石墨烯為單一原子層的二維材料，具有優異的材料性質包含：高光穿透率、可彎折、高熱傳導、電傳導等性質，近年來石墨烯的相關研究發展相當快速，但大多數元件都需基板支撐，當石墨烯薄膜被基板支撐時，基板會參與石墨烯的聲子、電子等粒子的傳遞，導致無法呈現本質石墨烯性質，因此石墨烯懸空便成為實現常溫下超高速元件的一個選擇；但目前單層石墨烯以背向漂浮法能懸空的尺度為直徑500μm，製程複雜不穩定且容易於附著高分子殘留物。本研究主要發展一種簡易且可靠的方法來研製大面積的懸空石墨烯。首先，將銅箔基板藉由電化學拋光後，以常壓化學氣相沉積法進行成長，改變氫氣流量得到高品質單層石墨烯薄膜，其製程優化之單晶高品質石墨烯的晶粒可達~50μm。第二部分將單層石墨烯堆疊五層並以熱裂解法進行轉印，得到最大尺度可達1,500μm石的懸空墨烯薄膜，成功懸空的比率皆較背向漂浮法提高200%，且能排除高分子殘餘物的影響，氧化基團鍵結分別下降4～6%不等，載子遷移率提高154%。此外，本研究也演示了電容式壓力感測器的應用，結果顯示電容值與壓力變化具有良好的線性趨勢，而其感測之靈敏度為15.15aF/Pa，相對於矽基材料提升達七倍(~770%)，基於此種懸空結構的製程，在未來將可望應用於微機電和生醫感測器、高頻電子元件等廣泛的應用。

Graphene is a one atom thickness 2D material that shows remarkable material properties, including high optical transparency, mechanical flexibility, high thermal conductivity, and superior high conductivity. In the last decade, graphene research and its related applications have been attracted intensive attentions. However, the earlier research on graphene device were performed on substrate. The substrate induced carrier scattering, charge impurity doping and corrugation that drastically degrade the intrinsic properties of graphene. Thus the suspended graphene shows superior intrinsic material properties on carrier transport, thermal conductivity and mechanical elasticity. Especially the practical application in ultra-high speed device. Before this study, the suspended graphene membrane made by the inverted floating method can yield the large size about 500μm in diameter; however, the suspended graphene by this approach were suffered from issues of the difficulty for manipulation and complicated process as well as the large amounts of polymer residue on graphene. This study was to develop a simple and reliable route to achieve a large area of suspended graphene. The proposed process including (1) the optimization of graphene growth conditions by atmospheric pressure chemical vapor deposition (APCVD) and (2) the transferring process for suspended graphene by solvent replacing and thermal decomposition method. It was found out that the optimized graphene single crystalline size with high quality could be up to ~50μm. The results shows that the largest suspended graphene membrane over 1,500μm in diameter can be obtained by stacking and transferring 5-layered graphene on a holy substrate. The XPS characterization shows that the extremely low oxygen functional groups of 4～6% on graphene membrane after thermal annealing can be achieved, suggesting the ultra-clean and high quality of suspended graphene can be made from our approach. To study the intrinsic properties and application of our suspended graphene membrane, the devices integrated with suspended graphene were fabricated. The results shows that the carrier mobility on suspended graphene is enhanced up to 154% when compared with the substrate supported graphene. In addition, the capacitive pressure sensor made by our ultra-large suspended graphene membrane, showing a superior high sensitivity and excellent signal linearity than conventional capacitive pressure sensors. The sensitivity of 15.15 aF / Pa were measured which is increased about 422~ 770% than silicon-based material. The developed method for ultra-large suspended graphene pave the way for the potential applications on electromechanical actuator, ultra-sensitive chemical/bio sensors as well as the high-frequency electronic devices.

1. Novoselov, K.S., et al., Electric field effect in atomically thin carbon films. Science, 2004. 306(5696): p. 666-669.
2. Castro Neto, A.H., et al., The electronic properties of graphene. Reviews of Modern Physics, 2009. 81(1): p. 109-162.
3. R. Satio, G.D.a.M.S.D., Physical Properties of Carbon Nanotube. Imperial College Press, London, 1998.
4. Li, X.S., et al., Transfer of Large-Area Graphene Films for High-Performance Transparent Conductive Electrodes. Nano Letters, 2009. 9(12): p. 4359-4363.
5. Stoller, M.D., et al., Graphene-Based Ultracapacitors. Nano Letters, 2008. 8(10): p. 3498-3502.
6. Tech., G.t.p.b.B.G., 2013.
7. He, Y.M., et al., Freestanding Three-Dimensional Graphene/MnO2 Composite Networks As Ultra light and Flexible Supercapacitor Electrodes. Acs Nano, 2013. 7(1): p. 174-182.
8. Edwards, R.S. and K.S. Coleman, Graphene synthesis: relationship to applications. Nanoscale, 2013. 5(1): p. 38-51.
9. Hummers, W.S. and R.E. Offeman, Preparation of Graphitic Oxide. J. Am. Chem. Soc, 1958: p. 80 (6), p 1339–1339.
10. He, H.Y., et al., A new structural model for graphite oxide. Chemical Physics Letters, 1998. 287(1-2): p. 53-56.
11. Paredes, J.I., et al., Graphene oxide dispersions in organic solvents. Langmuir, 2008. 24(19): p. 10560-10564.
12. Loh, K.P., et al., Graphene oxide as a chemically tunable platform for optical applications. Nature Chemistry, 2010. 2(12): p. 1015-1024.
