Aerographite phonon density of states affects double resonant Raman scattering

Raman spectra of aerographite, graphite oxide, graphite flakes, and kish graphite were investigated with different laser excitation energies (wavelengths, λL), namely, 2.81 eV (442 nm), 2.41 eV (514 nm), 2.33 eV (532 nm), and 1.96 eV (633 nm). X-ray diffraction analysis showed that aerographite and graphite oxide are structurally disordered. The Raman spectra of both exhibit typical graphitic features, namely, G, D, D′, and 2D bands. The D and 2D bands exhibit a "blue-shift"with laser excitation energies, EL, while the G bands remain invariant. The intensity ratio between the D and G bands (ID/IG) ranges from 0.70 to 1.25 for aerographite and graphite oxide and from 0.04 to 0.24 for graphite flakes and kish graphite. The dependence of ID/IG on λL4 is linear for graphite flakes and kish graphite, while it saturates at the longest λL for aerographite and graphite oxide. A physical explanation of this unexpected saturation is proposed within the double resonant Raman scattering model, taking into account the disorder-induced changes of the phonon density of states.

DDC Class

600: Technik

620: Ingenieurwissenschaften

More Funding Information

We acknowledge the Australian Research Council for financial support. We also thank Dr. Anne Rich (University of New South Wales) for assistance with the Raman spectra. R.A. and B.F. acknowledge Deutsche Forschungsgemeinschaft (DFG), Germany (Grant Nos. AD 183/27-1 and SCHU 926/25-1). Y.K.M. acknowledges the financial support from Swedish Research Council (Grant No. VR-2016-06014).

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Aerographite phonon density of states affects double resonant Raman scattering