Diffusion on Amorphous Substrates

We consider diffusion on substrate with a frozen disorder. While in ordered state the moving particle meets always the same energy barrier in amorphous state there is a more or less broad distribution of the height of barriers. The effective activation energy Eeff that controls the diffusion process is not equal to the average activation energy barrier. Actually, Eeff is the highest barrier that the moving particle must overcome. In this way Eeff can be determined by solving a particular percolation problem. The threshold concentration depends on the length of the percolating cluster. Consequently, Eeff is also size dependent. So it is shown that the diffusion coefficient depends on the distance of diffusion The determination of the effective activation energy from the slope of the Arrhenius plot of the diffusion coefficient is misleading. The mean diffusion distance λ decreases strongly with temperature. . INTRODUCTION The aim of the present contribution is to investigate the temperature dependence of some parameters important for the surface diffusion on amorphous substrates. It is also demonstrated that, because of the disorder, the diffusion coefficient is becoming distance dependent D=D(L). We investigate the diffusion coefficient D and the mean diffusion distance λ. The latter depends on the average desorbtion time τdes (see [1,2]) as: des Dτ = λ (1) where the diffusion coefficient D depends on the intermolecular distance d and is reverse proportional to the average jump time τ.