Plasmon excitation by multiply charged Neq+ ions interacting with an Al surface

The emission of low-energy electrons caused by 4.5 keV Neq+ ion impact on an Al surface was measured for incident charge states q = 1-6. The electron spectra exhibit structures near 6.5 and 11 eV which are attributed to the creation of surface and bulk plasmons, respectively. The signature for bulk plasmon disappears for q = 6. It is argued that, for the higher charge states, the bulk plasmons are selectively created below the surface where the resonance condition for plasmon-assisted electron capture is achieved.