Menú secundario

Artículos SCI


Influence of the chemical and electronic structure on the electrical behavior of zirconium oxynitride films

Carvalho, P; Chappe, JM; Cunha, L; Lanceros-Mendez, S; Alpuim, P; Vaz, F; Alves, E; Rousselot, C; Espinos, JP; Gonzalez-Elipe, AR
Journal of Applied Physics, 103 (2008) 104907
Nanotecnología en Superficies y Plasma


This work is devoted to the investigation of decorative zirconium oxynitride, ZrOxNy, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The color of the films changed from metallic-like, very bright yellow pale, and golden yellow, for low gas mixture flows [from 0 to about 9 SCCM (SCCM denotes cubic centimeter per minute at STP)] to red brownish for intermediate gas flows (values up to 12 SCCM). Associated to this color change there is a significant decrease of brightness. With further increase of the reactive gas flow, the color of the samples changed from red brownish to dark blue (samples prepared with 13 and 14 SCCM). The films deposited with gas flows above 14 SCCM showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (characteristic of a transition from metallic to insulating-type materials), promoted by the change in gas flow values, revealed that significant changes were occurring in the film structure and electronic properties, thus opening new potential applications for the films, beyond those of purely decorative ones. Taking this into account, the electrical behavior of the films was investigated as a function of the reactive gas flow and correlated with the observed chemical, electronic, and structural features. The variations in composition disclosed the existence of four different zones, which were correlated to different crystalline structures. For the so-called zone I, x-ray diffraction revealed the development of films with a B1 NaCl face-centered cubic zirconium nitride-type phase, with some texture changes. Increasing the reactive gas flow, the structure of the films is that of a poorly crystallized overstoichiometric nitride phase, which may be similar to that of Zr3N4, but with some probable oxygen inclusions within nitrogen positions. This region was characterized as zone II. Zone III was indexed as an oxynitride-type phase, similar to that of gamma-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions. Finally, occurring at the highest flow rates, zone IV was assigned to a ZrO2 monoclinic-type structure. The composition/structure variations were consistent with the chemical bonding analysis carried out by x-ray photoelectron spectroscopy, which showed oxygen doping in both Zr3N4- and ZrN-type grown films. The electronic properties of the films exhibited significant changes from zone to zone. Resistivity measurements revealed a very wide range of values, varying from relatively highly conductive materials (for zone I) with resistivity values around few hundreds of mu Omega cm to highly insulating films within zones III and IV, which presented resistivity values in the order of 10(15) mu Omega cm. Regarding zone II, corresponding to oxygen doped Zr3N4-type compounds, the observed behavior revealed resistivity values increasing steeply from about 10(3) up to 10(15) mu Omega cm, indicating a systematic transition from metallic to insulating regimes. 

Mayo, 2008 | DOI: 10.1063/1.2927494

Ar+NO microwave plasmas for Escherichia coli sterilization

Hueso, JL; Rico, VJ; Frias, JE; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physics D-Applied Physics, 41 (2008) 092002
Nanotecnología en Superficies y Plasma


Ar + NO microwave discharges are used for sterilization and the results are compared with additional experiments with Ar, O(2) and N(2)-O(2) plasma mixtures. The NO* species produced in the Ar - NO mixtures remain up to long distances from the source, thus improving the sterilization efficiency of the process. E. coli individuals exposed to the Ar + NO plasma undergo morphological damage and cell lysis. Combined effects of etching ( by O* and Ar* species) and UV radiation ( from deactivation of NO* species) are responsible for the higher activity found for this plasma mixture.

