Angle-resolved ultraviolet photoelectron spectroscopy of the unoccupied band structure of graphite

The energy dispersion of conduction (or unoccupied) bands of graphite has been studied by angle-resolved ultraviolet photoelectron spectroscopy. Photoemission peaks originating in the conduction bands were successfully separated from those of the valence bands by comparing two sets of angle-resolved ultraviolet photoelectron spectra excited by the He and He resonance lines. Three conduction bands were found in the energy range of 7--13 eV above the Fermi level and one of them showed a remarkable energy dispersion in the plane in the Brillouin zone. The present experimental results have been compared with the results of earlier experiments using photoelectron, secondary-electron, electron-energy-loss, photoyield, and inverse photoelectron spectroscopies as well as with some theoretical calculations. The usefulness of angle-resolved (secondary) photoelectron spectroscopy to study unoccupied band structure has been demonstrated.