Criticality effects on diffusion on heterogeneous surfaces

In this work, we investigate the influence of energetical lattice heterogeneities on the finite-size scaling behavior of the tracer diffusion coefficient in the vicinity of a critical point. For this purpuse, we study a lattice gas with pairwise repulsive nearest-neighbor (NN) interactions on a square bivariate trap surface, with deep trap concentrations Θ ranging from 0 to 5%. This well-known and frequently studied system exhibits c(2×2) ordering below the critical temperature Tc=0.567ϕNN/kB. We show that the presence of a small amount of deep adsorption sites (traps) strongly influences adsorbate diffusion near the phase transition. Dt depends on the lattice size L of the lattice near Tc. For all values of L studied, Dt(T)θ=0.5 is a smooth function and exhibits an inflexion point at or near Tc. Its derivative, ∂Dt/∂(1/kBT), exhibits cusp-like maxima. The behavior of these maxima is analyzed in terms of finite-size scaling theory.