Herein, we study the electronic states of single-layer graphene doped in an ionic liquid electrochemical cell using Raman scattering spectroscopy. The doping level dependence of the G and D′ modes at 16 different Raman spectra points is investigated by changing the applied voltage. From the fitting analysis of the experimental results, the study finds that the G mode's asymmetric line shape depends on the doping level and periodicity defect concentration. The results suggest that the periodicity defects caused by ionic liquid molecules' adsorption modify the electronic state of single-layer graphene. By scrutinizing the G phonon mode's asymmetric line shape, the background electronic Raman scattering spectra are unraveled through the Fano resonance effect.
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