Dimer Shearing as a Novel Mechanism for Cluster Diffusion and Dissociation on Metal (100) Surfaces

Using bond-counting arguments and embedded-atom calculations, we establish the crucial importance of dimer shearing in metal (100) submonolayer epitaxy. This process provides the easiest pathway for diffusion of compact clusters of sizes 4, 6, and 8, and introduces a rich variety of localized cluster dynamics. A combination of the dimer shear motion and the traditional mechanism of sequential motion of individual atoms provides a better interpretation of the oscillatory behavior of cluster mobility with cluster size. This combination also defines a new set of critical cluster sizes that are likely to be selected in epitaxial growth.