Stokes and anti-Stokes Raman scattering in mono- and bilayer graphene

Stokes and anti-Stokes Raman spectroscopy associated with the intervalley double resonance (DR) process in carbon materials is a unique technique to reveal the relationship between their characteristic electronic band structures and phonon dispersion. Here, we report the Stokes and anti-Stokes Raman scattering of the 2D mode in pristine graphene. The excitation energy (E_ex)-dependent frequency discrepancy between anti-Stokes and Stokes components of the 2D mode (Δω(2D)) is observed, which is in good agreement with the theoretical results. E_ex-dependent Δω(2D) is attributed to the nonlinear dispersion of the in-plane transverse optical (iTO) phonon branch near the K point, confirmed by the nonlinear E_ex-dependent frequency of the 2D mode (ω(2D)) in the range of 1.58–3.81 eV. The wavevector-dependent phonon group velocity of the iTO phonon branch is directly derived from Δω(2D). We also report Stokes and anti-Stokes Raman scattering of the D mode in defected graphene and the 2D mode in bilayer graphene associated with intervalley DR Raman processes.