a, b, c) Typical high vacuum (10 −5 Torr), low temperature (80 K) I DS versus V DS measurements (linear scale) of the w~50, ~25 and ~15 nm GNR-film devices and the corresponding absolute ( I DS) versus V DS curves (logarithmic scale) show nonlinear transport behaviour (panels d and g: schematic diagram of the device and a typical optical image of the device). The edges of the bandgap were determined from the sharp current increase in the log-scale curve (red). Owing to the relatively large channel lengths of the GNR film-devices, the channel-length dependence of the nonlinear transport gap is expected to be negligible. A bandgap scaling with GNR width was observed: the bandgaps for the as-produced films with w=~50, 25 and 15 nm GNRs were ~0 meV, ~10 meV and ~35 meV, respectively (this is appropriate because panel h shows that the conductivity is well centred around zero volt bias). Insets of panels b and c show an optical image of the respective GNR films on the polycarbonate filter after drying. After deposition of electrodes, these polycarbonate sheets were deposited on gold substrates as shown in panel d. ( e) FESEM image of a typical GNR film (as shown w~15 nm GNR film) on a polycarbonate filter substrate. ( f) Tapping-mode AFM (left inset) image of the GNR film shows a typical thickness of ~50 nm (right inset). ( h) A 15-nm GNR film at 10 mV ( V DS), gated with voltage in the ±25 V range exhibits a semiconducting behaviour with symmetric hole and electron densities. The electron mobility measured from transconductance is ~20 cm 2 V −1 s −1.