The diffusion of Si ad-dimers on Si(001) surfaces was simulated at 1300K using an environment-dependent tight-binding model. Three diffusion pathways parallel to the dimer rows were considered. One of them was a diffusion path along the top of the dimer rows, without dissociation and with a low energy barrier. The other two paths were along the trough. One of them was a leapfrog mechanism, without dissociation and in agreement with a previous 0K prediction, and the other was not activated at low temperature and proceeds via a complex exchange mechanism involving the motion of substrate atoms. The results suggested that dimers were able to diffuse as a unit on Si(001), up to very high temperatures, and that the diffusion mechanism consisted mainly of successive small-angle rotations about an individual adatom binding site rather than of a simple translation.

Diffusion Pathways for Si Ad-Dimers on Si(001): a High Temperature Molecular Dynamics Study. Fu, C.C., Weissmann, M., Saul, A.: Surface Science, 2001, 481[1-3], 97-104