Concentration dependences of diffusion coefficients of atoms adsorbed on heterogeneous surfaces

Concentration dependences of self-diffusion coefficients and mass transfer of atoms adsorbed on heterogeneous surfaces are investigated within the entire range of monolayer coverage. Hops of atoms to the neighboring free adsorption sites within the monolayer and lateral interactions between the nearest neighbors are taken into account in the quasi-chemical approximation. Model surfaces of various topography - spotty, chaotic, and ordered of the c(2 × 2) type containing two sorts of adsorption sites and also an amorphous TiO2 (rutile) surface with a great number of adsorption site types - are considered. The peculiarity of Ar adsorption on rutile is Ar atom blocking of several neighboring adsorption sites. To allow for this fact, we use a quasi-one-site model based on dividing the area occupied by an atom with a finer lattice. The feasibility of predicting the concentration dependences of self-diffusion and diffusion coefficients using equilibrium data on heats and isotherms of adsorption is discussed.