Electron-induced desorption of O+ ions from W,Mo and Cr

We have studied the electron-induced desorption (EID) of O⁺ ions from oxygen-covered polycrystalline W, Mo and Cr surfaces. As the incident electron energy is increased, desorption begins at about 25 eV, and increases dramatically at the binding energy major low-lying substrate core levels. In the range of electron energy studied, below about 200 eV, there are also other variations in ion yield not associated with known core levels. The peak ion kinetic energy is 7.8, 5.3 and 3.4 eV for W, Mo and Cr respectively, and is independent of incident electron energy. These measurements imply that the desorption is initiated by a core level ionization event, although the subsequent electronic transitions leading to desorption apparently differ from those occurring on metallic oxide surfaces.