The coverage dependence of surface diffusion coefficients for the strongly interacting adsorption system of O on (110)W was studied via Monte Carlo simulations of a lattice-gas model. In particular, the emergence of memory effects - as contained in the corresponding correlation factors for tracer and collective diffusion - was considered. It was shown that memory effects could be very pronounced deep within the ordered phases, and in regions close to the first- and second-order phase transition boundaries. Particular attention was paid to the detailed time-dependence of the memory effects. The memory effect in tracer diffusion was found to decay according to a power law, following an initial transient period. This behavior persisted until the hydrodynamic regime was reached; after which, the memory effect decayed exponentially. The time which was required, to reach the hydrodynamic regime and the related exponential decay, was strongly affected by critical effects that were related to long-wavelength fluctuations and to the local order in the overlayer. An analysis was also made of the effect of memory upon the effective diffusion barriers that were deduced from Arrhenius data. It was found that the contribution of memory effects to tracer diffusion could amount to 50% of the total barrier. The role of memory effects was generally less marked in the case of collective diffusion.

Memory Effects and Coverage Dependence of Surface Diffusion in a Model Adsorption System. I.Vattulainen, S.C.Ying, T.Ala-Nissila, J.Merikoski: Physical Review B, 1999, 59[11], 7697-707