本研究係利用水熱法成長氧化鋅奈米線製成感測元件，並改變不同之鎵摻雜量，藉此探討一氧化碳氣體感測特性。首先，利用溶膠凝膠法製備氧化鋅材料，以旋轉塗佈製備一層氧化鋅種子層，加以進行不同溫度的退火處理，再以此當作基底成長氧化鋅奈米線，再探討其CO感測特性。實驗結果發現，種子層經500 C退火處理後成長的奈米線具有最佳(002)優先成長方向而種子層經700 C 退火處理後成長的氧化鋅奈米線可得到最佳長寬比，且在感測溫度250 C、CO濃度為200 ppm時具有最佳的感測靈敏度。另一方面，本研究分別以500 C及700 C退火種子層當作基底，在水熱法環境分別摻雜0.5 at. %、1 at. %、2 at.%的硝酸鎵成長氧化鋅奈米線，發現摻鎵濃度增加，氧化鋅奈米線的長寬比會降低，且經由700 C退火處理成長摻雜0.5 at. %硝酸鎵氧化鋅奈米線在感測溫度200 C時具有最佳的感測靈敏度，可達到12.64。最後，藉由改變水熱法溫度成長摻鎵氧化鋅奈米線，發現種子層700 C退火當作基底，在85 C條件下成長摻鎵氧化鋅奈米線具有最佳的長寬比，在感測溫度200 C時具有最佳的CO感測靈敏度為14.48。

This research uses sol-gel method for producing ZnO thin films as seed layers to prepare ZnO nanowires. The seed layers accept annealing treatment at different temperature to obtain crystal structure. A low-temperature solution process is used on the ZnO seed layer to construct a well-collimating, high length-diameter ratio array of nanowires. Sensitivity of CO gas sensing is expected to increase by applying the array of nanowires. According to the experimental results, ZnO nanowires have (002) preferential orientation when grown on the seed layers annealed at 500 C. However, it can obtain the better length-diameter ratio of nanowire when the nanowires grown on the seed layers annealed at 700 C. This nanowire array is applied on gas sensor can get the best sensitivity at the test temperature of 250 C when CO gas concentration is 200 ppm. Furthermore, the effects of Ga-doped ZnO (GZO) nanowires applied on gas sensor have been discussed. It can be found that the length-diameter ratio of ZnO nanowires decreases with Ga-doping concentration. When GZO nanowires with doping 0.5 at. % Ga grown on the seed layer annealed at 700 C, it can obtain the maximun length-diameter ratio of nanowire and reduce the best sensitivity temperature to 200 C. Finally, the sensing sensitivity can be improved by alter the heating temperature to 85 C during the hydrothermal process.

1. http://www.nfpa.org/index.asp
2. M. Zhou, H. Zhu, Y. Jiao, Y. Rao, S. Hark, Y. Liu, L. Peng, and Quan Li,Optical and Electrical Properties of Ga-Doped ZnO Nanowire Arrays on Conducting Substrates, The Journal of Physical Chemistry C, Volume 113, pp. 8945-8947 (2009).
3. K. Kim, Y. W. Song, S. Chang, I. H. Kim, S. Kim, and S. Y. Lee, Fabrication and characterization of Ga-doped ZnO nanowire gas sensor for thedetection of CO, Thin Solid Films Volume 518, pp. 1190-1193 (2009).
4. Y. Li, G. S. Tompa, S. Liang, C. Gorla, C. Lu, and J. Doyle, Transparent and conductive Ga-doped ZnO films grown by low pressure metal organic chemical vapor deposition, Journal of Vacuum Science & Technology A, Volume 15, pp. 1063-1068 (1997).
5. M. Liu, A. H. Kitai, and P. Mascher, Point defects and luminescence centres in zinc oxide and zinc oxide doped with manganese, Journal of Luminescence, Volume 54, pp. 35-42 (1992).
6. S. J. Pearton, D. P. Norton, K. Ip, Y. W. Heo, and T. Steiner, Recent progress in processing and properties of ZnO, Progress in Materials Science, Volume 50, pp. 293-340 (2005).
7. J. Jagadish and S.J. Pearton, Zinc Oxide Bulk, Thin Film and Nanostructures, Elsevier (2006).
8. T. Seiyama, A. Kato, K. Fulishi, and M. Nagatani, A new detector for gaseous components using semiconductive thin films, Analytical Chemistry, Volume 34, pp. 1502–1503 (1962).
