Electron-stimulated desorption of europium atoms from the surface of oxidized tungsten: Concentration dependence of the low-energy peak

The nature of electron-stimulated desorption of europium atoms Eu-0 at low incident electron energies E-e (similar to30 eV) and the specific features of the dependence of the yield of europium atoms Eu-0 on their concentration on the surface of oxidized tungsten are discussed. The crucial stage is found to be the primary event of vacancy creation in the inner 5p shell of the europium adatom. As follows from estimates, only the first of the two possible ionization scenarios (intratomic electron transfer to the outer shell of the Eu adatom or ejection of the knocked-out electron into vacuum) results in Eu-0 desorption. The concentration threshold of the Eu-0 yield is determined. (C) 2002 MAIK "Nauka/Interperiodica".