Surface oxide on thin films of yttrium hydride studied by neutron reflectometry

The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride films

Transparent yttrium hydride thin films prepared by reactive sputtering

Metal hydrides have earlier been suggested for utilization in solar cells. With this as a motivation we have prepared thin films of yttrium hydride by reactive magnetron sputter deposition. The resulting films are metallic for low partial pressure of hydrogen during the deposition, and black or yellow-transparent for higher partial pressure of hydrogen. Both metallic and semiconducting transparent YHx films have been prepared directly in-situ without the need of capping layers and post-deposition hydrogenation. Optically the films are similar to what is found for YHx films prepared by other techniques, but the crystal structure of the transparent films differ from the well-known YH3 phase, as they have an fcc lattice instead of hcp

Analysis of TihxOy Films Produced by Physical Vapor Deposition Method

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Una nueva arquitectura para la Red de Bibliotecas del CSIC

En esta ponencia, después de un breve repaso al proceso de automatización de las Bibliotecas del CSIC y al desarrollo de la Red de Bibliotecas, se exponen y analizan una serie de cambios importantes que van a tener lugar a medio plazo en la arquitectura de la Red. Por una parte, el paso de una arquitectura distribuida, con cuatro nodos zonales, a una arquitectura centralizada en un solo nodo, y por otra, la introducción de una nueva versión del programa de automatización Aleph, con una estructura y filosofía de funcionamiento totalmente nuevas respecto a la versión actual

Electronic properties of Β-TaON and its surfaces for solar water splitting

This is the final version of the article. Available from Elsevier via the DOI in this record.Recently, oxynitrides materials such as β-TaON has been using as a photoanode material in the field of photocatalysis and is found to be promising due to its suitable band gap and charge carrier mobility. Computational study of the crystalline β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic density functional theory (DFT). Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta 2 O 5 and Ta 3 N 5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction.We acknowledge the financial support of Engineering and Physical Science Research Council, UK (EPSRC)under the research grant Nos. EP/P510956/1, EP/P003435/1 and EP/R512801/1. S.K acknowledges the Notur Norwegian supercomputing facilities through project nn4608k and the HyMatSiRen project 272806 by the Research Council of Norway. We also acknowledge Prof. Neil Allan and Dr. Sergio C. Espindola for their help in completing this work

Electronic structure, structural and optical properties of thermally evaporated CdTe thin films

Copyright © 2007 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Physica B: Condensed Matter. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Physica B: Condensed Matter (2007), DOI: 10.1016/j.physb.2006.04.008Thin films of CdTe were deposited on glass substrates by thermal evaporation. From the XRD measurements itis found that the films are of zinc-blende-type structure. Transmittance, absorption, extinction, and refractive coefficients are measured. Electronic structure, band parameters and optical spectra of CdTe were calculated from ab initio studies within the LDA and LDA+U approximations. It is shown that LDA underestimates the band gap, energy levels of the Cd-4d states, s-d coupling and band dispersion. However, it calculates the spin-orbit coupling correctly. LDA+U did not increase much the band gap value, but it corrected the s-d coupling by shifting the Cd-4d levels towards the experimentally determined location and by splitting the LDA-derived single s peak into two peaks, which originates from admixture of s and d states. It is shown that the sd coupling plays an important role in absorption and reflectivity constants. The calculated optical spectra fairly agree with experimental data. Independent of wave-vector scissors operator is found to be a good first approximation to shift rigidly the band gap of CdTe underestimated by LDA.Research Council of NorwayAcademy of Sciences of UzbekistanUniversity Grants Commission (UGC), Indi