MONTE-CARLO INVESTIGATION OF SURFACE SELF-DIFFUSION - THE ROLE OF ANISOTROPIC NEXT-NEAREST-NEIGHBOR INTERACTIONS

The asymmetric next-nearest neighbor (NNN) Ising model has been studie d for describing the self-diffusion of adsorbate atoms at low temperat ure, furthermore adding a relevant ingredient in such a regime, i.e., a finite value Q for the trapping potential barrier. The Monte Carlo t echnique leads to the components of the (tracer) diffusion coefficient . An interesting feature is seen: a ''V-Lambda transition'' occurs at half-coverage (c=0.5) when the temperature is lowered. The activation energy (obtained from an Arrhenius plot) is seen to be varying as a fu nction of coverage, and is not symmetrical with respect to c=0.5. The anisotropy of the diffusion and the change in its pattern as a functio n of the temperature and coverage are presented and discussed. Monte C arlo snapshots are shown at various coverage and temperature values.