It was noted that non-equilibrium processes in an over-layer in a changing system (ordering, disordering, adsorbing) could be used to study surface diffusion. Diffraction studies of O on W(110) at high coverages yielded an activation energy of 0.6eV during ordering and of 1eV during disordering. These results were consistent with diffusion experiments which had been carried out using fluctuation and Boltzmann-Matano methods. The difference between the measured activation energies could be accounted for in terms of interactions which contributed differently to various over-layer configurations. Computer simulations of lattice gas models illustrated the dependence upon configuration by comparing the diffusion coefficients which had been obtained using various methods.

J.Haas, K.R.Roos, A.Jesina, M.C.Tringides: Surface Science, 1994, 307-309, 465-70