Lattice-site location of ion-implanted impurities in copper and other fcc metals

Abstract

The backscattering-channeling technique has been used to study the lattice location of various heavy atoms implanted in a channeling direction to high doses in copper and other fcc metals. Gold implanted into Cu, Pd, and Ag is found to be (100 ± 1)% on substitutional sites (in Ni, Au is 96% substitutional). Investigations of the lattice location of heavy metallic atoms implanted in Cu (Ag, Sb, W, Pt, Au, Hg, Tl, Pb, and Bi) show that these impurities occupy with a high probability (≥ 60%) regular fcc lattice sites for atomic concentrations ≲ 1%. In contrast, I shows a lower probability for occupying Cu lattice sites and the substitutionality is a function of depth, whereas Xe is entirely nonsubstitutional. There is no implantation temperature dependence of the substitutionality of Au, W, or Xe in Cu between 15 K and room temperature. These results are compared with criteria such as the size, electronegativity, and the binary phase diagrams of the implanted systems involved, but it is concluded that the final position of metallic atoms is determined mainly by nonequilibrium processes occurring near the end of the ion range. For atomic concentrations > 10%, Au remains 100% substitutional in Cu but W produces a highly disordered layer in which the W atoms occupy no regular lattice site. Low levels of damage are seen in the host copper crystals after high-dose channeled implantations of heavy ions. The results indicate an absence of displaced host atoms and a layer of dechanneling centers which is approximately coincident in depth with the implanted species. These results suggest that lattice strain around the implanted atoms is the major cause of dechanneling.