Observation off-band final-state structures in gold by ultraviolet photoemission spectroscopy

The availability of synchrotron radiation from storage rings makes possible a new technique for studying final-state structures in ultraviolet photoemission spectroscopy (UPS). By synchronously varying the photoelectron kinetic energy and the photon energy, constant initial-state-energy spectra were obtained for Au in the spectral range $8<h\nu <30\mathrm{}$ eV; these data complement previous UPS and x-ray photoemission spectroscopy data which have been used to elucidate the properties of electron states near the Fermi energy, $E_F$. Pronounced structures attributed to $d\to f$ transitions near the center of the Brillouin zone were observed for final-state energies about 16 eV above $E_F$. The amplitude of these structures is a sensitive function of initial-state energy. Although a complete band-structure interpretation was not attempted, the data support the relativistic band calculation of Christensen and Seraphin, which places the $f$-band edge, ${\Gamma }_6^{-}$, at 15.6 eV above $E_F$. Thermoreflectance data on Au near 20 eV are reinterpreted in the light of this finding.