13. Su, C.Y., et al., Highly Efficient Restoration of Graphitic Structure in Graphene Oxide Using Alcohol Vapors. Acs Nano, 2010. 4(9): p. 5285-5292.
14. Hernandez, Y., et al., High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotechnology, 2008. 3(9): p. 563-568.
15. Su, C.Y., et al., High-Quality Thin Graphene Films from Fast Electrochemical Exfoliation. Acs Nano, 2011. 5(3): p. 2332-2339.
16. Pierson, H.O., Handbook of Chemical Vapour Deposition. Noyes Publications, Park Ridge, NJ 1992.
17. Yu, Q.K., et al., Graphene segregated on Ni surfaces and transferred to insulators. Applied Physics Letters, 2008. 93(11): p. 1031-1033.
18. Nezich, D., A. Reina, and J. Kong, Electrical characterization of graphene synthesized by chemical vapor deposition using Ni substrate. Nanotechnology, 2012. 23(1): p. 9.
19. Li, X.S., et al., Evolution of Graphene Growth on Ni and Cu by Carbon Isotope Labeling. Nano Letters, 2009. 9(12): p. 4268-4272.
20. Hao, Y.F., et al., The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper. Science, 2013. 342(6159): p. 720-723.
21. Wu, W., et al., Control of thickness uniformity and grain size in graphene films for transparent conductive electrodes. Nanotechnology, 2012. 23(3): p. 8.
22. Bae, S., et al., Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nature Nanotechnology, 2010. 5(8): p. 574-578.
23. Wang, Y., et al., Electrochemical Delamination of CVD-Grown Graphene Film: Toward the Recyclable Use of Copper Catalyst. Acs Nano, 2011. 5(12): p. 9927-9933.
24. Wang, D.Y., et al., Clean-Lifting Transfer of Large-area Residual-Free Graphene Films. Advanced Materials, 2013. 25(32): p. 4521-4526.
25. Su, C.Y., et al., Direct Formation of Wafer Scale Graphene Thin Layers on Insulating Substrates by Chemical Vapor Deposition. Nano Letters, 2011. 11(9): p. 3612-3616.
26. https://graphene-supermarket.com/CVD-Graphene-on-Metals/.
27. Kobayashi, T., et al., Production of a 100-m-long high-quality graphene transparent conductive film by roll-to-roll chemical vapor deposition and transfer process. Applied Physics Letters, 2013. 102(2): p. 4.
28. Yu, Q.K., et al., Control and characterization of individual grains and grain boundaries in graphene grown by chemical vapour deposition. Nature Materials, 2011. 10(6): p. 443-449.
29. Huang, P.Y., et al., Grains and grain boundaries in single-layer graphene atomic patchwork quilts. Nature, 2011. 469(7330): p. 389-392.
30. Han, G.H., et al., Influence of Copper Morphology in Forming Nucleation Seeds for Graphene Growth. Nano Letters, 2011. 11(10): p. 4144-4148.
31. Lee, J.H., et al., Wafer-Scale Growth of Single-Crystal Monolayer Graphene on Reusable Hydrogen-Terminated Germanium. Science, 2014. 344(6181): p. 286-289.
32. Bolotin, K.I., et al., Ultrahigh electron mobility in suspended graphene. Solid State Communications, 2008. 146(9–10): p. 351-355.
33. Balandin, A.A., et al., Superior thermal conductivity of single-layer graphene. Nano Letters, 2008. 8(3): p. 902-907.
34. Lee, C., et al., Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science, 2008. 321(5887): p. 385-388.
35. Meyer, J.C., et al., The structure of suspended graphene sheets. Nature, 2007. 446(7131): p. 60-63.
36. Du, X., et al., Approaching ballistic transport in suspended graphene. Nature Nanotechnology, 2008. 3(8): p. 491-495.
37. Aleman, B., et al., Transfer-Free Batch Fabrication of Large-Area Suspended Graphene Membranes. Acs Nano, 2010. 4(8): p. 4762-4768.
38. Lee, C.K., et al., Monatomic Chemical-Vapor-Deposited Graphene Membranes Bridge a Half-Millimeter-Scale Gap. Acs Nano, 2014. 8(3): p. 2336-2344.
39. Celebi, K., et al., Ultimate Permeation Across Atomically Thin Porous Graphene. Science, 2014. 344(6181): p. 289-292.
40. Smith, A.D., et al., Electromechanical Piezoresistive Sensing in Suspended Graphene Membranes. Nano Letters, 2013. 13(7): p. 3237-3242.
41. 吳裕弘, 簡昭珩. 應用熱壓崁入技術製作電容式壓力感測器. 大同大學, 機械工
程研究所碩士論文, 中華民國九十七年七月
42. Sherif, S., et al., Modeling of Sensitivity of fabricated Capacitive Pressure Sensor.
IEEE Industrial Electronics, IECON 2006 - 32nd Annual Conference, p.3166 - 3169