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Sorting carbon nanotubes by electronic structure using density differentiation


The heterogeneity of as-synthesized single-walled carbon nanotubes (SWNTs) precludes their widespread application in electronics, optics and sensing. We report on the sorting of carbon nanotubes by diameter, bandgap and electronic type using structure-discriminating surfactants to engineer subtle differences in their buoyant densities. Using the scalable technique of density-gradient ultracentrifugation, we have isolated narrow distributions of SWNTs in which >97% are within a 0.02-nm-diameter range. Furthermore, using competing mixtures of surfactants, we have produced bulk quantities of SWNTs of predominantly a single electronic type. These materials were used to fabricate thin-film electrical devices of networked SWNTs characterized by either metallic or semiconducting behaviour.

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Figure 1: Sorting of SWNTs by diameter, bandgap and electronic type using density gradient ultracentrifugation.
Figure 2: Refinement by repeated centrifugation in density gradients.
Figure 3: Tuning the structure–density relationship for optimal separation by diameter and bandgap or electronic type (metal–semiconductor).
Figure 4: Electrical devices of semiconducting and metallic SWNTs.


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This work was supported by the US Army Telemedicine and Advanced Technology Research Center, the National Science Foundation and the Department of Energy. A National Science Foundation Graduate Student Fellowship (M.S.A.), a Natural Sciences and Engineering Research Council of Canada Postgraduate Scholarship (A.A.G.), and an Alfred P. Sloan Research Fellowship (M.C.H.) are also acknowledged. Furthermore, J. Suntivich, X. Du and M. Disabb are gratefully recognized for measurement of optical absorbance spectra (J.S., X.D.) and evaporation of Au electrodes (M.D.). We thank J. Widom and the Keck Biophysics Facility for use of their ultracentrifuges, J. Chen for providing laser-ablation-grown SWNTs, and L. Palmer and Ph. Avouris for useful discussions.

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All authors conceived and designed the experiments; M.S.A. and A.A.G. performed the experiments; J.F.H. measured and analysed the optical spectra; and all authors co-wrote the paper.

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Correspondence to Mark C. Hersam.

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The authors declare no competing financial interests.

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Arnold, M., Green, A., Hulvat, J. et al. Sorting carbon nanotubes by electronic structure using density differentiation. Nature Nanotech 1, 60–65 (2006).

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