本研究嘗試利用反應性射頻磁控濺鍍法製備不同結構之MoO3薄膜，在固定O2流量分率35%，Mo靶濺鍍槍功率170 W，改變工作壓力製備MoO3初鍍膜，並改變不同退火熱處理參數，探討工作壓力及退火熱處理參數對MoO3結構之影響，再以特定濺鍍及退火製程參數之β-MoO3及α-MoO3，對乙醇氣體及氨氣之感測性能作研究。薄膜結構以X光粉晶繞射分析儀(XRD)、低掠角X光繞射儀(GIAXRD)、場發射型掃描式電子顯微鏡(FE-SEM)，以及背散射電子取向分析技術(EBSD)等進行薄膜結構分析，並以本實驗室組裝之氣體感測儀器量測氣體感測性質。
研究結果顯示，濺鍍MoO3初鍍膜之沉積速率隨工作壓力3 mTorr上升至14 mTorr時，其濺鍍速率由9 nm/min降至3.8 nm/min。在不同工作壓力(3、7、14 mTorr)下退火450℃持溫一小時之MoO3薄膜，其結構皆為α-MoO3。工作壓力3 mTorr下成膜之試片，退火溫度由200℃增加至450℃時，低溫穩定相β-MoO3會轉變為高溫穩定相α-MoO3，其相變態溫度介於350℃與400℃之間。退火450℃持溫一小時之鍍膜，具[0 1 0]擇優取向(Preferred orientation)之α-MoO3。氣體感測實驗中，當操作溫度上升，試片之靈敏度也隨著上升，由於較高溫度，會有較高之活化能提高反應速率。β-MoO3薄膜在操作溫度250℃下反應時間約3~5秒，回復時間約85秒，對乙醇氣體之靈敏度(Sensitivity)較佳，α-MoO3薄膜同樣在操作溫度250℃下反應時間約3~5秒，回復時間約200秒，對氨氣之靈敏度較佳。

Molybdenum trioxide (MoO3), which has phases of α-MoO3, β-MoO3, h-MoO3, is one of the gas sensing materials and a well-known catalyst. Gas sensing properties are influenced by the structure, shape, grain size, morphology. Specially, the resistivity changes occur in the reaction with oxidizing and reducing gases.
In this study, MoO3 thin films were prepared by reactive RF sputtering under O2 flow ratio (35%) and Mo target power (170 W). In order to investigate the phases and morphology of the prepared samples, working pressure, annealing temperature and annealing time were the process parameters. Film structures were analyzed by X-ray powder diffraction (XRD), glancing incident angle X-ray diffraction (GIAXRD), SEM and electron back scattering diffraction (EBSD).
β-MoO3 is formed at annealing temperature 200~300℃ for 1hr in air and α-MoO3 is formed at annealing temperature above 450℃ for 1hr in air. α-MoO3 is stable at annealing temperature 450℃ and shows (0 1 0) preferred orientation. In the gas sensing experiment, β-MoO3 in reaction with ethanol has response time 3~5s and recovery time 85s, and the optimum temperature is 250℃. However, α-MoO3 in reaction with ammonia gas has response time 3~5s and recovery time 200s, and the optimum temperature is 250℃.

[1] S. S. Sunu, E. Prabhu, V. Jayaraman, K. I. Gnanasekar, T. K. Seshagiri, T. Gnanasekaran, "Electrical conductivity and gas sensing properties of MoO3", Sensors and Actuators B: Chemical, 101 (2004) 161-174.
[2] C. Imawan, H. Steffes, F. Solzbacher, E. Obermeier, "A new preparation method for sputtered MoO3 multilayers for the application in gas sensors", Sensors and Actuators B: Chemical, 78 (2001) 119-125.
[3] M. Ferroni, V. Guidi, G. Martinelli, P. Nelli, M. Sacerdoti, G. Sberveglieri, "Characterization of a molybdenum oxide sputtered thin film as a gas sensor", Thin Solid Films, 307 (1997) 148-151.
