A new kinetic theory for thermal desorption of two‐dimensional islands

Abstract

The theory for the desorption kinetics of adsorbates on solid surfaces usually contains a factor Nx where N is the adsorbate concentration and x is the order parameter. In the case of weak adsorption in which attractive lateral interactions are stronger than the bonding to the surface, two‐dimensional (2D) circular islands often form with desorption limited by atomic dissociation from island edges; here x=1/2 is often used. This is correct only if all islands have the same diameter, which explains why fits to experimental data are often poor. This paper describes a new theory that avoids this difficulty. Following earlier work on indiffusion from adsorbate islands, it is based on the reasonable assumption that the probability that an edge atom will dissociate is independent of the island diameter. Therefore, the velocity of decrease of an island radius is the same for all islands. It provides an excellent fit to published data, and yields a value for the dissociation energy and information on the distribution of island sizes.