Mayo, 2008 | DOI: 10.1088/0022-3727/41/9/092002

Tribological behaviour of titanium carbide/amorphous carbon nanocomposite coatings: From macro to the micro-scale

Sanchez-Lopez, JC; Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A
Surface & Coatings Technology, 202 (2008) 4011-4018
Materiales Nanoestructurados y Microestructura, Tribología y Protección de Superficies


The tribological behaviour of nanocomposite coatings made of nanocrystalline metal carbides and amorphous carbon (a-C) prepared by PVD/CVD techniques is found to be very dependant on the film deposition technique, synthesis conditions and testing parameters. Focusing in the TiC/amorphous carbon-based nanostructured system, this paper is devoted to an assessment of the factors governing the tribological performance of this family of nanocomposites using a series of TiC/a-C films prepared by magnetron sputtering technique varying the power applied to each target (titanium or graphite) as model system to establish correlations between film microstructure and chemical compositions and tribological properties measured by a pin-on-disk tribometer. The film microstructure goes from a quasi -polycrystalline TiC to a nanocomposite formed by nanocrystals of TiC embedded in an amorphous carbon matrix as observed by transmission electron microscopy (TEM). The nanocrystalline/amorphous ratio appears to be the key-parameter to control the tribological properties and its quantification has been done by electron energy-loss spectroscopy (EELS). A significant change in the tribological performance is observed for nanocomposites with amorphous carbon phase contents above 60-65%. The friction coefficient decreases from 0.3 to 0.1 and the film wear rates by a factor of 10. Examination of the wear scars on ball and film surfaces by laser micro-Raman spectroscopy has allowed to determine the presence of metallic oxides and carbonaceous compounds responsible of the observed friction behaviour. The revision of the literature results in view of the conclusions obtained enabled to explain their apparent dispersion in the tribological performance.

Mayo, 2008 | DOI: 10.1016/j.surfcoat.2008.02.012

Study of the synergic effect of sulphate pre-treatment and platinisation on the highly improved photocatalytic activity of TiO2

Hidalgo, MC; Maicu, M; Navio, JA; Colon, G
Applied Catalysis B-Environmental, 81 (2008) 49-55
Fotocatálisis Heterogénea: Aplicaciones, Materiales y Procesos Catalíticos de Interés Ambiental y Energético


An important improvement of the photocatalytic activity of sol-gel prepared TiO2 has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.
The presence of sulphuric acid clearly stabilised TiO2 surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO2 surface was studied.
Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO2. Simultaneously sulphated and platinised TiO2 samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO2 Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.
A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.

Mayo, 2008 | DOI: 10.1016/j.apcatb.2007.11.036

Critical study of the isoconversional methods of kinetic analysis

Criado, J. M.; Sanchez-Jimenez, P. E.; Perez-Maqueda, L. A.
Journal of Thermal Analysis and Calorimetry, 92 (2008) 199-203
Reactividad de Sólidos


A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, alpha, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with alpha is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and alpha is really occurring.

Abril, 2008 | DOI: 10.1007/s10973-007-8763-7

CO and VOCs oxidation over Pt/SiO2 catalysts prepared using silicas obtained from stainless steel slags

Dominguez, MI; Barrio, I; Sanchez, M; Centeno, MA; Montes, M; Odriozola, JA
Catalysis Today, 133 (2008) 467-474
Química de Superficies y Catálisis


Stainless steels slags are mainly composed of low specific surface area calcium silicates together with a variable amount of metallic cations dispersed in such silicate matrix. These silicates due to their heavy metals content have to be considered as hazardous wastes that cannot be reclaimed easily. An alternative to reclamation is the production of valuable materials designed to accomplish processes without economic profit as the abatement of VOCs. In this paper we describe a method for obtaining high specific surface area (up to 290 m(2) g(-1)) metal-doped SiO2 and SiO2/ Al2O3 supports for catalytic applications using as raw materials stainless steel slags. The acid digestion of these slags followed by a hydrothermal treatment results in transition metal oxides doped silicas and silica-aluminas that are used as support for platinum catalysts. The prepared catalysts are active in the total oxidation of CO and toluene, showing comparable activities to those shown by Pt catalysts supported on commercial SiO2.(

Abril, 2008 | DOI: 10.1016/j.cattod.2007.11.033

Degradation of gold and false golds used as gildings in the cultural heritage of Andalusia, Spain

