六方氮化硼(hexagonal boron nitride, hBN)薄膜在二維材料中有極佳的應用潛力，至今成功成長出大面積高品質 hBN 薄膜的團隊皆使用 CVD 系統以及金屬基板，後續若要應用需轉移至其他基板上，不僅可能產生缺陷也有與基板有晶格不匹配的問題。
我們的目標是利用 MBE 系統將大面積高品質 hBN 直接成長在可應用的基板上，避免轉移造成薄膜品質下降。
本論文利用不同錯切角的碳化矽以及不同退火溫度的成長條件，先在碳化矽基板上成長出不同表面形貌的石墨烯，使用 SEM、AFM 與 Raman 量測石墨烯特徵後再放入 MBE 系統中成長 hBN。成長完後從 SEM、AFM 與 Raman 量測中觀察到 hBN 薄膜在筆直且密集的石墨烯表面上有最高品質的六角型結晶，單晶石墨烯的台階表面幫助 hBN 沿基板的單一晶格方向生長並合併成薄膜，此結論在 MBE 系統中初次發現並驗證文獻中提出的二維材料生長模式。
掌握大面積高品質 hBN 薄膜的生長關鍵後，我們進一步控制 hBN 的生長時間達成對 hBN 的層數控制，由 SEM、AFM、Raman 以及 ARPES 證實我們在石墨烯/碳化矽基板上成功長出單層與雙層的 hBN 薄膜。

Hexagonal boron nitride (hBN) has great potential in 2D material application. Recent studies have shown the growth of single-crystal hBN on metal substrates by chemical vapor deposition (CVD) where transfer processes might contaminate the surface. Here, we successfully grow single-crystal hBN on high-quality epitaxial graphene by Plasmaassisted molecular beam epitaxy (PA-MBE) and achieve the layer control of hBN by controlling growth time. According to SEM and AFM measurement, it was found that the hBN is well-aligned with the Graphene surfaces, which verified the 2D materials epitaxy growth mechanism in MBE System. Our ARPES results show strong evidence of growing single-crystal hBN monolayer and bilayer on Graphene.

[1]. K. S. Novoselov,1 A. K. Geim et al. Electric Field Effect in Atomically Thin Carbon Films. Science 306, 666-669 (2004).
[2]. A. K. Geim & K. S. Novoselov. The rise of graphene. Nature Materials 6, 183-191 (2007).
[3]. A. K. Geim & I. V. Grigorieva. Van der Waals heterostructures. Nature volume 499, 419–425 (2013).
[4]. Yankowitz M, Xue J. & LeRoy B J. Graphene on hexagonal boron nitride. J. Phys.: Condens. Matter 26, 303201 (2014).
[5]. Song X et al. Chemical vapor deposition growth of large-scale hexagonal boron nitride with controllable orientation. Nano Res. 8, 3164–76 (2015).
[6]. Han X, Lin J, Liu J, Wang N & Pan D. Effects of hexagonal boron nitride encapsulation on the electronic structure of few-layer MoS2. J. Phys. Chem. C 123, 14797–802 (2019).
[7]. Watanabe K, Taniguchi T & Kanda H. Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal. Nat. Mater. 3, 404–9 (2004).
[8]. Cassabois G, Valvin P & Gil B. Hexagonal boron nitride is an indirect bandgap semiconductor. Nat. Photon. 10, 262–6 (2016).
[9]. Tran T T, Bray K, Ford M J, Toth M & Aharonovich I. Quantum emission from hexagonal boron nitride monolayers. Nat. Nanotechnol. 11, 37–41 (2016).
[10]. Roland Yingjie Tay & Mark H. Griep et al. Growth of Large Single-Crystalline Two-Dimensional Boron Nitride Hexagons on Electropolished Copper. Nano Lett. 14, 839–846 (2014).
[11]. Xin Li, Suresh Sundaram et al. Large-Area Two-Dimensional Layered Hexagonal Boron Nitride Grown on Sapphire by Metalorganic Vapor Phase Epitaxy. Cryst. Growth Des. 16, 3409–3415 (2016).
[12]. Sabina Caneva, Robert S. Weatherup et al. Controlling Catalyst Bulk Reservoir Effects for Monolayer Hexagonal Boron Nitride CVD. Nano Lett. 16, 1250–1261 (2016).
[13]. Jeong, H., Kim, D.Y., Kim, J. et al. Wafer-scale and selective-area growth of high-quality hexagonal boron nitride on Ni(111) by metal-organic chemical vapor deposition. Sci Rep 9, 5736 (2019).
[14]. Pallecchi, E., Lafont, F., Cavaliere, V. et al. High Electron Mobility in Epitaxial Graphene on 4H-SiC(0001) via post-growth annealing under hydrogen. Sci Rep 4, 4558 (2014).
[15]. Cassabois, G., Valvin, P. & Gil, B. Hexagonal boron nitride is an indirect bandgap semiconductor. Nature Photon 10, 262–266 (2016).
[16]. Dean, C., Young, A., Meric, I. et al. Boron nitride substrates for high-quality graphene electronics. Nature Nanotech 5, 722–726 (2010).
[17]. Chen, TA., Chuu, CP., Tseng, CC. et al. Wafer-scale single-crystal hexagonal boron nitride monolayers on Cu (111). Nature 579, 219–223 (2020).
