Dynamical nature of the high-temperature Pb/Si(111)-1×1 phase

Abstract

Temperature-induced structural change of the Pb/Si(111)-root 7 x root 3 surface has been studied by using ab initio molecular dynamics simulations. The ordered root 7 x root 3 surface is found to evolve into a diffusive phase at elevated temperatures. Identified as responsible for the diffusive phase is a low-barrier concerted motion of two Pb atoms, one located on a hollow site and the other on an adjacent on-top site, which leads to an effective hollow-to-hollow Pb diffusion occurring in the background 1 x 1 lattice of the on-top Pb atoms. This diffusion picture explains well the "1 x 1" diffraction pattern with diffuse streaks observed in the high-temperature phase of the root 7 x root 3 surface and is proposed as the common structural and dynamical feature of all the high-temperature Pb/Si(111)-1 x 1 phases evolving from different ordered phases.