Self-diffusion of Adatoms and Dimers on fcc (100) Surfaces

C. M. Chang ； C. M. Wei

《Chinese Journal of Physics》 43卷1S期 (2005/02) Pp. 169-175

並列摘要

Using ab initio density-functional theory, the self-diffusion of adatom and dimer on fcc(100) metal surfaces are studied. For adatom diffusion, we find that the exchange mechanism is favored for Al, Ir, Ni, Pd, Pt and Au, while the hopping mechanism is favored for Rh, Cu, and Ag. Except for Ir/Ir(100), the exchange diffusion energy has a surprising large size-effect and decreases as the surface unit cell increases. This is due to the long-ranged strain-field created at the exchange transition state, which needs a larger cell to relax. The hopping diffusion energy, on the other hand, has a very small size-effect and keeps approximately the same value for various surface unit cells. For self-diffusion on Ir(100), the formation of covalent bonds are found at the exchange transition state, and thus the exchange diffusion energy has a little size-effect. Our results also indicate that the exchange mechanism is energetically more favorable for dimer diffusion on fcc(100) surface whenever it is favored for adatom diffusion on fcc(100) surface.