Atomic-resolution observations were made of clusters, on (111) surfaces, which comprised between 18 and 39 Ir atoms. It was found that, in the case of clusters which could not adopt an hexagonal structure, diffusion at temperatures above 550K involved atoms which moved along the edges and changed the cluster shape. No shape changes were observed in the case of Ir19, which involved a compact hexagonal arrangement of atoms,. Diffusion occurred without loss of atoms; with the cluster frequently moving over distances that were larger than a nearest-neighbor spacing.

Diffusion of Large Surface Clusters: Direct Observations on Ir (111) S.C.Wang, G.Ehrlich: Physical Review Letters, 1997, 79[21], 4234-7