Dynamic charge states of energetic He ions in silicon single crystals.

Abstract

The dynamic screening and the approach to charge-state equilibrium of energetic He ions passing through a silicon lattice is studied using the Rutherford backscattering technique. Measurements of breakthrough angles ${\ensuremath{\psi}}_{M}$ for planar channeled protons and He ions provide information on the dynamic equilibrium charge state of 250-keV He ions in silicon. The results can be described with a screened Moli\`ere-type potential, the He data requiring a shorter screening length than the proton data. Comparison of ${\mathrm{He}}^{+}$ and ${\mathrm{He}}^{2+}$ data shows that the time needed to establish charge-state equilibrium is not longer than approximately ${10}^{\mathrm{\ensuremath{-}}15}$ sec corresponding to a distance travelled of about 40 A\r{}.