of damage mechanisms of nanocolumnar TiO2-SiO2 multilayer coatings prepared by physical vapour oblique angle deposition at different configurations (slanted, zigzag or chiral) and two zenithal evaporation angles (70 degrees or 85 degrees). The characterization at micro-and nanometric length scales of the mechanical properties of the multilayers has been carried out by nanoindentation and nanoscratch tests, while the morphological evaluation of the surface and sub-surface damages produced with a sharp indenter and the adhesive and/or cohesive failures between coating and substrate have been investigated by field emission scanning electron microscopy and focused ion beam, respectively. The obtained results have shown that the main processing parameters controlling the mechanical response of the different multilayers is the zenithal angle of deposition and the number of layers in the multilayer stack, while the coating architecture had only a minor effect on the mechanical response. This analysis also revealed a higher resistance to scratch testing and a brittle failure behaviour for the low zenithal angle coatings as compared with the high angle ones.

February, 2016 | DOI: 10.1088/0022-3727/49/13/135104

Determination of the Anisotropic Elastic Properties of Rocksalt Ge2Sb2Te5 by XRD, Residual Stress, and DFT

Cecchini, R; Kohary, K; Fernandez, A; Cabibbo, M; Marmier, A
Journal of Physical Chemistry C, 120 (2016) 5624-5629


The chalcogenide material Ge2Sb2Te5 is the prototype phase-change material, with widespread applications for optical media and random access memory. However, the full set of its independent elastic properties has not yet been published. In this study, we determine the elastic constants of the rocksalt Ge2Sb2Te5, experimentally by X-ray diffraction (XRD) and residual stress and computationally by density functional theory (DFT). The stiffnesses (XRD-stress/DFT) in GPa are C-11 = 41/58, C-12 = 7/8, and C-44 = 8/12, and the Zener ratio is 0.46/0.48. These values are important to understand the effect of elastic distortions and nonmelting processes on the performances of increasingly small phase change data bits.

February, 2016 | DOI: 10.1021/acs.jpcc.5b09867

Vacuum template synthesis of multifunctional nanotubes with tailored nanostructured walls

Filippin, AN; Macias-Montero, M; Saghi, Z; Idigoras, J; Burdet, P; Barranco, A; Midgley, P; Anta, JA; Borras, A
Scientific Reports, 5 (2016) 20637


A three-step vacuum procedure for the fabrication of vertical TiO2 and ZnO nanotubes with three dimensional walls is presented. The method combines physical vapor deposition of small-molecules, plasma enhanced chemical vapor deposition of inorganic functional thin films and layers and a post-annealing process in vacuum in order to remove the organic template. As a result, an ample variety of inorganic nanotubes are made with tunable length, hole dimensions and shapes and tailored wall composition, microstructure, porosity and structure. The fabrication of multishell nanotubes combining different semiconducting oxides and metal nanoparticles is as well explored. This method provides a feasible and reproducible route for the fabrication of high density arrays of vertically alligned nanotubes on processable substrates. The emptying mechanism and microstructure of the nanotubes have been elucidated through SEM, STEM, HAADF-STEM tomography and energy dispersive X-ray spectroscopy. In this article, as a proof of concept, it is presented the straightforward integration of ZnO nanotubes as photoanode in a photovoltaic cell and as a photonic oxygen gas sensor.

February, 2016 | DOI: 10.1038/srep20637

Ripening and recrystallization of NaCl nanocrystals in humid conditions

Oliva-Ramirez, M; Macias-Montero, M; Borras, A; Gonzalez-Elipe, AR
RSC Advances, 6 (2016) 3778-3782


This study shows that Ostwald ripening, a universal mechanism responsible for the increase of crystal size during precipitation from solutions, can be meditated by ion diffusion through condensed monolayers of water that connect separated nanocrystals. In an environmental electron microscope we have observed "in situ" the time evolution of the number, shape, size and crystallographic texture of NaCl nanoparticles deposited by electron beam evaporation at oblique angles. Analysis of NaCl nanoparticles before and after water vapor condensation has evidenced that the size of nanocrystals is not the unique driving force inducing nanoparticle ripening and recrystallization, but the faceting of their crystalline habits and the amorphisation degree of the initially deposited nuclei also play important roles. These findings have implications for other crystallization and nucleation processes and can be of relevance for rock weathering and related phenomena.

February, 2016 | DOI: 10.1039/C5RA22425J

Nanostructured Ti thin films by magnetron sputtering at oblique angles

Alvarez, R; Garcia-Martin, JM; Garcia-Valenzuela, A; Macias-Montero, M; Ferrer, FJ; Santiso, J; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Journal of Physics D-Applied Physics, 49 (2016) 045303


The growth of Ti thin films by the magnetron sputtering technique at oblique angles and at room temperature is analysed from both experimental and theoretical points of view. Unlike other materials deposited in similar conditions, the nanostructure development of the Ti layers exhibits an anomalous behaviour when varying both the angle of incidence of the deposition flux and the deposition pressure. At low pressures, a sharp transition from compact to isolated, vertically aligned, nanocolumns is obtained when the angle of incidence surpasses a critical threshold. Remarkably, this transition also occurs when solely increasing the deposition pressure under certain conditions. By the characterization of the Ti layers, the realization of fundamental experiments and the use of a simple growth model, we demonstrate that surface mobilization processes associated to a highly directed momentum distribution and the relatively high kinetic energy of sputtered atoms are responsible for this behaviour.

February, 2016 | DOI: 10.1088/0022-3727/49/4/045303

Optofluidic Modulation of Self-Associated Nanostructural Units Forming Planar Bragg Microcavities

Oliva-Ramirez, M; Barranco, A; Loffler, M; Yubero, F; Gonzalez-Elipe, AR
ACS Nano, 10 (2016) 1256-1264


Bragg microcavities (BMs) formed by the successive stacking of nanocolumnar porous SiO2 and TiO2 layers with slanted, zigzag, chiral, and vertical configurations are prepared by physical vapor deposition at oblique angles while azimuthally varying the substrate orientation during the multilayer growth. The slanted and zigzag BMs act as wavelength-selective optical retarders when they are illuminated with linearly polarized light, while no polarization dependence is observed for the chiral and vertical cavities. This distinct optical behavior is attributed to a self-nanostructuration mechanism involving a fence-bundling association of nanocolumns as observed by focused ion beam scanning electron microscopy in the slanted and zigzag microcavities. The outstanding retarder response of the optically active BMs can be effectively modulated by dynamic infiltration of nano- and mesopores with liquids of different refraction indices acting as a switch of the polarization behavior. The unprecedented polarization and tunable optofluidic properties of these nanostructured photonic systems have been successfully simulated with a simple model that assumes a certain birefringence for the individual stacked layers and accounts for the light interference phenomena developed in the BMs. The possibilities of this type of self-arranged nanostructured and optically active BMs for liquid sensing and monitoring applications are discussed.

January, 2016 | DOI: 10.1021/acsnano.5b06625

Highly Porous ZnO Thin Films and 1D Nanostructures by Remote Plasma Processing of Zn-Phthalocyanine

Alcaire, M; Filippin, AN; Macias-Montero, M; Sanchez-Valencia, JR; Rojas, TC; Mora-Boza, A; Lopez-Santos, C; Espinos, JP; Barranco, A; Borras, A
Plasma Processes and Polymers, 13 (2016) 287-297


In this paper the fabrication of highly porous 1D nanostructures by a vacuum and plasma etching combined protocol is presented. Zn-phthalocyanine (ZnPc) is utilized as a solid precursor to form the ZnO. First the ZnPc is sublimated in low argon pressure. Depending on the substrate temperature and microstructure, polycrystalline films or single crystal ZnPc nanowires are grown. These starting materials are then subjected to a remote plasma oxidizing treatment. Experimental parameters such as substrate position, plasma power, treatment duration, and substrate temperature determine the microstructure and properties of the final ZnO nanostructures. The article gathers an in depth study of the obtained porous nanostructured films following scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV-Vis transmittance, and fluorescence spectroscopies.

January, 2016 | DOI: 10.1002/ppap.201500133

Application of Prussian Blue electrodes for amperometric detection of free chlorine in water samples using Flow Injection Analysis

Salazar, P; Martin, M; Gonzalez-Mora, JL; Gonzalez-Elipe, AR
Talanta, 146 (2016) 410-416


The performance for free chlorine detection of surfactant-modified Prussian Blue screen printed carbon electrodes (SPCEs/PB-BZT) have been assessed by cyclic voltammetry and constant potential amperometry. The characterization of SPCEs/PB-BZT by X-ray photoemission, Raman and infrared spectroscopies confirmed the correct electrodeposition of the surfactant-modified PB film. These electrodes were incorporated in a Flow Injection device and the optimal working conditions determined as a function of experimental variables such as detection potential, electrolyte concentration or flow-rate. The sensor presented a linear response in the range 0–3 ppm free chlorine, with a sensitivity of 16.2 μA ppm−1 cm−2. The limit of detection (LOD) (S/N=3.3) and the limit of quantification (S/N=10) amounted to 8.25 and 24.6 ppb, respectively, adequate for controlling tap and drinking waters. To demonstrate the feasibility of using this free chlorine sensor for real applications possible interferences such as nitrate, nitrite and sulfate ions were successfully tested and discarded. Real free chlorine analysis was carried out in spiked tap water samples and commercial bleaches.

January, 2016 | DOI: 10.1016/j.talanta.2015.08.072

Investigation of a Pt containing washcoat on SiC foam for hydrogen combustion applications

Fernandez, A; Arzac, GM; Vogt, UF; Hosoglu, F; Borgschulte, A; de Haro, MCJ; Montes, O; Zuttel, A
Applied Catalysis B: Environmental, 180 (2016) 336-343


A commercial Pt based washcoat, used for catalytic methane combustion, was studied supported on a commercial SiC foam as catalytic material (Pt/SiC) for catalytic hydrogen combustion (CHC). Structural and chemical characterization was performed using Electron Microscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The reaction was monitored following water concentration by Fourier Transform Infrared spectra (FTIR). The FTIR method was compared with H2 detection by Gas Cromatography (GC) and has shown to be adequate to study the kinetics of the CHC reaction in steady state under our experimental conditions (very lean 1% (v/v) H2/air mixtures). The catalyst is composed of 5–20 nm disperse Pt nanoparticles decorating a mixture of high surface area Al2O3 and small amounts of ceria supported on the SiC foam which also contains alumina as binder. The Pt/SiC catalytic material has demonstrated to be active enough to start up the reaction in a few seconds at room temperature. The material has been able to convert at least 18.5 Lhydrogen min−1 gPt−1 at room temperature in conditions of excess of catalyst. The Pt/SiC material was studied after use using XPS and no significant changes on Pt oxidation states were found. The material was characterized from a kinetic point of view. From the conversion-temperature plot a T50(temperature for 50% conversion) of 34 °C was obtained. Activation energy measured in our conditions was 35 ± 1 kJ mol−1.

January, 2016 | DOI: 10.1016/j.apcatb.2015.06.040

A novel 3D absorption correction method for quantitative EDX-STEM tomography

Burdet, P; Saghi, Z; Filippin, AN; Borras, A; Midgley, PA
Ultramicroscopy, 160 (2016) 118-129


This paper presents a novel 3D method to correct for absorption in energy dispersive X-ray (EDX) microanalysis of heterogeneous samples of unknown structure and composition. By using STEM-based tomography coupled with EDX, an initial 3D reconstruction is used to extract the location of generated X-rays as well as the X-ray path through the sample to the surface. The absorption correction needed to retrieve the generated X-ray intensity is then calculated voxel-by-voxel estimating the different compositions encountered by the X-ray. The method is applied to a core/shell nanowire containing carbon and oxygen, two elements generating highly absorbed low energy X-rays. Absorption is shown to cause major reconstruction artefacts, in the form of an incomplete recovery of the oxide and an erroneous presence of carbon in the shell. By applying the correction method, these artefacts are greatly reduced. The accuracy of the method is assessed using reference X-ray lines with low absorption.

January, 2016 | DOI: 10.1016/j.ultramic.2015.09.012

Disorder-order phase transformation in a fluorite-related oxide thin film: In-situ X-ray diffraction and modelling of the residual stress effects

Gaboriaud, RJ; Paumier, F; Lacroix, B
Thin Solid Films, 601 (2016) 84-88


This work is focused on the transformation of the disordered fluorite cubic-F phase to the ordered cubic-C bixbyite phase, induced by isothermal annealing as a function of the residual stresses resulting from different concentrations of microstructural defects in the yttrium oxide, Y2O3. 

This transformation was studied using in-situ X-ray diffraction and was modelled using Kolmogorov-Johnson-Mehl-Avrami (KJMA) analysis. The degree of the disorder of the oxygen network was associated with the residual stress, which was a key parameter for the stability and the kinetics of the transition of the different phases that were present in the thin oxide film. When the degree of disorder/residual stress level is high, this transition, which occurs at a rather low temperature (300 degrees C), is interpreted as a transformation of phases that occurs by a complete recrystallization via the nucleation and growth of a new cubic-C structure. Using the KJMA model, we determined the activation energy of the transformation process, which indicates that this transition occurs via a one-dimensional diffusion process. Thus, we present the analysis and modelling of the stress state. When the disorder/residual stress level was low, a transition to the quasi-perfect ordered cubic-C structure of the yttrium oxide appeared at a rather high temperature (800 degrees C), which is interpreted as a classic recovery mechanism of the cubic-C structure.

January, 2016 | DOI: 10.1016/j.tsf.2015.08.030

Quantitative analysis of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix

Pauly, N; Yubero, F; Garcia-Garcia, FJ; Tougaard, S
Surface Science, 644 (2016) 46-52


In X-ray excited photoelectron emission (XPS), besides the initial excitation process, the shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. To make an accurate quantitative interpretation of features observed in XPS, these effects must be included in the theoretical description of the emitted photoelectron spectra. It was previously shown [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17] that these three effects can be calculated by means of the QUEELS-XPS software (Quantitative analysis of Electron Energy Losses at Surfaces for XPS) in terms of effective energy-differential inelastic electron scattering cross-sections. The only input needed to calculate these cross-sections is the energy loss function of the media which is determined from analysis of Reflection Electron Energy Loss Spectra (REELS). The full XPS spectrum is then modeled by convoluting this energy loss cross-section with the primary excitation spectrum that accounts for all effects which are part of the initial photo-excitation process, i.e. lifetime broadening, spin-orbit coupling, and multiplet splitting. In this paper we apply the previously presented procedure to the study of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix (Ni:SiO2), samples being prepared by reactive magnetron sputtering at room temperature. We observe a significant difference between the corresponding Ni 2p primary excitation spectra. The procedure allows quantifying the relative intensity of the c3d(9)L, c3d(10)L(2), and c3d(8) final states contributing to the Ni 2p photoemission spectra of the Ni2+ species in the oxide matrices. Especially, the intensity ratio in NiO between the non-local and local contributions to the 3d(9)L configuration is determined to be 2.5. Moreover the relative intensity ratio of the c3d(9)L/c3d(10)L(2)/c3d(8) configurations is found to be 1.0/0.83/0.11 for both the NiO and Ni:SiO2 samples. 

January, 2016 | DOI: 10.1016/j.susc.2015.09.012


"In Operando" X-ray Absorption Spectroscopy Analysis of Structural Changes During Electrochemical Cycling of WO3 and WxSiyOz Amorphous Electrochromic Thin Film Cathodes

Garcia-Garcia, FJ; Gil-Rostra, J; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR; Chaboy, J
Journal of Physical Chemistry C, 119 (2015) 644-652


This work reports a X-ray absorption spectroscopy (XAS) study under in operando conditions of the structural and chemical changes undergone by WO3 and WxSiyOz thin films used as electrochromic cathodes. The electrochromic films were prepared by magnetron sputtering deposition at oblique angles and then characterized by a large variety of techniques. The voltammograms and chronoamperometric diagrams in both aqueous and organic electrolyte media revealed a total reversibility of the electrochromic behavior, a low response time, and a high coloration efficiency for the two types of thin films. The in operando X-ray absorption study of the films working in aqueous solutions revealed that when they were electrochemically cycled the average WO distances reversibly varied by a Delta d of 0.06 and 0.08 angstrom for, respectively, WO3 and WxSiyOz. These changes are discussed by assuming the reduction of W6+ cations and the transformation of W-O double bonds into single WO bond structures during the electrochemical cycling of the films.

January, 2015 | DOI: 10.1021/jp508377v

Optical properties of zirconium oxynitride films: The effect of composition, electronic and crystalline structures

Carvalho, P; Borges, J; Rodrigues, MS; Barradas, NP; Alves, E; Espinos, JP; Gonzalez-Elipe, AR; Cunha, L; Marques, L; Vasilevskiy, MI; Vaz, F
Applied Surface Science, 358 (2015) 660-669


This work is devoted to the investigation of zirconium oxynitride (ZrOxNy) films with varied optical responses prompted by the variations in their compositional and structural properties. The films were prepared by dc reactive magnetron sputtering of Zr, using Ar and a reactive gas mixture of N-2 + O-2 ( 17:3). The colour of the films changed from metallic-like, very bright yellow-pale and golden yellow, for low gas flows to red-brownish for intermediate gas flows. Associated to this colour change there was a significant decrease of brightness. With further increase of the reactive gas flow, the colour of the samples changed from red-brownish to dark blue or even to interference colourations. The variations in composition disclosed the existence of four different zones, which were found to be closely related with the variations in the crystalline structure. XRD analysis revealed the change from a B1 NaCl face-centred cubic zirconium nitride-type phase for films prepared with low reactive gas flows, towards a poorly crystallized over-stoichiometric nitride phase, which may be similar to that of Zr3N4 with some probable oxygen inclusions within nitrogen positions, for films prepared with intermediate reactive gas flows. For high reactive gas flows, the films developed an oxynitride-type phase, similar to that of gamma-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions, evolving to a ZrO2 monoclinic type structure within the zone where films were prepared with relatively high reactive gas flows. The analysis carried out by reflected electron energy loss spectroscopy (REELS) revealed a continuous depopulation of the d-band and an opening of an energy gap between the valence band (2p) and the Fermi level close to 5 eV. The ZrN-based coatings (zone land II) presented intrinsic colourations, with a decrease in brightness and a colour change from bright yellow to golden yellow, red brownish and dark blue. Associated to these changes, there was also a shift of the reflectivity minimum to lower energies, with the increase of the non-metallic content. The samples lying in the two last zones (zone III, oxynitride and zone IV, oxide films) revealed a typical semi-transparent-optical behaviour showing interference-like colourations only due to the complete depopulation of the d band at the Fermi level. The samples lying in these zones presented also an increase of the optical bandgap from 2 to 3.6 eV. 

December, 2015 | DOI: 10.1016/j.apsusc.2015.09.129

Efficient synthesis of ammonia from N-2 and H-2 alone in a ferroelectric packed-bed DBD reactor

Gomez-Ramirez, A; Cotrino, J; Lambert, RM; Gonzalez-Elipe, AR
Plasma Sources Science and Technology, 24 (2015) 065011


A detailed study of ammonia synthesis from hydrogen and nitrogen in a planar dielectric barrier discharge (DBD) reactor was carried out. Electrical parameters were systematically varied, including applied voltage and frequency, electrode gap, and type of ferroelectric material (BaTiO3 versus PZT). For selected operating conditions, power consumption and plasma electron density were estimated from Lissajous diagrams and by application of the Bolsig + model, respectively. Optical emission spectroscopy was used to follow the evolution of plasma species (NH*, N*, N-2(+) and N-2*) as a function of applied voltage with both types of ferroelectric material. PZT gave both greater energy efficiency and higher ammonia yield than BaTiO3: 0.9 g NH3 kWh(-1) and 2.7% single pass N-2 conversion, respectively. This performance is substantially superior to previously published findings on DBD synthesis of NH3 from N-2 and H-2 alone. The influence of electrical working parameters, the beneficial effect of PZT and the importance of controlling reactant residence time are rationalized in a reaction model that takes account of the principal process variables

December, 2015 | DOI: 10.1088/0963-0252/24/6/065011

Atomic scale characterization of SiO2/4H-SiC interfaces in MOSFETs devices

Beltran, AM; Duguay, S; Strenger, C; Bauer, AJ; Cristiano, F; Schamm-Chardon, S
Solid State Communications, 221 (2015) 28-32


The breakthrough of 4H-SiC MOSFETs is stemmed mainly due to the mobility degradation in their channel in spite of the good physical intrinsic material properties. Here, two different n-channel 4H-SiC MOSFETs are characterized in order to analyze the elemental composition at the SiC/SiO2 interface and its relationship to their electrical properties. Elemental distribution analyses performed by EELS reveal the existence of a transition layer between the SiC and the SiO2 regions of the same width for both MOSFETs despite a factor of nearly two between their electron mobility. Additional 3D compositional mapping by atom probe tomography corroborates these results, particularly the absence of an anomalous carbon distribution around the SiC/SiO2interface.

November, 2015 | DOI: 10.1016/j.ssc.2015.08.017

Plasma reforming of methane in a tunable ferroelectric packed-bed dielectric barrier discharge reactor

Montoro-Damas, AM; Brey, JJ; Rodriguez, MA; Gonzalez-Elipe, AR; Cotrino, J
Journal of Power Sources, 296 (2015) 268-275


In a tunable circular parallel plate dielectric barrier discharge reactor with pellets of a ferroelectric material separating the electrodes we investigate the plasma reforming of methane trying to maximize both the reaction yield and the energetic efficiency of the process. The geometrical configuration of the reactor (gap between electrodes, active electrode area) and the ferroelectric pellet size have been systematically varied to determine their influence on the process efficiency. The comparison between wet (with H2O as reactant), oxidative (with O2), and dry (with CO2) reforming reactions reveals a higher efficiency for the former with CO + H2 as main reaction products. The maximum energetic efficiency EE, defined as the produced number of litres of H2 per kWh, found for optimized working conditions at low-level applied power is higher than the up to date best-known results. A comprehensive discussion of the influence of the different parameters affecting the reaction yield is carried out.

November, 2015 | DOI: 10.1016/j.jpowsour.2015.07.038

Single-step fabrication process of 1-D photonic crystals coupled to nanocolumnar TiO2 layers to improve DSC efficiency

Gonzalez-Garcia, L; Colodrero, S; Miguez, H; Gonzalez-Elipe, AR
Optics Express, 23 (2015) A1642-A1650


The present work proposes the use of a TiO2 electrode coupled to a one-dimensional photonic crystal (1DPC), all formed by the sequential deposition of nanocolumnar thin films by physical vapor oblique angle deposition (PV-OAD), to enhance the optical and electrical performance of DSCs while transparency is preserved. We demonstrate that this approach allows building an architecture combining a non-dispersive 3 µm of TiO2 electrode and 1 µm TiO2-SiO2 1DPC, both columnar, in a single-step process. The incorporation of the photonic structure is responsible for a rise of 30% in photovoltaic efficiency, as compared with a transparent cell with a single TiO2 electrode. Detailed analysis of the spectral dependence of the photocurrent demonstrates that the 1DPC improves light harvesting efficiency by both back reflection and optical cavity modes confinement within the TiO2 films, thus increasing the overall performance of the cell.

November, 2015 | DOI: 10.1364/OE.23.0A1642

Full solution processed mesostructured optical resonators integrating colloidal semiconductor quantum dots

Calvo, ME; Hidalgo, N; Schierholz, R; Kovacs, A; Fernandez, A; Bellino, MG; Soler-Illia, GJAA; Miguez, H
Nanoscale, 7 (2015) 16583-16589


Herein we show a solution based synthetic pathway to obtain a resonant optical cavity with embedded colloidal semiconductor quantum dots (CSQDs). The optical cavity pore network, surrounded by two dense Bragg mirrors, was designed ad hoc to selectively host the quantum dots, while uncontrolled infiltration of those in the rest of the layered structure was prevented. Coupling between the optical resonant modes of the host and the natural emission of the embedded nanoparticles gives rise to the fine tuning of the luminescence spectrum extracted from the ensemble. Our approach overcomes, without the need for an encapsulating agent and exclusively by solution processing, the difficulties that arise from the low thermal and chemical stability of the CSQDs. It opens the route to achieving precise control over their location and hence over the spectral properties of light emitted by these widely employed nanomaterials. Furthermore, as the porosity of the cavity is preserved after infiltration, the system remains responsive to environmental changes, which provides an added value to the proposed structure.

October, 2015 | DOI: 10.1039/C5NR03977K

Role of Y in the oxidation resistance of CrAlYN coatings

Dominguez-Meister, S; El Mrabet, S; Escobar-Galindo, R; Mariscal, A; de Haro, CJ; Justo, A; Brizuela, M; Rojas, TC; Sanchez-Lopez, JC
Applied Surface Science, 363 (2015) 504-511


CrAlYN coatings with different aluminum (4–12 at.%) and yttrium (2–5 at.%) contents are deposited by d.c. reactive magnetron sputtering on silicon and M2 steel substrates using metallic targets and Ar/N2 mixtures. The influence of the nanostructure and chemical elemental distribution on the oxidation resistance after heating in air at 1000 °C is studied by means of cross-sectional scanning electron microscopy (X-SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GD-OES). The sequential exposure to the metallic targets during the synthesis leads to a multilayer structure where concentration of metallic elements (Cr, Al and Y) is changing periodically. A good oxidation resistance is observed when Al- and Y-rich regions are separated by well-defined CrN layers, maintaining crystalline coherence along the columnar structure. This protective behavior is independent of the type of substrate and corresponds to the formation of a thin mixed (Al, Cr)-oxide scale that protects the film underneath. The GD-OES and XRD analysis have demonstrated that Y acts as a reactive element, blocking the Fe and C atoms diffusion from the steel and favoring higher Al/Cr ratio in the passivation layer after heating. The coating with Y content around 4 at.% exhibited the best performance with a thinner oxide scale, a delay in the CrN decomposition and transformation to Cr2N, and a more effective Fe and C blocking.

October, 2015 | DOI: 10.1016/j.apsusc.2015.06.099

Amperometric magnetobiosensors using poly(dopamine)-modified Fe3O4 magnetic nanoparticles for the detection of phenolic compounds

Martin, M; Salazar, P; Campuzano, S; Villalonga, R; Pingarron, JM; Gonzalez-Mora, JL
Analytical Methods, 7 (2015) 8801-8808


The synthesis of poly(dopamine)-modified magnetic nanoparticles (MNPs) and their application in preparing electrochemical enzyme biosensors that are useful to detect phenolic compounds is reported in this work. MNPs of about 16 nm were synthesized by a co-precipitation method and conveniently modified with poly(dopamine). Non-modified and modified MNPs were characterized using X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). Horseradish peroxidase (HRP) was covalently immobilized onto the surface of the poly(dopamine)-modified MNPs via Michael addition and/or Schiff base formation and used to construct a biosensor for phenolic compounds by capturing the HRP-modified-nanoparticles onto the surface of a magnetic-modified glassy carbon electrode (GCE). Cyclic voltammetry and amperometry were used to study the electrochemical and analytical properties of the biosensor using hydroquinone (HQ) as a redox probe. Among the different phenolic compounds studied, the biosensor exhibited higher sensitivity for HQ, 1.38 A M−1 cm−2, with limits of detection and quantification of 0.3 and 1.86 μM, respectively. The analytical biosensor performance for HQ and 2-aminophenol compared advantageously with those of previous phenolic biosensors reported in the literature.

October, 2015 | DOI: 10.1039/C5AY01996F

"In situ" XPS studies of laser-induced surface nitridation and oxidation of tantalum

Lahoz, R; Espinos, JP; Yubero, F; Gonzalez-Elipe, AR; de la Fuente, GF
Journal of Materials Research, 30 (2015) 2967-2976


This work studies the nitridation of Ta by laser irradiation by means of x-ray photoelectron spectroscopy. The study has been carried out under "in situ" conditions by controlling the nitrogen partial pressure, the presence of traces of oxygen, and the irradiance of the laser. It is found that a thin layer of Ta2O5 is directly obtained when irradiating in the presence of oxygen, while a Ta3N5 surface compound and some minor contributions of nonstoichiometric phases are formed in the presence of nitrogen. For O-2:N-2 mixtures at 0.1 Pa, preferential nitride formation occurs up to a ratio of 1:4, while Ta2O5 starts to be predominant for ratios above this value. The air stability of the tantalum nitride layer formed by laser irradiation and the surface topography of the irradiated metal are also studied. The possible factors determining this behavior are discussed.

October, 2015 | DOI: 10.1557/jmr.2015.190

Physiological Degradation Mechanisms of PLGA Membrane Films under Oxygen Plasma Treatment

Lopez-Santos, C; Terriza, A; Portoles, J; Yubero, F; Gonzalez-Elipe, AR
Journal fo Physical Chemistry C, 119 (2015) 20446–20452


Degradation under simulated physiological conditions of poly(lactic-co-glycolic) (PLGA) copolymer membrane films subjected to an oxygen plasma treatment compared to its “as prepared” state has been studied by gas cluster ion beam assisted X-ray photoelectron spectroscopy for chemical depth profiling analysis. This investigation is complemented with atomic force microscopy, weight loss measurements, and visual inspection of the films at the different stages of the degradation process. The obtained results show that the carbon functional groups of the PLGA membrane films undergo a heterogeneous hydrolytic degradation to different rates depending on the plasma pretreatment. The content of glycolic groups (GA) in untreated PLGA samples immersed for 3 weeks in a phosphate-buffered saline solution decreased at the surface, whereas the ratio between glycolic and lactic units (LA) did not vary in the inner regions (∼400 nm depth) of the degraded membrane films. By contrast, oxygen plasma pretreatment enhances the degradation efficiency and causes that both lactic and glycolic functional components decreased at the surface and in the interior of the film, although with less prevalence for the lactic units that present a comparatively higher resistance to degradation.

September, 2015 | DOI: 10.1021/acs.jpcc.5b05011

Microstructure of mixed oxide thin films prepared by magnetron sputtering at oblique angles

Gil-Rostra, J; Garcia-Garcia, FJ; Ferrer, FJ; Gonzalez-Elipe, AR; Yubero, F
Thin Solid Films, 591 (2015) 330-335


Several mixed oxide thin film series of samples (Si–Co–O, Si–Ni–O, Si–W–O) have been prepared by reactive magnetron sputtering at oblique angle geometries. The paper focuses on the description of microstructure of the films as a function of their stoichiometry. It is found that for identical process parameters (gas mixture, pressure, magnetron-substrate distance, incidence angle of the vapour flux, etc.) the tilt angle of the developed columnar microstructure and the film porosity is strongly dependent on the stoichiometry of the films. The results are discussed in the framework of several theoretical models on this topic.

September, 2015 | DOI: 10.1016/j.tsf.2015.01.058

Direct observation of doping incorporation pathways in self-catalytic GaMnAs

Kasama, T.; Thuvander, M.; Siusys, A.; Gontard, L. C.; Kovacs, A.; Yazdi, S.; Duchamp, M.; Gustafsson, A.; Dunin-Borkowski, R. E.; Sadowski, J.
Journal of Applied Physics, 118 (2015) 054302


Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 °C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography. Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga0.82Mn0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22 ± 4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga0.82Mn0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process.

August, 2015 | DOI: 10.1063/1.4927623

Ultraviolet Pretreatment of Titanium Dioxide and Tin-Doped Indium Oxide Surfaces as a Promoter of the Adsorption of Organic Molecules in Dry Deposition Processes: Light Patterning of Organic Nanowires

Oulad-Zian, Y; Sanchez-Valencia, JR; Parra-Barranco, J; Hamad, S; Espinos, JP; Barranco, A; Ferrer, J; Coll, M; Borras, A
Langmuir, 31 (2015) 8294-8302


In this article we present the preactivation of TiO2 and ITO by UV irradiation under ambient conditions as a tool to enhance the incorporation of organic molecules on these oxides by evaporation at low pressures. The deposition of p-stacked molecules on TiO2 and ITO at controlled substrate temperature and in the presence of Ar is thoroughly followed by SEM, UV-vis, XRD, RBS, and photoluminescence spectroscopy, and the effect is exploited for the patterning formation of small-molecule organic nanowires (ONWs). X-ray photoelectron spectroscopy (XPS) in situ experiments and molecular dynamics simulations add critical information to fully elucidate the mechanism behind the increase in the number of adsorption centers for the organic molecules. Finally, the formation of hybrid organic/inorganic semiconductors is also explored as a result of the controlled vacuum sublimation of organic molecules on the open thin film microstructure of mesoporous TiO2.

August, 2015 | DOI: 10.1021/acs.langmuir.5b01572

Modulating Low Energy Ion Plasma Fluxes for the Growth of Nanoporous Thin Films

Alvarez, Rafael; Lopez-Santos, Carmen; Ferrer, Francisco J.; Rico, Victor; Cotrino, Jose; Gonzalez-Elipe, Agustin R.; Palmero, Alberto
Plasma Processes and Polymers, 12 (2015) 719-724


The growth of nanoporous layers by plasma-assisted deposition techniques is strongly mediated by the ion fluxes in the reactor. To analyze their influence we have deposited different nanostructured thin films by the magnetron sputtering technique at oblique angles, modulating the ion fluxes in the plasma by tuning the frequency of the electromagnetic signal from pure DC to 160 kHz DC pulsed mode. In the DC case, ions possess energies below 5 eV and do not induce noticeable changes in the film structure. However, when the signal is pulsed, ions with energies up to 40 eV impinge on the film, decreasing the porosity of the layers and tilting down the porous/nanocolumnar structures. As a result, we demonstrate that the overall porosity of the layers and the tilt angle of the columns can be tailored as two independent morphological quantities.

August, 2015 | DOI: 10.1002/ppap.201400209

Rapid Legionella pneumophila determination based on a disposable core–shell Fe3O4@poly(dopamine) magnetic nanoparticles immunoplatform

Martin, M; Salazar, P; Jimenez, C; Lecuona, M; Ramos, MJ; Ode, J; Alcoba, J; Roche, R; Villalonga, R; Campuzano, S; Pingarron, JM; Gonzalez-Mora, JL
Analytica Chimica Acta, 887 (2015) 51-58


A novel amperometric magnetoimmunoassay, based on the use of core–shell magnetic nanoparticles and screen-printed carbon electrodes, was developed for the selective determination of Legionella pneumophila SG1. A specific capture antibody (Ab) was linked to the poly(dopamine)–modified magnetic nanoparticles (MNPs@pDA-Ab) and incubated with bacteria. The captured bacteria were sandwiched using the antibody labeled with horseradish peroxidase (Ab-HRP), and the resulting MNPs@pDA-Ab-Legionella neumophila-Ab-HRP were captured by a magnetic field on the electrode surface. The amperometric response measured at −0.15 V vs. Ag pseudo-reference electrode of the SPCE after the addition of H2O2 in the presence of hydroquinone (HQ) was used as transduction signal. The achieved limit of detection, without pre-concentration or pre-enrichment steps, was 104 Colony Forming Units (CFUs) mL−1. The method showed a good selectivity and the MNPs@pDA-Ab exhibited a good stability during 30 days. The possibility of detecting L. pneumophila at 10 CFU mL−1 level in less than 3 h, after performing a membrane-based preconcentration step, was also demonstrated.

August, 2015 | DOI: 10.1016/j.aca.2015.05.048

Fabrication of Optical Multi layer Devices from Porous Silicon Coatings with Closed Porosity by Magnetron Sputtering

Caballero-Hernandez, Jaime; Godinho, Vanda; Lacroix, Bertrand; Jimenez de Haro, Maria C.; Jamon, Damien; Fernandez, Asuncion
ACS Applied Materials & Interfaces, 7 (2015) 13880-13897


The fabrication of single-material photonic-multilayer devices is explored using a new methodology to produce porous silicon layers by magnetron sputtering. Our bottom-up methodology produces highly stable amorphous porous silicon films with a controlled refractive index using magnetron sputtering and incorporating a large amount of deposition gas inside the closed pores. The influence of the substrate bias on the formation of the closed porosity was explored here for the first time when He was used as the deposition gas. We successfully simulated, designed, and characterized Bragg reflectors and an optical microcavity that integrates these porous layers. The sharp interfaces between the dense and porous layers combined with the adequate control of the refractive index and thickness allowed for excellent agreement between the simulation and the experiments. The versatility of the magnetron sputtering technique allowed for the preparation of these structures for a wide range of substrates such as polymers while also taking advantage of the oblique angle deposition to prepare Bragg reflectors with a controlled lateral gradient in the stop band wavelengths.

