High energy electrons in He+/HOPG induced electron emission

N. BAJALES, S.MENDOZA, L. J. CRISTINA, J.C.MORENO, M.C.G.PASSEGGI (JR.), E. C. GOLDBERG, J. FERRÓN, R.BARAGIOLA, G.ZAMPIERI

San Carlos de Bariloche, Argentina

Conferencia; 13th International Conference on Solid Films and Surface; 2006

The processes leading to the secondary electron emission (SEE), induced by low energy ions, have been historically divided in two mechanisms: kinetic and potential electron emission. The release of the incoming ion potential energy can occur through Auger neutralization (AN) or resonant neutralization (RN), which may be followed by an Auger de-excitation (AD). If the incoming ion hole is bond by at least twice the work function of the solid, the electron emission occurs. Although ion induced electron emission has been a matter of an enormous amount of work, a permanent revival of its interest is prompted by new experiments promoting new theories and indeed a lot  of debate. In this line, we present measurements of He+ on HOPG induced electron emission revealing the presence of secondary electrons of high energy, far beyond the energies expected on the basis of AN, RN and AD. Since in HOPG, plasmons do not decay through electron emission, a new mechanism is needed. Supported on a quantum time-dependent calculation, we propose an Auger de excitation of ion induced excitons,  for explaining  the appearance of these high energy secondary electrons. Preliminary results about the effect of ion bombardment on HOPG density of states, studied through ELS, e-SEE, K-edge and STM are also presented.