Structural, electronic, and dynamical properties of amorphous gallium arsenide: a comparison between two topological models

We present a detailed study of the effect of local chemical ordering on the structural, electronic, and dynamical properties of amorphous gallium arsenide. Using the recently-proposed ``activation-relaxation technique'' and empirical potentials, we have constructed two 216-atom tetrahedral continuous random networks with different topological properties, which were further relaxed using tight-binding molecular dynamics. The first network corresponds to the traditional, amorphous, Polk-type, network, randomly decorated with Ga and As atoms. The second is an amorphous structure with a minimum of wrong (homopolar) bonds, and therefore a minimum of odd-membered atomic rings, and thus corresponds to the Connell-Temkin model. By comparing the structural, electronic, and dynamical properties of these two models, we show that the Connell-Temkin network is energetically favored over Polk, but that most properties are little affected by the differences in topology. We conclude that most indirect experimental evidence for the presence (or absence) of wrong bonds is much weaker than previously believed and that only direct structural measurements, i.e., of such quantities as partial radial distribution functions, can provide quantitative information on these defects in a-GaAs.Comment: 10 pages, 7 ps figures with eps

Caractérisation électronique d'interfaces profondes Al-InP

Des interfaces Al-InP (110) et (100) préparées par différentes méthodes ont été caractérisées par I-V, C-V, SCS, EXES. Ces mesures confirment l'existence sur InP n d'une hauteur de barrière significative (> 0,35 eV) et sensible à la méthode de préparation. Elles mettent en évidence la présence d'états d'interface discrets pour les échantillons clivés, ou répartis dans un continuum pour ceux ayant subi un nettoyage chimique. Des modifications très nettes de la densité des états p du phosphore sont observées aux différentes interfaces par rapport à InP en volume. Ceci implique la présence d'une zone interfaciale perturbée sur plusieurs dizaines d'angströms

Caractérisation électronique d'interfaces profondes Al-InP

Al-InP (110) and (100) interfaces, obtained by means of various methods have been characterized by I-V, C-V, SCS, EXES. The measurements confirm the existence, for the n-InP material, of a significant barrier height (> 0.35 eV ) which is sensitive to the method of preparation. They show the presence of discrete interface states for cleaved samples and of states lying in a continuum for chemically etched samples. Very clear modifications, compared to the bulk, of the p density of states of phosphorus are observed at the various interfaces. They imply that the perturbed interfacial region is several tens of Å thick.Des interfaces Al-InP (110) et (100) préparées par différentes méthodes ont été caractérisées par I-V, C-V, SCS, EXES. Ces mesures confirment l'existence sur InP n d'une hauteur de barrière significative (> 0,35 eV) et sensible à la méthode de préparation. Elles mettent en évidence la présence d'états d'interface discrets pour les échantillons clivés, ou répartis dans un continuum pour ceux ayant subi un nettoyage chimique. Des modifications très nettes de la densité des états p du phosphore sont observées aux différentes interfaces par rapport à InP en volume. Ceci implique la présence d'une zone interfaciale perturbée sur plusieurs dizaines d'angströms

X-ray photoelectron spectra of adhesion-enhanced a-Si:H on stainless steel induced by plasma treatments

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Local Atomic Configuration in Laser Synthesized Si/C/N Powders Studied by X-Ray Photoelectron Spectroscopy

Nanometric Si/C/N powders have been obtained from the laser synthesis of a liquid precursor: hexamethydisilazane. The chemical composition of the products is a function of the experimental parameters: the C/N ratio in the powders is controlled in the range 0.34 to 1.34 by varying the ammonia content in the flowing gas (argon). This paper presents some results obtained by X-ray Photoelectron Spectroscopy (XPS) about the local atomic structure of these powders. The evolution of the powders after annealing treatments at 1500 and 1600 °C under nitrogen atmosphere has been studied. The chemical composition deduced from XPS wide spectra axe compared with chemical analysis. From the analysis of the Si-2p core level, information about the local atomic bonding around silicon atoms are obtained. The different environments present in the system and their evolution with temperature have been deduced from the comparison with data obtained for stoichiometric compounds (SiC, Si$_3$N$_4$ and SiO$_2$). The existence of local chemical disorder is shown in the as-formed powders. For powders with C/N : $\approx 0.6$, the samples remains amorphous until 1500 °C; crystallization which starts around 1500 °C is total at 1600 °C. The existence of C–N bonds at 1500 and 1600 °C is evidenced. This result is in good agreement with results obtained by neutron diffraction and X-ray absorption (XAS)

XPS studies on the interaction of CeO2 with Silicon in magnetron sputtered CeO2 thin films on Si and Si3N4 substrates

CeO2 thin films were deposited on silicon and silicon nitride substrates by magnetron sputtering at room temperature and annealed at 400 and 600 °C in air and vacuum. Interaction between deposited CeO2 and Si in CeO2/Si and CeO2/Si3N4 systems was investigated by XPS. The results show that Ce is present as both Ce4+ and Ce3+ oxidation states in CeO2 film deposited on Si substrate, whereas Ce4+ is the main species in as-deposited CeO2/Si3N4 film. Detailed analyses of Ce3d, Si2p and O1s core level spectra demonstrate that Ce2O3 and SiOx or cerium silicate type of species are formed at the interface of CeO2 and Si. Concentrations of Ce3+ species increase drastically in CeO2/Si thin films after annealing at 400 °C in vacuum due to enhanced interfacial reaction. On the other hand, interfacial reaction between CeO2 and Si3N4 substrate is limited in as-deposited as well as 600 °C heat treated films

Déterminants du Binge Drinking en milieu étudiant : le rôle décisif des motivations au bien-être et au coping, de la norme subjective et de l'identité de rôle.

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