Plasmon Excitation by Multiply ChargedNeq+Ions Interacting with an Al Surface

The emission of low-energy electrons caused by $4.5\mathrm{keV}\mathrm{Ne}{}^{q+}$ ion impact on an Al surface was measured for incident charge states $q=1\mathrm{}–6$. 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 $q=6\mathrm{}$. 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.