Electron-stimulated desorption of Li+ ions from silicon film-covered tantalum surfaces

The electron-stimulated desorption (ESD) yield for Li+ ions has been measured from Li layers adsorbed at T = 300K on silicided tantalum surfaces heated to different temperatures. The measurement were carried out using a static magnetic mass spectrometer combined with a retarding field analyzer. The ESD appearance threshold for Li+ ions is independent of the heating temperature and is close to the lithium 2s level ionization energy of 56 eV. Secondary thresholds for Li+ ions are observed at about 133 and 150 eV in ESD from layers adsorbed on silicided tantalum surfaces. The former is associated with double-ionization and subsequent inter-atomic Auger decay. The latter is attributed to the ionization of the silicon 2s level. The ESD yield of Li+ passes through a maximum as the concentration of deposited lithium increases. The peak width decreases and its height increases with the substrate heating temperature. The data can be interpreted within the Auger stimulated desorption model taking into account the local surface field relaxation.