Diffusion on a face-centred cubic (111) surface in the presence of two non-equivalent adsorption sites

Abstract The interrelation between the surface symmetry and diffusion of adsorbed atoms is studied theoretically on a model face-centred cubic (fcc) (111) surface within the lattice-gas approximation. Diffusion proceeds through two non-equivalent sites on the fcc(111) surface. Short-range repulsive interaction between particles in the nearest-neighbour non-equivalent sites is considered. This repulsion leads to a modification of the occupation numbers of both kinds of site and to changes in the energy barrier height for diffusion. The chemical surface diffusion coefficient, D , has been found to be strongly dependent on coverage, Θ , the interaction strength between adatoms, and the difference between the activation energies, Δ E . In the case of a small Δ E value, the diffusion coefficient D increases with Θ , as was expected for repulsive interaction. In our model the increase of D at Θ =0.5 is reduced for higher values of Δ E and a local maximum of D ( Θ ) is observed.