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Gas sensor has been widely used to monitor the air quality. Metal oxide semiconductor (MOS) is one of the most popular materials used for gas sensors due to its low-cost, easy preparation and good sensing properties. However, the working temperature of tungsten oxide gas sensor is still high, which restricts its applications in special environment. Researchers try to lower the working temperature of WO3 by doping or changing morphology. Tungsten oxide nanowire has great potential to be applied to the gas sensing field because of its high specific surface area. In this work, one-dimensional WO3 nanowire structure is synthesized by sputtering W and followed by the twostep thermally oxidation method. The first step of oxidation is carried out in vacuum tube furnace to obtain the WO2 nanowires and the second step of oxidation is an air annealing treatment in which we will control the temperatures (S0, without treatment; S1, 300℃; S2, 400℃) to study the morphologies and gas sensing properties. The obtained WO3 nanowires are investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM) techniques. The SEM results indicate that WO3 nanowires grow along different directions in space. Nanowires have an average length of 1 μm and a diameter of 40 nm. Besides, nanowires have better crystallinity after higher-temperature (400℃) annealing as indicated by the XRD results, which means less surface defects and surface states. The XPS spectrum indicates the existence of oxygen vacancy in nanowires after 300℃ annealing. The TEM results show that nanowires preferred growth direction is changed after different annealing treatments and the crystal lattice of nanowires after 400℃ has better order than that of nanowires after 300℃. The influences of annealing temperature in the second step on the sensing properties to variousconcentration NO2 gases are investigated at working temperature ranging from room temperature (RT) to 150℃. The results show that the WO3 nanowires after 300℃ annealing show better response than after 400℃ annealing and without annealing treatment. The best response of nanowires to 6 ppm NO2 is 2.5 at RT after 300℃ annealing treatment, and the lowest NO2 detection limit is 0.5 ppm. The room temperature enhancement in gas sensing property may be attributed to the large WO3 nanowire surface states caused by oxidation degree controlled twostep thermal oxidation method. Besides, p-type response to testing gas is found. This might be caused by the lattice defect and the adsorption of oxygen from atmosphere which leads to the formation of surface inversion layer. And the dominated carriers of nanowires will convert from electrons into holes. In conclusion, these results demonstrate that the WO3 nanowires have great potential applications in future NO2 gas detection with low consumption and good performance.
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Keywords:
- tungsten oxide /
- nanowires /
- NO2 gas sensors /
- response types
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[21] Li H, Xie W, Ye T, Liu B, Xiao S, Wang C, Wang Y, Li Q, Wang T 2015 Appl. Mater. Interfaces 7 24887
