二維層狀半導體第六族過渡金屬硫族化物由於具備極大延續摩爾定律潛力，近年來廣受關注。為了達到大規模商業化生產，生長高品質與大面積第六族過渡金屬硫族化物薄膜成為重要議題之一。因此，本研究利用化學氣相沉積法成長單層二硫化鎢、二硫化鉬與二硫化鎢/二硫化鉬側向異質結構於藍寶石基板。藉由控制氫氣流量、硫粉溫度、氬氣流量、成長溫度與腔體壓力等生長條件，三角形單晶與薄膜第六族過渡金屬二硫化物成功生長。此外，更進一步利用二步驟磊晶成長合成二硫化鎢/二硫化鉬側向異質結構。經由拉曼、光致發光光譜與原子力顯微鏡分析證實成長第六族過渡金屬二硫化物與其異質結構樣品為單層厚度。綜合以上結果，本研究提供第六族過渡金屬二硫化物可控性與大面積成長，其有利於未來商業化生產與相關元件應用。

Two-dimensional (2D) semiconducting layered Group-VI transition metal dichalcogenides (TMDs) offer great potential for sustaining Moore’s law. To meet the requirement for commercial need and mass production, the growth of Group-VI TMDs thin film with high crystallinity and large area has become one of the most vital challenge. In this work, herein, monolayered molybdenum disulfide (MoS2), tungsten disulfide (WS2) and their lateral heterostructures were grown on sapphire substrates via chemical vapor deposition (CVD). Meanwhile, both triangular single domains and thin film of Group VI transition metal disulfides has been attained in success by controlling growth conditions such as hydrogen (H2) flow rate, temperature of sulfur powders, argon (Ar) flow rate, growth temperature and chamber pressure. In addition, two-step epitaxial growth of lateral WS2/MoS2 heterostructure were further synthesized under optimization. Thereafter, the optical properties of WS2, MoS2 and lateral WS2/MoS2 heterostructure were confirmed by the Raman and photoluminescence (PL) spectroscopies. Atomic force microscopy (AFM) was also utilized to attest single-layer thickness of all as-grown samples. This work would benefit the controllable and large-scale growth of Group-VI transition metal disulfides, and provide the feasibility in the commercialization of device-related application in the future as well.

[1] M.-Y. Li, S.-K. Su, H.-S. P. Wong, and L.-J. Li, "How 2D Semiconductors Could Extend Moore’s Law," Nature, vol. 567, no. 7747, pp. 169-170, 2019.
[2] G. Iannaccone, F. Bonaccorso, L. Colombo, and G. Fiori, "Quantum Engineering of Transistors Based on 2D Materials Heterostructures," Nat. Nanotechnol., vol. 13, no. 3, pp. 183-191, 2018.
[3] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, "Single-layer MoS2 Transistors," Nat. Nanotechnol., vol. 6, no. 3, pp. 147-50, 2011.
[4] A. K. Geim, "Graphene: Status and Prospects," Science, vol. 324, no. 5934, pp. 1530-1534, 2009.
[5] J. D. Caldwell, I. Aharonovich, G. Cassabois, J. H. Edgar, B. Gil, and D. N. Basov, "Photonics with Hexagonal Boron Nitride," Nat. Rev. Mater., vol. 4, no. 8, pp. 552-567, 2019.
[6] K. Chen, X. Wan, and J. Xu, "Epitaxial Stitching and Stacking Growth of Atomically Thin Transition-Metal Dichalcogenides (TMDCs) Heterojunctions," Adv. Funct. Mater., vol. 27, no. 19, p. 1603884, 2017.
[7] A. Castellanos-Gomez, "Black Phosphorus: Narrow Gap, Wide Applications," J Phys. Chem. Lett., vol. 6, no. 21, pp. 4280-4291, 2015.
[8] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, "Emerging Device Applications for Semiconducting Two-dimensional Transition Metal Dichalcogenides," ACS Nano, vol. 8, no. 2, pp. 1102-1120, 2014.
[9] Z. Cai, B. Liu, X. Zou, and H. M. Cheng, "Chemical Vapor Deposition Growth and Applications of Two-Dimensional Materials and Their Heterostructures," Chem. Rev., vol. 118, no. 13, pp. 6091-6133, 2018.
