Dehydrogenation and Polymerization of TiO x H y Films in Obtaining Anatase Coating at Low Temperature
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W11.4.1
Dehydrogenation and Polymerization of TiOxHy Films in Obtaining Anatase Coating at Low Temperature
Kouichi Takayama, Shigeo Ohshio and Hidetoshi Saitoh Department of Chemistry, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan
ABSTRACT Chemical-vapor-deposition of titanium tetra-isopropoxide (TTIP) under the atmosphere at low temperature has been conducted. The structure of the obtained films was assessed using Fourier transform infrared spectroscopy, X-ray diffractometry and Raman spectroscopy. These analyses indicated that amorphous TiOxHy films were obtained at gas temperatures in the range of 150–300 ˚C, and crystalline anatase-TiO2 film was formed at 350 ˚C. This distinction is accounted for by plausible chemical reactions as follows; the hydroxyl reaction of TTIP below 350 ˚C promotes the formation of the amorphous TiOxHy. As the temperature goes up to 350 ˚C, dehydrogenation of the TiOxHy films promotes to form crystalline TiO2. Also the obtained amorphous films were annealed for 10 min under the atmosphere in assessing the transformation proceeding in the solid state. The structural change is shown at 350 ˚C, indicating that the crystalline phase would be formed via dehydrogenation and polymerization on the surface of the amorphous phase under the atmosphere. The crystal size of the annealed films was evaluated in assessment for the transformation.
INTRODUCTION There are increasing interests in development of organic-inorganic composed hybrid materials [1]. The features of the hybrid materials are high hardness, thermal and chemical stabilities, and flexibility that are attributable to the intrinsic features of the individual inorganic and organic materials, e.g., compositions between SiO2 film and opto-plastic material [2] and between photocatalyst and resin sheet [3]. For the preparation of such materials, the low-temperature deposition process would be required in avoiding the chemical and physical damages against the organic substrate such as resin sheet. The crystalline anatase TiO2 is well-known as one of the suitable inorganic materials in the surface coating technology owing to its high optical reflection. Its preparation, however, is troublesome because many titanium compounds as source of titanium are vaporized at high temperature. As a consequence, the deposition method available at low temperature is essential as the design of novel hybrid materials. An atmospheric chemical-vapor deposition (CVD) technique is novel for the thin film fabrication and achieves both high-rate deposition and creation of micro- or nano-architecture of oxide films [4-9]. Our previous investigations have obtained the crystalline anatase TiO2 film by employing the apparatus with the starting material, titanium tetra-isopropoxide (TTIP, Ti(O-i-C3H7)4) [6,7] and discussed the morphological instabilities arising from step wandering and formation of three-dimensional nuclei in the crystal growth process [6]. However, the film was prepared at moderate temperature conditions. Fr
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