XPS and electronic structure of quasi-one-dimensional BiSI crystals

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels (CL) from the (1 1 0) and (0 0 1) planes for the quasi-one-dimensional high dielectric permittivity BiSI single crystal. The XPS were measured with monochromatized Al Kα radiation in the energy range of 0-1400 eV at room temperature. The VB is located from 1.4 to 23 eV below the Fermi level. Experimental energies of the VB and CL are compared with the results of theoretical ab initio calculations of the molecular model of the BiSI crystal. The electronic structure of the VB and CL is revealed and described theoretically. The surface and bulk atoms influence the shape of the VB and CL, which is crystallographic plane dependent. The chemical shifts in the BiSI crystal for the Bi, I and S states are obtained. General features of the VB and CL are common to all the SbSI-type crystals.