本實驗以鮮少研究的一維ITO奈米線修飾上銀奈米顆粒作為氣體感測器元件的材料，透過ITO奈米線表面存在的大量氧空缺容易吸引氧氣的特性以及修飾上銀奈米顆粒後形成的異質接面結構所造成的電子傳輸通道縮減及其引起的溢出效應，希望能夠以此來達到提升對氣體感測的靈敏度，並比較修飾上兩種不同比例的銀的ITO奈米線與純奈米線對5 ppm CO2、CO及乙醇氣體的靈敏度來了解本實驗製備之Ag-ITO奈米線適合感測的氣體。透過CVD法經由VLS途徑來合成出ITO奈米線，並且利用電化學法將銀奈米顆粒鍍在奈米線的表面，並透過TEM、EDS、XRD、XPS、PL來鑑定結構與成分。量測單根奈米線電阻率來佐證修飾上銀所產生電阻上升的效應。本研究感測三種氣體，在感測溫度下溫度越高靈敏度越高；本實驗所合成的奈米線對乙醇的靈敏度遠大於CO，又CO略大於CO2，而三種奈米線中，3%Ag-ITO有最好的感測效果，在150 ℃下對 5 ppm乙醇的靈敏度有24.4，350 ℃下可以高達100.2。

In this experiment, one-dimensional indium tin oxide (ITO) nanowires, which have been rarely studied, were modified with silver (Ag) nanoparticles as the material of a gas sensor. Many oxygen vacancies on the surface of ITO nanowires could easily attract oxygen. The Ag nanoparticles-decorated nanowire formed a heterojunction structure, causing shrinkage of the electron conduction channel and the spillover effect to improve the response of gas sensing. ITO nanowires were synthesized by chemical vapor deposition (CVD) via vapor-liquid-solid (VLS) route. The Ag nanoparticles were attached on the surface of the ITO nanowires by an electrochemical method. The structure and composition of the nanowires re characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Comparing the gas sensing ability of pure ITO, 1%Ag-ITO and 3%Ag-ITO gas based-sensor for CO2, CO and C2H5OH gas, we investigated the sensitivity of the ITO and Ag-ITO nanowire-based sensors prepared here. It has been found that at a higher operating temperature, there would be more Ag nanoparticles decorated on the surface of the ITO nanowire, leading to higher response. The nanowire synthesized in this experiment was much more sensitive to C2H5OH, as compared with CO and CO2. Among the three types of nanowires 3% Ag-ITO has the best sensing performance, with a response of 24.4 to 5 ppm ethanol at 150 ℃ and as high as 100.2 at 350 ℃.

1. Int Panis, L.L.R., The Effect of Changing Background Emissions on External Cost Estimates for Secondary Particulates. Open Environmental Sciences, 2008. 2(1): p. 47-53.
2. Wang, C., Yin, L., Zhang, L., Xiang, D. and Guo, R., Metal oxide gas sensors: sensitivity and influencing factors. Sensors (Basel), 2010. 10(3): p. 2088-106.
3. Chen, X., Wang, K.Y., Yuan, C. A. and Zhang, G., Nanowire-based gas sensors. Sensors and Actuators B: Chemical, 2013. 177: p. 178-195.
4. Bierwagen, O., Indium oxide—a transparent, wide-band gap semiconductor for (opto)electronic applications. Semiconductor Science and Technology, 2015. 30(2).
5. Quaas, M., Eggs, C., and H. Wulff, Structural studies of ITO thin films with the Rietveld method. Thin Solid Films, 1998. 332(1-2): p. 277-281.
6. Meng, G., Yanagida, T., Nagashima, K., Yoshida, H., Kanai, M., Klamchuen, A., Zhuge, F., He, Y., Rahong, S., Fang, X., Takeda, S. and Kawai, T., Impact of preferential indium nucleation on electrical conductivity of vapor-liquid-solid grown indium-tin oxide nanowires. J Am Chem Soc, 2013. 135(18): p. 7033-8.
