SURFACE-DIFFUSION OF PB ON (100) CU - COVERAGE DEPENDENCE AND INFLUENCE OF ORDERED-PHASE FORMATION

The spread of two-dimensional submonolayer Pb deposits on (100) Cu has been measured as a function of coverage theta and temperature T by Ru therford backscattering in ultra-high vacuum, providing the chemical-d iffusion coefficient D(theta, T). An overall increase of D with theta is observed (more than 3 orders of magnitude) with a lowering in the t heta and T domain where ordered Pb structures exist. These effects are qualitatively predicted by Monte Carlo simulations in the framework o f a simple square lattice gas model with nearest-neighbour repulsive i nteractions.