July, 2015 | DOI: 10.1021/acsami.5b02356

Removing the effects of the "dark matter" in tomography

Gontard, Lionel C.
Ultramicroscopy, 154 (2015) 64-72


Electron tomography (ET) using different imaging modes has been progressively consolidating its position as a key tool in materials science. The fidelity of a tomographic reconstruction, or tomogram, is affected by several experimental factors. Most often, an unrealistic cloud of intensity that does not correspond to a real material phase of the specimen ("dark matter") blurs the tomograms and enhances artefacts arising from the missing wedge (MW). Here we show that by simple preprocessing of the background level of any tomographic tilt series, it is possible to minimise the negative effects of that "dark matter". Iterative reconstruction algorithms converge better, leading to tomograms with fewer streaking artefacts from the MW, more contrast, and increased accuracy. The conclusions are valid irrespective of the imaging mode used, and the methodology improves the segmentation and visualisation of tomograms of both crystalline and amorphous materials. We show examples of HAADF STEM and BF TEM tomography.

July, 2015 | DOI: 10.1016/j.ultramic.2015.03.017

New Copper wide range nanosensor electrode prepared by physical vapor deposition at oblique angles for the non-enzimatic determination of glucose

Salazar, P; Rico, V; Rodriguez-Amaro, R; Espinos, JP; Gonzalez-Elipe, AR
Electrochimica Acta, 169 (2015) 195-201


In this work a novel Cu nanostructured electrode is presented. Cu tilted nanocolumnar and porous thin films have been prepared by physical vapor deposition (PVD) in an oblique angle configuration and characterized by different techniques. Cyclic voltammetry and amperometry were used to study the sensing ability of the copper films deposited on ITO to quantitatively determine glucose and to optimize the experimental conditions of detection. Scanning electron microscopy data revealed that the film microstructure consists of tilted nanocolumns of around 70 nm of diameter and an inclination of 65° with respect to the surface normal that extend through the total thickness of the layer of ca. 300 nm. X ray photoelectron spectroscopy and Raman, used to determine the oxidation state of Cu, revealed that an oxy/hydroxide external layer formed around the nanocolumns is the active phase responsible for the electrocatalytic detection of glucose. Under optimized conditions, the CuO/Cu nanoporous/ITO electrode presented a sensitivity of 1.41 A mol dm−3 cm−2 (R2:0.999) with a limit of detection of 0.36 μmol dm−3 and a reproducibility of 3.42%.The selectivity of the proposed sensor was checked against various interferences, including physiological compounds, different sugars and ethanol, thereby showing excellent anti-interference properties. The CuO/Cu nanoporous/ITO electrode was also used successfully to determine glucose in blood samples showing a performance comparable to that of a commercial glucometer. An extended working range covering from 1 to 5 × 10−3 mol dm−3 was determined for these sensor films which, in this way, could be applied for different analytical purposes including agro industrial liquids.

July, 2015 | DOI: 10.1016/j.electacta.2015.04.092

Nanocolumnar 1-dimensional TiO2 photoanodes deposited by PVD-OAD for perovskite solar cell fabrication

Javier Ramos, F.; Oliva-Ramirez, Manuel; Nazeeruddin, Mohammad Khaja; Graetzel, Michael; Gonzalez-Elipe, Agustin R.; Ahmad, Shahzada
Journal of Materials Chemistry A, 3 (2015) 13291-13298


Perovskite solar cells have attracted increasing interest among the photovoltaic community in the last few years owing to their unique properties and high efficiency. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional porous TiO2 photoanodes, which are uniform on a large area. These nanocolumnar porous TiO2 photoanodes were deposited by physical vapor deposition in an oblique angle configuration (PVD-OAD) by varying the zenithal angle between the target and the substrate normal. Perovskite infiltration into these 1-dimensional nanocolumnar structures was homogeneous through the entire thickness of the porous layer as revealed by secondary ion mass spectroscopy studies. The fabricated solar cells, with an optimized thickness of the photoanode and with industrially accepted methods, will pave the way for easy implementation on a large scale.

July, 2015 | DOI: 10.1039/c5ta02238j

A novel and improved surfactant-modified Prussian Blue electrode for amperometric detection of free chlorine in water

Salazar, Pedro; Martin, Miriam; Garcia-Garcia, Francisco J.; Luis Gonzalez-Mora, Jose; Gonzalez-Elipe, Agustin R.
Sensors and Actuators B: Chemical, 213 (2015) 116-123


A surfactant-modified Prussian Blue (PB) electrochemical sensor has been developed. Benzethonium was used to assist the electrodeposition of PB onto a glassy carbon electrode (GCE). The surface coverage ( [View the MathML source] ) was 7.75 × 10−8 mol cm−2, five times higher than the value obtained in the absence of surfactant, and the film thickness of ca. 123 nm. SEM, EDX, Raman were used to characterize the electrodes while their electrochemical analysis proved a superior performance for the surfactant modified PB film. Cyclic voltammetry and amperometry were used to study the sensor ability to detect chlorine, and the main experimental variables were optimized. Under optimized conditions, the sensor presented a sensitivity of 12 μA ppm−1 cm−2, a linear range from 9 ppb to 10 ppm and a reproducibility of 4.2%. For the first time, we proved the sensor performance for real applications. Thus, chlorine was determined in tap water and the obtained concentrations validated with a standard colorimetric method. The obtained results showed that our sensor is highly performant and reliable for applications involving determinations of environmental residual chlorine.

July, 2015 | DOI: 10.1016/j.snb.2015.02.092

Core-shell polydopamine magnetic nanoparticles as sorbent in micro-dispersive solid-phase extraction for the determination of estrogenic compounds in water samples prior to high-performance liquid chromatography-mass spectrometry analysis

Socas-Rodriguez, B; Hernandez-Borges, J; Salazar, P; Martin, M; Rodriguez-Delgado, MA
Journal of Chromatography A, 1397 (2015) 1-10


In this work, core-shell Fe3O4@poly(dopamine) magnetic nanoparticles (m-NPs) were prepared and characterized in our laboratory and applied as sorbents for the magnetic-micro solid phase extraction (m-mu SPE) of twelve estrogenic compounds of interest (i.e. 17 alpha-estradiol, 17 beta-estradiol, estrone, hexestrol, 17 alpha-ethynylestradiol, diethylstibestrol, dienestrol, zearalenone, alpha-zearalanol,beta-zearalanol, alpha-zearalenol and beta-zearalenol) from different water samples. Separation, determination and quantification were achieved by high-performance liquid chromatography coupled to ion trap mass spectrometry with electrospray ionization. NPs@poly(dopamine) were synthesized by a chemical coprecipitation procedure and characterized by different surface characterization techniques (X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission and scanning electron microscopy, infrared and Raman spectroscopy, vibrating sample magnetometry, microelectrophoresis and adsorption/desorption isotherms). Parameters affecting the extraction efficiency of m-mu SPE (i.e. polymerization time, pH of the sample, extraction and elution conditions) were studied and optimized. The methodology was validated for Milli-Q, mineral, tap and wastewater using 2-methoxyestradiol as internal standard, obtaining recoveries ranging from 70 to 119% with relative standard deviation values lower than 20% and limits of quantification in the range 0.02-1.1 mu g/L.

June, 2015 | DOI: 10.1016/j.chroma.2015.04.010

Porous, robust highly conducting Ni-YSZ thin film anodes prepared by magnetron sputtering at oblique angles for application as anodes and buffer layers in solid oxide fuel cells

Garcia-Garcia, Francisco J.; Yubero, Francisco; Gonzalez-Elipe, Agustin R.; Balomenou, Stella P.; Tsiplakides, Dimitris; Petrakopoulou, Ioanna; Lambert, Richard M.
Inernational Journal of Hydrogen Energy, 40 (2015) 7382-7387


Uniform, highly porous, columnar thin films incorporating YSZ and NiO prepared by magnetron sputtering with deposition at glancing incidence exhibited stoichiometries close to that of the Y-Zr-Ni sputter target. Characterization by means of SEM, XRD, XPS and RBS revealed that the uniformly distributed nickel component in the as-deposited films consisted of NiO, and that the YSZ component was essentially amorphous. Annealing such films at 850 degrees C in hydrogen resulted in crystallization of the YSZ phase with preservation of the columnar morphology, while the NiO underwent reduction to metallic Ni, which partially segregated to the film surface. The hydrogen-annealed thin film anodes exhibited high conductivity, comparable to that of conventionally-prepared anodes, in both hydrogen and hydrogen/water mixtures at temperatures relevant to SOFC operation. They were also robust against strain-induced separation from the substrate under limited thermal cycling in both oxidizing and reducing atmospheres and are promising candidates for use as anodes in their own right and as strain-accommodating buffer layers between conventional anodes and the electrolyte for use in SOFC applications.

June, 2015 | DOI: 10.1016/j.ijhydene.2015.04.001

Island-type growth of Au–Pt heterodimers: direct visualization of misfit dislocations and strain-relief mechanisms

Garcia-Negrete, CA; Knappett, BR; Schmidt, FP; Rojas, TC; Wheatley, AEH; Hofer, F; Fernandez, A
RSC Advances, 5 (2015) 55262-55268


Structural and analytical characterization related to the formation mechanism of Au–Pt heterodimers from polyhedral Pt nanocrystals is reported. The observation of specific lattice strain effects and the emergence of misfit dislocations point to the relevance of the Stranski–Krastanov growth mode as a means of explaining the previously reported dimerisation reaction between Au and Pt. Two size-dependent strain relief mechanisms were identified. For dimers grown from 4.7 nm seeds, the mechanism is related to bulk lattice strain accumulation at {111} planes along with lattice relaxation effects on other crystalline planes. However, for dimers grown from 11.2 nm seed sizes, the formation of misfit dislocations proved to be a highly efficient mechanism by which to release interface mismatch strain. Nanoscale chemical mapping at Au–Pt interfaces also revealed Au–Pt alloying to be unlikely under the mild temperature conditions employed in this work for Au–Pt heterodimer synthesis.

June, 2015 | DOI: 10.1039/C5RA09808D

Theory and Practice: Bulk Synthesis of C3B and its H2- and Li-Storage Capacity

King, TC; Matthews, PD; Glass, H; Cormack, JA; Holgado, JP; Leskes, M; Griffin, JM; Scherman, OA; Barker, PD; Grey, CP; Dutton, SE; Lambert, RM; Tustin, G; Alavi, A; Wright, DS
Angewandte Chemie International Edition, 54 (2015) 5919-5923


Previous theoretical studies of C3B have suggested that boron-doped graphite is a promising H2- and Li-storage material, with large maximum capacities. These characteristics could lead to exciting applications as a lightweight H2-storage material for automotive engines and as an anode in a new generation of batteries. However, for these applications to be realized a synthetic route to bulk C3B must be developed. Here we show the thermolysis of a single-source precursor (1,3-(BBr2)2C6H4) to produce graphitic C3B, thus allowing the characteristics of this elusive material to be tested for the first time. C3B was found to be compositionally uniform but turbostratically disordered. Contrary to theoretical expectations, the H2- and Li-storage capacities are lower than anticipated, results that can partially be explained by the disordered nature of the material. This work suggests that to model the properties of graphitic materials more realistically, the possibility of disorder must be considered.

May, 2015 | DOI: 10.1002/anie.201412200

Electrochemical activation of an oblique angle deposited Cu catalyst film for H-2 production

Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, A
Catalysis Science & Technology, 5 (2015) 2203-2214


A novel Cu catalyst film was prepared by oblique angle physical vapour deposition (OAD) on a K-βAl2O3 solid electrolyte (alkaline ionic conductor) for catalytic/electrocatalytic purposes. This technique allowed us to obtain a highly porous and electrically conductive Cu catalyst electrode which was tested in the partial oxidation of methanol (POM) reaction for H2 production and its catalytic activity was in situ enhanced via electrochemical promotion of catalysis (EPOC). The electropromotional effect was reversible and reproducible, and allowed us to increase both hydrogen and methyl formate production rates by almost three times under optimal promotion conditions (320 °C, 2.2 × 10−7 mol of K+ transferred). The observed promotional effect was attributed to a decrease in the Cu catalyst work function as a consequence of the controlled migration of electropositive K+ ions which favoured the chemisorption of electron acceptor molecules (O2) at the expense of the electron donor ones (CH3OH). Under the reaction conditions these ions formed some kinds of potassium surface compounds as demonstrated by SEM, EDX and XPS post-reaction characterization analyses. The obtained results demonstrate the interest of the used catalyst-electrode preparation technique for the electrochemical activation of non-noble metal catalyst films.

May, 2015 | DOI: 10.1039/c4cy01524j

Anisotropic In-Plane Conductivity and Dichroic Gold Plasmon Resonance in Plasma-Assisted ITO Thin Films e-Beam-Evaporated at Oblique Angles

Parra-Barranco, Julian; Garcia-Garcia, Francisco J.; Rico, Victor; Borras, Ana; Lopez-Santos, Carmen; Frutos, Fabian; Barranco, Angel; Gonzalez-Elipe, Agustin R.
ACS Applied Materials & Interfaces, 7 (2015) 10993-11001


ITO thin films have been prepared by electron beam evaporation at oblique angles (OA), directly and while assisting their growth with a downstream plasma. The films microstructure, characterized by scanning electron microscopy, atomic force microscopy, and glancing incidence small-angle X-ray scattering, consisted of tilted and separated nanostructures. In the plasma assisted films, the tilting angle decreased and the nanocolumns became associated in the form of bundles along the direction perpendicular to the flux of evaporated material. The annealed films presented different in-depth and sheet resistivity as confirmed by scanning conductivity measurements taken for the individual nanocolumns. In addition, for the plasma-assisted thin films, two different sheet resistance values were determined by measuring along the nanocolumn bundles or the perpendicular to it. This in-plane anisotropy induces the electrochemical deposition of elongated gold nanostructures. The obtained Au-ITO composite thin films were characterized by anisotropic plasmon resonance absorption and a dichroic behavior when examined with linearly polarized light.

May, 2015 | DOI: 10.1021/acsami.5b02197

Free-Base Carboxyphenyl Porphyrin Films Using a TiO2 Columnar Matrix: Characterization and Application as NO2 Sensors

Roales, Javier; Pedrosa, Jose M.; Guillen, Maria G.; Lopes-Costa, Tania; Castillero, Pedro; Barranco, Angel; Gonzalez-Elipe, Agustin R.
Sensors, 15 (2015) 11118-11132


The anchoring effect on free-base carboxyphenyl porphyrin films using TiO2 microstructured columns as a host matrix and its influence on NO2 sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 composite films has revealed that m-TCPP/TiO2 films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO2 through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 films to NO2 has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO2 sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO2 confirm the potential of m-TCPP as a NO2 sensor.

May, 2015 | DOI: 10.3390/s150511118

STEM-in-SEM high resolution imaging of gold nanoparticles and bivalve tissues in bioaccumulation experiments

C.A. García-Negrete; M.C. Jiménez de Haro; J. Blasco; M. Soto; A. Fernández
Analyst, 140 (2015) 3082-3089


The methodology termed scanning transmission electron microscopy in scanning electron microscopy (STEM-in-SEM) has been used in this work to study the uptake of citrate stabilized gold nanoparticles (AuNPs) (average particle sizes of 23.5 ± 4.0 nm) into tissue samples uponin vitro exposure of the dissected gills of the Ruditapes philippinarum marine bivalve to the nanoparticle suspensions. The STEM-in-SEM methodology has been optimized for achieving optimum resolution under SEM low voltage operating conditions (20–30 kV). Based on scanning microscope assessments and resolution testing (SMART), resolutions well below 10 nm were appropriately achieved by working at magnifications over 100k×, with experimental sample thickness between 300 and 200 nm. These relatively thick slices appear to be stable under the beam and help avoid NP displacement during cutting. We herein show that both localizing of the internalized nanoparticles and imaging of ultrastructural disturbances in gill tissues are strongly accessible due to the improved resolution, even at sample thicknesses higher than those normally employed in standard TEM techniques at higher voltages. Ultrastructural imaging of bio-nano features in bioaccumulation experiments have been demonstrated in this study.

May, 2015 | DOI: 10.1039/C4AN01643B

Hydrogen production through sodium borohydride ethanolysis

Arzac, GM; Fernandez, A
International Journal of Hydrogen Energy, 40 (2015) 5326-5332


In this work, sodium borohydride (SB) ethanolysis was explored for the first time as a method to generate hydrogen for Polymer Exchange Membrane Fuel Cells. Ethanolysis by-product was characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, and Nuclear Magnetic Resonance. Metal and acid catalysts were tested. RuCl3 center dot 3H(2)O was the best metal catalyst. Acetic acid was selected for the study because of its effectiveness, low cost and relative greenness. The maximum gravimetric hydrogen density obtained was 2.1% wt. The addition of water produces an increase in hydrogen generation rate and a decrease in conversion. The use of ethanol-methanol mixtures produces an increase in reaction rates in absence of catalyst. As a proof of concept the reaction was performed in a small reactor which operates by the addition of ethanolic acetic acid solutions to solid SB (in the form of granules). The reactor produces stable and constant hydrogen generation in the range of 20-80 ml min(-1) during 1 h at constant temperature (around 27-35 degrees.

April, 2015 | DOI: 10.1016/j.ijhydene.2015.01.115

Self-lubricity of WSex nanocomposite coatings

S. Dominguez-Meister; M. Conte; A. Igartua; T.C. Rojas; J.C. Sánchez-López
ACS Applied Materials & Interfaces, 7 (2015) 7979-7986


Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in the presence of oxygen and/or moisture. Here we present a tailored WSex coating with low friction (0.07) and low wear rates (3 × 10–7 mm3 Nm–1) even in ambient air. To understand the low friction behavior and lower chemical reactivity a tribological study is carried out in a high-vacuum tribometer under variable pressure (atmospheric pressure to 1 × 10–8 mbar). A detailed investigation of the film nanostructure and composition by advanced transmission electron microscopy techniques with nanoscale resolution determined that the topmost layer is formed by nanocrystals of WSe2 embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe2 lamellas along the sliding direction were observed in the interfacial region. On the basis of high angle annular dark field, scanning transmission electron microscopy, and energy dispersive X-ray analysis, the release of W atoms from the interstitial basal planes of the a-W(Se) phase is proposed. These W atoms reaching the surface, play a sacrificial role preventing the lubricant WSe2 phase from oxidation. The increase of the WSe2 crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.

April, 2015 | DOI: 10.1021/am508939s

Transmission electron microscopy of thiol-capped Au clusters on C: Structure and electron irradiation effects

Lionel C. Gontard, Rafal E. Dunin-Borkowski


High-resolution transmission electron microscopy is used to study interactions between thiol-capped Au clusters and amorphous C support films. The morphologies of the clusters are found to depend both on their size and on the local structure of the underlying C. When the C is amorphous, larger Au clusters are crystalline, while smaller clusters are typically disordered. When the C is graphitic, the Au particles adopt either elongated shapes that maximize their contact with the edge of the C film or planar arrays when they contain few Au atoms. We demonstrate the influence of electron beam irradiation on the structure, shape and stability of the Au clusters, as well as on the formation of holes bounded by terraces of graphitic lamellae in the underlying C.

March, 2015 | DOI: 10.1016/j.micron.2014.12.001

High N-content a-C:N films elaborated by femtosecond PLD with plasma assistance

Maddi, C; Donnet, C; Loir, AS; Tite, T; Barnier, V; Rojas, TC; Sanchez-Lopez, JC; Wolski, K; Garrelie, F
Applied Surface Science, 332 (2015) 346-353


Amorphous carbon nitride (a-C:N) thin films are a interesting class of carbon-based electrode materials. Therefore, synthesis and characterization of these materials have found lot of interest in environmental analytical microsystems. Herein, we report the nitrogen-doped amorphous carbon thin film elaboration by femtosecond pulsed laser deposition (fs-PLD) both with and without a plasma assistance. The chemical composition and atomic bonding configuration of the films were investigated by multi-wavelength (MW) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The highest nitrogen content, 28 at.%, was obtained with plasma assistance. The I(D)/I(G) ratio and the G peak position increased as a function of nitrogen concentration, whereas the dispersion and full width at half maximum (FWHM) of G peak decreased. This indicates more ordered graphitic like structures in the films both in terms of topological and structural, depending on the nitrogen content. EELS investigations were correlated with MW Raman results. The interpretation of XPS spectra of carbon nitride films remains a challenge. Plasma assisted PLD in the femtosecond regime led to a significant high nitrogen concentration, which is highlighted on the basis of collisional processes in the carbon plasma plume interacting with the nitrogen plasma.

March, 2015 | DOI: 10.1016/j.apsusc.2015.01.123

Nanocolumnar coatings with selective behavior towards osteoblast and Staphylococcus aureus proliferation

Izquierdo-Barba, Isabel; Miguel Garcia-Martin, Jose; Alvarez, Rafael; Palmero, Alberto; Esteban, Jaime; Perez-Jorge, Concepcion; Arcos, Daniel; Vallet-Regi, Maria
Acta Biomaterialia, 15 (2015) 20-28


Bacterial colonization and biofilm formation on orthopedic implants is one of the worst scenarios in orthopedic surgery, in terms of both patient prognosis and healthcare costs. Tailoring the surfaces of implants at the nanoscale to actively promote bone bonding while avoiding bacterial colonization represents an interesting challenge to achieving better clinical outcomes. Herein, a Ti6Al4V alloy of medical grade has been coated with Ti nanostructures employing the glancing angle deposition technique by magnetron sputtering. The resulting surfaces have a high density of nanocolumnar structures, which exhibit strongly impaired bacterial adhesion that inhibits biofilm formation, while osteoblasts exhibit good cell response with similar behavior to the initial substrates. These results are discussed on the basis of a "lotus leaf effect" induced by the surface nanostructures and the different sizes and biological characteristics of osteoblasts and Staphylococcus aureus.

March, 2015 | DOI: 10.1016/j.actbio.2014.12.023

Laser Treatment of Ag@ZnO Nanorods as Long-Life-Span SERS Surfaces

Macias-Montero, M; Pelaez, RJ; Rico, VJ; Saghi, Z; Midgley, P; Afonso, CN; Gonzalez-Elipe, AR; Borras, A
ACS Applied Materials & Interfaces, 7 (2015) 2331-2339


UV nanosecond laser pulses have been used to produce a unique surface nanostructuration of Ag@ZnO supported nanorods (NRs). The NRs were fabricated by plasma enhanced chemical vapor deposition (PECVD) at low temperature applying a silver layer as promoter. The irradiation of these structures with single nanosecond pulses of an ArF laser produces the melting and reshaping of the end of the NRs that aggregate in the form of bundles terminated by melted ZnO spherical particles. Well-defined silver nanoparticles (NPs), formed by phase separation at the surface of these melted ZnO particles, give rise to a broad plasmonic response consistent with their anisotropic shape. Surface enhanced Raman scattering (SERS) in the as-prepared Ag@ZnO NRs arrays was proved by using a Rhodamine 6G (Rh6G) chromophore as standard analyte. The surface modifications induced by laser treatment improve the stability of this system as SERS substrate while preserving its activity.

February, 2015 | DOI: 10.1021/am506622x

STEM-EELS analysis reveals stable highdensity He in nanopores of amorphous silicon coatings deposited by magnetron sputtering

Schierholz, Roland; Lacroix, Bertrand; Godinho, Vanda; Caballero-Hernandez, Jaime; Duchamp, Martial; Fernandez, Asuncion
Nanotechnology, 26 (2015) 075703


A broad interest has been showed recently on the study of nanostructuring of thin films and surfaces obtained by low-energy He plasma treatments and He incorporation via magnetron sputtering. In this paper spatially resolved electron energy-loss spectroscopy in a scanning transmission electron microscope is used to locate and characterize the He state in nanoporous amorphous silicon coatings deposited by magnetron sputtering. A dedicated MATLAB program was developed to quantify the helium density inside individual pores based on the energy position shift or peak intensity of the He K-edge. A good agreement was observed between the high density (~35–60 at nm−3) and pressure (0.3–1.0 GPa) values obtained in nanoscale analysis and the values derived from macroscopic measurements (the composition obtained by proton backscattering spectroscopy coupled to the macroscopic porosity estimated from ellipsometry). This work provides new insights into these novel porous coatings, providing evidence of high-density He located inside the pores and validating the methodology applied here to characterize the formation of pores filled with the helium process gas during deposition. A similar stabilization of condensed He bubbles has been previously demonstrated by high-energy He ion implantation in metals and is newly demonstrated here using a widely employed methodology, magnetron sputtering, for achieving coatings with a high density of homogeneously distributed pores and He storage capacities as high as 21 at%.

February, 2015 | DOI: 10.1088/0957-4484/26/7/075703

Tribocorrosion behavior of TiBxCy/a-C nanocomposite coating in strong oxidant disinfectant solutions

Gracia-Escosa, E; Garcia, I; Sanchez-Lopez, JC; Abad, MD; Mariscal, A; Arenas, MA; de Damborenea, J; Conde, A
Surface & Coatings Technology, 263 (2015) 78-85


Corrosion and tribocorrosion studies of a TiBxCy/a-C coating deposited on AISI 316L steel have been performed in an aqueous solution of 026 vol.% acetic, 0.16 vol.% peracetic and 0.18 vol.% hydrogen peroxide (commercial product Oxonia I vol.%). The corrosion current density of the TiBxCy/a-C coating ranges on the same order as bare steel but with a significantly decreasing friction (0.1 vs. 0.6) and wear rate (similar to 10 times lower). The compact microstructure of the coating hinders the access of the aggressive electrolyte to the substrate, preventing the onset of the corrosion attack, while maintaining an excellent tribological behavior in strong oxidant solutions.

February, 2015 | DOI: 10.1016/j.surfcoat.2014.12.047

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

Longtin, R; Sanchez-Valencia, JR; Shorubalko, I; Furrer, R; Hack, E; Elsener, H; Groning, O; Greenwood, P; Rupesinghe, N; Teo, K; Leinenbach, C; Groning, P
Science and Technology of Advanced Materials, 16 (2015) 015005 (11 pp)


The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 degrees C with a Ag-Cu-Ti alloy and at 880 degrees C with a Cu-Sn-Ti-Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Omega. The improved interfacial transport properties in the brazed films lead to superior electron fieldemission properties when compared to the as-grown films. An emission current of 150 mu A was drawn from the brazed nanotubes at an applied electric field of 0.6 V mu m(-1). The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

February, 2015 | DOI: 10.1088/1468-6996/16/1/015005

Uniform, luminescent Eu: LuF3 nanoparticles

Becerro, AI; Gonzalez-Mancebo, D; Ocana, M
Journal of Nanoparticle Research, 17 (2015) 58


A simple procedure for the synthesis of orthorhombic, uniform, LuF3 particles with two different morphologies (rhombus- and cocoon-like) and nanometer and sub-micrometer size, respectively, is reported. The method consists in the aging, at 120 °C for 2 h, a solution containing [BMIM]BF4 ionic liquid (0.5 mL) and lutetium acetate (in the case of the rhombi) or lutetium nitrate (in the case of the cocoons) (0.02 M) in ethylene glycol (total volume 10 mL). This synthesis method was also adequate for the synthesis of Eu3+-doped LuF3 particles of both morphologies, whose luminescence properties were investigated in detail. The experimental observations reported herein suggest that these materials are suitable phosphors for optoelectronic as well as in vitro biotechnological applications.

January, 2015 | DOI: 10.1007/s11051-015-2874-z

Biotribological behavior of Ag–ZrCxN1−x coatings against UHMWPE for joint prostheses devices

Calderon, SV; Sanchez-Lopez, JC; Cavaleiro, A; Carvalho, S
Journal of the Mechanical Behavior of Biomedical Materials, 41 (2015) 83-91


This study aims to evaluate the structural, mechanical and tribological properties of zirconium carbonitrides (ZrCxN1−x) coatings with embedded silver nanoparticles, produced with the intention of achieving a material with enhanced multi-functional properties, including mechanical strength, corrosion resistance, tribological performance and antibacterial behavior suitable for their use in joint prostheses. The coatings were deposited by direct current (DC) reactive magnetron sputtering onto 316 L stainless steel, changing the silver content from 0 to 20 at% by modifying the current density applied to the targets. Different nitrogen and acetylene gas fluxes were used as reactive gases. The coatings revealed different mixtures of crystalline ZrCxN1−x, silver nanoparticles and amorphous carbon phases. The hardness of the films was found to be mainly controlled by the ratio between the hard (ZrCxN1−x) and soft (Ag and amorphous carbon) phases in the films, fluctuating between 7.4 and 20.4 GPa. The coefficient of friction, measured against ultra-high molecular weight polyethylene (UHMWPE) in Hank’s balanced salt solution with 10 g L−1albumin, is governed by the surface roughness and hardness. The UHMWPE wear rates were in the same order of magnitude (between 1.4 and 2.0×10−6 mm3 N−1 m−1), justified by the effect of the protective layer of albumin formed during the tests. The small differences were due to the hydrophobic/hydrophilic character of the surface, as well as to the silver content.

January, 2015 | DOI: 10.1016/j.jmbbm.2014.09.028

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid

Garcia-Garcia, FJ, Chiu, TY, Skeldon, P, Thompson, GE
Surface and Interface Analysis, 47 (2015) 30-36


Cathodic polarization of aluminium and Al-0.18wt.%Mg and Al-0.08wt.% Ti alloys in 0.24moldm(-3) nitric acid solution at 38 degrees C has been employed to assist understanding of the roles of alloying elements in electrograining. The findings indicate that additions of magnesium and titanium to aluminium accelerate the corrosion of the substrate under the alkalization caused by the cathodic reactions. The accelerated dissolution and the consequent formation of hydrated alumina result in a decreased net cathodic current density in potentiostatic and potentiodynamic polarization conditions relative to the behaviour of aluminium. 

January, 2015 | DOI: 10.1002/sia.5640

Sonogashira Cross-Coupling and Homocoupling on a Silver Surface: Chlorobenzene and Phenylacetylene on Ag(100)

Sanchez-Sanchez, C; Orozco, N; Holgado, JP; Beaumont, SK; Kyriakou, G; Watson, DJ; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM
Journal of the American Chemical Society, 137 (2015) 940-947


Scanning tunneling microscopy, temperature-programmed reaction, near-edge X-ray absorption fine structure spectroscopy, and density functional theory calculations were used to study the adsorption and reactions of phenylacetylene and chlorobenzene on Ag(100). In the absence of solvent molecules and additives, these molecules underwent homocoupling and Sonogashira cross-coupling in an unambiguously heterogeneous mode. Of particular interest is the use of silver, previously unexplored, and chlorobenzene—normally regarded as relatively inert in such reactions. Both molecules adopt an essentially flat-lying conformation for which the observed and calculated adsorption energies are in reasonable agreement. Their magnitudes indicate that in both cases adsorption is predominantly due to dispersion forces for which interaction nevertheless leads to chemical activation and reaction. Both adsorbates exhibited pronounced island formation, thought to limit chemical activity under the conditions used and posited to occur at island boundaries, as was indeed observed in the case of phenylacetylene. The implications of these findings for the development of practical catalytic systems are considered.

January, 2015 | DOI: 10.1021/ja5115584


Transmission electron microscopy of unstained hybrid Au nanoparticles capped with PPAA (plasma-poly-allylamine): Structure and electron irradiation effects

Gontard, LC; Fernandez, A; Dunin-Borkowski, RE; Kasama, T; Lozano-Perez, S; Lucas, S
Micron, 67 (2014) 1-9


Hybrid (organic shell–inorganic core) nanoparticles have important applications in nanomedicine. Although the inorganic components of hybrid nanoparticles can be characterized readily using conventional transmission electron microscopy (TEM) techniques, the structural and chemical arrangement of the organic molecular components remains largely unknown. Here, we apply TEM to the physico-chemical characterization of Au nanoparticles that are coated with plasma-polymerized-allylamine, an organic compound with the formula C3H5NH2. We discuss the use of energy-filtered TEM in the low-energy-loss range as a contrast enhancement mechanism for imaging the organic shells of such particles. We also study electron-beam-induced crystallization and amorphization of the shells and the formation of graphitic-like layers that contain both C and N. The resistance of the samples to irradiation by high-energy electrons, which is relevant for optical tuning and for understanding the degree to which such hybrid nanostructures are stable in the presence of biomedical radiation, is also discussed.

December, 2014 | DOI: 10.1016/j.micron.2014.06.004

LMM Auger primary excitation spectra of copper

Pauly, N; Tougaard, S; Yubero, F
Surface Science, 630 (2014) 294-299


The shape and intensity of measured Auger peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and to intrinsic excitations induced by the sudden creation of the two static core holes. Following a method developed for XPS in a previous work [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17], we have calculated the effective energy-differential inelastic electron scattering cross-sections, including the effects of the surface and of the two core holes, within the dielectric response theory by means of the QUEELS-XPS software (QUantitative analysis of Electron Energy Losses at Surfaces for XPS). The Auger spectra are then modeled by convoluting this energy loss cross section with the primary excitation spectrum that accounts for all effects which are part of the initial Auger process, i.e. L–S coupling and vacancy satellite effects. The shape of this primary excitation spectrum is fitted to get close agreement between the theoretical and the experimental spectra obtained from X-ray excited Auger electron spectroscopy (XAES). We have performed these calculations of XAES spectra for various LMM Auger transitions of pure Cu (L3M45M45, L3M23M45, L3M23M23 and L2M45M45 transitions). We compare the resulting primary excitation spectra with theoretical results published in the literature and obtain reasonable quantitative agreement. In particular, we extract from experimental spectra quantitative intensities due to Coster–Kronig, shake-off and shake-up processes relative to the intensity from the “normal” Auger process.

December, 2014 | DOI: 10.1016/j.susc.2014.08.029

Quinone-Rich Poly(dopamine) Magnetic Nanoparticles for Biosensor Applications

Martin, M; Orive, AG; Lorenzo-Luis, P; Creus, AH; Gonzalez-Mora, JL; Salazar, P
ChemPhysChem, 15 (2014) 3742-3752


Novel core-shell quinone-rich poly(dopamine)–magnetic nanoparticles (MNPs) were prepared by using an in situ polymerization method. Catechol groups were oxidized to quinone by using a thermal treatment. MNPs were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, magnetic force microscopy, UV/Vis, Fourier-transform infrared spectroscopy, and electrochemical techniques. The hybrid nanomaterial showed an average core diameter of 17 nm and a polymer-film thickness of 2 nm. The core-shell nanoparticles showed high reactivity and were used as solid supports for the covalent immobilization of glucose oxidase (Gox) through Schiff base formation and Michael addition. The amount of Gox immobilized onto the nanoparticle surface was almost twice that of the nonoxidized film. The resulting biofunctionalized MNPs were used to construct an amperometric biosensor for glucose. The enzyme biosensor has a sensitivity of 8.7 mA m−1 cm−2, a low limit of detection (0.02 mm), and high stability for 45 days. Finally, the biosensor was used to determine glucose in blood samples and was checked against a commercial glucometer.

December, 2014 | DOI: 10.1002/cphc.201402417

Chemistry, nanostructure and magnetic properties of Co-Ru-B-O nanoalloys

Arzac, GM; Rojas, TC; Gontard, LC; Chinchilla, LE; Otal, E; Crespo, P; Fernandez, A
RSC Advances, 4 (2014) 46576-46586


In our previous works, Co–B–O and Co–Ru–B–O ultrafine powders with variable Ru content (xRu) were studied as catalysts for hydrogen generation through sodium borohydride hydrolysis. These materials have shown a complex nanostructure in which small Co–Ru metallic nanoparticles are embedded in an amorphous matrix formed by Co–Ru–B–O based phases and B2O3. Catalytic activity was correlated to nanostructure, surface and bulk composition. However, some questions related to these materials remain unanswered and are studied in this work. Aspects such as: 3D morphology, metal nanoparticle size, chemical and electronic information on the nanoscale (composition and oxidation states), and the study of the formation or not of a CoxRu1−x alloy or solid solution are investigated and discussed using XAS (X-ray Absorption Spectroscopy) and Scanning Transmission Electron Microscopy (STEM) techniques. Also magnetic behavior of the series is studied for the first time and the structure–performance relationships discussed. All Co-containing samples exhibited ferromagnetic behavior up to room temperature while the Ru–B–O sample is diamagnetic. For the xRu = 0.13 sample, an enhancement in the Hc (coercitive field) and Ms (saturation magnetization) is produced with respect to the monometallic Co–B–O material. However this effect is not observed for samples with higher Ru content. The presence of the CoxB-rich (cobalt boride) amorphous ferromagnetic matrix, very small metal nanoparticles (Co and CoxRu(1−x)) embedded in the matrix, and the antiferromagnetic CoO phase (for the higher Ru content sample, xRu = 0.7), explain the magnetic behavior of the series.

