本實驗透過電漿輔助硒化的方式達到低溫合成大面積二維材料二硒化鎢，大約在攝氏300度下即可讓氧化鎢完全轉變，此方法和其他傳統電化學氣相沈積或是一般硒化的製成相比，其製成溫度是相對低許多，因此也相當有機會運用在軟性電子元件上，其實在合成端，我們探討許多影響，像是氣氛比例和電漿瓦數大小對硒化的程度，前驅物的結晶性對於二硒化鎢的合成是否有品質上的提升，還有基板的平坦度對於透過熱蒸度的方式鍍膜其連續性的影響等等。除此之外，我們可以利用控制前驅物的厚度來達到二硒化鎢的層數控制，如果是以二氧化矽當作基板，最少層數約3層。
我們知道二維材料由於具備半導體性和高體表面積比，因此相當俱有潛力當作氣體感測器，文獻上雖已有人展示過其運用，但是仍有些問題存在於二維材料的表現，例如重複性使用性的能力相當差，需要透過長時間來回到原本的電流狀態，還有目前的偵測極限為ppm等級，而本實驗成功透過電漿來部分硒化氧化鎢，讓二硒化鎢以片狀的方式堆疊在表面或是嵌入在氧化鎢裡，如此的結構可以產生較多的缺陷和懸鍵，其相當有助於偵測物一氧化氮的吸附，借此來達到更低濃度的偵測，目前偵測極限最低為25 ppb，在二維材料的表現中算是相當好的，除此之外我們發現混合的氧化鎢/二硒化鎢薄膜透過紫外線照光的方式，可以加速偵測物的脫附，讓脫附時間縮短到只需要大約250秒，比純的二維材料在紫外光照射下脫附的更快速，因此能解決二維材料在氣體感測上重複使用性的問題。

In this work, we have successfully synthesized tungsten trioxide (WO3) / tungsten diselenide (WSe2) hybrid films in different ratios at low temperature through plasma-enhanced selenization process. The temperature for the synthesis of transition metal dichalcogenides (TMDs) through conventional chemical vapor deposition or selenization/sulfurization processes usually require temperatures higher than 500oC. It means that the thermal budget is still too high. But for our method, the synthesis temperature can be lower than 300oC. Lowering the process temperature not only can lower the cost; but also, show the potential for fabrication of flexible electrical, optoelectrical and sensing devices between other applications. Parameters such as the effect of plasma power, forming gas ratio (H2/N2), crystallinity of precursor and the substrate have major influence in the reduction process of WO3. Besides, the thickness control for synthesis of WSe2 is also addressed in this work.
Recent reports have demonstrated that TMDs at atomic thickness are suitable to serve as gas sensors due to its high surface-to-volume ratio and semiconducting property. However, there are still some problems using TMDs as the reactive layer. For example, it is inevitable to take a long time for detachment, resulting in a poor reproducibility of the electrical results. Besides, so far, the limit of detection for TMDs base sensor is about ppm level. In this work, we use hybrid WO3/WSe2 film as the reactive layer for the NO gas detection. The film is formed through a partial selenization. This hybrid WO3/WSe2 film exhibit ultra-high performance as a gas sensor application. The limit of detection can be largely decreased to 25 ppb. We infer that the reason for such a high sensitivity is that there are more edge sites on the surface. Moreover, the gas detachment time is much faster than that of a pure TMDs case under UV illumination. The detachment time can be reduced from tenths of minutes to only 250s. The result implies that the hybrid WSe2/WO3 can overcome the problem of reproducibility in TMDs based gas sensor. More significant, the hybrid film displays ultra-high sensitivity for NO gas.

1. B. Sipos1, A. F. K., A. Akrap1, H. Berger1, L. Forró1 & E. Tutis caron2, From Mott state to superconductivity in 1T-TaS2. Nature Materials 960 - 965 (2008)
2. Qing Hua Wang1, K. K.-Z., Andras Kis3, Jonathan N. Coleman4,5 and Michael S. Strano1*, Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. nature nanotechnology 6 NOVEMBER 2012.
