Stacking Fault Formation Created By Plastic Deformation At Low Temperature And Small Scales In Silicon

Several studies have recently reported the formation of stacking faults in silicon compressed at low temperatures and high stresses. This observation contradicts the generally accepted framework for the plastic deformation of silicon. We propose here an original plasticity mechanism that could potentially explain stacking fault formation in these conditions: the nucleation and migration of a partial edge dislocation with Burgers vector 1/3 < 112 >. These results are obtained thanks to a multiscale approach combining three computational methods. Dislocation nucleation is determined by molecular dynamics in both a nanowire and a 2D slab. The latter results are used as inputs for hybrid MD/DFT "learn on the fly" calculations, allowing for studying the dynamical propagation of the dislocation. Selected configurations at different steps are next used for initiating nudged elastic band density functional theory calculations. These calculations revealed that the dislocation displacement mechanism depends on the compression strain. For low values, a dangling bond is temporarily created in the core, resulting in high activation energies. For compression strains larger than about 8%, the reduction of the interlayer distance allows for a more complex displacement mechanism with no dangling bonds in the dislocation core and a significant decrease of the activation energy.