Electron Phonon Coupling Mechanism in Thermally Reduced Graphene

Infrared absorption of atomic and molecular vibrations in solids can be affected by electronic contributions through non-adiabatic interactions, such as the Fano effect. Typically, the IR absorption lineshapes are modified or IR forbidden modes are detectable as a modulation of the electronic absorption. In contrast to such known phenomena, we report here the observation of a giant IR absorption band in reduced graphene oxide (GO), arising from the coupling of electronic states to the asymmetric stretch mode of a yet unreported structure [1], consisting of oxygen atoms aggregated at edges of defects. DFT calculations show that free electrons are induced by the displacement of the oxygen atoms, leading to a strong IR absorption that is in-phase with the phonon mode. This new phenomenon is only possible when all other oxygen-containing chemical species including hydroxyl, carboxyl, epoxide and ketonic functional groups are removed from the region adjacent to the edges, i.e. clean graphene patches are present. *The authors acknowledge funding from the NRI SWAN program and Texas Instruments. [1] Acik, M.; Lee, G.; Mattevi, C.; Chhowalla, M.; Cho, K.; Chabal, Y. J. \textit{Nature Materials}. \textbf{9,} 840-845 (2010)