The scattering of low energy helium ions and atoms from a copper single crystal. Elastic and inelastic effects

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Abstract
The scattering of 4–10 keV Helium ions from a copper surface can be described reasonably well with elastic, single collisions, even for fairly small scattering angles. However, in a more refined analysis of the experimental results, deviations from this behaviour are observed. Measurements of the energy and the width (FWHM) of the surface peak have been performed. The general behaviour can be explained by differences in inelastic energy losses for scattering from an ideal surface and from surface structures (surface damage). By comparing measurements in which the target is bombarded along different directions, it is shown that multiple scattering effects have only a minor influence. Additional information about the inelastic processes is obtained by performing scattering experiments with a primary atom beam. It appears that, for large angles of incidence, the energy of the reflected ions is reduced about 20 eV if the primary beam consists of atoms instead of ions. This difference is almost independent of the energy of the projectiles. An explanation of this effect is given by the charge exchange model, proposed previously by the authors. The model also explains the different behaviour at small angles of incidence. Indications were found which suggested that in the investigated energy range the electronic stopping power depends on the charge state of the primary particles. The results have been compared with the Lindhard theory. The agreement between our experiments and the LSS theory is rather good.