Ion-induced electron emission from crystal targets with noncrystalline overlayers

We have measured keV secondary electrons induced by 56 MeV O8+ under channeling and nonchanneling incidence conditions for Si and Ge crystals covered with noncrystalline Al, Si, Ag, and Au layers less than 350 Angstrom thick. The analysis indicates that the enhanced electron yield due to the thin overlayer in the channeling case results dominantly from the effective increase in the number of high-energy recoiled electrons that are incident on the underlying crystal region. In the nonchanneling case, backscattering of the recoiled electrons from the overlaid atoms is of essential importance to account for the observed yield. (C) 1998 Elsevier Science B.V.