Near-surface segregation in irradiated Ni3Si

The radiation-induced growth of Ni3Si films on the surfaces of Ni(Si) alloys containing =< 13 at.% Si is well established. Additional segregation of silicon during irradiation within the ordered Ni3Si phase has been observed. Post-irradiation depth profiling by Auger electron spectroscopy, as well as in situ analysis by high-resolution Rutherford backscattering spectrometry, reveals Si-enrichment at the surfaces of Ni(Si) alloys in excess of stoichiometric Ni3Si during irradiation. Thin, near-surface layers with silicon concentrations of 28 to 30 at.% are observed, and even higher Si enrichment is found in the first few atom layers. Transmission electron microscopy and selected area-electron diffraction were employed to characterize these Si-enriched layers. A complex, multiple-spot diffraction pattern is observed superposed on the diffraction pattern of ordered Ni3Si. The d-spacings obtained from the extra spots are consistent with those of the orthohexagonal intermetallic compound Ni5Si2. (author)