Surface-charging effects in the X-ray photoelectron spectra of some semiconducting oxides

Abstract

The irradiation of poor electrical conductors in X-ray photoelectron spectroscopy induces an equilibrium charge at the sample surface. The resulting shifts in the spectra have been measured for a number of semi-conducting metal oxides (NiO, Co₃O₄ and ZnO) with a variety of pretreatment conditions. Heating the samples, or the adsorption of electron-donating or-withdrawing gases, causes potential shifts which could be related to the electrical properties of the substrate. These effects were investigated for nickel, cobalt and zinc oxides with the adsorbates NO, NO₂, NH₃, CO and O₂. The reactive system NO + O₂ was also investigated with the nickel oxide catalyst. It is found that, for a given sample configuration, this effect is reproducible, and can provide important information on the nature of adsorbed species.