ELECTRON-STIMULATED DESORPTION OF SODIUM ATOMS FROM OXIDIZED MOLYBDENUM

The time-of-flight technique combined with a surface-ionization-based detector has been used to investigate the yield and energy distributio n of sodium atoms escaping in electron-stimulated desorption (ESD) fro m adlayers on the surface of molybdenum oxidized to various degrees an d maintained at T=300 K as functions of incident electron energy and s urface coverage by sodium. The sodium-atom ESD threshold is about 25 e V, irrespective of sodium coverage and extent of molybdenum oxidation. Molybdenum covered by an oxygen monolayer exhibits secondary threshol ds at similar to 40 eV and similar to 70 eV, as well as low-energy tai ling of the energy distributions, its extent increasing with surface c overage by sodium theta. The most probable kinetic energies of sodium atoms are about 0.23 eV, irrespective of the degree of molybdenum oxid ation and incident electron energy at theta=0.125, and decrease to 0.1 7 eV as the coverage grows to theta=0.75. The results obtained are int erpreted within a model of Auger-stimulated desorption, in which adsor bed sodium ions are neutralized by Auger electrons appearing as the co re holes in the 2sO, 4sMo, and 4pMo levels are filled. It has been fou nd that the appearance of secondary thresholds in ESD of neutrals, as well as the extent of their energy distributions, depend on surface co verage by the adsorbate. (C) 1998 American Institute of Physics.