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 1s 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.
Oetelaar, van den, R. J. A., & Flipse, C. F. J. (1995). Charge exchange in low-energy He+ ion scattering from solid surfaces. Physical Review B: Condensed Matter, 52(15), 10807-10807. https://doi.org/10.1103/PhysRevB.52.10807