9. L. Qin, J. Xu, X. Dong, Q. Pan, Z. Cheng, Q. Xiang, and F. Li, The template-free synthesis of square-shaped SnO2 nanowires: the temperature effect and acetone gas sensors, Nanotechnology, Volume 19, pp. 185705 (2008).
10. L. Liao, H. B. Lu, M. Shuai, J. C. Li, Y. L. Liu, C. Liu, Z. X. Shen, and T. Yu, A novel gas sensor based on field ionization from ZnO nanowires: moderate working voltage and high stability, Nanotechnology, Volume 19, pp. 175501 (2008) .
11. C. S. Rout, M. Hegde, and C. N. R. Rao, H2S sensors based on tungsten oxide nanostructures, Sensors Actuators B, Volume 128, pp. 488–493 (2008).
12. M. Kaur, N. Jain, K. Sharma, S. Bhattacharya, M. Roy, A. K. Tyagi, S. K. Gupta, and J. V. Yakhmi, Room-temperature H2S gas sensing at ppb level by single crystal In2O3 whiskers, Sensors Actuators B, Volume 133, pp. 456–461 (2008).
13. I. Raible, M. Burghard, U. Schlecht, A. Yasuda, and T. Vossmeyer, V2O5 nanofibres: novel gas sensors with extremely high sensitivity and selectivity to amines, Sensors Actuators B, Volume 106, pp. 730-735 (2005) .
14. Z. Li, H. Zhang,W. Zheng, W.Wang, H. Huang, C. Wang, A. G. MacDiamid, and Y. Wei, Highly sensitive and stable humidity nanosensors based on LiCl doped TiO2 electrospun nanofibers, Journal of the American Chemical Society, Volume 130, pp. 5036–5037 (2008).
15. C. C. Li, Z. F. Du, L. M. Li, H. C. Yu, Q. Wan, and T. H. Wang, Surface-depletion controlled gas sensing of ZnO nanorods grown at room temperature, Applied Physics Letters, Volume 91, pp. 032101 (2007).
16. L. Liao, H. B. Lu, J. C. Li, H. He, D. F. Wang, D. J. Fu, C. Liu, and W. F. Zhang, Size Dependence of Gas Sensitivity of ZnO Nanorods, The Journal of Physical Chemistry C, Volume 111, pp. 1900–1903 (2007).
17. J. Y. Park, D. E. Song, and S. S. Kim, An approach to fabricating Chemical sensors based on ZnO nanorod arrays, Nanotechnology, Volume 19, pp. 105503 (2008).
18. M. W. Ahn, K. S. Park, J. H. Heo, D. W. Kim, K. J. Choi, and J.-G. Park, On-chip fabrication of ZnO-nanowire gas sensor with high gas sensitivity, Sensors and Actuators B, Volume 138, pp. 168-173 (2009).
19. S. J. Chang, T. J. Hsueh, I. C. Chen, and B. R. Huang, Highly sensitive ZnO nanowire CO sensors with the adsorption of Au nanoparticles, Nanotechnology, Volume 19, pp. 175502 (2008).
20. S. M. Sze, Semiconductor Sensors, John Wiely & Sons (1994).
21. K. Govender, D. S. Boyle, P. B. Kenway and P. O’Brien, Understanding the factors that govern the deposition and morphology of thin films of ZnO from aqueous solution, Journal of Materials Chemistry, Volume 14, pp. 2575 - 2591 (2004).
22. K. Byrappa and T. Adschiri, Hydrothermal technology for nanotechnology, Progress in Crystal Growth and Characterization of Materials, Volume 53, pp. 117-166 (2007).
23. L. Vayssieres, Growth of Arrayed Nanorods and Nanowires of ZnO from Aqueous Solutions, Advanced Materials, Volume 15, pp. 464-466 (2003).
24. P. Yang, H. Yan, S. Mao, R. Russo, J. Johnson, R. Saykally, N. Morris, J. Pham, R. He, and H. J. Choi, Controlled Growth of ZnO Nanowires and Their Optical Properties, Advanced Functional Materials, Volume 12, pp. 323–331 (2002).
25. M. J. Zheng, L. D. Zhang, G. H. Li, and W. Z. Shen, Fabrication and optical properties of large-scale uniform zinc oxide nanowire arrays by one-step electrochemical deposition technique, Chemical Physics Letters, Volume 363, pp. 123-128 (2002).