3. Manish Chhowalla1*, H. S. S., Goki Eda3,4,5, Lain-Jong Li6, Kian Ping Loh4,5 and Hua Zhang7, The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. nature chemistry 20 MARCH 2013.
4. Wilson, J. A.; Yoffe, A. D., Transition Metal Dichalcogenides Discussion and Interpretation of Observed Optical, Electrical and Structural Properties. Adv Phys 1969, 18 (73), 193-&.
5. Py, M. A.; Haering, R. R., Structural Destabilization Induced by Lithium Intercalation in Mos2 and Related-Compounds. Can J Phys 1983, 61 (1), 76-84.
6. Ganal, P.; Olberding, W.; Butz, T.; Ouvrard, G., Soft Chemistry Induced Host Metal Coordination Change from Octahedral to Trigonal Prismatic in 1t-Tas2. Solid State Ionics 1993, 59 (3-4), 313-319.
7. Lorenz, T.; Teich, D.; Joswig, J. O.; Seifert, G., Theoretical Study of the Mechanical Behavior of Individual TiS2 and MoS2 Nanotubes. J Phys Chem C 2012, 116 (21), 11714-11721.
8. Yun, W. S.; Han, S. W.; Hong, S. C.; Kim, I. G.; Lee, J. D., Thickness and strain effects on electronic structures of transition metal dichalcogenides: 2H-M X-2 semiconductors (M = Mo, W; X = S, Se, Te). Phys Rev B 2012, 85 (3).
9. Splendiani, A.; Sun, L.; Zhang, Y. B.; Li, T. S.; Kim, J.; Chim, C. Y.; Galli, G.; Wang, F., Emerging Photoluminescence in Monolayer MoS2. Nano Lett 2010, 10 (4), 1271-1275.
10. Cheiwchanchamnangij, T.; Lambrecht, W. R. L., Quasiparticle band structure calculation of monolayer, bilayer, and bulk MoS2. Phys Rev B 2012, 85 (20).
11. Xiao, D.; Liu, G. B.; Feng, W. X.; Xu, X. D.; Yao, W., Coupled Spin and Valley Physics in Monolayers of MoS2 and Other Group-VI Dichalcogenides. Phys Rev Lett 2012, 108 (19).
12. Zeng, H. L.; Liu, G. B.; Dai, J. F.; Yan, Y. J.; Zhu, B. R.; He, R. C.; Xie, L.; Xu, S. J.; Chen, X. H.; Yao, W.; Cui, X. D., Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides. Sci Rep-Uk 2013, 3.
13. Verble, J. L.; Wieting, T. J., Lattice Mode Degeneracy in Mos2 and Other Layer Compounds. Phys Rev Lett 1970, 25 (6), 362-&.
14. Berkdemir, A.; Gutierrez, H. R.; Botello-Mendez, A. R.; Perea-Lopez, N.; Elias, A. L.; Chia, C. I.; Wang, B.; Crespi, V. H.; Lopez-Urias, F.; Charlier, J. C.; Terrones, H.; Terrones, M., Identification of individual and few layers of WS2 using Raman Spectroscopy. Sci Rep-Uk 2013, 3.
15. The International Technology Roadmap for Semiconductors. http://www.itrs.net/Links/2011ITRS/Home2011.htm (Semiconductor Industry Association, 2011).
16. Kaasbjerg, K.; Thygesen, K. S.; Jacobsen, K. W., Phonon-limited mobility in n-type single-layer MoS2 from first principles. Phys Rev B 2012, 85 (11).
17. Deep Jariwala, V. K. S., † Lincoln J. Lauhon,† Tobin J. Marks,†,‡ and Mark C. Hersam†,‡,§,*, Emerging Device Applications for Semiconducting Two-Dimensional Transition Metal Dichalcogenides. ACS nano January 29, 2014.
18. Kim, S.; Konar, A.; Hwang, W. S.; Lee, J. H.; Lee, J.; Yang, J.; Jung, C.; Kim, H.; Yoo, J. B.; Choi, J. Y.; Jin, Y. W.; Lee, S. Y.; Jena, D.; Choi, W.; Kim, K., High-mobility and low-power thin-film transistors based on multilayer MoS2 crystals. Nat Commun 2012, 3.
