On the large-strain plasticity of silicon nanowires: Effects of axial orientation and surface

The large strain (over 30%) plasticity of silicon-crystalline nanowires (Si NWs) under tension is presented by using the molecular dynamics simulations with the new optimized modified embedded-atom-method (MEAM) potential (Timonova and Thijsse, 2011). The results are consistent with experimental observations, which demonstrate the strain-induced structural evolution processes and the large strain plasticity of <110> Si NWs. The <111> Si NWs fracture in brittle manner, while the <110> and <100> ones elongate plastically beyond the yield point. Detailed analyses reveal that the initial yielding behaviors of <110> and <100> Si NWs are due to dislocation emission and crystal-to-amorphous transition, respectively in line with their axial orientations. Additionally, the surface effect on the yield strength is studied by examining the size dependence of each wire with various orientations. Finally, the participations of the two effects, to what extent determining the incipient fracture behaviors of Si NWs, are discussed.