Collective diffusion of O/W(1 1 0) at high coverages: Monte Carlo simulations

The diffusion coefficient of the O/W(1 1 0) system at low temperatures, below critical point, exhibits some interesting properties. It is observed that the activation energy of the diffusion process increases rapidly at the phase transition from disordered to the ordered (2 × 1) phase. It is possible to model this rapid change in the activation energy, by proper choice of the transition probabilities in the lattice gas model. This rapid increase of the activation energy is visible as the change of the scaling of the diffusion curves. In the present work we use the same transition rates to calculate the diffusion coefficient at higher densities from 0.5 to 1. Scaling function shows how the activation energy varies with density. The density dependence of the activation energy changes its character on coming from lower to higher temperatures, what can be related to the changes in the phase diagram.