19. Sze, S. M.; Ng, K. K. Physics of Semiconductor Devices, 3rd ed.; Wiley: New York, 2007.
20. Jariwala, D.; Sangwan, V. K.; Wu, C. C.; Prabhumirashi, P. L.; Geier, M. L.; Marks, T. J.; Lauhon, L. J.; Hersam, M. C., Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode. P Natl Acad Sci USA 2013, 110 (45), 18076-18080.
21. Yu, W. J.; Liu, Y.; Zhou, H. L.; Yin, A. X.; Li, Z.; Huang, Y.; Duan, X. F., Highly efficient gate-tunable photocurrent generation in vertical heterostructures of layered materials. Nature Nanotechnology 2013, 8 (12), 952-958.
22. Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A., Ultrasensitive photodetectors based on monolayer MoS2. Nature Nanotechnology 2013, 8 (7), 497-501.
23. Roy, K.; Padmanabhan, M.; Goswami, S.; Sai, T. P.; Ramalingam, G.; Raghavan, S.; Ghosh, A., Graphene-MoS2 hybrid structures for multifunctional photoresponsive memory devices. Nature Nanotechnology 2013, 8 (11), 826-830.
24. Guoxiong Su, V. G. H., ‡ Phillip E. Loya,§ Jing Zhang,§ Sidong Lei,§ Surendra Maharjan,† Pei Dong,§ Pulickel M. Ajayan,§ Jun Lou,§ and Haibing Peng*,†, Chemical Vapor Deposition of Thin Crystals of Layered Semiconductor SnS2 for Fast Photodetection Application. Nano Lett. 2015 December 10, 2014.
25. Hai Li, J. W., Zongyou Yin, and Hua Zhang*, Preparation and Applications of Mechanically Exfoliated Single-Layer and Multilayer MoS2 and WSe2 Nanosheets. Accounts of Chemical Research April 3, 2014.
26. Qiyuan He , Z. Z., Zongyou Yin , Hai Li , Shixin Wu , Xiao Huang ,and Hua Zhang *, Fabrication of Flexible MoS 2 Thin-Film Transistor Arrays for Practical Gas-Sensing Applications. small 2012.
27. J. K. Nørskov, a., *,z T. Bligaard,a A. Logadottir,a J. R. Kitchin,b,* J. G. Chen,b S. Pandelov,c and U. Stimmingc,*, Trends in the Exchange Current for Hydrogen Evolution. Journal of The Electrochemical Society January 24, 2005.
28. Haotian Wang, D. K., ‡ Petr Johanes,‡ Judy J. Cha,‡ Guangyuan Zheng,§ Kai Yan,‡ Nian Liu,∥; and Yi Cui*, ⊥, MoSe2 and WSe2 Nanofilms with Vertically Aligned Molecular Layers on Curved and Rough Surfaces. Nano Lett, June 25, 2013.
29. Junfeng Xie , H. Z., Shuang Li , Ruoxing Wang , Xu Sun , Min Zhou , Jingfang Zhou ,; Xiong Wen (David) Lou , a. Y. X., Defect-Rich MoS 2 Ultrathin Nanosheets with Additional Active Edge Sites for Enhanced Electrocatalytic Hydrogen Evolution. Adv. Mater. 2013.
30. Yanguang Li, H. W., Liming Xie, Yongye Liang, Guosong Hong, and Hongjie Dai*, MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction. 7298 dx.doi.org/10.1021/ja201269b |J. Am. Chem. Soc. 2011, 133, 7296–7299 Journal of the American Chemical Society April 21, 2011.
31. Coleman, J. N.; Lotya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H. Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V., Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331 (6017), 568-571.
32. Joensen, P.; Frindt, R. F.; Morrison, S. R., Single-Layer Mos2. Mater Res Bull 1986, 21 (4), 457-461.
33. Zeng, Z. Y.; Yin, Z. Y.; Huang, X.; Li, H.; He, Q. Y.; Lu, G.; Boey, F.; Zhang, H., Single-Layer Semiconducting Nanosheets: High-Yield Preparation and Device Fabrication. Angew Chem Int Edit 2011, 50 (47), 11093-11097.
