Oxygen interaction with disordered and nanostructured Ag(001) surfaces

We investigated O-2 adsorption on Ag(001) in the presence of defects induce d by Ne+ sputtering at different crystal temperatures, corresponding to dif ferent surface morphologies recently identified by scanning tunneling micro scopy. The gas-phase molecules were dosed with a supersonic molecular beam. The total sticking coefficient and the total uptake were measured with the retarded reflector method, while the adsorption products were characterize d by high resolution electron energy loss spectroscopy. We find that, for t he sputtered surfaces, both sticking probability and total O-2 uptake decre ase. Molecular adsorption takes place also for heavily damaged surfaces but , contrary to the flat surface case, dissociation occurs already at a cryst al temperature, T, of 105 K. The internal vibrational frequency of the O-2 admolecules indicates that two out of the three O-2(-) moieties present on the flat Ag(001) surface are destabilized by the presence of defects. The d issociation probability depends on surface morphology and drops for sputter ing temperatures larger than 350 K, i.e., when surface mobility prevails he aling the defects. The latter, previously identified with kink sites, are s aturated at large O-2 doses. The vibrational frequency of the oxygen adatom s, produced by low temperature dissociation, indicates the formation of at least two different adatom moieties, which we tentatively assign to oxygen atoms at kinks and vacancies. (C) 2001 American Institute of Physics.