[18]. Cho, YJ., Summerfield, A., Davies, A. et al. Hexagonal Boron Nitride Tunnel Barriers Grown on Graphite by High Temperature Molecular Beam Epitaxy. Sci Rep 6, 34474 (2016).
[19]. Elias, C., Valvin, P., Pelini, T. et al. Direct band-gap crossover in epitaxial monolayer boron nitride. Nat Commun 10, 2639 (2019).
[20]. Kangkang Wang & ArthurR. Smith. Efficient kinematical simulation of reflection high-energy electron diffractionstreak patterns for crystal surfaces. Computer Physics Communications 182, 2208-2212 (2011).
[21]. S. Maghsoudy-Louyeh et al. Review of Progress in Atomic Force Microscopy. Bentham Open 12, 86-104 (2018).
[22]. Ramazan Asmatulu & Waseem S. Khan. Synthesis and Applications of Electrospun Nanofibers. Elsevier ,257-281 (2018).
[23]. Uroš Maver et al. Recent progressive use of atomic force microscopy in biomedical applications. Trends in Analytical Chemistry 80, 96-111 (2016).
[24]. Andrea Damascelli. Probing the Electronic Structure of Complex Systems by ARPES. Physica Scripta. T109, 61–74 (2004).
[25]. Thomas Schmid & Petra Dariz. Raman Microspectroscopic Imaging of Binder Remnants in Historical Mortars Reveals Processing Conditions. Heritage 2(2), 1662-1683 (2019).
[26]. Hiroyuki Matsunami. Technological Breakthroughs in Growth Control of Silicon Carbide for High Power Electronic Devices. Jpn. J. Appl. Phys. 43, 6835 (2004)
[27]. Oliveira, M. H., Jr.; Schumann, T.; Ramsteiner, M.; Lopes, J. M. J.; Riechert, H. Influence of the Silicon Carbide Surface Morphology on the Epitaxial Graphene Formation. Appl. Phys. Lett. 99, 111901 (2011).
[28]. L.A.Galvesa, J.M.Wofford et al. The effect of the SiC(0001) surface morphology on the growth of epitaxial mono-layer graphene nanoribbons. Carbon 115, 162(2017).
[29]. Satoru Tanaka, Kouhei Morita, and Hiroki Hibino. Anisotropic layer-by-layer growth of graphene on vicinal SiC(0001) surfaces. PHYSICAL REVIEW B 81, 041406 (2010).
[30]. J. Röhrla, M. Hundhausen et al. Raman spectra of epitaxial graphene on SiC(0001). Appl. Phys. Lett. 92, 201918 (2008).
[31]. Roman V. Gorbachev, Ibtsam Riaz et al. Hunting for Monolayer Boron Nitride: Optical and Raman Signatures. mall 7, 465–468 (2011).
[32]. Leining Zhang, Jichen Dong, & Feng Ding. Strategies, Status, and Challenges in Wafer Scale Single Crystalline Two-Dimensional Materials Synthesis. Chemical Reviews 121 (11), 6321-6372 (2021).
[33]. M. Yagmurcukardes, C. Bacaksiz, E. Unsal, B. Akbali, R. T. Senger, & H. Sahin. Strain mapping in single-layer two-dimensional crystals via Raman activity. PHYSICAL REVIEW B 97, 115427 (2018).
[34]. Joshua Robinson, Xiaojun Weng, Kathleen Trumbull, Randall Cavalero, Maxwell Wetherington, Eric Frantz, Michael LaBella, Zachary Hughes, Mark Fanton, & David Snyder. Nucleation of Epitaxial Graphene on SiC(0001). ACS Nano 4 (1), 153-158 (2010).
[35]. Ivan Shtepliuk,Ivan G. Ivanov et al. Raman probing of hydrogen-intercalated graphene on Si-face 4H-SiC. Materials Science in Semiconductor Processing 96, 145-152 (2019).
[36]. Attias Kruskopf et al. Epitaxial graphene on SiC: Modification of structural and electron transport properties by substrate pretreatment. J. Phys.: Condens. Matter 27, 185303 (2015).
[37]. Dong Su Lee, Christian Riedl et al. Raman Spectra of Epitaxial Graphene on SiC and of Epitaxial Graphene Transferred to SiO2. Nano Lett. 8, 4320–4325 (2008).
[38]. T. M. G. Mohiuddin, A. Lombardo et al. Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Grüneisen parameters, and sample orientation. PHYSICAL REVIEW B 79, 205433 (2009).
[39]. Das, A., Pisana, S., Chakraborty, B. et al. Monitoring dopants by Raman scattering in an electrochemically top-gated graphene transistor. Nature Nanotech 3, 210–215 (2008).
[40]. Melios, C., Panchal, V., Giusca, C. et al. Carrier type inversion in quasi-free standing graphene: studies of local electronic and structural properties. Sci Rep 5, 10505 (2015).
[41]. Davood Momeni Pakdehi, Philip Schädlich et al. Silicon Carbide Stacking-Order-Induced Doping Variation in Epitaxial Graphene. Adv. Funct. Mater. 30, 2004695 (2020).
[42]. Zhizhuang Liua, Qingfang Xu et al. Laser-induced growth of large-area epitaxial graphene with low sheet resistance on 4H-SiC(0001). Applied Surface Science 514, 145938 (2020)