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The influence of edge structure on the electronic properties of graphene quantum dots and nanoribbons

Abstract

Graphene shows promise as a future material for nanoelectronics owing to its compatibility with industry-standard lithographic processing, electron mobilities up to 150 times greater than Si and a thermal conductivity twice that of diamond. The electronic structure of graphene nanoribbons (GNRs) and quantum dots (GQDs) has been predicted to depend sensitively on the crystallographic orientation of their edges; however, the influence of edge structure has not been verified experimentally. Here, we use tunnelling spectroscopy to show that the electronic structure of GNRs and GQDs with 2–20 nm lateral dimensions varies on the basis of the graphene edge lattice symmetry. Predominantly zigzag-edge GQDs with 7–8 nm average dimensions are metallic owing to the presence of zigzag edge states. GNRs with a higher fraction of zigzag edges exhibit a smaller energy gap than a predominantly armchair-edge ribbon of similar width, and the magnitudes of the measured GNR energy gaps agree with recent theoretical calculations.

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Figure 1: Atomic-resolution imaging of GQDs and GNRs.
Figure 2: Energy gap (Eg)–size (L) relation for GQDs.
Figure 3: STM topographs of the GQDs included in the EgL plot in Fig. 2.
Figure 4: Comparison of a zigzag- and mixed-edge GQD using spatially resolved tunnelling spectroscopy.
Figure 5: Detection of zigzag-edge state for GQDs.
Figure 6: Tunnelling spectroscopy of three 20–30-nm-long, 2–3-nm-wide GNRs.

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Acknowledgements

This work was supported by the Office of Naval Research under grant number N000140610120 and by the National Science Foundation grant number NSF ECS 04-03489. K.A.R. acknowledges support from a NDSEG fellowship. We thank J. Koepke for assistance with a portion of the data collection, L. Ruppalt for providing the code for the normalized dI/dV calculations and P. Albrecht, P. Dollfus, D. Querlioz, A. Rockett, M. Sztelle and J. Weaver for helpful discussions.

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K.A.R and J.W.L. conceived the experiments. K.A.R. carried out the experiments, analysed the data and wrote the manuscript. J.W.L. provided technical support for the instrumentation, discussed the data and commented on the manuscript.

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Correspondence to Kyle A. Ritter.

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Ritter, K., Lyding, J. The influence of edge structure on the electronic properties of graphene quantum dots and nanoribbons. Nature Mater 8, 235–242 (2009). https://doi.org/10.1038/nmat2378

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