Structural transformations in overlayer and sticking probability during chemisorption: oxygen on(100) surface of metals

The effect of the formation of p(2 x 2) and c(2 X 2) adsorption structures on the O-2 sticking probability was studied by the Monte Carlo simulation o f the O-2 chemisorption on a (100) metal surface. The model used in the sim ulation took into account the direct and indirect adsorption pathways and r epulsive lateral interactions in the adsorption layer. The ratio between th e activation energy of adsorption via the direct and indirect pathways ( E- dir/E-indir) determines the character of the structural transformations in the adsorption layer, which in turn determines the type of the S(theta) dep endence. At E-dir/E-indir < 7-8, the direct pathway predominates over the i ndirect one. In this case, a lot of small adsorption islands nucleate to fo rm a disordered p(2 X 2) and c(2 x 2) adsorption layers, i.e. Langmuir adso rption is observed, and S smoothly decreases with the a growth. At E-dir/E- indir > 7-8, the indirect pathway predominates over the direct one. In this case, after slow nucleation, the adsorption islands grow quickly to form o rdered p(2 X 2) and c(2 X 2) adsorption layers, i.e. the island-mediated ad sorption is observed and S(theta) dependence passes over a maximum. (C) 200 0 Elsevier Science B.V. All rights reserved.