This review presented an introduction to the experimental techniques used in surface diffusion investigations and to some of the theoretical challenges which arose in the interpretation of experimental results on surface diffusion. It was stressed that surface diffusion was essentially a many-body (collective) phenomenon. Even in the case where random walks of an individual atom were observed, their kinetics depended upon the interaction of the adatom with substrate atoms, concerted motions of the atoms, lattice dynamics, and energy exchange and dissipation. At low adatom concentrations, the lateral (inter-adatom) interactions could result in the formation of clusters. This demonstrated the wide diversity of surface diffusion mechanisms and substantially affected the kinetics. At dense (approaching one monolayer) coverages, the lateral interactions gave rise to the formation of various 2-dimensional adatom structures in the surface diffusion zone. Self-organization of this zone occurred. It represented a non-equilibrium phase portrait of the adsorbed layer. The adsorbate phases that provided fast surface diffusion occupied major areas in the surface diffusion zone. It was noted that surface diffusion was of utmost importance in nanostructures, but its effect could be both good and bad. Of particular interest were non-linear processes in surface diffusion.
Collective Surface Diffusion - an Experimentalist’s View. A.G.Naumovets: Physica A, 2005, 357, 189-215