Adsorption of oxygen on potassium- and barium-dosed au surfaces: X-ray photoelectron and ultraviolet photoelectron spectroscopy studies

Abstract

XPS and UPS studies on potassium- and barium-covered Au surfaces show increased adsorption of oxygen relative to that on clean gold. Below 150 K, the peroxide species O^2–₂(ad) and the ionic species O^–(ad) are seen. The peroxide species is characterised by an O (1s) peak at 533 eV and O (2p) bands at 6.4, 9.2 and 12.1 eV. O^–(ad) species associated with the alkali metal is characterised by O (1s) at 531 eV and O (2p) at 8.5 and 11 eV. A small amount of O^2–(oxidic) oxygen is also seen at low alkali-metal coverages at 300 K with O (1s) at 529.5 eV and O (2p) at 4.8 eV. O^2–₂ is stable below 150 K and O^– and O^2– are stable up to 500 K. Intermixing of the surface Au layers with a K adlayer is indicated with possible diffusion of K into the subsurface region.