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Study of Phase Transformation of Rapid-Thermal-Annealed TiOx Films and Their Photo-Induced Hydrophilicity

Authors

  • Chen-Kuei Chung,

    Corresponding author
    • Department of Mechanical Engineering, Center for Micro/Nano Science and Technology, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan
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  • Ming-Wei Liao

    1. Department of Mechanical Engineering, Center for Micro/Nano Science and Technology, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan
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Author to whom correspondence should be addressed. e-mail: ckchung@mail.ncku.edu.tw

Abstract

Crystalline structure and bonding behavior of promising titanium oxide material strongly influenced the performance of photocatalysis or photovoltaics devices in application. A novel method to control phase formation of sputtered TiOx films was investigated by various as-sputtered nonstoichiometry x of TiOx and followed by rapid thermal annealing (RTA) at 550°C–750°C for 2 min in air. The as-deposited TiOx films were amorphous with no X-ray diffraction peak whereas the significant crystalline peaks of anatase or rutile phases were detected after RTA at 550°C–750°C. The nonstoichiometry x of TiOx films greatly influenced formation of crystalline TiO2 phase structures as annealed at 750°C. Pure anatase was detected in nonstoichiometry x > 1.97 specimens whereas pure rutile phase was detected in x < 1.61 specimens, respectively. An anatase-rutile mixture obtained at 1.61 < x < 1.97 showed highly photo-enhanced hydrophilic property after UV irradiation. Different crystalline phase structures of TiO2 films including the rutile, anatase, and mixture can be prepared by reactive sputtering and post RTA for enhancing performance of films. The relationship between process and phase transformation mechanism was also correlated and discussed.

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