XPS and UPS studies of oxygen adsorption over clean and carbon-modified silver surfaces

Abstract

Oxygen adsorption over clean and carbon-modified silver surfaces has been studied by XPS and UPS in the temperature range 300–700 K under O 2 pressures from 10 −3 to 10 Pa. Adsorption over a clean silver surface at T>420 K leads to the appearance of atomically adsorbed oxygen on the surface, which is characterized by E B(O 1s) = 528.5 eV, high reactivity towards CO and a heat of adsorption of 100 kJ/mol. Subsurface oxygen is formed in small amounts. Increasing the O 2 pressure to 10 Pa does not lead to the formation of new adsorption forms. At T < 420 K carbonate structures with E B(C 1s)=287.8 eV and E B(O 1s)=530.6 eV are formed on the surface. During interaction of O 2 with the silver surface containing dissolved carbon in the bulk, the surface is modified by O and C due to CO bond formation in the subsurface region. The O 2 adsorption at high pressures (10 Pa) on the modified surface is characterized by the formation of a new oxygen state with E B=530.3 eV. Based on UPS spectra characteristics (the peak at E B θ9.5 eV), this state is supposed to be of molecular form.