The random motion of large 2-dimensional adatom clusters and vacancy clusters over a metal surface was described by a diffusion coefficient which was proportional to d-n, where d was the diameter of the cluster and n identified the operating diffusion mechanism. In the case of circular clusters, n was equal to 3 when center-of-mass motion occurred via adatom diffusion along the periphery of the cluster. On the other hand, n was equal to 2 or 1 when cluster diffusion occurred via correlated or uncorrelated adatom evaporation and condensation, respectively. A faceted adatom cluster diffused via the evaporation and condensation of facet ledges; giving an n-value of 0 when cluster diffusion was governed by the rate at which erosion of a ledge was initiated.

C.D.Van Siclen: Physical Review Letters, 1995, 75[8], 1574-7