CHARGE-EXCHANGE IN LOW-ENERGY HE+ ION-SCATTERING FROM SOLID-SURFACES

We present a model for neutralization of He+ based on resonant charge transfer from a surface valence band to the He 2s level, followed by Auger deexcitation or autoionization, thus creating a He atom in the ground state. If a He+ ion approaches a surface, it is energetically favorable for the He-surface system to screen the Is core hole by putting an electron in the 2s level. By taking into account this Coulomb interaction Q we are able to explain the trend in the neutralization behavior of 1-5-keV He+ ions scattered from clean metal surfaces. It is shown that the neutralization probability of He+ is mainly determined by the work function and the surface local density of states.