Use of the channeling technique and calculated angular distributions to locate Br implanted into Fe single crystals

The channeling and backscattering of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ions of several MeV have been used in an experiment to determine the lattice location of Br implanted into Fe single crystals. Use has been made of fast electronics to reduce pulse pileup in the backscattered energy spectra. Angular scans have been carried out across the three major crystal axes and the three major planes. For the {211} plane a triple peak is observed in the Br-yield curve. This triple peak and a peak observed in the {100} planar scan indicate that a substantial fraction of the Br atoms occupies an interstitial site of low symmetry in the Fe lattice. A systematic analysis reveals three possible interstitial sites qualitatively consistent with the data. Theoretical calculations of angular-yield curves, using both Monte Carlo computer simulations and an analytical model based on the continuum theory of channeling, have been performed. Various possible distributions of Br atoms are considered, and with the aid of the calculated curves a quantitative interpretation of the location is made. Good agreement with the data is obtained for a distribution of 60% of the Br in one of the interstitial sites and the remaining 40% substitutional. Possible physical interpretations of this result, and its significance for hyperfine field measurements on Br implanted in Fe, are briefly discussed.