碲化鉍(Bi2Te3)是現今室溫下最普遍的商用熱電材料，由於其結構為非均向性(anisotropy)，所以在製備Bi2Te3時其結晶方向將會影響熱電性質的好壞。在製備Bi2Te3中，電鍍法是一種低成本、高鍍率以及製程簡單的技術，且生長的Bi2Te3晶粒有特定結晶方向。然而，目前對於電鍍Bi2Te3的成長結構尚無完整的研究，所以本實驗將對於此結構做一系列研究，以了解此種生長成特定結晶方向的機制。
本實驗主要探討電鍍法製備的Bi2Te3晶體形貌、晶體結構以及成長機制之關係。電鍍Bi2Te3晶體在SEM下觀察發現呈現片狀交叉結構，形成三角錐-四角錐的形狀。此片狀結構經由穿透式電子顯微鏡(TEM)分析確認此結構為一單晶，垂直其扁平面方向為[00.1]方向。電鍍Bi2Te3晶體片狀交叉結構推論與 及 雙晶結構生成有關。理論計算因雙晶結構形成的片狀物夾角為63.82o及77.5o，與根據SEM分析量測片狀物的夾角－65o以及77o大致相符。最後，根據X-ray繞射(XRD)分析得到電鍍Bi2Te3薄膜隨著電鍍的時間增長，具有愈強的{11.0}繞射峰，此結果是因為在Bi2Te3結構中基面(basal plane)是電阻率最低的部分，所以在電鍍過程中電子流主要沿著基面方向傳導，鉍與碲離子亦將沿此方向沉積，導致垂直於基面的{11.0}晶面成為優選的晶面方向。

Bismuth telluride (Bi2Te3) is the most well known thermoelectric material at near-room-temperature regime. Due to the anisotropic nature of the material, thermoelectric properties will be strongly dependent on its crystal orientation. Electrodeposition, one of many methods of preparing Bi2Te3, has the advantages of being low cost, high efficiency, and simple process, with the additional attribute of grain growth under a distinct crystallization mechanism. Findings in this research provide a thorough understanding of the structural evolution during the electrodeposition process.
In this study, structural features and growth mechanism of electrodeposited Bi2Te3 grains are carefully investigated. From scanning electron microscopy (SEM), the interpenetrating discs exhibit a distinctly pyramidal shape with combined triangular and square bases. Further analysis with transmission tunneling electron microscopy (TEM) shows that each individual disk is a single crystal, with the c-direction [00.1] perpendicular to the flat surface of the crystal. The interpenetrating structure is speculated to be related to the twin structure of Bi2Te3 crystals with and twin plane, based on the similarities between the measured angles 65o and 77o from SEM micrographs and the theoretical calculated included angles 63.82o and 77.5o. Finally, the XRD diffraction patterns indicate that the intensity of {11.0} plane increases with increasing electrodeposition time. Such preferential growth plane is the result of electrons preferably traveling through the basal plane, which has the lowest electrical resistivity. Subsequently, bismuth and tellurium ions would likewise deposit along the same path near the basal plane, leading to the plane perpendicular to the basal plane {11.0} being the preferred orientation.

[1] 經濟部能源局：永續能源政策綱領,民國97年6月5日
[2] http://yonggaoqixie.diytrade.com/sdp/435424/2/main.html 瀋陽市永高養殖器械設備有限公司
[3] Hicks, L. D. and Dresselhaus, M. S., Effect of quantum-well structures on the thermoelectric figure of merit. Physical Review B, 47 (19), 12727 (1993)
[4] Yamashita, O., Tomiyoshi, S., and Makita, K., Bismuth telluride compounds with high thermoelectric figures of merit. Journal of Applied Physics, 93 (1), 368 (2003).
[5] Laudise, R. A., Sunder, W. A., Barns, R. L., Cava, R. J., and Kometani, T. Y., Czochralski growth of doped single-crystals of Bi2Te3. Journal of Crystal Growth, 94 (1), 53 (1989).
