Desorption of negative ions on metallic samples by very low energy electrons

Abstract

Electro-stimulated experiments were performed in a classical microscope for secondary ion emission; the immersion collection lens is providing a very good collection of the ions emitted with low initial energies. The electron beam decelerated just as the sample neighbourhood is bombarding the target with a low and easily adjustable energy and with a high density nearly independent of the electron energy. The variations of desorption yields with electron energy and the energy distributions of the desorbed ions could be recorded directly. Among the preliminary results one should emphasize: (i) The desorbed H − yields exhibit a sharp peak at low energies depending on the metal of the sample (varying from 3.2 to 6.7 eV for Al and Cr, respectively), (ii) The O − desorption yield is modified by the electron energy during the adsorption process; the desorption curves show distinct changes in their slopes, (iii) H − and O − ions are emitted with very low initial energies; their spread in energy (about 1 eV) remains nearly independent of the incident electron energy.