利用熱蒸鍍系統在氧氣環境下蒸鍍金屬鋅顆粒，成長出單晶鋅-氧化鋅核殼結構奈米線，鋅奈米線直徑約為50 nm，並包覆一層厚約為7.5 nm的氧化鋅層，其成長方向皆為 ，經過熱氧化後，鋅-氧化鋅奈米線內部的金屬鋅向外擴散成長，造成奈米線內部空洞，形成多晶的氧化鋅奈米管。由光偵測特性量測結果顯示，熱氧化時間的長短及不同環境下氧濃度的差別皆會影響光響應度及光電流上升/衰減的速率，隨著熱氧化時間的增加，作為貢獻電子的金屬鋅逐漸氧化，並且造成缺陷的產生，導致自由載子密度降低，因此光響應度減小，而隨著熱氧化時間的增加改善結晶尺寸，因此有較快的上升/衰減速率，並由量測結果顯示，當鋅-氧化鋅奈米線經過350oC、10分鐘熱氧化後，光響應度可達1.1 A/W，正規化之光增益可高達1.1×10-7 m2V-1。

Single crystalline Zn-ZnO core-shell nanowires have been successfully prepared by thermal evaporation of metallic zinc in oxygen ambient. The diameter of the zinc core is ~ 50 nm, while the thickness of the outer ZnO shell is ~ 7.5 nm, both are grown along the direction. Post-growth annealing causes out-diffusion and oxidation of the Zn core that result in the formation of polycrystalline ZnO nanotubes. Photosensing property measurement shows that both the responsivity and rise/decay time depend on annealing time and ambient oxygen concentrations. The responsivity decreases as annealing time increases, while the decay time shortens as annealing time increases. The decay of the responsivity after annealing is due to the loss of excess zinc which acts as donors. The shortening of the decay time after annealing is likely due to improved grain size. An optimized UV responsivity of 1.1 A/W can be achieved with a normalized gain of 1.110-7 m2V-1 after 10 minutes of post-growth annealing at 350C.

參考文獻
[1] W. K. Hong, B. J. Kim, T. W. Kim, G. Jo, S. Song, S. S. Kwon, A. Yoon, E. A. Stach, and T. Lee, “Electrical properties of ZnO nanowire field effect transistors by surface passivation,” Colloids Surf., Vol. 313-314, pp. 378-382, 2008.
[2] M. H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, “Room-temperature ultraviolet nanowire nanolasers,” Science, Vol. 292, pp. 1897-1899, 2001.
[3] Q. Wan, Q. H. Li, Y. J. Chen, T. H. Wang, X. L. He, J. P. Li, and C. L. Lin, “Fabrication and ethanol sensing characteristics of ZnO nanowire gas sensors,” App. Phys. Lett., Vol. 84, pp. 3654-3456, 2004.
[4] C. Soci, A. Zhang, B. Xiang, S. A. Dayeh, D. P. R. Aplin, J. Park, X. Y. Bao, Y. H. Lo, and D. Wang, “ZnO nanowire UV photodetectors with high internal gain,” Nano Lett., Vol. 7, pp. 1003-1009, 2007.
[5] H. Wan, B. B. Li, and H. E. Ruda, “Influence of growth conditions on morpholopgy of ZnO nanostructures in CVD process,” IEEE International Conference on Nano/Micro Engineered and Molecular Systems, pp. 1110-1115, 2010.
[6] H. Yan, J. Hou, Z. Fu, B. Yang, P. Yang, K. Liu, M. Wen, Y. Chen, S. Fu, and F. Li, “Growth and photocatalytic properties of one-dimensional ZnO nanostructures prepared by thermal evaporation,” Materials Research Bulletin, Vol. 44, pp. 1954-1958, 2009.
[7] B. P. Zhang, N. T. Binh, Y. Segawa, K. Wakatsuki and N. Usami, “Optical properties of ZnO rods formed by metalorganic chemical vapor deposition,” Appl. Phys. Lett., Vol. 83, No 8, pp. 1635-1637, 2003.
[8] T. L. Chou, W. Y. Wu, and J. M. Ting, “Sputter deposited ZnO nanowires/thin film structures on glass substrate,” Thin Solid Films, Vol. 518, pp. 1553-1556, 2009.
[9] H. Wei, Y. Wu, N. Lun, and C. Hu, “Hydrothermal synthesis and characterization of ZnO nanorods,” Mater. Sci. and Eng. A, Vol. 393, pp. 80-82, 2005.
[10] R. S. Wagner and W. C. Ellis, “Vapor-liquid-solid mechanism of single crystal growth,” App. Phys. Lett., Vol. 4, pp. 89-90, 1964.
