Characterization of 1T-TiSe2 surface by means of STM and XPD experiments and model calculations

Scanning tunneling microscopy (STM) and X-ray photoelectron diffraction (XPD) are applied to study the surface of layered dichalcogenide 1T-TiSe2. XPD pattern simulation for the 1T-TiSe2 surface is performed in the approach of electron multiple scattering within the EDAC code: considered are models of structural defects in the 1T-TiSe2 lattice, relaxation contraction (expansion) of surface layers and van der Waals gap, and deviation of the 1T-TiSe2 surface geometry from the basal plane (001). The atomic structure of 1T-TiSe2 surface layers is reconstructed from the XPD pattern on Se(LMM) and Ti2p core level using the photoelectron holography scattering pattern extraction algorithm with maximum entropy method (SPEA-MEM). The results of the 3D reconstruction are in agreement with the XPD pattern simulation data. In both cases, the TiSe2 surface corresponds to 1T polytype; an increase is observed in the parameter a0 and in the van der Waals gap between two surface slabs. It is assumed that similar structural distortions of the 1T-TiSe2 lattice lead to the formation of an energy gap between the valence band and the conduction band of titanium diselenide, which was observed earlier by photoemission spectroscopy and follows from the theoretical calculations.