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Photoemission measurements have been made at photon energies from 3 to 12 eV on Cs,Te films at pressures less than 5 X 10 ' Torr. Inelastic electron-electron scattering and electron-phonon scattering have a dramatic effect on the photoemission data, By using the three-step model of photoexcitation, hot-electron transport, and escape to describe photoemission in Cs,Te, both the quantum yield above the main threshold and the energy distributions of photoemitted electrons (EDC's) can be qualitatively understood. Important features in the band structure Cs2Te have also been deduced from the behavior of structure in the EDC's. Three maxima in the conduction-band density of states are located at 4.05 + 0.1, 4.9 + 0.1, and 5.4+ 0.1 eV above the top of the valence band. Two peaks observed in the valence-band density of states at 0.7 + 0.1 and 1. 4 + 0.1 eV below the top of the valence band have been assigned to the spin-orbit-split 5p orbitals of Te. The value for the spin-orbit splitting (0.65 + 0.1 eV) is in excellent agreement with the theoretical free-atom value. In addition, an upper bound of 2 eV was set for the over-all width of the valence band in Cs,Te. Cs2Te fin(ns overcoated with 5% additional Te were also studied. Both these films and the Cs,Te films prepared without additional Te display a low yield (& 10 ' electrons/incident photon) below the main threshold of the quantum yield. It was found that this low yield cannot be explained in terms of a simple excess of Cs or Te in an otherwise stoichiometric single-phase compound.

Ultraviolet photoemission spectroscopy has been used to search for surface states on SrTiO, . No evidence was found for such states and an upper limit of about 3 &( 10"/cm' is placed on surface states in the gap from the valence-band maximum to within 0.2 eV of the conduction-band minimum. (The latter limit is set by the bulk Fermi-level position of the n-type crystal studied. ) These results are discussed in terms of the large (=10"/cm') density of empty surface states predicted by Morin and Wolfram.