Optical Microscopy. The fabricated GFET arrays were observed with a motorized optical microscope (DSX510, Olympus) using a 10× objective lens and a digital zoom of 5×, with an exposure time of 7 ms. Based on the obtained α, Fermi energy EF is derived through EF = (-18α -83)×10 -3 . 27 Additionally, EF is a function of nH as EF(nH) = -ℏvF(πnH) , where ħ is the reduced Planck's constant and vF = 1.1 × 10 6 m s -1 is the Fermi velocity of graphene on the SiO2 substrate. Conversely, the obtained β is converted to ε via β = 23.5 ε. Therefore, nH and ε can be derived from (ωG, ω2D) using these equations. The corresponding nH and ε images were generated because (ωG, ω2D) were obtained from every pixel in Raman images.