Adsorption of gases on polycrystalline nickel films studied by X-ray and ultra-violet photoelectron spectroscopy

Abstract

The adsorption of a series of gases onto clean evaporated films of polycrystalline nickel has been studied using ultraviolet and X-ray photoelectron (u.p.e. and X.p.e. respectively) spectroscopy. Observation of the intensity of photoemission from states close to the Fermi level enables conclusions to be drawn regarding the nature of the adsorbate–metal bond. Different mechanisms are shown to be involved between the two series CO—, C₂H₄—, O₂— and H₂S—Ni, and H₂O—, CO₂—Ni. It is further demonstrated that u.p.e. may be used to follow a surface reaction; results show the progressive displacement by O₂ of CO adsorbed on clean Ni. Interpretation of the ultra-violet spectra of adsorbed species is discussed in terms of a possible correlation with energy states of the free molecules.