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 {ital D}{proportional_to}{ital d}{sup {minus}{ital n}}, where {ital d} is the diameter of the cluster and the integer {ital n} identifies the diffusion mechanism. For {ital circular} clusters, {ital n}=3 when center-of-mass motion occurs by adatom diffusion along the periphery of the cluster, while {ital n}=2 or 1 when cluster diffusion occurs by {ital correlated} or {ital uncorrelated} adatom evaporation and condensation, respectively. A {ital faceted} adatom cluster diffuses by evaporation and condensation of facet ledges, giving {ital n}=0 when cluster diffusion is determined by the rate at which erosion of a ledge is initiated.