[6] 陳柏志, 粉末粒徑與燒結溫度對Bi0.5Sb1.5Te3化合物熱電特性影響之研究, 國立清華大學碩士論文(2008)
[7] Yang, J. Y., Fan, X. A., Chen, R. G., Zhu, W., Bao, S. Q., Duan, X. K., Consolidation and thermoelectric properties of n-type bismuth telluride based materials by mechanical alloying and hot pressing. Journal of Alloys and Compounds, 416 (1-2), 270 (2006).
[8] Zhao, L. D., Zhang, B. P., Li, J. F., Zhang, H. L., and Liu, W. S., Enhanced thermoelectric and mechanical properties in textured n-type Bi2Te3 prepared by spark plasma sintering. Solid State Sciences, 10 (5), 651 (2008).
[9] 王亞帆, 能障散射效應對Bi0.5Sb1.5Te3薄膜熱電性質影響之研究, 國立清華大學碩士論文(2007).
[10] El-Sayed, H. E. A., Structural and optical properties of thermally evaporated Bi2Te3 films. Applied Surface Science, 250 (1-4), 70 (2005).
[11] Boulouz, A., Giani, A., Pascal-Delannoy, F., Boulouz, M., Foucaran, A., and Boyer, A, Preparation and characterization of MOCVD bismuth telluride thin films. Journal of Crystal Growth, 194 (3-4), 336 (1998).
[12] Cao, Y. Q., Zhao, X. B., Zhu, T. J., Zhang, X. B., and Tu, J. P., Syntheses and thermoelectric properties of Bi2Te3/Sb2Te3 bulk nanocomposites with laminated nanostructure. Applied Physics Letters, 92 (14), 3 (2008).
[13] Mishra, S. K., Satpathy, S., and Jepsen, O., Electronic structure and thermoelectric properties of bismuth telluride and bismuth selenide. Journal of Physics-Condensed Matter, 9 (2), 461 (1997).
[14] Urazhdin, S., Bilc, D., Tessmer, S. H., Mahanti, S. D., Kyratsi, T., and Kanatzidis, M. G., Scanning tunneling microscopy of defect states in the semiconductor Bi2Se3. Physical Review B, 66 (16), 4 (2002).
[15] Ben-Yehuda, O., Gelbstein, Y., Dashevsky, Z., Shuker, R., and Dariel, M.P., Improved power factor of Bi0.4Sb1.6Te3 – based samples prepared by cold pressing and sintering. Thermoelectrics, 2006. ICT '06. 25th International Conference. 6-10 Aug (2006).
[16] Ben-Yehuda, O., Shuker, R., Gelbstein, Y., Dashevsky, Z., and Dariel, M. P, Highly textured Bi2Te3-based materials for thermoelectric energy conversion. Journal of Applied Physics, 101 (11), 6 (2007).
[17] Rowe, D. M., CRC handbook of thermoelectrics, CRC Press, Boca Raton, P.221(1995).
[18] Rowe, D. M., Thermoelectrics Handbook : Macro to Nano, CRC/Taylor & Francis, Boca Raton ,Chap27 : P.27-4(2006).
[19] 朱旭山, 熱電材料元件之發展與應用, 工業材料雜誌 220, 93(2005).
[20] Martin-Gonzalez, M., Prieto, A. L., Gronsky, R., Sands, T., and Stacy, A. M., Insights into the electrodeposition of Bi2Te3. Journal of the Electrochemical Society, 149 (11), C546 (2002).
[21] Michel, S., Diliberto, S., Boulanger, C., Stein, N., and Lecuire, J. M., Galvanostatic and potentiostatic deposition of bismuth telluride films from nitric acid solution: effect of chemical and electrochemical parameters. Journal of Crystal Growth, 277 (1-4), 274 (2005).
[22] Miyazaki, Y. and Kajitani, T., Preparation of Bi2Te3 films by electrodeposition. Journal of Crystal Growth, 229 (1), 542 (2001).
