Surface‐embedded oxygen: Electronic structure of Ag(111) and Cu(poly) oxidized at atmospheric pressure

Abstract

AbstractWe investigated the surface electronic structure of an oxidized Ag(111) single crystal and a polycrystalline Cu foil prepared under conditions of pressure and temperature (1000 mbar and 900 K) far beyond those used in usual UHV studies. It has recently been shown that a strongly bound oxygen species (Oγ) apart from oxygen atoms chemisorbed on the surface (Oα) or oxygen atoms dissolved in the bulk (Oβ) can be prepared on silver surfaces. Using core‐level photoemission we show these three atomic oxygen species, Oα, Oβ and Oγ, exhibit characteristic spectral properties. X‐ray absorption spectroscopy at the O K‐edge indicates that the formation of the strongly bound Oγ species is accompanied by a strong hybridization between O2p and Ag4d states and that also the Ag5sp states are important for the metal‐to‐oxygen covalent interaction. The reaction with methanol was used to selectively remove the surface‐embedded atomic species and to study the effect of the strongly bound oxygen Oγ species on the valence electronic structure of silver. This separation of the oxygen species did not work for the more reactive copper‐oxygen system. The chemical bonding interaction of the novel Oγ species with silver is discussed in terms of the ligand‐field theory emphasizing the covalent character of the interaction. For copper, the spectroscopic analysis is complicated by the existence of a stable oxide Cu2O with similar bonding properties of the oxygen than postulated for the surface‐embedded species in silver.