Kinetic model for desorption of paired adatoms

Abstract

By employing an extension of the Glauber–Ising model, the kinetics of the desorption of paired adatoms from a linear chain is studied. Three competitive mechanisms for changing a state of the system are allowed, namely desorption from or readsorption onto the chain or migration of the adatoms from site to site on the chain. The transition probabilities depend on an external field, on the interaction between nearest neighbors, and on three proper rate constants characterizing desorption, readsorption, and migration processes. An infinite set of coupled kinetic equations is obtained from the master equation. In order to compute the adsorption degree ϑ and the fraction of adjacent adatom pairs η, a ’’closure’’ approximation is taken. The steady-state solution is in agreement with the exact result of the equilibrium statistical mechanics. We find that relaxation far from equilibrium is, in general, not describable by a single exponential. The relaxation is slower when mobility does not exist than when adatoms are mobile, though the system behavior is similar in both cases. Equilibrium state is reached most quickly when lateral interaction does not exist and the final adsorption degree is 0.5. Attractive lateral interaction yields relaxation slower than when interaction is null, while repulsive interaction favors an initial relaxation very quickly, and the system reaches an adsorption degree lower than the final one, passes through a minimum and tends to equilibrium state slowly.