Duran, A; Perez-Rodriguez, JL; de Haro, MCJ; Herrera, LK
Journal of Cultural Heritage, 9 (2008) 184-188


The causes and degree of alteration of metals such as gold, tin, silver and bronze powders from ornamental implements of Andalusia Cultural Heritage have been studied. The unaltered gold is lost due to the alteration of the material used to adhere the leaf gold on the ceramic. Tin is transformed to romarchite and is lost due to a similar alteration as with the gold leaf adhesive. Silver is altered to Ag2S due to environmental contamination. Part of the bronze powders and silver used in Huercal-Overa altarpiece are altered to atacamite and AgCl, respectively, due to an unsuitable cleaning process.

Abril, 2008 | DOI: 10.1016/j.culher.2007.10.005

Modification of the photocatalytic activity of Pd/TiO2 and Zn/TiO2 systems through different oxidative and reductive calcination treatments

Aramendia, MA; Borau, V; Colmenares, JC; Marinas, A; Marinas, JM; Navio, JA; Urbano, FJ
Applied Catalysis B-Environmental, 80 (2020) 88-97
Fotocatálisis Heterogénea: Aplicaciones


Two different solids consisting of Pd or Zn-containing titania systems (metal/titanium nominal ratio of 1%) were submitted to diverse oxidative and reductive calcination treatments and tested for gas-phase selective photooxidation of 2-propanol. As regards the Pd system, reduction at low temperature (<= 500 degrees) resulted in a gradual increase in catalytic activity which was ascribed to the gradual reduction of bulk palladium to Pd-0. Thermal treatment of the system at high temperature (850 degrees C) in static air, air flow or hydrogen flow led to a decrease in activity as the result of the sharp decrease in surface area. Nevertheless, those systems containing Pd-0 only were more active than the one consisting of Pd + PdO. Finally, Pd-system overcame I'd migration to the surface on reduction at 850 degrees C which resulted in a significant increase in selectivity to acetone up to 97% for a time on stream of 5 h. As regards the Zn-containing system, none of the applied treatments resulted in improvement in photocatalytic activity. It seems that the most favourable situation for photocatalysis is that on which Zn atoms are substituting titanium ones in the lattice, whereas segregation of Zn to form small ZnO clusters is especially detrimental to activity.

Abril, 2008 | DOI: 10.1016/j.apcatb.2007.11.017

The effect of ultrasound in the synthesis of clays used as catalysts in oxidation reactions

Perez, A; Centeno, MA; Odriozola, JA; Molina, R; Moreno, S
Catalysis Today, 133 (2020) 526-529
Química de Superficies y Catálisis


The effect of ultrasound in the modification of a Colombian bentonite pillared with mixed solutions of Al-Ce and Al-Ce-Fe was obtained. The solids were characterized by means of X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. The catalysts were very efficient in the phenol oxidation reaction in diluted aqueous medium under mild experimental conditions (298 K and atmospheric pressure) and in the CO oxidation reaction. The use of ultrasound showed a clear effect in the synthesis of this type of solids allowing to make their synthesis in a shorter period of time and conserving the physical-chemical characteristics as well as catalytic activity in the oxidation reactions. 

Abril, 2008 | DOI: 10.1016/j.cattod.2007.12.129

Surface plasmon resonance and magnetism of thiol-capped gold nanoparticles

Guerrero, E.; Munoz-Marquez, M. A.; Garcia, M. A.; Crespo, P.; Fernandez-Pinel, E.; Hernando, A.; Fernandez, A.
Nanotechnology, 19 (2008) 17501
Materiales Nanoestructurados y Microestructura