[22] Zhang C, Debliquy M, Boudiba A, Liao H, Coddet C 2010 Sens. Actuators B 144 280
[23] Xu L, Wang C, Zhang X, Guo D, Pan Q, Zhang G, Wang S 2017 Sens. Actuators B 245 533
[24] Wu Y Q, Hu M, Wei X Y 2014 Chin. Phys. B 23 040704
[25] Yan W, Hu M, Zeng P, Ma S, Li M 2014 Appl. Surf. Sci. 292 551
[26] Li Y, Wang C, Zheng H, Wan F, Yu F, Zhang X, Liu Y 2017 Appl. Surf. Sci. 391 654
[27] Liu E K, Zhu B S, Luo J S 2013 The Physics of Semiconductors (7th Ed.) (Beijing: Publishing House of Electronics Industry) pp93-94 (in Chinese) [刘恩科, 朱秉升, 罗晋生 2013 半导体物理学(第七版)(北京: 电子工业出版社)第93–94页]
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[1] Chen H, Cai H, Zhang Y 2017 J. EMCC 27 68 (in Chinese) [陈滑维, 蔡浩洋, 张阳 2017 中国环境管理干部学院学报 27 68]
[2] Fonollosa J, Lrene R L, Abhijit V S, Margie L H, Margaret A R, Ramon H 2014 Sens. Actuators B 199 398
[3] Mews M, Korte L, Rech B 2016 Sol. Energy Mater. Sol. Cells 158 77
[4] Yao Y, Yin M, Yan J, Yang D, Liu S 2017 Sens. Actuators B 251 583
[5] Wei S, Zhao J, Hu B, Wu K, Du W, Zhou M 2017 Ceram. Int. 43 2579
[6] Barbara U, Vincent T A, Chowdhury M F, Gardner J W 2017 Sens. Actuators B 239 1051
[7] Zeng W, Dong C, Miao B, Zhang H, Xu S, Ding X, Hussain S 2014 Mater. Lett. 117 41
[8] Hemberg A, Konstantinidis S, Viville P, Renaux F, Dauchot J P, Llobet E, Snyders R 2012 Sens. Actuators B 171–172 18
[9] Shendage S S, Patil V L, Vanalakar S A, Patil S P, Harale N S, Bhosale J L, Kim J H, Patil P S 2017 Sens. Actuators B 240 426
[10] Hieu N V, Vuong H V, Duy N V, Hoa N D 2012 Sens. Actuators B 171–172 760
[11] Zhao Y M, Zhu Y Q 2009 Sens. Actuators B 137 27
[12] Luo J Y, Chen F, Cao Z, Zheng W H, Liu C H, Li Y D, Yang G T, Zeng G Q 2015 Cryst. Eng. Comm. 17 889
[13] Ma S, Hu M, Zeng P, Li M, Yan W, Qin Y 2014 Sens. Actuators B 192 341
[14] Li M, Hu M, Jia D, Ma S, Yan W 2013 Sens. Actuators B 186 140
[15] Li M, Hu M, Zeng P, Ma S, Yan W, Qin Y 2013 Electrochim. Acta 108 167
[16] Boyadijev S I, Georgieva V, Stefan N, Stan G E, Mihailescu N, Visan A, Mihailescu I N, Besleaga C, Szilagyi I M 2017 Appl. Surf. Sci. 417 218
[17] Jie X, Zeng D, Zhang J, Xu K, Wu, J, Zhu B, Xie C 2015 Sens. Actuators B 220 201
[18] Wei Y, Chen C, Yuan G, Gao S 2016 J. Alloys Compd. 681 43
[19] Shen Y, Zhao S, Ma J, Chen X, Wang W, Wei D, Gao S, Liu W, Han C, Cui B 2016 J. Alloys Compd. 664 229
[20] Qin Y X, Liu K X, Liu C Y, Sun X B 2013 Acta Phys. Sin. 62 208104 (in Chinese) [秦玉香, 刘凯轩, 刘长雨, 孙学斌 2013 物理学报 62 208104]
[21] Li H, Xie W, Ye T, Liu B, Xiao S, Wang C, Wang Y, Li Q, Wang T 2015 Appl. Mater. Interfaces 7 24887
[22] Zhang C, Debliquy M, Boudiba A, Liao H, Coddet C 2010 Sens. Actuators B 144 280
[23] Xu L, Wang C, Zhang X, Guo D, Pan Q, Zhang G, Wang S 2017 Sens. Actuators B 245 533
[24] Wu Y Q, Hu M, Wei X Y 2014 Chin. Phys. B 23 040704
[25] Yan W, Hu M, Zeng P, Ma S, Li M 2014 Appl. Surf. Sci. 292 551
[26] Li Y, Wang C, Zheng H, Wan F, Yu F, Zhang X, Liu Y 2017 Appl. Surf. Sci. 391 654
[27] Liu E K, Zhu B S, Luo J S 2013 The Physics of Semiconductors (7th Ed.) (Beijing: Publishing House of Electronics Industry) pp93-94 (in Chinese) [刘恩科, 朱秉升, 罗晋生 2013 半导体物理学(第七版)(北京: 电子工业出版社)第93–94页]
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