Cross sections for electron-stimulated desorption of alkali-metal atoms from adlayers on oxidized tungsten

Earlier cross-section measurements of electron-stimulated desorption (ESD) of Li, Na, K, and Cs atoms from adlayers on oxidized tungsten are analyzed with respect to substrate temperature and degree of oxidation. It is conjectured that the ESD cross sections are determined by the ratio of the rates of neutral alkali-metal re-ionization on the surface and of relaxation of the O + charge in the substrate. A comparison with experiment revealed the dependence of the re-ionization rate of an alkali-metal adatom on its size and mass, as well as the dependence of the O + charge relaxation rate on substrate temperature and degree of oxidation. The relation of the charge relaxation time to the substrate band structure is discussed.