A coverage study of the self-diffusion and chemical diffusion constants for disordered overlayers of Xe on W(110)

Abstract

The coverage dependence of the self-diffusion and chemical diffusion of submonolayer, disordered overlayers of Xe on W(110) at 150 K is found to be weak. The activation energies are all approximately 0.7 ± 0.2 kcal/mol for low to moderate ( θ = 0.2 to 0.6) coverages. The pre-exponential factors are on the order of 10 −3 to 10 −4 in the same range of coverages. In all cases, the chemical diffusion constant is found to be slightly larger than the self-diffusion constant. On the average, the velocities of different particles are positively correlated. The equal-time particle fluctuations are on the order of the average number of particles in a fixed probe area within the molecular dynamics cell. Consequently, for these disordered systems, we find the chemical diffusion constant to be comparable in magnitude to the self-diffusion constant.