Plasmon-Assisted Electron Emission from Al and Mg Surfaces by Slow Ions

We report energy distributions of electrons emitted from Al and Mg surfaces bombarded by 30–4500 eV ${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, and ${\mathrm{Ar}}^{+}$ ions, which contain structure consistent with the decay of surface and bulk plasmons. We propose that plasmon excitation is due to the sudden change of the surface dipole (incident ion plus image charge) resulting from the disappearance of the image charge and appearance of a hole in the metal.