Exact interband transition energies of VO2 films

The temperature dependent optical constants of VO2 thin films with different thicknesses on variable substrates were measured by spectroscopic ellipsometry. The exact interband transition energies crossover metal-to-insulator transition of VO2 were obtained using a standard critical point model fitting based on the measured optical constants. The dynamic image of all critical points was obtained during the heating and cooling processes within the measured energy region. By introducing the fine orbital structure into the band model, every critical point was assigned to the corresponding band transition. The critical point of 4.7 eV predicted theoretically, which is response to the transition from O2P to upper a1g, was obtained experimentally for the first time. Our work provides a new view for the complex band scheme of the monoclinic and rutile phase VO2. Moreover, the insulator-to-metal transition temperature is modified by regulating both film thickness and substrate.