X-Ray Photoemission Spectroscopic Study of Impurity Effect and d-Band Formation Induced by the Substituted 4dTransition Metal Atoms in Ni1-xRhxS

Abstract

The effect of Rh substitution on the electronic structure of charge transfer type compound NiS is studied by XPS. We find the following results. (1) A narrow band is newly superimposed on the main peak ( d 8 L ) of NiS in the valence band region and its width increases with x . (2) The peak position and the line shape of Rh 3 d core level spectra are very close to that of Rh metal. (3) The S 2 s and the S 2 p 3/2 core level peaks shift toward higher binding energy ( E B ) with increasing x . (4) The Ni 2 p 3/2 core level main peak ( d 9 L ) shifts toward lower E B with increasing x . (5) The E B separation of the Ni 2 p 3/2 main and satellite peaks decreases as x increases, while the relative intensity of the latter peak to the former one increases. We suggest a tentative model that a Mott-Hubbard type metallic d -band is superimposed on charge transfer type host NiS, and that this contribution is one of the electronic origin for d T t /d x <0 reported previously. The origin of the metallic band is attributed to the Rh–Rh and/or Ni–Rh interactions in Ni 1- x Rh x S.