DIFFUSION OF MONOLAYER ADATOM AND VACANCY CLUSTERS - LANGEVIN ANALYSIS AND MONTE-CARLO SIMULATIONS OF THEIR BROWNIAN-MOTION

In recent observations of Brownian motion of islands of adsorbed atoms and of vacancies with mean radius R, the cluster diffusion constant varies as R(-1) and R(-2). From an analytical Langevin description of the cluster's Steplike boundary, we find three cases, R(-1), R(-2), and R(-3), corresponding to the three microscopic surface mass-transport mechanisms of straight steps. We thereby provide a unified treatment of the dynamics of steps and of clusters. For corroboration, we perform Monte Carlo simulations of simple lattice gases and derive atomistic diffusion constants.