ON THE UNOCCUPIED ELECTRONIC STATES OF VANADIUM DISELENIDE

The unoccupied electronic states of the group Vb transition metal dichalcogenide compound vanadium diselenide have been measured up to about 10 eV above the Fermi level using isochromat momentum-resolved iverse photoemission. Bands along the GAMMA-A direction of the Brillouin zone were probed by recording normal-incidence spectra at photon energies between 17 and 28 eV. Band dispersion in the two principal symmetry planes of the Brillouin zone, GAMMA-ALM and GAMMA-AHK, were determined from off-normal-incidence spectra recorded at a photon energy of 20 eV. Strong features resulting from transitions into the unoccupied V 3d-derived bands are seen at about 1 eV and about 3 eV above the Fermi level; the variation of the intensity of these features with the azimuthal angle of electron incidence reflects the three-fold symmetry of the 1 T crystal structure adopted by Vse2. A broad feature centred at about 8 eV, and showing an onset at about 6 eV, is associated with higher-lying s/p bands while a weak peak at about 5 eV, which shows no dispersion along GAMMA-A, is tentatively identified as a surface resonance. The results are compared with published band-structure calculations.