Angular distribution ofKAuger electrons ejected by highly charged ions interacting with an Al(111) surface

Secondary electron spectra of the H-like ${\mathrm{Ne}}^{9+}$ ion incident with impact energies of 135 eV up to 90 keV on a solid Al(111) surface were measured. The dependence of the K Auger electron yield on the angle of observation is studied in detail. It is found to be cosine like in case of the 90-keV ${\mathrm{Ne}}^{9+}$ ions and to be more and more isotropic at lower ion energies although a clear anisotropy remains. Information about the rates of the filling of the L and K shells inside the solid is obtained from a comparison of the measured angular distributions with the calculation of a two-step model for the successive filling of the L and K shells. The data show clear evidence for Auger electron emission from below the surface for ion energies as low as 135 eV.