XPS and UPS study of oxygen states on silver

An investigation of the nature of the silver–oxygen bond for different oxygen states on the silver surface has been carried out by XPS and UPS. The XPS analysis shows the Eb(O1s) to range from 528.0 to 534.0 eV, which is much wider than for other oxygen–metal systems. The low O1s binding energies with Eb(O1s)=528.0−529.0eV can be reliably related to atomic oxygen of oxide-like structures characterized by ionic O–Ag bonding. The higher binding energies indicate the covalent character of the Ag–O bond with no charge polarization. UPS allowed us to reveal five additional characteristics in the valence band after high-temperature oxygen treatment, when the oxygen states with Eb(O1s)=530.4eV appear in spectra. They are related to quasimolecular oxygen species. On the basis of these data, the quasimolecular character of the oxygen states with Eb(O1s)>530 eV is postulated. The experiments demonstrate an abnormally high thermal stability (Tdes>800 K) of these oxygen states. Some proposals to account for the results obtained are discussed.