Electron-stimulated desorption of lithium atoms from oxidized molybdenum surface

The yield and energy distributions of lithium atoms upon electron-stimulate d desorption from lithium layers adsorbed on the molybdenum surface coated with an oxygen monolayer have been measured as functions of the impact elec tron energy and lithium coverage. The measurements are performed using the time-of-flight technique and a surface ionization detector. The threshold o f the electron-stimulated desorption of lithium atoms is equal to 25 eV, wh ich is close to the ionization energy of the O 2s level. Above a threshold of 25 eV, the yield of lithium atoms linearly increases with an increase in the lithium coverage. In the coverage range from 0 to 0.45, an additional threshold is observed at an energy of 55 eV. This threshold can be associat ed with the ionization energy of the Li 1s level. At the electron energies above a threshold of 55 eV, as the coverage increases, the yield of lithium atoms passes through a maximum at a coverage of about 0.1. Additional thre sholds for the electron-stimulated desorption of the lithium atoms are obse rved at electron energies of 40 and 70 eV for the coverages larger than 0.6 and 0.75, respectively. These thresholds correlate with the ionization ene rgies of the Mo 4s and Mo 4p levels. Relatively broad peaks in the range of these thresholds indicate the resonance excitation of the bond and can be explained by the excitation of electrons toward the band of free states abo ve the Fermi level. The mean kinetic energy of the lithium atoms is equal t o several tenths of an electronvolt. At electron energies less than 55 eV, the energy distributions of lithium atoms involve one peak with a maximum a t about 0.18 eV. For the lithium coverages less than 0.45 and electron ener gies higher than 55 eV, the second peak with a maximum at 0.25 eV appears i n the energy distributions of the lithium atoms. The results obtained can b e interpreted in the framework of the Auger-stimulated desorption model, in which the adsorbed lithium ions are neutralized after filling holes inside inner shells of the substrate and lithium atoms. (C) 2000 MAIK "Nauka/Inte rperiodica".