A model involving a two-dimensional system of charged particles and vacancies was investigated. The particles interacted via isotropic forces, attractive or repulsive, with nearest and next-nearest neighbours and could move through the lattice. Using Monte Carlo simulations, the mean-square displacement was determined as a function of time, temperature, coverage and range of interaction. Also estimated was the tracer diffusion coefficient and the activation energy. It was shown that some characteristics were rather insensitive to the range of interaction, while others varied markedly. In particular, the formation of a single domain along one direction was possible for rather high coverages in the case of interaction with nearest-neighbours but could occur at much lower coverages when the interactions were also with next-nearest neighbours. Such a situation could be temporarily unstable in that single-cluster stretching along the lattice in one direction could break, and then re-join again; sometimes in a direction orthogonal to the original one. It was shown that, depending upon the temperature, coverage and range of interaction, the model exhibited sub-diffusion, normal diffusion or super-diffusion. The movements of the particles could sometimes not be described by a power-law function. It was also demonstrated that the type of pattern formed, and the type of diffusion, depended upon whether the lattice had an odd or even number of sites.

Surface Diffusion of Charged Particles - Monte Carlo Study. K.Pawlikowski, A.Pękalski: Physical Review B, 2009, 79[4], 045419