[4] M. Ferroni, V. Guidi, G. Martinelli, M. Sacerdoti, P. Nelli, G. Sberveglieri, "MoO3-based sputtered thin films for fast NO2 detection", Sensors and Actuators B: Chemical, 48 (1998) 285-288.
[5] S. S. Sunu, E. Prabhu, V. Jayaraman, K. I. Gnanasekar, T. Gnanasekaran, "Gas sensing properties of PLD made MoO3 films", Sensors and Actuators B: Chemical, 94 (2003) 189-196.
[6] C. Imawan, F. Solzbacher, H. Steffes, E. Obermeier, "Gas-sensing characteristics of modified-MoO3 thin films using Ti-overlayers for NH3 gas sensors", Sensors and Actuators B: Chemical, 64 (2000) 193-197.
[7] A. K. Prasad, P. I. Gouma, "MoO3 and WO3 based thin film conductimetric sensors for automotive applications", Journal of Materials Science, 38 (2003) 4347-4352.
[8] D. B. Dadyburjor, S. S. Jewur, E. Ruckenstein, "Selective oxidation of hydrocarbons on composite oxides", Catalysis Reviews-Science and Engineering, 19 (1979) 293-350.
[9] M. A. Larrubia, G. Ramis, G. Busca, "An FT-IR study of the adsorption of urea and ammonia over V2O5-MoO3-TiO2 SCR catalysts", Applied Catalysis B: Environmental, 27 (2000) L145-L151.
[10] M. Di Giulio, G. Micocci, A. Serra, A. Tepore, R. Rella, P. Siciliano, "SnO2 thin films for gas sensor prepared by r.f. reactive sputtering", Sensors and Actuators B: Chemical, 25 (1995) 465-468.
[11] T. Sahm, A. Gurlo, N. Bârsan, U. Weimar, "Basics of oxygen and SnO2 interaction; work function change and conductivity measurements", Sensors and Actuators B: Chemical, 118 (2006) 78-83.
[12] P. Mars, D. W. v. Krevelen, "Oxidations carried out by means of vanadium oxide catalysts", Chemical Engineering Science, 3 (1954) 41-53.
[13] A. Abdellaoui, G. Lévêque, A. Donnadieu, A. Bath, B. Bouchikhi, "Iteratively derived optical constants of MoO3 polycrystalline thin films prepared by CVD", Thin Solid Films, 304 (1997) 39-44.
[14] L. Boudaoud, N. Benramdane, R. Desfeux, B. Khelifa, C. Mathieu, "Structural and optical properties of MoO3 and V2O5 thin films prepared by Spray Pyrolysis", Catalysis Today, 113 (2006) 230-234.
[15] A. K. Prasad, D. J. Kubinski, P. I. Gouma, "Comparison of sol-gel and ion beam deposited MoO3 thin film gas sensors for selective ammonia detection", Sensors and Actuators B: Chemical, 93 (2003) 25-30.
[16] E. M. Gaigneaux, K.-i. Fukui, Y. Iwasawa, "Morphology of crystalline [alpha]-MoO3 thin films spin-coated on Si (100)", Thin Solid Films, 374 (2000) 49-58.
[17] S. Swann, "Magnetron sputtering", Physics and Technology, 19 (1988) 67-75.
[18] R. Goswami, H. Herman, S. Sampath, X. Jiang, Y. Tian, G. Halada, "Plasma sprayed Mo-Mo oxide nanocomposites: synthesis and characterization", Surface and Coatings Technology, 141 (2001) 220-226.
[19] L. Zheng, Y. Xu, D. Jin, Y. Xie, "Novel Metastable Hexagonal MoO3 Nanobelts: Synthesis, Photochromic, and Electrochromic Properties", Chemistry of Materials, 21 (2009) 5681-5690.
[20] M. B. Rahmani, S. H. Keshmiri, J. Yu, A. Z. Sadek, L. Al-Mashat, A. Moafi, K. Latham, Y. X. Li, W. Wlodarski, K. Kalantar-zadeh, "Gas sensing properties of thermally evaporated lamellar MoO3", Sensors and Actuators B: Chemical, 145 (2010) 13-19.
