Atomic Structure of the Si(111) 7×7 Surface

Abstract

A model for the atomic structure of the Si(111) 7×7 surface is presented on the basis of recent experimental low-energy electron diffraction (LEED) studies. The seventhorder diffracted beams are attributed to interference in the coherent scattering from the first two lattice double layers which are considered rippled with a space periodicity of seven unit cells of the ideally terminated lattice. This distortion is caused by compressive stress in the surface plane that stems from the trend toward $s{p}^2$ hybridization in these two double layers due to the presence of the free surface.