Thickness-Dependence of Surface Reconstruction on the (001) Surface of Ultrathin Silicon Nanosheets by Density Functional Tight Binding Simulations

Abstract

The influences of the thickness of ultrathin Si nanosheets on the (001) surface morphologies and charge distribution were identified by using density functional tight binding (DFTB) simulations. The differences in structure and electronic properties were elucidated on the basis of bond lengths, bond angle distribution, and arrangement patterns in (001) surface atoms of Si nanosheets with their thickness decreasing from 1.5 nm to 0.4 nm. The surface atoms in some nanosheets present perfect zig-zag patterns in their dimers. The amounts of the trimers are far less than those of the dimers in the surface. The formation of the dimers lowers the surface energy of the nanosheets. Analysis of Mülliken gross populations indicates that there is the charge transfer from the inner part of the nanosheet to the surface. The moving distance and direction of the surface atoms can affect the charge distribution.