[21] L. Eckertova, T. Ruizicka: Diagnostics and Applications of Thin Films, Institute of Physics Publishing, 1993.
[22] J. Venables, "Nucleation and Growth of Thin films", Reports on Progress in Physics, 47 (1984) 399-459.
[23] L. John Vossen, W. Kerm: Thin Film Process, Academic Press, New York, 1999.
[24] K. Ihokura, J. Watson: The Stannic Oxide Gas Sensor-Principles and Applications, CRC press, Toyko, 1994.
[25] G. Sberveglieri: Gas sensors: Principle, operation and developments, Kluwer Academic Publishers, Netherlands, 1992.
[26] 蔡嬪嬪, 曾明漢, "氣體感測器之簡介，應用市場", 材料與社會, 68 (1992) 50-61.
[27] 一之瀨昇, 小林哲二: 感測器原理與應用技術, 全華, 1986, pp. 144-153.
[28] 林鴻明, 曾世杰, "奈米半導體材料之特殊氣體感測性質", 工業材料, 157 (2000) 163-169.
[29] C. C. Li, Z. F. Du, L. M. Li, H. C. Yu, Q. Wan, T. H. Wang, "Surface-depletion controlled gas sensing of ZnO nanorods grown at room temperature", Applied Physics Letters, 91 (2007).
[30] K. Zakrzewska, "Gas sensing mechanism of TiO2-based thin films", Vacuum, 74 (2004) 335-338.
[31] Y. Pimtong-Ngam, S. Jiemsirilers, S. Supothina, "Preparation of tungsten oxide-tin oxide nanocomposites and their ethylene sensing characteristics", Sensors and Actuators A: Physical, 139 (2007) 7-11.
[32] V. S. Vaishnav, P. D. Patel, N. G. Patel, "Indium Tin Oxide thin film gas sensors for detection of ethanol vapours", Thin Solid Films, 490 (2005) 94-100.
[33] M. Batzill, U. Diebold, "The surface and materials science of tin oxide", Progress in Surface Science, 79 (2005) 47-154.
[34] S.-S. Park, J. D. Mackenzie, "Thickness and microstructure effects on alcohol sensing of tin oxide thin films", Thin Solid Films, 274 (1996) 154-159.
[35] N. Jankovic, "Semiconductor sensors: S.M. Sze (ed.), John Wiley & Sons, New York, 1994", Microelectronics Journal, 28 (1997) 360-360.
[36] H. Ohnishi, H. Sasaki, T. Matsumoto, M. Ippommatsu, "Sensing mechanism of SnO2 thin film gas sensors", Sensors and Actuators B: Chemical, 14 (1993) 677-678.
[37] D. Kohl, "Surface processes in the detection of reducing gases with SnO2-based devices", Sensors and Actuators, 18 (1989) 71-113.
[38] S. R. Morrison: The Chemical Physics of Surfaces, Plenum Press New York, 1990.
[39] N. Yamazoe, J. Fuchigami, M. Kishikawa, T. Seiyama, "Interactions of tin oxide surface with O2, H2O and H2", Surface Science, 86 (1979) 335-344.
[40] P. B. Weisz, "Effects of electronic charge transfer between adsorbate and solid on chemisorption and catalysis", The Journal of Chemical Physics, 21 (1953) 1531-1538.
[41] 高正雄: 超LSI時代-電漿化學, 復漢出版社, 台南市, 1999.
[42] 楊錦昌, "基礎濺鍍電漿", 電子發展月刊, 68 (1983) 13.
[43] 李玉華, "透明導電膜及其應用", 科儀新知, 12 (1980) 94.
[44] C S Barrett, T. B. Massalski: Structure of Metals: Crystallographic Methods, Principles and Data, New York: Pergamon, 1980.
[45] Hiroshi Negishi, Saiko Negishi, Yoshihiro Kuroiwa, Nobufumi Sato, S. Aoyagi, "Anisotropic thermal expansion of layered MoO3 crystals", PHYSICAL REVIEW B, 69 (2004) 064111.