A study was made of the role of the double rotation mechanism in the concerted diffusion of two-dimensional small Cu clusters (up to 10 atoms) over Cu{111} surfaces. The results showed that the necessary energy to diffuse the cluster on any direction over the surface (overall activation energy) increased proportionally to the cluster size. However, the minimum energy necessary to just move the cluster center of mass presented a non-monotonic increase. The reason for this behavior relied on the double rotation mechanism, which was observed in some clusters with diamond shape configuration. Consequently, clusters as big as hexamers could be expected to be surprisingly mobile with activation energies around 0.15eV.

Double Rotation Mechanism in Small Cu Clusters Concerted Diffusion over Cu{111} Surfaces. J.C.Flores, B.H.Aguilar, A.M.Coronado, H.Huang: Surface Science, 2007, 601[4], 931-5