Dimensionality effects in crystal plasticity, from 3D silicon to 2D silicene

Abstract

To characterize the effects of free surfaces on dislocation mobility, the edge dislocation glide process in thin silicon films is modeled using an interatomic potential and first principles calculations. The influence of film thickness is determined, starting with the simulation of a silicene monolayer and then increasing the number of layers. The energy barrier for dislocation glide in silicene was calculated to be 1.5 eV, indicating a relatively high mobility of dislocation defects. In thin Si films a glide mechanism via consecutive bond rotations was identified, with kink nucleation being observed at the free surfaces of the film with subsequent migration. The influence of the free edge in finite size films is shown to be negligible in relation to glide for dislocations at distances from the free edge larger than three Burgers vectors. Molecular dynamics simulations reveal the possibility of more complex but lower energy barrier atomic reconstructions triggered at the free surfaces of the film near the dislocation core that may increase dislocation mobility at higher temperatures.