[10] L. Tang, J. Tan, H. Nong, B. Liu, and H. M. Cheng, "Chemical Vapor Deposition Growth of Two-Dimensional Compound Materials: Controllability, Material Quality, and Growth Mechanism," Acc. Mater. Res., vol. 2, no. 1, pp. 36-47, 2020.
[11] M. Chhowalla, H. S. Shin, G. Eda, L. J. Li, K. P. Loh, and H. Zhang, "The Chemistry of Two-dimensional Layered Transition Metal Dichalcogenide Nanosheets," Nat. Chem., vol. 5, no. 4, pp. 263-75, 2013.
[12] A. Kuc and T. Heine, "The Electronic Structure Calculations of Two-dimensional Transition-metal Dichalcogenides in the Presence of External Electric and Magnetic Fields," Chem. Soc. Rev., vol. 44, no. 9, pp. 2603-2614, 2015.
[13] E. Kahn, M. Liu, T. Zhang, H. Liu, K. Fujisawa, G. Bepete, P. M. Ajayan and M. Terrones, "Functional Hetero-interfaces in Atomically Thin Materials," Mater. Today, vol. 37, pp. 74-92, 2020.
[14] W. Zhao, R. M. Ribeiro, and G. Eda, "Electronic Structure and Optical Signatures of Semiconducting Transition Metal Dichalcogenide Nanosheets," Acc. Chem. Res., vol. 48, no. 1, pp. 91-99, 2015.
[15] D. Xiao, G. B. Liu, W. Feng, X. Xu, and W. Yao, "Coupled Spin and Valley Physics in Monolayers of MoS2 and Other Group-VI Dichalcogenides," Phys. Rev. Lett., vol. 108, no. 19, p. 196802, 2012.
[16] A. Kumar and P. K. Ahluwalia, "Electronic Structure of Transition Metal Dichalcogenides Monolayers 1H-MX2 (M = Mo, W; X = S, Se, Te) from Ab-initio Theory: New Direct Band Gap Semiconductors," Euro. Phys. J. B, vol. 85, no. 6, p. 186, 2012.
[17] M. Tebyetekerwa, J. Zhang, Z. Xu, T. N. Truong, Z. Yin, Y. Lu, "Mechanisms and Applications of Steady-State Photoluminescence Spectroscopy in Two-Dimensional Transition-Metal Dichalcogenides," ACS Nano, vol. 14, no. 11, pp. 14579-14604, 2020.
[18] K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, "Atomically Thin MoS2: A New Direct-gap Semiconductor," Phys. Rev. Lett., vol. 105, no. 13, p. 136805, 2010.
[19] M. Samadi, N. Sarikhani, M. Zirak, H. Zhang, H. L. Zhang, and A. Z. Moshfegh, "Group 6 Transition Metal Dichalcogenide Nanomaterials: Synthesis, Applications and Future Perspectives," Nanoscale Horiz., vol. 3, no. 2, pp. 90-204, 2018.
[20] W. Zhao, Z. Ghorannevis, L. Chu, M. Toh, C. Kloc and P.-H. Tan, "Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2," ACS Nano, vol. 7, no. 1, pp. 791-797, 2013.
[21] K. J. I. Ember, M. A. Hoeve, S. L. McAughtrie, M. S. Bergholt, B. J. Dwyer and M. M. Stevens, "Raman Spectroscopy and Regenerative Medicine: a Review," NPJ Regen. Med., vol. 2, p. 12, 2017.
[22] M. Yamamoto, S. T. Wang, M. Ni, Y.-F. Lin, S. L. Li and S. Aikawa, "Strong Enhancement of Raman Scattering from a Bulk-Inactive Vibrational Mode in Few-layer MoTe2," ACS Nano, vol. 8, no. 4, pp. 3895-3903, 2014.
[23] C. Lee, H. Yan, L. E. Brus, T. F. Heinz, J. Hone, and S. Ryu, "Anomalous Lattice Vibrations of Single-and Few-layer MoS2," ACS Nano, vol. 4, no. 5, pp. 2695-2700, 2010.
