Low-Energy He, Ne And Ar Ion-Scattering From Metal-Surfaces - Background And Inelastic Effects

The 139° ion scattering spectra of He, Ne and Ar ions incident on polycrystalline W, Ta and Au are measured for incident energies ranging from 0.8 keV to 4 keV. The He + and Ar + scattering behaviour from W is found to be very similar to that from Ta and different from that from Au. The single collision peak is shifted of about 20 eV to lower energy when calibrated with the Au single collision peak and for He + scattering an important background contribution increasing with the incident energy is observed. These results cannot be explained by structure effects in the first atomic planes is revealed by simulation. They relate rather to differences in the charged fraction of ions scattered from inside the solid. This is interpreted on the basis of reionization at metal surfaces having a high density of electronic states above the Fermi level.