We present a detailed study of the electron emission from a thin MgO(100) film on a Mo substrate, bombarded with slow ${\mathrm{H}\mathrm{e}}^{+}$, ${\mathrm{N}\mathrm{e}}^{+}$, and ${\mathrm{A}\mathrm{r}}^{+}$ ions. Neither the high absolute number of emitted electrons per incoming ion nor the electron spectra can be due to Auger neutralization of the incoming ions at the MgO surface alone. Therefore, an additional mechanism is proposed: holes created in the MgO film are transported to the MgO-substrate interface where they give rise to an Auger neutralization process involving two electrons from the metal substrate conduction band.

• Received 12 April 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.167601