By means of  ab initio  calculations, estimates were made of self-diffusion on a flat (110) surface, or close to a {111}-faceted step on (111). The diffusivity was found to be very similar in both cases, and resulted from the similar local bonding configurations of the 5-fold coordinated equilibrium site and of the transition states. The preferred diffusion mechanism was always that of atomic exchange, even in the so-called easy direction parallel to close-packed rows. A factor which was relevant to layer-by-layer growth was that diffusion across the descending step involved a barrier of only 0.06eV. This was not much higher than the barrier (0.04eV) at a flat (111) surface. The adsorption energy differences could be explained in terms of the efficient screening of Al and an embedding-like interaction model.

R.Stumpf, M.Scheffler: Surface Science, 1994, 307-309, 501-6