Angular Studies of Potential Electron Emission in the Interaction of Slow Ions with Al Surfaces

We report energy distributions of electrons emitted from Al surfaces under impact by $1{\mathrm{keV}\mathrm{Ar}}^{+}$ and $1–5{\mathrm{keV}\mathrm{Ne}}^{+}$ ions. The variation of the energy distributions with the angle of incidence is different for both ions and provides information on the mechanism responsible for electron emission. For ${\mathrm{Ar}}^{+}$ electron emission results mainly from Auger neutralization, while for ${\mathrm{Ne}}^{+}$ an important emission mechanism is the decay of plasmon excitations. We find a transition between surface and bulk plasmon excitations as the energy of the ion is increased.