Supplementary Figure S1. AFM images of GraNRs grown with standard growth process. Each of these pictures show GraNRs prepared independently,

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1 Supplementary Figure S1. AFM images of GraNRs grown with standard growth process. Each of these pictures show GraNRs prepared independently, suggesting that the results is reproducible.

2 Supplementary Figure S2. TEM images of GraNRs grown with standard growth process. They are imaged at various magnifications, scale bar is 50 nm in all figures.

3 Supplementary Figure S3. SEM images of GraNRs prepared using standard growth process. A) Low magnification showing several GraNRs and B) Zoom in on a single GraNR.

4 Supplementary Figure S4. AFM image of DNA film spin-coated on a SiO 2 substrate.

5 Intensity (a.u.) Film Ribbon Raman Shift (cm-1) Supplementary Figure S5. Raman analysis of GraNR. Comparison of DNA film (black) and stretched DNA (red) after being subjected to standard growth process.

6 Supplementary Figure S6. High resolution C1s XPS spectra showing de-convoluted peaks of DNA following the thermal treatments. A) SGP H 2 /CH 4, B) H 2 only, C) Ar only, D) graphene, E) DNA before growth and F) SGP, but without Cu 2+ infused into DNA. Measured curve (black), Fit (red), Fit de-convoluted components (blue). Curve fitting of C1s spectra of each sample was performed by using the Gaussian-Lorentzian distribution

7 Supplementary Figure S7. Evolution of XPS spectra of DNA with standard growth process. DNA was infused with Cu 2+ before (black) and after the SGP H 2 /CH 4 (red), A) Cu2p 3/2, (blue) after annealing at 600 C with H 2, B) N1s and C) P2p.

8 Supplementary Figure S8. Raman spectra of GraNRs from literature showing undetectable or very weak 2D peaks. A) Adapted from Wang et al., 2010,, showing a 20 nm GraNR (blue) and an 8 nm GraNR (red). 48 B) Adapted from Jiao et al., 2010, showing a GraNR from a plasma etched carbon nanotube. 49 C) Adapted from Pan et al., 2011, showing a 7.4 nm GraNR from folded, plasma-etched graphene sheets. 50 D) Adapted from Bischoff et al., 2011, showing a 30 nm GraNR from a plasma etched graphene flake, inset shows a magnification of the peaks. 37

9 Supplementary Figure S9. AFM images of stretched DNA after undergoing various thermal conditions. A) H 2 only, B) Ar only.

10 Supplementary Figure S10. Raman mapping of GraNRs. A) Mapping image of G-band intensity, B) Corresponding AFM height image of Raman-mapped region, showing a cleaner square region corresponding to the Raman mapped region indicating some carbon structure have been removed C) The same image from (B) was overlaid with a drawing of Raman mapped region and the GraNRs seen in the Raman mapping in (A), showing good agreement with the Raman map in A, D) Zoom-in phase image of the GraNRs still present after Raman mapping.

11 Supplementary Figure S11. Optical image of a sample electrical device with electrodes deposited through a parylene mask. The channel length is 5 um and channel width is 100 um.

12 Supplementary Figure S12. FET device characterisation of the GraNRs grown on Si 3 N 4. A) the pristine (p-type) device, and B) the O-MeO-DMBI doped, n-type device.

13 Supplementary Figure S13. FET device characterisation of the GraNRs at elevated temperature and humidity. A) Saturation regime transfer plot of the semiconducting GraNR (Shown as Figure 5 in main text). B) Linear regime transfer plot of the semiconducting GraNR. C) Output plot of the GraNR. The V DS is -90 V.

14 Supplementary Figure S14. Transfer plot showing the dependence of the GraNR on relative humidity. The percentage relative humidity is shown in the legend.

15 Supplementary Table S1. Relative percentage composition for the sp 2 and sp 3 carbons of the GraNRs and starting materials characterised after processing under varying conditions Growth Condition sp 2 location ev (FWHM) sp 2 quantity (%) sp 3 location ev (FWHM) sp 3 quantity (%) C-O, C=O location ev (FWHM) C-O, C=O quantity (%) CVD graphene (1.2) (1.75) SGP (1.2) (1.80) (3.0) 14.8 H (1.2) (1.65) (3.0) 19.8 Ar (1.2) (1.80) (3.0) 15.9 DNA Film (1.2) (1.36) SGP -No Cu (1.2) (1.75) (3.0) 20.2

16 Supplementary Note 1 In-situ doping studies of conducting GraNR The typical electrical characteristics of the metallic GraNRs were measured under ambient conditions (V GS sweep from +20 to -30V, V DS of -5V, channel length of 5 µm). For data presented, the I GS leakage was below 1 na. The transfer plot showed p-type transistor behaviour with the Dirac point at +7V. To confirm that the GraNRs were indeed the active elements of charge transport, we used 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium (O- MeO-DMBI) to n-dope the GraNRs and indeed achieved n-type GraNR devices. O-MeO-DMBI is a very effective n-type dopant recently reported by our group. 51 The doped GraNR device showed clear n-type behaviour with the Dirac point shifted to -10V (see Supplementary Figure S12), which suggests that the conductivity of the GraNRs may be modulated by the external environment to create both p- and n-type devices. The GraNRs were considered metallic as they did not exhibit a modulation of the drain current (I DS ) upon the change in the gate voltage (V GS ). However, the devices were also evaluated in a FET geometry. The FET performance of the two devices is shown in Supplementary Figure S12. The mobilities and on/off ratios for the devices were measured to be cm 2 V^-1 s^-1, three (3) and cm 2 V^-1 s^-1, two (2) for the pristine (p-type) device and the O-MeO-DMBI device, respectively.