November, 2014 | DOI:

Tribological comparison of different C-based coatings in lubricated and unlubricated conditions

Ciarsolo, I; Fernandez, X; de Gopegui, UR; Zubizarreta, C; Abad, MD; Mariscal, A; Caretti, I; Jimenez, I; Sanchez-Lopez, JC
Surface and Coatings Technology, 257 (2014) 278-285


The use of carbon-based coatings (hydrogenated and non-hydrogenated DLC, doped and alloyed-DLC) is of wide interest due to its applications in mechanical components submitted to friction and wear including sliding parts in automotive engines. A tribological comparative analysis using a reciprocating (SRV) tester in lubricated and unlubricated conditions with a 4-stroke motor oil has been carried out on six currently relevant state-of-the-art coatings (namely WC/a-C, TiBC/a-C and TiC/a-C:H nanocomposites, Ti-doped DLC, BCN film and a crystalline monolithic TiC film as reference). The quantification of the fraction of the sp(2)-bonded matrix has been done by fitting of C 1s XPS peak and the mechanical properties evaluated by nanoindentation. The comparative analysis has allowed us to identify the capabilities of each system depending on the testing conditions and the possible synergies as a function of the chemical composition and film nature. Under lubricated harsh conditions (max. contact pressure 1.7 GPa) only coatings displaying hardness superior to 20 GPa could stand the sliding motion without failure. At lower contact pressures, a significant fraction of sp(2) carbon (>= 75%) is advantageous for reducing wear in boundary lubrication. WC/a-C, BCN and Ti-DLC films showed the best tribological response in dry sliding conditions. This fundamental information would be of relevance for assisting engineers in selecting best partnership for lubrication systems. 

October, 2014 | DOI: 10.1016/j.surfcoat.2014.07.068

Study of the early stages of growth of Co oxides on oxide substrates

Diaz-Fernandez, D; Mendez, J; Yubero, F; Dominguez-Canizares, G; Gutierrez, A; Soriano, L
Surface and Interface Analysis, 46 (2014) 975-979


The growth of Cobalt oxides by reactive thermal evaporation of metallic Cobalt in an oxygen atmosphere on a series of oxide substrates, namely SiO2, Al2O3 and MgO, has been chemically and morphologically studied by means of XPS and atomic force microscopy (AFM). The XPS results reveal that cobalt oxide grows as CoO (Co2+) for coverages up to some tens of equivalent monolayers on all substrates. For larger coverages, the formation of the spinel oxide Co3O4 has been observed. AFM and XPS quantification allowed us to determine the way of growth of CoO on all substrates, being of Volmer-Weber (i.e. islands) mode for SiO2, whereas for Al2O3 and MgO, the growth follows the Frank-van der Merwe (i.e. layer-by-layer) mode. The results are discussed in terms of the mismatch of the lattice parameters of the CoO adsorbates with the substrates

October, 2014 | DOI: 10.1002/sia.5366

Interpretation of electron Rutherford backscattering spectrometry for hydrogen quantification

Alvarez, R; Yubero, F
Surface and Interface Analysis, 46 (2014) 812-816


In the last few years, several papers have appeared showing the capabilities of electron Rutherford backscattering spectrometry (eRBS) to quantify the H content at surfaces. The basis of the H detection in this technique relies on the difference in recoil energy of the incident electrons depending on the mass of the atoms located at the surface that act as scatter centers. In this paper, we address the interpretation of eRBS spectra of hydrogen containing surfaces. The aim is to compare the naive single elastic scattering approximation with a more realistic description of eRBS spectra including multiple elastic scattering using the HQ-eRBS (hydrogen quantification eRBS) software based on a Monte Carlo algorithm. It is concluded that multiple elastic scattering is a significant contribution to experimentally measured eRBS spectra of a polyethylene surface. It induces significant broadening of the distribution of the maximum elastic scattering angle along the electron trajectories contributing to the measured spectra. However, it has weak effect in the energy distribution of the collected electrons (about 10% overestimation of the H content in the particular case of a polyethylene surface with respect to the corresponding ratio of elastic scattering cross sections).

October, 2014 | DOI: 10.1002/sia.5486

Modeling of X-ray photoelectron spectra: surface and core hole effects

Pauly, N; Tougaard, S; Yubero, F
Surface and Interface Analysis, 46 (2014) 920-923


The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and by intrinsic excitations induced by the sudden creation of the static core hole. Besides, elastic electron scattering may also be important. These effects should be included in the theoretical description of the emitted photoelectron peaks. To investigate the importance of surface and core hole effects relative to elastic scattering effect, we have calculated full XPS spectra for the Cu 2p emissions of Cu and CuO with the simulation of electron spectra for surface analysis (SESSA) software and with a convolution procedure using the differential inelastic electron scattering cross-section obtained with the quantitative analysis of electron energy loss in XPS (QUEELS-XPS) software. Surface and core hole effects are included in QUEELS-XPS but absent in SESSA while elastic electron scattering effects are included in SESSA but absent in QUEELS-XPS. Our results show that the shape of the XPS spectra are strongly modified because of surface and core hole effects, especially for energy losses smaller than about 20eV.

October, 2014 | DOI: 10.1002/sia.5372

The Use of Fluorocarbons to Mitigate the Oxygen Dependence of Glucose Microbiosensors for Neuroscience Applications

Martin, M; O'Neill, RD; Gonzalez-Mora, JL; Salazar, P
Journal of The Electrochemical Society, 161 (2014) H689-H695


First-generation amperometric glucose biosensors are the most commonly used method for glucose monitoring in neuroscience. Nevertheless, biosensors of this genre suffer from the so-called "oxygen deficit". This problem is particularly acute when the oxygen concentration is low, as is the case in brain extracellular fluid. In the present work we use different fluorocarbons, such as Nafion and H700, to mitigate the oxygen deficit. These fluorocarbon-derived materials display a remarkable solubility for oxygen, and are able to act as oxygen reservoirs supporting the enzymatic reaction. Different biosensor configurations are presented, evaluating their sensitivity, linear range and oxygen dependence. Optimized Nafion- and H700-modified biosensors displayed a remarkable oxygen tolerance, with K-M(O-2) values as low as 11 and 4 mu mol L-1, respectively, and an appropriate sensitivity for in-vivo applications. Finally, in-vivo data are reported in order to illustrate the application of such devices in neuroscience applications.

October, 2014 | DOI: 10.1149/2.1071410jes

Shape-defined nanodimers by tailored heterometallic epitaxy

Garcia-Negrete, Carlos A; Rojas, Teresa C; Knappett, Benjamin R; Jefferson, David A; Wheatley, Andrew E H; Fernandez, Asuncion
Nanoscale, 6 (2014) 11090-11097


The systematic construction of heterogeneous nanoparticles composed of two distinct metal domains (Au and Pt) and exhibiting a broad range of morphologically defined shapes is reported. It is demonstrated that careful Au overgrowth on Pt nanocrystal seeds with shapes mainly corresponding to cubeoctahedra, octahedra and octapods can lead to heterometallic systems whose intrinsic structures result from specific epitaxial relationships such as {111} + {111}, {200} + {200} and {220} + {220}. Comprehensive analysis shows also that nanoparticles grown from octahedral seeds can be seen as comprising of four Au tetrahedral subunits and one Pt octahedral unit in a cyclic arrangement that is similar to the corresponding one in decahedral gold nanoparticles. However, in the present case, the multi-component system is characterized by a broken five-fold rotational symmetry about the [011] axis. This set of bimetallic dimers could provide new platforms for fuel cell catalysts and plasmonic devices.

October, 2014 | DOI: 10.1039/C4NR01815J

Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis

Paladini, M; Arzac, GM; Godinho, V; De Haro, MCJ; Fernandez, A
Applied Catalysis B: Environmental, 158-159 (2014) 400-409


Supported Co catalysts were prepared for sodium borohydride and ammonia borane hydrolysis by magnetron sputtering for the first time under different conditions. Ni foam was selected as support. Deposition conditions (time, pressure, and power) were varied to improve catalytic activity. A decrease in deposition power from 200 to 50 W, leads to a decrease in crystallite and column size and a higher activity of catalysts. The increase in deposition pressure from 1.5 × 10−2 to 4.5 × 10−2 mbar produces same effect but in this case the enhancement in activity is higher because amorphous materials were obtained. The highest activity for SB hydrolysis was 2650 ml min−1 gcat−1 for the 50 W Co 4.5 (4 h) sample (Ea = 60 ± 2 kJ mol−1). For AB hydrolysis activity for the 50 W Co 3.2 (4 h) sample was similar. Durability of the thin films was tested for both reactions upon cycling (14 cycles). Diluted acid washing was effective to recover the activity for sodium borohydride reaction but not for ammonia borane hydrolysis. The strong Co–NH3 interactions explain the non-efficiency of the acid washing.

October, 2014 | DOI: 10.1016/j.apcatb.2014.04.047

Reticulated bioactive scaffolds with improved textural properties for bone tissue engineering: Nanostructured surfaces and porosity

Ramiro-Gutierrez, ML; Will, J; Boccaccini, AR; Diaz-Cuenca, A
Journal of Biomedical Materials Research Part A, 102 (2014) 2982-2992


Organised nanoporous SBA-15 type silica precursor (SP) particulate material has been processed into three-dimensional macroporous, reticulated structures using a novel strategy consisting of blending increasing percentages of SP with a SiO2-CaO-P2O5 (80Si15Ca5P) mesoporous bioactive glass (MBG) sol. The procedure successfully produced consolidated and functionally competent open-cell scaffolds while preserving the nanoporous order of the SP. Scaffolds were prepared using four different (MBG)/(SP) ratios. These structures were then characterized using field emission gun scanning electron microscopy, X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and compressive strength testing. Open-cell interconnected structures with dual macro (150-500 mu m) and nano (4-6 nm)-organised porosity were produced. Both the textural and mechanical properties were found to improve with increasing SBA-15 content. The in vitro bioactive response using simulated body fluid confirmed high reactivity for all prepared scaffolds. In addition, the SBA-15 containing scaffolds exhibited a superior ability to delay the pH-triggered lysozyme release with antibiotic activity. (C) 2013 Wiley Periodicals, Inc.

September, 2014 | DOI: 10.1002/jbm.a.34968

Impregnation of carbon black for the examination of colloids using TEM

Gontard, LC; Knappett, BR; Wheatley, AEH; Chang, SLY; Fernandez, A
Carbon, 76 (2014) 464-468


Nanoparticles are frequently synthesised as colloids, dispersed in solvents such as water, hexane or ethanol. For their characterisation by transmission electron microscopy (TEM), a drop of colloid is typically deposited on a carbon support and the solvent allowed to evaporate. However, this method of supporting the nanoparticles reduces the visibility of fine atomic details, particularly for carbonaceous species, due to interference from the 2-dimensional carbon support at most viewing angles. We propose here the impregnation of a 3 dimensional carbon black matrix that has been previously deposited on a carbon film as an alternative means of supporting colloidal nanoparticles, and show examples of the application of this method to advanced TEM techniques in the analysis of monometallic, core@shell and hybrid nanoparticles with carbon-based shells.

Nanoparticles represent one of the most studied structures in nanotechnology and nanoscience because of the wide range of applications arising from their unique optical, physical and chemical properties [1]. Often they have core@shell structures, or are coated with organic molecules. Nanoparticle functionality is largely affected by the specific configuration of the outer surface atoms. For example, in heterogeneous catalysis activity and selectivity are mostly determined by the type of atomic defects present at the surface of metallic nanoparticles, and in the field of biomedicine the surface coating of hybrid (inorganic core@organic shell) nanoparticles regulates their stability, solubility and targeting.

Nanoparticles are frequently synthesised using solution techniques that yield colloids, i.e., a solid–liquid mixture containing solid particles that are dispersed to various degrees in a liquid medium; most frequently water, ethanol or hexane. Colloid characterisation generally employs a variety of techniques to establish understanding and control over nanoparticle synthesis and properties. Electron microscopy in transmission mode (TEM) and in scanning transmission mode (STEM) are widely used for particle characterisation, and advances in these techniques mean that it is now routinely possible to resolve single atoms at the surfaces of nanoparticles using aberration-corrected microscopes, to elucidate the three-dimensional shapes of nanoparticles using electron tomography, and to enhance the contrast in very low density materials (e.g., carbonaceous materials) using electron holography [2] and [3]. However, the significant potential of these (S)TEM techniques is ultimately limited by the sample and the techniques available for sample preparation.

Typically, examination by (S)TEM requires that a nanoparticulate sample be prepared by depositing a drop of colloid on a thin, electron-transparent support. It is usual that an amorphous carbon film, silicon nitride film or graphene layers deposited on a copper grid constitute the support [4]. Crucially, these sample preparation techniques suffer from the major limitation that the contrast from the support often shadows atomic details at the particle surface. Moreover, it has been established that the thinnest supports can degrade under electron-beam irradiation, affecting particle stability [5], and also that hydrocarbon contamination can be an issue [6]. The most widely used commercially available TEM support is holey carbon, which comprises of a perforated carbon thin film. In this case, sample preparation aims to locate at least some of the nanoparticles of interest at the edges of the perforations. However, the concave nature of the holes means that solvent contaminants tend to accumulate preferentially at these sites. Moreover, if the TEM sample holder is tilted a particle attached to the edge of a hole is very likely to be shadowed by the carbon film. Taken together, these drawbacks significantly limit the application of techniques such as electron tomography [6].

We propose here a method of circumventing some of these fundamental problems by developing a technique for mounting nanoparticulate samples using a carbon matrix that is inspired by the way samples used in electrocatalysis are prepared [7]. Fig. 1 shows an image of a typical Pt-based electrocatalyst supported on carbon black as used in proton-electron membrane fuels cells, and which consists of Pt nanoparticles formed by calcination of a carbon black impregnated with a solution of salt precursor. Carbon black is a low-grade form of graphite, which is composed of nanocrystallites and no long-range order [8]. In Fig. 1 the carbon black is Vulcan XC-72R, which is widely used as a catalyst support in fuel cells because it provides high electrical conductivity, good reactant gas access, adequate water handling and good corrosion resistance, whilst allowing high dispersion of the particles. In electrocatalyst samples it is common to find particles, like the 5 nm Pt particle shown in Fig. 1, attached strongly to the surface of the support and viewed edge-on against a vacuum so as to provide optimal conditions for high-resolution TEM (HRTEM). Fig. 1B is a quantitative phase image of a Pt particle obtained from a defocus series of 20 images at intervals of 5 nm acquired in a FEGTEM JEOL 2020 at 200 kV with spherical aberration of −30 μm and applying the exit-wave restoration technique [2]. The contrast between details of the particle finestructure is very high compared to conventional HRTEM images, and details such as the presence of monoatomic carbon ribbons surrounding the particle can be seen.

September, 2014 | DOI: 10.1016/j.carbon.2014.05.006

On the formation of the porous structure in nanostructured a-Si coatings deposited by dc magnetron sputtering at oblique angles

Godinho, V; Moskovkin, P; Alvarez, R; Caballero-Hernandez, J; Schierholz, R; Bera, B; Demarche, J; Palmero, A; Fernandez, A; Lucas, S
Nanotechnology, 25 (2014) 355705


The formation of the porous structure in dc magnetron sputtered amorphous silicon thin films at low temperatures is studied when using helium and/or argon as the processing gas. In each case, a-Si thin films were simultaneously grown at two different locations in the reactor which led to the assembly of different porous structures. The set of four fabricated samples has been analyzed at the microstructural level to elucidate the characteristics of the porous structure under the different deposition conditions. With the help of a growth model, we conclude that the chemical nature of the sputter gas not only affects the sputtering mechanism of Si atoms from the target and their subsequent transport in the gaseous/plasma phase towards the film, but also the pore formation mechanism and dynamics. When Ar is used, pores emerge as a direct result of the shadowing processes of Si atoms, in agreement with Thornton's structure zone model. The introduction of He produces, in addition to the shadowing effects, a new process where a degree of mobility results in the coarsening of small pores. Our results also highlight the influence of the composition of sputtering gas and tilt angles (for oblique angle deposition) on the formation of open and/or occluded porosity.

September, 2014 | DOI: 10.1088/0957-4484/25/35/355705

Simultaneous quantification of light elements in thin films deposited on Si substrates using proton EBS (Elastic Backscattering Spectroscopy)

Ferrer, FJ; Alcaire, M; Caballero-Hernandez, J; Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Godinho, V; Garcia-Lopez, J; Barranco, A; Fernandez-Camacho, A
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 332 (2014) 449-453


Quantification of light elements content in thin films is an important and difficult issue in many technological fields such as polymeric functional thin films, organic thin film devices, biomaterials, and doped semiconducting structures.
Light elements are difficult to detect with techniques based on X-ray emission, such as energy dispersive analysis of X-rays (EDAX). Other techniques, like X-ray photoelectron spectroscopy (XPS), can easily quantify the content of light elements within a surface but often these surface measurements are not representative of the lights elements global composition of the thin film. Standard Rutherford backscattering spectroscopy (RBS), using alpha particles as probe projectiles, is not a good option to measure light elements deposited on heavier substrates composed of heavier elements like Si or glass. Nuclear Reaction Analysis (NRA) offers a good quantification method, but most of the nuclear reactions used are selective for the quantification of only one element, so several reactions and analysis are necessary to measure different elements.
In this study, Elastic Backscattering Spectroscopy (EBS) using proton beams of 2.0 MeV simultaneously quantified different light elements (helium, carbon, nitrogen, oxygen, and fluorine) contained in thin films supported on silicon substrates. The capabilities of the proposed quantification method are illustrated with examples of the analysis for a series of thin film samples: amorphous silicon with helium bubbles, fluorinated silica, fluorinated diamond-like carbon and organic thin films. It is shown that this simple and versatile procedure allows the simultaneous quantification of light elements in thin films with thicknesses in the 200–500 nm range and contents lower than 10 at.%.

August, 2014 | DOI: 10.1016/j.nimb.2014.02.124

Chromium removal on chitosan-based sorbents - An EXAFS/XANES investigation of mechanism

Vieira, RS; Meneghetti, E; Baroni, P; Guibal, E; de la Cruz, VMG; Caballero, A; Rodriguez-Castellon, E; Beppu, MM
Materials Chemistry and Physics, 146 (2014) 412-417


Chitosan is known to be a good sorbent for metal-containing ions as the presence of amino groups and hydroxyl functions act as effective binding sites. Its crosslinking, employing glutaraldehyde or epichlorohydrin, may change the sorption properties (sorption capacity or diffusion properties) of this biopolymer, since the available functional groups are different in each case. X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), Fourier-transformed infrared spectroscopy with attenuated total reflectance device (FTIR-ATR) was used along with speciation diagrams, in order to identify the binding groups involved in chromate sorption and its mechanisms. In pristine chitosan and epichlorohydrin-crosslinked chitosan membranes, amino groups are most likely responsible for adsorption, although the contribution of hydroxyl groups cannot be excluded (especially for metal-sorbent stabilization). In this case, when adsorbed about 70% of chromate ions remain in the Cr(VI) oxidation state. In the case of glutaraldehyde-crosslinked membranes, the functional groups involved are different. Carbonyl groups and imino bonds – resulting from the reaction of the crosslinking agent and amino groups – may be involved in the adsorption mechanism. Additionally, a higher fraction of chromate anions, around 44% are reduced to Cr(III) oxidation state in loaded sorbent. The presence of free aldehyde groups may explain this partial reduction.

August, 2014 | DOI: 10.1016/j.matchemphys.2014.03.046

Luminescent 3-hydroxyflavone nanocomposites with a tuneable refractive index for photonics and UV detection by plasma assisted vacuum deposition

Aparicio, FJ; Alcaire, M; Borras, A; Gonzalez, JC; Lopez-Arbeloa, F; Blaszczyk-Lezak, I; Gonzalez-Elipe, AR; Barranco, A
Journal of Materials Chemistry C, 2 (2014) 6561-6573


Luminescent organic-thin-films transparent in the visible region have been synthesized by a plasma assisted vacuum deposition method. The films have been developed for their implementation in photonic devices and for UV detection. They consist of a plasma polymeric matrix that incorporates 3-hydroxyflavone molecules characterized by absorption of UV radiation and emission of green light. The present work studies in detail the properties and synthesis of this kind of transparent and luminescent material. The samples were characterized by X-ray photoemission (XPS), infrared (FT-IR) and secondary ion mass (ToF-SIMS) spectroscopies; and their optical properties were analysed by UV-Vis absorption, fluorescence and ellipsometry (VASE) spectroscopies. The key factors controlling the optical and luminescent properties of the films are also discussed. Indeed, our experimental results show how the optical properties of the films can be adjusted for their integration in photonic devices. Moreover, time resolved and steady state fluorescence analyses, including quantum yield determination, indicate that the fluorescence efficiency is a function of the deposition parameters. An outstanding property of these materials is that, even for high UV absorption values (i.e. large layer thickness and/or dye concentration), the emitted light is not reabsorbed by the film. Such highly UV absorbent and green emitting films can be used as UV photodetectors with a detection threshold smaller than 10 mu W cm(-2), a value similar to the limit of some commercial UV photodetectors. Based on these properties, the use of the films as visual tags for the detection of solar UV irradiation is proposed.

August, 2014 | DOI: 10.1039/c4tc00294f

Bending Induced Self-Organized Switchable Gratings on Polymeric Substrates

Parra-Barranco, J; Oliva-Ramirez, M; Gonzalez-Garcia, L; Alcaire, M; Macias-Montero, M; Borras, A; Frutos, F; Gonzalez-Elipe, AR; Barranco, A
ACS Applied Materials & Interfaces, 6 (2014) 11924-11931


We present a straightforward procedure of self-surface patterning with potential applications as large area gratings, invisible labeling, optomechanical transducers, or smart windows. The methodology is based in the formation of parallel micrometric crack patterns when polydimethylsiloxane foils coated with tilted nanocolumnar SiO2 thin films are manually bent. The SiO2 thin films are grown by glancing angle deposition at room temperature. The results indicate that crack spacing is controlled by the film nanostructure independently of the film thickness and bending curvature. They also show that the in-plane microstructural anisotropy of the SiO2 films due to column association perpendicular to the growth direction determines the anisotropic formation of parallel cracks along two main axes. These self-organized patterned foils are completely transparent and work as customized reversible diffraction gratings under mechanical activation.

August, 2014 | DOI: 10.1021/am5037687

Bifunctional, Monodisperse BiPO4-Based Nanostars: Photocatalytic Activity and Luminescent Applications

Becerro, AI; Criado, J; Gontard, LC; Obregon, S; Fernandez, A; Colon, G; Ocana, M
Crystal Growth & Design, 14 (2014) 3319-3326


Monodisperse, monoclinic BiPO4 nanostars have been synthesized by a homogeneous precipitation reaction at 120 °C through controlled release of Bi3+ cations from a Bi–citrate chelate, in a mixture of glycerol and ethylene glycol, using H3PO4 as the phosphate source. The set of experimental conditions necessary to obtain uniform nanoparticles is very restrictive, as the change in either the polyol ratio or the reactant concentrations led to ill-defined and/or aggregated particles. The morphology of the particles consists of a starlike, hierarchical structure formed by the ordered arrangement of nanorod bundles. Transmission electron tomography has revealed that the nanostars are not spherical but flattened particles. Likewise, Fourier transform infrared spectroscopy and thermogravimetry have shown that the synthesized nanostars are functionalized with citrate groups. The mechanism of formation of the nanostars has been analyzed to explain their morphological features. The as-synthesized BiPO4 nanostars exhibit an efficient photocatalytic performance for the degradation of Rhodamine B. Finally, it has been demonstrated that the stars can be Eu3+-doped up to 2 mol % without any change in the particle morphology or symmetry, and the doped samples show emission in the orange-red region of the visible spectrum after ultraviolet excitation. These experimental observations make this material a suitable phosphor for biotechnological applications.

July, 2014 | DOI: 10.1021/cg500208h

Influence of thickness and coatings morphology in the antimicrobial performance of zinc oxide coatings

Carvalho, P; Sampaio, P; Azevedo, S; Vaz, C; Espinos, JP; Teixeira, V; Carneiro, JO
Applied Surface Science, 307 (2014) 548-557


In this research work, the production of undoped and silver (Ag) doped zinc oxide (ZnO) thin films for food-packaging applications were developed. The main goal was to determine the influence of coatings morphology and thickness on the antimicrobial performance of the produced samples. The ZnO based thin films were deposited on PET (Polyethylene terephthalate) substrates by means of DC reactive magnetron sputtering. The thin films were characterized by optical spectroscopy, X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The antimicrobial performance of the undoped and Ag-doped ZnO thin films was also evaluated. The results attained have shown that all the deposited zinc oxide and Ag-doped ZnO coatings present columnar morphology with V-shaped columns. The increase of ZnO coatings thickness until 200 nm increases the active surface area of the columns. The thinner samples (50 and 100 nm) present a less pronounced antibacterial activity than the thickest ones (200–600 nm). Regarding Ag-doped ZnO thin films, it was verified that increasing the silver content decreases the growth rate of Escherichia coli and decreases the amount of bacteria cells present at the end of the experiment

July, 2014 | DOI: 10.1016/j.apsusc.2014.04.072

Nanocolumnar growth of thin films deposited at oblique angles: Beyond the tangent rule

Alvarez, R; Lopez-Santos, C; Parra-Barranco, J; Rico, V; Barranco, A; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Journal of Vacuum Science & Technology B, 32 (2014) 041802


The growth of nanostructured physical vapor deposited thin films at oblique angles is becoming a hot topic for the development of a large variety of applications. Up to now, empirical relations, such as the so-called tangent rule, have been uncritically applied to account for the development of the nanostructure of these thin films even when they do not accurately reproduce most experimental results. In the present paper, the growth of thin films at oblique angles is analyzed under the premises of a recently proposed surface trapping mechanism. The authors demonstrate that this process mediates the effective shadowing area and determines the relation between the incident angle of the deposition flux and the tilt angle of the columnar thin film nanostructures. The analysis of experimental data for a large variety of materials obtained in our laboratory and taken from the literature supports the existence of a connection between the surface trapping efficiency and the metallic character of the deposited materials. The implications of these predictive conclusions for the development of new applications based on oblique angle deposited thin films are discussed.

July, 2014 | DOI: 10.1116/1.4882877

Tomographic Heating Holder for In Situ TEM: Study of Pt/C and PtPd/Al2O3 Catalysts as a Function of Temperature

Gontard, LC; Dunin-Borkowski, RE; Fernandez, A; Ozkaya, D; Kasama, T
Microscoy and Microanalysis, 20 (2014) 982-990


A tomographic heating holder for transmission electron microscopy that can be used to study supported catalysts at temperatures of up to similar to 1,500 degrees C is described. The specimen is placed in direct thermal contact with a tungsten filament that is oriented perpendicular to the axis of the holder without using a support film, allowing tomographic image acquisition at high specimen tilt angles with minimum optical shadowing. We use the holder to illustrate the evolution of the active phases of Pt nanoparticles on carbon black and PtPd nanoparticles on gamma-alumina with temperature. Particle size distributions and changes in active surface area are quantified from tilt series of images acquired after subjecting the specimens to increasing temperatures. The porosity of the alumina support and the sintering mechanisms of the catalysts are shown to depend on distance from the heating filament.

June, 2014 | DOI: 10.1017/S1431927614000373

The Flexible Surface Revisited: Adsorbate-Induced Reconstruction, Homocoupling, and Sonogashira Cross-Coupling on the Au(100) Surface

Sanchez-Sanchez, C; Yubero, F; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM
Journal of Physical Chemistry C, 118 (2014) 11677-11684


Phenylacetylene (PA) and iodobenzene (IB) are prototypical reactants in Sonogashira cross-coupling. Their adsorption behavior and reactivity on the Au(100) surface were studied by STM, temperature-programmed desorption and reaction, and DFT calculations that included the effect of dispersion forces. The two species exhibited very different behavior. Thus, even at 200 K, PA rearranged Au surface atoms so as to lift the hex reconstruction and adsorb in 4-fold-symmetric islands on the unreconstructed 100 surface. On the other hand, IB adsorbed on the reconstructed hex surface, again as islands, forming three different coexisting close-packed structures. The DFT results are in good accord with these findings, demonstrating the strong preference of PA and IB for the (100) and hex surfaces, respectively. Moreover, the calculated adsorption energies were in satisfactory agreement with values estimated from the desorption data. Adsorbed separately, both PA and IB underwent homocoupling yielding diphenyl diacetylene and biphenyl, respectively; in the former case, reaction appeared to originate at island boundaries. On the well-annealed surface, coadsorbed PA and IB behaved independently, generating only products of homocoupling. However, on the Ar+ roughened surface, Sonogashira cross-coupling also occurred, yielding diphenyl acetylene. These findings are discussed in terms of the island-forming propensity of the reactants, amplified by the labile nature of the Au 100 surface under adsorption and the marked preference of the two reactants for different substrate structures, factors that act to inhibit the formation of a mixed adlayer and suppress reactivity. The implications for the behavior of practical Au nanoparticle catalysts are considered.

June, 2014 | DOI: 10.1021/jp501321u

A study of the optical properties of metal-doped polyoxotitanium cages and the relationship to metal-doped titania

Lv, YK; Cheng, J; Matthews, PD; Holgado, JP; Willkomm, J; Leskes, M; Steiner, A; Fenske, D; King, TC; Wood, PT; Gan, LH; Lambert, RM; Wright, DS
Dalton Transactions, 43 (2014) 8679-8689


To what extent the presence of transition metal ions can affect the optical properties of structurally well-defined, metal-doped polyoxotitanium (POT) cages is a key question in respect to how closely these species model technologically important metal-doped TiO2. This also has direct implications to the potential applications of these organically-soluble inorganic cages as photocatalytic redox systems in chemical transformations. Measurement of the band gaps of the series of closely related polyoxotitanium cages [MnTi14(OEt)28O14(OH)2] (1), [FeTi14(OEt)28O14(OH)2] (2) and [GaTi14(OEt)28O15(OH)] (3), containing interstitial Mn(II), Fe(II) and Ga(III) dopant ions, shows that transition metal doping alone does not lower the band gaps below that of TiO2 or the corresponding metal-doped TiO2. Instead, the band gaps of these cages are within the range of values found previously for transition metal-doped TiO2 nanoparticles. The low band gaps previously reported for 1 and for a recently reported related Mn-doped POT cage appear to be the result of low band gap impurities (most likely amorphous Mn-doped TiO2).

June, 2014 | DOI: 10.1039/C4DT00555D

On the Deposition Rates of Magnetron Sputtered Thin Films at Oblique Angles

Alvarez, R; Garcia-Martin, JM; Lopez-Santos, MC; Rico, V; Ferrer, FJ; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Plasma Processes and Polymers, 11 (2014) 571-576


We describe here the deposition of thin films using magnetron sputtering at oblique angles. General relations between the deposition rates of the films and experimental parameters, such as gas pressure or substrate tilt angles, are deduced and experimentally tested. The model also permits the direct determination of the thermalization mean free path of the sputtered particles in the plasma gas, a key parameter defining the balance between ballistic and diffusive flows in the deposition reactor. The good agreement between experimental and calculated results supports the validity of our description, which becomes a useful tool to explain the main features of the magnetron sputtering deposition of thin films at oblique angles.

June, 2014 | DOI: 10.1002/ppap.201300201

The growth of cobalt oxides on HOPG and SiO2 surfaces: A comparative study

Diaz-Fernandez, D; Mendez, J; Bomati-Miguel, O; Yubero, F; Mossanek, RJO; Abbate, M; Dominguez-Canizares, G; Gutierrez, A; Tougaard, S; Soriano, L
Surface Science, 624 (2014) 145-153


The growth of cobalt oxides by reactive thermal evaporation of metallic cobalt on highly oriented pyrolytic graphite (HOPG) and SiO2 (X cut quartz surface), in an oxygen atmosphere at room temperature, has been chemically and morphologically studied by means of X-ray photoelectron spectroscopy and atomic force microscopy. The chemical analysis, which also includes cluster calculations, reveals that for the early deposition stages on both substrates, Co2 + species are stabilized at the surface up to a coverage which depends on the substrate. Further coverages lead to the formation of the spinel oxide Co3O4. The results are discussed in terms of the dependence of the surface energy on the size of the CoO deposited moieties. On the other hand, it has been found that the initial way of growth of cobalt oxides on HOPG is of Stranski–Krastanov mode whereas on SiO2 the growth is of Volmer–Weber mode. The differences in the growth morphology have been discussed in terms of the surface diffusivity of the CoO deposits on the substrates.

June, 2014 | DOI: 10.1016/j.susc.2014.02.007

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

Lapresta-Fernandez, A; Salinas-Castillo, A; de la Llana, SA; Costa-Fernandez, JM; Dominguez-Meister, S; Cecchini, R; Capitan-Vallvey, LF; Moreno-Bondi, MC; Marco, MP; Sanchez-Lopez, JC; Anderson, IS
Critical Reviews in Solid State and Materials Sciences, 39 (2014) 423-458


This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.

June, 2014 | DOI: 10.1080/10408436.2014.899890

Oxygen Optical Sensing in Gas and Liquids with Nanostructured ZnO Thin Films Based on Exciton Emission Detection

Sanchez-Valencia, JR; Alcaire, M; Romero-Gomez, P; Macias-Montero, M; Aparicio, FJ; Borras, A; Gonzalez-Elipe, AR; Barranco, A
Journal of Physical Chemistry C, 118 (2014) 9852-9859


Transparent nanocolumnar porous ZnO thin films have been prepared by plasma-enhanced chemical vapor deposition. By controlling the H-2/O-2 ratio in the plasma gas, the deposition conditions were optimized to obtain an intense exciton emission at around 381 nm and virtually no luminescence in the visible region associated with electronic states in the gap. The intensity of the exciton band varied significantly and reversibly with the partial pressure of oxygen in the environment. This behavior and its variations with temperature and water vapor sustain the use of these thin films as photonic sensors of oxygen. Further experiments in liquid water show that fluorescence intensity also varies with the amount of dissolved oxygen even for concentrations lower than 0.02 mg/L where commercial oxygen galvanic sensors show limited sensitivity. These results and the use of ZnO as photonic sensor of oxygen are discussed by assuming a classical mechanism involving the photoactivated adsorption of oxygen when this oxide is irradiated with UV light during its fluorescence interrogation.

May, 2014 | DOI: 10.1021/jp5026027

Structure determination and electronic structure of Cu3Au0.5N

Soto, G; Ponce, I; Moreno, MG; Yubero, F; De la Cruz, W
Journal of Alloys and Compounds, 594 (2014) 48-51


This study investigated the formation of a Cu3Au-nitride alloy using both experimental and computational methods. The alloy was produced as thin film by sputtering a Cu3Au target in a nitrogen atmosphere. The films were characterized for structure and composition by spectroscopic and diffraction techniques. The structure was established by Rietveld and ab inito methods. The structure is cubic and of the Fm3m space group, with a composition close to Cu6AuN2. Relative to the Cu3N structure, the Cu atoms occupy the faces, Au the half corners, and N the centers. The compound is a narrow-gap semiconductor with a positive hall coefficient that could be used for infrared detection.

