First principles calculation of ion induced kinetic electron emission from nearly free-electron metals below the plasmon threshold

The excitation of electrons by decay of plasmons generated directly during the interaction of the impinging particle with the system of conduction electrons of the metal results in an important contribution to the electron emission at higher impact energies. However, also below the so-called plasmon threshold (nearly 40 keV for proton impact on Al), when a direct excitation of plasmons is impossible, several experimental investigations show a remarkable contribution of kinetic excitation of plasmons. Starting from first principles, a theoretical description of the plasmon excitation during the electron capture process as well as by fast secondary electrons generated by binary ion-electron collisions is given. Explicit calculations were performed for proton impact on Al