(color online) (a) 2D peak region of the Raman spectra of the graphene heater shown in Fig. 3(b) at different temperatures. The excited laser is 633 nm. (b) Shift in 2D peak position extracted from panel (a). A linear formula ω 2D ≈ 2709.5 − 0.062 T is used to describe the relationship of the 2D peak position and temperature. The dashed line is a guide to the eyes. (c) The relationship of the 2D peak position and gate voltage when the heater is sourced with a current with a density of 4.5×10⁷ A/cm². The temperatures of the graphene heater estimated from the above formula are also plotted. The solid lines are a guide to the eyes.