Qualitative XANES and XPS Analysis of Substrate Effects in VO2 Thin Films: A Route to Improving Chemical Vapor Deposition Synthetic Methods?

Vanadium(IV) oxide thin films were synthesized via atmospheric pressure chemical vapor deposition by the reaction between vanadium(IV) chloride and ethyl acetate at 550 degrees C. The substrate was varied with films being deposited on glass, SnO2, and F-doped SnO2. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV vis spectroscopy, scanning electron microscopy, and X-ray absorption near-edge structure. The influence of the electronic contribution of the substrate on the deposited VO2 film was found to be key to the functional properties observed. Highly electron withdrawing substituents, such as fluorine, favored the formation of V5+ ions in the crystal lattice and so reduced the thermochromic properties. By considering both the structural and electronic contributions of the substrate, it is possible to establish the best substrate choices for the desired functional properties of the VO2 thin films synthesized.