Spectra of secondary electrons induced by channeled and nonchanneled ions in Si and Al

Energy spectra are measured in the (1 endash 2)-keV range of secondary electrons induced by bombardment of Si(100) and Al(110) with a 1.5-MeV He+ beam. The ion beam is either aligned with a major crystallographic direction or incident along a random direction. The shape of the experimental secondary electron spectra are successfully compared with that of spectra calculated with an efficient Monte Carlo model for electron-transport simulation. In addition, the effective layer thickness L for secondary electron generation under channeling incidence conditions is determined. It is found that LA for KLL Auger electron generation is equal to the surface peak area in the spectra of the backscattered ions. This similarity is a consequence of the small values of the backscattering collision diameter and the adiabatic radius for K-shell ionization, as compared to the atomic vibration amplitude. In contrast, LB for the generation of electrons by direct Coulomb ionization is much larger than that for Auger emission. The large value for LB emdash an indication of a reduced channeling effect emdash is attributed to the relatively large contribution from the moderately localized L shell to the measured spectra. copyright 1996 The American Physical Society