Surface plasmon resonance measurements and magnetic characterization studies have been carried out for two types of thiol-capped gold nanoparticles (NPs) with similar diameters between 2.0 and 2.5 nm and different organic molecules linked to the sulfur atom: dodecanethiol and tiopronin. In addition, Au NPs capped with tetraoctyl ammonium bromide have also been included in the investigation since such capping molecules weakly interact with the gold surface atoms and, therefore, this system can be used as a model for naked gold NPs; such particles presented a bimodal size distribution with diameters around 1.5 and 5 nm. The plasmon resonance is non-existent for tiopronin-capped NPs, whereas a trace of such a feature is observed for NPs covered with dodecanethiol molecules and a bulk-like feature is measured for NPs capped with tetralkyl ammonium salts. These differences would indicate that the modification of the surface electronic structure of the Au NPs depends on the geometry and self-assembling capabilities of the capping molecules and on the electric charge transferred between Au and S atoms. Regarding the magnetization, dodecanethiol-capped NPs have a ferromagnetic-like behaviour, while the NPs capped with tiopronin exhibit a paramagnetic behaviour and tetralkyl ammonium-protected NPs are diamagnetic across the studied temperature range; straight chains with a well-defined symmetry axis can induce orbital momentum on surface electrons close to the binding atoms. The orbital momentum not only contributes to the magnetization but also to the local anisotropy, giving rise to permanent magnetism. Due to the domain structure of the adsorbed molecules, orbital momentum is not induced for tiopronin-capped NPs and the charge transfer only induces a paramagnetic spin component.

Abril, 2008 | DOI: 10.1088/0957-4484/19/17/175701

A universal curve for the magnetocaloric effect: an analysis based on scaling relations

Colodrero, Silvia; Ocana, Manuel; Miguez, Hernan
Langmuir, 24, (2008) 4430–4434
Materiales Coloidales, Materiales Ópticos Multifuncionales


Herein we present a fast, reliable method for building nanoparticle-based 1D photonic crystals in which a periodic modulation of the refractive index is built by alternating different types of nanoparticles and by controlling the level of porosity of each layer. The versatility of the method is further confirmed by building up optically doped photonic crystals in which the opening of transmission windows due to the creation of defect states in the gap is demonstrated. The potential of this new type of structure as a sensing material is illustrated by analyzing the specific color changes induced by the infiltration of solvents of different refractive indexes.

Marzo, 2008 | DOI: 10.1021/la703987r

Nanostructured Ti-M mixed-metal oxides: Toward a visible light-driven photocatalyst

Kubacka, A.; Fernandez-Garcia, M.; Colon, G.
Journal of Catalysis, 254 (2008) 272-284
Materiales y Procesos Catalíticos de Interés Ambiental y Energético


In this report we investigate the structure-activity relationship in Ti-M (M = V, Mo, Nb, W) mixed-metal oxides with anatase structure used for the photoelimination of toluene under sunlight-type excitation. These systems were prepared by a microemulsion method, and their physicochemical properties were characterized by a multitechnique approach using X-ray diffraction-Rietveld, photoelectron spectroscopy, and Raman and UV-visible spectroscopy. The preparation method allowed the incorporation of up to around 20 at % of Mo, Nb, and W, whereas a significantly inferior solubility limit, below 5 at % was observed for V. The presence of nonpunctual defects, intimately related to the existence of MOx clustering, produced electronic mid-gap states involved in charge recombination and appeared to be the most negative factor influencing photoactivity. The maximization of photoactivity occurred for Ti-M samples with the highest doing level, together with a minimum structural disturbance of the anatase-type structure. The physicochemical bases for the photoactivity behavior of the Ti-M samples as function of the M content and, in particular, the presence of partial (for a specific Ti-M series) or global maxima are discussed. 

