X-Ray Photoemission Spectroscopic Study of Impurity Eflfect and d-Band Formation Induced by the Substituted 4d Transition Metal Atoms in Ni₁-_xRh_xS

The eEect of Rh substitution on the electronic structure of charge transfer type compound NiS is studied by XPS. We hnd the following results. (1) A narrow band is newly superimposed on the main peak (d 8L) of NiS in the valence band region and its width increases with x. (2) The peak position and the line shape of Rh 3d core level spectra are very close to that of Rh metal. (3) The S 2s and the S 2p3/2 core level peaks shift toward higher binding energy (EB) with increasing x. (4) The Ni 2p3/2 core level main peak (d9L) shifts toward lower EB with increasing x. (5) The EB separation of the Ni 2p312 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 dT,/dx=O reported previously. The origin of the metallic band is attributed to the Rh-Rh and/or Ni-Rh interactions in Nii.RhxS•.