[23] Heo, P., Hagiwara, K., Ichino, R., and Okido, M., Electrodeposition and thermoelectric characterization of Bi2Te3. Journal of the Electrochemical Society, 153 (4), C213 (2006).
[24] 王文琳, 電化學法製備熱電製冷器之薄膜及Bi2Te3奈米線之研究, 國立清華大學博士論文(2008).
[25] Yoo, B. Y., Huang, C. K., Lim, J. R., Herman, J., Ryan, M. A., Fleurial, J. P., and Myung, N. V., Electrochemically deposited thermoelectric n-type Bi2Te3 thin films. Electrochimica Acta, 50 (22), 4371 (2005).
[26] Li, S. H., Soliman, H. M. A., Zhou, J., Toprak, M. S., Muhammed, M., Platzek, D., Ziolkowski, P., and Muller, E., Effects of annealing and doping on nanostructured bismuth telluride thick films. Chemistry of Materials, 20 (13), 4403 (2008).
[27] Chaouni, H., Bessieres, J., Modaressi, A., and Heizmann, J. J., Texture prediction of Bi2Te3 electroplated layers using Hartman's theory of crystal growth. Journal of Applied Electrochemistry, 30 (4), 419 (2000).
[28] Hartman P., Crystal Growth, American Elsevier, North-Holland Pub. Co., P.376 (1973).
[29] Michel, S., Diliberto, S., Boulanger, C., and Bolle, B., Effect of electrochemical deposition conditions on the crystallographic texture of bismuth telluride alloys. Journal of Crystal Growth, 296 (2), 227 (2006).
[30] Liu, D. W. and Li, J. F., Electrocrystallization process during deposition of Bi-Te films. Journal of the Electrochemical Society, 155 (7), D493 (2008).
[31] Richoux, V., Diliberto, S., Boulanger, C., and Lecuire, J. M., Pulsed electrodeposition of bismuth telluride films: Influence of pulse parameters over nucleation and morphology. Electrochimica Acta, 52 (9), 3053 (2007).
[32] Diliberto, S., Richoux, V., Stein, N., and Boulanger, C., Influence of pulsed electrodeposition on stoichiometry and thermoelectric properties of bismuth telluride films. Physica status solidi a, 205 (10), 2340 (2008).
[33] Zhu, W., Yang, J. Y., Zhou, D. X., Mao, C. J., and Duan, X. K, Electrochemical atom-by-atom growth of highly uniform thin sheets of thermoelectric bismuth telluride via the route of ECALE. Journal of Electroanalytical Chemistry, 614 (1-2), 41 (2008).
[34] Ma, Y. Y., Jiang, Z. Y., Kuang, Q., Zhang, S. H., Xie, Z. X., Huang, R. B., and Zheng, L. S., Twin-crystal nature of the single-crystal-like branched Cu2O particles. Journal of Physical Chemistry C, 112 (35), 13405 (2008).
[35] Ronning, C., Shang, N. G., Gerhards, I., Hofsass, H., and Seibt, M., Nucleation mechanism of the seed of tetrapod ZnO nanostructures. Journal of Applied Physics, 98 (3), 5 (2005).
[36] Lu, W. G., Ding, Y., Chen, Y. X., Wang, Z. L., and Fang, J. Y, Bismuth telluride hexagonal nanoplatelets and their two-step epitaxial growth. Journal of the American Chemical Society, 127 (28), 10112 (2005).
[37] Zhao, X. B., Ji, X. H., Zhang, Y. H., Cao, G. S., and Tu, J. P, Hydrothermal synthesis and microstructure investigation of nanostructured bismuth telluride powder. Applied Physics a-Materials Science & Processing, 80 (7), 1567 (2005).
[38] Personal communication with Doctor Jing-Feng Li and PhD student Da-Wei Liu ,Tsinghua University, Beijing.
[39] Grimmer, H. and Kunze, K., Twinning by reticular pseudo-merohedry in trigonal, tetragonal and hexagonal crystals. Acta Crystallographica Section A, 60, 220 (2004).