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Evidence for charge transfer in doped carbon nanotube bundles from Raman scattering

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Abstract

Single-walled carbon nanotubes1 (SWNTs) are predicted to be metallic for certain diameters and pitches of the twisted graphene ribbons that make up their walls2. Chemical doping is expected to substantially increase the density of free charge carriers and thereby enhance the electrical (and thermal) conductivity. Here we use Raman spectroscopy to study the effects of exposing SWNT bundles1 to typical electron-donor (potassium, rubidium) and electron-acceptor (iodine, bromine) dopants. We find that the high-frequency tangential vibrational modes of the carbon atoms in the SWNTs shift substantially to lower (for K, Rb) or higher (for Br2) frequencies. Little change is seen for I2 doping. These shifts provide evidence for charge transfer between the dopants and the nanotubes, indicating an ionic character of the doped samples. This, together with conductivity measurements3, suggests that doping does increase the carrier concentration of the SWNT bundles.

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Figure 1: Raman scattering spectra for pristine SWNT bundles reacted with various donor and acceptor reagents.

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Acknowledgements

We thank L. Grigorian (Univ. Kentucky) for experimental assistance. We also thank K. R. Subbaswamy and E. Richter (Univ. Kentucky), and M. S. Dresselhaus and G. Dresselhaus (MIT), for discussions. This work was supported by the NSF and DDE.

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Authors and Affiliations

  1. *Department of Physics and Astronomy and Center for Applied Energy Research, University of Kentucky, Lexington, 405060055, Kentucky, USA

    A. M. Rao & P. C. Eklund

  2. †Instrument Center, Institute for Molecular Science, Myodaiji, 444, Okazaki, Japan

    Shunji Bandow

  3. Rice Quantum Institute and Departments of Chemistry and Physics, Center for Nanoscale Science and Technology, Rice University, Houston, 77251, Texas, USA

    A. Thess & R. E. Smalley

Authors
  1. A. M. Rao
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  2. P. C. Eklund
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  3. Shunji Bandow
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  4. A. Thess
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  5. R. E. Smalley
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Correspondence to P. C. Eklund.

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Rao, A., Eklund, P., Bandow, S. et al. Evidence for charge transfer in doped carbon nanotube bundles from Raman scattering. Nature 388, 257–259 (1997). https://doi.org/10.1038/40827

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  • DOI: https://doi.org/10.1038/40827

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