COMPETITION BETWEEN ORDERING AND HETEROGENEITY EFFECTS ON SURFACE-DIFFUSION

Tracer and collective diffusion of repulsively interacting particles a dsorbed on a bivariate trap surface are studied by means of Monte Carl o modelling. Adsorption isotherms are obtained via simulations in the grand-canonical ensemble. Simulations in the canonical ensemble are us ed to mimick surface diffusion and to calculate the tracer, jump and c hemical diffusion coefficients. The latter is determined utilizing the fluctuation and Kubo-Green methods. Both methods are in good agreemen t at high temperatures, but produce significantly different results at low temperatures where the repulsive nearest-neighbor interaction fav ors c(2 x 2) ordering of the adatoms. These discrepancies are discusse d and explained. The effects of both the heterogeneities and the ad-ad interactions on surface diffusion are prominent at low temperatures. The existence of heterogeneities disturbs c(2 x 2) ordering at theta = 0.5. It is shown that this breakdown of the order substantially affec ts surface diffusion. (C) 1998 Elsevier Science B.V. All rights reserv ed.