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Conductivity enhancement in single-walled carbon nanotube bundles doped with K and Br

Abstract

Single-walled carbon nanotubes (SWNTs), prepared by metal-catalysed laser ablation of graphite, form close-packed bundles or ‘ropes;1. These rope crystallites exhibit metallic behaviour above 50K (ref. 2), and individual tubes behave as molecular wires, exhibiting quantum effects at low temperatures3,4. They offer an all-carbon host lattice that, by analogy with graphite5 and solid C60 (ref. 6), might form intercalation compounds with interesting electronic properties, such as enhanced electrical conductivity and superconductivity. Multi-walled nanotube materials have been doped with alkali metals7 and FeCl3 (ref. 8). Here we report the doping of bulk samples of SWNTs by vapour-phase reactions with bromine and potassium—a prototypical electron acceptor and donor respectively. Doping decreases the resistivity at 300K by up to a factor of 30, and enlarges the region where the temperature coefficient of resistance is positive (the signature of metallic behaviour). These results suggest that doped SWNTs represent a new family of synthetic metals.

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Figure 1: Directionally averaged resistivity (300K) of a bulk SWNT sample versus time of exposure to Br2 vapour.
Figure 2: Resistivity versus temperature for a bulk SWNT sample.
Figure 3: Resistivity versus temperature for a bulk SWNT sample.

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Acknowledgements

H.J.K. is on leave from Hallym University, South Korea. We thank M. Clement for experimental assistance. Work at Penn was supported by the Department of Energy; work at Rice was supported by the Office of Naval Research and the Robert A. Welch Foundation.

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Correspondence to J. E. Fischer.

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Lee, R., Kim, H., Fischer, J. et al. Conductivity enhancement in single-walled carbon nanotube bundles doped with K and Br. Nature 388, 255–257 (1997). https://doi.org/10.1038/40822

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