石墨烯，特殊的二維結構使其具有很多優異特性，非常有潛力應用為可撓曲透明導電膜，此類型石墨烯適合以化學氣相沉積法製備，但此法製備之石墨烯為多晶態(數個單晶組成)，產生晶界阻礙電子傳導，降低其導電性。常見的方法為堆疊多層或摻雜載子，皆能有效改善其導電性，但是皆有各自的缺點；本研究著重於控制石墨烯的單晶，以減少其晶界數量，降低單層石墨烯本身的片電阻。
本研究獨特的分析方法，利用ImageJ影像處理與分析軟體，對SEM所拍攝的圖片進行處理及統計，比較不同製程情況下的單晶密度、形貌和成長，加上拉曼光譜儀掃描的結晶性，及四點探針量測的片電阻，全方位探討製程中每個環節對石墨烯單晶之影響，以減少晶界的數量、提升成長的品質，製備導電性最佳的石墨烯。使用電化學拋光銅箔作為基板，調整氬氣、氫氣、甲烷流量分別為1000、30、0.5 sccm，在1070℃下以APCVD製備石墨烯，單層石墨烯的片電阻約310 Ω/□，波長350~1000 nm的平均穿透率約97.7 %，透過摻雜片電阻可達到約180 Ω/□，與其他文獻相比，本研究之石墨烯擁有較佳的透明導電特性，並足以應用為透明導電膜。

Graphene is a two-dimensional monolayer of sp2-bonded carbon atoms. In cases where synthesized by chemical vapor deposition (CVD), graphene is especially a promising candidate for the flexible transparent conductive films due to its flexibility, high optical transmittance and exceptional electrical conductivity. However, when graphene is deposited by CVD, it will be polycrystalline with grain (or domain) boundaries segregating grains, which means that graphene’s electrical properties would consequently be degraded. Both multilayer stacking and carrier doping have often been adopted to reduce the sheet resistance of the graphene films, but both have their own flaws. This study aims at increasing the grain size of the graphene films in order to reduce the quantity of grain boundaries, achieving a result of low sheet resistance of single-layer graphene.
We have developed a unique method to analyze the grain density, the grain shape and the growth model of the graphene films at different processes: in order to investigate the grains of the graphene films comprehensively and find out a best procedure to fabricate graphene films with lowest sheet resistance, ImageJ, an image processing program, was utilized to analyze the grains of the grapheme films. Besides, the crystallized quality and the sheet resistance were surveyed respectively by Raman spectroscopy and four-point probe. Finally, the best procedure we have been able to find is: to grow the graphene films on electrochemical polishing Cu foils at 1070℃ with 1000 sccm Argon, 30 sccm Hydrogen and 0.5 sccm methane by ambient pressure CVD; the resulting sheet resistance of the single-layer grapheme has reached 310 Ω/□ and the average transmittance is 97.7 % between 350-1000 nm wavelengths; the sheet resistance has further reduced to 180 Ω/□ after doping process. It meets the industrial requirements of the transparent conductive films.

[1] A.K. Geim, K.S. Novoselov, The rise of graphene, Nature Materials, 6 (2007).
[2] Graphene, in: Wikipedia.
[3] J.S. Bunch, Mechanical and electrical prperties of graphene sheets, in, 2008.
[4] R.R. Nair, P. Blake, A.N. Grigorenko, K.S. Novoselov, T.J. Booth, T. Stauber, N.M.R. Peres, A.K. Geim, Fine structure constant defines visual transparency of graphene, Science, 320 (2008).
[5] K.I. Bolotina, K.J. Sikes, Z. Jiang, M. Klimac, G. Fudenberga, J. Honec, P. Kima, H.L. Stormer, Ultrahigh electron mobility in suspended graphene, Solid State Communications, 146 (2008) 351-355.
