Very-low-energy electron diffraction from TiS2: experiment and ab initio theory

An experimental and theoretical study of very-low-energy electron diffraction from the (0001) surface of 1T TiS2 is presented. The normal incidence electron transmission spectrum is measured up to 37 eV above the Fermi level. Ab initio calculations of the spectra are performed with the full-potential extended linear augmented plane wave k.p method. The experimental spectrum is interpreted in terms of the unoccupied complex band structure (CBS) of the semi-infinite crystal. Three CBS branches responsible for the electron transmission at normal incidence are determined. The role of inelastic scattering is discussed. The energy dependence of the optical potential Vi is determined from the shape of the experimental spectral structures. A sharp increase of Vi at 21.5 eV is detected, which is associated with a plasmon peak in the electron energy-loss function.