May, 2014 | DOI: 10.1016/j.jallcom.2014.01.113

Osteoconductive Potential of Barrier NanoSiO(2) PLGA Membranes Functionalized by Plasma Enhanced Chemical Vapour Deposition

Terriza, A; Vilches-Perez, JI; de la Orden, E; Yubero, F; Gonzalez-Caballero, JL; Gonzalez-Elipe, AR; Vilches, J; Salido, M
BioMed Research International, 2014 (2014) 253590


The possibility of tailoring membrane surfaces with osteoconductive potential, in particular in biodegradable devices, to create modified biomaterials that stimulate osteoblast response should make them more suitable for clinical use, hopefully enhancing bone regeneration. Bioactive inorganic materials, such as silica, have been suggested to improve the bioactivity of synthetic biopolymers. An in vitro study on HOB human osteoblasts was performed to assess biocompatibility and bioactivity of SiO2 functionalized poly(lactide-co-glycolide) (PLGA) membranes, prior to clinical use. A 15 nm SiO2 layer was deposited by plasma enhanced chemical vapour deposition (PECVD), onto a resorbable PLGA membrane. Samples were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and infrared spectroscopy (FT-IR). HOB cells were seeded on sterilized test surfaces where cell morphology, spreading, actin cytoskeletal organization, and focal adhesion expression were assessed. As proved by the FT-IR analysis of samples, the deposition by PECVD of the SiO2 onto the PLGA membrane did not alter the composition and other characteristics of the organic membrane. A temporal and spatial reorganization of cytoskeleton and focal adhesions and morphological changes in response to SiO2 nanolayer were identified in our model. The novedous SiO2 deposition method is compatible with the standard sterilization protocols and reveals as a valuable tool to increase bioactivity of resorbable PLGA membranes.

May, 2014 | DOI: 10.1155/2014/253590

Tuning the transmittance and the electrochromic behavior of CoxSiyOz thin films prepared by magnetron sputtering at glancing angle

Gil-Rostra, J; Garcia-Garcia, F; Yubero, F; Gonzalez-Elipe, AR
Solar Energy Materials and Solar Cells, 123 (2014) 130-138


This work reports the synthesis and the characterization of amorphous CoxSiyOz thin films prepared by magnetron sputtering from a single cathode. Porous layers with outstanding electrochromic properties are obtained at room temperature in one step by performing the deposition at a glancing angle configuration. The electrochromic behavior of these layers in a basic aqueous medium was dependent on the Co/Si ratio in the films and in all cases was characterized by a fast response, a high coloration efficiency and a complete reversibility after several hundred cycles. A characteristic feature of these electrochromic layers is that, for a similar thickness, the range of transmittance modulation can be tuned by changing the Co/Si ratio in the films and, specifically for films with a high concentration of silicon, to change their aspect from an almost transparent to a full colored state.

April, 2014 | DOI: 10.1016/j.solmat.2013.12.020

Mechanisms of Electron Transport and Recombination in ZnO Nanostructures for Dye-Sensitized Solar Cells

Vega-Poot, AG; Macias-Montero, M; Idigoras, J; Borras, A; Barranco, A; Gonzalez-Elipe, AR; Lizama-Tzec, FI; Oskam, G; Anta, JA
Chemphyschem, 15 (2014) 1088-1097


ZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes.

April, 2014 | DOI: 10.1002/cphc.201301068

Perovskite Solar Cells Based on Nanocolumnar PlasmaDeposited ZnO Thin Films

Ramos, FJ; Lopez-Santos, MC; Guillen, E; Nazeeruddin, MK; Gratzel, M; Gonzalez-Elipe, AR; Ahmad, S
Chemphyschem, 15 (2014) 1148-1153


ZnO thin films having a nanocolumnar microstructure are grown by plasma-enhanced chemical vapor deposition at 423 K on pre-treated fluorine-doped tin oxide (FTO) substrates. The films consist of c-axis-oriented wurtzite ZnO nanocolumns with well-defined microstructure and crystallinity. By sensitizing CH3NH3PbI3 on these photoanodes a power conversion of 4.8 % is obtained for solid-state solar cells. Poly(triarylamine) is found to be less effective when used as the hole-transport material, compared to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), while the higher annealing temperature of the perovskite leads to a better infiltration in the nanocolumnar structure and an enhancement of the cell efficiency.

April, 2014 | DOI: 10.1002/cphc.201301215

Detecting single-electron events in TEM using low-cost electronics and a silicon strip sensor

Gontard, LC; Moldovan, G; Carmona-Galn, R; Lin, C; Kirkland, AI
Microscopy, 63(2) (2014) 119-130


There is great interest in developing novel position-sensitive direct detectors for transmission electron microscopy (TEM) that do not rely in the conversion of electrons into photons. Direct imaging improves contrast and efficiency and allows the operation of the microscope at lower energies and at lower doses without loss in resolution, which is especially important for studying soft materials and biological samples. We investigate the feasibility of employing a silicon strip detector as an imaging detector for TEM. This device, routinely used in high-energy particle physics, can detect small variations in electric current associated with the impact of a single charged particle. The main advantages of using this type of sensor for direct imaging in TEM are its intrinsic radiation hardness and large detection area. Here, we detail design, simulation, fabrication and tests in a TEM of the front-end electronics developed using low-cost discrete components and discuss the limitations and applications of this technology for TEM.

April, 2014 | DOI: 10.1093/jmicro/dft051

Osteoblasts Interaction with PLGA Membranes Functionalized with Titanium Film Nanolayer by PECVD. In vitro Assessment of Surface Influence on Cell Adhesion during Initial Cell to Material Interaction

Terriza, A; Vilches-Perez, JI; Gonzalez-Caballero, JL; de la Orden, E; Yubero, F; Barranco, A; Gonzalez-Elipe, AR; Vilches, J; Salido, M
Materials, 7(3) (2014) 1687-1708


New biomaterials for Guided Bone Regeneration (GBR), both resorbable and non-resorbable, are being developed to stimulate bone tissue formation. Thus, the in vitro study of cell behavior towards material surface properties turns a prerequisite to assess both biocompatibility and bioactivity of any material intended to be used for clinical purposes. For this purpose, we have developed in vitro studies on normal human osteoblasts (HOB®) HOB® osteoblasts grown on a resorbable Poly (lactide-co-glycolide) (PLGA) membrane foil functionalized by a very thin film (around 15 nm) of TiO2 (i.e., TiO2/PLGA membranes), designed to be used as barrier membrane. To avoid any alteration of the membranes, the titanium films were deposited at room temperature in one step by plasma enhanced chemical vapour deposition. Characterization of the functionalized membranes proved that the thin titanium layer completely covers the PLGA foils that remains practically unmodified in their interior after the deposition process and stands the standard sterilization protocols. Both morphological changes and cytoskeletal reorganization, together with the focal adhesion development observed in HOB osteoblasts, significantly related to TiO2 treated PLGA in which the Ti deposition method described has revealed to be a valuable tool to increase bioactivity of PLGA membranes, by combining cell nanotopography cues with the incorporation of bioactive factors.

March, 2014 | DOI: 10.3390/ma7031687

c- C4F8 Plasmas for the Deposition of Fluorinated Carbon Films

Terriza, A; Macias-Montero, M; Lopez-Santos, MC; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 11 (2014) 289-299


Highly fluorinated polymeric (CFX), fluorine containing diamond-like carbon (F-DLC) and, for comparison, diamond-like carbon (DLC) films have been plasma deposited in a RF parallel plate reactor by using c-C4F8 as fluorine precursor and different mixtures of argon, C2H2, and H2. Plasmas have been characterized by optical emission spectroscopy, mass spectrometry, and Langmuir probe measurements. Differences in the film composition and structure have been related with the type of species formed in the plasma and with the self-bias potential developed at the deposition electrode. Additional experiments using CF4 have confirmed that the formation in the plasmas of neutral or ionized CxFy species with x > 2 is a critical factor for the synthesis of fluorine rich films.

March, 2014 | DOI: 10.1002/ppap.201300129

Long-term high temperature oxidation of CrAl(Y)N coatings in steam atmosphere

Mato, S; Alcala, G; Brizuela, M; Galindo, RE; Perez, FJ; Sanchez-Lopez, JC
Corrosion Science, 80 (2014) 453-460


The oxidation resistance of CrAl(Y)N coatings deposited by reactive magnetron sputtering on P92 steel substrates was tested at 650 °C in 100% steam atmosphere up to 2000 h of oxidation. Mass gain measurements and characterisation of coatings and scales after oxidation show the enhanced oxidation resistance provided by the coatings with respect to that of the substrate. The dominant influence of the film microstructure developed due to the presence of an adhesion interlayer of CrN at the coating/substrate interface over Y additions is evidenced. The best performance is achieved by a CrAlN dense coating of around 6 μm without adhesion interlayer.

March, 2014 | DOI: 10.1016/j.corsci.2013.11.066

Mechanical and phase stability of TiBC coatings up to 1000 degrees C

Abad, MD; Veldhuis, SC; Endrino, JL; Beake, BD; Garcia-Luis, A; Brizuela, M; Sanchez-Lopez, JC
Journal of Vacuum Science & Technology A, 32 (2014) 021508


TiBC coatings with different phase compositions (nanocrystalline TiBxCy or TiB2 phases mixed or not with amorphous carbon, a-C) were prepared by magnetron sputtering. These coatings were comparatively studied in terms of phase stability after thermal annealing at 250, 500, 750, and 1000 °C in argon using Raman and x-ray absorption near-edge spectroscopy techniques. The main differences were observed at temperatures above 500 °C when oxidation processes occur and the mechanical properties deteriorate. At 1000 °C, the samples were fully oxidized forming a-C, TiO2, and B2O3 as final products. Higher hardness and reduced indentation modulus values and better tribological properties were observed at 750 °C for nanocomposite structures including amorphous carbon and ternary TiBxCy phases. This behavior is attributed to a protective effect associated with the a-C phase which is achieved by the encapsulation of the nanocrystals in the coating and the better hard/lubricant phase ratio associated with this type of coating.

March, 2014 | DOI: 10.1116/1.4861365

Low Temperature Production of Formaldehyde from Carbon Dioxide and Ethane by Plasma-Assisted Catalysis in a Ferroelectrically Moderated Dielectric Barrier Discharge Reactor

Gomez-Ramirez, A; Rico, VJ; Cotrino, J; Gonzalez-Elipe, A; Lambert, RM
ACS Catalysis, 4 (2014) 402-408


Plasma-assisted catalysis of the reaction between CO2 and C2H6 in a single-pass, ferroelectrically moderated dielectric barrier discharge reactor has been studied at near ambient temperature as a function of physicochemical and electrical reaction variables. The presence of small amounts of a vanadia/alumina catalyst dispersed on the BaTiO3 ferroelectric markedly enhanced the production of formaldehyde, the focus of this work. A maximum HCOH selectivity of 11.4% (defined with respect to the number of ethane carbon atoms consumed) at 100% ethane conversion was achieved, the other products being CO, H2O, H2, CH4 and a small amount of C3H8. N2O was also an effective partial oxidant (HCOH selectivity 8.9%) whereas use of O2 led to complete combustion, behavior that may be rationalized in terms of the electron impact excitation cross sections of the three oxidants. Control experiments with the coproducts CH4 and C3H8 showed that these species were not intermediates in HCOH formation from C2H6. Analysis of reactor performance as a function of discharge characteristics revealed that formaldehyde formation was strongly favored at low frequencies where the zero-current fraction of the duty cycle was greatest, the implication being that plasma processes also acted to destroy previously formed products. A tentative reaction mechanism is proposed that accounts for the broad features of formaldehyde production.

February, 2014 | DOI: 10.1021/cs4008528

Comparative Study of Micro- and Nano-structured Coatings for High-Temperature Oxidation in Steam Atmospheres

Perez, FJ; Castaneda, SI; Hierro, MP; Galindo, RE; Sanchez-Lopez, JC; Mato, S
Oxidation of Metals, 81 (2014) 227-236


For many high-temperature applications, coatings are applied in order to protect structural materials against a wide range of different environments: oxidation, metal dusting, sulphidation, molten salts, steam, etc. The resistance achieved by the use of different kind of coatings, such as functionally graded material coatings, has been optimized with the latest designs. In the case of supercritical steam turbines, many attempts have been made in terms of micro-structural coatings design, mainly based on aluminides, and other diffusion coating systems in order to consider alternatives, nano-structured coatings based on Cr and Al compositions and deposited by a physical vapor deposition technique, were assessed to high-temperature oxidation resistance in steam environments. The oxidation kinetics where analyzed for up to 2,000 h at 650 °C by means of gravimetric measurements. The evaporation behavior was also analyzed by thermogravimetric-mass spectrometry. Excellent results where observed for some of the nano-structured coatings tested. Those results where compared to results obtained for micro-structured coatings. Based on that comparison, it was deduced that the nano-structured coatings have a potential application as protective systems in high-temperature steam environments.

February, 2014 | DOI: 10.1007/s11085-013-9447-2

Plasma Deposition of Superhydrophobic Ag@ TiO2 Core@ shell Nanorods on Processable Substrates

Macias-Montero, M; Borras, A; Romero-Gomez, P; Cotrino, J; Frutos, F; Gonzalez-Elipe, AR
Plasma Process and Polymers, 11 (2014) 164-174


This work reports the low temperature plasma formation of Ag@TiO2 nanorods (NRs) on processable substrates. The layers have been analyzed by electron microscopy and secondary ion mass spectroscopy. The NRs morphologies suggest that the plasma sheath, the high mobility of the silver and the incoming direction of the precursor moieties are key factors determining their shape, dimensions, and tilting orientation. Both amorphous and anatase Ag@TiO2 NRs surfaces are superhydrophobic, and turn into superhydrophilic by irradiation with UV light. This wetting behavior is discussed by considering the water penetration in the inter-NR space during the light-mediated transformation.

February, 2014 | DOI: 10.1002/ppap.201300112

A Nanoscale Characterization with Electron Microscopy of Multilayered CrAlYN Coatings: A Singular Functional Nanostructure

Rojas, TC; Dominguez-Meister, S; Brizuela, M; Garcia-Luis, A; Fernandez, A; Sanchez-Lopez, JC
Microscoy and Microanalysis, 20 (2014) 14-24


A combination of transmission electron microscopy techniques and spatially resolved microanalysis is used to investigate the nanostructure, constituting phases, and chemical elemental distribution in CrAlYN multilayered coatings. The location of the metallic elements and their chemical state are needed to understand their functional properties. Samples were prepared with variable Al (4-12 at%) and Y (2-5 at%) contents by direct current reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N-2 mixtures under different deposition parameters (power applied to the target and rotation speed of the sample holder). The changes produced in the nanostructure and chemical distribution were investigated. Nanoscale resolution electron microscopy analysis has shown that these coatings present a singular nanostructure formed by multilayers containing at a certain periodicity nanovoids filled with molecular nitrogen. Spatially resolved energy dispersive spectroscopy and electron energy loss elemental mappings and profiles showed that the chromium, aluminum, and yttrium atoms are distributed in a sequential way following the position of the targets inside the deposition chamber. Analysis of the different atomic distribution and phases formed at the nanoscale is discussed depending on the deposition parameters.

February, 2014 | DOI: 10.1017/S1431927613013962

Tribological behaviour at high temperature of hard CrAlN coatings doped with Y or Zr

Sanchez-Lopez, JC; Contreras, A; Dominguez-Meister, S; Garcia-Luis, A; Brizuela, M
Thin Solid Films, 550 (2014) 413-420


The tribological properties of CrAlN, CrAlYN and CrAlZrN coatings deposited by direct current reactive magnetron sputtering are studied by means of pin-on-disc experiments at room temperature, 300, 500 and 650 °C using alumina balls as counterparts. The influence of the metallic composition (Al, Y and Zr) on the friction, wear properties and oxidation resistance is studied by means of scanning electron microscopy, energy dispersive X-ray analysis and Raman analysis of the contact region after the friction tests. The results obtained allow us to classify the tribological behaviour of the CrAl(Y,Zr)N coatings into three groups according to the nature of the dopant and aluminium content. The sliding wear mechanism is characterized by the formation of an overcoat rich in chromium and aluminium oxides whose particular composition is determined by the initial chemical characteristics of the coating and the testing temperature. The fraction of Cr2O3 becomes more significant as the Al content decreases and the temperature increases. The addition of Y, and particularly Zr, favours the preferential formation of Cr2O3 versus CrO2 leading to a reduction of friction and wear of the counterpart. Conversely, the tribological behaviour of pure CrAlN coatings is characterized by higher friction but lower film wear rates as a result of higher hardness and major presence of aluminium oxides on the coating surface.

January, 2014 | DOI: 10.1016/j.tsf.2013.10.041

Nanoindentation of nanocolumnar TiO2 thin films with single and stacked zig-zag layers

Jimenez-Pique, E; Gonzalez-Garcia, L; Rico, VJ; Gonzalez-Elipe, AR
Thin Solid Films, 550 (2014) 444-449


This paper reports a systematic analysis of the mechanical properties of nanocolumnar TiO2 thin films prepared by evaporation at a glancing geometry. A systematic study of the mechanical properties is carried out by comparing the hardness and the Young's modulus determined by nanoindentation for thin films prepared at different deposition angles and characterized by a tilted nanocolumnar structure and others where the nanocolumns are perpendicular to the substrate or are arranged as zig-zag stacked layers. A correlation between mechanical properties and glazing angle geometry is proposed. Differences in the results are discussed in view of the cross section images obtained by focused ion beam and of the deformed areas. Zig-zagged layers present lower values of hardness and Young's modulus due to the collapse of the angles of the columns, but at the same time this configuration impedes the appearance of fracture or delamination, as observed for tilted columns.

January, 2014 | DOI: 10.1016/j.tsf.2013.10.022

On the kinetic and thermodynamic electron temperatures in non-thermal plasmas

Alvarez, R; Cotrino, J; Palmero, A
EPL (Europhysic Letters), 105 (2014)


The framework to describe the out-of-equilibrium free electrons in cold plasmas is developed assuming the electron entropy is defined through the Boltzmann H-theorem. Our theory explains why the Saha-Boltzmann relation among higher-lying excited states by means of the electron kinetic temperature is fulfilled, even when free electrons are far from equilibrium. The thermodynamic electron temperature, pressure and chemical potential have been introduced through the derivatives of the electron entropy. It is demonstrated that under usual conditions in cold plasmas, e.g. when the electron distribution function possesses the Maxwellian, Druyvestein or Kappa functional forms, kinetic and thermodynamic electron temperatures yield the same value.

January, 2014 | DOI: 10.1209/0295-5075/105/15001

Anchoring effect on (tetra)carboxyphenyl porphyrin/TiO2 composite films for VOC optical detection

Roales, J; Pedrosa, JM; Cano, M; Guillen, MG; Lopes-Costa, T; Castillero, P; Barranco, A; Gonzalez-Elipe, AR
RSC Advances, 4 (2014) 1974-1981


The optical gas sensing properties of Zn-(II)-5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP) and Zn-(II)-5,10,15,20-tetra(4-carboxyphenyl)porphyrin (p-ZnTCPP) bound to microcolumnar TiO2 thin films have been compared and explained in terms of their different molecular structure and anchoring to the titania surface. This different binding has been confirmed by specular reflectance FTIR revealing that m-ZnTCPP is bound by its four carboxylic groups in contrast to p-ZnTCPP where two or three of these groups remain unanchored. As a consequence, the Soret band of the para derivative is blue shifted with respect to the solution, indicating H aggregation, while m-ZnTCPP remained in its monomeric form due to the planar anchoring by the four COOH groups to the titania matrix that would avoid porphyrin aggregation. The sensing performance of the two systems has been assessed by analyzing the spectral changes in their UV-visible spectra under exposure to six volatile organic compounds. Although the highly porous and non-dispersive TiO2 matrix allow good sensing ability in both cases, the response of the m-ZnTCPP/TiO2 composite has been found to be more intense and faster than that of p-ZnTCPP. Moreover, the use of identification patterns also indicates that the meta derivative achieves a more selective recognition of the selected analytes. This improvement in the sensing capabilities of m-ZnTCPP has been attributed to the absence of aggregation between adjacent macrocycles.

January, 2014 | DOI: 10.1039/C3RA42443J


Vertically Aligned Hybrid Core/Shell Semiconductor Nanowires for Photonics Applications

Macias-Montero, M; Filippin, AN; Saghi, Z; Aparicio, FJ; Barranco, A; Espinos, JP; Frutos, F; Gonzalez-Elipe, AR; Borras, A
Advanced Functional Materiales, 23 (2013) 5981-5989


A family of 1D organic/inorganic core/shell materials formed by an inner organic nanowire (ONW) conformally covered with an inorganic wide band gap semiconductor (ZnO or TiO2) layer is presented. The developed procedure is a two-steps vacuum methodology involving the formation of supported single crystal small-molecule nanowires by physical vapor deposition and plasma enhance chemical vapor deposition (PECVD) of the inorganic shell. Critical characteristics of the last technique are the possibilities of low temperature and remote configuration deposition. Additionally, an initial step has to be included in order to create nucleation centers for the growth of the ONWs. The procedure and its general character in terms of the variability in organic core and inorganic shells composition and the applicability of the technique to different substrates are presented. The formation of the inorganic shell with no damage of the organic core single-crystalline structure is demonstrated by high resolution transmission electron microscopy. The vertical alignment of the hybrid nanostructure is achieved thanks to the interaction of the 1D organic nanostructured surfaces and the glow discharge during the deposition of the inorganic shell by PECVD. The optical properties of these core/shell NWs are studied by fluorescence spectroscopy and microscopy, and their application as nanoscale waveguides in the 550–750 nm range addressed.

December, 2013 | DOI: 10.1002/adfm.201301120

A single-source route to bulk samples of C3N and the co-evolution of graphitic carbon microspheres

King, TC; Matthews, PD; Holgado, JP; Jefferson, DA; Lambert, RM; Alavi, A; Wright, DS
Carbon, 64 (2013) 6-10


The thermolysis of commercially available m-phenylenediamine (1,3-(NH2)2C6H4) at 800 °C under a static vacuum in a sealed quartz tube provides the first bulk synthesis of C3N, whose properties have only been predicted theoretically previously. Hollow carbon microspheres (CMSs) which do not contain significant nitrogen doping (1–3 μm diameter) are co-produced in the reaction and readily separated from the C3N flakes. The separate C3N flakes and CMSs have been characterized by electron microscopy, X-ray spectroscopy and X-ray diffraction. These studies show that the samples of C3N and CMSs both possess multi-layered turbostratic graphitic structures. A new mechanism for the template-free assembly of CMSs is proposed on the basis of electron microscopy that involves bubble evolution from a static carbonized layer.

November, 2013 | DOI: 10.1016/j.carbon.2013.04.043

Synthesis and tribological properties of WSex films prepared by magnetron sputtering

Dominguez-Meister, S; Justo, A; Sanchez-Lopez, JC
Materials Chemistry and Physics, 142 (2013) 186-194


WSex films with variable Se/W ratio were deposited by non-reactive r.f. magnetron sputtering from WSe2 target changing the applied d.c. pulsed bias conditions and substrate temperature. The structural and chemical properties were measured by cross-sectional scanning electron microscopy (X-SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The tribological properties were measured in ambient air (RH = 30–40%) and dry nitrogen by means of a reciprocating ball-on-disk tribometer. A clear correlation was found between the Se/W ratio and the measured friction coefficient displaying values below 0.1 (in ambient air) and 0.03 (in dry N2) for ratios Se/W ≥ 0.6 as determined by electron probe microanalysis (EPMA). The results demonstrated that notable tribological results could be obtained even in ambient air (friction ≤ 0.07 and wear rate ≈10−7 mm3 Nm−1) by controlling the film microstructure and chemical composition. By incorporating carbon, wear and chemical resistance can be gained by formation of non-stoichiometric carbides and/or alloying into the defective WSex hexagonal structure. The existence of a WSe2 rich interfacial layer (either on the ball scar or embedded in the film track) was evidenced by Raman in low friction conditions. The improvement in tribological performance is therefore obtained by means of layered WSex, the formation of gradient composition from metallic W (hard) to WSe2 (lubricant) and carbon incorporation.

October, 2013 | DOI: 10.1016/j.matchemphys.2013.07.004

Mechanosynthesis of nanocrystalline ZrB2-based powders by mechanically induced self-sustaining reaction method

Jalaly, M; Bafghi, MS; Tamizifar, M; Gotor, FJ
Advances in Applied Ceramics, 112 (2013) 383-388


Preparation of nanocrystalline ZrB2-based powder by aluminothermic and magnesiothermic reductions in M/ZrO2/B2O3 (M=Al or Mg) systems was investigated. In this research, high energy ball milling was employed to persuade necessary conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR). The course of MSR reactions were recorded by a noticeable pressure rise in the system during milling. Ignition times for ZrB2 formation by aluminothermic and magnesiothermic reductions were found to be 13 and 6 min, respectively. Zirconium diboride formation mechanism in both systems was explained through the analysis of the relevant sub-reactions.

October, 2013 | DOI: 10.1179/1743676113Y.0000000091

Atomistic model of ultra-smooth amorphous thin film growth by low-energy ion-assisted physical vapour deposition

Alvarez, R; Vazquez, L; Gago, R; Redondo-Cubero, A; Cotrino, J; Palmero, A
Journal of Physics D: Applied Physics, 46 (2013) 395303


The growth of ultra-smooth amorphous thin films induced by low-energy (below 1 keV) ion-assistance processes is studied. The relative contribution of ion-induced smoothening effects is analysed by means of a Monte Carlo model and experimental data. In general, highly rough granular or ultra-smooth (with roughness below one monolayer) films are produced depending on the competition between surface shadowing and ion-induced adatom mobility and sputtering. The ultra-smooth growth regime is experimentally and theoretically consistent with the Edwards–Wilkinson growth mode, which is related to the ion-induced enhancement of surface mobility. Overall, the framework and the fundamentals to analyse this type of growth are developed and discussed.

September, 2013 | DOI: 10.1088/0022-3727/46/39/395303

Enhancement of visible light-induced surface photo-activity of nanostructured N–TiO2 thin films modified by ion implantation

Romero-Gomez, P; Lopez-Santos, C; Borras, A; Espinos, JP; Palmero, A; Gonzalez-Elipe, AR
Chemical Physics Letters, 582 (2013) 95-99


This work reports the morphological and chemical modifications induced in TiO2 thin films by bombardment with high energy N+ ions at different temperatures and their different photo-activity responses after implantation under visible and UV light illumination. When implanted samples are illuminated with visible light, no dye photo-decolouration takes place despite that light transformed the surfaces from hydrophobic to hydrophilic. In agreement with the Wenzel model of wetting, correlation is found between visible light photo-activity and film morphology. We conclude that the photo-activity response can be separated into shallow and Schottky barrier photo-activity, this latter involving a thicker layer of material.

September, 2013 | DOI: 10.1016/j.cplett.2013.07.025

Enhanced reactivity and related optical changes of Ag nanoparticles on amorphous Al2O3 supports

Pelaez, RJ; Castelo, A; Afonso, CN; Borras, A; Espinos, JP; Riedel, S; Leiderer, P; Boneberg, J
Nanotechnology, 24 (2013) 365702


Pairs of samples containing Ag nanoparticles (NPs) of different dimensions have been produced under the same conditions but on different substrates, namely standard glass slides and a thin layer of amorphous aluminum oxide (a-Al2O3) on-glass. Upon storage in ambient conditions (air and room temperature) the color of samples changed and a blue-shift and damping of the surface plasmon resonance was observed. The changes are weaker for the samples on-glass and tend to saturate after 12 months. In contrast, the changes for the samples on a-Al2O3 appear to be still progressing after 25 months. While x-ray photoelectron spectroscopy shows a slight sulfurization and negligible oxidation of the Ag for the on-glass samples upon 25 months aging, it shows that Ag is strongly oxidized for the on a-Al2O3 samples and sulfurization is negligible. Both optical and chemical results are consistent with the production of a shell at the expense of a reduction of the metal core dimensions, the latter being responsible for the blue-shift and related to the small (<10 nm initial diameter) of the NPs. The enhanced reactivity of the Ag NPs on the a-Al2O3 supports goes along with specific morphological changes of the Ag NPs and the observation of nitrogen.

September, 2013 | DOI: 10.1088/0957-4484/24/36/365702

A low-temperature single-source route to an efficient broad-band cerium(III) photocatalyst using a bimetallic polyoxotitanium cage

Lv, YK; Yao, MM; Holgado, JP; Roth, T; Steiner, A; Gan, LH; Lambert, RM; Wright, DS
RSC Advances, 3 (2013) 13659-13662


Aqueous hydrolysis of a series of cerium-containing polyoxotitanium cages gives Ce(III)-doped TiO2 [TiO2(Ce)] or TiO2-supported Ce(III)2Ti2O7, depending on the starting Ti : Ce ratio of the precursor. TiO2-supported Ce2Ti2O7 exhibits superior photocatalytic activity to the Ce-doped TiO2 materials and unusual broad-band absorption behaviour across the visible and near-infrared regions.

September, 2013 | DOI: 10.1039/C3RA41524D

Low refractive index SiOF thin films prepared by reactive magnetron sputtering

Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Gonzalez, JC; Cotrino, J; Frutos, F; Ferrer, FJ; Gonzalez-Elipe, AR; Yubero, F
Thin Solid Films, 542 (2013) 332-337


We have studied low refractive index fluorine doped silica thin films prepared by reactive magnetron sputtering. Two experimental parameters were varied to increase the porosity of the films, the geometry of the deposition process (i.e., the use of glancing angle deposition) and the presence of chemical etching agents (fluorine species) at the plasma discharge during film growth. The microstructure, chemistry, optical properties, and porosity of the films have been characterized by scanning electron and atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis, and spectroscopic ellipsometry. It is found that either the deposition at glancing angles or the incorporation of CFx species in the plasma discharge during film growth produces a decrease in the refractive index of the deposited films. The combined effect of the two experimental approaches further enhances the porosity of the films. Finally, the films prepared in a glancing geometry exhibit negative uniaxial birefringence.

September, 2013 | DOI: 10.1016/j.tsf.2013.07.009

Tuning of Cell–Biomaterial Anchorage for Tissue Regeneration

Leal-Egana, Aldo; Diaz-Cuenca, Aranzazu; Boccaccini, Aldo R
Advanced Materials, 25 (2013) 4049-4057


Which mechanisms mediate cell attachment to biomaterials? What role does the surface charge or wettability play on cell–material anchorage? What are the currently investigated strategies to modify cell–matrix adherence spatiotemporally? Considering the development of scaffolds made of biocompatible materials to temporarily replace the structure and/or function of the extracellular matrix, focus is given to the analysis of the specific (i.e., cell adhesive peptide sequences) and unspecific (i.e., surface charge, wettability) mechanisms mediating cell-matrix interactions. Furthermore, because natural tissue regeneration is characterized by the dynamic attachment/detachment of different cell populations, the design of advanced scaffolds for tissue engineering, based in the spatiotemporal tuning of cell–matrix anchorage is discussed.

August, 2013 | DOI: 10.1002/adma.201301227

Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy

Knappett, BR; Abdulkin, P; Ringe, E; Jefferson, DA; Lozano-Perez, S; Rojas, TC; Fernandez, A; Wheatley, AEH
Nanoscale, 5 (2013) 5765-5772


Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.

July, 2013 | DOI: 10.1039/C3NR33789H

A new bottom-up methodology to produce silicon layers with a closed porosity nanostructure and reduced refractive index

Godinho, V; Caballero-Hernandez, J; Jamon, D; Rojas, TC; Schierholz, R; Garcia-Lopez, J; Ferrer, FJ; Fernandez, A
Nanotechnology, 24 (2013) 275604


A new approach is presented to produce amorphous porous silicon coatings (a-pSi) with closed porosity by magnetron sputtering of a silicon target. It is shown how the use of He as the process gas at moderated power (50–150 W RF) promotes the formation of closed nanometric pores during the growth of the silicon films. The use of oblique-angle deposition demonstrates the possibility of aligning and orientating the pores in one direction. The control of the deposition power allows the control of the pore size distribution. The films have been characterized by a variety of techniques, including scanning and transmission electron microscopy, electron energy loss spectroscopy, Rutherford back scattering and x-ray photoelectron spectroscopy, showing the incorporation of He into the films (most probably inside the closed pores) and limited surface oxidation of the silicon coating. The ellipsometry measurements show a significant decrease in the refractive index of porous coatings (n500 nm = 3.75) in comparison to dense coatings (n500 nm = 4.75). The capability of the method to prepare coatings with a tailored refractive index is therefore demonstrated. The versatility of the methodology is shown in this paper by preparing intrinsic or doped silicon and also depositing (under DC or RF discharge) a-pSi films on a variety of substrates, including flexible materials, with good chemical and mechanical stability. The fabrication of multilayers of silicon films of controlled refractive index in a simple (one-target chamber) deposition methodology is also presented.

July, 2013 | DOI: 10.1088/0957-4484/24/27/275604

Preparation and characterization of CrO2 films by Low Pressure Chemical Vapor Deposition from CrO3

Aguilera, C; Gonzalez, JC; Borras, A; Margineda, D; Gonzalez, JM; Gonzalez-Elipe, AR; Espinos, JP
Thin Solid Films, 539 (2013) 1-11


Highly oriented CrO2 thin films have been heteroepitaxially grown on TiO2 rutile (110), (100) and (001) single crystalline substrates, by Low Pressure Chemical Vapor Deposition from CrO3 as precursor and flowing oxygen as carrier gas, under a pressure of 67 Pa. The experimental conditions were fine tuned by depositing on polycrystalline Ti foils, to improve the purity of the films and the deposition rate. A maximum deposition rate of 175 nm h− 1 was obtained.

The composition and texture of films, up to 2 μm thick, have been determined by X-ray diffraction (XRD) and Micro Raman, while their microstructure has been examined by Scanning Electron Microcopy and Atomic Force Microscopy, and their magnetic behavior has been tested by superconducting quantum interference device magnetometry. These techniques reveal that the phase purity, texture, microstructure and thickness of these films are dependent on the crystalline face of the rutile substrate and the deposition temperature. Thus, microscopy techniques, XRD and Raman spectroscopy confirm that highly textured CrO2 films were always obtained on the three rutile substrate faces when deposition temperature ranges between 616 K and 636 K. But these techniques also show that CrO2 films are unpurified with inclusions or patches of Cr2O3, for the most of the substrates and especially at high deposition temperatures. Magnetic measurements conclusively demonstrate that pure CrO2 films are only obtained when TiO2 (110) is used as a substrate.

July, 2013 | DOI: 10.1016/j.tsf.2013.04.118

Liquids Analysis with Optofluidic Bragg Microcavities

Oliva-Ramirez, M; Gonzalez-Garcia, L; Parra-Barranco, J; Yubero, F; Barranco, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 5 (2013) 6743-650


Porous Bragg microcavities formed by stacking a series of porous nanocolumnar layers with alternate low (SiO2) and high (TiO2) refractive index materials have been prepared by physical vapor deposition at glancing angles (GLAD). By strictly controlling the porosity and refractive index of the individual films, as well as the relative orientation of the nanocolumns from one layer to the next, very porous and nondispersive high optical quality microcavities have been manufactured. These photonic structures have been implemented into responsive devices to characterize liquids, mixtures of liquids, or solutions flowing through them. The large displacements observed in the optical spectral features (Bragg reflector gap and resonant peak) of the photonic structures have been quantitatively correlated by optical modeling with the refractive index of the circulating liquids. Experiments carried out with different glucose and NaCl solutions and mixtures of water plus glycerol illustrate the potentialities of these materials to serve as optofluidic devices to determine the concentration of solutions or the proportion of two phases in a liquid mixture.

July, 2013 | DOI: 10.1021/am401685r

Exploring the benefits of depositing hard TiN thin films by non-reactive magnetron sputtering

Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A; Sanchez-Lopez, JC
Applied Surface Science, 275 (2013) 121-126


The aim of this paper is to compare the mechanical and tribological properties of TiN coatings prepared in a conventional magnetron sputtering chamber according to two different routes: the usual reactive sputtering of a Ti target in an Ar/N2 atmosphere vs. the comparatively more simple sputtering of a TiN target in a pure Ar atmosphere. Improved properties in term of hardness and wear rates were obtained for films prepared by non-reactive sputtering route, due to the lower presence of oxynitride species and larger crystalline domain size. Additionally, a significant hardness enhancement (up to 45 GPa) is obtained when a −100 V d.c. bias is applied during growth. This behaviour is explained by non-columnar growth and small grain size induced by effective ion bombarding. These results demonstrate that non-reactive sputtering of TiN target appears a simple and efficient method to prepare hard wear-resistant TiN films.