7. Zervos, M., Mihailescu, C. N., Giapintzakis, J., Luculescu, C.R., Florini, N., Komninou, Ph., Kioseoglou, J. and Othonos, A., Broad compositional tunability of indium tin oxide nanowires grown by the vapor-liquid-solid mechanism. APL Materials, 2014. 2(5).
8. Hernandez, J.A., Carpena-Nunez, J., Fonseca, L. F., Pettes, M. T., Yacaman, M. J, Benitez, A., Thermoelectric properties and thermal tolerance of indium tin oxide nanowires. Nanotechnology, 2018. 29(36): p. 364001.
9. Kovtyukhova, N.I. and T.E. Mallouk, Conductive indium-tin oxide nanowire and nanotube arrays made by electrochemically assisted deposition in template membranes: switching between wire and tube growth modes by surface chemical modification of the template. Nanoscale, 2011. 3(4): p. 1541-52.
10. Kim, I.D., Rothschild, A, and Tuller, H. L., Advances and new directions in gas-sensing devices. Acta Materialia, 2013. 61(3): p. 974-1000.
11. Gopel, W., Chemisorption and charge transfer at ionic semiconductor surfaces: implications in designing gas sensors. PrSS, 1985. 20(1): p. 9-103.
12. Awang, Z., Gas sensors: a review. Sens. Transducers, 2014. 168: p. 61-75.
13. Lee, A.P. and B.J. Reedy, Temperature modulation in semiconductor gas sensing. Sensors and Actuators B: Chemical, 1999. 60(1): p. 35-42.
14. Jung, S.J. and Yanagida, H., The characterization of a CuO/ZnO heterocontact-type gas sensor having selectivity for CO gas. Sensors and Actuators B: Chemical, 1996. 37(1-2): p. 55-60.
15. Drobek, M., Kim, J. H., Bechelany, M., Vallicari, C., Julbe, A. and Kim. S. S., MOF-Based Membrane Encapsulated ZnO Nanowires for Enhanced Gas Sensor Selectivity. ACS Appl Mater Interfaces, 2016. 8(13): p. 8323-8.
16. Yu, J.H. and Choi, G. M., Selective CO gas detection of CuO-and ZnO-doped SnO2 gas sensor. Sensors and Actuators B: Chemical, 2001. 75(1-2): p. 56-61.
17. Lin, Y.-H., Hsueh, Y. C., Lee, P. S., Wang, C. C., Wu, J. M. Perng, T. P. and Shih, H. C., Fabrication of tin dioxide nanowires with ultrahigh gas sensitivity by atomic layer deposition of platinum. Journal of Materials Chemistry, 2011. 21(28).
18. Hongsith, N., Viriyaworasakul, C., Mangkorntong, P., Mangkorntong N. and Choopun, S., Ethanol sensor based on ZnO and Au-doped ZnO nanowires. Ceramics International, 2008. 34(4): p. 823-826.
19. Walker, J.M., Akbar, S.A. and Morris, P.A., Synergistic effects in gas sensing semiconducting oxide nano-heterostructures: A review. Sensors and Actuators B: Chemical, 2019. 286: p. 624-640.
20. Wang, B., Zhu, L. F., Yang, Y. H., Xu, N. S. and Yang, G. W., Fabrication of a SnO2 nanowire gas sensor and sensor performance for hydrogen. The Journal of Physical Chemistry C, 2008. 112(17): p. 6643-6647.
21. Ménini, P., Parret, F., Guerrero, M., Soulantica, K., Erades, L., Maisonnat, A. and Chaudret, B., CO response of a nanostructured SnO2 gas sensor doped with palladium and platinum. Sensors and Actuators B: Chemical, 2004. 103(1-2): p. 111-114.
22. Sharifpour-Boushehri, S., Hosseini-Golgoo, S.M. and M.-H. Sheikhi, M.-H. A low cost and reliable fiber optic ethanol sensor based on nano-sized SnO2. Optical Fiber Technology, 2015. 24: p. 93-99.
