Electron-stimulated desorption of lithium ions from silicided tantalum surfaces

Electron-stimulated desorption (ESD) of lithium ions has been studied from lithium layers adsorbed on silicided tantalum surfaces, by means of a static magnetic mass spectrometer combined with a retarding field analyzer. The concentration of silicon in the subsurface region of the samples has been measured using Auger electron spectroscopy. The silicided tantalum surfaces are prepared by depositing silicon onto tantalum at room temperature, followed by annealing at different temperatures. The ESD appearance threshold for lithium ions is close to the Li Is ionization energy of 55 eV and is independent of the deposited lithium concentration. Additional thresholds are observed at about 130 and 150 eV. The 130 eV threshold exceeds by about 30 eV the ionization energy of the Si 2p level and may be due to double ionization. The 150 eV threshold may be related to the ionization of the Si 2s level. The ESD yields of lithium ions associated with the 55 eV and with the 130 eV (150 eV) thresholds peak at different concentrations of deposited lithium. There is no correlation between the maximum ESD yield of lithium ions and the concentration of silicon on the surface. This effect may be associated with phase transitions in silicided tantalum occurring at different annealing temperatures. The results can be interpreted in terms of the Auger stimulated desorption model, taking into account the local surface field relaxation. (C) 2000 Elsevier Science B.V. All rights reserved.