Infrared reflectance and photoemission spectroscopy studies across the phase transition boundary in thin film vanadium dioxide

Optical properties and valence band density of states near the Fermi level of high-quality VO(2) thin films have been investigated by mid-infrared reflectometry and hard-UV (hν = 150 eV) photoemission spectroscopy. An exceptionally large change in reflectance from 2 to 94% is found upon the thermally driven metal-insulator transition (MIT). The infrared dispersion spectra of the reflectance across the MIT are presented and evidence for the percolative nature of the MIT is pointed out. The discrepancy between the MIT temperatures defined from the electrical and optical properties is found and its origin is discussed. The manifestation of the MIT is observed in the photoemission spectra of the V 3d levels. The analysis of the changes of the V 3d density of states is done and the top valence band shift upon the MIT is measured to be 0.6 eV.