Journal of Applied Physics vol:92 issue:7 pages:3688-3693
Co1-xFexSi2 and Ni1-xFexSi2 metastable ternary phases were formed by sequentially implanting Co, Ni, and Fe into Si (111) at 623 K. In order to compare the phases formed by ion implantation, the Ni1-xFexSi2 stable bulk ternary phase with a wide variety of x values was synthesized. The samples were studied by Mossbauer effect, transmission electron microscopy (TEM), x-ray diffraction, and Rutherford backscattering and channeling. X-ray diffraction and TEM results on the as-implanted samples with x=0.5 indicate a cubic (fluorite) structure. Fe-57 Mossbauer spectra show three resonanceline components. Comparison of the isomer shift values of the components with those measured in the stable and metastable transition-metal silicide phases indicated three different sites for iron atoms: Fe substituting Co or Ni; Fe in the empty cubes of the fluorite-type lattices; and Fe populating sites in the CsCl-type B2 lattice. In samples of Ni1-xFexSi2 annealed at 1273 K, alpha-FeSi2 and a fraction of Fe dissolved in NiSi2 appeared. It was found that Fe is more soluble (maximum 30 at. %) in NiSi2 than it is in CoSi2. Implanting and annealing Co or Ni or both Co and Ni at relatively low concentration in Si already implanted with Fe resulted in beta-FeSi2 with Co, Ni, and Co+Ni content, respectively. The hyperfine interaction parameters of Fe-57 were slightly modified by the dissolved Co and Ni in the beta-FeSi2 lattice. (C) 2002 American Institute of Physics.