A MOLECULAR-DYNAMICS STUDY OF SELF-DIFFUSION ON METAL-SURFACES

We propose in this paper a theoretical model to investigate surface se lf-diffusion of single adatoms on the face-centered-cubic metals. Calc ulations are performed on the channeled (110), densely packed (111) an d loosely packed (001) surfaces of iridium at temperature T = 800 K. T hree realistic model potentials, Embedded Atom method, Sutton-Chen and Rosato-Guillope-Legrand potentials, are applied to describe the inter atomic interaction of the adatom/substrate systems. These potentials a ll involve a few empirical fittings of bulk properties of solid which incorporate with many-body effects. With these potentials, conventiona l molecular dynamics (MD) is employed to obtain trajectories of the at oms. On the (111) plane, via the Einstein relation, the estimated rand om walk exponential prefactors and activation energies do exhibit Arrh enius behavior, which are in reasonably good agreement with the experi mental results. On the (001) and (110) faces, a number of theoretical evidences for atomic diffusion by exchange mechanism of the adatom wit h a surface atom are presented, which are again in fairly good agreeme nt with the experiments. In addition, an examination of the exchange d iffusion characteristics on several systems (Cu, Rh and Pt) is also pr esented.