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Raman spectrum of the CVD graphene grown on copper. Inset shows an AFM image (5 μm × 5 μm) of graphene with a 2 μm long scale bar (top) and cross sectional plot along the black line (bottom).
(a) Current-voltage family curves for back gated graphene FET. Inset shows optical image of the same device with graphene channel between Ti/Au contact pads. The graphene channel is pointed by a dashed box. Scale bar is 20 μm long. (b) Current-voltage transfer characteristics of a back-gated CVD graphene FET in air and in the presence of NO2 and NH3. Inset shows the percentage conductance changes of CVD grown MLG with the flow of 20 ppm NO2 and 550 ppm NH3.
Variation of back gated graphene sensor response for (a) 20 ppm NO2 exposure with the increase in gate bias from negative to positive values and (b) 550 ppm NH3 exposure with the gate bias change from negative to positive values. The gas flow was turned on after 30 s for both the gases and shut off after 150 s.
Band diagrams showing shift in Fermi level in back gated graphene sensor as a result of gate bias and NO2 adsorption at (a) no bias, (b) positive and, (c) negative gate bias. Fermi level moves downward upon exposure to NO2 in all 3 cases.
Effect of back gate bias on initial carrier density, Fermi level position, and charge exchange due to flow of NO2.
Effect of back gate bias on initial carrier density, Fermi level position, and charge exchange due to flow of NH3.
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