[24] Y. Li, X. Li, T. Yu, G. Yang, H. Chen, C. Zhang, "Accurate Identification of Layer Number for Few-layer WS2 and WSe2 via Spectroscopic Study," Nanotechnology, vol. 29, no. 12, p. 124001, 2018.
[25] Z. Liu, A. W. A. Murphy, C. Kuppe, D. C. Hooper, V. K. Valev, and A. Ilie, "WS2 Nanotubes, 2D Nanomeshes, and 2D In-plane Films through One Single Chemical Vapor Deposition Route," ACS Nano, vol. 13, no. 4, pp. 3896-3909, 2019.
[26] X. Ling, Y. Lin, Q. Ma, Z. Wang, Y. Song, L. Yu, S. Huang, W. Fang, X. Zhang, A. L. Hsu, Y. Bie, Y. H. Lee, Y. Zhu, L. Wu, J. Li, P. J. Jarillo-Herrero, M. Dresselhaus, T. Palacios and J. Kong, "Parallel Stitching of 2D Materials," Adv. Mater., vol. 28, no. 12, pp. 2322-2329, 2016.
[27] S. Wang, X. Cui, C. Jian, H. Cheng, M. Niu, J. Yu, J. Yan and W. Huang, "Stacking-Engineered Heterostructures in Transition Metal Dichalcogenides," Adv. Mater., vol. 33, no. 16, p. 2005735, 2021.
[28] P. Rivera, H. Yu, K. L. Seyler, N. P. Wilson, W. Yao, and X. Xu, "Interlayer Valley Excitons in Heterobilayers of Transition Metal Dichalcogenides", Nat. Nanotechnol., vol. 13, no. 11, pp. 1004-1015, 2018.
[29] Y. Liu, N. O. Weiss, X. Duan, H. C. Cheng, Y. Huang, and X. Duan, "Van der Waals Heterostructures and Devices," Nat. Rev. Mater., vol. 1, no. 9, p.16042, 2016.
[30] Y. Gong, J. Lin, X. Wang, G. Shi, S. Lei, Z. Lin, X. Zou, G. Ye, R. Vajtai, B. I. Yakobson, H. Terrones, M. Terrones, B. K. Tay, J. Lou, S. T. Pantelides, Z. Liu, W. Zhou and P. M. Ajayan, "Vertical and In-plane Heterostructures from WS2/MoS2 Monolayers," Nat. Mater., vol. 13, no. 12, pp. 1135-42, 2014.
[31] L. Sun, G. Yuan, L. Gao, J. Yang, M. C. Gharahcheshmeh, K. K. Gleason, Y. S. Choi, B. H. Hong and Z. Liu, "Chemical Vapour Deposition," Nat. Rev. Meth. Primers, vol. 1, no. 1, p.5, 2021.
[32] H. F. Liu, S. L. Wong, and D. Z. Chi, "CVD Growth of MoS2-based Two-dimensional Materials," Chem. Vap. Depos., vol. 21, no. 10-11-12, pp. 241-259, 2015.
[33] Y. Shi, H. Li, and L. J. Li, "Recent Advances in Controlled Synthesis of Two-Dimensional Transition Metal Dichalcogenides via Vapour Deposition Techniques," Chem. Soc. Rev., vol. 44, no. 9, pp. 2744-2756, 2015.
[34] M.-Y. Li, Y. Shi, C. C. Cheng, L. S. Lu, Y. C. Lin, H. L. Tang, M. L. Tsai, C. W. Chu, K. H. Wei, J. H. He, W. H. Chang, K. Suenaga and L. J. Li, "Epitaxial Growth of a Monolayer WSe2-MoS2 Lateral pn Junction with an Atomically Sharp Interface," Science, vol. 349, no. 6247, pp. 524-528, 2015.
[35] H. G. Ji, Y. C. Lin, K. Nagashio, M. Maruyama, P. Solís-Fernández, A. S. Aji, V. Panchal, S. Okada, K. Suenaga and H. Ago, "Hydrogen-Assisted Epitaxial Growth of Monolayer Tungsten Disulfide and Seamless Grain Stitching," Chem. Mater., vol. 30, no. 2, pp. 403-411, 2018.
