本篇論文主要探討使用熱蒸鍍與化學氣相成沉積法合成的三奈米半導體薄膜材料二硫化鉬(MoS2)在光催化二氧化碳還原的反應機制，而我們也藉由薄膜材料對環境感測優異的特性，製作光感測裝置並且使用四極式半導體探針體測量儀去觀測光電導在光催化反應中變化，來幫助我們更深入反應中電子傳遞機制。
在我們所測量光導數據主要所做的差異化實驗有環境變因和波長變因去設計實驗，而在光催化方面我們是採用氣體氣相層析去量測與計算產量，再使用長時間光導測量去比較在不同氣體環境下的數據差異，可以得知在二氧化碳和水氣得環境下確實能使光電流下降，即代表載子被氣體分子吸收還原為可循環利用的有機分子燃料。
而在波長上主要是紫外光有最佳的光響應，甚至造成了特殊的巨大持久性光導（GPPC） 性質，藉由上述兩者的數據結合，我們能推導出光激發載子與反應氣體間的電子傳遞機制。
為了解釋電子傳遞的行為，從能帶彎曲的兩種模式表面電子聚集（SEA）和表面電子消耗(SED)，並且參考了光電導的載子活期和光電流大小等特性，推論出表面電子聚集為本薄膜材料提出一個合理和完善的解釋。
本研究為了解電子傳遞效應如何影響材料的催化效率，主要的方法即是生成凡德瓦二維異質材料，藉由生長三奈米二硫化鉬薄膜於單層石墨烯來達到材料之間優異的原子級接觸和特殊傳遞特性，更藉此影響和增進光催化二氧化碳還原產率。

In this thesis ,We successfully fabricate 3nm molybdenum disulfide ultra thin films on silicon dioxide and sapphire substrate by using the two steps synthesis ,thermal evaporation and chemical vapor deposition process. In addition, we focus on the photocatalytic CO2 reduction reaction process of MoS2 thin films because it has excellent photo-sensitivity on the different environment. The photoconductivity measurement is the important way to help us understand charge transfer in the reaction.
The photoconductivity measurement can be divided into three parts. First, we compare the results of product yield and long time-scale photoconductivity (PC) measurement from photocatalytic CO2 reduction reaction(CO2RR). This comparison illustrated that when the CO2 RR happened on the 3nm MoS2 thin films ,it can effectively decrease photocurrent. It proved the carrier able to react with CO2 and Water vapor and become the valuable gas product. Second, the wavelength-dependent PC measurement show that UV light source contribute the most part of photo-response in AM1.5G sunlight source and cause special great persistent photoconductivity (GPPC). Last but not least, the environment-dependent PC measurement demonstrate carrier life time is decreasing from vacuum to CO2 and H2O environment.
We consider two surface band bending model, surface electron accumulation (SEA) and surface electron depletion (SED), to explain charge transfer model of CO2RR. We compare photocurrent and carrier life time from PC measurement. The SEA model can get more suitable and perfect explanation on photocatalytic CO2RR of MoS2 thin films
Additionally, we want to realize how charge transfer affect the production of photocatalytic CO2 reduction, so we apply the Van der Waals 2D heterostructure growth way to our material. By the special charge transfer and atomic contact between 3nm MoS2 and monolayer graphene, it can affect and even improve the production of photocatalytic CO2 reduction in this thesis.

1. (NOAA), N. O. a. A. A. Monthly Average Mauna Loa CO2. https://gml.noaa.gov/ccgg/trends/.
2. (NOAA), N. O. a. A. A. Carbon cycle. https://www.noaa.gov/education/resource-collections/climate/carbon-cycle.
3. Yang, M.-Q.; Xu, Y.-J., Photocatalytic conversion of CO 2 over graphene-based composites: current status and future perspective. Nanoscale Horizons 2016, 1 (3), 185-200.
4. Fujishima; Akira; Honda; Kenichi, Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238 (5358), 37-38.
5. Inoue, T.; Fujishima, A.; Konishi, S.; Honda, K., Photoelectrocatalytic reduction of carbon dioxide in aqueous suspensions of semiconductor powders. Nature 1979, 277 (5698), 637-638.
6. Ran, J.; Jaroniec, M.; Qiao, S. Z., Cocatalysts in semiconductor‐based photocatalytic CO2 reduction: achievements, challenges, and opportunities. Advanced materials 2018, 30 (7), 1704649.
