Figure 1.

(a–c) Schematic process flow of TLM device fabrication: (a) Thermal oxide (300 nm thick) was grown on a silicon substrate. (b) Metal electrodes were deposited by evaporation and structured using a lift-off process. (c) Graphene was transferred to the substrate and etched into a rectangular patch using O₂ plasma. Bottom right: Colorized scanning electron microscopy (SEM) picture of a TLM device with gold contacts (yellow) and a 60 μm wide graphene area (blue). (d) Manual probe station for device characterization. The inset shows a device contacted by probe needles and the reference humidity sensor at the bottom-right. (e) Schematic illustration of water molecules adsorbing on the graphene surface. (f) Measured resistance change of a graphene device (60 μm by 24 μm) as the relative humidity (RH) is decreased.