Vol.9 No.3 2017

Research paper : High quality and large-area graphene synthesis with a high growth rate using plasma-enhanced CVD (M. Hasegawa et al.)−135−Synthesiology - English edition Vol.9 No.3 (2017) ・High temperature process・Deposition area is limited by CVD furnace size ・Narrow layer control range・Low growth rate ・Low throughput (Pretreatment and synthesis process are not integrated )・High cost・Low temperature process・Large area deposition (Deposition area increases by antenna)・Wide layer control range・High growth rate and continuous deposition ・High throughput (Integration of pretreatment and synthesis process)・Low costThermal CVDPlasma CVDabIII100 nm100 nmdcFig. 16 (a) TEM image, (b) the selected area electron diffraction pattern, and (c) (d) The dark-eld TEM images[15] Copyright (2015), with permission from Elsevier Table 2. Comparison table of graphene synthesis by plasma CVD and thermal CVDdark-eld TEM images of each spot are shown in Fig. 16(c) and (d). Both figures suggest that the domain size is about 100 nm, which is consistent with the domain size estimated from the Raman measurement.7 Comparison of graphene synthesis by plasma CVD and thermal CVDFinally, based on results obtained in this study, comparison of graphene synthesis by plasma CVD and thermal CVD methods is shown in Table 2.8 Summary and Future PerspectivesIn this paper, we reported the attempt of the establishment of high-throughput plasma-enhanced CVD for high-quality graphene. By using plasma CVD methods, we elucidated the mechanism of attaining high purity of the copper foil surface by He/H2 plasma pretreatment and the suppression of silicon impurities from the quartz window. Furthermore, we developed a plasma CVD method using ultralow carbon sources for reduction of nucleation density, and the selective bilayer graphene synthesis was attained combining plasma CVD and joule heating. The grain size of graphene was expanded to 10 times and the Hall mobility was improved to 1000 cm2/Vs. Though we did not mention in detail the difference between plasma CVD and thermal CVD in this paper, we have recently clarified the advantages of plasma CVD from the view point of reduction of process time and process temperature.[16] In the near future, we want to push forward the establishment of a high-throughput plasma CVD method for high-quality and large-area graphene which exceeds the graphene quality synthesized by the main current high-temperature thermal CVD methods.Acknowledgements Part of the results was attained through the NEDO Project for “Basic Research and Development of Graphene.”References[1]K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov: Electric eld effect in atomically thin carbon lms, Science, 306, 666–669 (2004).[2]A. Kumar and C. Zhou: The race to replace tin-doped indium oxide: Which material will win?, ACS Nano, 4 (1), 11–14 (2010).[3]A. K. Geim: Graphene: Status and prospects, Science, 324, 1530–1534 (2009).[4]K.H. Liao, A. Mittal, S. Bose, C. Leighton, K. A. Mkhoyan and C. W. Macosko: Aqueous only route toward graphene from graphite oxide, ACS Nano, 5 (2), 1253–1258 (2011).[5]C. Virojanadara, M. Syväjarvi, R. Yakimova, L. I. Johansson, A. A. Zakharov and T. Balasubramanian: Homogeneous large-area graphene layer growth on 6H-SiC(0001), Phys. Rev., B 78, 245403-1–245403-6 (2008).[6]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 and R. S. Ruoff: Large-area synthesis of high-quality and uniform graphene lms on copper foils, Science, 324, 1312–1314 (2009).

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