[36] A. Aljarb, Z. Cao, H. L. Tang, J. K. Huang, M. Li, W. Hu, L. Cavallo and L. J. Li, "Substrate Lattice-Guided Seed Formation Controls the Orientation of 2D Transition-Metal Dichalcogenides," ACS Nano, vol. 11, no. 9, pp. 9215-9222, 2017.
[37] P. Liu, T. Luo, J. Xing, H. Xu, H. Hao, H. Liu and J. Dong, "Large-Area WS2 Film with Big Single Domains Grown by Chemical Vapor Deposition," Nanoscale Res. Lett., vol. 12, no. 1, p. 558, 2017.
[38] Y. Zhang, Y. Zhang, Q. Ji, J. Ju, H. Yuan, T. Gao, D. Ma, M. Liu, Y. Chen, X. Song, H. Y. Hwang, Y. Cui and Z. Liu, "Controlled Growth of High-quality Monolayer WS2 Layers on Sapphire and Imaging its Grain Boundary," ACS Nano, vol. 7, no. 10, pp. 8963-8971, 2013.
[39] M. H. Chiu, H. L. Tang, C. C. Tseng, Y. Han, A. Aljarb, J. K. Huang, Y. Wan, J. H. Fu, X. Zhang, W. H. Chang, D. A. Muller, T. Takenobu, V. Tung and L. J. Li, "Metal-Guided Selective Growth of 2D Materials: Demonstration of a Bottom-Up CMOS Inverter," Adv. Mater., vol. 31, no. 18, p. 1900861, 2019.
[40] Y. Y. Chung, K. C. Lu, C. C. Cheng, M. Y. Li, C. T. Lin, C. F. Li, J. M. Shieh, S. K. Su, H. L. Chiang, T. C. Chen, L. J. Li, H. P. Wong, W. B. Jian and C. H. Chien, "Demonstration of 40-nm Channel Length Top-Gate p-MOSFET of WS2 Channel Directly Grown on SiOx/Si Substrates Using Area-Selective CVD Technology," IEEE Trans. Electron Devices, vol. 66, no. 12, pp. 5381-5386, 2019.
[41] Y. Sheng, H. Tan, X. Wang, and J. H. Warner, "Hydrogen Addition for Centimeter-Sized Monolayer Tungsten Disulfide Continuous Films by Ambient Pressure Chemical Vapor Deposition," Chem. Mater., vol. 29, no. 11, pp. 4904-4911, 2017..
[42] Y. H. Lee, X. Q. Zhang, W. Zhang, M. T. Chang, C. T. Lin, K. Chang, Y. C. Yu, J. T. Wang, C. S. Chang, L. J. Li and T. W. Lin, "Synthesis of Large-area MoS2 atomic Layers with Chemical Vapor Deposition," Adv. Mater., vol. 24, no. 17, pp. 2320-2325, 2012.
[43] G. Bar, Y. Thomann, R. Brandsch, H. J. Cantow, and M. H. Whangbo, "Factors Affecting the Height and Phase Images in Tapping Mode Atomic Force Microscopy. Study of Phase-separated Polymer Blends of Poly(ethene-co-styrene) and Poly(2, 6-dimethyl-1, 4-phenylene oxide)," Langmuir, vol. 13, no. 14, pp. 3807-3812, 1997.
[44] Y. Wan, J. K. Huang, C. P. Chuu, W. T. Hsu, C. J. Lee, A. Aljarb, C. W. Huang, M. H. Chiu, H. L. Tang, C. Lin, X. Zhang, C. M. Wei, S. Lin, W. H. Chang, L. J. Li and V. Tung, "Strain-Directed Layer-By-Layer Epitaxy Toward van der Waals Homo-and Heterostructures," ACS Mater. Lett., vol. 3, no. 4, pp. 442-453, 2021.
[45] J. Chen, W. Zhou, W. Tang, B. Tian, X. Zhao, H. Xu, Y. Liu, D. Geng, S. J. .R. Tan, W. Fu and K. P. Loh, "Lateral Epitaxy of Atomically Sharp WSe2/WS2 Heterojunctions on Silicon Dioxide Substrates," Chem. Mater., vol. 28, no. 20, pp. 7194-7197, 2016.