Photoemission studies of graphite high-energy conduction-band and valence-band states using soft-x-ray synchrotron radiation excitation

Abstract

Photoemission spectra of the valence band of single-crystal graphite were measured using synchrotron radiation in the energy range 33-200 eV. For $\hslash \omega =122\mathrm{}$ eV, good agreement was found with the calculated density of states since the matrix elements for the $p$-like and $s$-like states are nearly the same. Using constant-initial-state spectroscopy, we have found that, for $\hslash \omega <90\mathrm{}$ eV, the cross section of the transitions from the $\pi$ and $\sigma$ initial states in the valence band to the high-energy final states is governed by the joint density of states and the selection rules. We have verified the theoretical prediction of the energy and symmetry of the conduction bands between 30 and 50 eV above the Fermi energy. For $\hslash \omega >90\mathrm{}$ eV, the transition cross sections are mainly determined by the atomic character of the initial states.