Ultraviolet-infrared dielectric functions and electronic band structures of monoclinic VO₂ nanocrystalline film: Temperature-dependent spectral transmittance

Nanocrystalline vanadium dioxide (VO₂) film on c-plane sapphire substrate has been prepared by direct-current magnetron sputter deposition. The electronic band structures of the VO₂ film with monoclinic phase have been investigated by ultraviolet-infrared transmittance spectra in the temperature range of 5.3-300 K. It was found that the transmittance decreases while the dielectric functions slightly increase with the temperature. The optical bandgap decreases from 0.839 ± 0.003 to 0.788 ± 0.003 eV with increasing the temperature due to the variations of lattice constant and V_d-O_p hybridization. Moreover, three higher-order interband electronic transitions can be uniquely distinguished and the temperature effects on the higher-order transition energy become much weaker.