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Ultrahard carbon film from epitaxial two-layer graphene

An Author Correction to this article was published on 21 May 2018

This article has been updated


Atomically thin graphene exhibits fascinating mechanical properties, although its hardness and transverse stiffness are inferior to those of diamond. So far, there has been no practical demonstration of the transformation of multilayer graphene into diamond-like ultrahard structures. Here we show that at room temperature and after nano-indentation, two-layer graphene on SiC(0001) exhibits a transverse stiffness and hardness comparable to diamond, is resistant to perforation with a diamond indenter and shows a reversible drop in electrical conductivity upon indentation. Density functional theory calculations suggest that, upon compression, the two-layer graphene film transforms into a diamond-like film, producing both elastic deformations and sp2 to sp3 chemical changes. Experiments and calculations show that this reversible phase change is not observed for a single buffer layer on SiC or graphene films thicker than three to five layers. Indeed, calculations show that whereas in two-layer graphene layer-stacking configuration controls the conformation of the diamond-like film, in a multilayer film it hinders the phase transformation.

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Fig. 1: TEM images and experimental stiffness curves for multilayer epitaxial graphene and buffer layer on SiC.
Fig. 2: Experimental stiffness measurements in 2-L graphene.
Fig. 3: Microhardness and C-AFM measurements.
Fig. 4: DFT and indentation calculations.

Change history

  • 21 May 2018

    In the version of this Article originally published, the second affiliation for Walter A. de Heer had not been included; it should be ‘TICNN, Tianjin University, Tianjin, China’. This has now been added and the numbering of subsequent affiliations amended accordingly in all versions of the Article.


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The authors acknowledge support from the Office of Basic Energy Sciences of the US Department of Energy (grant no. DE-SC0016204). E.T. thanks the European ERC (320796 MODPHYSFRICT). The authors acknowledge support from the CUNY High Performance Computing Center and the Extreme Science and Engineering Discovery Environment (XSEDE). The authors thank T. Wang for support with TEM measurements, C. Dean for insights on the C-AFM measurements, and M. Moseler for discussions on indentation simulations.

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Authors and Affiliations



Y.G. and F.C. performed nanomechanics experiments and data analysis. T.C. carried out DFT calculations and indentation simulations. E.R. conceived and designed the experiments and analysed the data. A.B. and E.T. analysed the experimental data and delineated the modelling strategy. C.B. and W.A.d.H. synthesized the EG samples. All authors contributed to writing the manuscript.

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Correspondence to Elisa Riedo or Angelo Bongiorno.

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The authors declare no competing financial interests.

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Supplementary Figures 1–17, Supplementary references

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Gao, Y., Cao, T., Cellini, F. et al. Ultrahard carbon film from epitaxial two-layer graphene. Nature Nanotech 13, 133–138 (2018).

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