Desorption kinetics from disordered surfaces: partial initial coverage

To fully study the kinetics of desorption from disordered surfaces, both energetically homogeneous and heterogeneous, it is necessary to model the desorption process considering various partial initial coverages. The challenge arises from the fact that the initial equilibrium configuration is fitted to a Fermi-Dirac distribution function, where each set of adsorption sites has a statistical weight associated with it. When all sites are equally accessible this statistical weight can be calculated by a simple ratio of available sites to total sites. An amorphous surface on the other hand presents the difficulty of sites not being equally accessible due to varying numbers of nearest neighbors, with some even becoming completely inaccessible once particles desorb from them. By using a kinetic Monte Carlo scheme we can keep track of the rates of desorption rates from all groups of sites, while also calculating transient variations in the energy of activation and preexponential factor. We attempt to find statistical weights to properly model the equilibrium configuration for partial coverage, not only for thermal desorption, but also for adsorption kinetics on disordered surfaces.