Low-Energy Electron Interaction with Coadsorbates on Tungsten

Abstract

The effect of low-energy electrons (20–300 eV) impinging on cesium, mercury, and oxygen adsorbed on clean and oxygenated tungsten has been studied by field-emission techniques. Desorption cross sections were determined from the work-function changes and the known relationships between work function and coverage for the various systems studied. For cesium on clean tungsten and for mercury on both clean and oxygenated tungsten, the cross sections are less than 10−21 cm2, the minimum level of sensitivity for these experiments. Cesium is desorbed from an oxygenated tungsten surface by the impact of 250 eV electrons without disturbing the underlying chemisorbed oxygen layer. Cross sections for the desorption of cesium from oxygenated tungsten increase with increasing cesium coverage to a maximum of 8×10−20 cm2, and are insensitive to the amount of underlying oxygen. These results suggest that an important change in the character of the surface bond is effected by the underlying oxygen layer, in particular, a greater localization of the bonding electrons in the cesium-oxygen bond as compared to the cesium-tungsten bond.