[6] I.W. Frank, D.M. Tanenbaum, A.M. van der Zande, P.L. McEuen, Mechanical properties of suspended graphene sheets, Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 25 (2007) 2558.
[7] G. Jo, M. Choe, S. Lee, W. Park, Y.H. Kahng, T. Lee, The application of graphene as electrodes in electrical and optical devices, Nanotechnology, 23 (2012) 112001.
[8] L. Colombo, X. Li, B. Han, W. Cai, Y. Zhu, R.S. Ruoff, Growth kinetics and defects of CVD graphene on Cu, The Electrochemical Society, (2010).
[9] R. Martinazzo, S. Casolo, G.F. Tantardini, The effect of atomic-scale defects and dopants on graphene electronic structure, in: D.S. Mikhailov (Ed.) Physics and Applications of Graphene - Theory, 2011.
[10] S. Ulstrup, M. Bianchi, R. Hatch, D. Guan, A. Baraldi, D. Alf, L. Hornekær, P. Hofmann, High-temperature behaviour of supported graphene: electron-phonon coupling and substrate-induced doping, Physical review B, (2012).
[11] A. Kasry, M.A. Kuroda, G.J. Martyna, G.S. Tulevski, A.A. Bol, Chemical doping of large-area stacked graphene films for use as transparent,conducting electrodes, ACS Nano, (2010).
[12] A. Bostwick, J. McChesney, T. Ohta, E. Rotenberg, T. Seyller, K. Horn, Experimental studies of the electronic structure of graphene, in, 2009.
[13] A.H. Castro Neto, N.M.R. Peres, K.S. Novoselov, A.K. Geim, The electronic properties of graphene, Reviews of Modern Physics, 81 (2009) 109-162.
[14] A.K. Geim, Graphene: status and prospects, Science, 324 (2009) 1530-1534.
[15] B. Pollard, Growing Graphene via Chemical Vapor Deposition, in, 2011.
[16] 林永昌, 呂俊頡, 鄭碩方, 邱博文, 石墨烯之電子能帶特性與其元件應用, in, Physics bimonthly, 2011.
[17] A. Teng, Physical properties of carbon nanotubes, in, 2010.
[18] S. Reich, J. Maultzsch, C. Thomsen, P. Ordejón, Tight-binding description of graphene, Physical Review B, 66 (2002).
[19] F. Bonaccorso, Z. Sun, T. Hasan, A.C. Ferrari, Graphene photonics and optoelectronics, Nature Photonics, 4 (2010).
[20] E.Y. Andrei, G. Li, X. Du, Electronic properties of graphene: a perspective from scanning tunneling microscopy and magnetotransport, Rep Prog Phys, 75 (2012) 056501.
[21] http://bluestonegt.com/applications/, in, Bluestone.
[22] BluestoneGlobalTech, Graphene Applications: thin, flexible touch panel/display, LED and batteries, in, Youtube, 2013.
[23] 楊明輝, 透明導電膜, (2006).
[24] 楊明輝, 工業材料, 2001.
[25] L.G.D. Arco, C. Zhou, Y. Zhang, C.W. Schlenker, K. Ryu, M.E. Thompson, Continuous, highly flexible, and transparent graphene films by chemical vapor deposition for organic photovoltaics, ACS Nano, 4 (2010) 2865–2873.
[26] X. Li, Y. Zhu, W. Cai, M. Borysiak, B. Han, D. Chen, R.D. Piner, L. Colombo, R.S. Ruoff, Transfer of large-area graphene films for high-performance transparent conductive electrodes, Nano Lett, 9 (2009) 4359-4363.
[27] H. Medina, Y.-C. Lin, D. Obergfell, P.-W. Chiu, Tuning of charge densities in graphene by molecule doping, Advanced Functional Materials, 21 (2011) 2687-2692.
[28] S. Tongay, K. Berke, M. Lemaitre, Z. Nasrollahi, D.B. Tanner, A.F. Hebard, B.R. Appleton, Stable hole doping of graphene for low electrical resistance and high optical transparency, Nanotechnology, 22 (2011) 425701.
