Exceptional ballistic transport in epitaxial graphene nanoribbons

Abstract

Graphene nanoribbons will be essential components in future graphene nanoelectronics1. However, in typical nanoribbons produced from lithographically patterned exfoliated graphene, the charge carriers travel only about ten nanometres between scattering events, resulting in minimum sheet resistances of about one kilohm per square2,3,4,5. Here we show that 40-nanometre-wide graphene nanoribbons epitaxially grown on silicon carbide6,7 are single-channel room-temperature ballistic conductors on a length scale greater than ten micrometres, which is similar to the performance of metallic carbon nanotubes. This is equivalent to sheet resistances below 1 ohm per square, surpassing theoretical predictions for perfect graphene8 by at least an order of magnitude. In neutral graphene ribbons, we show that transport is dominated by two modes. One is ballistic and temperature independent; the other is thermally activated. Transport is protected from back-scattering, possibly reflecting ground-state properties of neutral graphene. At room temperature, the resistance of both modes is found to increase abruptly at a particular length—the ballistic mode at 16 micrometres and the other at 160 nanometres. Our epitaxial graphene nanoribbons will be important not only in fundamental science, but also—because they can be readily produced in thousands—in advanced nanoelectronics, which can make use of their room-temperature ballistic transport properties.

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Figure 1: Structure and characterization of nanoribbons and devices.
Figure 2: Scanning tunnelling analysis of ex situ produced sidewall ribbons similar to those used in fixed geometry transport measurements.
Figure 3: Multiprobe in situ transport measurements of sidewall ribbons.
Figure 4: Gated ribbon transport (see Fig. 1c).
Figure 5: Comparison with other work.

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Acknowledgements

C.T. thanks the German Research Foundation Priority Program 1459 ‘Graphene’ for financial support. C.B., E.H.C. and W.A.d.H. thank R. Dong, P. Goldbart, Z. Guo, J. Hankinson, J. Hicks, Y. Hu, J. Kunc, M. Kindermann, D. Mayou, M. Nevius, J. Palmer, A. Sidorov and P. de Heer for assistance and comments. C.B., E.H.C. and W.A.d.H. thank the AFOSR, NSF (MRSEC – DMR 0820382), W. M. Keck Foundation and Partner University Fund for financial support. Work at ORNL was supported by the Scientific User Facilities Division, BES of the DOE.

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Contributions

J.B. and F.E. produced samples and performed the in situ transport experiments in Hannover relating to Fig. 3. C.T. performed and supervised the transport experiments in Fig. 3, discussed the data and commented on the paper. M.R. produced the samples and performed transport experiments shown in Fig. 4 and Supplementary Figs 3–6. E.H.C., A.T. and A.T.-I. performed ARPES experiments, and A.T. and M.S. the STM and STS experiments. Z.J. performed confirming spin transport measurements and contributed to C-AFM results shown in Supplementary Fig. 6b. A.-P.L. performed earlier SPM measurements. W.A.d.H. conceived and supervised the experiment and interpreted the data. C.B. supervised and performed the Atlanta based experiments. W.A.d.H. and C.B. wrote the paper.

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Correspondence to Walt A. de Heer.

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The authors declare no competing financial interests.

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Baringhaus, J., Ruan, M., Edler, F. et al. Exceptional ballistic transport in epitaxial graphene nanoribbons. Nature 506, 349–354 (2014). https://doi.org/10.1038/nature12952

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