23. Choi, Y.J., Hwang, I. S. Park, J. G., Choi1, K. J., Park, J. H. and Lee, J. H., Novel fabrication of an SnO(2) nanowire gas sensor with high sensitivity. Nanotechnology, 2008. 19(9): p. 095508.
24. Ivanov, P., Llobet, E., Vilanova, X., Brezmes, J., Hubalek, J. and Correig, X., Development of high sensitivity ethanol gas sensors based on Pt-doped SnO2 surfaces. Sensors and Actuators B: Chemical, 2004. 99(2-3): p. 201-206.
25. Sun, G.J., Choi, S. W., Jung, S. H., Katoch, A. and Kim, S. S., V-groove SnO2 nanowire sensors: fabrication and Pt-nanoparticle decoration. Nanotechnology, 2013. 24(2): p. 025504.
26. Shao, F., Hoffmann, M.W.G., Prades, J.D., Zamani, R., Arbiol, J. Morante, J.R., Varechkina, E., Rumyantseva, M., Gaskov, A., Giebelhaus, I., Fischer, T., Mathur, S. and Hernández-Ramírez, F., Heterostructured p-CuO (nanoparticle)/n-SnO2 (nanowire) devices for selective H2S detection. Sensors and Actuators B: Chemical, 2013. 181: p. 130-135.
27. Ahn, M.W., Park, K.S., Heo, J.H. Park, J. G., Kim, D. W., Choi, K. J., Lee, J. H. and Hong S. H., Gas sensing properties of defect-controlled ZnO-nanowire gas sensor. Applied Physics Letters, 2008. 93(26).
28. Ahn, M.W., Park, K.S., Heo, J.H. Kim, D. W., Choi, K. J., and Park, J. G., On-chip fabrication of ZnO-nanowire gas sensor with high gas sensitivity. Sensors and Actuators B: Chemical, 2009. 138(1): p. 168-173.
29. Kim, K., Kim, K., Song, Y.W., Chang, S., Kim, I.H., Kim, S. and Lee, S.Y., Fabrication and characterization of Ga-doped ZnO nanowire gas sensor for the detection of CO. Thin Solid Films, 2009. 518(4): p. 1190-1193.
30. Zhang, N., Yu, K., Li, Q. Zhu, Z. Q. and Wan Q., Room-temperature high-sensitivity H2S gas sensor based on dendritic ZnO nanostructures with macroscale in appearance. Journal of Applied Physics, 2008. 103(10).
31. Zeng, Z., Wang, K., Zhang, Z., Chen, J. and Zhou, L., The detection of H2S at room temperature by using individual indium oxide nanowire transistors. Nanotechnology, 2009. 20(4): p. 045503.
32. Zhang, D., et al., Doping dependent NH3 sensing of indium oxide nanowires. Applied Physics Letters, 2003. 83(9): p. 1845-1847.
33. Lim, S.K., Hwang, S. H., Chang, D. and Kim, S., Preparation of mesoporous In2O3 nanofibers by electrospinning and their application as a CO gas sensor. Sensors and Actuators B: Chemical, 2010. 149(1): p. 28-33.
34. Xu, P., Cheng, Z., Pan, Q., Xu, J., Xiang, Q., Yu, W. and Chu, Y., High aspect ratio In2O3 nanowires: Synthesis, mechanism and NO2 gas-sensing properties. Sensors and Actuators B: Chemical, 2008. 130(2): p. 802-808.
35. Lin, T., Lv, X., Hu, Z., Xu A. and Feng, C., Semiconductor Metal Oxides as Chemoresistive Sensors for Detecting Volatile Organic Compounds. Sensors (Basel), 2019. 19(2).
