Ultraviolet Raman spectra of double-resonant modes of graphene

Ultraviolet (UV) Raman spectroscopy is a powerful technique for applications in fundamental and applied sciences of condensed matter and material science. To investigate double-resonant Raman scattering processes of graphene, we study the characteristic 2D Raman mode profiles of 1–4 layer graphene (supported and suspended) and graphite using both UV and visible excitation lasers at room temperature. At UV excitation energy of 3.81 eV, we observe that three scattering processes contribute dominantly to 2D mode profiles, which is a general feature for all graphene samples, showing the intensity diminishing of other scattering processes as theoretically predicted. We also find the asymmetric G∗ double resonant mode is sensitive to the high incident laser energy, and I(G)/I(2D) of monolayer graphene is most sensitive to UV laser energy due to near off resonant behavior of 2D modes at high excitation energy. Our results provide direct experimental evidences to further understand double-resonance scattering mechanism of few layer graphene.