Molecular Dynamics Studies of Dislocations in CdTe Crystals from a New Bond Order Potential

Cd1-xZnxTe (CZT) crystals are the leading semiconductors for radiation detection, but their application is limited by the high cost of detector-grade materials. High crystal costs primarily result from property non-uniformity that causes low manufacturing yield. While tremendous efforts have been made in the past to reduce Te inclusions / precipitates in CZT, this has not resulted in an anticipated improvement in material property uniformity. Moreover, it is recognized that in addition to Te particles, dislocation cells can also cause electric field perturbation and the associated property non-uniformity. Further improvement of the material, therefore, requires that dislocations in CZT crystals be understood and controlled. Here we use a recently developed CZT bond order potential to perform representative molecular dynamics simulations to study configurations, energies, and mobilities of 29 different types of possible dislocations in CdTe (i.e., x = 1) crystals. An efficient method to derive activation free energies and activation volumes of thermally activated dislocation motion will be explored. Our focus gives insight into understanding important dislocations in the material, and gives guidance toward experimental efforts for improving dislocation network structures in CZT crystals

Etude des phénomènes de précipitation dans un acier austénitique à 19% de chrome et 19% de manganèse, et à très forte teneur en azote

This paper describes the precipitation evolution that occurs in a not prestmined 1%N Mn-Cr austenitic steel aged in the [40O°C-900°C] temperature range, and for various times up to 150 hours. Thermal treatments carried out between 700°C and 900°C lead to a discontinuous precipitation of plates of Cr2N at grain boundaries. The nucleation stage of this precipitation reaction arises fiom the migration of the grain boundary along the high-energy interface, in order to reduce the interfacial energy of the primary surface between the plate and the grain boundary. On the contrary, the cell growth is characterized by numerous properties that differ from the hypotheses of usual theories. These non-steady state growth features arise from the continuous modifications of the diffusion-controlled mechanisms during isothermal aging. Beside this cellular precipitation, the sigma phase forms with significant volume fractions in the cells

In situ TEM study of dislocation mobility in semiconducting materials

In situ straining experiments have been conducted in Toulouse and Grenoble on elemental semiconductors, III-V and II-VI compounds. This article gives a common interpretation of the results obtained, which allows us to discuss the effect of the strength of covalent bonding on the mobility of dislocations under different conditions.Des expériences de déformation in situ de semiconducteurs élémentaires, et de composés III-V et II-VI, ont été réalisées à Toulouse et Grenoble. Cet article donne une interprétation commune des résultats obtenus, ce qui permet de discuter l'effet de la force des liaisons covalentes sur les mobilités des dislocations dans divers cas de figure