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Probing Graphene Edges via Raman Scattering

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journal contribution
posted on 27.01.2009, 00:00 by Awnish K. Gupta, Timothy J. Russin, Humberto R. Gutiérrez, Peter C. Eklund
We present results of a Raman scattering study from the region near the edges of n-graphene layer films. We find that a Raman band (D) located near 1344 cm−1 (514.5 nm excitation) originates from a region next to the edge with an apparent width of ∼70 nm (upper bound). The D-band was found to exhibit five important characteristics: (1) a single Lorentzian component for n = 1, and four components for n = 2−4, (2) an intensity ID ∼ cos4 θ, where θ is the angle between the incident polarization and the average edge direction, (3) a local scattering efficiency (per unit area) comparable to the G-band, (4) dispersive behavior (∼50 cm−1/eV for n = 1), consistent with the double resonance (DR) scattering mechanism, and (5) a scattering efficiency that is almost independent of the crystallographic orientation of the edge. High-resolution transmission electron microscope images reveal that our cleaved edges exhibit a sawtooth-like roughness of ∼3 nm (i.e., ∼20 times the C−C bond length). We propose that in the double resonance Raman scattering process the photoelectron scatters diffusely from our edges, obscuring the recently proposed strong variation in the scattering from armchair versus zigzag symmetry edges based on theoretical arguments.