本研究旨在利用的低壓化學氣相沉積法爐管配置，藉此控制蒸氣首先成長出二硫化鎢與二硒化鎢兩者單層結晶，接著利用二階段法合成出WS2-WSe2與WSe2-WS2兩個內外層相反之N-P與P-N側向異質結構，從光學顯微鏡上可看到兩者對比的差異，並透過拉曼、PL與原子力顯微鏡確定兩者皆為單層材料。同時我們觀察異質結構的界面，發現角落處發生拉曼與PL強度的變化，現象類似於因應力擠壓造成結晶性的改變，交叉比對後發現此現象只存在於異質結構上，因此判斷出此改變是在二階段成長中發生的。最後我們使用濕式轉印法將材料移到已預鍍電極的二氧化矽基板上，並使用電子束微影定位量測其基本電子特性。

In this research, we developed a modified furnace configuration to control vapor during the chemical vapor deposition(CVD) process. By this idea, we first synthesized WS2 and WSe2 single layer crystal on sapphire substrate and followed by an epitaxial growth of WSe2 and WS2 on the edge with two-step CVD to get WS2/WSe2 and WSe2/WS2 two different lateral junctions. We can see the color contrast between them from optical microscope image, and confirmed the single layer charteristic by Raman、PL and AFM analysis. Furthermore, we discovered the different of Raman peak intensity between corner and edge in the outer region of lateral junction and concluded this phenomenon which caused by the decrease of crystallinity occurred only during the second step CVD.

目錄……………………………………………………………1
圖目錄…………………………………………………………4
表目錄…………………………………………………………8
摘要……………………………………………………………9
Abstract…………………………………………...………….10
致謝……………………………………………………….…..11
第一章 緒論與文獻回顧………………………………….11
1-1二維材料( 2D material )…………………………………12
1-1-1 二硫化鎢( WS2 )與二硒化鎢 ( WSe2 )……..……...13
1-2二維異質結構的種類…………………………………….15
1-2-1 側向磊晶(Lateral epitaxy)異質結構………………15
1-2-2 垂直堆疊(Vertical stacking)異質結構…………….16
1-3過渡金屬二硫族化合物(TMDs)異質材料的合成方式...18
1-3-1 機械堆疊法(Mechanical stacking)……………...…18
1-3-2 直接硫化法(Sulfurization)………………………....19
1-3-3 化學氣相沉積法(Chemical Vapor Deposition,
CVD)……………………………………………….20
1-3-3-1 單階段成長法(Single-step growth)…………...21
1-3-3-2 多階段成長法(Multi-step growth)……………22
1-4二維異質材料的應用…………………………………….24
1-4-1 太陽能電池(Solar cells)…………………………….24
1-4-2 記憶體(Memory)………………...…………………25
1-4-3 光感測器(Photodetector)…………………………..26
1-5 研究動機………………………………………...……….29
第二章 實驗步驟…………………...……………………..30
2-1化學氣相沉積成長WS2/WSe2異質結構……….………31
2-2濕式轉印( Transfer )……………………………………..33
2-3電子束微影（Electron beam lithography）…………...34
2-4儀器使用介紹…………………………………………….36
2-4-1 三區真空爐管(Three-zone vacuum furnace)……..36
2-4-2 光學顯微鏡(Optical Microscope, OM)……………37
2-4-3 µ-拉曼頻譜儀( µ-Raman spectroscope )………..….38
2-4-4光激發螢光頻譜( Photoluminescence, PL )……….39
2-4-5原子力顯微鏡(Atomic Force Microscope, AFM)…40
2-4-6 掃描式電子顯微鏡(Scanning Electronic
Microscope, SEM)…………………………………41
2-4-7 電子束微影系統(Electron beam lithography)……42
2-4-8 電子槍真空蒸鍍系統( Electron gun)…….……..43
2-4-9電性量測系統(Electrical measurement system)..44
第三章 結果與討論……………………………………….45
3-1化學氣相沉積成長WS2與WSe2………...……………..45
3-1-1 WS2特性探討……………………………………….45
3-1-2 WSe2特性探討…………………..………………….47
3-1-3 無檔板之成長結果………………………………….49
3-2 二階段成長WS2/WSe2異質結構………………..……...50
3-2-1 WS2-WSe2異質結構………………………………...50
3-2-2 WSe2-WS2異質結構………………………………...54
3-3 異質結構界面分析………………………………………56
3-4 電性分析…………………………………………………58
第四章 結論………………………………………………….60
第五章 未來展望…………………………………………….61
參考文獻……………………………………………………...62

