Tuning the stoichiometry of surface oxide phases by step morphology: Ag(511) versus Ag(210).

We show by vibrational and photoemission spectroscopy and by ab initio calculations that in ultrahigh vacuum oxygen adsorption at stepped Ag surfaces causes the formation of surface oxide phases with different stoichiometry, depending on the morphology of the steps involved in the nucleation process. On Ag(511), characterized by close-packed steps and (100) terraces, subsurface O occupies tetrahedral interstitials and an Ag2O-like phase forms; on Ag(210), showing open step edges, subsurface oxygen ends up off center in octahedral sites and an AgO-like structure nucleates.