[11] Y. W. Wang, L. D. Zhang, G. Z. Wang, X. S. Peng, Z. Q. Chu, and C. H. Liang, “Catalytic growth of semiconducting zinc oxide nanowires and their photoluminescence properties,” J. Cryst. Growth, Vol. 234, pp. 171-175, 2002.
[12] C. Y. Lee, T. Y. Tseng, S. Y. Li, and P. Lin, “Growth of zinc oxide nanowires on silicon (100),” Tamkang Journal of Science and Engineering, Vol. 6, pp. 127-132, 2003.
[13] W. I. Park, D. H. Kim, S. W. Jung, and G.-C. Yi, “Metalorganic vapor-phase epitaxial growth of vertically well-aligned ZnO nanorods,” App. Phys. Lett., Vol. 80, pp. 4232-4234, 2002.
[14] L. Y. Chen, S. H. Wu, and Y. T. Yin, “Catalyst-free growth of vertical alignment ZnO nanowire arrays by a two-stage process,” J. Phys. Chem. C, Vol. 113, pp. 21572-21576, 2009.
[15] F. Yakuphanoglu, Y. Caglar, S. Ilican, and M. Caglar, “The effects of fluorine on the structural, surface morphology and optical properties of ZnO thin films,” Physica B, Vol. 394, pp. 86-92, 2007.
[16] Ü. Özgür, Y. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S. J. Cho, and H. Morkoç, “A comprehensive review of ZnO materials and device,” J. Appl. Phys., Vol. 98, pp. 041301-1 - 041301-103, 2005.
[17] C. G. Van De Walle, “Hydrogen as a cause of doping in zinc oxide,” Phys. Rev. Lett., Vol. 85, pp. 1012-1015, 2000.
[18] A. B. Djurišić, Y. H. Leung, K. H. Tam, Y. F. Hsu, L. Ding, W. K. Ge, Y. C. Zhong, K. S. Wong, W. K. Chan, H. L. Tam, K. W. Cheah, W. M. Kwok, and D. L. Phillips, “Defect emissions in ZnO nanostructures,” Nanotechnology, Vol. 18, pp. 095702-1-095702-8, 2007.
[19] B. Lin, Z. Fu, Y. Jia, and G. Liao, “Defect photoluminescence of undoping ZnO films and its dependence on annealing conditions,” J. Electrochem. Soc., Vol. 148, pp. 110-113, 2001.
[20] S. A. Studenikin, N. Golego, and M. Cocivera, “Fabrication of green and orange photoluminescent, undoped ZnO films using spray pyrolysis,” J. Appl. Phys., Vol. 84, pp. 2287-2294, 1998.
[21] X. L. Wu, G. G. Siu, C. L. Fu, and H. C. Ong, “Photoluminescence and cathodoluminescence studies of stoichiometric and oxygen-deficient ZnO films,” App. Phys. Lett., Vol. 78, pp. 2285-2287, 2001.
[22] S. Cho, J. Ma, Y. Kim, Y. Sun, G. K. L. Wong, and J. B. Ketterson, “Photoluminescence and ultraviolet lasing of polycrystalline ZnO thin films prepared by the oxidation of the metallic Zn,” App. Phys. Lett., Vol. 75, pp. 2761-2763, 1999.
[23] K. Vanheusden, W. L. Warren, C. H. Seager, D. R. Tallant, J. A. Voigt, and B. E. Gnade, “Mechanisms behind green photoluminescence in ZnO phosphor powders,” J. Appl. Phys., Vol. 79, pp. 7983-7990, 1996.
[24] C. Y. Zhao, X. H. Wang, J. Y. Zhang, Z. G. Ju, C. X. Shan, B. Yao, D. X. Zhao, D. Z. Shen, and X. W. Fan, “Ultraviolet photodetector fabricated from metal-organic chemical vapor deposited MgZnO,” Thin Solid Films, Vol. 519, pp. 1976-1979, 2011.
[25] H. Zhu, C. X. Shan, B. H. Li, J. Y. Zhang, B. Yao, Z. Z. Zhang, D. X. Zhao, D. Z. Shen, and X. W. Fan, “Ultraviolet electroluminescence from mgzno-based heterojunction light-emitting diodes,” J. Phys. Chem. C, Vol. 113, pp. 2980-2982, 2009.
[26] S. Basu and A. Dutta, “Modified heterojunction based on zinc oxide thin film for hydrogen gas-sensor application,” Sens. Actuators B, Vol. 22, pp. 83-87, 1994.
[27] F. Chaabouni, M. Abaab, and B. Rezig, “Metrological characteristics of ZnO oxygen sensor at room temperature,” Sens. Actuators B, Vol. 100, pp. 200-204, 2004.
[28] U. Lampe and J. Muller, “Thin-film oxygen sensors made of reactively sputtered ZnO,” Sens. Actuators B, Vol. 18, pp. 269-284, 1989.