1. Novoselov, K.S., et al., Electric field effect in atomically thin carbon films. Science, 2004. 306(5696): p. 666-669.
2. Desai, S.B., et al., MoS2 transistors with 1-nanometer gate lengths. Science, 2016. 354(6308): p. 99-102.
3. Mak, K.F., et al., Atomically Thin MoS2: A New Direct-Gap Semiconductor. Physical Review Letters, 2010. 105(13).
4. Radisavljevic, B., et al., Single-layer MoS2 transistors. Nature Nanotechnology, 2011. 6(3): p. 147-150.
5. Tan, C.L. and H. Zhang, Two-dimensional transition metal dichalcogenide nanosheet-based composites. Chemical Society Reviews, 2015. 44(9): p. 2713-2731.
6. Zhao, W.J., et al., Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2. Acs Nano, 2013. 7(1): p. 791-797.
7. Ataca, C., H. Sahin, and S. Ciraci, Stable, Single-Layer MX2 Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure. Journal of Physical Chemistry C, 2012. 116(16): p. 8983-8999.
8. Zeng, H.L., et al., Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides. Scientific Reports, 2013. 3: p. 5.
9. Kosmider, K. and J. Fernandez-Rossier, Electronic properties of the MoS2-WS2 heterojunction. Physical Review B, 2013. 87(7): p. 4.
10. Britnell, L., et al., Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films. Science, 2013. 340(6138): p. 1311-1314.
11. Fang, H., et al., High-Performance Single Layered WSe2 p-FETs with Chemically Doped Contacts. Nano Letters, 2012. 12(7): p. 3788-3792.
12. Gutierrez, H.R., et al., Extraordinary Room-Temperature Photoluminescence in Triangular WS2 Monolayers. Nano Letters, 2013. 13(8): p. 3447-3454.
13. Huang, J.K., et al., Large-Area Synthesis of Highly Crystalline WSe2 Mono layers and Device Applications. Acs Nano, 2014. 8(1): p. 923-930.
14. Sasaki, S., et al., Growth and optical properties of Nb-doped WS2 monolayers. Applied Physics Express, 2016. 9(7): p. 4.
15. Yun, W.S., et al., Thickness and strain effects on electronic structures of transition metal dichalcogenides: 2H-M X-2 semiconductors (M = Mo, W; X = S, Se, Te). Physical Review B, 2012. 85(3): p. 5.
16. Xing, L. and L.Y. Jiao, Recent Advances in the Chemical Doping of Two-Dimensional Molybdenum Disulfide. Acta Physico-Chimica Sinica, 2016. 32(9): p. 2133-2145.
17. Huang, C.M., et al., Lateral heterojunctions within monolayer MoSe2-WSe2 semiconductors. Nature Materials, 2014. 13(12): p. 1096-1101.
18. Chiu, M.H., et al., Spectroscopic Signatures for Interlayer Coupling in MoS2-WSe2 van der Waals Stacking. Acs Nano, 2014. 8(9): p. 9649-9656.
19. Zhang, J., et al., Observation of Strong Interlayer Coupling in MoS2/WS2 Heterostructures. Advanced Materials, 2016. 28(10): p. 1950-1956
20. Choudhary, N., et al., Centimeter Scale Patterned Growth of Vertically Stacked Few Layer Only 2D MoS2/WS2 van der Waals Heterostructure. Scientific Reports, 2016. 6: p. 7.