June, 2013 | DOI: 10.1016/j.apsusc.2013.01.098

Structure and tribological properties of MoCN-Ag coatings in the temperature range of 25–700 °C

Shtansky, DV; Bondarev, AV; Kiryukhantsev-Korneev, PV; Rojas, TC; Godinho, V; Fernandez, A
Applied Surface Science, 273 (2013) 408-414


The preparation of hard coatings with low friction coefficient over a wide temperature range is still a challenge for the tribological community. The development of new nanocomposite materials consisting of different metal-ceramic phases, each of which exhibiting self-lubricating characteristics at different temperatures, may help to solve this problem. We report on the structure and tribological properties of MoCN-Ag coatings deposited by magnetron co-sputtering of Mo and C (graphite) targets and simultaneous sputtering of an Ag target either in pure nitrogen or in a gaseous mixture of Ar + N2. The structure and elemental composition of the coatings were studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, Raman spectroscopy, and glow discharge optical emission spectroscopy. The tribological properties of the coatings against an Al2O3 ball were investigated first at discrete temperatures of 25, 500, and 700 °C, and then during continuous heating in the temperature range of 25–700 °C. The coating structure and their respective wear tracks were also examined to elucidate their phase transformations during heat treatments. The lowest friction coefficients (<0.4) were observed in the temperature ranges of 25–100 °C and 400–700 °C and can be explained by the presence of a free amorphous carbon phase, which served as a lubricant at low temperatures, and by a positive role of silver and two phases forming at elevated temperatures, molybdenum oxide and silver molybdate, which provided lubrication above 400 °C. In the temperature range between 100 and 400 °C, the friction coefficient was relatively high. This problem is to be addressed in future works.

May, 2013 | DOI: 10.1016/j.apsusc.2013.02.055

Combined reactive magnetron sputtering and plasma decomposition of non-volatile precursors to grow luminescent thin films

Gil-Rostra, J; Yubero, F; Ferrer, FJ; Gonzalez-Elipe, AR
Surface and Coatings Technology, 222 (2013) 144-150


This paper reports a new procedure of the preparation of mixed oxide thin films that combines the traditional reactive magnetron sputtering deposition with the plasma activated decomposition of non-volatile precursors sublimated by means of an effusion cell. The possibilities of this new experimental procedure are illustrated with the preparation of luminescent thin films consisting of rare earth (RE) cations (Tb3 +, Eu3 +) incorporated in an oxide matrix (TiO2 and SiO2). The oxide matrix component was supplied by reactive magnetron sputtering from metallic Ti or Si targets, while the RE cation was dosed by sublimation of acetylacetonate compounds of the selected elements. The obtained mixed oxide thin films have been fully characterized by different methods and their luminescent properties studied as a function of the matrix type and concentration of the RE element present in the film. The advantages of the synthesis procedure are highlighted with regard to its versatility and the possibility of tailoring the properties of complex luminescent materials.

May, 2013 | DOI: 10.1016/j.surfcoat.2013.02.016

Tuning Dichroic Plasmon Resonance Modes of Gold Nanoparticles in Optical Thin Films

Gonzalez-Garcia, L; Parra-Barranco, J; Sanchez-Valencia, JR; Ferrer, J; Garcia-Gutierrez, MC; Barranco, A; Gonzalez-Elipe, AR
Advanced Functional Materials, 23 (2013) 1655-1663


A simple method is presented to tune the gold surface plasmon resonance (SPR) modes by growing anisotropic nanoparticles into transparent SiO2 thin films prepared by glancing angle deposition. In this type of composite film, the anisotropy of the gold nanoparticles, proved by gracing incidence small angle X-ray scattering, is determined by the tilted nanocolumnar structure of the SiO2 host and yields a strong film dichroism evidenced by a change from an intense colored to a nearly transparent aspect depending on light polarization and/or sample orientation. The formation in these films of lithographic non-dichroic SPR patterns by nanosecond laser writing demonstrates the potentialities of this procedure to develop novel optical encryption or anti-counterfeiting structures either at micrometer- or macroscales.

April, 2013 | DOI: 10.1002/adfm.201201900

Light induced hydrophilicity and osteoblast adhesion promotion on amorphous TiO2

Terriza, A; Diaz-Cuenca, A; Yubero, F; Barranco, A; Gonzalez-Elipe, AR; Caballero, JLG; Vilches, J; Salido, M
Journal of Biomedical Materials Research A, 101A (2013) 1026-1035


We have studied the effect of the UV induced superhydrophilic wetting of TiO2 thin films on the osteoblasts cell adhesion and cytoskeletal organization on its surface. To assess any effect of the photo-catalytic removal of adventitious carbon as a factor for the enhancement of the osteoblast development, 100 nm amorphous TiO2 thin layers were deposited on polyethylene terephthalate (PET), a substrate well known for its poor adhesion and limited wettability and biocompatibility. The TiO2/PET materials were characterized by X-ray photoelectron spectroscopy, and atomic force microscopy and their wetting behavior under light illumination studied by the sessile drop method. The amorphous TiO2 thin films showed a very poor photo-catalytic activity even if becoming superhydrophilic after illumination. The illuminated samples recovered partially its initial hydrophobic state only after their storage in the dark for more than 20 days. Osteoblasts (HOB) were seeded both on bare PET and on TiO2/PET samples immediately after illumination and also after four weeks storage in darkness. Cell attachment was much more efficient on the immediately illuminated TiO2/PET samples, with development of focal adhesions and cell traction forces. Although we cannot completely discard some photo-catalytic carbon removal as a factor contributing to this cell enhanced attachment, our photodegradation experiments on amorphous TiO2 are conclusive to dismiss this effect as the major cause for this behavior. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.

April, 2013 | DOI: 10.1002/jbm.a.34405

Growth of SiO2 and TiO2 thin films deposited by reactive magnetron sputtering and PECVD by the incorporation of non-directional deposition fluxes

Alvarez, R; Romero-Gomez, P; Gil-Rostra, J; Cotrino, J; Yubero, F; Gonzalez-Elipe, AR; Palmero, A
Physica Status Solidi (a), 210 (2013) 796-801


We have deposited TiO2 and SiO2 thin films by techniques as different as plasma-enhanced chemical vapor deposition (PECVD) and reactive magnetron sputtering under experimental conditions where highly directional deposition fluxes are avoided. The results indicate that whatever the deposition technique employed or even the precursor gas in the PECVD technique, films share common microstructural features: a mounded surface topography and a columnar arrangement in the bulk, with the column width growing linearly with film thickness. With the help of a Monte Carlo model of the deposition, we conclude that these common aspects are explained by solely taking into consideration the incorporation of a low-energy, isotropically directed, deposition flux onto a substrate at low temperature and under a weak plasma/surface interaction environment.

April, 2013 | DOI: 10.1002/pssa.201228656

Differences in n-type doping efficiency between Al- and Ga-ZnO films

Gabas, M; Landa-Canovas, A; Costa-Kramer, JL; Agullo-Rueda, F; Gonzalez-Elipe, AR; Diaz-Carrasco, P; Hernandez-Moro, J; Lorite, I; Herrero, P; Castillero, P; Barranco, A; Ramos-Barrado, JR
Journal of Applied Physics, 113 (2013) 163709 (9 pages)


A careful and wide comparison between Al and Ga as substitutional dopants in the ZnO wurtzite structure is presented. Both cations behave as n-type dopants and their inclusion improves the optical and electrical properties of the ZnO matrix, making it more transparent in the visible range and rising up its electrical conductivity. However, the same dopant/Zn ratio leads to a very different doping efficiency when comparing Al and Ga, being the Ga cation a more effective dopant of the ZnO film. The measured differences between Al- and Ga-doped films are explained with the hypothesis that different quantities of these dopant cations are able to enter substitutionally in the ZnO matrix. Ga cations seem to behave as perfect substitutional dopants, while Al cation might occupy either substitutional or interstitial sites. Moreover, the subsequent charge balance after doping appear to be related with the formation of different intrinsic defects that depends on the dopant cation. The knowledge of the doped-ZnO films microstructure is a crucial step to optimize the deposition of transparent conducting electrodes for solar cells, displays, and other photoelectronic devices.

April, 2013 | DOI: 10.1063/1.4803063

The distribution of elements in sequentially prepared MgB2 on SiC buffered Si substrate and possible pinning mechanisms

S. Chromik; A. Nishida; V. Strbik; M. Gregor; J.P. Espinós; J. Liday; R. Durny
Applied Surface Science, 269 (2013) 29-32


MgB2 thin films are prepared by sequential evaporation of boron and magnesium bilayers on SiC buffered Si substrates followed by an in situ annealing. Precursor Mg–B bilayers are deposited by electron beam evaporation at room temperature. The amount of B is varied so as to result in different thickness (15 nm and 50 nm) of stoichiometric MgB2 final film after an in situ reaction with the excess Mg top layer in the vacuum. We show the distribution of the elements through the film.

X-ray photoelectron spectroscopy analyses have shown that carbon is not free in the films (except the surface of the film) and silicon is in the compound form, too. In the case of the 15 nm thick films we see a strong interdiffusion of the elements (C, B) and we observe a suppression of TC of the film to 20 K. We register different slope of the HC2(T)HC2(T) dependence – the lowest temperature value of HC2HC2 for the 15 nm thick film exceeds the one for the 50 nm thick film in spite of lower TC. We suppose that δl pinning mechanism is dominant for the 15 nm thick film.

March, 2013 | DOI: 10.1016/j.apsusc.2012.10.019

Solvent-Controlled Synthesis and Luminescence Properties of Uniform Eu:YVO4 Nanophosphors with Different Morphologies

Nunez, N; Sabek, J; Garcia-Sevillano, J; Cantelar, E; Escudero, A; Ocañaa, M
European Journal of Inorganic Chemistry, 8 (2013) 1301-1309


A facile solvothermal route has been developed for the preparation of tetragonal europium-doped yttrium orthovanadate nanoparticles (Eu:YVO4) and is based on a homogeneous precipitation reaction at 120 °C from solutions of rare earth precursors (yttrium acetylacetonate and europium nitrate) and sodium orthovanadate in ethylene glycol or ethylene glycol/water mixtures. The nature of the solvent has a dramatic effect on the morphology and crystallinity of the resulting nanoparticles. Polycrystalline nanoellipsoids (130 × 60 nm) were obtained in pure ethylene glycol, whereas quasispherical nanoparticles (100 nm) with monocrystalline character precipitated in ethylene glycol/water (7:3 by volume) mixtures. To explain these different morphological and structural features, the mechanism of particles formation was investigated. The effects of the doping level on the luminescence properties (emission spectra and luminescence lifetime) were also evaluated to find the optimum nanophosphors. Finally, it is shown that the luminescent efficiency of the quasispherical nanoparticles was higher than that of the nanoellipsoids; this can be related to differences in crystallinity and in impurity content.

March, 2013 | DOI: 10.1002/ejic.201201016

Growth of silver on ZnO and SnO2 thin films intended for low emissivity applications

Alvarez, R; Gonzalez, JC; Espinos, JP; Gonzalez-Elipe, AR; Cueva, A; Villuendas, F
Applied Surface Science, 268 (2013) 507-515


In the present work we have investigated the relationships existing between the optical properties and the growth mechanism, microstructure and surface roughness of SnO2 and ZnO oxide films prepared by magnetron sputtering under conditions resembling those utilized in industry. Thin films of these oxides with different thicknesses were characterized by atomic force microscopy, glancing incidence X-ray diffraction (GIXRD), X-ray reflectometry and spectroscopic ellipsometry. The roughness evolution of the film properties (density, surface roughness and refraction index) as a function of their thickness has been evaluated within the concepts of the Dynamic Scaling Theory of thin film growth. Zinc oxide films were rougher than tin oxide films of similar thickness, indicating a different growing mechanism for the two materials. Silver was evaporated onto the surface of the two oxide thin films and its earlier stages of nucleation studied by background analysis of the X-ray photoemission spectra. A different nucleation mechanism was found depending on the nature of the oxide acting as substrate. The superior performance of the zinc oxide based low emissive coatings is related with a better wetting of silver on the surface of this oxide despite the comparatively lower roughness of the tin oxide layers.

March, 2013 | DOI: 10.1016/j.apsusc.2012.12.156

Competing Misfit Relaxation Mechanisms in Epitaxial Correlated Oxides

Sandiumenge, F; Santiso, J; Balcells, L; Konstantinovic, Z; Roqueta, J; Pomar, A; Espinos, JP; Martinez, B
Physical Review Letters, 110 (2013) 107206


Strain engineering of functional properties in epitaxial thin films of strongly correlated oxides exhibiting octahedral-framework structures is hindered by the lack of adequate misfit relaxation models. Here we present unreported experimental evidence of a four-stage hierarchical development of octahedral-framework perturbations resulting from a progressive imbalance between electronic, elastic, and octahedral tilting energies in La0.7Sr0.3MnO3 epitaxial thin films grown on SrTiO3 substrates. Electronic softening of the Mn-O bonds near the substrate leads to the formation of an interfacial layer clamped to the substrate with strongly degraded magnetotransport properties, i.e., the so-called dead layer, while rigid octahedral tilts become relevant at advanced growth stages without significant effects on charge transport and magnetic ordering.

March, 2013 | DOI: 10.1103/PhysRevLett.110.107206

Behaviour of Au-citrate nanoparticles in seawater and accumulation in bivalves at environmentally relevant concentrations

Garcia-Negrete, C. A.; Blasco, J.; Volland, M.; Rojas, T. C.; Hampel, M.; Lapresta-Fernandez, A.; Jimenez de Haro, M. C.; Soto, M.; Fernandez, A.
Environmental Pollution, 174 (2013) 134-141


The degree of aggregation and/or coalescence of Au-citrate nanoparticles (AuNPs, mean size 21.5 ± 2.9 nm), after delivery in simulated seawater, are shown to be concentration-dependent. At low concentrations no coalescence and only limited aggregation of primary particles were found. Experiments were performed in which the marine bivalve (Ruditapes philippinarum) was exposed to AuNPs or dissolved Au and subsequently, bivalve tissues were studied by Scanning and Transmission Electron Microscopy and chemical analyses. We show that the bivalve accumulates gold in both cases within either the digestive gland or gill tissues, in different concentrations (including values of predicted environmental relevance). After 28 days of exposure, electron-dense deposits (corresponding to AuNPs, as proven by X-ray microanalysis) were observed in the heterolysosomes of the digestive gland cells. Although non-measurable solubility of AuNPs in seawater was found, evidence is presented of the toxicity produced by Au3+ dissolved species (chloroauric acid solutions) and its relevance is discussed.

March, 2013 | DOI: 10.1016/j.envpol.2012.11.014

Colored and Transparent Oxide Thin Films Prepared by Magnetron Sputtering: The Glass Blower Approach

Gil-Rostra, J; Chaboy, J; Yubero, F; Vilajoana, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 5 (2013) 1967-1976


This work describes the reactive magnetron sputtering processing at room temperature of several mixed oxide MxSiyOz thin films (M: Fe, Ni, Co, Mo, W, Cu) intended for optical, coloring, and aesthetic applications. Specific colors can be selected by adjusting the plasma gas composition and the Si–M ratio in the magnetron target. The microstructure and chemistry of the films are characterized by a large variety of techniques including X-ray photoemission spectroscopy, X-ray absorption spectroscopy (XAS), and infrared spectroscopy, while their optical properties are characterized by UV–vis transmission and reflection analysis. Particularly, XAS analysis of the M cations in the amorphous thin films has provided valuable information about their chemical state and local structure. It is concluded that the M cations are randomly distributed within the SiO2 matrix and that both the M concentration and its chemical state are the key parameters to control the final color of the films.

March, 2013 | DOI: 10.1021/am302778h

Growth regimes of porous gold thin films deposited by magnetron sputtering at oblique incidence: from compact to columnar microstructures

Alvarez, R; Garcia-Martin, JM; Macias-Montero, M; Gonzalez-Garcia, L; Gonzalez, JC; Rico, V; Perlich, J; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Nanotechnology, 24 (2013) 045604


Growth regimes of gold thin films deposited by magnetron sputtering at oblique angles and low temperatures are studied from both theoretical and experimental points of view. Thin films were deposited in a broad range of experimental conditions by varying the substrate tilt angle and background pressure, and were analyzed by field emission scanning electron microscopy and grazing-incidence small-angle x-ray scattering techniques. Results indicate that the morphological features of the films strongly depend on the experimental conditions, but can be categorized within four generic microstructures, each of them defined by a different bulk geometrical pattern, pore percolation depth and connectivity. With the help of a growth model, a microstructure phase diagram has been constructed where the main features of the films are depicted as a function of experimentally controllable quantities, finding a good agreement with the experimental results in all the studied cases.

February, 2013 | DOI: 10.1088/0957-4484/24/4/045604

Effects of plasma surface treatments of diamond-like carbon and polymeric substrata on the cellular behavior of human fibroblasts

Lopez-Santos, C; Fernandez-Gutierrez, M; Yubero, F; Vazquez-Lasa, B; Cotrino, J; Gonzalez-Elipe, A; San Roman, J
Journal of Biomaterials Applications, 27 (2013) 669-683


Surface properties play an important role in the functioning of a biomaterial in the biological environment. This work describes the influence of the changes that occurred on diamond-like carbon (DLC) and polymeric substrata by different nitrogen and ammonia plasmas treatments and its effects on the cell proliferation on these materials. All substrata were additionally subjected to the effect of neutral beams of nitrogen atoms and NH species for comparison purposes. Results about the proliferation, viability, and morphology of fibroblasts were correlated with surface chemical composition, surface tension, and topography. It was found that the presence of amine groups on the surface and the surface tension are beneficial factors for the cell growth. Surface roughness in DLC also plays a positive role in favoring cell adhesion and proliferation, but it can be detrimental for some of the treated polymers because of the accumulation of low molecular weight fragments formed as a result of the plasma treatments. Analysis of the overall results for each type of material allowed to define a unique parameter called ‘factor of merit’ accounting for the influence of the different surface characteristics on the cell deployment, which can be used to predict qualitatively the efficiency for cell growth.

February, 2013 | DOI: 10.1177/0885328211422832

Valence band electronic structure characterization of the rutile TiO2 (110)-(1 x 2) reconstructed surface

Sanchez-Sanchez, C; Garnier, MG; Aebi, P; Blanco-Rey, M; de Andres, PL; Martin-Gago, JA; Lopez, MF
Surface Science, 608 (2013) 92-96


The electronic structure of the TiO2 (110)-(1 × 2) surface has been studied by means of angular resolved ultraviolet photoemission spectroscopy (ARUPS). The valence band dispersion along the high symmetry surface directions, [001] and [1–10], has been recorded. The experimental data show no dispersion of the band-gap Ti 3d states. However, the existence of dispersive bands along the [001] direction located at about 7 eV below the Fermi level is reported. The existence of two different contributions in the emission from the defects-related state located in the gap of the surface is univocally shown for the first time.

February, 2013 | DOI: 10.1016/j.susc.2012.09.019

Laser induced enhancement of dichroism in supported silver nanoparticles deposited by evaporation at glancing angles

Filippin, AN; Borras, A; Rico, VJ; Frutos, F; Gonzalez-Elipe, AR
Nanotechnology, 24 (2013) 045301


Silver nanoparticles (NPs) depicting well defined surface plasmon resonance (SPR) absorption were deposited on flat substrates by physical vapor deposition in a glancing angle configuration. The particles were characterized by scanning electron microscopy and atomic force microscopy and their optical properties examined by UV–vis absorption spectroscopy using linearly polarized light. It was found that, depending on the amount of deposited silver and the evaporation angle, part of the 'as-prepared' samples present NPs characterized by an anisotropic shape and a polarization dependent SPR absorption and different colors when using polarized white light at 0° and 90°. Low-power irradiation of these materials with an infrared Nd-YAG nanosecond laser in ambient conditions produced an enhancement in such dichroism. At higher powers, the dichroism was lost and the SPR bands shifted to lower wavelengths as a result of the reshaping of the silver NPs in the form of spheres. The possible factors contributing to the observed changes in dichroism are discussed.

February, 2013 | DOI: 10.1088/0957-4484/24/4/045301

Strong quantum confinement effects in SnS nanocrystals produced by ultrasound-assisted method

Azizian-Kalandaragh, Y; Khodayari, A; Zeng, ZP; Garoufalis, CS; Baskoutas, S; Gontard, LC
Journal of Nanoparticle Research, 15 (2013) 1388


Nanocrystalline SnS powder has been prepared using tin chloride (SnCl2) as a tin ion source and sodium sulfide (Na2S) as a sulfur ion source with the help of ultrasound irradiation at room temperature. The as-synthesized SnS nanoparticles were quantitatively analyzed and characterized in terms of their morphological, structural, and optical properties. The detailed structural and optical properties confirmed the orthorhombic SnS structure and a strongly blue shifted direct band gap (1.74 eV), for synthesized nanoparticles. The measured band gap energy of SnS nanoparticles is in a fairly good agreement with the results of theoretical calculations of exciton energy based on the potential morphing method in the Hartree–Fock approximation.

January, 2013 | DOI: 10.1007/s11051-012-1388-1

Small Pt nanoparticles on the TiO2 (110)–(1 × 2) surface

Sanchez-Sanchez, C; Martin-Gago, JA; Lopez, MF
Surface Science, 607 (2013) 159-163


Scanning tunnelling microscopy (STM) has been used to study the initial stages of Pt deposition on the TiO2 (110)–(1 × 2) surface. Experimental STM images recorded for Pt coverage of 0.1 and 0.4 ML, suggest a Volmer-Weber growth. For low coverage and RT deposition, small clusters homogeneously distributed on the surface terraces are observed. However, after annealing at 825 K, material agglomeration, with nucleation mainly at the cross-links, is observed as a consequence of Pt diffusion on the surface. Finally, the structure of small clusters has been determined, in good agreement with previous theoretical calculations.

January, 2013 | DOI: 10.1016/j.susc.2012.08.028

Electrochromism in WOx and WxSiyOz Thin Films Prepared by Magnetron Sputtering at Glancing Angles

Garcia-Garcia, FJ; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR
Nanoscience and Nanotechnology Letters, 5 (2013) 89-93


This work reports the electrochromic evaluation of WxSiyOz and WOx glad thin films deposited by reactive magnetron sputtering at glancing angle. Their electrochemical properties were assessed by the analysis of cyclic voltammetry and chronoamperometry measurements in 0.1 M HClO4, whereas their optical properties were determined by studying their transmission and absorption spectra under operation conditions. Both types of thin films presented outstanding electrochromic properties characterized by a fast response, a high coloration and a complete reversibility after more than one thousand cycles.

January, 2013 | DOI: 10.1166/nnl.2013.1449

Tribological properties of surface-modified Pd nanoparticles for electrical contacts

Abad, MD; Sanchez-Lopez, JC
Wear, 297 (2013) 943-951


A fully comprehensive study of the tribological behavior of palladium nanoparticles (Pd NPs) capped by tetrabutylammonium chains using a ball-on-disk tribometer under different conditions of applied load, concentration, tribometer motion, linear speed and nature of the counterface is revised. A low concentration of NPs (2 wt%) in tetrabutylammonium acetate was found sufficient to improve the tribological properties due to the formation of a protective transfer film (TF) comprised of metallic Pd. The increase of the applied load (up to 20 N, 1.82 GPa of contact pressure) confirmed the excellent extreme-pressure behavior avoiding the counterfaces from severe wear. After a running-in period whose duration depends on the operating conditions, the TF build-up allows to maintain a low contact electrical resistance through the contact (<0.1 kΩ) during the entire test. When the Pd NPs are used with ceramic counterfaces, the nanoparticles increase the load-bearing capabilities and performance of the base without forming TF, likely by mixed or boundary lubrication and healing effects. Finally, the Pd NPs are demonstrated to be useful as a thin solid lubricant film in reciprocating motion yielding a comparable tribological behavior. Hence, the presented surface Pd NPs can be very helpful to extend life of sliding components due to their high strength resistance providing a gateway to electrical conduction as well.

January, 2013 | DOI: 10.1016/j.wear.2012.11.009


XPS and AES analyses of cerium conversion coatings generated on AA5083 by thermal activation

Sanchez-Amaya, JM; Blanco, G; Garcia-Garcia, FJ; Bethencourt, M; Botana, FJ
Surface and Coatings Technology, 213 (2012) 105-116


This paper describes the deep analysis of cerium conversion coatings developed with thermal activation on AA5083 under optimum processing conditions. Scanning electron microscopy (SEM), electron dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were employed to study these layers. Ar+ sputtering was also employed to analyse the coatings' core. Although conversion coatings based on Ce salts have been widely characterised in the literature for different aluminium alloys, the coatings developed with thermal activation on Al–Mg alloys have not been previously investigated with these techniques. SEM/EDX studies have demonstrated the existence of a heterogeneous layer formed by a film of aluminium oxide/hydroxide on the matrix as well as a series of dispersed islands of cerium deposited on the cathodic intermetallics. These results have been further confirmed by means of XPS. The XPS and AES results revealed that the outer layer comprises a mixture coating of Ce3 + (70%) and Ce4 + (30%) compounds. Although only Ce3 + compounds were detected at the inner part of the coating, possible reduction of Ce(IV) to Ce(III) due to the Ar+ beam could not be discarded. Obtained results allowed authors to confirm that the cerium conversion coatings developed have a similar structure to those previously reported for other aluminium alloys.

December, 2012 | DOI:

Nanoporous silica microparticle interaction with toll-like receptor agonists in macrophages

Cejudo-Guillen, M; Ramiro-Gutierrez, M L; Labrador-Garrido, A; Diaz-Cuenca, A; Pozo, D
Acta Biomaterialia, 8 (2012) 4295-4303


Nanoporous silica microparticles (NSiO2-MP) are considered to be potential drug delivery systems and scaffolding platforms in tissue engineering. However, few biocompatibility studies regarding NSiO2-MP interaction with the immune system have been reported. Toll-like receptors (TLR) are involved in host defence as well as autoimmune and inflammatory diseases. The results show that NSiO2-MP up to 100 μg ml−1 do not affect macrophage cell viability after 24 h cell culture. Moreover, NSiO2-MP do not compromise the cell viability of TLR-activated Raw 264.7 cells, for either cell surface TLR (TLR1/TLR2/TLR4/TLR6) or endocytic compartment TLR (TLR3/TLR7/TLR9). Furthermore, Raw 264.7 cells do not respond to NSiO2-MP exposure in terms of IL-6 or IL-10 secretion. NSiO2-MP co-treatment in the presence of TLR ligands does not impair or enhance the secretion of the pro-inflammatory cytokine IL-6 or the regulatory cytokine IL-10. Thus, NSiO2-MP do not affect macrophage polarization towards a pro-inflammatory or immunosuppressive status, representing added value in terms of biocompatibility compared with other SiO2-based micro- and nanoparticles.

December, 2012 | DOI: 10.1016/j.actbio.2012.07.026

New insights into the synergistic effect in bimetallic-boron catalysts for hydrogen generation: The Co–Ru–B system as a case study

Arzac, G. M.; Rojas, T. C.; Fernandez, A.
Applied Catalysis B-Environmental, 128 (2012) 39-47


Catalysed sodium borohydride hydrolysis is a high-potential method to produce hydrogen for portable applications. Co–B catalysts are the most chosen because they are easily prepared, cheap and efficient. The addition of small amounts of Ru produces a significant enhancement in catalytic activity.

In the present work a series of Co–Ru–B catalysts with variable Ru content was prepared, isolated and characterized. The comprehension of the synergistic effect was achieved trough the incorporation of the nanostructural dimension to the study of surface and bulk chemical states of the involved atoms along the series. It was found that up to 70% (of total metal) atomic content of Ru the catalysts can be considered isostructural to the single Co–B catalyst in the nanoscale. A structural transition occurs in the case of the pure Ru–B material to produce a boron deficient material with higher nanoparticle size. This structural transition together with Co segregation and Ru dispersion play a key role when explaining a [OH−] dependent effect.

The inexistence of borate layers in Ru rich catalysts is suggestive in the research for non deactivating catalysts.

November, 2012 | DOI: 10.1016/j.apcatb.2012.02.013

Deactivation, reactivation and memory effect on Co–B catalyst for sodium borohydride hydrolysis operating in high conversion conditions

Arzac, GM; Hufschmidt, D; De Haro, MCJ; Fernandez, A; Sarmiento, B; Jimenez, MA; Jimenez, MM
International Journal of Hydrogen Energy, 37 (2012) 14373-14381


A system with a continuous reactor to produce hydrogen by sodium borohydride hydrolysis was designed and built. The purpose was to test a supported Co–B catalyst durability upon cycling and long life experiments in high conversion conditions. A Stainless Steel monolith was built and calcined to improve adherence. For comparison a Ru–B catalyst was tested upon cycling. Both Co–B and Ru–B catalysts are durable during 6 cycles and then deactivate. A known reactivation procedure has proven to be more effective for the Co–B than for the Ru–B catalyst. This is related to stronger adsorption of B–O based compounds on the Co–B catalyst which is reversible upon acid washing. For the Ru–B catalyst deactivation may be more related to particle agglomeration than to the adsorption of B–O based species. The continuous system enlarges the catalysts durability because of the continuous borate elimination at elevated temperatures.

October, 2012 | DOI: 10.1016/j.ijhydene.2012.06.117

DLC coatings for UHMWPE: Relationship between bacterial adherence and surface properties

Del Prado, G; Terriza, A; Ortiz-Perez, A; Molina-Manso, D; Mahillo, I; Yubero, F; Puertolas, JA; Manrubia-Cobo, M; Barrena, EG; Esteban, J
Journal of Biomedical Materials Research Part A, 100A (2012) 2813-2820


Development of intrinsically antibacterial surfaces is of key importance in the context of prostheses used in orthopedic surgery. This work presents a thorough study of several plasma-based coatings that may be used with this functionality: diamond-like carbon (DLC), fluorine-doped DLC (F-DLC), and a high-fluorine-content-carbon-fluor polymer (CFX). The coatings were obtained by a radio-frequency plasma-assisted deposition on ultra high molecular weight polyethylene (UHMWPE) samples and physicochemical properties of the coated surfaces were correlated with their antibacterial performance against collection and clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The fluorine content and the relative amount of CC and CF bonds were controlled by X-ray photoelectron spectroscopy, and hydrophobicity and surface tension by contact angle measurements. Surface roughness was studied by Atomic Force Microscopy. Additional nanoidentation studies were performed for DLC and F-DLC coatings. Unpaired t test and regression linear models evaluated the adherence of S. aureus and S. epidermidis on raw and coated UHMWPE samples. Comparing with UHMWPE, DLC/UHMWPE was the least adherent surface with independence of the bacterial species, finding significant reductions (p ≤ 0.001) for nine staphylococci strains. Bacterial adherence was also significantly reduced in F-DLC/ UHMWPE and CFx/UHMWPE for six strains. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A:2813–2820, 2012.

October, 2012 | DOI: 10.1002/jbm.a.34220

Chemical and microstructural characterization of (Y or Zr)-doped CrAlN coatings

Rojas, T. C.; El Mrabet, S.; Dominguez-Meister, S.; Brizuela, M.; Garcia-Luis, A.; Sanchez-Lopez, J. C.
Surface and Coatings Technology, 211 (2012) 104-110


Magnetron sputtered chromium aluminium nitride films are excellent candidates for advanced machining and protection for high temperature applications. In this work CrAlN-based coatings including Y or Zr as dopants (≈ 2 at.%) are deposited by d.c. reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N2 mixtures. The hardness properties are found in the range of 22–33 GPa with H/E ratios close to 0.1. The influence of the dopant element in terms of oxidation resistance after heating in air at 1000 °C is studied by means of X-ray diffraction (XRD), cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray analysis (EDX). The microstructure and chemical bonding are investigated using a transmission electron microscope (TEM) and electron energy-loss spectroscopy (EELS) respectively. The improvement in oxidation resistance as compared to pure CrN coating is manifested in the formation of a Al-rich outer layer that protects the underneath coating from oxygen diffusion. The best performance obtained with the CrAlYN film is investigated by in situ annealing of this sample inside the TEM in order to gain knowledge about the structural and chemical transformations induced during heating.

October, 2012 | DOI: 10.1016/j.surfcoat.2011.07.071

Following the Wetting of One-Dimensional Photoactive Surfaces

Macias-Montero, M; Borras, A; Alvarez, R; Gonzalez-Elipe, AR
Langmuir, 28 (2012) 15047-15055


This article aims toward a full description of the wetting conversion from superhydrophobicity to superhydrophilicity under illumination with UV light of high-density ZnO nanorods surfaces by (i) following the evolution of the clusters and superstructures formed by the nanocarpet effect as a function of the water contact angle (WCA); (ii) characterization of the superhydrophobic and superhydrophilic states with an environmental scanning electron microscope (ESEM); and (iii) using the nanocarpet effect as a footprint of both local and apparent water contact angles. Thus, the main objective of the article is to provide a general vision of the wettability of 1D photoactive surfaces. In parallel, the nanocarpet (NC) formation by clustering of vertically aligned ZnO nanorods (NR) when water is dripped on their surface and then dried is studied for the first time by taking advantage of the possibility of tuning the surface water contact angle of the ZnO NR structure under UV preillumination. As a result, we demonstrate the feasibility of controlling the size and other morphological characteristics of the NCs. Moreover, a strong anisotropic wetting behavior, characterized by a Δθ = θ – θ = 30°, is shown on an asymmetrically aligned NC surface resulting from arrays of tilted NRs. The study of the condensation/evaporation of water on/from an as-prepared (superhydrophobic) or a preilluminated (superhydrophilic) NR surface examined by an environmental scanning electron microscope has evidenced the formation of supported water droplets with polygonal shapes in the first case and the complete filling of the inter-NR space in the latter. The long-term stability of the NC clusters has been utilized as a footprint to track the penetration depth of water within the inter-NR space in the three borderline regions of water droplets. This analysis has shown that for moderately hydrophobic surfaces (i.e., water contact angles lower than 130°) water droplets do not present a well-defined borderline trace but a spreading region where water penetrates differently with the NR interspace. The transition from a Cassie–Baxter to a modified Cassie–Baxter to finish in a Wenzel wetting state is found on these surfaces depending on the UV preillumination time and is explained with a model where water interaction with the NR units is the critical factor determining the macroscopic wetting behavior of these surfaces.

October, 2012 | DOI: 10.1021/la3028918

Selective Detection of Volatile Organic Compounds by Spectral Imaging of Porphyrin Derivatives Bound to TiO2 Porous Films

Roales, J; Pedrosa, JM; Castillero, P; Cano, M; Richardson, TH; Barranco, A; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 4 (2012) 5147-5154


In this work, the carboxylic acid derivatives of a free-base porphyrin, 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin, and 10 of its metal derivatives (TCPPs) have been used for optical gas sensing. For this purpose, microstructured columnar TiO2 thin films prepared by GAPVD (glancing angle physical vapor deposition) have been used as host materials for the porphyrins as they are non–dispersive and porous, allowing their use for UV–visible spectroscopy and gas sensing. The chemical binding between the dye molecules and the TiO2 has been studied through infrared spectroscopy, and the obtained spectral changes have been found to be compatible with chelating and/or bidentate binding modes of the carboxylate groups on the TiO2 surface. When hosted in the film, the UV–visible spectra of the porphyrins featured a blue shift and broadening of the Soret band with respect to the solution, which has been attributed to the formation of π–π aggregates between porphyrin molecules. The composite porphyrin/TiO2 films obtained from each of the 11 porphyrins have been exposed to 12 different volatile organic compounds (VOCs), and their respective gas–sensitive properties have been analyzed as a function of the spectral changes in their Soret band region in the presence of the analytes. The set of composite films has shown high selectivity to the analyzed volatile compounds. For each analyte, an innovative way of showing the different responses has been developed. By means of this procedure, an imagelike recognition pattern has been obtained, which allows an easy identification of every compound. The kinetics of the exposure to several analytes showed a fast, reversible and reproducible response, with response times of a few seconds, which has been attributed to both the sensitivity of the porphyrins and the high porosity of the TiO2 films. Also, increasing concentrations of the analytes resulted in an increase in the magnitude of the response, indicating that the sensor behavior is also concentration-dependent.

