Size-Dependent Elastic Behavior of Silicon Nanofilms: Molecular Dynamics Study

In this paper, the size-dependence of the elastic behavior of silicon nanofilms terminated by (100) surfaces is studied by means of molecular dynamics with the modified embedded atom method (MEAM). The results indicate that the (100) surfaces undergo 2×1 reconstruction, which significantly influences the mechanical properties of ultra-thin films. The simulations are carried out at room temperature and structural relaxation is performed. The effective Young’s modulus, in extensional mode, is determined for different thicknesses. The surface energy, surface stress and surface elasticity of layers near the surfaces (non-bulk layers) in the thin silicon films are obtained. The surface properties of nanofilms of a few layers are shown to deviate from thicker films, suggesting a size-dependence of surface parameters and, especially, surface energy. Finally, the results of a recently developed semi-continuum approach are compared with the molecular dynamics results. Below 3 nm, there is a difference between the effective Young’s modulus, calculated by the semi-continuum approach and that provided by MD, suggesting that the continuum approach can no longer provide accurate results.