First-principles study on the electro-mechanical coupling of the Si/Ge core-shell nanowires

We have simulated the piezoresistance coefficients (Pie coefficients) in Si/Ge core-shell nanowires with a certain diameter and different thickness Ge-shell in the longitudinal direction on the basis of First-Principles calculations of models. Through calculations, it was found that the Pie coefficients of the nanowire constructed with an axis of Si atoms and three layers of Ge atoms outside (Si₁Ge₃ in Figure1) almost kept consistent with the GeNW as negative values. Under the compressive condition, the Pie coefficient of the Si₂Ge₂ can reach up to-21.20 × 10^-11Pα^-1. However, when the Ge-shell was decreased to only one Ge-atom layer, the Pie coefficients varied from negative values to positive ones. We also obtained the pie coefficients of the SiNW: 9.46 x 10^-11Pa^-1 and 35.77 x 10^-11Pa^-1 respectively under compression and tension.