Diffusion pathways for Si ad-dimers on Si(0 0 1): a high temperature molecular dynamics study

The diffusion of Si ad-dimers on Si(0 0 1) surfaces is simulated at 1300 K with molecular dynamics using an environment-dependent tight-binding model for Si. Three diffusion pathways parallel to the dimer rows are shown here. One of them is a new diffusion path along the top of the dimer rows, without dissociation and with a low energy barrier. The other two paths are along the trough. One of them is a leapfrog mechanism without dissociation and in agreement with a previous 0 K prediction, and the other is not activated at low temperature and proceeds by means of a complex exchange mechanism involving the motion of substrate atoms. These results suggest that dimers are able to diffuse as a unit on Si(0 0 1), up to very high temperatures, and that the diffusion mechanism consists principally of successive small angle rotations about an individual adatom binding site rather than of a simple translation.