Temperature effects on the Raman spectra of graphenes: dependence on the number of layers and doping.

Temperature effects on the various features in the Raman spectra of several graphene samples and graphene nanoribbons have been investigated over the temperature range 77-573 K. The temperature coefficient of the G and 2D band frequencies are found to depend on the number of layers, the former decreasing with the increase in the number of layers. The number of layers also affects the temperature coefficients of the FWHMs of these bands. Doping of graphene affects these Raman features significantly. The defect-related bands D and D(') bands are not sensitive to the number of layers or doping. We can understand the observed temperature effects on the basis of electron-phonon coupling, thermal expansion and anharmonic phonon-phonon interactions.