PHOTOEMISSION FROM VO2

Photoemission quantum yield and energy distribution curves have been measured for VO2 in the tetragonal (100°C) and monoclinic (25°C) phases over the photon energy range from 7 to 11.5 eV. The VO2 studied was a polycrystalline film of several microns thickness formed by oxidizing vanadium. The experimental data, although somewhat broadened, show most of the major features expected on the basis of a simple model of VO2, and support the interpretation of optical data given by Verleur et al. In both the semiconductor and metallic phases, there is evidence of a high-density-of-states band starting approximately 2.5 eV below the Fermi level. This band is believed to be due primarily to the oxygen 2p orbitals in VO2. The photoelectric yield is considerably higher at 100°C than at temperatures below 68°C. This effect, and changes in the energy distribution curves, indicate that a band gap in excess of 0.6 eV has collapsed on heating VO2 above 68°C. © 1969 The American Physical Society.