The depth and angular dependence of the mid-channel flux of He ions in Al crystals

Abstract

The normalized flux of 0.5, 1.0 and 2.0 MeV 4He ions at the center of a〈100〉 channel in an Al-0.02 at.% In crystal has been measured as a function of depth and incident angle. The crystal was first irradiated with 1 MeV 4He + at 35 K to a fluence of 2 × 10 16 cm −2 and then annealed for 600 s at 220 K, in order to displace ∼40% of the In atoms into tetrahedral lattice sites. Measurement of the backscattering yield of 4He ions from the In atoms directly gave the 〈100〉 mid-channel flux. The observed depths of the first maximum in flux were (26 ± 2), (35 ± 3) and (46 ± 6) nm for 0.5, 1.0 and 2.0 MeV, respectively, following the expected E 1 2 dependence. The widths (fwhm) of the 〈100〉 peak in the ion scattering yield from In atoms for a depth interval of 40–120 nm were (0.39 ± 0.03)°, (0.28 ± 0.04)° and (0.23 ± 0.04)° for 0.5, 1.0 and 2.0 MeV, respectively; this energy dependence agreed with the E − 1 2 dependence observed for the Al widths.