Boron-doped SWNTs for Electromagnetic Interference Shielding

SWNTs have been proposed for electromagnetic interference shielding as an additive in polymers. However, 2/3 of the SWNTs are expected to be semiconducting and only 1/3 are metallic. B-doping of graphite is known to lead to strongly p-doped material. In SWNTs, doping is therefore expected to lead to degenerately-doped semiconducting tubes and then a shielding benefit can be derived from all tubes in the sample. We find that 1-2 at{\%} B-doping is possible at 25-50 gr/hr production. The quality of the HCl-purified product has been investigated by Raman scattering (RS), optical adsorption, transmission electron microscopy and temperature programmed oxidation . RS spectra were found to exhibit sharp G,R bands and a very weak D-band component is also observed. We note that after B-doping the 2$^{nd}$ order RS cross section is enhanced, as reported previously for pulsed laser produced B-doped SWNTs by Rao et al. All band positions are very close to that observed for undoped SWNTs, indicating a reasonably good molecular structure of the B-SWNTs and consistent with the small size of atomic boron (i.e., substitutional dopant). OA show that the interband absorption peaks associated with semiconducting and metallic tubes upshift by 20-50 meV, indicating p-doping.