Simulations of dislocation nucleation from atomic size surface steps and grooves

The stress field in the neighborhood of a surface step and a surface groove in a stressed crystal has been evaluated, in the frame of elasticity, usin g the point force model. This analysis shows that in the groove case the st ress concentration induces a shear stress in the glide planes in zone with the groove direction, which can directly favor nucleation of dislocations. On the contrary, in the step case, there is no local shear stress in the gl ide planes in zone with the step. Atomistic simulations show that before di slocations nucleation, a local shear strain appears in the glide planes whe re nucleation will occur for both structures. This shear, precursor of the dislocation formation, is well explained by the stress concentration for th e groove. For the surface step, the origin of the shear is more indirectly linked to the stress concentration: by increasing the interplanar separatio n, the stress concentration makes shear easier in some planes. The assumpti on of an effect of the interplanar distance on the shear localization has b een checked using an analysis based on the Frenkel model. (C) 2001 Elsevier Science B.V. All rights reserved.