Supporting Information

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1

Supporting Information

Transfer-Free Synthesis of Atomically Precise Graphene Nanoribbons

on Insulating Substrates

Zafer Mutlu,†,‡_{Juan Pablo Llinas,}†,‡_{Peter H. Jacobse,}§_{Ilya Piskun,}_∥_{Raymond Blackwell,}_∥

Michael F. Crommie,§,⊥,#_{Felix R. Fischer,}∥,⊥,# and Jeffrey Bokor*,†,⊥

†_{Department of Electrical Engineering and Computer Sciences, UC Berkeley, Berkeley,}

California 94720, United States

‡_{The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720,}

United States

§_{Department of Physics, UC Berkeley, Berkeley, California 94720, United States} ∥Department of Chemistry, UC Berkeley, Berkeley, California 94720, United States

⊥Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California

94720, United States

#_{Kavli Energy NanoSciences Institute at the University of California Berkeley and the Lawrence}

Berkeley National Laboratory, Berkeley, California 94720, United States

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2 Figure S1. (a) Atomic force microscopy (AFM) height image of the Au/mica substrate prepared similar to the Au/SiO2/Si substrate. The root-mean-square (rms) surface roughness is measured

to be ~0.42 nm. (b) AFM height image of a commercial Au(111)/mica substate. The rms surface roughness is measured to be ~0.27 nm. Corresponding X-ray diffraction patterns of the (c) Au/mica and (d) Au(111)/mica samples, revealing a strong (111) gold peak as well as substrate-related peaks with no signatures of other phases of gold.

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3 Figure S2. (a) Optical microscopy image of a two-dimensional hexagonal-boron nitride (h-BN) flake exfoliated on a SiO2/Si substrate. The scale bar is 5 µm. (b) Corresponding AFM height

image of the flake, showing an atomically flat surface with a rms roughness of ~0.18 nm. (c) AFM height image of an annealed ~100 nm gold thin film prepared on the flake. The surface of the gold film is atomically smooth with a rms roughness of ~0.21 nm, which is even smaller than that of the epitaxial Au(111) thin films (Figure S1b).

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4 Figure S3. Raman spectrum of a 7-AGNR/Au/SiO2/Si sample before and after subject to argon

ion sputtering (1 kV Ar+_{sputtering along the direction perpendicular to the sample for ~10 s at}

24 °C). After sputtering, only the D and G peaks exist in the spectrum whereas the RBLM, RBLM3 and C–H peaks completely disappear. In addition, the D peak is broadened, and the intensity of the D and G peaks is increased. The presence of the D and G peaks shows that the GNRs are not completely etched away while the disappearance of the characteristics peaks in the spectrum indicates that the GNRs are structurally damaged during sputtering. These results suggest that the D and G peaks can be used to evaluate the structural quality of the GNRs.

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5 Figure S4. (a) Raman spectrum comparison of 7-AGNRs prepared on the SiO2/Si via

transfer-free and standard transfer methods as described in the experimental section. Raman spectrum of both samples is almost identical. (b) The changes in the D and G peaks after the placement of the GNRs on the SiO2/Si substrate. The G peak upshifts while the intensity ratio of the D and G

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6 Figure S5. Optical microscopy images of the field-effect transistor (FET) arrays (a) before and (b) after etching of the gold. (c) AFM height image (5 × 5 µm) of the HfO2 film (~5.5 nm)

deposited onto a W (~8 nm) film by atomic layer deposition (ALD), which is serving as a local back gate. High magnification AFM height image (0.5 × 0.5 µm) of the local back gate (d) before the placement of the GNRs, and after the placement of the GNRs via the (e) transfer and (f) transfer-free methods. The rms surface roughness is measured to be ~0.59, ~0.96, and ~0.91 nm in (d), (e), and (f), respectively.

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7 Figure S6. Raman spectrum of the (a) transferred and (b) transfer-free GNRs before and after device processing.

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8 Figure S7. ID-VG characteristics of the 7-AGNR FETs made with the (a) transferred and (b)

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9 Figure S8. Cumulative distribution function (CDF) of Ion in 7-AGNR FETs. The CDF is defined

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10 Supplementary Note: For the transfer-free process, we grow GNRs on the surface of the gold thin films deposited on a SiO2/Si chip that is pre-patterned with Pt metal. Gold annealing and

GNR growth are peformed at 480 °C and 400 °C, respectively. At such high temperatures, Pt can diffuse in the gold thin film. The diffusion of Pt adversely affects the growth of GNRs and present even after etching of the gold, which could be responsible for the observed high off-current and thus the low on/off ratio. We found that the device that was not subjected to the high annealing and growth temperatures exhibit higher on/off ratio as shown in Figure S9 (The GNRs were grown on a gold/SiO2/Si substrate, followed by transferring the GNRs/gold thin film to the

chip, where the gold film was facing to the SiO2. The GNRs were obtained on the chip via

etching of the gold under the GNRs). We thus believe that on/off ratio can be improved by patterning all metals after the placement of the GNRs on insulator layer via transfer-free method.

Figure S9. ID-VG characteristic of the 7-AGNR FET device that was not subjected to the high