[29] H. Nanto, T. Minami, and S. Takata, “Zinc-oxide thin-film ammonia gas sensors with high sensitivity and excellent selectivity,” J. Appl. Phys., Vol. 60, pp. 482-484, 1986.
[30] P. P. Sahay, S. Tewari, S. Jha, and M. Shamsuddin, “Sprayed ZnO thin films for ethanol sensors,” J. Mater. Sci., Vol. 40, pp. 4791-4793, 2005.
[31] R. Jaramillo and S. Ramanathan, “Kelvin force microscopy studies of work function of transparent conducting ZnO:Al electrodes synthesized under varying oxygen pressures,” Sol. Energy Mater. Sol. Cells, Vol. 95, pp. 602-605, 2011.
[32] J. Yi, J. M. Lee, and W. I. Park, “Vertically aligned ZnO nanorods and graphene hybrid architectures for high-sensitive flexible gas sensors,” Sens. Actuators, B, Vol. 155, pp. 264-269, 2011
[33] Q. H. Li, T. Gao, Y. G. Wang, and T. H. Wang, “Adsorption and desorption of oxygen probed from ZnO nanowire films by photocurrent measurements,” App. Phys. Lett., Vol. 86, pp. 123117-1-123117-3, 2005.
[34] S. Dhara and P. Giri, “Enhanced UV photosensitivity from rapid thermal annealed vertically aligned ZnO nanowires,” Nanoscale Res. Lett., Vol. 6, pp. 504-1-504-8, 2011.
[35] S. Y. Li, C. Y. Lee and T. Y. Tseng, “Copper-catalyzed ZnO nanowires on silicon (100) grown by vapor-liquid-solid process,” J. Cryst. Growth, Vol. 247, pp. 357-262, 2003.
[36] Y. Ding, P. X. Gao, and Z. L. Wang, “Catalyst-nanostructure interfacial lattice mismatch in determining the shape of VLS grown nanowires and nanobelts : A Case of Sn / ZnO,” J. Am. Chem. Soc., Vol. 126, pp. 2066-2072, 2004.
[37] S. Li, X. Zhang, B. Yan, and T. Yu, “Growth mechanism and diameter control of well-aligned small-diameter ZnO nanowire arrays synthesized by a catalyst-free thermal evaporation method,” Nanotechnology, Vol. 20, pp. 495604-1-495604-9, 2009.
[38] J. B. K. Law, C. B. Boothroyd, and J. T. L. Thong, “Site-specific growth of ZnO nanowires from patterned Zn via compatible semiconductor processing,” J. Cryst. Growth, Vol. 310, pp. 2485-2492, 2008.
[39] H. J. Fan, R. Scholz, F. M. Kolb, and M. Zacharias, “Two-dimensional dendritic ZnO nanowires from oxidation of Zn microcrystals,” App. Phys. Lett., Vol. 85, pp. 4142-4144, 2004.
[40] T. W. Kim, T. Kawazoe, S. Yamazaki, M. Ohtsu, and T. Sekiguchi, “Low-temperature orientation-selective growth and ultraviolet emission of single-crystal ZnO nanowires,” App. Phys. Lett., Vol. 84, pp. 3358-3360, 2004.
[41] S. Rackauskas, A. G. Nasibulin, H. Jiang, Y. Tian, G. Statkute, S. D. Shandakov, H. Lipsanen, and E. I. Kauppinen, “Mechanistic investigation of ZnO nanowire growth,” Appl. Phys. Lett., Vol. 95, pp. 183114, 2009.
[42] A. M. B. Gonçalves, L. C. Campos, A. S. Ferlauto, and R. G. Lacerda, “On the growth and electrical characterization of CuO nanowires by thermal oxidation,” J. Appl. Phys., Vol. 106, pp. 034303, 2009.
[43] X. Y. Kong, Y. Ding, and Z. L. Wang, “Metal-semiconductor Zn-ZnO core- shell nanobelts and nanotubes,” J. Phys. Chem. B, Vol. 108, pp. 570-574, 2004.
[44] D.M. Mattox, J. Vac. Sci. Technol, A7, 1105, 1989.
[45] C. Y. Liu, B. P. Zhang, Z. W. Lu, N. T. Binh, K. Wakatsuki, Y. Segawa, and R. Mu, “Fabrication and characterization of ZnO film based UV photodetector,” J. Mater Sci.：Mater. Electron., Vol. 20, pp. 197-201, 2009.
[46] W. Y. Weng, S. J. Chang, C. L. Hsu, T. J. Hsueh, and S. P. Chang, “A lateral ZnO nanowire photodetector prepared on glass substrate,” J. Electrochemical Soc., Vol. 157, pp. K30-K33, 2010.