7. Li, K.; An, X.; Park, K. H.; Khraisheh, M.; Tang, J., A critical review of CO2 photoconversion: Catalysts and reactors. Catalysis Today 2014, 224, 3-12.
8. Saravanan, R.; Gracia, F.; Stephen, A., Basic Principles, Mechanism, and Challenges of Photocatalysis. In Nanocomposites for Visible Light-induced Photocatalysis, Khan, M. M.; Pradhan, D.; Sohn, Y., Eds. Springer International Publishing: Cham, 2017; pp 19-40.
9. Khan, M. M.; Ansari, S. A.; Pradhan, D.; Ansari, M. O.; Lee, J.; Cho, M. H., Band gap engineered TiO 2 nanoparticles for visible light induced photoelectrochemical and photocatalytic studies. Journal of Materials Chemistry A 2014, 2 (3), 637-644.
10. Wu, J.; Huang, Y.; Ye, W.; Li, Y., CO2 reduction: from the electrochemical to photochemical approach. Advanced Science 2017, 4 (11), 1700194.
11. Hong, J.; Zhang, W.; Ren, J.; Xu, R., Photocatalytic reduction of CO 2: a brief review on product analysis and systematic methods. Analytical methods 2013, 5 (5), 1086-1097.
12. Park, H.-a.; Choi, J. H.; Choi, K. M.; Lee, D. K.; Kang, J. K., Highly porous gallium oxide with a high CO2 affinity for the photocatalytic conversion of carbon dioxide into methane. Journal of Materials Chemistry 2012, 22 (12), 5304-5307.
13. Li, Y.; Wang, W.-N.; Zhan, Z.; Woo, M.-H.; Wu, C.-Y.; Biswas, P., Photocatalytic reduction of CO2 with H2O on mesoporous silica supported Cu/TiO2 catalysts. Applied Catalysis B: Environmental 2010, 100 (1-2), 386-392.
14. Zhang, Q.; Li, Y.; Ackerman, E. A.; Gajdardziska-Josifovska, M.; Li, H., Visible light responsive iodine-doped TiO2 for photocatalytic reduction of CO2 to fuels. Applied Catalysis A: General 2011, 400 (1-2), 195-202.
15. Stock, M.; Dunn, S., LiNbO3—a polar material for solid-gas artificial photosynthesis. Ferroelectrics 2011, 419 (1), 9-13.
16. Hsu, H.-C.; Shown, I.; Wei, H.-Y.; Chang, Y.-C.; Du, H.-Y.; Lin, Y.-G.; Tseng, C.-A.; Wang, C.-H.; Chen, L.-C.; Lin, Y.-C., Graphene oxide as a promising photocatalyst for CO 2 to methanol conversion. Nanoscale 2013, 5 (1), 262-268.
17. Xi, G.; Ouyang, S.; Li, P.; Ye, J.; Ma, Q.; Su, N.; Bai, H.; Wang, C., Ultrathin W18O49 nanowires with diameters below 1 nm: synthesis, near‐infrared absorption, photoluminescence, and photochemical reduction of carbon dioxide. Angewandte Chemie International Edition 2012, 51 (10), 2395-2399.
18. Wang, W.-N.; An, W.-J.; Ramalingam, B.; Mukherjee, S.; Niedzwiedzki, D. M.; Gangopadhyay, S.; Biswas, P., Size and structure matter: enhanced CO2 photoreduction efficiency by size-resolved ultrafine Pt nanoparticles on TiO2 single crystals. Journal of the American Chemical Society 2012, 134 (27), 11276-11281.
19. Li, X.; Pan, H.; Li, W.; Zhuang, Z., Photocatalytic reduction of CO2 to methane over HNb3O8 nanobelts. Applied Catalysis A: General 2012, 413, 103-108.
20. Ong, W.-J.; Gui, M. M.; Chai, S.-P.; Mohamed, A. R., Direct growth of carbon nanotubes on Ni/TiO 2 as next generation catalysts for photoreduction of CO 2 to methane by water under visible light irradiation. Rsc Advances 2013, 3 (14), 4505-4509.
21. Zhai, Q.; Xie, S.; Fan, W.; Zhang, Q.; Wang, Y.; Deng, W.; Wang, Y., Photocatalytic conversion of carbon dioxide with water into methane: platinum and copper (I) oxide co‐catalysts with a core–shell structure. Angewandte Chemie 2013, 125 (22), 5888-5891.
