By combining molecular dynamics simulations with reaction pathway sampling, the nucleation of a 3-dimensional dislocation loop from a sharp corner in Si was observed and an investigation was made of the shear stress dependence of the activation energy and saddle-point configuration. The nucleated shuffle-set half-loop consisted of two 60° segments and one screw segment; each lying along a Peierls valley. The half-hexagonal shape was in good agreement with low-temperature experimental data. Under high stresses (90 to 95% of athermal shear stress), the dislocation embryo was far from perfect, with a half-size Burgers vector (about 0.2nm) and a 0.4 to 0.7nm radius forming a diffuse core region. One consequence was that the Rice-Thompson theory gave incorrect predictions regarding the activation energy and saddle-point configuration. With decreasing applied stress (less than 70%), the embryo approached that of a perfect dislocation.

Dislocation Nucleation From a Sharp Corner in Silicon. S.Izumi, S.Yip: Journal of Applied Physics, 2008, 104[3], 033513