Intrinsic phonon anharmonicity in heavily doped graphene probed by Raman spectroscopy

The temperature-dependent (T-dependent) linewidth (Gamma(G)) and frequency shift (Delta omega(G)) of the G mode provide valuable information on the phonon anharmonicity of graphene-based materials. In contrast to the negligible contribution from electron-phonon coupling (EPC) to the linewidth of a Raman mode in semiconductors, Gamma(G) in pristine graphene is dominated by EPC contribution at room temperature due to its semimetallic characteristics. This leads to difficulty in resolving intrinsic contribution from phonon anharmonicity to Gamma(G). Here, we probed the intrinsic phonon anharmonicity of heavily-doped graphene by T-dependent Raman spectra based on FeCl3-based stage-1 graphite intercalation compound (GIC), in which the EPC contribution is negligible due to the large Fermi level (E-F) shift. The Delta omega(G) and Gamma(G) exhibit a nonlinear decrease and noticeable broadening with increasing temperature, respectively, which are both dominated by phonon anharmonicity processes. The contribution of phonon anharmonicity to Gamma(G) of heavily-doped graphene decreases as the E-F approaches to the Dirac point. However, the T dependence of Delta omega(G) is almost independent on E-F and qualitatively agrees with the theoretical result of pristine graphene. These results provide a deeper understanding of the role of phonon anharmonicity on the Raman spectra of heavily doped graphene. (C) 2021 Elsevier Ltd. All rights reserved.