Angle-resolved photoemission from valence bands of Cu and Au single crystals using 32-200-eV synchrotron radiation

Abstract

The directional anisotropy in photoemission from valence bands of Cu and Au single crystals has been studied in the photon energy ranges $32\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}200$ eV, and $32\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}130$ eV, respectively. Angle-resolved photoemission energy distributions were obtained for electrons emitted in the [001] and [111] directions. Dramatic differences were found between the two directions and strong variations with energy were obtained over the entire energy range. The results are discussed in terms of final-state band-structure effects and/versus strong inelastic damping in the final state. For Cu, spectra taken at $h\ensuremath{\nu}=90$ eV along the same symmetry directions at high (90\ifmmode^\circ\else\textdegree\fi{}) and low (35\ifmmode^\circ\else\textdegree\fi{}) take-off angles from the surface show a pronounced narrowing of the $d$ band at low take-off angles. This is attributed to a preferential sampling of the local density of states at the surface by using an appropriate photon energy and take-off angle. The energy dependence of the Au $5d$ intensity has been measured and is found to decrease by a factor of \ensuremath{\sim} 50 over the investigated photon energy range 40-190 eV.