Electron-stimulated desorption of europium atoms from an oxidized tungstensurface

The yield of europium atoms in electron-stimulated desorption from Eu layer s adsorbed on the surface of oxidized tungsten was studied with a surface-i onization detector as a function of the incident-electron energy, surface c overage by europium, and degree of tungsten oxidation. The yield of Eu atom s measured as a function of electron energy exhibits a distinct resonant ch aracter with peaks at electron energies corresponding to europium and tungs ten core-level ionization energies. The peaks associated with the europium ionization reach a maximum intensity at europium coverages less than 0.1 an d decrease subsequently to zero with increasing coverage, while the peaks d ue to tungsten ionization pass through the maximum intensity at a monolayer europium coverage. The coverage corresponding to the maximum europium atom yield grows with increasing tungsten oxidation. The results obtained are a ccounted for by the formation of the europium and tungsten core excitons. I n the first case, the particles desorb in the reverse motion toward the sur face of the oxidized tungsten; in the second, they desorb as a result of re pulsion between the tungsten core exciton and the EuO molecule. (C) 2001 MA IK "Nauka/Interperiodica".