X-ray photoemission and optical spectra of NiPS3, FePS3, and ZnPS3

X-ray-induced photoemission spectra were obtained for the valence bands and core levels of ZnPS3 and FePS3 for comparison with earlier XPS spectra of NiPS3. The valence band spectra are interpreted on the basis of a two-dimensional model in which the transition metal is ionized, with the two electrons appearing in covalent bonds in the SP3 groups. The absorption edge for each crystal was obtained by optical transmission measurements and the dielectric function for energies above the edge was obtained from a Kramers-Kronig analysis of the reflectance up to an energy of 30 eV. The optical properties are consistent with the view that the transition metals exist primarily as ions, with localized 3d levels. There is evidence, however, that transition metal 4s and 4p states mix with ligand states.