Temperature and gate voltage dependent Raman spectra of single-layer graphene.

Raman spectra of electrostatically gated single-layer graphene are measured from room temperature to 560 K to sort out doping and thermally induced effects. Repeated heating cycles under Ar led to convergent first-order temperature coefficients of the G-band (χ(G) = -0.03 cm(-1)/K) and the 2D-band (χ(2D) = -0.05 cm(-1)/K) frequencies, which are independent of doping level as long as the Fermi level does not shift with temperature. While the intrinsic behavior may be different (e.g., χ(G) ∼ -0.02 cm(-1)/K near room temperature), these values appear more appropriate in describing responses of most graphene samples on SiO(2) substrates. The more negative χ(G) value than theoretical expectations may be explained by interactions with the substrate reducing the lattice thermal expansion contribution to the temperature dependence of G-band frequency. Enhanced interactions with the substrate may also be responsible for zero-charge, room-temperature G-band line width increase and 2D-band frequency downshift.