Determination of the Origin of Crystal Orientation for Nanocrystalline Bismuth Telluride-Based Thin Films Prepared by Use of the Flash Evaporation Method |
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Authors: | M. Takashiri S. Tanaka K. Miyazaki |
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Affiliation: | 1. Department of Materials Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan 2. Department of Mechanical Engineering, College of Engineering, Nihon University, Nakagawara, Tokusada, Tamuramachi, Koriyama, Fukushima, 963-8642, Japan 3. Department of Mechanical and Control Engineering, Kyushu Institute of Technology, 1-1 Sensui, Tobata-ku, Kitakyushu, 804-8550, Japan
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Abstract: | We have investigated the origin of crystal orientation for nanocrystalline bismuth telluride-based thin films. Thin films of p-type bismuth telluride antimony (Bi–Te–Sb) and n-type bismuth telluride selenide (Bi–Te–Se) were fabricated by a flash evaporation method, with exactly the same deposition conditions except for the elemental composition of the starting powders. For p-type Bi–Te–Sb thin films the main x-ray diffraction (XRD) peaks were from the c-axis (Σ{00l}/Σ{hkl} = 0.88) whereas n-type Bi–Te–Se thin films were randomly oriented (Σ{00l}/Σ{hkl} = 0.40). Crystal orientation, crystallinity, and crystallite size were improved for both types of thin film by sintering. For p-type Bi–Te–Sb thin films, especially, high-quality structures were obtained compared with those of n-type Bi–Te–Se thin films. We also estimated the thermoelectric properties of the as-grown and sintered thin films. The power factor was enhanced by sintering; maximum values were 34.9 μW/cm K2 for p-type Bi–Te–Sb thin films at a sintering temperature of 300°C and 23.9 μW/cm K2 for n-type Bi–Te–Se thin films at a sintering temperature of 350°C. The exact mechanisms of film growth are not yet clear but we deduce the crystal orientation originates from the size of nano-clusters generated on the tungsten boat during flash evaporation. |
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