SURFACE-DIFFUSION IN TEMPORALLY AND SPATIALLY INHOMOGENEOUS SYSTEMS

Non-equilibrium processes in an overlayer with the system evolving between two different states (i.e., ordering, disordering, adsorption) can be used to study surface diffusion. Diffraction experiments on O/W(110) at high coverage measure an activation energy E(d) = 0.6 +/- 0.05 eV during ordering and E(d) = 1 +/- 0.05 eV during disordering. These results are consistent with other diffusion experiments carried out with the fluctuation and Boltzmann-Matano methods. The difference between the measured activation energies can be accounted for in terms of the interactions which contribute differently in different overlayer configurations. Computer simulations on lattice gas models illustrate the dependence on the configuration, by comparing diffusion coefficients obtained with different methods.