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Doping effect multiplying the conductivity of carbon nanotube fibers by a factor of 7

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Doping effect on a double wall carbon nanotubes fiber

When double-wall carbon nanotubes are combined with iodine and chlorosulfonic acid, the charge transfer increases the conductivity by a factor of 7. The doping species move the Fermi level up to -1.1 eV while not changing the average electronic mean free path at 30 nm. Two strategies are possible to obtain high electrical conductivity values in carbon nanotube (CNT) fibers,: (1) increasing the electronic mean free path and (2) increasing the number of electronic conduction channels in each NTC by moving the Fermi level through charge transfer (determined by Raman spectroscopy). Chlorosulfonic acid (CSA) is a true solvent of CNT. If, during CNT fiber synthesis, a part of CSA remains in the material, a charge transfer thus occurs and leads to an shift of the Fermi level of 0.7 eV. The consequence is an increase of the conductivity by a factor of 5 compared to a system composed of CNT only. Similar properties can be obtained in pure CNT fiber impregnate with iodine. In that case, the conductivity gain is a slightly larger, approaching factor of 7, and the Fermi level shift is 1.1 eV.

Collaboration with J. Kono and M. Pasquali, Rice University and LPCNO with I Gerber