Marzo, 2008 | DOI: 10.1016/j.jcat.2008.01.005

Sorption properties of mesoporous multilayer thin films

Fuertes, MC; Colodrero, S; Lozano, G; Gonzalez-Elipe, AR; Grosso, D; Boissiere, C; Sanchez, C; Soler-Illia, GJDAA; Miguez, H
Journal of Physical Chemistry C, 112 (2008) 3157-3163
Nanotecnología en Superficies y Plasma, Materiales Ópticos Multifuncionales


The vapor sorption properties of multilayers made of ordered mesoporous thin films with tailored composition and mesostructure are herein investigated. Optical reflectance measurements versus partial pressure of several vapors are performed to analyze the interplay between the affinity to and the accessibility of the different types of layers in the structure. We find that the behavior of a mesoporous oxide layer within the multilayer largely differs from that of the isolated thin film, its sorption properties being determined by the interaction with neighboring films. An explanation of the phenomena observed in these complex systems is provided in terms of the pore size, the affinity of each type of layer to specific compounds, and the effect of neighboring layers in the sorption properties of bilayers by an independent environmental ellipsometric study.

Marzo, 2008 | DOI: 10.1021/jp710612y

Preparation of Au-CeO2 and Au-Al2O3/AISI 304 austenitic stainless steel monoliths and their performance in the catalytic oxidation of CO

Martinez, LM; Frias, DM; Centeno, MA; Paul, A; Montes, M; Odriozola, JA
Chemical Engineering Journal, 136 (2008) 390-397
Química de Superficies y Catálisis


The use of austenitic stainless steel (AISI 304) as metallic substrate for monolithic catalytic devices is explored in this work as well as an alternative procedure to the washcoating of Al2O3 and CeO2 supported Au catalysts. Thermal treatment of the metallic surface ensured a good adherence of the catalysts. Some preparation parameters, like the number of dipping and drying steps, were controlled in order to obtain an homogeneous and adherent layer of catalyst. The resulting surfaces were characterized by X-ray diffraction (XRD), N-2 Sorption and scanning electron microscopy (SEM), and were tested in the CO oxidation reaction. The highest conversion to CO2 was obtained with the monolith coated with 1% Au-CeO2 in the presence of water.

Marzo, 2008 | DOI: 10.1016/j.cej.2007.05.040

Self-assembled polyhydroxy fatty acids vesicles: a mechanism for plant cutin synthesis

Heredia-Guerrero, JA; Benitez, JJ; Heredia, A
Bioessays, 30 (2008) 273-277
Materiales de Diseño para la Energía y Medioambiente


Despite its biological importance, the mechanism of formation of cutin, the polymeric matrix of plant cuticles, has not yet been fully clarified. Here, for the first time, we show the participation in the process of lipid vesicles formed by the self-assembly of endogenous polyhydroxy fatty acids. The accumulation and fusion of these vesicles (cutinsomes) at the outer part of epidermal cell wall is proposed as the mechanism for early cuticle formation.

Marzo, 2008 | DOI: 10.1002/bies.20716

Relation between growth dynamics and the spatial distribution of intrinsic defects in self-assembled colloidal crystal films

Lozano, G; Miguez, H
Applied Physics Letters, 92 (2008) 091904
Materiales Ópticos Multifuncionales


Herein we establish a clear relation between the parameters that govern the growth dynamics and the structural quality of colloidal crystal films. We report an optical analysis of the spatial distribution of intrinsic defects in colloidal crystal films and correlate our results with a theoretical model describing the growth dynamics of such lattices. We find that the amount of defects fluctuates periodically and decreases along the growth direction of the lattice. We demonstrate that these spatial variations are a direct consequence of the temporal oscillations of the crystal film formation velocity, which are inherent to the colloidal particle deposition process.

Marzo, 2008 | DOI: 10.1063/1.2883943

Reaction-formation mechanisms and microstructure evolution of biomorphic SiC

Varela-Feria, FM; Ramirez-Rico, J; de Arellano-Lopez, AR; Martinez-Fernandez, J; Singh, M
Journal of Materials Science, 43 (2008) 933-941
Materiales de Diseño para la Energía y Medioambiente


Biomorphic SiC is fabricated by liquid Si infiltration of a carbon preform obtained from pyrolized wood that can be selected for tailored properties. The microstructure and reaction kinetics of biomorphic SiC have been investigated by means of TEM, SEM, EBSD, and partial infiltration experiments. The microstructure of the material consists of SiC and Si and a small fraction of unreacted C. The SiC follows a bimodal size distribution of grains in the micrometer and the nanometer range with no preferential orientation. The infiltration-reaction constant has been determined as 18 x 10(-3) s(-1). These observations suggest that the main mechanism for SiC formation is solution-precipitation in the first stage of growth. If the pores in the wood are small enough they can be choked by SiC grains that act as a diffusion barrier between Si and C. If that is the case, Si will diffuse through SiC forming SiC grains in the nanometer range.

