DynamicK- andL-shell filling ofNe9+projectiles interacting with an Al(111) surface

Secondary-electron spectra of H-like ${\mathrm{Ne}}^{9+}$ ions incident with energies from 135 eV to 22.5 keV on an Al(111) surface were measured. The dependence of the K and L Auger electron yield on the energy of the projectile is studied. It is found for low impact energies that the angular distributions of the overall K Auger peak and the 740-eV component, which was formerly attributed to above-surface emission, show nearly the same anisotropy. Hence, the data provide evidence for K Auger emission from below the surface. Furthermore, for low projectile energies, it is found that, on average, two to three electrons are present in the L shell during the L and K Auger emission. For higher energies, the L shell is nearly empty during the L Auger emission, whereas five to six electrons are present in the L shell during the K Auger emission. Moreover, it is found that for higher energies the L Auger intensity is strongly reduced. These findings are attributed to the enhanced absorption of the L-shell electrons in the solid, as well as to a strong velocity dependence of the charge transfer directly into the Ne L shell.