Bernal- and non-Bernal-stacked graphene layers have been systematically studied by Raman imaging and spectroscopy. Two dominant Raman modes, $G$ and $G^{\prime }$ (or 2$D$), of folded graphene layers exhibit three types of spectral features when interlayer lattice mismatches, defined by a rotational angle varies. Among these folded graphene layers, the most interesting one is the folded graphene layers that present an extremely strong $G$ mode enhanced by a twist-induced Van Hove singularity. The evolution of Raman $G$ and $G^{\prime }$ modes of such folded graphene layers are probed by changing the excitation photon energies. In this paper, doublet splitting of the $G^{\prime }$ mode in a folded double-layer (1 + 1) and of the $G$ mode in a folded tetralayer (2 + 2) graphene are observed and discussed. The $G^{\prime }$ mode splitting in folded double-layer graphene is attributed to the coexistence of inner and outer scattering processes and the trigonal warping effect as well as further downward bending of the inner dispersion branch at a visible excitation energy. The two peaks of the $G$ mode in folded tetralayer graphene are assigned to Raman-active mode ($E_{2\mathrm{g}}$) and lattice mismatch activated infrared-active mode ($E_{1\mathrm{u}}$), which is further verified by the temperature-dependent Raman measurements. Our study provides a summary and discussion of Raman spectra of Bernal- and non-Bernal-stacked graphene layers and further demonstrates the versatility of Raman spectroscopy for exploiting electronic band structures of graphene layers.

• Received 6 March 2014
• Revised 22 May 2014

DOI:https://doi.org/10.1103/PhysRevB.89.235430