October, 2012 | DOI: 10.1021/am301069

Critical thickness and nanoporosity of TiO2 optical thin films

Borras, A; Alvarez, R; Sanchez-Valencia, JR; Ferrer, J; Gonzalez-Elipe, AR
Microscopy and Microanalysis, 18 (2012) 1-9


This work reports on the porosity and refraction index of TiO2 thin films as a function of the film thickness. Samples were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a microwave electron cyclotron resonance (MW-ECR) reactor at room temperature using titanium tetra-isopropoxide (MP) as precursor. Experimental parameters such as plasma gas composition (pure oxygen and argon/oxygen mixtures) and pressure (either ECR conditions or "normal" pressure, i.e. 10(-4) or 10(-3) torrs correspondently) were varied. The evolution of the thin film microstructure, porosity and optical properties is critically studied by AFM, SEM, water adsorption isotherms, ellipsometry and UV-Vis transmittance and the existence of a certain critical thickness (t(c)) demonstrated. The porosity of the films with thicknesses ranging from several tens of nanometers up to half a micrometer is evaluated by QCM-isotherms at room temperature. The dependency of this critical thickness with the plasma conditions is evaluated experimental and theoretically. Thus, the microstructure change at t(c) is attributed to a transition from a surface diffused dominated growth mechanism for t < t(c) to another where shadowing is predominant. Dynamic scaling analysis of the two regimes and their Monte Carlo simulation complete the reported study.

September, 2012 | DOI: 10.1016/j.micromeso.2012.04.035

Phase composition and tribomechanical properties of Ti-B-C nanocomposite coatings prepared by magnetron sputtering

Sanchez-Lopez, JC; Abad, MD; Justo, A; Gago, R; Endrino, JL; Garcia-Luis, A; Brizuela, M
Journal of Physics D: Applied Physics, 45 (2012) 375401


Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti–B–C nanocomposite coatings were prepared by co-sputtering of graphite and TiB2 targets. Varying the discharge power ratio applied to the graphite and TiB2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and x-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB2-like structure to a distorted TiBxCy ternary compound with increasing C concentration. X-ray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiBxCy phase. A fitting analysis of the C 1s XPS peak allowed us to evaluate the relative amount of a-C and TiBxCy components. A drastic change in hardness (from 52 to 13 GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45%. Raman observation of the wear tracks determined the presence of disordered sp2-bonded carbon phase associated with the diminution of the friction level.

September, 2012 | DOI: 10.1088/0022-3727/45/37/375401

Wall slip phenomena in concentrated ionic liquid-based magnetorheological fluids

Gomez-Ramirez, A; Lopez-Lopez, MT; Gonzalez-Caballero, F; Duran, JDG
Rheologica Acta, 51 (2012) 793-803


Ionic liquids (ILs) have been recently proposed as carrier for magnetorheological (MR) fluids. Their special properties, such as very low vapor pressure and high thermal stability, make ILs highly suitable dispersion media to increase the broad range of technological applications that magnetorheological fluids already have. It has been just reported that using ILs as carriers in MR fluids an improvement in the colloidal stability and suspension redispersibility is obtained. In this work, the magnetorheological behavior of highly concentrated suspensions in ILs is studied. Two kinds of suspensions were analyzed: using an ionic liquid of low conductivity and a mineral oil as carriers. In both cases, silica-coated iron microparticles were used as solid phase, being the solid volume concentration of 50% vol. A complete magnetorheological analysis focused on the wall slip phenomenon was performed. Steady-state and oscillatory experiments were carried out. In order to study wall slip effects, all experiments were performed with a plate-plate system, using both smooth and rough measuring surfaces. A significant effect of wall slip was observed when the experiments were performed using smooth surfaces. The novelty of this paper is mainly based on (1) the use of an ionic liquid as carrier to prepare magnetic suspensions, and (2) the analysis of wall slip phenomena in MR fluids with a particle content close to the maximum packing fraction.

September, 2012 | DOI: 10.1007/s00397-012-0639-5

Microstructural characterization of hydrophobic Ti1−xAlxN coatings with moth-eye-like surface morphology

Godinho, V; Lopez-Santos, C; Rojas, TC; Philippon, D; de Haro, MCJ; Lucas, S; Fernandez, A
Journal of Alloys and Compounds, 536 (2012) S398-S406


Ti1−xAlxN thin films with different Al content were deposited by magnetron sputtering. The combination of electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) was used to evaluate the composition of the coatings. The effect of Al content on the morphology and properties of the coatings was investigated. High resolution electron microscopy and related techniques revealed the formation of a pillared moth-eye-like nanostructure with variable size and distribution of meso- and nano-columns and different degree of open porosity that depends on the Al content on the coating. For low Al content (x ≤ 0.21) c-(Ti,Al)N highly porous columns ending in a sharp pyramidal shape present low reflectivity and high hydrophobicity. While the precipitation of h-AlN phase at the column boundaries for x = 0.71 suppresses the c-(Ti,Al)N columnar growth and produces a smother surface, with higher reflectivity and less hydrophobic character.

September, 2012 | DOI: 10.1016/j.jallcom.2012.02.178

Characterization of highly crosslinked polyethylenes by colorimetry

Martinez-Morlanes, MJ; Terriza, A; Yubero, F; Puertolas, JA
Polymer Testing, 31 (2012) 841-847


Colour analysis appears to be a robust technique for characterizing vitamin E doping and gamma irradiation of medical grade polyethylene samples. The analysis procedure described in this paper is of great interest because it can easily distinguish between polyethylene samples with differences in vitamin E (α-tocopherol) doping of about 0.1 wt% and gamma irradiation doses of 30 kGy. It is found that the colour differences (with respect to untreated samples) induced by gamma irradiation and/or vitamin E doping add-up linearly. This method for detecting the presence of vitamin E is fast, simple and non-destructive.

September, 2012 | DOI: 10.1016/j.polymertesting.2012.06.005

Software package to calculate the effects of the core hole and surface excitations on XPS and AES

Tougaard, S; Yubero, F
Surface and Interface Analysis, 44 (2012) 1114-1118


We report on a new software package that allows to calculate the energy loss processes in a photo- and Auger electron spectrum. The calculations are performed within our previously published semiclassical dielectric response model. The model takes into account energy loss, which takes place because of the sudden creation of the static core hole and as the photoelectron travels in the bulk, passes the surface region and continues in the vacuum where it interacts with its image charge before it ends up in the electron spectrometer. It is a one-step model, which includes interference effects between these excitations. The only input in the calculations is the dielectric function of the material. We discuss the capabilities of the software and illustrate some examples of its practical application, including comparison with experimental spectra. We hope the software will be useful for the investigations of fundamental excitation mechanisms in XPS and AES. The software is free for noncommercial use.

August, 2012 | DOI: 10.1002/sia.4855

Charge collection properties of dye-sensitized solar cells based on 1-dimensional TiO2 porous nanostructures and ionic-liquid electrolytes

Gonzalez-Garcia, Lola; Idigoras, Jesus; Gonzalez-Elipe, Agustin R.; Barranco, Angel; Anta, Juan A.
Journal of Photochemistry and Photobiology A-Chemistry, 241 (2012) 58-66


Dye solar cells consisting of mesoporous TiO 2 nanocolumnar films sensitized with a highly absorptive indoline dye were studied to estimate the charge collection efficiency provided by porous 1-dimensional (1-D) nanostructures in combination with viscous, fast-recombining electrolytes. The TiO 2 mesoporous nanostructured films were prepared by physical vapor deposition at glancing incidence (GLAD-PVD). Electrochemical Impedance Spectroscopy (EIS) in the dark was utilized to extract the transport and recombination properties of the fabricated devices. Due to their high porosity, the TiO 2 nanocolumnar electrodes incorporated a dye amount similar to that admitted by nanoparticulated electrodes with higher thickness. This fact, together with the longer lifetimes of electrons obtained for the GLAD-PVD electrodes, lead to an overall improvement of the charge collection and photovoltaic properties with respect to randomly packed electrodes. Measured diffusion lengths were improved by a factor between 2 and 3 with respect to the disordered nanostructure. The present results demonstrate the capability of partially ordered nanostructures to improve charge collection in devices constructed with fast-recombining electrolytes.

August, 2012 | DOI: 10.1016/j.jphotochem.2012.05.015

The effect of nickel on alloy microstructure and electrochemical behaviour of AA1050 aluminium alloy in acid and alkaline solutions

Garcia-Garcia, FJ; Skeldon, P; Thompson, GE; Smith, GC
Electrochimica Acta, 75 (2012) 229-238


The study investigates the influence of nickel and magnesium additions to AA1050 aluminium alloy on the alloy electrochemical behaviour in sodium hydroxide and hydrochloric solutions under conditions relevant to industries that use alkaline etching as a standard surface treatment procedure and to the lithographic and electronic industries where surface convolution is assisted by pitting in hydrochloric acid. Scanning and transmission electron microscopes were used to characterize the intermetallic particles, and scanning Kelvin probe microscopy was utilised in monitoring the surface potential. Nickel is shown to be incorporated into second phase particles, which mostly consisted of Al3Fe and α-(AlFeSi) phases, resulting in enhanced cathodic activity on the aluminium surface. Consequently, the dissolution rates of the superpure aluminium, alloys without nickel addition and alloy with nickel addition are increased respectively in sodium hydroxide, and increased pitting is respectively promoted in hydrochloric acid. In contrast, the addition of magnesium to the alloy had negligible influence on the etching and pitting behaviour.

July, 2012 | DOI: 10.1016/j.electacta.2012.04.106

Microstructural and chemical characterization of nanostructured Tialsin coatings with nanoscale resolution

Godinho, V; Rojas, TC; Trasobares, S; Ferrer, FJ; Delplancke-Ogletree, MP; Fernandez, A
Microscopy and Microanalysis, 18 (2012) 568-581


Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).

June, 2012 | DOI: 10.1017/S1431927612000384

Vertical and tilted Ag-NPs@ZnO nanorods by plasma-enhanced chemical vapour deposition

Macias-Montero, M; Borras, A; Saghi, Z; Espinos, JP; Barranco, A; Cotrino, J; Gonzalez-Elipe, AR
Nanotechnology, 23 (2012) 255303


Supported ZnO nanorods have been prepared at 405 K by plasma-enhanced chemical vapour deposition (PECVD) using diethylzinc as precursor, oxygen plasma and silver as the promotion layer. The nanorods are characterized by a hollow and porous microstructure where partially percolated silver nanoparticles are located. By changing different deposition parameters like the thickness of the silver layer, the type of oxidation pretreatment or the geometry of the deposition set-up, the length, the width and the tilting angle of the nanorods with respect to the substrate can be modified. Other nanostructures like nanobushes, zigzag linear structures and stacked bilayers with nanocolumns of TiO 2 can also be prepared by adjusting the deposition conditions. A phenomenological model relying on the assessment of the diverse nanostructure morphologies and the evidence provided by an in situ x-ray photoelectron spectroscopy (XPS) experiment has been proposed to describe their formation mechanism. From this analysis it is deduced that the effect of the electrical field of the plasma sheath, the high mobility of silver and silver oxide, and the diffusion of the precursor molecules are some of the critical factors that must converge by the formation of the nanorods.

June, 2012 | DOI: 10.1088/0957-4484/23/25/255303

Three-dimensional fabrication and characterisation of core-shell nano-columns using electron beam patterning of Ge-doped SiO2

Gontard, LC; Jinschek, JR; Ou, HY; Verbeeck, J; Dunin-Borkowski, RE
Applied Physics Letters, 100 (2012) 263113


A focused electron beam in a scanning transmission electron microscope (STEM) is used to create arrays of core-shell structures in a specimen of amorphous SiO2 doped with Ge. The same electron microscope is then used to measure the changes that occurred in the specimen in three dimensions using electron tomography. The results show that transformations in insulators that have been subjected to intense irradiation using charged particles can be studied directly in three dimensions. The fabricated structures include core-shell nano-columns, sputtered regions, voids, and clusters.

June, 2012 | DOI: 10.1063/1.4731765

Roughness assessment and wetting behavior of fluorocarbon surfaces

Terriza, A; Alvarez, R; Borras, A; Cotrino, J; Yubero, F; Gonzalez-Elipe, AR
Journal of Colloid and Interface Science, 376 (2012) 274-282


The wetting behavior of fluorocarbon materials has been studied with the aim of assessing the influence of the surface chemical composition and surface roughness on the water advancing and receding contact angles. Diamond like carbon and two fluorocarbon materials with different fluorine content have been prepared by plasma enhanced chemical vapor deposition and characterized by X-ray photoemission, Raman and FT-IR spectroscopies. Very rough surfaces have been obtained by deposition of thin films of these materials on polymer substrates previously subjected to plasma etching to increase their roughness. A direct correlation has been found between roughness and water contact angles while a superhydrophobic behavior (i.e., water contact angles higher than 150° and relatively low adhesion energy) was found for the films with the highest fluorine content deposited on very rough substrates. A critical evaluation of the methods currently used to assess the roughness of these surfaces by atomic force microscopy (AFM) has evidenced that calculated RMS roughness values and actual surface areas are quite dependent on both the scale of observation and image resolution. A critical discussion is carried out about the application of the Wenzel model to account for the wetting behavior of this type of surfaces.

June, 2012 | DOI: 10.1016/j.jcis.2012.03.010

Investigation of the growth mechanisms of a-CH x coatings deposited by pulsed reactive magnetron sputtering

Lopez-Santos, C; Colaux, JL; Gonzalez, JC; Lucas, S
Journal of Physical Chemistry C, 116 (2012) 12017-12026


The study of the growth mechanisms of amorphous hydrogenated carbon coatings (a-CH x) deposited by reactive pulsed magnetron discharge in Ar + C 2H 2, Ar + H 2, and Ar + C 2H 2 + H 2 low-pressure atmospheres is presented in this work. Hydrogen-containing species of the reactant gas affect the microstructure and surface properties of the a-CH x thin films. The dynamic scaling theory has been used to relate the main reactive species involved in the deposition process to the growth mechanisms of the thin film by means of the analysis of the roughness evolution. Anomalous scaling effects have been observed in smooth a-CH x coatings. Dynamic scaling exponents α, β, and z indicate a general growth controlled by surface diffusion mechanisms. Hydrogen species have an influence on the lateral growth of the a-CH x coatings and are involved in the development of a polymeric-like structure. Meanwhile, hydrocarbon species promote the generation of higher aggregates, which increases the roughness of a more sp 2 clustering structure of the a-CH x coating.

June, 2012 | DOI: 10.1021/jp300697s

Weakly Interacting Molecular Layer of Spinning C60 Molecules on TiO2 (110) Surfaces

Sanchez-Sanchez, C; Lanzilotto, V; Gonzalez, C; Verdini, A; de Andres, PL; Floreano, L; Lopez, MF; Martin-Gago, JA
Chemistry-A European Journal, 18 (2012) 7382-7387


The adsorption of C60, a typical acceptor organic molecule, on a TiO2 (110) surface has been investigated by a multitechnique combination, including van der Waals density functional calculations. It is shown that the adsorbed molecules form a weakly interacting molecular layer, which sits on the fivefold-coordinated Ti that is confined between the prominent bridging oxygen rows (see figure).

June, 2012 | DOI: 10.1002/chem.201200627

Correlation lengths, porosity and water adsorption in TiO2 thin films prepared by glancing angle deposition

Gonzalez-Garcia, L; Parra-Barranco, J; Sanchez-Valencia, JR; Barranco, A; Borras, A; Gonzalez-Elipe, AR; Garcia-Gutierrez, MC; Hernandez, JJ; Rueda, DR; Ezquerra, TA
Nanotechnology, 23 (2012) 205701


This paper reports a thorough microstructural characterization of glancing angle deposited (GLAD) TiO 2 thin films. Atomic force microscopy (afm), grazing-incidence small-angle x-ray scattering (GISAXS) and water adsorption isotherms have been used to determine the evolution of porosity and the existence of some correlation distances between the nanocolumns constituting the basic elements of the films nanostructure. It is found that the deposition angle and, to a lesser extent, the film thickness are the most important parameters controlling properties of the thin film. The importance of porosity and some critical dimensions encountered in the investigated GLAD thin films is highlighted in relation to the analysis of their optical properties when utilized as antireflective coatings or as hosts and templates for the development of new composite materials.

May, 2012 | DOI: 10.1088/0957-4484/23/20/205701

Tuning liver stiffness against tumours: An in vitro study using entrapped cells in tumour-like microcapsules

Leal-Egana, A; Fritsch, A; Heidebrecht, F; Diaz-Cuenca, A; Nowicki, M; Bader, A; Kas, J
Journal of the mechanical behavior of biomedical materials, 9 (2012) 113-121


Liver fibrosis is a reversible pathology characterized by the up-regulated secretion and deposition of ECM proteins and inhibitors of metalloproteinases, which increase the stiffness and viscosity of this organ. Since recent studies have shown that fibrosis preceded the generation of hepatocellular carcinomas, we hypothesize that liver fibrosis could play a role as a mechanism for restricting uncontrolled cell proliferation, inducing the mortality of cancer cells and subsequent development of primary tumours.

With this purpose, in this work we analysed in vitro how the modulation of stiffness can influence proliferation, viability and aggregation of hepatocarcinoma cells (HepG(2)) embedded in 3D micromilieus mimicking values of elasticity of fibrotic liver tissues.

Experiments were performed by immobilizing up to 10 HepG(2) cells within microcapsules made of 0.8%, 1.0% and 1.4% w/v alginate which, besides having values of elasticity from the lower-healthy to the upper-fibrotic range liver tissues, lacked domains for proteases, mimicking the micromilieu existing in hepatic primary tumours.

Our results show that entrapped cells exhibited a short duplication phase followed by an irreversible decay stage, in which cell mortality could be mediated by two mechanisms: mechanical stress, in the case of cells entrapped in a stiffer micromilieu; and mass transfer limitations produced by pore coarsening at the interface cell-matrix, in softer micromilieus.

According to the authors' knowledge, this work represents the first attempt to elucidate the role of liver fibrosis during Hepatocarcinoma pathologies, suggesting that the generation of a non-biodegradable and mechanically unfavourable environment surrounding cancer cells could control the proliferation, migration of metastatic cells and the subsequent development of primary tumours.

May, 2012 | DOI: 10.1016/j.jmbbm.2012.01.013

Attenuation lengths of high energy photoelectrons in compact and mesoporous SiO2 films

Ferrer, FJ; Gil-Rostra, J; Gonzalez-Garcia, L; Rubio-Zuazo, J; Romero-Gomez, P; Lopez-Santos, MC; Yubero, F
Surface Science, 606 (2012) 820-824


We have experimentally evaluated attenuation lengths (AL) of photoelectrons traveling in compact and micro and mesoporous (∼ 45% voids) SiO 2 thin films with high (8.2-13.2 keV) kinetic energies. The films were grown on polished Si(100) wafers. ALs were deduced from the intensity ratio of the Si 1s signal from the SiO 2 film and Si substrate using the two-peaks overlayer method. We obtain ALs of 15-22 nm and 23-32 nm for the compact and porous SiO 2 films for the range of kinetic energies considered. The observed AL values follow a power law dependence on the kinetic energy of the electrons where the exponent takes the values 0.81 ± 0.13 and 0.72 ± 0.12 for compact and porous materials, respectively.

May, 2012 | DOI: 10.1016/j.susc.2012.01.017

Plasma deposition of perylene-adamantane nanocomposite thin films for NO 2 room-temperature optical sensing

Aparicio, FJ; Blaszczyk-Lezak, I; Sanchez-Valencia, JR; Alcaire, M; Gonzalez, JC; Serra, C; Gonzalez-Elipe, AR; Barranco, A
Journal of Physical Chemistry C, 116 (2012) 8731-8740


This work reports the preparation, by a new remote assisted plasma deposition process, of luminescent nanocomposite thin films consisting of an insoluble organic matrix where photonically active perylene molecules are embedded. The films are obtained by the remote plasma deposition of adamantane and perylene precursor molecules. The results show that the adamantane precursor is very effective to improve the perylene–adamantane nanocomposite transparency in comparison with plasma deposited perylene films. The plasma deposited adamantane films have been characterized by secondary-ion mass spectrometry and FT-IR spectroscopy. These techniques and atomic force microscopy (AFM) have been also used for the characterization of the nanocomposite films. Their optical properties (UV–vis absorption, fluorescence, and refractive index) have been also determined and their sensing properties toward NO2 studied. It is found that samples with the perylene molecules embedded within the transparent plasma deposited matrix are highly sensitive toward this gas and that the sensitivity of the films can be adjusted by modifying the aggregation state of the perylene molecules, as determined by the analysis of their fluorescence spectra. By monitoring the fluorescence emission of these films, it has been possible to detect a NO2 concentration as low as 0.5 ppm in air at room temperature. Because of their chemical stability and transparency in the UV region, the remote plasma deposited adamantane thin films have revealed as an optimum host matrix for the development of photonically active composites for sensing applications.

April, 2012 | DOI: 10.1021/jp209272s

Self-assembly at room temperature of thermally stable discrete and extended oligomers of polycyclic aromatics on Ag(100): induced dipoles and cooperative effects

Papageorgiou, AC; Alavi, A; Lambert, RM
Chemical Communications, 48 (2012) 3394-3396


Thermally stable nanoarchitectures are realized on the Ag(100) surface by self-assembly of asymmetrically substituted arenes. The process is instigated by adsorption-induced molecule → surface charge transfer that gives rise to in-plane dipole moments. Observation and calculation indicate that cooperative interactions further enhance the stability of these polarizable systems.

April, 2012 | DOI: 10.1039/c2cc17728e

Influence of plasma-generated negative oxygen ion impingement on magnetron sputtered amorphous SiO2 thin films during growth at low temperatures

Macias-Montero, M; Garcia-Garcia, FJ; Alvarez, R; Gil-Rostra, J; Gonzalez, JC; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A
Journal of Applied Physics, 111 (2012) 054312 (6 pages)


Growth of amorphous SiO2 thin films deposited by reactive magnetron sputtering at low temperatures has been studied under different oxygen partial pressure conditions. Film microstructures varied from coalescent vertical column-like to homogeneous compact microstructures, possessing all similar refractive indexes. A discussion on the process responsible for the different microstructures is carried out focusing on the influence of (i) the surface shadowing mechanism, (ii) the positive ion impingement on the film, and (iii) the negative ion impingement. We conclude that only the trend followed by the latter and, in particular, the impingement of O- ions with kinetic energies between 20 and 200 eV, agrees with the resulting microstructural changes. Overall, it is also demonstrated that there are two main microstructuring regimes in the growth of amorphous SiO2 thin films by magnetron sputtering at low temperatures, controlled by the amount of O2 in the deposition reactor, which stem from the competition between surface shadowing and ion-induced adatom surface mobility.

March, 2012 | DOI: 10.1063/1.3691950

Quantification of low levels of fluorine content in thin films

Ferrer, FJ; Gil-Rostra, J; Terriza, A; Rey, G; Jimenez, C; Garcia-Lopez, J; Yubero, F
Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms, 274 (2012) 65-69


Fluorine quantification in thin film samples containing different amounts of fluorine atoms was accomplished by combining proton-Rutherford Backscattering Spectrometry (p-RBS) and proton induced gamma-ray emission (PIGE) using proton beams of 1550 and 2330 keV for p-RBS and PIGE measurements, respectively. The capabilities of the proposed quantification method are illustrated with examples of the analysis of a series of samples of fluorine-doped tin oxides, fluorinated silica, and fluorinated diamond-like carbon films. It is shown that this procedure allows the quantification of F contents as low as 1 at.% in thin films with thicknesses in the 100-400 nm range.

March, 2012 | DOI: 10.1016/j.nimb.2011.11.042

An international round-robin calibration protocol for nanoindentation measurements

Cabibbo, M; Ricci, P; Cecchini, R; Rymuza, Z; Sullivan, J; Dub, S; Cohen, S
Micron, 43 (2012) 215-222


Nanoindentation has become a common technique for measuring the hardness and elastic–plastic properties of materials, including coatings and thin films. In recent years, different nanoindenter instruments have been commercialised and used for this purpose. Each instrument is equipped with its own analysis software for the derivation of the hardness and reduced Young's modulus from the raw data. These data are mostly analysed through the Oliver and Pharr method. In all cases, the calibration of compliance and area function is mandatory. The present work illustrates and describes a calibration procedure and an approach to raw data analysis carried out for six different nanoindentation instruments through several round-robin experiments. Three different indenters were used, Berkovich, cube corner, spherical, and three standardised reference samples were chosen, hard fused quartz, soft polycarbonate, and sapphire. It was clearly shown that the use of these common procedures consistently limited the hardness and reduced the Young's modulus data spread compared to the same measurements performed using instrument-specific procedures. The following recommendations for nanoindentation calibration must be followed: (a) use only sharp indenters, (b) set an upper cut-off value for the penetration depth below which measurements must be considered unreliable, (c) perform nanoindentation measurements with limited thermal drift, (d) ensure that the load–displacement curves are as smooth as possible, (e) perform stiffness measurements specific to each instrument/indenter couple, (f) use Fq and Sa as calibration reference samples for stiffness and area function determination, (g) use a function, rather than a single value, for the stiffness and (h) adopt a unique protocol and software for raw data analysis in order to limit the data spread related to the instruments (i.e. the level of drift or noise, defects of a given probe) and to make the H and Er data intercomparable.

February, 2012 | DOI: 10.1016/j.micron.2011.07.016

Magnetron sputtered a-SiO xN y thin films: A closed porous nanostructure with controlled optical and mechanical properties

Godinho, V; Rojas, TC; Fernandez, A
Microporous and Mesoporous Materials, 149 (2012) 142-146


Amorphous silicon oxynitride coatings with similar composition and different closed porosity were prepared by magnetron sputtering. Pores size, shape and distribution were evaluated by scanning electron microscopy and transmission electron microscopy. Raman and EELS analysis proved that the pores are filled with molecular nitrogen trapped during deposition. The mechanical properties evaluated by nanoindentation shows that the presence of closed nano-porosity does not compromise the mechanical integrity of these coatings. The introduction of closed porosity is shown as a good strategy for obtaining lower dielectric constant silicon oxynitride coatings with similar composition while keeping the good mechanical properties (∼13 GPa) characteristic of this type of coatings. The presence of close porosity gives also a good stability of coatings properties as compared to open porosity microstructures where gas phase in contact with the coatings can affect coatings properties.

February, 2012 | DOI: 10.1016/j.micromeso.2011.08.018

Electrochromic Behavior of WxSiyOz Thin Films Prepared by Reactive Magnetron Sputtering at Normal and Glancing Angles

Gil-Rostra, J; Cano, M; Pedrosa, JM; Ferrer, FJ; Garcia-Garcia, F; Yubero, F; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 4 (2012) 628-638


This work reports the synthesis at room temperature of transparent and colored WxSiyOz thin films by magnetron sputtering (MS) from a single cathode. The films were characterized by a large set of techniques including X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), Fourier transform infrared (FT-IR), and Raman spectroscopies. Their optical properties were determined by the analysis of the transmission and reflection spectra. It was found that both the relative amount of tungsten in the W–Si MS target and the ratio O2/Ar in the plasma gas were critical parameters to control the blue coloration of the films. The long-term stability of the color, attributed to the formation of a high concentration of W5+ and W4+ species, has been related with the formation of W–O–Si bond linkages in an amorphous network. At normal geometry (i.e., substrate surface parallel to the target) the films were rather compact, whereas they were very porous and had less tungsten content when deposited in a glancing angle configuration. In this case, they presented outstanding electrochromic properties characterized by a fast response, a high coloration, a complete reversibility after more than one thousand cycles and a relatively very low refractive index in the bleached state.

February, 2012 | DOI: 10.1021/am2014629

Nanoecotoxicity effects of engineered silver and gold nanoparticles in aquatic organisms

Lapresta-Fernandez, A; Fernandez, A; Blasco, J
TrAC Trends in Analytical Chemistry, 32 (2012) 40-59


Engineered nanoparticles (ENPs) are increasingly being incorporated into commercial products. A better understanding is required of their environmental impacts in aquatic ecosystems.

This review deals with the ecotoxicity effects of silver and gold ENPs (AgNPs and AuNPs) in aquatic organisms, and considers the means by which these ENPs enter aquatic environments, their aggregation status and their toxicity. Since ENPs are transported horizontally and vertically in the water column, we discuss certain factors (e.g., salinity and the presence of natural organic materials), as they cause variations in the degree of aggregation, size range and ENP toxicity. We pay special attention to oxidative stress induced in organisms by ENPs.

We describe some of the main analytical methods used to determine reactive oxygen species, antioxidant enzyme activity, DNA damage, protein modifications, lipid peroxidation and relevant metabolic activities. We offer an overview of the mechanisms of action of AgNPs and AuNPs and the ways that relevant environmental factors can affect their speciation, agglomeration or aggregation, and ultimately their bio-availability to aquatic organisms.

Finally, we discuss similarities and differences in the adverse effects of ENPs in freshwater and salt-water systems.

February, 2012 | DOI: 10.1016/j.trac.2011.09.007

Microwave-Assisted Synthesis and Luminescence of Mesoporous REDoped YPO4 (RE = Eu, Ce, Tb, and Ce plus Tb) Nanophosphors with Lenticular Shape

Rodriguez-Liviano, S; Aparicio, FJ; Rojas, TC; Hungria, AB; Chinchilla, LE; Ocana, M
Crystal Growth and Design, 12 (2012) 635-645


Mesoporous tetragonal RE:YPO 4 nanophosphors (RE = Eu, Ce, Tb, and Ce + Tb) with a lenticular morphology, narrow size distribution, and high surface area have been prepared by an homogeneous precipitation procedure consisting of aging, at low temperature (80-120 °C) in a microwave oven, ethylene glycol solutions containing only yttrium acetylacetonate and phosphoric acid. This synthesis method involves important advantages such as its simplicity, rapidness (reaction time = 7 min), and high reaction yields. The mechanism of nanoparticle growth has been also addressed finding that the lenticular nanoparticles are formed through an ordered aggregation of smaller entities, which explains their porosity. In all cases, the doping levels were systematically varied in order to optimize the nanophosphors luminescence. All optimum nanophosphors presented a high luminescence quantum yield (QY). In particular, for the Eu and Tb doped systems, the obtained QY values (60% for Eu and 80% for Tb) were the highest so far reported for this kind of nanomaterial. The morphological, microstructural, and luminescent properties of these nanophosphors and their dispersibility in water make them suitable for biomedical applications.

February, 2012 | DOI: 10.1021/cg201358c

Public concern over ecotoxicology risks from nanomaterials: Pressing need for research-based information

Lapresta-Fernandez, A; Fernandez, A; Blasco, J
Environment International, 39 (2012) 148-149


[No abstract available]

February, 2012 | DOI: 10.1016/j.envint.2011.10.012

Adsorption Geometry Determines Catalytic Selectivity in Highly Chemoselective Hydrogenation of Crotonaldehyde on Ag(111)

Brandt, Katrin; Chiu, May E.; Watson, David J.; Tikhov, Mintcho S.; Lambert, Richard M.
Journal of Physical Chemistry C, 116 (2012) 4605-4611


The chemoselective hydrogenation of crotonaldehyde to crotyl alcohol was studied by temperature-programmed desorption/reaction, high-resolution XPS, and NEXAFS. The organic molecule adsorbed without decomposition, all three possible hydrogenation products were formed and desorbed, and the clean overall reaction led to no carbon deposition. Selectivities up to 95% were found under TPR conditions. The observed behavior corresponded well with selectivity trends previously reported for Ag/SiO2 catalysts, and the present findings permit a rationalization of the catalytic performance in terms of pronounced coverage-dependent changes in adsorption geometries of the reactant and the products. Thus, at low coverages, the C═O bond in crotonaldehyde lies almost parallel to the metal surface, whereas the C═C was appreciably tilted, favoring hydrogenation of the former and disfavoring hydrogenation of the latter. With increasing coverage of reactants, the C═C bond was forced almost parallel to the surface, rendering it vulnerable to hydrogenation, thus markedly decreasing selectivity toward formation of crotyl alcohol. Butanol formation was the result of an overall two-step process: crotonaldehyde → crotyl alcohol → butanol, further hydrogenation of the desired product crotyl alcohol being promoted at high hydrogen coverage due to the C═C bond in the unsaturated alcohol being driven from a tilted to a flat-lying geometry. Finally, an explanation is offered for the strikingly different behavior of Ag(111) and Cu(111) in the chemoselective hydrogenation of crotonaldehyde in terms of the different degrees of charge transfer from metal to C═O π bond, as suggested by C 1s XPS binding energies.

January, 2012 | DOI: 10.1021/jp208831h

Analysis and application of the theories that rationalize the crystalline structures of fluorite-related rare earth oxides

Lopez-Cartes, C; Perez-Omil, JA; Rodriguez-Izquierdo, JM; Calvino, JJ
Catalysis Today, 180 (2012) 161-180


The main current theories dealing with the crystalline structures of the fluorite related rare earth oxides, including those corresponding to reduced oxides, one based on the distribution of the coordination defect inside the fluorite structure, and the other which proposes the establishment of modular sequences constituted by modules with fluorite structure, are presented and comparatively explored in detail. Our in-depth analysis of both approximations indicates that they in fact provide smart and efficient rationalizations of the currently known intermediate rare earth oxides structures. We prove however that the strict application of the principles and rules proposed by each theory does not yield unique and unambiguous results for most of the members of the homologous series, as it has been claimed up to now. Moreover, the controversy about the reliability of these two, apparently different and competing, theories is definitely clarified and the exact equivalence of their structural predictions is demonstrated. Finally, we propose new extra systematization rules, not considered up to now in neither of these theoretical approaches, to overcome the observed limitations to properly rationalize the structure of this so technologically important family of oxides.

January, 2012 | DOI: 10.1016/j.cattod.2011.04.032

Influence of silver content on the tribomechanical behavior on Ag-TiCN bioactive coatings

Sanchez-Lopez, JC; Abad, MD; Carvalho, I; Galindo, RE; Benito, N; Ribeiro, S; Henriques, M; Cavaleiro, A; Carvalho, S
Surface and Coatings Technology, 206 (2012) 2192-2198


Surface modification of bulk materials used in biomedical applications has become an important prerequisite for better biocompatibility. In particular, to overcome the particle generation, low-wear coatings based on carbon (nitrogen) and containing antimicrobial elements such as silver are promising candidates. Thus, the present work explores the potentialities of silver-containing carbonitride-based (Ag-TiCN) thin films prepared by direct current unbalanced reactive magnetron sputtering. The silver content in the coatings was varied from 0 to 26.7at.% by changing the targets and the fraction of C 2H 2 and N 2 in the gas mixture with Ar. The obtained Ag-TiCN based coatings were characterized in terms of composition and microstructure. Mechanical and tribological properties of the films were studied by nanoindentation and reciprocating pin-on disk testing in a fetal bovine serum solution, respectively. Raman, scanning electron microscope and energy dispersive X-ray analysis was carried out in the contact region after tribological tests to obtain information about the friction mechanism. The cytotoxicity of the coatings was assessed by in vitro tests using fibroblast cells. The coatings comprised a mixture of TiC xN 1-x, Ag and a-C(N) x phases whose relative proportion varied depending on the Ag/Ti ratio. The mechanical, tribological and cytotoxicity properties were correlated with the chemical and phase composition. When the Ag/Ti ratios were below 0.20 (Ag contents <6.3at.%) the films resulted harder (~18GPa) with higher wear resistance (~10 -6mm 3/Nm), showing similar friction coefficient (~0.3) and good biocompatibility.

