Proton-induced kinetic plasmon excitation in Al and Mg

We report energy distributions of electrons emitted from Al and Mg surfaces bombarded by 3--100-keV/amu hydrogen and deuterium ions. The energy spectra contain structure consistent with the decay of bulk plasmons, even below the velocity threshold expected from current theories. To explain the results we compare the importance of additional mechanisms involving electron capture, lattice-assisted excitation, and excitation by fast secondary electrons.