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EFFECT OF ANNEALING CONDITIONS ON VO2 THIN FILMS PREPARED BY SOL-GEL METHOD
Sub.Lt.Pongsatorn Panburana, Salinporn Kittiwatanakul
Abstract
Vanadium Dioxide has attracted considerable attention because of the metal-semiconductor phase transition at 68oC. This reversible transition changes crystal structure from monoclinic to rutile resulting in tremendously change of transmittance and reflectance of Infrared wavelength and electrical resistance making VO2 thin film potential candidate for energy-saving smart windows (automatically block heat).
However, its preparation is very challenging due to the multivalence of Vanadium element. In this study, we explored different annealing conditions for thin films synthesized by sol-gel method which has advantage over other methods such as lower cost, simpler process and ability to make large scale thin film.
In the experiment, we used vanadium (V) triisopropoxy oxide (VO(OC3H7)3) as precursor. The annealing conditioned explored are annealing temperature and annealing time of thin films in low pressured Argon rich atmosphere. The spin-coated films were annealed at 350-530 ºC for 30 minutes, while another set were annealed at 450 ºC for 30, 60, 90, and 120 minutes. Then the films were characterized with Raman spectroscopy and temperature dependent resistance measurement. The results show that the longer the annealing time and the higher the temperature are better for film formation —closer to VO2 (higher V:O ratio).
In addition, the effect of various substrate types was also explored, another set of thin films were coated on c-plane sapphire (c-Al2O3) and Soda lime glass (SiO2) to compare the effect. Then the films were characterized with Raman spectroscopy and X-Ray Diffraction. The result showed that sapphire substrate yielded better film formation.
Keywords: VO2 thin film;; Argon atmosphere; electrical resistance property; annealing temperature ; XRD; Raman spectroscopy spectroscopy
