The Location of Displaced Impurity Atoms in Irradiated Aluminum Crystals by Backscattering

Abstract

The energy spectra of 1 MeV He + ions backscattered from single crystals of Al alloys containing 0.09 at.% Mn, 0.09 at.% Zn, 0.08 at.% Ag, or 0.03 at.% Sn have been examined in different crystallographic directions. For the annealed crystals, the minimum yield of back-scattered He + ions from Al atoms at 40 K in a [Formula: see text] direction was [Formula: see text], and the corresponding yield from Mn, Zn, or Ag impurity atoms was (χ min ) i ≤ 0.06, indicating that at least 96% of these impurity atoms had replaced Al atoms at normal lattice sites. For the Al–0.03 at.% Sn alloy, the substitutional fraction of Sn atoms was only ~50% for a slowly cooled crystal, but was increased to ~90% by a rapid (water) quench from 600 °C. Irradiation of the crystals at 40–70 K with 0.3–1.0 MeV He + ions to doses of 10 15 –10 16 /cm 2 caused the Mn, Zn, and Ag atoms to be displaced from lattice sites by the trapping of self-interstitial Al atoms. From an analysis of [Formula: see text], [Formula: see text], {100}, and {111} channeling, it was shown that the trapping configuration was the [Formula: see text] dumbbell. Both the irradiation induced dechanneling and the displacement of these impurity atoms annealed out in recovery stage III, from 180–220 K, because of vacancy interstitial annihilation. The Sn atoms were not displaced appreciably by He + ion irradiation at 40–70 K, but a displacement occurred during stage III recovery.