Activation barriers and pre-factors were presented for the migration of heterogeneous adatoms on fcc(100) surfaces. Two mechanisms were considered: hopping of the adatom from one four-fold hollow site to an adjacent four-fold hollow site via a two-fold bridge site, and exchange of the adatom with an atom in the first surface layer. Twenty heterogeneous combinations of Ni, Cu, Rh, Pd and Ag were treated using transition state theory, and select comparisons were made with the results of finite temperature molecular dynamics simulations. The interaction potentials were generated using the molecular dynamics/Monte Carlo corrected effective medium theory throughout. It was found that the final state energies differed due to variation of metallic bonding with coordination for the different types of metal atoms. This variation with coordination was reflected in the surface energies of the two metals, and thus this macroscopic quantity could be used to correlate the amount of energy gained or released when the adatom displaced a surface atom. Due to the non-directional character of metallic bonding in the fcc metals, this difference in energetic stability of final configurations was also found to generally determine whether bridge hopping diffusion or atomic displacement was the dominant kinetic process in these heterogeneous systems.

Heterogeneous Adatom Diffusion on FCC(100) Surfaces: Ni, Cu, Rh, Pd, and Ag. L.S.Perkins, A.E.DePristo: Surface Science, 1994, 319[3], 225-31