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Optical contrast imaging of mono, bi, and trilayer graphene on 300 nm SiO2 under white light illumination. Optical images of graphene layers and the corresponding Raman spectra are also indicated by arrows.
Raman spectra of graphene layers grown by intercalating (a) DMF, (b) PC, and (c) THF. D band (∼1350 cm−1) is present in graphene synthesized in DMF and PC, but absent in graphene synthesized in THF. Intensity ratio IG/I2D is 0.3 for graphene sheet synthesized using THF, which is the lowest as compared to that in DMF and PC. Confocal Raman images generated by spatial distribution of intensity of D, G, and 2D bands indicated by arrows showing the absence of D band over whole graphene sheet synthesized in THF.
Raman spectra of (a) monolayer and (b) bilayer graphene sheet. Raman spectra and Lorentzian fitting of 2D peak of (c) monolayer and (d) bilayer graphene sheets. In monolayer graphene, violet dots are experimental data and black line is Lorentzian fit. In the case of bilayer graphene, red dots are experimental data and black line is resultant fit by 4 Lorentzian functions. The lines of other colors are Lorentzian components of the fit. Figure clearly shows that monolayer graphene has a sharp and symmetric 2D peak whereas bilayer has asymmetric and broader 2D peak, which consists of 4 different peaks due to double resonance process.
UV-vis spectra of suspended graphene sheets in DMF (green) and in propylene carbonate (red). Inset shows the absorption spectra of suspended graphene in THF (blue). This reveals that graphene exfoliated in THF has low/negligible oxygen content as compared to that in DMF and PC.
Transfer characteristics (IDS vs VGS) of field effect transistors fabricated on graphene monolayer exfoliated in (a) THF and (b) PC at VDS = 0.1 V. Dirac points (VDI) are at ∼0.6 V and −12.0 V for THF and PC, respectively, as indicated by arrows. Carrier concentration (n) as a function of gate voltage (VGS) is also shown.
Position, FWHM, and intensity ratios of different (D, G, and 2D) bands in graphene sheets exfoliated in PC, DMF, and THF, respectively.
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