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.)−132−Synthesiology - English edition Vol.9 No.3 (2017) 37 %63 %60 %40 % ratio (a. u.)-- Gauss tting curve■ Disoriented bilayer graphene■ AB-stacked bilayer grapheneFWHM of 2D-band (cm-1)Normalized frequency (%)-- Gauss tting curve■ Disoriented bilayer graphene■ AB-stacked bilayer grapheneNormalized frequency (%)05151020(b)(a)2800270026002500Raman shift (cm-1)Raman shift (cm-1)Intensity (a. u.)Intensity (a. u.)2800270026002500method cited in References [46] and [47]. AB-stacked bilayer graphene is fitted by the sum of four Lorentzian peaks of the 2D-band with FWHM from 41.0–59.5 cm-1 (Fig. 10(a)). On the other hand, a disoriented stacked bilayer graphene is tted by a symmetric single Lorentzian peak with FWHM of 36.0–40.5 cm-1 (Fig. 10(b)). To examine the yield of AB-stacked bilayer and disoriented bilayer graphene, histograms of FWHM values of the 2D-band and Raman intensity of the 2D-band/G-band ratio are shown in Fig. 11. In the case of Raman intensity ratio (2D-band/G-band), the range of 0.7–2.7 is for AB-stacked bilayer graphene and 2.8–5.1 is for disoriented bilayer graphene. These results indicate a graphene yield of 60 % of AB-stacked bilayer graphene and 40 % of disoriented bilayer graphene on the copper foil substrate synthesized by hydrogen plasma treatment during heat treatment by joule heating. The D-band (1338cm-1) due to the defects in graphene crystal was observed with very weak intensity. With the identification of the number of layers and the stacked structure by Raman spectroscopy, single layer graphene and trilayer graphene were not observed in all samples synthesized by this plasma treatment condition. The crystal size of graphene was about 100 nm by estimated Raman intensity D-band/G-band ratio. (Described later) While the crystal size of synthesized graphene by using carbon source gas of the previous method was less than 10 nm, it is possible to definitely improve the crystal size by plasma CVD using a carbon source of ultralow concentration of the present method. In addition, it is suggested that this method is quite suitable for industrial continuous production such as the high-throughput roll-to-roll method from the point of view of very short process time and high growth rate.Then, the synthesized graphene in this study was transferred to a slightly-adhesive resin film in order to measure the optical transmittance. Fig. 12 shows the optical transmittance Fig. 10 Raman spectrum tting analysis of 2D-band[14](a) AB-stacked bilayer graphene which ts sum of four Lorentzian peaks, and (b) disorder-stacked bilayer graphene which ts the symmetric peak Copyright (2014), with permission from Elsevier Fig. 11 The histograms of FWHM values of 2D-band and intensity ration of 2D-band/G-band[14] Red bar is AB-stacked bilayer graphene and blue bar is disorder-stacked bilayer graphene. Copyright (2014), with permission from Elsevier

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