Electron induced ion desorption of oxygen adsorbed on rhenium

The behavior of low energy electron-stimulated O⁺ ions desorbing from oxygen adsorbed on polycrystalline rhenium samples has been found to be significantly different from those observed desorbing from other oxygen ad layers. Oxygen initially adsorbed at 300°K has an ionic desorption cross section below the level of detectability, (< 10⁻⁹ ions/electron) in these experiments, a result in accordance with that previously observed on other metals. On continued oxygen exposure, the O⁺ signal first increases to a maximum value and then decays to a lower level; the rate of both these processes is directly proportional to the oxygen pressure in the gas phase. If the temperature of the ad layer is raised above 300°K, the adsorbed species with high ionic desorption cross section are removed at about 500°K. At higher temperatures, O⁺ ions which can be related to the oxygen initially adsorbed are detected. The possible reasons for the observed O⁺ desorption characteristics for oxygen on rhenium are discussed.