Composition Dependence of the Structure and Electronic Properties of Liquid Ga-Se Alloys Studied by Ab Initio Molecular Dynamics Simulation

Ab initio molecular dynamics simulation is used to study the structure and electronic properties of the liquid Ga-Se system at the three compositions Ga$_2$Se, GaSe and Ga$_2$Se$_3$, and of the GaSe and Ga$_2$Se$_3$ crystals. The calculated equilibrium structure of GaSe crystal agrees well with available experimental data. The neutron-weighted liquid structure factors calculated from the simulations are in reasonable agreement with recent neutron diffraction measurements. Simulation results for the partial radial distribution functions show that the liquid structure is closely related to that of the crystals. A close similarity between solid and liquid is also found for the electronic density of states and charge density. The calculated electronic conductivity decreases strongly with increasing Se content, in accord with experimental measurements.Comment: REVTeX, 8 pages and 12 uuencoded PostScript figures, submitted to Phys. Rev. B. corresponding author: [email protected]

Angle-resolved photoemission study and first principles calculation of the electronic structure of GaTe

The electronic band structure of GaTe has been calculated by numerical atomic orbitals density-functional theory, in the local density approximation. In addition, the valence-band dispersion along various directions of the GaTe Brillouin zone has been determined experimentally by angle-resolved photoelectron spectroscopy. Along these directions, the calculated valence-band structure is in good concordance with the valence-band dispersion obtained by these measurements. It has been established that GaTe is a direct-gap semiconductor with the band gap located at the Z point, that is, at Brillouin zone border in the direction perpendicular to the layers. The valence-band maximum shows a marked \textit{p}-like behavior, with a pronounced anion contribution. The conduction band minimum arises from states with a comparable \textit{s}- \textit{p}-cation and \textit{p}-anion orbital contribution. Spin-orbit interaction appears to specially alter dispersion and binding energy of states of the topmost valence bands lying at $\Gamma$. By spin-orbit, it is favored hybridization of the topmost \textit{p}$_z$-valence band with deeper and flatter \textit{p$_x$}-\textit{p$_y$} bands and the valence-band minimum at $\Gamma$ is raised towards the Fermi level since it appears to be determined by the shifted up \textit{p$_x$}-\textit{p$_y$} bands.Comment: 7 text pages, 6 eps figures, submitted to PR

Pulsed laser deposition of Ga-La-S chalcogenide glass thin film optical waveguides

Thin film optical waveguides of the chalcogenide glass Ga-La-S have been deposited on substrates of CaF2 and microscope glass by the technique of pulsed laser deposition. The chalcogenide properties of photobleaching, photodoping, and photoinduced refractive index changes have been observed and preliminary experiments carried out. The refractive index and thickness of the layer were verified using a waveguide "dark mode" analysis technique

Desistance from crime and probation supervision: Comparing experiences of English and French probationers

This research compares how English and French desisters experience and perceive probation supervision. In this qualitative study, desisters of both countries were interviewed to collect narratives of change within the context of punishment in the community. The aim of this research was to explore and compare the role of probation in desistance processes, in different national, socio-economic, and criminal justice settings. The findings demonstrate similarities in perceptions of probation officers as people with resources. Differences emerged in the types of resources engaged with and the perceived punitiveness of mandatory supervision

Nucleation in xerogels of the SiO2-Al2O3-ZnO-Cr2O3 system studied by EXAFS spectroscopy

During nucleation and crystallisation processes from xerogels of the system studied, crystallites Zn(A11-xCrx)2O4 are formed. Analysis by EXAFS spectroscopy at the Zn K-edge of gels with different Cr concentration and thermal treatments compared to that of reference compounds ZnA12O4 and ZnCr2O4 allow to identify the nature of the nucleating precursors and the phases formed in the crystallization steps.The formation of ZnCr2O4 nanocrystallites during the first steps of nucleation cannot be confirmed, while for high temperature treatments, the x value close to 0 as previously obtained is verified

Apport de l’EXAFS à la connaissance de la structure des verres de chalcogénures

Cet article de revue rassemble les résultats de travaux engagés par spectroscopie EXAFS, sur la famille des verres de chalcogénures. Après une brève description de la méthode, son application à l’étude de la structure de ces verres et à l’interprétation de quelques propriétés physiques est présentée

NON-STŒCHIOMÉTRIE ET MACLES DANS LES POLYSÉLÉNIURES DE LANTHANE

Trois polyséléniures de lanthane A, B, C ont été trouvés au sein de différentes préparations de LaSe2-x (0 ⩽ x ⩽ 0,12). Tous trois sont des surstructures de type-anti Fe2As. On ne peut obtenir de monocristal d'aucun de ces composés : ils sont tous maclés. Nous avons complétement défini les structures de A et B avec des facteurs de confiance cristallographique respectivement égaux , à 0,07 et 0,06. Le composé B répond à la formule non stœchiométrique LaSe1,88, les lacunes y sont totalement désordonnées. Le composé A répond à la formule stœchiométrique LaSe2 Les lois de macle de A et B sont différentes. La macle de B est vraisemblablement polysynthétique.Three lanthanum polyselenides A, B, C have been found in various preparations of LaSe2-x (0 ⩽ x ⩽ 0.12). They are superstructures of anti-Fe2As type. We have not been able to find a single crystal because all that compounds are twinned. The A and B structures have been completely determined, the final R values are respectively 0.07 and 0.06. The B compound is non stoichiometric, its formula is LaSe1.88, and the vacancies are entirely disordered. The A compound is stoichiometric with the formula LaSe2. The A and B twin-laws are different. Probably B consists of a polysynthetic twin

Pharmaceutical silver doped clays : an EXAFS study from silver to silicon K-edges absorption

The remarkable adsorption properties of the montmorillonite clay are used to elaborate a silver doped clay, intented to a therapeutical application to burns. The unstable properties of the material obtained lead us to examine the localization of the added silver in the clay matrix by EXAFS spectroscopy performed at the Ag and Si K-edge. The results show that Ag atoms formed in triangular clusters are coordinated to the triangular designs of oxygen atoms on the border plane of the layers of the clay. The local negative charge in the border plane explains the reduction of Ag+ ions, at the origin of the unstability observed for this material