36. Lupan, O., Cretu, V., Postica, V., Ahmadi, M., Cuenya, B. R., Chow, L., Tiginyanu, I., Viana, B., Pauporté, T. and Adelung, R., Silver-doped zinc oxide single nanowire multifunctional nanosensor with a significant enhancement in response. Sensors and Actuators B: Chemical, 2016. 223: p. 893-903.
37. Anand, K., Kaur, J., Singh, R. C. and Thangaraj, R., Preparation and characterization of Ag-doped In2O3 nanoparticles gas sensor. Chemical Physics Letters, 2017. 682: p. 140-146.
38. Gao, J., Chen, R., Li, D. H., Jiang, L., Ye, J. C., Ma, X. C., Chen, X. D., Xiong, Q. H., Sun, H. D. and Wu. T., UV light emitting transparent conducting tin-doped indium oxide (ITO) nanowires. Nanotechnology, 2011. 22(19): p. 195706.
39. Ho, C. H., Chan, C. H., Tien, L. C. and Huang Y. S., Direct Optical Observation of Band-Edge Excitons, Band Gap, and Fermi Level in Degenerate Semiconducting Oxide Nanowires In2O3. The Journal of Physical Chemistry C, 2011. 115(50): p. 25088-25096.
40. Arooj, S., Xu, T. T., Hou, X., Wang, Y., Tong, T., Chu R. and Liu, B., Green emission of indium oxide via hydrogen treatment. RSC Advances, 2018. 8(21): p. 11828-11833.
41. Huang, S., Ou, G., Cheng, J., Li H. and Pan W., Ultrasensitive visible light photoresponse and electrical transportation properties of nonstoichiometric indium oxide nanowire arrays by electrospinning. Journal of Materials Chemistry C, 2013. 1(39).
42. Zhang, F., Wu, J., Li, Q., Hu, H., Yang, L., Li, T. and Wu, L., Plasmon-controlled, ultra-bright, excitation-polarization-independent photoluminescence from individual Ag nanoplates. Nanophotonics, 2020. 0(0).
43. Gu, W., Choi, H. and Kim, K., Universal approach to accurate resistivity measurement for a single nanowire: Theory and application. Applied Physics Letters, 2006. 89(25).
44. Chavan, D.N., Patil, G. E., Kajale, D. D., Gaikwad, V. B., Khanna, P. K. and Jain G. H., Nano Ag-DopedIn2O3Thick Film: A Low-TemperatureH2SGas Sensor. Journal of Sensors, 2011. 2011: p. 1-8.
45. Zhou, J.Y., Bai, J. L., Zhao, H., Yang, Z. Y., Gu, X. Y., Huang, B. Y., Zhao, C. H., Cairang, L., Sun, G. Z., Zhang, Z. X., Pan, X. J. and Xie, E. Q., Gas sensing enhancing mechanism via doping-induced oxygen vacancies for gas sensors based on indium tin oxide nanotubes. Sensors and Actuators B: Chemical, 2018. 265: p. 273-284.
46. Du, W., Si, W. X., Wang, F. L., Lv, L. F., Wu, L., Wang, Z., Liu, J. R. and Liu, W., Creating oxygen vacancies on porous indium oxide nanospheres via metallic aluminum reduction for enhanced nitrogen dioxide detection at low temperature. Sensors and Actuators B: Chemical, 2020. 303.
47. Wu, L., Xu, J., Li, Q., Fan, Z., Mei, F., Zhou, Y., Yan, J., and Chen, Y., Enhanced performance of In2O3 nanowire field effect transistors with controllable surface functionalization of Ag nanoparticles. Nanotechnology, 2020. 31(35): p. 355703.
48. Hwang, I.S., Choi, J. K., Woo, H. S., Kim, S. J. Jung, S. Y. Seong, T. Y., Kim, I. D. and Lee, J. H., Facile control of C(2)H(5)OH sensing characteristics by decorating discrete Ag nanoclusters on SnO(2) nanowire networks. ACS Appl Mater Interfaces, 2011. 3(8): p. 3140-5.