LAUSR

Amorphous VO2 thin films were grown on anatase TiO2-buffered polyimide (PI) films using radio-frequency magnetron sputtering deposition with a VO2 target as low as at 175 °C. For comparison, the authors grew VO2 films on TiO2-buffered SiO2/Si substrates. The structural and morphological properties of the VO2 films were evaluated by x-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. VO2 films grown on TiO2/SiO2/Si were crystalline at 200 and 250 °C and were amorphous at 175 °C. VO2 films grown on TiO2/PI were amorphous. No peak corresponding to the monoclinic phase of VO2 appeared in the Raman spectra of VO2/TiO2/PI films grown at 175 or 200 °C. The chemical compositions of VO2 and the binding energy spectra of V and O atoms were probed by x-ray photoelectron spectroscopy. The authors discussed the multivalence states of V atoms and oxygen vacancies based on the x-ray photoemission spectroscopy of crystalline and amorphous VO2 films. Th...