XPS and UPS study of oxygen states on silver

An investigation of the nature of the silver-oxygen bond for different oxyg en states on the silver surface has been carried out by XPS and UPS. The XP S analysis shows the Eb(Ols) to range from 528.0 to 534.0 eV, which is much wider than for other oxygen-metal systems. The low O1s binding energies wi th E-b(O1s) = 528.0-529.0 eV can be reliably related to atomic oxygen of ox ide-like structures characterized by ionic O-Ag bonding. The higher binding energies indicate the covalent character of the Ag-O bond with no charge p olarization. UPS allowed us to reveal five additional characteristics in th e valence band after high-temperature oxygen treatment, when the oxygen sta tes with E-b(O1s) = 530.4 eV appear in spectra. They are related to quasimo lecular oxygen species. On the basis of these data, the quasimolecular char acter of the oxygen states with E-b(O1s) > 530 eV is postulated. The experi ments demonstrate an abnormally high thermal stability (T-des > 800 K) of t hese oxygen states. Some proposals to account for the results obtained are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.