Abstract
We measured a 2D peak line shape of epitaxial graphene grown on SiC in high vacuum, argon and graphene prepared by hydrogen intercalation from the so called buffer layer on a silicon face of SiC. We fitted the 2D peaks by Lorentzian and Voigt line shapes. The detailed analysis revealed that the Voigt line shape describes the 2D peak line shape better. We have determined the contribution of the homogeneous and inhomogeneous broadening. The homogeneous broadening is attributed to the intrinsic lifetime. Although the inhomogeneous broadening can be attributed to the spatial variations of the charge density, strain and overgrown graphene ribbons on the sub-micrometer length scales, we found dominant contribution of the strain fluctuations. The quasi free-standing graphene grown by hydrogen intercalation is shown to have the narrowest linewidth due to both homogeneous and inhomogeneous broadening.
Highlights
The Raman spectra show typical characteristics of the single-layer graphene. These are the ratio of the integrated 2D peak to G peak intensity larger than
The hydrogenated (QFMLG) and non-hydrogenated (SLG-vac, single layer graphene (SLG)-Ar) samples can be distinguished by a low intensity background in the spectral range of the D peak
The quasi free-standing monolayer graphene (QFMLG) sample shows the smallest inhomogeneous broadening, as we showed in spectral analysis of the 2D peak line shape fitted by the Voigt function
Summary
The Raman spectroscopy of graphene is a well-established technique [1,2,3] to determine number of graphene layers [4], strain [5,6], charge density [6,7,8,9], grain size [10,11,12,13,14], graphene functionalization [15], misorientation of graphene layers [16] or degree of hydrogen intercalation of epitaxial graphene onSiC [17,18]. The D peak reflects the amount of defects, or the graphene grain size. The G peak is related to the in-plane bond-stretching optical vibrations of sp hybridized carbon atoms in the graphene lattice [19,20]. The predicted unique property of the 2D peak is its line shape. The 2D peak is predicted to have a Lorentzian line shape in the case of the single layer graphene (SLG) [21]. The 2D peak is predicted to have four components in the case of bilayer graphene.
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