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Etude par simulations et calculs atomistiques, de la formation de dislocations aux défauts de surface dans un cristal de silicium soumis à des contrainte

Abstract : During this thesis, we have studied the dislocation nucleation from a surface step of a stressed silicon crystal. In order to determine the most appropriate inter-atomic potential for this study, we have compared the semi-empirical potentials of Stillinger-Weber (SW), Tersoff and EDIP with ab initio methods on the homogeneous shear
calculations {111} <110> of bulk silicon, and the generalized stacking fault energy along the {111} planes. The ab initio calculations show the strain localization in the shuffle set planes, and at large strains, that the covalent bonds of these planes become temporarily metallic. For our study, we have chosen the SW potential which is the most appropriate for representing these shear properties.
With the inter-atomic potentials, mainly the SW potential, we have modelled a silicon crystal with surface steps which has been submitted to different stress orientations. The results show that the surface steps are privileged sites for the onset of plasticity. The strains analysis shows the dislocation nucleation, in particular perfect
60°,slipping in the shuffle set planes. Moreover, the kind of the nucleated dislocation can be determined by the resolved shear stress along the glide planes and the Peierls stresses. No elastic shear is present in the plane where the nucleation will occur, conversely to metals, the non linear coupling between tension and shear stress of the glide planes being then relatively small in semi-conductors. This nucleation mechanism has been confirmed by an ab initio calculation, where a 60° dislocation has been nucleated in the shuffle set plane. Moreover, we have shown that the surface dangling bonds make easier the breaking/rebonding of the atomic bonds required for nucleation.
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Julien Godet. Etude par simulations et calculs atomistiques, de la formation de dislocations aux défauts de surface dans un cristal de silicium soumis à des contrainte. Matière Condensée [cond-mat]. Université de Poitiers, 2004. Français. ⟨tel-00154364⟩

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