On-surface and subsurface adsorption of oxygen on stepped Ag(210) and Ag(410) surfaces

The adsorption of atomic oxygen and its inclusion into subsurface sites on Ag(2 1 0) and Ag(4 1 0) surfaces have been investigated using density functional theory. We find that-in the absence of adatoms on the first metal layer-subsurface adsorption results in strong lattice distortion which makes it energetically unfavoured. However subsurface sites are significantly stabilised when a sufficient amount of O adatoms is present on the surface. At high enough O coverage on the Ag(2 1 0) surface the mixed on-surface + subsurface O adsorption is energetically favoured with respect to the on-surface only adsorption. Instead, on the Ag(4 1 0) surface, at the coverage we have considered (3/8 ML), the existence of stable terrace sites makes the subsurface O incorporation less favourable. These findings are compatible with the results of recent HREEL experiments which have actually motivated this work.