  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.
