Diffusion and Stability of Large Clusters on Crystal Surfaces

Diffusion and stability of large two-dimensional clusters (consisting of hundreds to thousands of atoms) are discussed. Scaling laws for the diffusion constant and the decay time of clusters as a function of the cluster size are derived from a microscopic point of view by treating atom diffusion near the cluster edge as a random walk problem of a single particle in the vicinity of an adsorbing boundary. This treatment establishes the connection between the quantities which can be determined by experiment (i.e., the cluster diffusion constant and the decay rate) to the microscopic diffusion processes of single atoms. The results are illustrated by experimental examples for diffusion and decay of adatom and vacancy clusters on a Ag(111) surface.