Charge states of fast ions in glancing collisions with aligned atoms in Si crystals

We have measured keV secondary electrons induced by 2.5- and 3.5-MeV/u ions under Si〈100〉 and Si〈110〉 channeling-incidence conditions. From a comparison of the electron yields for the ions of equal velocity, the effective nuclear charges of the ions in glancing collisions with aligned Si atoms have been determined. The results indicate that He2+, B5+, C4+, C6+, O5+, and C8+ do not capture target electrons, while Si, S, and Cl ions capture or lose electrons depending on the incident charge state. For the heavy ions, the number of bound electrons in the charge equilibrium is greater than for the random case, for example, by 2–4 and 3–5 for 2.5-MeV/u Si and S, respectively