First-principles study on the mechanical and electrical properties of unpassivated Si nanowires in <111> direction

Through systematic first-principles calculations, We have obtained the Young´s modulus and piezoresistance coefficients in unpassivated Si nanowires in <;111> direction. All the models are with different diameters. The results based on density functional theory (DFT) have revealed that with the decrease of the diameter, the length of unit cell decreases, and Young´s modulus changes bigger sharply as the diameter is small enough. For the piezoresistive properties, Si₇₄ nanowires are more sensitive than the others under different strain conditions, and the piezoresistance coefficients have reached as much as 41.3×10^-11Pa^-1. However, the piezoresistance coefficients of Si₁₂₂ and Si₁₈₂, especially Si182, have changed little under different strain conditions. All these stem from the different kinds of the surface reconstructions and size effects. What´s more, the distribution of the partial charge density has been calculated for the further investigation about the electrical properties of unpassivated Si nanowires.