Titanium dioxide (TiO₂) thin film has attracted considerable interest as one of promising sensing materials applying for various thin-film gas sensors because of its outstanding sensing properties, chemical stability and electrical properties, etc. [1]. Among the three phases of TiO₂ films, anatase phase TiO₂ has better sensitivity to H₂ and volatile organic compound gases than rutile phase TiO₂ [2,3]. However, there were still issues on synthesizing the stable pure anatase phase TiO₂ using different methods. Compared with other reported methods, the mist chemical vapor deposition (mist CVD) [4] is an alternative method to synthesize TiO₂ thin films, by which the growth of oxide thin film can be precisely controlled according to our previously research [5].

In order to investigate the effect of substrates on structural properties of TiO₂ films fabricated by mist CVD method, four kinds of substrates were selected for comparison: glass, quartz glass, gallium doped zinc oxide (GZO) film and p-type silicon. During the mist CVD process, a solution of mixed precursors was prepared by dissolving titanium tetraisopropanolate in ethanol. The mist droplets were generated from the solution by ultrasonic transducer and transferred to the reaction chamber by compressed air. The substrates were set in the reaction chamber, which was heated and kept at 400 ˚C during the deposition. The structural properties of TiO₂ thin films were investigated by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope, atomic force microscope. The optical properties of TiO₂ thin films were investigated by transmittance spectroscopy.

According to the morphological analysis, TiO₂ films with uniform surface were observed on the different substrates. Examining the XRD patterns of TiO₂ films, the following diffraction peaks (101), (004), (200), (211), (201), (204) and (215) were observed, which corresponded to the diffraction peaks of anatase phase TiO₂. However, it was found that the intensity of dominated (101) peak increased with the order of TiO₂ films on quartz glass, GZO, silicon and glass. The results of TiO₂ films by Raman spectroscopy measurement were also agreed with that of XRD measurement. In summary, the pure anatase phase TiO₂ thin films could be synthesized by mist CVD method. The obtained anatase phase TiO₂ films have high potential to be applied to thin film gas sensors, photocatalyst and dye-sensitized solar cells. The growth mechanism of TiO₂ films on the different substrates will be revealed in the paper.

References

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4. T. Kawaharamura, K. Mori, H. Orita, T. Shirahata, S. Fujita, and T. Hirao, Japanese Journal of Applied Physics, 52, 035501 (2013).
5. X. Li, C. Li, T. Kawaharamura, D. Wang, N. Nitta, M. Furuta, H. Furuta, and A. Hatta, Transactions of the Materials Research Society of Japan, 39[2], 161-164 (2014).