January, 2012 | DOI: 10.1016/j.surfcoat.2011.09.059

Analysis of multifunctional titanium oxycarbide films as a function of oxygen addition

Chappe, JM; Fernandes, AC; Moura, C; Alves, E; Barradas, NP; Martin, N; Espinos, JP; Vaz, F
Surface and Coatings Technology, 206 (2012) 2525-2534


Reactive magnetron sputtering was used to deposit titanium oxycarbide thin films. The overall set of results showed that the oxygen flow rate, and thus the composition of the atmosphere in the deposition chamber, controls the composition of the titanium oxycarbide thin films obtained by reactive sputtering. Rutherford Backscattering Spectroscopy analysis revealed the existence of three major types of films, indexed to their particular composition ratios. A detailed study by X-ray photoelectron spectroscopy was carried out in order to characterize the evolution of the Tisingle bondC, Csingle bondO and Csingle bondC bonds induced by the increase of the oxygen partial pressure, which was found to be closely related with the different zones of composition that were suggested. Micro-Raman spectroscopy and X-ray diffraction measurements allowed describing the complex nature of the film structure, namely in what concerns different phases and their evolution, texture phenomena and grain size evolution as a function of the particular composition and film types (different zones). Electrical conductivity revealed a transition from a metallic to a semi-conducting behavior as a function of the oxygen concentration in the films, in good agreement with the different zones that were suggested. Similarly, optical properties supported this gradual change and for oxygen contents higher than 67 at.%, the films exhibited typical reflectance of insulator materials (interferences) in the UV, visible and near IR regions.

January, 2012 | DOI: 10.1016/j.surfcoat.2011.11.005

Microstructure, composition and P-T conditions of rutile from diamondiferous gneiss of the Saxonian Erzgebirge, Germany

Escudero, A; Miyajima, N; Langenhorst, F
Chemie der erde-geochemistry, 72 (2012) 25-30


The chemical composition and microstructure of rutile grains in a ultra-high pressure metamorphic gneiss of the Saxonian Erzgebirge, Germany have been studied by Raman spectroscopy, SEM, EMPA and TEM. Rutile inclusions in garnet contain free dislocations, iron-enriched dislocations and exsolved ilmenite lamellae, while subgrain boundaries are observed in rutile grains of the rock matrix. The previously reported alpha-PbO2 type TiO2 phase could not be confirmed by our TEM observations. On the basis of Zr solubility in the rutile and the presence of microdiamonds, minimum metamorphic peak conditions of 3.95 GPa and 915 degrees C are estimated.

January, 2012 | DOI: 10.1016/j.chemer.2011.11.001

Aluminum incorporation in alpha-PbO2 type TiO2 at pressures up to 20 GPa

Escudero, A; Langenhorst, F
Physics of the Earth and Planetary Interiors, 190 (2012) 87-94


Aluminum incorporation into the high pressure polymorph of TiO2 with the structure of alpha-PbO2 has been studied from 10 to 20 GPa and 1300 degrees C by XRD, high-resolution Al-27 MAS-NMR and TEM. Al-doped alpha-PbO2 type TiO2 can be recovered at atmospheric pressure. Al2O3 solubility in alpha-PbO2 type TiO2 increases with increasing the synthesis pressure. The alpha-PbO2 type TiO2 polymorph is able to incorporate up to 35 wt.% Al2O3 at 13.6 GPa and 1300 degrees C, being the substitution of Ti4+ by Al3+ on normal octahedral sites and the formation of oxygen vacancies the mechanism of solubility. The transition to the higher pressure TiO2 polymorph with the ZrO2 baddeleyite structure, akaogiite, has not been observed in the quenched samples at room pressure. The microstructure of the recovered sample synthesized at 16 GPa and 1300 degrees C points to the existence of an intermediate non-quenchable aluminum titanium oxide phase at these conditions.

January, 2012 | DOI: 10.1016/j.pepi.2011.11.002

Nanoscale mechanically induced structural and electrical changes in Ge 2Sb 2Te 5 films

Cecchini, R; Benitez, JJ; Sanchez-Lopez, JC; Fernandez, A
Journal of Applied Physics, 111 (2012) 016101 (3 pages)


We demonstrate that the microstructure and electrical properties of Ge2Sb2Te5 films can be changed by a nanoscale mechanical process. Nanoscratching is used to define modified areas onto an as-deposited crystalline Ge2Sb2Te5 film. Scanning tunneling microscopy measurements show that the modified areas have a very low electrical conductivity. Micro-Raman measurements indicate that the mechanically induced microstructural changes are consistent with a phase transformation from crystalline to amorphous, which can be reversed by laser irradiation.

January, 2012 | DOI: 10.1063/1.3673592

Superhydrophobic supported Ag-NPs@ZnO-nanorods with photoactivity in the visible range

Macias-Montero, M; Borras, A; Saghi, Z; Romero-Gomez, P; Sanchez-Valencia, JR; Gonzalez, JC; Barranco, A; Midgley, P; Cotrino, J; Gonzalez-Elipe, AR
Journal of Materials Chemistry, 22 (2012) 1341-1346


In this article we present a new type of 1D nanostructures consisting of supported hollow ZnO nanorods (NRs) decorated with Ag nanoparticles (NPs). The 3D reconstruction by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) electron tomography reveals that the Ag NPs are distributed along the hollow interior of the ZnO NRs. Supported and vertically aligned Ag-NPs@ZnO-NRs grow at low temperature (135 °C) by plasma enhanced chemical vapour deposition on heterostructured substrates fabricated by sputtered deposition of silver on flat surfaces of Si wafers, quartz slides or ITO. The growth mechanisms of these structures and their wetting behavior before and after visible light irradiation are critically discussed. The as prepared surfaces are superhydrophobic with water contact angles higher than 150°. These surfaces turn into superhydrophilic with water contact angles lower than 10° after prolonged irradiation under both visible and UV light. The evolution rate of the wetting angle and its dependence on the light characteristics are related to the nanostructure and the presence of silver embedded within the ZnO NRs.

January, 2012 | DOI: 10.1039/C1JM13512K


Comments on "an essay on contact angle measurements": Determination of surface roughness and modeling of the wetting behavior

Terriza, A; Alvarez, R; Yubero, F; Borras, A; Gonzalez-Elipe, AR
Plasma Processes and Polymers, 8 (2011) 998-1002


This commentary addresses the problem of determining surface roughness values and their use to assess the wetting behavior of surfaces. For very rough surfaces it is shown that depending on the observation scale by atomic force microscopy (AFM) quite different RMS roughness values can be obtained and that only the values taken at saturation can be used for properly describing the roughness of the examined materials. This effect has clear consequences when trying to apply wetting models to account for the influence of roughness on contact angles. These ideas are discussed with examples taken from rough polymer surfaces subjected to plasma etching. Debate - Discussion: To account for the wetting behavior of real surfaces within the Wenzel and similar models only surface roughness values determined at saturation can be used. This implies to check different observation areas by AFM and to choose the RMS roughness values once a maximum value of this parameter has been reached.

November, 2011 | DOI: 10.1002/ppap.201100081

Electrical properties and applications of carbon based nanocomposite materials: An overview

Sanjinés, R., Abad, M.D., Vâju, C., Smajda, R., Mionić, M., Magrez, A.
Surface and Coatings Technology, 206 (2011) 727-733


The allotropic forms of carbon (amorphous and polycrystalline graphite, carbon black, fullerenes, nanotubes, graphene) exhibit a large variety of charge transport properties which have been stimulating fundamental and applied research for the development of new devices based on micro and nano-sized electronic systems. Carbon based nanocomposites offer the possibility to improve the device performances and to develop novel multifunctional material systems by combining the properties of each individual phase. In this paper we review the electrical properties of carbon materials and some of the most exciting carbon based nanocomposites, as well as their potential technological applications. First, the electrical properties of amorphous and polycrystalline graphitic materials and those of their related nanocomposites materials are discussed. Second, an overview of the state-of-art on research and applications of carbon nanotube-based composites is presented. Third, we discuss briefly the emerging area of research related to graphene materials. Finally, the electrical properties and applications of conducting carbon black aggregates and carbon black/polymer composites are overviewed.

November, 2011 | DOI: 10.1016/j.surfcoat.2011.01.025

Soft plasma processing of organic nanowires: a route for the fabrication of 1D organic heterostructures and the template synthesis of inorganic 1D nanostructures

Maria Alcaire, Juan R. Sanchez-Valencia, Francisco J. Aparicio, Zineb Saghi, Juan C. Gonzalez-Gonzalez, Angel Barranco, Youssef Oulad Zian, Agustin R. Gonzalez-Elipe, Paul Midgley, Juan P. Espinos, Pierangelo Groening and Ana Borras
Nanoscale, 3 (2011) 4554-4559


Hierarchical (branched) and hybrid metal-NPs/organic supported NWs are fabricated through controlled plasma processing of metalloporphyrin, metallophthalocyanine and perylene nanowires. The procedure is also applied for the development of a general template route for the synthesis of supported metal and metal oxide nanowires.

November, 2011 | DOI: 10.1039/C1NR11001B

Enhanced gas sensing performance of TiO2 functionalized magneto-optical SPR sensors

M.G. Manera, G. Montagna, E. Ferreiro-Vila, L. González-García, J.R. Sánchez-Valencia, A.R. González-Elipe, A.Cebollada, J.M. Garcia-Martin, A. Garcia-Martin, G. Armelles and R. Rella
Journal of Materials Chemistry, 21 (2011) 16049-16056


Porous TiO2 thin films deposited by glancing angle deposition are used as sensing layers to monitor their sensing capabilities towards Volatile Organic Compounds both in a standard Surface Plasmon Resonance (SPR) sensor and in Magneto-Optical Surface Plasmon Resonance (MO-SPR) configuration in order to compare their sensing performances. Here our results on the enhanced sensing capability of these TiO2 functionalized MO-SPR sensors with Au/Co/Au transducers with respect to traditional SPR gas sensors are presented.

October, 2011 | DOI: 10.1039/c1jm11937k

Magnetic and fluorescent core-shell nanoparticles for ratiometric pH sensing

Lapresta-Fernández, A., Doussineau, T., Dutz, S., Steiniger, F., Moro, A.J., Mohr, G.J.
Nanotechnology, 22 (2011), Article number 415501


This paper describes the preparation of nanoparticles composed of a magnetic core surrounded by two successive silica shells embedding two fluorophores, showing uniform nanoparticle size (50-60nm in diameter) and shape, which allow ratiometric pH measurements in the pH range 5-8. Uncoated iron oxide magnetic nanoparticles (&#8764;10nm in diameter) were formed by the coprecipitation reaction of ferrous and ferric salts. Then, they were added to a water-in-oil microemulsion where the hydrophilic silica shells were obtained through hydrolysis and condensation of tetraethoxyorthosilicate together with the corresponding silylated dye derivatives - a sulforhodamine was embedded in the inner silica shell and used as the reference dye while a pH-sensitive fluorescein was incorporated in the outer shell as the pH indicator. The magnetic nanoparticles were characterized using vibrating sample magnetometry, dynamic light scattering, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The relationship between the analytical parameter, that is, the ratio of fluorescence between the sensing and reference dyes versus the pH was adjusted to a sigmoidal fit using a Boltzmann type equation giving an apparent pKa value of 6.8. The fluorescence intensity of the reference dye did not change significantly (&#8764;3.0%) on modifying the pH of the nanoparticle dispersion. Finally, the proposed method was statistically validated against a reference procedure using samples of water and physiological buffer with 2% of horse serum, indicating that there are no significant statistical differences at a 95% confidence level.

October, 2011 | DOI: 10.1088/0957-4484/22/41/415501

Colored semi-transparent Cu-Si oxide thin films prepared by magnetron sputtering

Gil-Rosta, J; Yubero, F; Fernandez, R; Vilajoana, T; Artus, P; Dursteler, JC; Cotrino, J; Ortega, I; Gonzalez-Elipe, AR
Optical Material Express, 1 (2011) 1100-1112


Colored semi-transparent Cu-Si oxide thin films have been prepared by reactive magnetron sputtering from a single cathode of copper-silicon composition. Thin films of different composition and optical response were obtained by changing process parameters like the relative amount of copper in the target and the O2/Ar mixture of the reactive plasma gas. The film characteristics were analyzed by several techniques. Their optical properties (refractive index, absorption coefficient, color) have been correlated with the process parameters used in the film preparation as well as with the film stoichiometry and chemistry.

September, 2011 | DOI: 10.1364/OME.1.001100

Aligned TiO(2) nanocolumnar layers prepared by PVD-GLAD for transparent dye sensitized solar cells

Gonzalez-Garcia, L; Gonzalez-Valls, I; Lira-Cantu, M; Barranco, A; Gonzalez-Elipe, AR
Energy and Environmental Science, 4 (2011) 3426-3435


Transparent thin film electrodes made of vertically aligned nanocolumns of TiO2 with well-controlled oblique angles were grown by physical vapor deposition at glancing incidence (PVD-GLAD). For an electrode thickness of 500 nm, we report a 40% variation on solar cell efficiency (from 0.6% to 1.04%) when the deposition angle was modified between 60° and 85°. Transparent thicker films with higher surface area deposited at the optimal angle of 70° were grown with a zigzag morphology which confers high mechanical strength to the thin films. Using this topology, the application of an electrode thickness of 3 m in a DSC resulted in a power conversion efficiency of 2.78% maintaining electrode transparency.

September, 2011 | DOI: 10.1039/C0EE00489H

Theoretical and experimental characterization of TiO2 thin films deposited at oblique angles

Álvarez, R., González-García, L., Romero-Gómez, P., Rico, V., Cotrino, J., Gonzalez-Elipe, A.R., Palmero, A.
Journal of Physics D: Applied Physics, 44 (2011) Article number 385302


The microstructural features of amorphous TiO2 thin films grown by the electron beam physical vapour deposition technique at oblique angles have been experimentally and theoretically studied. The microstructural features of the deposited films were characterized by considering both the column tilt angle and the increase in the column thickness with height. A Monte Carlo model of film growth has been developed that takes into account surface shadowing, short-range interaction between the deposition species and the film surface, as well as the angular broadening of the deposition flux when arriving at the substrate. The good match between simulations and experimental results indicates the importance of these factors in the growth and microstructural development of thin films deposited at oblique angles.

September, 2011 | DOI: 10.1088/0022-3727/44/38/385302

Aspects of heterogeneous enantioselective catalysis by metals

Kyriakou, G., Beaumont, S.K., Lambert, R.M.
Langmuir, 27 (2011) 9687-9695


Some aspects of metal-catalyzed heterogeneous enantioselective reactions are reviewed with specific reference to four different systems where the phenomena that control enantioselection appear to be very different. In the case of glucose electro-oxidation, it is clear that any intrinsic chirality present at the metal surface plays a vital role. With &#945;-keto hydrogenation, achiral surfaces modified by the adsorption of chiral agents become effective enantioselective catalysts and the formation of extended arrays of chiral species appears not to be of importance: instead a 1:1 docking interaction controlled by hydrogen bonding between the adsorbed chiral modifier and the prochiral reactant determines the outcome. Hydrogen bonding also plays a central role in &#946;-ketoester hydrogenation, but here fundamental studies indicate that the formation of ordered arrays involving the reactant and chiral ligand is of importance. Asymmetric C=C hydrogenation, though relatively little studied, has the potential for major impact in synthetic organic chemistry both on the laboratory scale and in the manufacture of fine chemicals and pharmaceuticals. The structural attributes that determine whether a given chiral ligand is effective have been identified; the ability to form strong covalent bonds with the metal surface while also resisting hydrogenation and displacement by the strongly adsorbing reactant under reaction conditions is an essential necessary condition. Beyond this, ligand rigidity in the vicinity of the chirality center coupled with resistance to SAM formation is a critically important factor whose absence results in racemic chemistry.

August, 2011 | DOI: 10.1021/la200009w

Boron Compounds as Stabilizers of a Complex Microstructure in a Co-B-based Catalyst for NaBH4 Hydrolysis

Arzac, G.M., Rojas, T.C., Fernández, A.
ChemCatChem, 3 (2011) 1305-1313


Co-B-based materials are widely used as catalysts for hydrogen generation through sodium borohydride self-decomposition. In the mid 1990s, the aqueous and organic chemistry involved in Co-B synthesis and handling was studied. Nevertheless, the exact microstructure of these catalysts has remained unsolved. Herein we present an exhaustive study which shows a new and complete microstructural view of a Co-B-based material together with the chemistry of the cobalt and boron involved. By using nanoscale-resolution microscopy and spectroscopy techniques, we have elucidated the role of boron compounds as stabilizers in a complex microstructure, which also explains its high catalytic performance and long-term stability. The catalyst is proposed to be made up of 1-3nm hcp Co0 nanoparticles embedded in amorphous CoxB (x=1, 2, 3), CoxOy, Co(BO2)2, and B2O3 phases alternatively or all together. All of these amorphous phases protect the nanocrystalline metallic core from growth and oxidation.

August, 2011 | DOI: 10.1002/cctc.201100101

Microstructure and chemical bonding of DLC films deposited on ACM rubber by PACVD

Martinez-Martinez, D., Schenkel, M., Pei, Y.T., Sánchez-López, J.C., De Hosson, J.T.H.M.
Surface and Coatings Technology, 205 (2011) S75-S78


The microstructure and chemical bonding of DLC films prepared by plasma assisted chemical vapor deposition on acrylic rubber (ACM) are studied in this paper. The temperature variation produced by the ion impingement during plasma cleaning and subsequent film deposition was used to modify the film microstructure by controlling the different degrees of strain applied to the substrate. The film microstructure is studied by top view and cross sectional SEM. The observed patch sizes are correlated with the variation of temperature that occurred during deposition. Finally, the chemical bonding of the samples is studied by Raman spectroscopy. All the samples show similar spectra regardless the bias voltage used.

July, 2011 | DOI: 10.1016/j.surfcoat.2011.02.067

Bacterial adherence on UHMWPE with vitamin E: an in vitro study

E. Gómez-Barrena, J. Esteban, D. Molina-Manso, H. Adames, M.J. Martínez-Morlanes, A. Terriza, F. Yubero and J. A. Puértolas
Journal of Materials Science: Materials in Medicine, 22 (2011) 1701-1706


Orthopaedic materials may improve its capacity to resist bacterial adherence, and subsequent infection. Our aim was to test the bacterial adherence to alpha-tocopherol (frequently named vitamin E, VE) doped or blended UHMWPE with S. aureus and S. epidermidis, compared to virgin material. Collection strains and clinical strains isolated from patients with orthopaedic infections were used, with the biofilm-developing ability as a covariable. While collection strains showed significantly less adherence to VE-UHMWPE, some clinical strains failed to confirm this effect, leading to the conclusion that VE doped or blended UHMWPE affects the adherence of some S. epidermidis and S. aureus strains, independently of the concentration in use, but the results showed important intraspecies differences and cannot be generalized.

July, 2011 | DOI: 10.1007/s10856-011-4340-5

Identification of Ternary Phases in TiBC/a-C Nanocomposite Thin Films: Influence on the Electrical and Optical Properties

Manuel David Abad, Rosendo Sanjinés, Jose Luis Endrino, Raúl Gago, Joakim Andersson, Juan Carlos Sánchez-López
Plasma Processes and Polymers, 8 (2011) 579-588


The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB2 (60:40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiBxCy) or mixed binary (TiB2 and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K- and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiBxCy compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiBxCy phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.

July, 2011 | DOI: 10.1002/ppap.201000182

Mechanical, microstructural and oxidation properties of reactively sputtered thin Cr-N coatings on steel

Cecchini, R., Fabrizi, A., Cabibbo, M., Paternoster, C., Mavrin, B.N., Denisov, V.N., Novikova, N.N., Haïdopoulo, M.
Thin Solid Films, 519 (2011) 6515-6521


Thin (40 nm and 160 nm) CrN coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N2 flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr2N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N2. Also intrinsic coating hardness is influenced by both N2 flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties.

July, 2011 | DOI: 10.1016/j.tsf.2011.04.115

Comparative investigation of Al- and Cr-doped TiSiCN coatings

D.V. Shtansky, K.A. Kuptsov, Ph.V. Kiryukhantsev-Korneev, A.N. Sheveiko, A. Fernandez and M.I. Petrzhik
Surface and Coatings Technology, 205 (2011) 4640-4648


The aim of this work was a comparative investigation of the structure and properties of Al- and Cr-doped TiSiCN coatings deposited by magnetron sputtering of composite TiAlSiCN and TiCrSiCN targets produced by self-propagating high-temperature synthesis method. Based on X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy data, the Al- and Cr-doped TiSiCN coatings possessed nanocomposite structures (Ti,Al)(C,N)/a-(Si,C) and (Ti,Cr)(C,N)/a-SiCxNy/a-C with cubic crystallites embedded in an amorphous matrix. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum at 1000, 1100, 1200, and 1300°C or in air at 1000°C for 1h. The results obtained show that the hardness of the Al-doped TiSiCN coatings increased from 41 to 46GPa, reaching maximum at 1000°C, and then slightly decreased to 38GPa at 1300°C. The Cr-doped TiSiCN coatings demonstrated high thermal stability up to 1100°C with hardness above 34GPa. Although both Al- and Cr-doped TiSiCN coatings possessed improved oxidation resistance up to 1000°C, the TiAlSiCN coatings were more oxidation resistant than their TiCrSiCN counterparts. The TiCrSiCN coatings showed better tribological characteristics both at 25 and 700°C and superior cutting performance compared with the TiAlSiCN coatings.

June, 2011 | DOI: 10.1016/j.surfcoat.2011.04.012

Surface-modified Pd and Au nanoparticles for anti-wear applications

J.C. Sánchez-López, M.D. Abad, L. Kolodziejczyk, E. Guerrero and A. Fernández
Tribology International, 44 (2011) 720-726


This work reports the employment of metallic nanoparticles (palladium and gold) with a mean particle size of 2.2 nm surface-protected with tetraalkylammonium and alkanethiolate chains, respectively, as lubricant additives. Dispersions of both types of nanoparticles (5 wt%) are prepared using tetrabutylammonium acetate (TBA) and paraffin as base oils, respectively. The tribological properties are then evaluated by a ball-on-disc tribometer at two different loads (7 and 15 N) with excellent results: friction (<0.1), wear rate (not, vert, similar10&#8722;10 mm3/Nm). The excellent anti-wear response is explained by the formation of a metal-containing transfer film and their action as counterface spacers avoiding direct contact.

June, 2011 | DOI: 10.1016/j.triboint.2009.12.013

Surface-functionalized fluorescent silica nanoparticles for the detection of ATP

Moro, AJ; Schmidt, J; Doussineau, T; Lapresta-Fernandez, A; Wegener, J; Mohr, GJ
Chemical Communications, 47 (2011) 6066-6068


The design of two-dyed fluorescent silica nanoparticles for ATP detection is presented. The indicator dye possesses a dipicolyl-amine (DPA) unit complexed with Zn(ii) as a receptor function for ATP while a rhodamine derivative is used as the reference dye. The nanoparticles were fully characterized regarding analytical performance, morphology and cytocompatibility.

June, 2011 | DOI: 10.1039/C1CC10419E

Determination of Pore Size Distribution at the Cell-Hydrogel Interface

Leal-Egana, A., Dietrich-Braumann, U., Diaz-Cuenca, A., Nowicki, M., Bader, A.
Journal of Nanobiotechnology, 9 (2011) Page 24


Analyses of the pore size distribution in 3D matrices such as the cell-hydrogel interface are very useful when studying changes and modifications produced as a result of cellular growth and proliferation within the matrix, as pore size distribution plays an important role in the signaling and microenvironment stimuli imparted to the cells. However, the majority of the methods for the assessment of the porosity in biomaterials are not suitable to give quantitative information about the textural properties of these nano-interfaces.

May, 2011 | DOI: 10.1186/1477-3155-9-24

Supported plasma-made 1D heterostructures: Perspectives and applications

Borras, A; Macias-Montero, M; Romero-Gomez, P; Gonzalez-Elipe, AR
Journal of Physics D: Applied Physics, 44 (2011) 174016


Plasma-related methods have been widely used in the fabrication of carbon nanotubes and nanofibres (NFs) and semiconducting inorganic nanowires (NWs). A natural progression of the research in the field of 1D nanostructures is the synthesis of multicomponent NWs and NFs. In this paper we review the state of the art of the fabrication by plasma methods of 1D heterostructures including applications and perspectives. Furthermore, recent developments on the use of metal seeds (Ag, Au, Pt) to obtain metal@oxide nanostructures are also extensively described. Results are shown for various metal substrates, either metal foils or supported nanoparticles/thin films of the metal where the effects of the size, surface coverage, percolation degree and thickness of the metal seeds have been systematically evaluated. The possibilities of the process are illustrated by the preparation of nanostructured films and supported NFs of different metal@oxides (Ag, Au and SiO2, TiO2, ZnO). Particularly, in the case of silver, the application of an oxygen plasma treatment prior to the deposition of the oxide was critical for efficiently controlling the growth of the 1D heterostructures. A phenomenological model is proposed to account for the thin-film nanostructuring and fibre formation by considering basic phenomena such as stress relaxation, inhomogeneities in the plasma sheath electrical field and the local disturbance of the oxide growth.

May, 2011 | DOI: 10.1088/0022-3727/44/17/174016

Hydroxyapatite Synthesis on Mesoporous Silica: A High Resolution Electron Microscopy Study

D.R. Acosta, A. Díaz-Cuenca, A.
Acta Microscopica, 20 (2011) 29-35


En este trabajo se presentan resultados de la síntesis de hidroxiapatita  (HA)  en sílice mesoporosa SBA-15. Se ha hecho un estudio de la síntesis de ambos materiales y un seguimiento del efecto del doble tratamiento térmico posterior a la síntesis. Las muestras se sometieron a distintas temperaturas de tratamiento hidrotermal entre 353 y 393 K con incrementos de 10 K durante 24 horas. En cada caso y una vez filtrado y seco el material se volvió a tratar con una calcinación a 773 K durante 10 hs. Se presentan los resultados del estudio del material compuesto SBA-15-HA por microscopia electrónica de transmisión convencional y avanzada  ( STEM, Contraste Z, HREM) . El crecimiento de HA en los túneles de la matriz de sílice mesoporosa y el nivel de ocupación de los mismos aumenta con la temperatura del primer tratamiento hidrotermal y también del segundo tratamiento que favorece el sinterizado dentro de los túneles.

May, 2011 | DOI:

Novel guests for porous columnar thin films: The switchable perchlorinated trityl radical derivatives

Oliveros, M; Gonzalez-Garcia, L; Mugnaini, V; Yubero, F; Roques, N; Veciana, J; Gonzalez-Elipe, AR; Rovira, C
Langmuir, 27 (2011) 5098-5106


TiO2 and SiO2 porous thin films consisting of tilted nanocolumns prepared by glancing angle evaporation (GLAD) have been infiltrated with guest derivatives belonging to the family of perchlorinated trityl radicals, novel guest molecules presenting an open-shell electronic configuration associated with paramagnetism, fluorescence, and electroactivity. The main driving forces for infiltration from aqueous solutions of the carboxylate-substituted radical derivatives are the electrostatic interactions between their negative charge and the net positive charges induced on the film pores. Positive charges on the internal surface of the films were induced by either adjusting the radical solution pH at values lower than the point of zero charge (PZC) of the oxide or passivating the nanocolumns oxide surface with a positively charged aminosilane. The infiltrated composite thin films are robust and easy to handle thanks to the physical protection exerted by the film columns. They also keep the multifunctionality of the used guests, as confirmed by electron paramagnetic resonance (EPR), UV-vis spectroscopy, and fluorescence spectroscopy. To prove the electroactivity of the infiltrated porous films, a porous TiO2 host layer was supported onto conductive indium tin oxide (ITO). By application of an appropriate redox potential, the guest radical molecules have been reversibly switched from their open-shell electronic configuration to their diamagnetic state and hence changed their optical properties. On the basis of these results, it is herein proposed that the appropriate surface functionalization of the pore internal surface of GLAD thin films can be used to prepare novel radical-oxide composite thin films usable for the development of robust switchable electrically driven photonic and magnetic devices.

April, 2011 | DOI: 10.1021/la200470f

Rhodamine 6G and 800 J-heteroaggregates with enhanced acceptor luminescence (HEAL) adsorbed in transparent SiO2 GLAD thin films

Sanchez-Valencia, JR; Aparicio, FJ; Espinos, JP; Gonzalez-Elipe, AR; Barranco, A
Physical Chemistry Chemical Physics, 13 (2011) 7071-7082


An enhanced fluorescent emission in the near infrared is observed when the Rhodamine 800 (Rh800) and 6G (Rh6G) dyes are coadsorbed in porous SiO 2 optical thin films prepared by glancing angle deposition (GLAD). This unusual behavior is not observed in solution and it has been ascribed to the formation of a new type of J-heteroaggregates with enhanced acceptor luminescence (HEAL). This article describes in detail and explains the main features of this new phenomenology previously referred in a short communication [J. R. Sánchez-Valencia, J. Toudert, L. González-García, A. R. González-Elipe and A. Barranco, Chem. Commun., 2010, 46, 4372-4374]. It is found that the efficiency and characteristics of the energy transfer process are dependent on the Rh6G/Rh800 concentration ratio which can be easily controlled by varying the pH of the solutions used for the infiltration of the molecules or by thermal treatments. A simple model has been proposed to account for the observed enhanced acceptor luminescence in which the heteroaggregates order themselves according to a "head to tail" configuration due to the geometrical constrains imposed by the SiO2 porous matrix thin film. The thermal stability of the dye molecules within the films and basic optical (absorption and fluorescence) principles of the HEAL process are also described.

April, 2011 | DOI: 10.1039/c0cp02421j

Nitridation of nanocrystalline TiO2 thin films by treatment with ammonia

Romero-Gomez, P; Rico, V; Espinos, JP; Gonzalez-Elipe, AR; Palgrave, RG; Egdell, RG
Thin Solid Films, 519 (2011) 3587-3595


Nanocrystalline anatase (TiO2) thin films prepared by a physical vapour deposition method were nitrided by annealing in flowing NH3 at temperatures ranging between 650 °C and 700 °C. It was established that there was a narrow window of temperatures which allowed both incorporation of interstitial nitrogen into the films with retention of the anatase phase without chemical reduction and preservation of the characteristic nanocrystalline morphology. These optimally modified films responded to visible light in photowetting tests and showed the ability to degrade an organic dye under visible light irradiation.

March, 2011 | DOI: 10.1016/j.tsf.2011.01.267

Endurance of TiAlSiN coatings: Effect of Si and bias on wear and adhesion

Philippon, D; Godinho, V; Nagy, PM; Delplancke-Ogletree, MP; Fernandez, A
Wear, 270 (2011) 541-549


In this work, the endurance of TiAlSiN nanocomposite thin films subjected to tribological solicitation is studied. These coating were deposited on M2 steel substrate by magnetron sputtering. Dry sliding experiments were conducted at ambient temperature against WC-Co ball. Coefficients of friction, wear rates and endurances were correlated with the composition, microstructure, mechanical properties, residual stress and adhesion of the coatings. The hardness and elastic modulus were found dependent not only on the composition but also on the residual stress induced by the deposition process. Friction coefficient was found to be independent on Si content while the wear rate is strongly reduced for higher Si contents. The formation of a nanocomposite microstructure, the amount of amorphous Si-based phase and both, wear resistance and adhesion are shown as the critical factors to determine the endurance of the coating.

March, 2011 | DOI: 10.1016/j.wear.2011.01.009

A comparative study of the role of additive in the MgH2 vs. the LiBH4&#8211;MgH2 hydrogen storage system

A. Fernández, E. Deprez, O. Friedrichs
International Journal of Hydrogen Energy, 36 (2011) 3932-3940


The objective of the present work is the comparative study of the behaviour of the Nb- and Ti-based additives in the MgH2 single hydride and the MgH2 + 2LiBH4 reactive hydride composite. The selected additives have been previously demonstrated to significantly improve the sorption reaction kinetics in the corresponding materials. X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-Ray Photoelectron Spectroscopy (XPS) and Electron Microscopy (TEM) analysis were carried out for the milled and cycled samples in absence or presence of the additives. It has been shown that although the evolution of the oxidation state for both Nb- and Ti-species are similar in both systems, the Nb additive is performing its activity at the surface while the Ti active species migrate to the bulk. The Nb-based additive is forming pathways that facilitate the diffusion of hydrogen through the diffusion barriers both in desorption and absorption. For the Ti-based additive in the reactive hydride composite, the active species are working in the bulk, enhancing the heterogeneous nucleation of MgB2 phases during desorption and producing a distinct grain refinement that favours both sorption kinetics. The results are discussed in regards to possible kinetic models for both systems.

March, 2011 | DOI: 10.1016/j.ijhydene.2010.12.112

Nitrogen plasma functionalization of low density polyethylene

Lopez-Santos, C; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Surface and Coatings Technology, 205 (2011) 3356-3365


Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface and analyzing the changes experienced in their surface tension. Effects of a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure are compared with those obtained by using an atom source supplied with N2 and mixtures Ar+NH3 as plasma gas. X-ray photoelectron spectroscopy (XPS) analysis has provided information about the chemical surface changes whereas the surface topography of the treated samples has been examined by atomic force microscopy (AFM). Non-destructive depth profiles of oxygen and carbon have been obtained for the treated and one month aged samples by means of the non-destructive Tougaard's method of XPS background analysis. Generally, an oxygen enrichment of the deeper region of treated LDPE surfaces has been observed. Chemical derivatization of the treated samples has shown that a DBD plasma with a mixture of Ar+NH3 was the most efficient treatment for nitrogen and amine group functionalization. It is argued that the high concentration of NH* species in this plasma is the most important factor in enhancing the nitrogen functionalization of this polymer. It has been also found that the observed increase in hydrophilicity and surface tension cannot be attributed to the anchored nitrogen functional groups formed on plasma treated LDPE. Differences in the plasma activation behaviour of LDPE and that of other polymers subjected to similar treatments are stressed.

February, 2011 | DOI: 10.1016/j.surfcoat.2010.11.038

Lateral and in-depth distribution of functional groups on diamond-like carbon after oxygen plasma treatments

Lopez-Santos, C; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
Diamond and Related Materials, 20 (2011) 49-56


A diamond like carbon material has been exposed to a low pressure microwave and atmospheric pressure plasma of oxygen to enhance its hydrophilicity and surface energy. For comparison, data are also reported after activation with a beam of neutral atoms of oxygen. The surface incorporation of oxygenated functional groups and the determination of the in-depth distribution of this element have been analysed by means of the X ray photoemission spectroscopy (XPS). Atomic force microscopy (AFM) has been used to get information of the surface topography and, by recording friction maps of the surface, the lateral distribution of oxygenated functional groups formed after the different activation treatments. Differences in surface composition, topography and in-depth and lateral distribution of oxygen have been correlated with the intrinsic characteristics of the activation plasma processes.

February, 2011 | DOI: 10.1016/j.diamond.2010.11.024

Selective Dichroic Patterning by Nanosecond Laser Treatment of Ag Nanostripes

Sanchez-Valencia, JR; Toudert, J; Borras, A; Barranco, A; Lahoz, R; de la Fuente, GF; Frutos, F; Gonzalez-Elipe, AR
Advanced Materials, 23 (2011) 848-853


A simple route for the fabrication of dichroic optical structures based on Ag nanoparticles deposited onto SiO2 nanocolumns is presented. The strict control of the optical response is achieved after infrared laser treatment of the supported nanoparticles with a commercial nanosecond pulsed laser. Preliminary examples of the utilization of the laser-treated AgNPs/SiO2 nanocolumn system for optical recoding and encryption are shown.

February, 2011 | DOI: 10.1002/adma.201003933

Transparent Nanometric Organic Luminescent Films as UV-Active Components in Photonic Structures

Aparicio, FJ; Holgado, M; Borras, A; Blaszczyk-Lezak, I; Griol, A; Barrios, CA; Casquel, R; Sanza, FJ; Sohlstrom, H; Antelius, M; Gonzalez-Elipe, AR; Barranco, A
Advanced Materials, 23 (2011) 761-765


A new kind of visible-blind organic thin-film material, consisting of a polymeric matrix with a high concentration of embedded 3-hydroxyflavone (3HF) dye molecules, that absorbs UV light and emits green light is presented. The thin films can be grown on sensitive substrates, including flexible polymers and paper. Their suitability as photonic active components photonic devices is demonstrated.

