Recent scanning tunneling microscopy results on the Brownian motion of 2-dimensional vacancy islands on Ag(110) were considered. While the detachment of adatoms from the island and their diffusion on the terrace was permitted between 180 and 220K, the peripheral diffusion of single adatoms was prohibited. The Brownian motion of the islands was found to obey a simple scaling law, with terrace diffusion being the rate-limiting process. The scaling of the experimental results was confirmed by kinetic Monte Carlo simulations. On the basis of the results, a detailed derivation of the equation that related the diffusivity of an anisotropic island to its size was presented. Further details and results of kinetic Monte Carlo simulations were also presented. The results shed light on the issue of the attempt frequencies for surface diffusion. Pre-factor ratios for exchange and hopping mechanisms were obtained in the specific case of an anisotropic surface.

Motion of Vacancy Islands on an Anisotropic Surface - Theory and Kinetic Monte Carlo Simulations. K.Morgenstern, E.Lægsgaard, F.Besenbacher: Physical Review B, 2002, 66[11], 115408 (6pp)