Single Jump Mechanisms for Large Cluster Diffusion on Metal Surfaces

The random motion of large, two-dimensional adatom clusters and vacancy clusters over a metal surface is described by a diffusion coefficient $D\propto d^{-n}$, where $d$ is the diameter of the cluster and the integer $n$ identifies the diffusion mechanism. For circular clusters, $n=3\mathrm{}$ when center-of-mass motion occurs by adatom diffusion along the periphery of the cluster, while $n=2\mathrm{}$ or 1 when cluster diffusion occurs by correlated or uncorrelated adatom evaporation and condensation, respectively. A faceted adatom cluster diffuses by evaporation and condensation of facet ledges, giving $n=0\mathrm{}$ when cluster diffusion is determined by the rate at which erosion of a ledge is initiated.