Memory effects and coverage dependence of surface diffusion in a model adsorption system

We study the coverage dependence of surface diffusion coefficients for a st rongly interacting adsorption system O/W(110) via Monte Carlo simulations o f a lattice-gas model. In particular, we consider the nature and emergence of memory effects as contained in the corresponding correlation factors in tracer and collective diffusion. We show that memory effects can be very pr onounced deep inside the ordered phases and in regions close to first and s econd order phase transition boundaries. Particular attention is paid to th e details of the time dependence of memory effects. The memory effect in tr acer diffusion is found to decay following a power law after an initial tra nsient period. This behavior persists until the hydrodynamic regime is reac hed, after which the memory effect decays exponentially. The time required to reach the hydrodynamical regime and the related exponential decay is str ongly influenced by both the critical effects related to long-wavelength fl uctuations and the local order in the overlayer. We also analyze the influe nce of the memory effects on the effective diffusion barriers extracted fro m the Arrhenius analysis. For tracer diffusion, we find that the contributi on from memory effects can be as large as 50% to the total barrier. For col lective diffusion, the role of memory effects is in general less pronounced . [S0163-1829(99)03011-8].