22. Zhang, Z.; Wang, Z.; Cao, S.-W.; Xue, C., Au/Pt nanoparticle-decorated TiO2 nanofibers with plasmon-enhanced photocatalytic activities for solar-to-fuel conversion. The Journal of Physical Chemistry C 2013, 117 (49), 25939-25947.
23. Tahir, M.; Amin, N. S., Photocatalytic reduction of carbon dioxide with water vapors over montmorillonite modified TiO2 nanocomposites. Applied Catalysis B: Environmental 2013, 142, 512-522.
24. Shi, H.; Chen, G.; Zhang, C.; Zou, Z., Polymeric g-C3N4 coupled with NaNbO3 nanowires toward enhanced photocatalytic reduction of CO2 into renewable fuel. Acs Catalysis 2014, 4 (10), 3637-3643.
25. Cao, S.-W.; Liu, X.-F.; Yuan, Y.-P.; Zhang, Z.-Y.; Liao, Y.-S.; Fang, J.; Loo, S. C. J.; Sum, T. C.; Xue, C., Solar-to-fuels conversion over In2O3/g-C3N4 hybrid photocatalysts. Applied Catalysis B: Environmental 2014, 147, 940-946.
26. He, Y.; Zhang, L.; Fan, M.; Wang, X.; Walbridge, M. L.; Nong, Q.; Wu, Y.; Zhao, L., Z-scheme SnO2− x/g-C3N4 composite as an efficient photocatalyst for dye degradation and photocatalytic CO2 reduction. Solar Energy Materials and solar cells 2015, 137, 175-184.
27. Li, Z.; Meng, X.; Zhang, Z., Recent development on MoS2-based photocatalysis: A review. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2018, 35, 39-55.
28. Djurišić, A. B.; Leung, Y. H.; Ng, A. M. C., Strategies for improving the efficiency of semiconductor metal oxide photocatalysis. Materials Horizons 2014, 1 (4), 400-410.
29. Hu, J. S.; Ren, L. L.; Guo, Y. G.; Liang, H. P.; Cao, A. M.; Wan, L. J.; Bai, C. L., Mass production and high photocatalytic activity of ZnS nanoporous nanoparticles. Angewandte Chemie International Edition 2005, 44 (8), 1269-1273.
30. Sathish, M.; Viswanathan, B.; Viswanath, R., Alternate synthetic strategy for the preparation of CdS nanoparticles and its exploitation for water splitting. International Journal of Hydrogen Energy 2006, 31 (7), 891-898.
31. Yin, H.; Wada, Y.; Kitamura, T.; Yanagida, S., Photoreductive dehalogenation of halogenated benzene derivatives using ZnS or CdS nanocrystallites as photocatalysts. Environmental science & technology 2001, 35 (1), 227-231.
32. Haque, F.; Daeneke, T.; Kalantar-zadeh, K.; Ou, J. Z., Two-Dimensional Transition Metal Oxide and Chalcogenide-Based Photocatalysts. Nano-Micro Letters 2017, 10 (2), 23.
33. Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A., Electric field effect in atomically thin carbon films. science 2004, 306 (5696), 666-669.
34. Lin, L.; Peng, H.; Liu, Z., Synthesis challenges for graphene industry. Nature materials 2019, 18 (6), 520-524.
35. Soldano, C.; Mahmood, A.; Dujardin, E., Production, properties and potential of graphene. Carbon 2010, 48 (8), 2127-2150.
36. Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, V.; Kis, A., Single-layer MoS 2 transistors. Nature nanotechnology 2011, 6 (3), 147-150.
37. Monga, D.; Sharma, S.; Shetti, N. P.; Basu, S.; Reddy, K. R.; Aminabhavi, T. M., Advances in transition metal dichalcogenide-based two-dimensional nanomaterials. Materials Today Chemistry 2021, 19, 100399.
38. Li, X.; Zhu, H., Two-dimensional MoS2: Properties, preparation, and applications. Journal of Materiomics 2015, 1 (1), 33-44.
39. Neamen, D. A., Semiconductor physics and devices: basic principles. New York, NY: McGraw-Hill: 2012.
40. Takahashi, Y.; Kanamori, M.; Kondoh, A.; Minoura, H.; Ohya, Y., Photoconductivity of ultrathin zinc oxide films. Japanese Journal of Applied Physics 1994, 33 (12R), 6611.
