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Concentration profiles on the different sites of tungsten screw dislocation are calculated as a function of the nominal carbon atom concentration, temperature and dislocation density. Rigid lattice Monte Carlo simulations and associated mean-field modelling are performed based on interaction energies from ab initio calculations. We show that the repulsive interactions induce ordering phenomena that drastically change the concentration in the core of the dislocation and leads to ordered structures among the octahedral sites. We detail the domains of short-range ordering (SRO) and long-range ordering (LRO). Evolution of the distribution of carbon atoms in tungsten screw dislocation with increasing temperature. The carbon atoms are in red on the prismatic line and in orange on the octahedral lines. Empty sites are in white. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the correlation between the optical properties and the chemical and electrical properties of amorphous silicon nitride (SiN X :H) films prepared by reactor Plasma-Enhanced Chemical Vapor Deposition (PECVD). The effects of temperature and mixture of gases (NH3/SiH4/N2) on these dielectric films are investigated in this study. Silane (SiH4) and ammonia (NH3) are used as the reactive species, while nitrogen (N2) is used as a dilution gas. A particular focus is made on the improvement of the electrical properties that are strongly correlated to the physicochemical bonds films properties. The incorporation of the N2 dilution leads to the deposition rate and hydrogen content reductions in the film. An optimal gases mixture with N2 is obtained to improve the breakdown voltage at low temperature, 200°C. Fundamental properties of these fabricated films are characterized by their elemental composition, chemical specification, residual stress, optical and electrical properties. The results experimentally show that this film can be used to improve some of the key deposition parameters for the reliability of semiconductor, microsystems and optical applications. [Copyright &y& Elsevier]

The structure and composition of a disordered Pt25Cu75(1 1 1) sample was studied by low energy electron diffraction. The r-factor, D1=0.096, illustrates a very good agreement between experimental and theoretical spectra. The Pt concentration versus depth oscillates around the bulk value (C1,C2,C3,C4)=(28,8,48,8 at.% Pt). The most striking result is the quite large and unusual Pt enrichment in layer 3 (C3=48%) followed by the still important Pt depletion in layer 4 as opposed to the damped oscillations observed for similar Pt–Ni(1 1 1) and Pt–Co(1 1 1) alloys. This result, which is in contradiction with a previous LEIS study, is interpreted within the Tight Binding Ising Model and is related to a termination of the L11 phase, which exists only in the Cu–Pt system. [Copyright &y& Elsevier]

We present the study of hydrogen atom segregation on screw dislocation in Fe and W metals by means of rigid lattice Monte Carlo simulations using interaction energies obtained from ab initio calculations. These interaction energies are attractive or repulsive depending on direction and distance. This high interaction anisotropy leads to the formation of a 3D compound for both iron and tungsten. A second consequence is that, within a given temperature range, hydrogen enrichment is greater at the outer than at the innermost sites of the dislocation. This unusual behavior is only observed for iron. We propose a mean-field model that accounts for the ordering phenomenon to explain the results and the differences between the two metals. Hydrogen segregation profiles on a screw dislocation in iron (left) and tungsten (right) at different temperatures. For iron, over a given temperature range, hydrogen enrichment is greater at the first outer sites than at the core sites of the dislocation. This behavior is not observed for tungsten. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Cluster dynamics is often used in the multi-scale procedure to link atomistic and macroscopic approaches, in particular when modelling precipitation processes. To extend its use to concentrated alloys, it is necessary to take into account accurately the exclusion zones and their overlap. By investigating the one-dimensional case, one obtains an exact formula for these zones, and its generalization to higher dimensions is proposed. By integrating cluster fragmentation/coagulation processes into cluster dynamics equations, a perfect agreement between atomistic simulations (Kinetic Monte Carlo) and cluster dynamics is reached on the whole range of concentrations for kinetics which govern microstructure in one dimension. [Copyright &y& Elsevier]