Absolute determination of the layer-perpendicular band structure of and by combined very-low-energy electron diffraction and photoemission

Abstract

The layer-perpendicular dispersions of the typical layered TMDCs and were studied by combining determination of the upper unoccupied bands by very-low-energy electron diffraction (VLEED) with mapping of the lower occupied bands by photoemission (PE). We found that the upper bands of these materials are very complicated, and are compatible neither with the free-electron, nor with the ground-state approximation. Knowledge of the upper bands allowed us to carry out a PE experiment optimized for the -resolved mapping of the lower bands. The PE data were consistently rationalized, using a map of the PE intensity as a function of the binding energy and the photon energy . We found that the PE intensity is well described by direct, -conserving, transitions, with minor shifts of PE peaks being basically a consequence of their broadening due to finite electron and hole lifetime. Finally the lower bands were mapped explicitly, using the PE peaks with minimal shifts and the experimental upper bands. The obtained is very consistent, and shows overall agreement with full-potential LAPW calculations.