X-ray photoelectron spectroscopy of ferroelectrics

The paper presents the X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels (CL) for SbSI-type and incommensurate TlInS2 single crystals. Form and electronic structure of the VB and CL splitting in the quasi-one-dimensional SbSI, SbSeI and BiSI, and in the incommensurate (IC) phase of TlInS2 crystals are discussed. Experimentally obtained energies were compared with the results of theoretical ab initio calculations. Large shifts (3 divided by 5 eV) in the CL binding energies in SbSI show a strong dependence on the surface crystallographic plane. The splitting of the CL was also obtained in the IC phase of TlInS2 crystals.