Directional Photoemission from Three Tungsten Single-Crystal Faces

Energy distribution spectra have been measured for photoelectrons emitted normal to three tungsten single-crystal faces, namely (100), (110), and (111), for photon energies between 7.7 and 11.7 eV. The spectra show marked differences for the different faces, in agreement with the assumption that the electrons originate from states along different symmetry lines in the Brillouin zone. Structure in the spectra is interpreted in terms of emission due to direct optical interband transitions and surface photoelectric emission.