Electron emission yield of Al, Cu and Au targets induced by fast hydrogen and helium ions

The electron emission yield γ is measured for impact of H ⁺, He ⁺, He ²⁺ ions and of electrons on Al, Cu, and Au targets. The ion energy is between 0.5 MeV (H ⁺) and 4.8 MeV (He ²⁺), the electron energies are around 1 keV. The bare ion yield is compared with predictions of a model, which assumes the yield to be proportional to the stopping power and takes collective electric fields generated by the projectiles into account. The He ⁺ yield is explained by investigating the additional electron production of stripped electrons. It is found that the mean depth He ⁺ ions penetrate the surface layer without losing their bound electron and is about 60% of the mean escape length of the emitted electrons.