Clear manifestation of phonon anomaly insingle-layer graphene by chemical p-type doping

A phenomenon of phonon anomaly is clearly observed in single-layer graphene (SG) doped chemically with AuCl₃ by using electric field effect-induced Raman spectroscopy. The variations of G-mode frequency and full-wave half-maximum in pristine graphene are asymmetric for positive and negative charging, but become more symmetric after the p-type doping due to the softening of the G band. The shows a steplike variation at doping concentrations of 10 and 20 mM because the AuCl₃ doping is uniformly done, thereby making the charge density of graphene uniformly distributed, consistent with theoretical expectation. A flat region of between Fermi levels =±łω_G/2, instead of its two logarithmic divergences as theoretically expected, is observed even in doped SG. These results suggest that the observation of the phonon anomaly is facilitated due to the charge uniformity improved by the doping even though it is not enough to show such divergences.