Inelastic energy losses of He+ ions singly scattered from polycrystalline chromium

The inelastic energy losses of He+ ions singly scattered from polycrystalline chromium (Cr) surface in the 0.7–2.0 keV energy range were experimentally investigated in this work. The energy spectra of ions scattered to 90° were measured. The peak corresponding to singly scattered ions is resolved into two Gaussians. The one at higher energies (elastic peak) corresponds to the He+ ions that were not neutralized along the trajectory, while that at lower energy (inelastic peak) is attributed to the He+ ions that were neutralized while approaching the surface and then reionized during the violent collision with Cr surface atoms. The difference between the positions of these Gaussians is a measure of the inelastic energy losses caused by the projectile reionization. These discrete inelastic losses are interpreted using the model of Tsuneyuki and Tsukada. It was observed that the energy difference between the elastic and inelastic peak increases with the incident ion energy. The elastic and inelastic peak intensities depend on the incoming angle and the character of this dependence abruptly changes for the incident ion energies in the range 1350–1400 eV, which cannot be explained by the existing theoretical models.