Effects of surface chemical structure on the mechanical properties of Si_1-xGe_x nanowires

The Young's modulus and fracture strength of Si_1-xGe_x nanowires (NWs) as a function of Ge concentration were measured from tensile stress measurements. The Young's modulus of the NWs decreased linearly with increasing Ge content. No evidence was found for a linear relationship between the fracture strength of the NWs and Ge content, which is closely related to the quantity of interstitial Ge atoms contained in the wire. However, by removing some of the interstitial Ge atoms through rapid thermal annealing, a linear relationship could be produced. The discrepancy in the reported strength of Si and Ge NWs between calculated and experimented results could be related to SiO_2-x/Si interfacial defects that are found in Si _1-xGe_x NWs. It was also possible to significantly decrease the number of interfacial defects in the NWs by incorporating a surface passivated Al₂O₃ layer, which resulted in a substantial increase in fracture strength.