Raman scattering of monolayer graphene: the temperature and oxygen doping effects

Raman spectra of monolayer graphene at various temperatures (303–473 K) are measured. In Raman scattering with wave numbers ranging from 1200 to 3400 cm−1, the four main Raman peaks (G, 2D, T + D and 2D′) show temperature-dependent behaviour, but have different frequency shifts with increase in temperature. We propose that the peak frequency shift is related mainly to the elongation of C–C bond due to thermal expansion or anharmonic coupling of phonon modes, and oxygen-induced strong hole doping on the graphene surface. The doping effect can be confirmed from the frequency shifts, full-width at half-maximum as well as the area and intensity ratios of G and 2D peaks in temperature-dependent Raman scattering of graphene, room-temperature Raman spectra of pristine graphene and graphene cooled down after Raman measurement at 473 K in air. Therefore, the oxygen doping effect and temperature effect coexist in temperature-dependent Raman scattering of monolayer graphene.