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Abstract:
A Monte Carlo simulation method was applied to study the desorption process of submonolayer amounts of Ag atoms from Ru(001). The attractive lateral interactions between Ag atoms leading to island formation are also manifested in the desorption kinetics. First the equilibrium configuration of the Ag overlayer of hexagonal symmetry was simulated for different coverages. In the simplest case the desorption rate is evaluated as the sum of first order desorption rates of Ag atoms having 0, 1, 2, ...6 nearest Ag-Ag bonds, assuming the preexponential factor for desorption to be constant. The stimulated desorption curves exhibit quasi-zeroth order desorption kinetics for initial Ag coverages less than 0.35 ML. At higher coverages the desorption spectra are shifted towards higher temperatures and no unique slope can be identified. When the pre-exponential factor, however, is assumed to increase with Ag coverage according to a simple combinatory formula, the calculated desorption spectra exhibit the quasi-zeroth order behaviour also up to higher coverages in qualitative agreement with experimental results.