[29] H. Bi, F. Huang, J. Liang, X. Xie, M. Jiang, Transparent conductive graphene films synthesized by ambient pressure chemical vapor deposition used as the front electrode of CdTe solar cells, Adv Mater, 23 (2011) 3202-3206.
[30] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Electric field effect in atomically thin carbon films, Science, 306 (2004) 666-669.
[31] Y. Zhang, J.P. Small, W.V. Pontius, P. Kim, Fabrication and electric field dependent transport measurements of mesoscopic graphite devices, Applied Physics Letters, 86 (2005).
[32] W.A.d. Heer, C. Berger, X. Wu, P.N. First, E.H. Conrad, X. Li, T. Li, M. Sprinkle, J. Hass, M.L. Sadowski, M. Potemski, G. Martinez, Epitaxial graphene, Solid State Communications, 143 (2007) 92-100.
[33] X. Li, G. Zhang, X. Bai, X. Sun, X. Wang, E. Wang, H. Dai, Highly conducting graphene sheets and Langmuir–Blodgett films, Nature Nanotechnology, 3 (2008) 538-542.
[34] Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Graphene and graphene oxide: synthesis, properties, and applications, Adv Mater, 22 (2010) 3906-3924.
[35] G. Eda, G. Fanchini, M. Chhowalla, Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material, Nature Nanotechnology, 3 (2008) 270-274.
[36] H. Mehdipour, K.K. Ostrikov, Kinetics of low-pressure, low-temperature graphene growth: toward single-layer, single-crystalline structure, ACS Nano, 6 (2012) 10276–10286.
[37] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S.K. Banerjee, L. Colombo, R.S. Ruoff, Large-area synthesis of high-quality and uniform graphene films on copper foils, Science, 324 (2009) 1312-1314.
[38] S. Bae, H. Kim, Y. Lee, X. Xu, J.-S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H.R. Kim, Y.I. Song, Y.-J. Kim, K.S. Kim, B. Özyilmaz, J.-H. Ahn, B.H. Hong, S. Iijima, Roll-to-roll production of 30-inch graphene films for transparent electrodes, Nature Nanotechnology, 5 (2010) 574-578.
[39] X. Li, C.W. Magnuson, A. Venugopal, J. An, J.W. Suk, B. Han, M. Borysiak, W. Cai, A. Velamakanni, Y. Zhu, L. Fu, E.M. Vogel, E. Voelkl, L. Colombo, R.S. Ruoff, Graphene films with large domain size by a two-step chemical vapor deposition process, Nano Lett, 10 (2010) 4328-4334.
[40] J. An, E. Voelkl, J.W. Suk, X. Li, C.W. Magnuson, L. Fu, P. Tiemeijer, M. Bischoff, B. Freitag, E. Popova, R.S. Ruoff, Domain (grain) boundaries and evidence of "twinlike" structures in chemically vapor deposited grown graphene, ACS Nano, 5 (2011) 2433-2439.
[41] K. Kim, Z. Lee, W. Regan, C. Kisielowsk, M.F. Crommie, a.A. Zettl, Grain boundary mapping in polycrystalline graphene, ACS Nano, 5 (2011).
[42] L.A. Jauregui, H. Caoa, W. Wud, Q. Yud, Y.P. Chen, Electronic properties of grains and grain boundaries in graphene grown by chemical vapor deposition, Solid State Communications, 151 (2011) 1100-1104.
[43] Q. Yu, Z. Liu, D. Pandey, DongguangWei, T.F. Chung, P. Peng, N.P. Guisinger, E.A. Stach, J. Bao, S.-S. Pei, Y.P. Chen, L.A. Jauregui, WeiWu, R. Colby, J. Tian, Z. Su, H. Cao, Control and characterization of individual grains and grain boundaries in graphene grown by chemical vapour deposition, Nature materials, 10 (2011).