Febrero, 2008 | DOI: 10.1007/s10853-007-2207-4

Interface effects in the Ni 2p x-ray photoelectron spectra of NiO thin films grown on oxide substrates

Preda, I; Gutierrez, A; Abbate, M; Yubero, F; Mendez, J; Alvarez, L; Soriano, L
Physical Review B, 77 (2008) 075411
Nanotecnología en Superficies y Plasma


We report the Ni 2p x-ray photoelectron spectra of NiO thin films grown on different oxide substrates, namely, SiO2, Al2O3, and MgO. The main line of the Ni 2p spectra is attributed to the bulk component, and the shoulder at 1.5 eV higher binding energies to the surface component. The spectra of the NiO thin films show strong differences with respect to that of bulk NiO. The energy separation between the main peak and the shoulder increases with the substrate covalence. This indicates the strong covalent interactions between the NiO thin films and the oxide substrates, and reflects changes in the bonding at the interface from a more ionic to a more covalent interaction. These conclusions are supported by cluster model calculations with a reduced O 2p-Ni 3d hybridization.

Febrero, 2008 | DOI: 10.1103/PhysRevB.77.075411

Carbothermal synthesis of silicon nitride(Si3N4): Kinetics and diffusion mechanism

Ortega, A.; Alcala, M. D.; Real, C.
Journmal of Materials Processing Technology, 195 (2008) 224-231
Reactividad de Sólidos


Sample controlled reaction temperature (SCRT) has been used for the first time to study the kinetics of the carbothermal reduction of silica in nitrogen to obtain silicon nitride (Si3N4). It is noteworthy to point out that SCRT method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperature gradients at a negligible level to avoid any heat or mass transfer phenomena. It has been shown that the carbothermal synthesis of silicon nitride is best described by a two-dimensional diffusion kinetic model with an activation energy of about 306 kJ/mol. Effects of experimental parameters on the activation energy has been investigated. By using SCRT it has been possible to obtain ceramic powder with a determined phase composition and a controlled microstructure. 

Enero, 2008 | DOI: 10.1016/j.jmatprotec.2007.05.004

Influence of amine template on the photoactivity of TiO2 nanoparticles obtained by hydrothermal treatment

Colon, G; Hidalgo, MC; Navio, JA; Melian, EP; Diaz, OG; Dona, JM
Applied Catalysis B-Environmental, 78 (2008) 176-182
Fotocatálisis Heterogénea: Aplicaciones, Materiales y Procesos Catalíticos de Interés Ambiental y Energético


TiO2 nanoparticles have been prepared by amine template-assisted sol-gel precipitation and further hydrothermal treatment. We have investigated the effect of different amines (hydrazine and triethylamine) in the final surface and structural properties. It has been stated that the different amounts of amine could act as an interesting template upon hydrothermal treatment. Further thermal treatment also leads to a significant improvement in the photocatalytic properties of the studied systems. Surface and morphological features notably differ from TiO2 prepared using different synthetic routes. Wide surface and structural characterization of the samples have been carried out, and correlations with precipitation pH are pointed out from this characterization. In all cases, amine template TiO2 obtained exhibit high conversion values for phenol photo-oxidation reaction. Further calcination treatment of all the studied systems clearly leads to photocatalytic conversions higher than that exhibited by TiO2 Degussa P25. 

Enero, 2008 | DOI: 10.1016/j.apcatb.2007.09.019