A photoelectron spectrometer for k-space mapping above the Fermi level

The setup of an electron spectrometer for angle-resolved photoemission is described. A sample goniometer offers the opportunity for angle scanned photoemission over 2 pi solid angle above the surface. A monochromatized high flux He discharge photon source is exploited to measure thermally populated electronic states above the Fermi level E-F. At energies greater than E-F +5k(B)T the signal from a constant density of states declines below the photoelectron background caused by photons with higher energies than He I alpha (21.2 eV). For He II alpha (40.8 eV) the residual photoelectron background is lower and photoemission up to 6k(B)T above EF can be performed. Data showing two cuts through the Fermi surface of silver are presented. Furthermore the dispersion of the Shockley surface state on Ag (111) above the Fermi energy is quantified. (C) 1997 American Institute of Physics.