Abstract
Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy–momentum dispersion relations which cross at the Dirac point1,2. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles3,4,5. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult6,7. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance8. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moiré patterns. However, contrary to predictions9,10, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron–hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene6, opening up Dirac point physics to more diverse experiments.
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Acknowledgements
The authors would like to thank W. Bao, Z. Zhao and C. N. Lau for providing the graphene on SiO2 samples used for the comparison with graphene on hBN. J.X., A.D. and B.J.L. were supported by US Army Research Laboratory and the US Army Research Office under contract/grant number W911NF-09-1-0333 and the National Science Foundation CAREER award DMR-0953784. P.J. was supported by the National Science Foundation under award DMR-0706319. J.S-Y., D.B. and P.J-H. were supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0001819 and by the 2009 US Office of Naval Research Multi University Research Initiative (MURI) on Graphene Advanced Terahertz Engineering (Gate) at MIT, Harvard and Boston Unversity.
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J.X. and B.J.L. performed the STM experiments for graphene on hBN. A.D. performed the STM experiments for graphene on SiO2. J.S-Y. and D.B. fabricated the devices. P.J. performed the theoretical calculations. K.W. and T.T. provided the single crystal hBN. P.J-H. and B.J.L. conceived and provided advice on the experiments. All authors participated in discussing the data and writing the manuscript.
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Xue, J., Sanchez-Yamagishi, J., Bulmash, D. et al. Scanning tunnelling microscopy and spectroscopy of ultra-flat graphene on hexagonal boron nitride. Nature Mater 10, 282–285 (2011). https://doi.org/10.1038/nmat2968
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DOI: https://doi.org/10.1038/nmat2968
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