Scientific Papers in SCI


Title: Valence band electronic structure characterization of the rutile TiO2 (110)-(1 x 2) reconstructed surface
Author(s): Sanchez-Sanchez, C; Garnier, MG; Aebi, P; Blanco-Rey, M; de Andres, PL; Martin-Gago, JA; Lopez, MF
Source: Surface Science, 608 (2013) 92-96

abstract | fulltext

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

Title: Preparation and characterization of CrO2 films by Low Pressure Chemical Vapor Deposition from CrO3
Author(s): Aguilera, C; Gonzalez, JC; Borras, A; Margineda, D; Gonzalez, JM; Gonzalez-Elipe, AR; Espinos, JP
Source: Thin Solid Films, 539 (2013) 1-11

abstract | fulltext

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

Title: Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups
Author(s): Medina, S; Benitez, JJ; Castro, MA; Cerrillos, C; Millan, C; Alba, MD
Source: Thin Solid Films, 539 (2013) 194-200

abstract | fulltext

Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer.

July, 2013 | DOI: 10.1016/j.tsf.2013.05.053

Title: Low refractive index SiOF thin films prepared by reactive magnetron sputtering
Author(s): Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Gonzalez, JC; Cotrino, J; Frutos, F; Ferrer, FJ; Gonzalez-Elipe, AR; Yubero, F
Source: Thin Solid Films, 542 (2013) 332-337

abstract | fulltext

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

Title: Tribological properties of surface-modified Pd nanoparticles for electrical contacts
Author(s): Abad, MD; Sanchez-Lopez, JC
Source: Wear, 297 (2013) 943-951

abstract | fulltext

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

Title: Enhanced general analytical equation for the kinetics of the thermal degradation of poly(lactic acid) driven by random scission
Author(s): Carrasco, F; Perez-Maqueda, LA; Sanchez-Jimenez, PE; Perejon, A; Santana, OO; Maspoch, ML
Source: Polymer Testing, 32 (2013) 937-945

abstract | fulltext

An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of poly(lactic acid) (PLA) at various linear heating rates and at constant rate conditions. This improvement consisted of replacing the n-order conversion function by a modified form of the Sestak-Berggren equation f(α) = c(1−α)nαm, which led to better adjustment of experimental data, and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function (α) = 2(α1/2−α), corresponding to a random scission mechanism, has been tested.

August, 2013 | DOI: 10.1016/j.polymertesting.2013.04.013

Title: Effect of sintering time on the microstructure and mechanical properties of (Ti,Ta)(C,N)-based cermets
Author(s): Chicardi, E; Torres, Y; Cordoba, JM; Sayagues, MJ; Rodriguez, JA; Gotor, FJ
Source: International Journal of Refractory Metals and Hard Materials, 38 (2013) 73-80

abstract | fulltext

Complete solid-solution cermets based on titanium–tantalum carbonitride using a starting nominal composition with 80 wt.% of (Ti0.8Ta0.2)(C0.5N0.5) and 20 wt.% of Co were performed by pressure-less sintering at 1550 °C for different times (from 0 to 180 min) in an inert atmosphere. Chemical and phase analyses were conducted using X-ray diffraction (XRD), elemental analysis and energy dispersive X-ray spectrometry (EDX). The binder mean free path and the contiguity of the carbonitride particles were used to rationalise the microstructural effects of the mechanical behaviour. Mechanical characterisation included determining the Vickers hardness, the fracture toughness (conventional indentation microfractures, IM), the dynamic Young's modulus (ultrasonic technique), the biaxial strength (ball on three ball) and a detailed fractographic examination. Finally, the experimental findings were combined with a theoretical fracture mechanics analysis to estimate the critical processing flaw sizes. Binder-less carbonitride clusters, pores and coarse carbonitride grains were the main defects observed and were responsible for the fractures.

May, 2013 | DOI: 10.1016/j.ijrmhm.2013.01.001

Title: Bio-inspired mechanochemical synthesis of semiconductor nanomaterial using eggshell membrane
Author(s): Balaz, M; Balaz, P; Sayagues, MJ; Zorkovska, A
Source: Materials Science in Semiconductor Processing, 16 (2013) 1899-1903

abstract | fulltext

Eggshell membrane and lead acetate were successfully used as precursors for the mechanochemical synthesis of lead sulphide nanocrystals with crystallite sizes ∼8 nm. XRD, specific surface area measurements, SEM and EDX were used to characterise the synthesised material. The mechanochemical synthesis follows three-step mechanism. The “fish-like” grains with sizes around 30 μm were obtained.

December, 2013 | DOI: 10.1016/j.mssp.2013.06.024

Title: Clarifications regarding the use of model-fitting methods of kinetic analysis for determining the activation energy from a single non-isothermal curve
Author(s): Sanchez-Jimenez, PE; Perez-Maqueda, LA; Perejon, A; Criado, JM
Source: Chemistry Central Journal, 7 (2013) 25

abstract | fulltext


This paper provides some clarifications regarding the use of model-fitting methods of kinetic analysis for estimating the activation energy of a process, in response to some results recently published in Chemistry Central journal.

The model fitting methods of Arrhenius and Savata are used to determine the activation energy of a single simulated curve. It is shown that most kinetic models correctly fit the data, each providing a different value for the activation energy. Therefore it is not really possible to determine the correct activation energy from a single non-isothermal curve. On the other hand, when a set of curves are recorded under different heating schedules are used, the correct kinetic parameters can be clearly discerned.

Here, it is shown that the activation energy and the kinetic model cannot be unambiguously determined from a single experimental curve recorded under non isothermal conditions. Thus, the use of a set of curves recorded under different heating schedules is mandatory if model-fitting methods are employed.

February, 2013 | DOI: 10.1186/1752-153X-7-25

Title: Growth of SiO2 and TiO2 thin films deposited by reactive magnetron sputtering and PECVD by the incorporation of non-directional deposition fluxes
Author(s): Alvarez, R; Romero-Gomez, P; Gil-Rostra, J; Cotrino, J; Yubero, F; Gonzalez-Elipe, AR; Palmero, A
Source: Physica Status Solidi (a), 210 (2013) 796-801

abstract | fulltext

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

Centro de Investigaciones Científicas Isla de la Cartuja. C/Américo Vespucio, 49 - 41092 Sevilla (España)
Tel.: [+34] 954489527 | Fax: [+34] 954460165 |