SURFACE-DIFFUSION IN TEMPORALLY AND SPATIALLY INHOMOGENEOUS SYSTEMS

Non-equilibrium processes in an overlayer with the system evolving bet ween two different states (i.e., ordering, disordering, adsorption) ca n be used to study surface diffusion. Diffraction experiments on O/W(1 10) 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 wi th the fluctuation and Boltzmann-Matano methods. The difference betwee n the measured activation energies can be accounted for in terms of th e interactions which contribute differently in different overlayer con figurations. Computer simulations on lattice gas models illustrate the dependence on the configuration, by comparing diffusion coefficients obtained with different methods.