February, 2011 | DOI: 10.1002/adma.201003088

Influence of OH− concentration on the illitization of kaolinite at high pressure

M. Mantovani, A. Escudero, A.I. Becerro,
Applied Clay Science, 51 (2011) 220-225


The products of hydrothermal reactions of kaolinite at 300 °C and 1000 bars were studied in KOH solutions covering an OH concentration, [OH], of 1 M to 3.5 M. XRD patterns indicated a notable influence of the [OH] on the reaction. At [OH] ≥ 3 M, the only stable phase was muscovite/illite. The content of muscovite/illite was calculated from the analysis of the diagnostic 060 reflections of kaolinite and muscovite/illite. The results showed a linear dependence of kaolinite and muscovite/illite contents with [OH]. 27Al MAS NMR spectroscopy revealed the formation of small nuclei of K-F zeolite at high [OH]. Finally, modelling of the 29Si MAS NMR spectra indicated that the Si/Al ratio of the muscovite/illite formed was very close to that of muscovite, at least in the mineral formed at low [OH]. In good agreement with the XRD data, the quantification of the reaction products by 29Si MAS NMR indicated a linear decrease of the kaolinite content with increasing OH concentration.

February, 2011 | DOI: 10.1016/j.clay.2010.11.021

Enhanced photoactivity in bilayer films with buried rutile-anatase heterojunctions

Romero-Gomez, P; Borras, A; Barranco, A; Espinos, JP; Gonzalez-Elipe, AR
ChemPhysChem, 12 (2011) 191-196


Herein, we study the photoactivity of anatase–rutile bilayer thin films consisting of an anatase overlayer of variable thickness from some tenths to some hundred nanometers deposited onto a rutile thin film. As references single anatase layers of equivalent thickness were deposited onto silicon. All the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The photoactivity of the samples was assessed by following the evolution with the UV illumination time of both the wetting angle on the thin film surface and the decoloration of a dye in a water solution. While a similar efficiency is found for the first type of experiments irrespective of the anatase thickness, in the second type a maximum in the photoactivity is found for a thickness of the anatase layer of about 130 nm. This enhanced photoactivity in bilayer systems with a buried anatase–rutile heterojunction is related to the formation of different Schottky potential barriers in the anatase layer, depending on its thickness and the substrate (i.e. rutile or SiO2) where it is deposited.

January, 2011 | DOI: 10.1002/cphc.201000734

Combined x-ray photoelectron spectroscopy and scanning electron microscopy studies of the LiBH4-MgH2 reactive hydride composite with and without a Ti-based additive

Deprez, E; Munoz-Marquez, MA; de Haro, MCJ; Palomares, FJ; Soria, F; Dornheim, M; Bormann, R; Fernandez, A
Journal of Applied Physics, 109 (2011) 014913 (10 pages)


A detailed electronic and microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite system with and without titanium isopropoxide as additive. Surface characterization by x-ray photoelectron spectroscopy combined to a morphological study by scanning electron microscopy as well as elemental map composition analysis by energy dispersive x-ray emission are presented in this paper for the first time for all sorption steps. Although sorption reactions are not complete at the surface due to the unavoidable superficial oxidation, it has been shown that the presence of the additive is favoring the heterogeneous nucleation of the MgB2 phase. Ti-based phases appear in all the samples for the three sorption steps well dispersed and uniformly distributed in the material. Li-based phases are highly dispersed at the surface while the Mg-based ones appear, either partially covered by the Li-based phases, or forming bigger grains. Ball milling is promoting mixing of phases and a good dispersion of the additive what favors grain refinement and heterogeneous reactions at the interfaces.

January, 2011 | DOI: 10.1063/1.3525803


Illization of kaolinite: The effect of pressure on the reaction rate

Mantovani, M; Becerro, AI
Clays and Clay Minerals, 58 (2010) 766-771


Studies of the paragenesis of authigenic illite in arkosic sandstonesof various regions and ages have revealed that the illitizationof kaolinite is an important reaction accounting for the formationof authigenic illite in sandstones during burial diagenesis.The illitization of kaolinite takes place at an intermediateburial depth of 3–4 km, where pressure can reach valuesof 100 MPa ({approx}1000 bars). The purpose of the present study wasto analyze the effect of pressure on the rate of kaolinite illitizationin alkaline conditions. Hydrothermal reactions were conductedon KGa-1b kaolinite in KOH solution at 300°C and under pressuresof 500, 1000, and 3000 bars for 1 to 24 h. The visual examinationof the X-ray diffraction (XRD) patterns indicated a notableinfluence of pressure on the reaction rate. Molar percentagesof muscovite/illite formed at each time interval were calculatedfrom the analysis of two diagnostic XRD peaks, representingthe 060 reflections of kaolinite and muscovite/illite. The datawere modeled to obtain the initial rate of conversion at eachpressure. The results indicated that the initial rate of kaoliniteto muscovite/illite conversion is one order of magnitude greaterat 3000 bars than at 500 or 1000 bars. Comparison of these datawith those in the literature show a faster conversion rate (severalorders of magnitude) in an initially high-alkaline solutionthan in a near-neutral solution.

December, 2010 | DOI: 10.1346/CCMN.2010.0580604

Effect of process parameters on mechanical and tribological performance of pulsed-DC sputtered TiC/a-C:H nanocomposite films

Shaha, KP; Pei, YT; Martinez-Martinez, D; Sanchez-Lopez, JC; De Hosson, JTM
Surface and Coatings Technology, 205 (2010) 2633-2642


Mechanical, structural, chemical bonding (sp(3)/sp(2)). and tribological properties of films deposited by pulsed-DC sputtering of Ti targets in Ar/C2H2 plasma were studied as a function of the substrate bias voltage, Ti-target current, C2H2 flow rate and pulse frequency by nanoindentation, Raman spectroscopy and ball-on-disc tribometry. The new findings in this study comprise: dense, column-free, smooth, and ultra-low friction TiC/a-C:H films are obtained at a lower substrate bias voltage by pulsed-DC sputtering at 200 and 350 kHz frequency. The change in chemical and phase composition influences the tribological performance where the TiC/a-C:H films perform better than the pure a-C:H films. In the case of TiC/a-C:H nanocomposite films, a higher sp(2) content and the presence of TiC nanocrystallites at the sliding surface promote formation of a transfer layer and yield lower friction. In the case of a-C:H films, a higher sp(3) content and higher stress promote formation of hard wear debris during sliding, which cause abrasive wear of the ball counterpart and yield higher friction.

December, 2010 | DOI: 10.1016/j.surfcoat.2010.10.020

Tunable Nanostructure and Photoluminescence of Columnar ZnO Films Grown by Plasma Deposition

Romero-Gomez, P; Toudert, J; Sanchez-Valencia, JR; Borras, A; Barranco, A; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 114 (2010) 20932-20940


Nanoporous ZnO thin films presenting a tunable nanostructure and photoluminescence (PL) were grown by plasma enhanced vapor deposition on surface oxidized Si substrates. These films consist of c-axis oriented wurtzite ZnO nanocolumns whose topology, crystallinity, and PL can be tuned through the substrate temperature (varied in the 300-573 K range) and the nature of the plasma assistance (pure O-2, O-2/Ar, O-2/H-2, or O-2/N-2 mixture). In particular, these processing parameters influence the intensity of the UV and visible PL bands of the films, related to excitonic and defective radiative transitions, respectively. Increasing the substrate temperature enhances the UV PL and rubs out the visible PL due to the increase of grain size and the removal of interstitial defects. Additional tuning of the intensity ratio between the UV and visible bands can be done by controlling the film thickness. A decrease of the UV PL is observed when the films go thicker, an effect that is likely to be linked to the microstructure of the films rather than to their crystallinity that is improved upon increasing of the film thickness, as seen from PL spectroscopy and XRD measurements. Indeed, a gradient of stress, decreasing from the substrate to the surface, is evidenced and related to a concentration gradient of interstitial defects. The drawbacks of the thickness effect, which prohibits growing thick films with a high optical quality, can be bypassed by growing the films in a O-2/H-2 plasma.

December, 2010 | DOI: 10.1021/jp103902u

Band Gap Narrowing versus Formation of Electronic States in the Gap in N-TiO2 Thin Films

Romero-Gomez, P; Hamad, S; Gonzalez, JC; Barranco, A; Espinos, JP; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physical Chemistry C, 114 (2010) 22546-22557


N-containing TiO2 thin films with different amounts of nitrogen have been prepared by plasma enhanced chemical vapor deposition (PECVD) by using different titanium precursors without (titanium isopropoxide, TTIP) and with (tetrakis diethylamino titanium, TDEAT and tetrakis dimethylamino titanium, TDMAT) nitrogen in their structures and different N-2/O-2 ratios as plasma gas. For low/high content of nitrogen, Ti-NO- and/or Ti-N-like species have been detected in the films by X-ray photoelectron spectroscopy (XPS). Their optical behavior is characterized by a red shift of their absorption edge when Ti-N species are a majority, and by an unmodified edge with localized absorption states in the gap when only Ti-NO-like species are present in the film. The experimental results have been interpreted by calculating the density of states of model systems consisting of a 2 x 2 x 3 repetition of the anatase unit cell. This basic structure incorporates nitrogen defects in either substitutional or interstitial lattice positions that are considered equivalent to the Ti-N- and Ti-NO-like species detected by XPS. To simulate the effect of, respectively, a low or a high concentration of nitrogen, calculations have been carried out by placing two nitrogen defects either in separated or in nearby positions of the anatase structure. The computational analysis reveals that the defects have different stabilization energies and confirm that an edge shift of the valence band is induced by the substitutional nitrogen centers, as observed when a high concentration of Ti-N species becomes incorporated into the films. In agreement with the experimental results, when only Ti-NO-like species are detected by XPS, no band gap narrowing is obtained by the calculations that predict the appearance of localized electronic states in the gap. The fact that only these latter films present water wetting angle photoactivity when irradiated with visible light supports that the presence of Ti-NO-like species is a required condition for visible light photoactivity.

December, 2010 | DOI: 10.1021/jp104634j

Effect of pressure on kaolinite illitization

Mantovani, M; Escudero, A; Becerro, AI
Applied Clay Science, 50 (2010) 342-347


The illitization of kaolinite at increasing pressures was followed by hydrothermal experiments of kaolinite in KOH solution at 300 degrees C for 12 h and pressures between 500 and 3000 bar XRD indicated a direct transformation of kaolinite into muscovite/illite with increasing pressure However the (27)AI MAS NMR spectra showed in addition to the muscovite/illite resonances the presence of a signal at 61 ppm that should correspond to a secondary phase not detected by XRD A second series of experiments at 300 degrees C and 1000 bar for 1 3 and 6 h was carried out to show direct evidence of such phase The XRD patterns of the products clearly showed the crystallization of K-F zeolite while the (27)AI MAS NMR spectra of these samples displayed a signal at 61 ppm that must correspond therefore to Al in the K-F zeolite structure In conclusion kaolinite transformed into muscovite/illite when submitted to hydrothermal reaction in KOH solution with increasing pressure with the formation of a secondary metastable phase called K-F zeolite whose coherent diffraction domains were too small as to be detected by XRD.Effect of pressure on kaolinite illitization

November, 2010 | DOI: 10.1016/j.clay.2010.08.024

Improved Non-Covalent Biofunctionalization of Multi-Walled Carbon Nanotubes Using Carbohydrate Amphiphiles with a Butterfly-Like Polyaromatic Tail

Assali, M; Leal, MP; Fernandez, I; Romero-Gomez, P; Baati, R; Khiar, N
Nano Research, 3 (2010) 764-778


We have developed an efficient strategy for the non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) which allows a biomimetic presentation of carbohydrates on their surface by pi-pi stacking interactions. The strategy is based on the use of sugar-based amphiphiles functionalized with tetrabenzo[a,c,g,i] fluorene (Tbf), a polyaromatic compound with a topology that resembles a butterfly with open wings. The new carbohydrate-tethered Tbf amphiphiles have been synthesized in a straightforward manner using click chemistry. The reported method has been developed in order to improve the rather low ability of pyrene-based systems to exfoliate MWCNTs in water. By means of thermogravimetric analysis (TGA), ultraviolet (UV), infrared (IR), and fluorescence spectroscopies the interaction between MWCNTs and the Tbf group has been found to be stronger than those involving pyrene-based amphiphilic carbohydrates. The resulting aggregates with a multivalent sugar exposition on their surface are able to engage in specific ligand-lectin interactions similar to glycoconjugates on a cell membrane.

November, 2010 | DOI: 10.1007/s12274-010-0044-2

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate

Hartmanova, M; Jergel, M; Holgado, JP; Espinos, JP
Vacuum, 85 (2010) 535-540


Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500 degrees and 700 degrees C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 degrees C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 degrees C whereas no texture was found for 700 degrees C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.

October, 2010 | DOI: 10.1016/j.vacuum.2010.09.003

Wetting Properties of Polycrystalline TiO2 Surfaces: A Scaling Approach to the Roughness Factors

Borras, A; Gonzalez-Elipe, AR
Langmuir, 26 (2010) 15875-15882


This work presents a thorough study on the wettability of polycrystalline anatase TiO2 thin films prepared at 250 degrees C in a microwave plasma enhanced chemical vapor deposition (MW-PECVD) reactor with Ar/O-2 plasmas. Anatase polycrystalline thin films with different microstructures, textures, and surface roughness were obtained as a function of their thickness. The water contact angle of the samples was analyzed within the assumptions of the Wenzel, Cassie, and Miwa models to ascertain the effect of roughness and other surface heterogeneities on their characteristic parameters. The roughness factors defined in the different models were calculated from the atomic force microscopy (AFM) images of the films for two different observation scales within the premises of the dynamic scaling theories. The obtained results indicate that the wetting angle of an equivalent flat anatase surface with a value of 82 degrees can only be properly estimated for observation scales of 5 x 5 mu m(2) and using the Miwa model. The analysis of the UV induced hydrophilization of the surface state of the anatase films and the posterior recovery of the partially hydrophobic character of these surfaces in the absence of UV photons suggest a clear dependence of the light induced wettability on their texture and size of crystalline domains.

October, 2010 | DOI: 10.1021/la101975e

Si-doped multifunctional bioactive nanostructured films

Shtansky, DV; Gloushankova, NA; Sheveiko, AN; Kiryukhantsev-Korneev, PV; Bashkova, IA; Mavrin, BN; Ignatov, SG; Filippovich, SY; Rojas, C
Surface and Coatings Technology, 205 (2010) 728-739


Si-doped multifunctional bioactive nanostructured films (MuBiNaFs) were deposited by DC magnetron sputtering of composite TiC0.5 + CaO + Si (A) and TiC0.5 + CaO + Si3N4 (B) targets produced by self-propagating high-temperature synthesis method. The films were characterized in terms of their structure, elemental and phase composition using X-ray diffraction, scanning and transmission electron microscopy, electron energy loss spectroscopy, glow discharge optical emission spectroscopy. Raman, and IR spectroscopy. The Ti-Si-Ca-P-C-O-(N) films consisted of TiC(N) as a main phase with a minor amount of TiOx, SiNx, SiOx, SiC, and CaO phases probably mainly in amorphous state at the grain boundaries and COO- groups on the film surface. The excess of carbon atoms in the Ti-Si-Ca-P-C-O-N film (target A) precipitated in a DLC form. The films showed hardness in the range of 26-31 GPa, reduced Young's modulus of 200-270 GPa, and high percentage of elastic recovery of 60-71%. The best Ti-Si-Ca-C-O-N films exhibited low friction coefficient both in physiological solution and Dulbecko modified Eagle medium with fetal calf serum, hydrophilic properties, improved electrochemical characteristics, and excellent impact resistance. Nevertheless, the wear resistance of the Ti-Si-Ca-C-O-N films against Al2O3 ball was lower compared with the best Si-free MuBiNaFs. In vitro studies showed that the Si-doped Ti-Ca-C-O-N films possess improved osteoconductive characteristics during early stage of cell/material interaction. The film surface was highly adhesive for IAR-2 epithelial and MC3T3-E1 osteoblastic cells. The films revealed a high level of biocompatibility and biostability in experiments in vivo. The Ti-Si-Ca-C-O-N film (target A) did not show any bactericidal activity during cultivation of bacterial strains both on solid and in liquid Luria Bertani mediums. The film did not reveal any bactericidal and toxic activity against macrophages and therefore did not change bacterial status and defence system of macro-organisms.

October, 2010 | DOI: 10.1016/j.surfcoat.2010.07.063

Tilt angle control of nanocolumns grown by glancing angle sputtering at variable argon pressures

Garcia-Martin, JM; Alvarez, R; Romero-Gomez, P; Cebollada, A; Palmero, A
Applied Physics Letters, 97 (2010) - 173103


We show that the tilt angle of nanostructures obtained by glancing angle sputtering is finely tuned by selecting the adequate argon pressure. At low pressures, a ballistic deposition regime dominates, yielding high directional atoms that form tilted nanocolumns. High pressures lead to a diffusive regime which gives rise to vertical columnar growth. Monte Carlo simulations reproduce the experimental results indicating that the loss of directionality of the sputtered particles in the gas phase, together with the self-shadowing mechanism at the surface, are the main processes responsible for the development of the columns.

October, 2010 | DOI: 10.1063/1.3506502

A transparent TMPyP/TiO2 composite thin film as an HCl sensitive optochemical gas sensor

Cano, M; Castillero, P; Roales, J; Pedrosa, JM; Brittle, S; Richardson, T; Gonzalez-Elipe, AR; Barranco, A
Sensors and Actuators B-Chemical, 150 (2010) 764-769


Tetracationic porphyrin (TMPyP) molecules were incorporated Into an optically transparent TiO2 thin film prepared by Glancing Angle Physical Vapour Deposition (GAPVD) by simple infiltration (at pH 6 4) The preparation of optically transparent TMPyP/TiO2 composite thin films provides a method for the integration of the porphyrin molecules Into photonic devices for direct monitoring of gases Previously UV-visible and fluorescence spectral techniques have been used to study the reversible protonation of TMPyP in aqueous solution The optical spectrum of TMPyP shows an intense Soret band at 423 nm with a 22 nm red shift upon protonation by HCl The experimental conditions for monitoring the concentration of HCl gas by absorption spectroscopy have been optimized The maximum absorbance change was observed at the Sorer band wavelength A selected temperature of 80 C and a 300 s recovery period were found to be the optimum operating parameters (response time t(50) = 16 8  7 s) The composite with smaller surface concentration of TMPyP (Gamma = 03 x 10(-9) mol cm(-2)) presented the best detection limit (0 1 ppm) The response of the composite sensor was highly stable for several months.

October, 2010 | DOI: 10.1016/j.snb.2010.07.059

Microstructural study of the LiBH4-MgH2 reactive hydride composite with and without Ti-isopropoxide additive

Deprez, E; Justo, A; Rojas, TC; Lopez-Cartes, C; Minella, CB; Bosenberg, U; Dornheim, M; Borrnann, R; Fernandez, A
Acta Materialia, 58 (2010) 5683-5694


An exhaustive microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite (RHC) system with and without titanium isopropoxide additive. X-ray diffraction with Rietveld analysis, transmission electron microscopy coupled to energy dispersive X-ray analysis, selected-area electron diffraction and electron energy loss spectroscopy are presented in this paper for the first time for this system for all sorption steps. New data are reported regarding average crystallite and grain size, microstrain, phase formation and morphology; these results contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics. Microstructural effects, related to the high dispersion of titanium-based additives, result in a distinct grain refinement of MgB2 and an increase in the number of reaction sites, causing acceleration of desorption and absorption reactions. Considerations on the stability of phases under electron beam irradiation have also been reported.

October, 2010 | DOI: 10.1016/j.actamat.2010.06.043

Tunable In-Plane Optical Anisotropy of Ag Nanoparticles Deposited by DC Sputtering onto SiO2 Nanocolumnar Films

Sanchez-Valencia, JR; Toudert, J; Borras, A; Lopez-Santos, C; Barranco, A; Feliu, IO; Gonzalez-Elipe, AR
Plasmonics, 5 (2010) 241-250


This work reports an easy-to-handle method for growing two-dimensional assemblies of Ag nanostructures presenting a tunable in-plane optical anisotropy. Ag is deposited by DC sputtering in an Ar plasma at room temperature onto bundled nanocolumnar SiO2 thin films grown by glancing angle physical vapor deposition. In contrast with previously reported processes involving the grazing angle deposition of the metal, DC sputtering is performed at normal incidence. By varying the deposition angle of SiO2 and the Ar pressure, it was possible to tune the deposited amount of Ag and thus the topology of the Ag deposit from isolated spherical Ag nanoparticles with isotropic optical properties to strongly dichroic Ag nanostripes oriented along the bundling direction of the SiO2 nanocolumns. Based on simple calculations taking into account the shadowing effects during metal deposition, it is proposed that the width and shape of the tip of the bundled SiO2 nanocolumns influence significantly the metal local atom flux arriving to them and thus the final structure of the deposit.

September, 2010 | DOI: 10.1007/s11468-010-9139-6

Surface nanostructuring of TiO2 thin films by high energy ion irradiation

Romero-Gomez, P; Palmero, A; Ben, T; Lozano, JG; Molina, SI; Gonzalez-Elipe, AR
Physical Review B, 82 (2010) - 115420 (8 pages)


The effects of a high ion dose irradiation on TiO2 thin films under different conditions of temperature and ion nature are discussed. We have shown that anatase TiO2 thin films irradiated with N+ ions at room temperature develop a typical microstructure with mounds and voids open to the surface whereas irradiations at 700 K generate a surface pattern of well-ordered nanorods aligned with the ion beam. The formation of these patterns is caused by the simultaneous effect of ion irradiation near the film surface and a film temperature favoring the structural mobilization of the defective network of the material. To explain these phenomena, a qualitative model has been proposed and further tested by irradiating the TiO2 thin films with F+ and S+ ions under different conditions. The obtained results demonstrate that ion irradiation techniques enable the formation of tilted nanorod surface patterns with lengths of about 100 nm on anatase TiO2 thin films.

September, 2010 | DOI: 10.1103/PhysRevB.82.115420

On the microstructure of thin films grown by an isotropically directed deposition flux

Alvarez, R; Romero-Gomez, P; Gil-Rostra, J; Cotrino, J; Yubero, F; Palmero, A; Gonzalez-Elipe, AR
Journal of Applied Physics, 108 (2010) 64316


The influence of isotropically directed deposition flux on the formation of the thin film microstructure at low temperatures is studied. For this purpose we have deposited TiO2 thin films by two different deposition techniques: reactive magnetron sputtering, in two different experimental configurations, and plasma enhanced chemical vapor deposition. The obtained results indicate that films grown under conditions where deposition particles do not possess a clear directionality, and in the absence of a relevant plasma/film interaction, present similar refractive indices no matter the deposition technique employed. The film morphology is also similar and consists of a granular surface topography and a columnarlike structure in the bulk whose diameter increases almost linearly with the film thickness. The deposition has been simulated by means of a Monte Carlo model, taking into account the main processes during growth. The agreement between simulations and experimental results indicates that the obtained microstructures are a consequence of the incorporation of low-energy, isotropically directed, deposition particles.

September, 2010 | DOI: 10.1063/1.3483242

Tailored synthesis of nanostructured WC/a-C coatings by dual magnetron sputtering

Abad, MD; Munoz-Marquez, MA; El Mrabet, S; Justo, A; Sanchez-Lopez, JC
Surface and Coatings Technology, 204 (2010) 3490-3500


Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation. the WC nanocrystalline phases evolve from gamma-W2C to beta-WC1-x. Further C enrichment leads to a nanocomposite structure of small WC1-x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36-40 GPa; mu=0.6-0.8) to moderate-hard/low friction (16-20 GPa; mu similar to 0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC1-x/a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.

August, 2010 | DOI: 10.1016/j.surfcoat.2010.04.019

TiO2-SiO2 one-dimensional photonic crystals of controlled porosity by glancing angle physical vapour deposition

Gonzalez-Garcia, L; Lozano, G; Barranco, A; Miguez, H; Gonzalez-Elipe, AR
Journal of Materials Chemistry, 20 (2010) 6408-6412


Herein we present a synthetic route to attain porous one-dimensional photonic crystals of high optical quality. The method employed, based on the alternate deposition of TiO2 and SiO2 porous layers by glancing angle physical vapour deposition, yields a highly accessible interconnected pore network throughout the entire multilayer structure. Furthermore, it allows a strict control over the average size and density of the interstitial sites, which results in the precise tuning of the refractive index of the individual layers and thus of the optical response of the ensemble. The controlled environmental response of the multilayer is confirmed by the optical monitoring of the infiltration of liquids of different refractive index.

August, 2010 | DOI: 10.1039/C0JM00680G

Characterization of Ti1-xAlxN coatings with selective IR reflectivity

Godinho, V; Philippon, D; Rojas, TC; Novikova, NN; Yakovlev, VA; Vinogradov, EA; Fernandez, A
Solar Energy, 84 (2010) 1397-1401


Ti1-xAlxN thin films were deposited by reactive magnetron sputtering. The obtained different stoichiometries give rise to different optical properties as the films change from metallic to dielectric. In this work the IR reflectivity of these coatings is investigated taking into account different application fields for IR selective Ti1-xAlxN thin films. Low Al content coatings present high reflectivity, high absorptance and low thermal emittance. High Al compositions give raise to coatings with high absorptance and high thermal emittance. The composition of the coatings was evaluated combining electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy. Scanning electron microscopy (SEM) revealed a columnar structure. Reflectance spectra for the visible and infrared spectral ranges were used to obtain the solar absorptance and thermal emittance values, used to calculate the equilibrium temperature of the coatings. The thermal stability in air from 300 to 600 degrees C was also evaluated.

August, 2010 | DOI: 10.1016/j.solener.2010.04.021

Improved wear performance of ultra high molecular weight polyethylene coated with hydrogenated diamond like carbon

Puertolas, JA; Martinez-Nogues, V; Martinez-Morlanes, MJ; Mariscal, MD; Medel, FJ; Lopez-Santos, C; Yubero, F
WEAR, 269 (2010) 458-465


Hydrogenated diamond like carbon (DLCH) thin films were deposited on medical grade ultra high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition. The DLCH coating thicknesses ranged from 250 to 700 nm The substrates were disks made of UHMWPEs typically used for soft components in artificial Joints, namely virgin GUR 1050 and highly crosslinked (gamma irradiated in air to 100 kGy) UHMWPEs Mechanical and tribological properties under bovine serum lubrication at body temperature were assessed on coated and uncoated polyethylenes by means of nano-hardness and ball-on-disk tests, respectively Morphological features of the worn surfaces were obtained by confocal microscopy and scanning electron microscopy This study confirms an increase in surface hardness and good wear resistance for coated materials after 24 h of sliding test compared to uncoated polyethylene. These results point out that to coat UHMWPE with DLCH films could be a potential method to reduce backside wear in total hip and knee arthroplasties.

July, 2010 | DOI: 10.1016/j.wear.2010.04.033

Preparation and structural properties of YBCO films grown on GaN/c-sapphire hexagonal substrate

Chromik, S; Gierlowski, P; Spankova, M; Dobrocka, E; Vavra, I; Strbik, V; Lalinsky, T; Sojkova, M; Liday, J; Vogrincic, P; Espinos, JP
Applied Surface Science, 256 (2010) 5618-5622


Epitaxial YBCO thin films have been grown on hexagonal GaN/c-sapphire substrates using DC magnetron sputtering and pulsed laser deposition. An MgO buffer layer has been inserted between the substrate and the YBCO film as a diffusion barrier. X-ray diffraction analysis indicates a c-axis oriented growth of the YBCO films. &#934;-scan shows surprisingly twelve maxima. Transmission electron microscopy analyses confirm an epitaxial growth of the YBCO blocks with a superposition of three a&#8211;b YBCO planes rotated by 120° to each other. Auger electron spectroscopy and X-ray photoelectron spectroscopy reveal no surface contamination with Ga even if a maximum substrate temperature of 700 °C is applied.

July, 2010 | DOI: 10.1016/j.apsusc.2010.03.035

Influence of carbon chemical bonding on the tribological behavior of sputtered nanocomposite TiBC/a-C coatings

Abad, MD; Sanchez-Lopez, JC; Brizuela, M; Garcia-Luis, A; Shtansky, DV
Thin Solid Films, 518 (2010) 5546-5552


The tribological performance of nanocomposite coatings containing Ti-B-C phases and amorphous carbon (a-C) are studied. The coatings are deposited by a sputtering process from a sintered TiB2:TiC target and graphite, using pulsed direct current and radio frequency sources. By varying the sputtering power ratio, the amorphous carbon content of the coatings can be tuned, as observed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The crystalline component consists of very disordered crystals with a mixture of TiB2/TiC or TiBxCy phases. A slight increase in crystalline order is detected with the incorporation of carbon in the coatings that is attributed to the formation of a ternary TiBxCy phase. An estimation of the carbon present in the form of carbide (TiBxCy or TiC) and amorphous (a-C) is performed using fitting analysis of the C 1s XPS peak. The film hardness (22 to 31 GPa) correlates with the fraction of the TiBxCy phase that exists in the coatings. The tribological properties were measured by a pin-on-disk tribometer in ambient conditions, using 6 mm tungsten carbide balls at 1 N. The friction coefficients and the wear rates show similar behavior, exhibiting an optimum when the fraction of C atoms in the amorphous phase is near 50%. This composition enables significant improvement of the friction coefficients and wear rates (mu similar to 0.1; k < 1 x 10(-6) mm(3)/Nm), while maintaining a good value of hardness (24.6 GPa). Establishing the correlation between the lubricant properties and the fraction of a-C is very useful for purposes of tailoring the protective character of these nanocomposite coatings to engineering applications.

July, 2010 | DOI: 10.1016/j.tsf.2010.04.038

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small-Angle X-ray Scattering

Gonzalez-Garcia, L; Barranco, A; Paez, AM; Gonzalez-Elipe, AR; Garcia-Gutierrez, MC; Hernandez, JJ; Rueda, DR; Ezquerra, TA; Babonneaum, D
Chemphyschem, 11 (2010) 2205-2208


For the first time, grazing incidence small-angle X-ray scattering (GISAXS) analysis is used to characterize the Morphology of TiO2 thin films grown by glancing angle physical vapor deposition (GLAD). According to cross-section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO2 columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the titled of the TiO2 columns. The patterns also show the existence of two populations of columns in these GLAD TiO2 films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.

July, 2010 | DOI: 10.1002/cphc.201000136

Effect of surface roughness and sterilization on bacterial adherence to ultra-high molecular weight polyethylene

Kinnari, TJ; Esteban, J; Zamora, N; Fernandez, R; Lopez-Santos, C; Yubero, F; Mariscal, D; Puertolas, JA; Gomez-Barrena, E
Clinical Microbiology and Infection, 16 (2010) 1036-1041


Sterilization with ethylene oxide (EO) and gas plasma (GP) are well-known methods applied to ultra-high molecular weight polyethylene (UHMWPE) surfaces in the belief that they prevent major material changes caused by gamma irradiation. However, the influence of these surface sterilization methods on bacterial adherence to UHMWPE is unknown. UHMWPE samples with various degrees of roughness (0.3, 0.8 and 2.0 mu m) were sterilized with either GP or EO. The variations in hydrophobicity, surface free energy and surface functional groups were investigated before and after sterilization. Sterilized samples were incubated with either Staphylococcus aureus or Staphylococcus epidermidis in order to study bacterial adherence to these materials. Fewer bacteria adhered to UHMWPE after sterilization with EO than after sterilization with GP, especially to the smoothest surfaces. No changes in chemical composition of the UHMWPE surface due to sterilization were observed using X-ray photoemission spectroscopy analysis. The decreased bacterial adherence to UHMWPE found at the smoothest surfaces after sterilization with EO was not directly related to changes in chemical composition. Increased bacterial adherence to rougher surfaces was associated with increased polar surface energy of EO-sterilized surfaces.

July, 2010 | DOI: 10.1111/j.1469-0691.2009.02995.x/full

Study of the morphology of NiO nanostructures grown on highly ordered pyrolytic graphite, by the Tougaard method and atomic force microscopy: a comparative study

Preda, I; Soriano, L; Alvarez, L; Mendez, J; Yubero, F; Gutierrez, A; Sanz, JM
Surface and Interface Analysis, 42 (2010) 869-873


We studied the morphology of the deposits of NiO grown on highly ordered pyrolytic graphite (HOPG), by means of inelastic peak shape analysis and atomic force microscopy. The results obtained by both techniques show an excellent agreement. The results indicate that NiO grows on HOPG by following the Stransky-Krastanov type of growth.

June, 2010 | DOI: 10.1002/sia.3222

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties

Godinho, V; de Haro, MCJ; Garcia-Lopez, J; Goossens, V; Terryn, H; Delplancke-Ogletree, MP; Fernandez, A
Applied Surface Science, 256 (2010) 4548-4553


In this work amorphous silicon oxynitride films with similar composition (ca. Si0.40N0.45O0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N-2-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus. The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N-2 gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.

May, 2010 | DOI: 10.1016/j.apsusc.2010.02.045

Permanent magnetism in phosphine- and chlorine-capped gold: from clusters to nanoparticles

Munoz-Marquez, MA; Guerrero, E; Fernandez, A; Crespo, P; Hernando, A; Lucena, R; Conesa, JC
Journal of Nanoparticle Research, 12 (2010) 1307-1318


Magnetometry results have shown that gold NPs (similar to 2 nm in size) protected with phosphine and chlorine ligands exhibit permanent magnetism. When the NPs size decreases down to the subnanometric size range, e.g. undecagold atom clusters, the permanent magnetism disappears. The near edge structure of the X-ray absorption spectroscopy data points out that charge transfer between gold and the capping system occurs in both cases. These results strongly suggest that nearly metallic Au bonds are also required for the induction of a magnetic response. Electron paramagnetic resonance observations indicate that the contribution to magnetism from eventual iron impurities can be disregarded.

May, 2010 | DOI: 10.1007/s11051-010-9862-0

Excitation transfer mechanism along the visible to the Near-IR in rhodamine J-heteroaggregates

Sanchez-Valencia, JR; Toudert, J; Gonzalez-Garcia, L; Gonzalez-Elipe, AR; Barranco, A
Chemical Communications, 46 (2010) 4372-4374


An enhanced fluorescent emission of the dye Rhodamine 800 in the Near-IR is observed in the presence of other xanthene dye molecules (RhX) when they are hosted in different matrices due to the formation of a new type of fluorescent J-heteroaggregates.

This enhanced emission of the acceptor occurs despite the low spectral overlapping and the low quantum yield of Rh800.

May, 2010 | DOI: 10.1039/c0cc00087f

Non-destructive depth compositional profiles by XPS peak-shape analysis

Lopez-Santos, MC; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR
Analytical and Bioanalytical Chemistry, 396 (2010) 2757-2768


The measured peak shape and intensity of the photoemitted signal in X-ray photoelectron spectroscopy (XPS) experiments (elastic and inelastic parts included) are strongly correlated, through electron-transport theory, with the depth distribution of photoelectron emitters within the analyzed surface. This is the basis of so-called XPS peak-shape analysis (also known as the Tougaard method) for non-destructive determination of compositional in-depth (up to 6-8 nm) profiles. This review describes the theoretical basis and reliability of this procedure for quantifying amounts and distributions of material within a surface. The possibilities of this kind of analysis are illustrated with several case examples related to the study of the initial steps of thin-film growth and the modifications induced in polymer surfaces after plasma treatments.

April, 2010 | DOI: 10.1007/s00216-009-3312-9

Surface Functionalization, Oxygen Depth Profiles, and Wetting Behavior of PET Treated with Different Nitrogen Plasmas

Lopez-Santos, C; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR
ACS Applied Materials & Interfaces, 2 (2010) 980-990


Polyethylene terephthalate (PET) plates have been exposed to different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure and those using an atom source working under ultrahigh vacuum conditions have been compared for N-2 and mixtures Ar + NH3 as plasma gases. The functional groups have been monitored by X-ray Photoemission Spectroscopy (XPS). Nondestructive oxygen and carbon depth profiles for the plasma treated and one month aged samples have been determined by means of the nondestructive Tougaard's method of XPS background analysis. The surface topography of the treated samples has been examined by Atomic Force Microscopy (AFM), while the surface tension has been determined by measuring the static contact angles of water and iodomethane. It has been found that the DBD with a mixture of Ar+NH3 is the most efficient treatment for nitrogen and amine group functionalization as determined by derivatization