Ultra-violet and X-ray photoelectron spectroscopy studies of oxygen chemisorption on copper, silver and gold

Abstract

A photoelectron study (HeI, HeII and Mg Kα) of the oxidation at ordinary temperatures of polycrystalline copper, silver and gold, by both ground-state molecular and excited oxygen has established which oxidation states of these metals are formed during and after the dissociative chemisorption of oxygen. Up to about a monolayer coverage, copper is converted to the Cu(I) state and thereafter, as oxygen uptake proceeds, to the Cu(II) state. Silver also initially forms a + 1 oxidation state, but both the magnitude of the line widths of, and the significant absence of satellites associated with the core-level peaks suggest that a diamagnetic Ag(III) oxide rather than Ag(II) is formed upon further oxidation. Gold does not proceed beyond the Au(I) state. The densities of states (as reflected in the HeII spectra) of the three metals offer less guidance as to the conditions or ease of formation of the M(I) oxide overlayers, than the energy differences between the s-band edges and the vacuum level.