Electrical response of graphene to various gases (a) Concentration of chemically induced charge carriers in single-layer graphene exposed to different concentrations of NO2. Upper inset: SEM micrograph of this device; the width of the Hall bar is 1 μm. Lower inset: the changes in resistivity and Hall resistivity of the device with gate voltage . The ambipolar field effect is clearly illustrated. (b) Changes in resistivity at zero magnetic field as caused by exposure of graphene to different gases diluted in a carrier gas of either He or N2 (final concentration 1 ppm). Region I: device is in vacuum; II: analyte exposure; III: analyte evacuation; and IV: annealing at 1500°C [153].
