Diffusion of particles over strongly anisotropic surface with traps

Abstract

We investigate surface diffusion in a system of particles adsorbed on a two-dimensional strongly anisotropic lattice. There are two kinds of the lattice sites – ordinary sites and deep traps. Particles adsorbed in the ordinary sites can migrate over the surface, but particles adsorbed in traps are immobile. These particles do not move over the surface and they obstacle also the mobile particles migration (surface defects). Using kinetic Monte Carlo simulations we obtained coverage dependencies of the tracer, jump, and chemical diffusion coefficients. The coefficients are rather sensitive to the defect concentration. Even small admixture of the defects decreases drastically the fast diffusion. The effect is rather specific: strong dependence of the pre-exponential factor on the defect concentration and almost independent activation energy. The defect influence on the slow diffusion is weak. It results in strong decreasing of the surface diffusion anisotropy with the defect concentration. Such unusual behavior of the diffusion coefficients was observed in many experimental investigations of the surface diffusion of lithium, cesium, potassium, and strontium over strongly anisotropic W(1 1 2) and Mo(1 1 2) planes. It was shown that this specific behavior arises exclusively due to the surface anisotropy, and does not depend on the lateral interaction between the particles.