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.)−133−Synthesiology - English edition Vol.9 No.3 (2017) *1 Small amount of trilayer graphene was also observed.*2 The rest of AB-stacked bilayer graphene was 32 % of single layer graphene.*3 The amount of trilayer graphene was 1 %.This study60[40]41-59.51000Cu(6.3 µm), 850 ℃L.Brown et al.,Nano.Lett.12,1609(2012)70[30]――Cu(25 µm), 980 ℃W.Liu et al.,Chem.Mater.26,907(2014)98*338.0-50.03485Cu(1.2 µm)-Ni(0.4 µm), 920 ℃S. Lee et al.,NanoLett.10,4702(2010)99*245.0-53.0580Cu(25 µm), 1000 ℃K. Yan et al.,NanoLett.11,6(2011)67*1―350-400Cu(25 µm), 1000 ℃L.Liu et al.,ACSNano.6, 8241(2012)90[10]47.4-62.01500-4400Cu(25 µm), 1050 ℃ReferenceYield of AB-stacked (%)[Yield of disoriented (%)]FWHM of 2D-band for AB-stacked (cm-1)Mobility(cm2/Vs)Growth process(Substrate & temperature)80070060050040060708090100(c) ━ Graphene only (calculated value)(b) ━ Blank resin lm(a) ━ Graphene/resin lmWavelength (nm)Transmittance (%)of a slightly-adhesive resin film (a), a graphene/slightly-adhesive resin film (b) and the ratio spectrum of only graphene (c) which is calculated by dividing (a) by (b). The optical transmittance of the slightly-adhesive resin film was 91.5 % and the graphene/slightly adhesive resin film was 86.4 % at wavelength of 550 nm. The only graphene lm transmittance was 94.5 % at wavelength of 550 nm. It was found that the layer number corresponded to 2 layers estimated from 2.3 % transmittance loss of single layer graphene.[49] The reported values of the mobility of bilayer graphene are listed together with the yield, synthesis temperature, and FWHM of AB-stacked bilayer graphene in Table 1. In this study, the synthesis temperature is lower and the synthesis time is shorter compared to past reported values. However, the carrier mobility of 1000 cm2/Vs obtained at room temperature showed signicant improvement from the one around 100 cm2/Vs[13] for previous plasma CVD. Higher mobility values than ours have been reported by Liu et al. of 1500–4400 cm2/Vs[48] and Liu et al. of 3845 cm2/Vs.[50] It is considered that the quality of bilayer graphene synthesized by plasma CVD can be improved further. The sheet resistance of synthesized graphene was 951 Ω on average in this study. This sample was doped by gold chloride. Figure 13 shows the sheet resistance map after being doped by gold chloride. As shown in Fig. 13, the average sheet resistance of a 6 × 6 mm2 sheet was 130 Ω and the lowest sheet resistance was less than 100 Ω. By the development of plasma CVD using ultralow carbon Fig. 12 Optical transmittance of base resin film and graphene/resin lms[14] Transmittance of graphene only (c) is calculated by dividing graphene/ resin lm (a) by blank resin lm (b). Interference fringes of (a) and (b) are due to a very thin resin lm.Copyright (2014), with permission from ElsevierTable 1. Mobility, FWHM of 2D-band, yield of AB-stacked bilayer graphene[14] Copyright (2014), with permission from Elsevier !"#""$""#"$!"#"%""#"%!"#"4231Sheet resistance ΩY mmX mm250.0200.0150.0100.050.0065423165Fig. 13 The sheet resistance map of graphene after wet doping with gold chloride[14] Copyright (2014), with permission from Elsevier

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