34. Zeng, Z. Y.; Sun, T.; Zhu, J. X.; Huang, X.; Yin, Z. Y.; Lu, G.; Fan, Z. X.; Yan, Q. Y.; Hng, H. H.; Zhang, H., An Effective Method for the Fabrication of Few-Layer-Thick Inorganic Nanosheets. Angew Chem Int Edit 2012, 51 (36), 9052-9056.
35. Lee, Y. H.; Zhang, X. Q.; Zhang, W. J.; Chang, M. T.; Lin, C. T.; Chang, K. D.; Yu, Y. C.; Wang, J. T. W.; Chang, C. S.; Li, L. J.; Lin, T. W., Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition. Adv Mater 2012, 24 (17), 2320-2325.
36. Lin, Y. C.; Zhang, W. J.; Huang, J. K.; Liu, K. K.; Lee, Y. H.; Liang, C. T.; Chu, C. W.; Li, L. J., Wafer-scale MoS2 thin layers prepared by MoO3 sulfurization. Nanoscale 2012, 4 (20), 6637-6641.
37. Liu, K. K.; Zhang, W. J.; Lee, Y. H.; Lin, Y. C.; Chang, M. T.; Su, C.; Chang, C. S.; Li, H.; Shi, Y. M.; Zhang, H.; Lai, C. S.; Li, L. J., Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates. Nano Lett 2012, 12 (3), 1538-1544.
38. A. Castellanos-Gomez, M. B., A. M. Goossens, V. E. Calado, H. S. J. van der Zant, and G. A. Steele*, Laser-Thinning of MoS2: On Demand Generation of a Single-Layer Semiconductor. NanoLett May 29, 2012.
39. Chua*, T. A. J. L. a. D. H. C., Growth Mechanism of Pulsed Laser Fabricated Few-Layer MoS2 on Metal Substrates. ACS Applied Materials & Interfaces September 9, 2014.
40. Yu-Ze Chen, H. M., † Teng-Yu Su,† Jian-Guang Li,† Kai-Yuan Cheng,‡ Po-Wen Chiu,‡ and; Yu-Lun Chueh*, Ultrafast and Low Temperature Synthesis of Highly Crystalline and Patternable Few-Layers Tungsten Diselenide by Laser Irradiation Assisted Selenization Process. ACS nano March 13, 2015.
41. Kreuzer, L. B.; Patel, C. K. N., Nitric Oxide Air Pollution - Detection by Optoacoustic Spectroscopy. Science 1971, 173 (3991), 45-&.
42. Frandsen, U.; LopezFigueroa, M.; Hellsten, Y., Localization of nitric oxide synthase in human skeletal muscle. Biochem Bioph Res Co 1996, 227 (1), 88-93.
43. Chao Zhanga, Marc Debliquya, Abdelhamid Boudibaa, Hanlin Liaob, Christian Coddetb, Sensing properties of atmospheric plasma-sprayed WO3 coating for sub-ppm NO2 detection. Sensors and Actuators B 2010.
44. Abbas, A. N.; Liu, B. L.; Chen, L.; Ma, Y. Q.; Cong, S.; Aroonyadet, N.; Kopf, M.; Nilges, T.; Zhou, C. W., Black Phosphorus Gas Sensors. Acs Nano 2015, 9 (5), 5618-5624.
45. Maria O’Brien, K. L., Rachel Morrishd, Nina C. Berner, Niall McEvoy,Colin A. Wolden, Georg S. Duesberg, Plasma assisted synthesis of WS2for gas sensing applications. Chemical Physics Letters 2014.
46. Kangho Lee , R. G., Niall McEvoy , Toby Hallam , and Georg S. Duesberg *, High-Performance Sensors Based on Molybdenum Disulfide Thin Films. Adv. Mater. 2013.
47. Bilu Liu, L. C., † Gang Liu, Ahmad N. Abbas, Mohammad Fathi, and Chongwu Zhou*, High-Performance Chemical Sensing Using Schottky-Contacted Chemical Vapor Deposition Grown Monolayer MoS2 Transistors. ACS nano
April 21, 2014.