26. Y. Sun, G. M. Fuge, and M. N. R. Ashfold, Growth mechanisms for ZnO nanorods formed by pulsed laser deposition, Superlattices and Microstructures, Volume 39, pp. 33-40 (2006).
27. W. Lee, M. C. Jeong, and J. M. Myoung, Catalyst-free growth of ZnO nanowires by metal-organic chemical vapour deposition(MOCVD) and thermal evaporation, Acta Materialia, Volume 52, pp.3949-3957 (2004).
28. Z. L. Wang, ZnO nanowire and nanobelt platform for nanotechnology, Materials Science and Engineering R, Volume 64, pp. 33–71 (2009).
29. D. Polsongkram, P. Chamninok, S. Pukird , L. Chow, O. Lupan, G. Chai, H. Khallaf, S. Park, and A. Schulte, "Effect of synthesis conditions on the growth of ZnO nanorods via hydrothermal method", Physica B, Volume 403, pp. 3713-3717 (2008).
30. J. Song and S. Lim, "Effect of Seed Layer on the Growth of ZnO Nanorods", The Journal of Physical Chemistry C, Volume 111, pp. 596-600 (2007).
31. S. H. Yoon, H. Yang, and Y. S. Kim, Ordered growth of ZnO nanorods for fabrication of a hybrid plasma display panel, Nanotechnology, Volume 18, pp. 205608 (2007).
32. Y. Zhang, G. Du, B. Liu, H. Zhu, T. Yang, W. Li, D. Liu, and S. Yang, Effects of ZnO buffer layer thickness on properties of ZnO thin films deposited by low-pressure MOCVD, Journal of Crystal Growth ,Volume 262, pp. 456-460 (2004).
33. J. S. Huang, Influences of ZnO sol-gel thin film characteristics on ZnO nanowire arrays prepared at low temperature using all solution-based processing, Journa of Applied Physics, Volume 103, pp. 014304 (2008).
34. H. W. Ryua, B. S. Park, S. A. Akbar, W. S. Lee, K. J. Honga, Y. J. Seo, D. C. Shin, J. S. Park, and G. P. Choi, "ZnO sol–gel derived porous film for CO gas sensing", Sensors and Actuators B, Volume 96, pp.717-722 (2003).
35. H. Gong, J. Q. Hu, J. H. Wang, C.H. Onga, and F.R. Zhu, Nano-crystalline Cu-doped ZnO thin film gas sensor for CO, Sensors and Actuators B, Volume 115, pp. 247-251 (2006).
36. J. X. Wang, X. W. Sun, Y. Yang, H. Huang, Y. C. Lee, O. K. Tan, and L. Vayssieres, Hydrothermally grown oriented ZnO nanorod arrays for gas sensing applications, Nanotechnology, Volume 17, pp. 4995-4998 (2006).
37. T. J. Hsueh, Y. W. Chenb, S. J. Changa, S. F. Wang,C. L. Hsuc, Y. R Lin d, T. S. Lin, and I. C. Chene, ZnO nanowire-based CO sensors prepared on patterned ZnO:Ga/SiO2/Si templates, Sensors and Actuators B, Volume 125, pp. 498-503 (2007).
38. E. Çetinörgü, S. Goldsmith, and R.L. Boxman, The effect of annealing on filtered vacuum arc deposited ZnO thin films, Surface & Coatings Technology, Volume 201, pp. 7266–7272 (2007).
39. X. Q. Zhao, C. R. Kim, J. Y. Lee, J. H. Heo, C. M. Shin, H. Ryu, J. H. Chang, H. C. Lee, C. S. Son, W. J. Lee, W. G. Jung, S. T. Tan, J. L. Zhao, and X. W. Sun, Effects of buffer layer annealing temperature on the structural and optical properties of hydrothermal grown ZnO, Applied Surface Science, Volume 255, pp. 4461–4465 (2009).
40. J. S. Huang and C. F. Lin, Influences of ZnO sol-gel thin film characteristics on ZnO nanowire arrays prepared at low temperature using all solution-based processing, Journal of Applied Physics, Volume 103, pp. 014304 (2008).
41. M. Takata, D. Tsubone, and H. Yanagida, Dependence of electrical conductivity of ZnO on degree of sensing, Journal of the American Ceramic Society, Volume 59, pp. 4-8 (1976).
42. A. E. Morales and U. Pal, Defect annihilation and morphological improvement of hydrothermally grown ZnO nanorods by Ga doping, Applied Physics Letters, Volume 93, pp. 193120 (2008).