Computer study of microtwins forming from surface steps of silicon

A model silicon sample with a free {1 0 0} surface containing atomic steps along the 〈1 1 0〉 dense directions has been submitted to a uniaxial compression stress, by numerical simulation. Silicon is modelled using the Stillinger–Weber empirical interatomic potential. An elementary microtwin has been nucleated from this surface step, although the resolved shear stress is in the anti-twinning direction. The microtwin is formed by two perfect 1/6 〈1 1 0〉 60° dislocations, gliding in two neighboring planes of the shuffle set, and rearrangement of the atoms belonging to the plane of the glide set in-between. An explanation of this plastic event has been found in examining the structures obtained in calculations of bulk silicon submitted to large 〈1 1 2〉 {1 1 1} homogeneous shear.