21. Dean, C.R., et al., Boron nitride substrates for high-quality graphene electronics. Nature Nanotechnology, 2010. 5(10): p. 722-726.
22. Lin, Y.C., et al., Wafer-scale MoS2 thin layers prepared by MoO3 sulfurization. Nanoscale, 2012. 4(20): p. 6637-6641.
23. Li, M.Y., et al., Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface. Science, 2015. 349(6247): p. 524-528.
24. Gong, Y.J., et al., Vertical and in-plane heterostructures from WS2/MoS2 monolayers. Nature Materials, 2014. 13(12): p. 1135-1142.
25. Zhang, Z.W., et al., Robust epitaxial growth of two-dimensional heterostructures, multiheterostructures, and superlattices. Science, 2017. 357(6353): p. 788-794.
26. Bernardi, M., M. Palummo, and J.C. Grossman, Extraordinary Sunlight Absorption and One Nanometer Thick Photovoltaics Using Two-Dimensional Monolayer Materials. Nano Letters, 2013. 13(8): p. 3664-3670.
27. Bertolazzi, S., D. Krasnozhon, and A. Kis, Nonvolatile Memory Cells Based on MoS2/Graphene Heterostructures. Acs Nano, 2013. 7(4): p. 3246-3252.
28. Huo, N.J., et al., Novel and Enhanced Optoelectronic Performances of Multilayer MoS2-WS2 Heterostructure Transistors. Advanced Functional Materials, 2014. 24(44): p. 7025-7031.
29. Mehew, J.D., et al., Fast and Highly Sensitive Ionic-Polymer-Gated WS2-Graphene Photodetectors. Advanced Materials, 2017. 29(23): p. 7.
30. Tan, C.L. and H. Zhang, Epitaxial Growth of Hetero-Nanostructures Based on Ultrathin Two-Dimensional Nanosheets. Journal of the American Chemical Society, 2015. 137(38): p. 12162-12174.
31. Li, H.L., et al., Composition-Modulated Two-Dimensional Semiconductor Lateral Heterostructures via Layer-Selected Atomic Substitution. Acs Nano, 2017. 11(1): p. 961-967.
32. Zheng, S.J., et al., Monolayers of WxMo1-xS2 alloy heterostructure with in-plane composition variations. Applied Physics Letters, 2015. 106(6): p. 5.
33. Bogaert, K., et al., Diffusion-Mediated Synthesis of MoS2/WS2 Lateral Heterostructures. Nano Letters, 2016. 16(8): p. 5129-5134.
34. Zhang, Y., et al., Controlled Growth of High-Quality Monolayer WS2 Layers on Sapphire and Imaging Its Grain Boundary. Acs Nano, 2013. 7(10): p. 8963-8971.
35. Molas, M.R., et al., Raman scattering excitation spectroscopy of monolayer WS2. Scientific Reports, 2017. 7: p. 8.
36. Chiu, K.C., et al., Synthesis of In-Plane Artificial Lattices of Monolayer Multijunctions. Advanced Materials, 2018. 30(7): p. 9.
37. Desai, S.B., et al., Strain-Induced Indirect to Direct Bandgap Transition in Multi layer WSe2. Nano Letters, 2014. 14(8): p. 4592-4597.
38. Fan, Y., et al., Photoinduced Schottky Barrier Lowering in 2D Monolayer WS2 Photodetectors. Advanced Optical Materials, 2016. 4(10): p. 1573-1581.
39. Duan, X.D., et al., Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions. Nature Nanotechnology, 2014. 9(12): p. 1024-1030.
40. Allain, A. and A. Kis, Electron and Hole Mobilities in Single-Layer WSe2. Acs Nano, 2014. 8(7): p. 7180-7185.