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Ultrafast carrier phonon dynamics in NaOH-reacted graphite oxide film

NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast carrier dynamics of the sample were studied by time-resolved transient differential reflection (\DeltaR/R). The data show two exponential relaxation processes. The slow relaxation process (\sim2ps) is ascribed to low energy acoustic phonon mediated scattering. The electron-phonon coupling and first-principles calculation results demonstrate that - OH and -ONa groups in the sample are strongly coupled. Thus, we attribute the fast relaxation process (\sim0.17ps) to the coupling of hydroxyl and -ONa groups in the sample.