SPECTRA OF SECONDARY ELECTRONS INDUCED BY CHANNELED AND NONCHANNELED IONS IN SI AND AL

Energy spectra are measured in the (1-2)-keV range of secondary electr ons induced by bombardment of Si(100) and Al(110) with a 1.5-MeV He+ b eam. The ion beam is either aligned with a major crystallographic dire ction or incident along a random direction. The shape of the experimen tal secondary electron spectra are successfully compared with that of spectra calculated with an efficient Monte Carlo model for electron-tr ansport simulation. In addition, the effective layer thickness L for s econdary electron generation under channeling incidence conditions is determined. It is found that L(A) for KLL Auger electron generation is equal to the surface peak area in the spectra of the backscattered io ns. This similarity is a consequence of the small values of the backsc attering collision diameter and the adiabatic radius for K-shell ioniz ation, as compared to the atomic vibration amplitude. Ln contrast, L(B ) for the generation of electrons by direct Coulomb ionization is much larger than that for Auger emission. The large value for L(B)-an indi cation of a reduced channeling effect-is attributed to the relatively large contribution from the moderately localized L shell to the measur ed spectra.