Fig. 4
Optical and electrical properties of super-clean graphene. a UV-vis spectra of monolayer (red line), bilayer (orange line) and trilayer (blue line) super-clean graphene films on quartz substrates. Inset: a photograph of large-area, super-clean graphene and unclean graphene transferred onto PET substrates. An iPad served as a size reference. Note that multilayer graphene was fabricated by layer-by-layer transfer. The contrast is enhanced for clarity. A slight fluctuation of measured values is visible across the entire measured spectrum, which might result in a small overshoot. b Measured contact resistance as a function of gate voltage. The orange and blue dashed lines denote the reported contact resistance of the CVD-grown and mechanically exfoliated graphene, respectively. Inset: false-coloured scanning electron microscopy (SEM) image of the measured devices. The channel lengths vary from 1 to 6 μm. The error bar represents the relative deviation. c Typical plot of the resistance of graphene as a function of the gate voltage (Vg) at room temperature (blue line) and 1.9 K (red line). Inset: longitudinal (Rxx, red line) and Hall resistance (Rxy, blue line) of super-clean graphene at magnetic field intensities of 5 T at 1.9 K. Contact metal: Pd/Au, 10/80 nm. The fitting is based on nonlinear fitting method (see Supplementary Fig. 22)
