Diffusion of vacancies and adatoms on stepped crystalline surfaces

We consider the diffusion of vacancies and adatoms at thermal equilibrium on stepped metallic surfaces in the random walk limit. For the simplest models of generation of adatoms and vacancies from the opposite edges of a terrace we point out that in the absence of annihilation the coverage on a terrace is uniform on average. We also give the average coverage profile in two-dimensions relative to the generating point for adatoms or vacancies. When terrace edge barriers imperfectly confine the walkers their average coverage acquires a linear decrease away from the generating edge. When adatom–vacancy annihilation processes are included the average coverage acquires an approximately parabolic dependence on distance from the generating terrace edge. We explore by calculation the effects of terrace width and asymmetric generation rate of adatoms and vacancies on the coverage variation.