Dynamics of adsorbed atoms under non-equilibrium conditions

Abstract

This paper deals with the determination of the tracer (DT) and chemical (Dch) surface diffusion coefficients in the presence of a gradient of the coverage . The lattice gas model and quasi-chemical approximation are taken as accepted in the theory. The results are discussed with respect to the interaction energy of particles, which influences the equilibrium energy of atoms as well as the saddle-point energy. Such interactions break the symmetry of jumps in the systems with gradient grad . This model predicts a decrease of DT with the square of the gradient of the coverage .Dch depends on the coefficient of proportionality of the difference between the mean jump rate in the direction of grad and that in the opposite direction. It has been found that, in the case of repulsive interaction, the coverage dependencies of DT and Dch have local maxima, whose positions depend on the rates of change of the saddle-point energy and of the equilibrium energy of the atoms due to the interaction. For attractive interaction, DT either decreases with or increases depending on the saddle-point energy changes. At low temperatures our results differ substantially from those of the calculations made within dynamical mean-field theory.