[44] L. Fan, Z. Li, X. Li, K. Wang, M. Zhong, J. Wei, D. Wu, H. Zhu, Controllable growth of shaped graphene domains by atmospheric pressure chemical vapour deposition, Nanoscale, 3 (2011) 4946.
[45] W. Wu, Q. Yu, P. Peng, Z. Liu, J. Bao, S.S. Pei, Control of thickness uniformity and grain size in graphene films for transparent conductive electrodes, Nanotechnology, 23 (2012) 035603.
[46] C.M. Orofeo, H. Hibino, K. Kawahara, Y. Ogawa, M. Tsuji, K.-i. Ikeda, S. Mizuno, H. Ago, Influence of Cu metal on the domain structure and carrier mobility in single-layer graphene, Carbon, 50 (2012) 2189-2196.
[47] G.H. Han, F. Gunes, J.J. Bae, E.S. Kim, S.J. Chae, H.J. Shin, J.Y. Choi, D. Pribat, Y.H. Lee, Influence of copper morphology in forming nucleation seeds for graphene growth, Nano Lett, 11 (2011) 4144-4148.
[48] Z. Yan, A.R. Barron, Characterization of graphene by raman spectroscopy, in, http://cnx.org/content/m34667/latest/.
[49] L.M. Malard, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Raman spectroscopy in graphene, Physics Reports, 473 (2009) 51-87.
[50] P. Blake, E.W. Hill, A.H. Castro Neto, K.S. Novoselov, D. Jiang, R. Yang, T.J. Booth, A.K. Geim, Making graphene visible, Applied Physics Letters, 91 (2007) 063124.
[51] J.M. Wofford, S. Nie, K.F. McCarty, N.C. Bartelt, O.D. Dubon, Graphene islands on cu foils: the interplay between shape, orientation, and defects, Nano Lett, (2010).
[52] Z. Luo, S. Kim, N. Kawamoto, A.M. Rappe, A.T.C. Johnson, Growth mechanism of hexagonal-shape graphene flakes with zigzag edges, ACS Nano, 5 (2011) 9154-9160.
[53] Z. Luo, Y. Lu, D.W. Singer, M.E. Berck, L.A. Somers, B.R. Goldsmith, A.T.C. Johnson, Effect of substrate roughness and feedstock concentration on growth of wafer-scale graphene at atmospheric pressure, Chemistry of Materials, 23 (2011) 1441-1447.
[54] Y. Zhang, Z. Li, P. Kim, L. Zhang, C. Zhou, Anisotropic hydrogen etching of chemical vapor deposited graphene, ACS Nano, 6 (2012).
[55] M. Losurdo, M.M. Giangregorio, P. Capezzuto, G. Bruno, Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure, Phys. Chem. Chem. Phys, 13 (2011) 20836–20843.
[56] I. Vlassiouk, M. Regmi, P. Fulvio, S. Dai, P. Datskos, G. Eres, S. Smirnov, Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene, ACS Nano, 5 (2011).
[57] H. Park, J.A. Rowehl, K.K. Kim, V. Bulovic, J. Kong, Doped graphene electrodes for organic solar cells, Nanotechnology, 21 (2010) 505204.
[58] J. Zhang, P. Hu, X. Wang, Z. Wang, D. Liu, B. Yang, W. Cao, CVD growth of large area and uniform graphene on tilted copper foil for high performance flexible transparent conductive film, Journal of Materials Chemistry, 22 (2012) 18283.
[59] K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, J.H. Ahn, P. Kim, J.Y. Choi, B.H. Hong, Large-scale pattern growth of graphene films for stretchable transparent electrodes, Nature, 457 (2009) 706-710.
[60] S. De, J.N. Coleman, Are there fundamental limitations on the sheet resistance and transmittance of thin graphene films?, ACS Nano, 4 (2010) 2713-2720.