Using the lattice gas model and the transition-type-dependent Monte Carlo method, the chemical surface diffusion coefficients on a stepped surface were calculated. It was assumed that the step exerted an attraction or repulsion on adsorbed particles (ad-particles) that occupied the up or down step sites, but no interactions between ad-particles. Two kinds of activation energy, calculated from the harmonic potential and from the difference between the saddle-point and single-site energy, were used in the calculations. The calculated results showed that perpendicular diffusion decreased greatly with increase in step repulsion and attraction at all coverages. However, for diffusion parallel to the steps, completely different results were obtained for these two calculation methods. If the energy barrier was calculated by the harmonic potential, diffusion parallel to the steps was both coverage and step independent. If the energy barrier was calculated by the second method, diffusion parallel to the steps was greatly enhanced with increase in the step repulsion and attraction at middle or high coverages but decreased slightly at low coverages. The calculated results explained the chemical diffusion anisotropy on a stepped surface. The results also showed that the popular harmonic potential method might be not suitable for explaining experiments where diffusion along step edges could be more rapid than on a flat surface.

A Study of Chemical Diffusion on a Stepped Surface by the Transition-Type-Dependent Monte Carlo Method. M.Qiu, P.L.Cao, J.H.Ruan: Journal of Physics - Condensed Matter, 1996, 8[27], 4867-79