Understanding mechanical properties and failure mechanism of germanium-silicon alloy at nanoscale

We used molecular dynamics (MD) simulations to investigate the mechanical properties of cubic zinc blende (ZB) Si0.5Ge0.5 alloy nanowire (NW). Tersoff potential is employed to elucidate the effect of nanowire size, crystal orientations, and temperature on the material properties. We found that the reduction in the cross-sectional area results in lower ultimate tensile strength and Youngs modulus of this alloy which can be attributed to the increased surface to volume ratio. The [111] oriented Si0.5Ge0.5 NW exhibits the highest fracture strength compared to other crystal orientations but [110] orientation possesses the highest fracture toughness. The effect of temperature depicts an inverse relationship with the ultimate tensile strength and Youngs modulus. The increased temperature facilitates the failure of the material, thus degrades the materials strength. Our study reveals that the vacancy defects introduced via removal of either Si or Ge atoms exhibit similar behavior, and with the increase in vacancy concentration, both ultimate tensile strength and Youngs modulus reduces linearly. We further illustrate the failure characteristics of Si0.5Ge0.5 NW at two extremely low and high temperatures. The intrinsic failure characteristics of Si0.5Ge0.5 alloy is found to be insensitive to the temperature. Interestingly, at both temperatures, with the increasing strain, the cross-section of Si0.5Ge0.5 eventually resembles a neck as typically observed in ductile materials, although the NW failure is brittle in nature. Overall, this work offers a new perspective on understanding material properties and failure characteristics of ZB Si0.5Ge0.5 NW that will be a guide for designing Si-Ge based nanodevices.