Reactions of oxygen atoms and molecules with Au, Be, and W surfaces

In this study, the adsorption of atomic oxygen on polycrystalline gold, tungsten and single crystalline beryllium (0001) surfaces is investigated at room temperature and compared with molecular oxygen. The O atoms are produced by microwave discharge in pure O2. The gaseous reactants effuse into a UHV chamber. The adsorption or chemical reaction of the oxygen atoms and molecules impinging on the metal surfaces is monitored by X-ray photoelectron spectroscopy (XPS). The main observations of this study are summarized as follows. The gold surface is inert to molecular oxygen but adsorbs O atoms up to a coverage of one monolayer. Beryllium adsorbs both molecular and atomic oxygen and is also oxidized by both species. The rate of oxide formation is significantly larger for O atoms. In the case of tungsten, there is no difference between atoms and molecules in the amount of oxygen adsorbed. Neither species, however, forms any phase of tungsten oxide. Only tungsten binding energies characteristic of the pure metal and for oxygen adsorbed within the first atomic layer are detected.