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Thermoelectric imaging of structural disorder in epitaxial graphene

Abstract

Heat is a familiar form of energy transported from a hot side to a colder side of an object, but not a notion associated with microscopic measurements of electronic properties. A temperature difference within a material causes charge carriers, electrons or holes to diffuse along the temperature gradient inducing a thermoelectric voltage. Here we show that local thermoelectric measurements can yield high-sensitivity imaging of structural disorder on the atomic and nanometre scales. The thermopower measurement acts to amplify the variations in the local density of states at the Fermi level, giving high differential contrast in thermoelectric signals. Using this imaging technique, we uncovered point defects in the first layer of epitaxial graphene, which generate soliton-like domain-wall line patterns separating regions of the different interlayer stacking of the second graphene layer.

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Figure 1: Thermoelectric imaging and its application to epitaxial graphene.
Figure 2: Evolution of strain-response patterns in epitaxial graphene.
Figure 3: Thermoelectric imaging at the atomic scale.
Figure 4: Local defect investigation by thermoelectric imaging.
Figure 5: Spectroscopic measurements of the thermoelectric voltage from various graphene samples as a function of applied temperature difference.

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Acknowledgements

We thank Y. Kuk for helpful comments. W. Kim thanks H-K. Lee and B-G. Park for their support in the experiments at Pohang Light Source II. This work was supported by the Converging Research Center Program of MEST (2012K001307) and the MEST-US Air Force Cooperation Program of NRF/MEST (2010-00303). The work at KAIST was supported by the WCU (R31-2008-000-10071-0) and NRF (2012-046191) programmes of MEST.

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Contributions

S.C., S.D.K. and H-K.L. performed the experiments, collected and analysed the data, and prepared the manuscript. W.K., I.K., T.Z. and J.A.S. prepared and characterized the samples. E-S.L., S-J.W., K-J.K. and Y-H.K. conducted the calculations. H-D.K. and I.K. carried out the ARPES measurements. H-K.L. and Y-H.K. administrated the research. H-K.L., Y-H.K. and J.A.S. edited the manuscript.

Corresponding authors

Correspondence to Yong-Hyun Kim or Ho-Ki Lyeo.

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The authors declare no competing financial interests.

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Cho, S., Kang, S., Kim, W. et al. Thermoelectric imaging of structural disorder in epitaxial graphene. Nature Mater 12, 913–918 (2013). https://doi.org/10.1038/nmat3708

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