Impurity-site distribution of implanted Bi in iron and nickel studied by channeling and nuclear orientation

The lattice position occupied by implanted bismuth atoms in iron and nickel single crystals has been studied by observation of Rutherford backscattering from channeled ion beams. In both hosts part of the bismuth distribution was at the surface of the crystal as a result of sputtering during implantation or enhanced diffusion in the heavily damaged region between the surface and the full range depth of the bismuth. Comparison between the bismuth at the full range and the host showed that in neither host did the bismuth occupy a purely substitutional site. In nickel the channeling data are reproduced if 40% of the impurities are associated with dislocation loops oriented in the close-packed (111) planes. In iron the situation is more complicated requiring association with isolated vacancies as well as dislocation loops. Nuclear orientation showed a reproducible hyperfine field for $\mathrm{Ni}\mathrm{Bi}$ but measurements for $\mathrm{Fe}\mathrm{Bi}$ depended on preparation technique. In both hosts a distortion of the host cubic symmetry is required to fit the anisotropies of $\gamma$ rays deexcitating the 0.128-msec isomer of ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ populated in the decay of ${}_{}{}^{206}{}_{}{}^{}\mathrm{Bi}$ in qualitative agreement with the distortion near dislocation loops required to fit the channeling results.