41. Wang, F.; Zhang, Y.; Gao, Y.; Luo, P.; Su, J.; Han, W.; Liu, K.; Li, H.; Zhai, T., 2D metal chalcogenides for IR photodetection. Small 2019, 15 (30), 1901347.
42. Green, M. A., Photovoltaic principles. Physica E: Low-dimensional Systems and Nanostructures 2002, 14 (1-2), 11-17.
43. Kasap, S.; Capper, P., Springer handbook of electronic and photonic materials. Springer: 2017.
44. Maiti, S.; Maiti, U. N.; Chowdhury, A.; Chattopadhyay, K. K., Ambient condition oxidation of zinc foil in supersaturated solution for shape tailored ZnO nanostructures: low cost candidates for efficient electron emitter and UV-detector. CrystEngComm 2014, 16 (9), 1659-1668.
45. Joshi, N., Photoconductivity: art, science, and technology. Routledge: 2017.
46. Shen, W.-C.; Chen, R.-S.; Huang, Y.-S., Photoconductivities in MoS 2 Nanoflake Photoconductors. Nanoscale research letters 2016, 11 (1), 1-7.
47. Chang, Y.; Chen, C.; Ho, C.; Cheng, C.; Chen, H.; Fu, T.; Huang, Y.; Ke, S.; Du, H.; Lee, K., Surface Electron Accumulation and Enhanced Hydrogen Evolution Reaction in MoSe2 Basal Planes. Nano Energy 2021, 105922.
48. Li, J.; Chen, X.; Zhang, D. W.; Zhou, P., Van der Waals Heterostructure Based Field Effect Transistor Application. Crystals 2018, 8 (1), 8.
49. Mei, J.; Liao, T.; Sun, Z., 2D/2D Heterostructures: Rational Design for Advanced Batteries and Electrocatalysis. ENERGY & ENVIRONMENTAL MATERIALS n/a (n/a).
50. Martín-Palma, R. J.; Lakhtakia, A., Chapter 15 - Vapor-Deposition Techniques. In Engineered Biomimicry, Lakhtakia, A.; Martín-Palma, R. J., Eds. Elsevier: Boston, 2013; pp 383-398.
51. Skoog, D. A.; West, D. M.; Holler, F. J.; Crouch, S. R., Fundamentals of analytical chemistry. Cengage learning: 2013.
52. 謝嘉民; 賴一凡; 林永昌; 枋志堯, 光激發螢光量測的原理, 架構及應用. 科儀新知 2005, (146), 39-51.
53. Zhang, X.; Qiao, X.-F.; Shi, W.; Wu, J.-B.; Jiang, D.-S.; Tan, P.-H., Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material. Chemical Society Reviews 2015, 44 (9), 2757-2785.
54. Wang, Y.; Cong, C.; Qiu, C.; Yu, T., Raman spectroscopy study of lattice vibration and crystallographic orientation of monolayer MoS2 under uniaxial strain. small 2013, 9 (17), 2857-2861.
55. Li, H.; Zhang, Q.; Yap, C. C. R.; Tay, B. K.; Edwin, T. H. T.; Olivier, A.; Baillargeat, D., From bulk to monolayer MoS2: evolution of Raman scattering. Advanced Functional Materials 2012, 22 (7), 1385-1390.
56. Mouri, S.; Miyauchi, Y.; Matsuda, K., Tunable photoluminescence of monolayer MoS2 via chemical doping. Nano letters 2013, 13 (12), 5944-5948.
57. Golovynskyi, S.; Irfan, I.; Bosi, M.; Seravalli, L.; Datsenko, O. I.; Golovynska, I.; Li, B.; Lin, D.; Qu, J., Exciton and trion in few-layer MoS2: Thickness-and temperature-dependent photoluminescence. Applied Surface Science 2020, 515, 146033.
58. Pham, T.; Ramnani, P.; Villarreal, C. C.; Lopez, J.; Das, P.; Lee, I.; Neupane, M. R.; Rheem, Y.; Mulchandani, A., MoS2-graphene heterostructures as efficient organic compounds sensing 2D materials. Carbon 2019, 142, 504-512.
59. Pierucci, D.; Henck, H.; Naylor, C. H.; Sediri, H.; Lhuillier, E.; Balan, A.; Rault, J. E.; Dappe, Y. J.; Bertran, F.; Le Fèvre, P., Large area molybdenum disulphide-epitaxial graphene vertical Van der Waals heterostructures. Scientific reports 2016, 6, 26656.