Microstructruture of Heteroepitaxially Grown TiO 2 Films by Magnetron Sputtering
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Microstructruture of Heteroepitaxially Grown TiO2 Films by Magnetron Sputtering Makiko Yamagishi, Pung Keun Song and Yuzo Shigesato College of Science & Engineering, Aoyama Gakuin University, 6-16-1 Chitosedai, Setagaya-ku, Tokyo 157-8572, Japan ABSTRACT Titanium dioxide (TiO2) films were deposited on (a) non-alkali glass, (b) MgO (100) and (c) SrTiO3 (100) single crystals by rf reactive magnetron sputtering using a Ti metal target. X-ray diffraction and a pole figure analysis revealed that TiO2 films on the (a) were anatase polycrystals with preferred orientation, whereas heteroepitaxial growth of anatase TiO2 was observed on the (b) and the (c) substrates. FE-SEM analyses on the crystal habit of the firm surfaces showed that the substrate temperature during the deposition (Ts) heavily affected the microstructure and surface morphology of the heteroepitaxially grown films, which could be clearly explained in terms of “Thornton’s zone model” or “epitaxial growth model of 2-dimensional ledge or kink modes” considering the normalized Ts by the phase transition temperature from anatase to rutile. INTRODUCTION On accounts of the strong oxidizing power of the photogenerated holes, the chemical stability and non-toxicity, titanium dioxide (TiO2) is the most investigated photocatalyst up to date. Not a few studies on the photocatalytic activities have been reported on TiO2, however most of them were carried out on polycrystalline anatase films synthesized by a wet sol-gel method utilizing titanium alkoxide [1]. With the comparison of the conventional wet processes, sputter depositions should be one of the most promising techniques for large-area uniform coatings with high packing density and strong adhesion. Furthermore dry processes including sputtering method should have high potential for epitaxial film growth [2,3], where the crystallographic structure or orientation can be controlled precisely and the basic study on the definitive structural factors dominating the chemical or physical properties of the films should become possible. In this study TiO2 films with rutile or anatase structure were epitaxially grown on MgO or SrTiO3 single crystals by rf reactive magnetron sputtering. The crystallographic properties and surface morphology of the heteroepitaxial films were analyzed in detail, which were discussed in relation to the film growth conditions and crystal growth mechanisms. O8.35.1
EXPERIMENT Titanium dioxide (TiO2) films were deposited by rf reactive magnetron sputtering (L-332F, ANELVA) using a Ti metal target (99.99%, Furu-uchi Kagaku) on to the following 3 different kinds of substrates, (a) non-alkali glass (AN, Asahi Glass Co., Ltd.), (b) MgO (100) and (c) SrTiO3 (100), where (b) and (c) were single crystals. The depositions were carried out at total o
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pressure ( Ptot ) of 1 and 3 Pa, substrate temperature (Ts) of 200 C and 400 C and rf power of 200W. Oxygen flow ratio [O2/(O2+Ar)] was kept constant at 40%, where the target surface should be fully oxidized and reactive sputtering mode was in “oxide mod
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