EXCITATION OF QUASI-PARTICLES DURING GRAZING-ANGLE ION REFLECTION AT AL SURFACES

We have studied ion-induced electron emission during grazing-angle scattering of 150 keV protons at clean and oxygen-covered Al surfaces. The angle-resolved energy distribution of emitted electrons reveals, in the energy range of 0-30 eV, characteristic peaks, which are directly correlated to various electron excitation mechanisms. For clean Al surfaces, these processes include single electron excitation and excitation of electrons by decay of ion-excited surface and bulk plasmons. At submonolayer oxygen coverages of the Al surfaces, we already find a drastic decrease of the electron emission peak at 6 eV, which is due to the decay of surface plasmons, and an increase of the O(2s2p2p) Auger electron emission peak located at about 5 eV.