17 Supplementary Note 2 Description of growth conditions for semiconducting GraNRs: To avoid the breakdown of the SiO 2 dielectric, GraNRs were also grown on SiO 2 substrates using the standard conditions but with a maximum temperature of 800 o C. The presence of the GraNRs was observed using AFM. However, when three-terminal FET devices were fabricated on SiO 2, the GraNRs showed semiconducting behaviour. The behaviour of the GraNRs was found to significantly depend on the temperature and humidity of the environment. At standard laboratory conditions (T ambient = o C and Relative Humidity = 20-30% RH), the GraNRs were mostly insulating, with I DS current observed in the range of pa even when V DS = -100V and V GS of -150V was used. The devices were subsequently characterised within a glove-bag equipped with a flow of a saturated water vapour used to control the humidity and temperature. As the %RH and T ambient was raised, the conductivity of the GraNRs significantly increased. At 73% RH and T=35 o C the devices demonstrated peak I DS of 1-10 µa. Moreover, the devices behaved as semiconductors with on/off ratios of A typical transfer plot is shown in Supplementary Figure S10. The device shown in Supplementary Figure S10 has a μ linear of 0.20 cm 2 V^-1 s^-1, μ saturated of 0.21 cm 2 V^-1 s^-1, and an on/off ratio of 192. It should be noted that a bulk capacitance value was used (10 nf cm^-2), rather than an electrostatic three dimensional simulation. 11 The device was biased with V G = -90V. The W/L for the device was taken to 0.1, as described above. While semiconductor behaviour was observed on all devices, the data was irregular and difficult to reproduce. This can be attributed to the required high humidity as well as the high resistance of the GraNRs. The large voltages required to operate the GraNR in the semiconductor regime typically resulted in the eventual electrical breakdown of the electrodes. We hypothesise that this is due to heat build-up at the electrode owing to the high resistance of the GraNR. The influence of humidity on a different GraNR device is shown in Supplementary Figure S11. These observations support the proposed model of amorphous carbon acting as a resistor in series with the graphitic regions within the GraNR. We hypothesise that relative humidity increases the conductivity of the amorphous carbon in the GraNR to a much greater extent than doping of the graphene components. This has been previously observed for nanoscale sp 3 carbon, termed nanocrystalline diamond. 42 These sp 3 materials can demonstrate an increase of up to 7 orders of magnitude upon the increase in humidity. This increase is hypothesised to occur through an electron-transfer mechanism, wherein the adsorbed water layer provides an electron sink for the subsurface hole accumulation layer. 52 Devices utilising nanodiamond have shown rectifying behaviour with an increase in p-type transport for sensing an oxidising material (e.g. H 2 O). This was attributed to the position of the valence band of nanodiamond, just above the chemical potential of an acidic water layer physisorbed on the surface. 53 The layer serves to remove electrons from the sp 3 carbon and leads to improved hole conductivity. Moreover, it has been suggested that nano-confinement of the material can lead to further separated quantum well states. These hypotheses are consistent with our observation of the doping effect on the graphitic devices. Upon the introduction of an oxidising material (i.e. H 2 O) we see an increase in p-type conductivity; however, the introduction of a strong electron donor O-MeO-DMBI leads to the decrease in hole transport and observation of n-type conductivity. 54 The decrease in hole transport of nanodiamond upon introduction of a reducing atmosphere has been previously shown with gas-phase studies upon the introduction of NH 3 gas. The decreased resistance of the amorphous carbon results in the observation of the

18 semiconducting device behaviour of the graphene carbons. It should be noted that high humidity can also result in the opening of a bandgap within graphene, thus, the increased humidity can also assist our devices in achieving the high on/off ratio. 43 Further optimisation of growth conditions is expected to lead to greatly improved device behaviour and provide critical data to assess the bandgap in GraNR transistors.

19 Supplementary References 48. Wang, X. & Dai, H. Etching and narrowing of graphene from the edges. Nat. Chem. 2, (2010). 49. Jiao, L., Zhang, L., Ding, L., Liu, J. & Dai, H. Aligned graphene nanoribbons and crossbars from unzipped carbon nanotubes. Nano Res. 3, (2010). 50. Pan, Z., Liu, N., Fu, L. & Liu, Z. Wrinkle engineering: a new approach to massive graphene nanoribbon arrays. J.Am. Chem. Soc. 133, (2011). 51. Wei, P. et al. 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium Iodide as a New Air-Stable n-type Dopant for Vacuum-Processed Organic Semiconductor Thin Films. J.Am. Chem. Soc. 134, (2012). 52. Maier, F., Riedel, M., Mantel, B., Ristein, J. & Ley, L. Origin of surface conductivity in diamond. Physi. Rev. Lett. 85, (2000). 53. Wang, Q. et al. Chemical gases sensing properties of diamond nanocone arrays formed by plasma etching. J. Appl. Phys. 102, (2007). 54. Wei, P. et al. Tuning the Dirac Point in CVD-Grown Graphene through Solution Processed n-type Doping with 2-(2-Methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1Hbenzoimidazole Nano Lett. 13, (2013).