Phase Stability and Thickness-Dependence of Properties in Silicon Nanomembranes Under Pressure

Elemental silicon is a material with a wide range of applications from the electronic to the optical to the mechanical. Recent advances in growth methodology have achieved the synthesis of flat, nanometer-scale thickness membranes. To understand and predict the energetic and mechanical properties of these membranes in contrast with bulk crystalline silicon, we model silicon nanomembranes at the electronic level in an atomistic model using density functional theory at varying levels of exchange-correlation functional. With a slab model for the nanomembrane, we investigate the pressure-based transition from the ambient-condition diamond phase to the higher-pressure beta-tin phase under out-of-plane uniaxial and in-plane biaxial compression. In addition to calculating the transition pressure and volume from one phase to the other under increasing slab thickness, we also investigate the change in elastic, electronic, and vibrational properties of each individual phase with slab thickness, aiming to make multiple experimentally testable predictions.