Raman Spectra of Epitaxial Graphene on SiC and of Epitaxial Graphene Transferred to SiO₂

Abstract

Raman spectra were measured for mono-, bi-and trilayer graphene grown on SiC by solid state graphitization, whereby the number of layers was pre-assigned by angle-resolved ultraviolet photoemission spectroscopy. It was found that the only unambiguous fingerprint in Raman spectroscopy to identify the number of layers for graphene on SiC(0001) is the linewidth of the 2D (or D*) peak. The Raman spectra of epitaxial graphene show significant differences as compared to micromechanically cleaved graphene obtained from highly oriented pyrolytic graphite crystals. The G peak is found to be blue-shifted. The 2D peak does not exhibit any obvious shoulder structures but it is much broader and almost resembles a single-peak even for multilayers. Flakes of epitaxial graphene were transferred from SiC onto SiO 2 for further Raman studies. A comparison of the Raman data obtained for graphene on SiC with data for epitaxial graphene transferred to SiO 2 reveals that the G peak blue-shift is clearly due to the SiC substrate. The broadened 2D peak however stems from the graphene structure itself and not from the substrate. 2Graphene is the building block of graphite and carbon-based nanomaterials such as carbon nanotubes and fullerenes. Since the development of the micromechanical cleavage method to obtain thermodynamically stable mono-and few-layer graphene, our understanding of this purely twodimensional system has improved significantly. 1 , 2 , 3 , 4 Graphene exhibits unconventional electronic properties, 1,2,5,6 such as high and nearly equal mobilities at room temperature for both electron and hole conduction, which makes it a strong candidate for nanoelectronic circuit applications. 5,7 However, the micromechanical cleavage method is not suitable for obtaining large area graphene. For practical applications requiring large areas of graphene, full graphitization on SiC seems to be the more promising route. 8,9,10,11 Indeed, devices of epitaxial graphene on SiC have been prepared using conventional e-beam lithography and a patterning method based on O 2 plasma etching 8,9 although several problems still remain: the nature of the (6√3×6√3)R30° reconstruction at the interface between SiC and graphene is still under debate and the proper conditions for the production of large areas of homogeneous mono-, biand few-layer graphene are not well developed. 10,12Raman spectroscopy is known to be a powerful tool to determine the electronic properties of carbonbased materials and there have been several reports about Raman measurements on graphene layers which were micromechanically exfoliated from highly oriented pyrolytic graphite (HOPG) on SiO 2 substrates. 13,14,15,16,17 Recently, Ferrari et al. have demonstrated that the shape of the 2D Raman peak may serve as the fingerprint to distinguish mono-, bi-and few-layer graphene. The 2D peak stems from a double resonance electron-phonon scattering process. 14 For monolayer graphene the 2D peak can be fitted to a single Lorentzian, whereas the multiple bands in bilayers or few-layer gra...

Effective mass of electron in monolayer graphene: Electron-phonon interaction

“…For the graphene layer on SiC, it is apparently difficult to distinguish the G and D peaks in the spectra because their intensities are much smaller than those of the surrounding peaks from the SiC substrate. 20 The sharp and strong peak at 775.0 cm À1 is the E 2 planar optical, 962.5 cm À1 is an A 1 longitudinal optical (LO) mode, and 201.5 cm À1 which is an E 2 planar or transverse acoustic mode of SiC. 21 The defectinduced D band peak, which should be near 1350 cm…”

Progress and Challenges in Transfer of Large‐Area Graphene Films

“…But the size of the transferred graphene was limited to be about 1 μm 2 or less 79. This method is not suitable to transfer LAG grown on SiC substrate.…”

Growth and Characterization of Graphene on Polycrystalline SiC Substrate Using Heating by CO2 Laser Beam

“…Lee D.S. et al 38 also reported results for the bi-and tri-layer graphene that exhibit a FWHM at approximately 64 cm -1 and 74 cm -1 , respectively. The FWHM of the graphene obtained in our process was found in the range between 43.5 cm -1 and 49.5 cm -1 .…”

“…As reported in literature, for a monolayer graphene, obtained by mechanical exfoliation, the FWHM was lower than 30 cm -1 31,38 . Using a Raman laser of 488 nm, Lee D.S et al 38 reported that due to the intrinsic disorder of the monolayer epitaxial graphene (grown on a Si terminated face of SiC), the FWHM was found at approximately 46 cm -1 , which is higher than that for exfoliated graphene. Lee D.S.…”