Monte Carlo investigation of surface self-diffusion: The role of anisotropic next-nearest neighbor interactions

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Abstract
The asymmetric next‐nearest neighbor (NNN) Ising model has been studied for describing the self‐diffusion of adsorbate atoms at low temperature, furthermore adding a relevant ingredient in such a regime, i.e., a finite value Q for the trapping potential barrier. The Monte Carlo technique leads to the components of the (tracer) diffusion coefficient. An interesting feature is seen: a ‘‘V–Λ 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 function 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 function of the temperature and coverage are presented and discussed. Monte Carlo snapshots are shown at various coverage and temperature values.