Synthesis and characterization of boron-doped single-wall carbon nanotubes produced by the laser vaporization technique

We present the first successful high-yield laser vaporization synthesis of high-quality boron-doped single-wall carbon nanotubes (B-SWNTs). Boron was loaded into graphite targets in the form of elemental B as well as nickel boride (NiB) and vaporized in a laser-oven apparatus in both Ar and N-2 ambients. Although targets containing elemental B produced no or low yields of SWNTs, the NiB catalyst in N-2 produced SWNT bundles comparable in quality to the best pure-carbon SWNTs produced from traditional Ni/Co catalysts. A variety of different samples were analyzed by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and nanoprobe electron energy loss spectroscopy (EELS). Boron was found to be doped substitutionally in the SWNT lattice at contents up to 1.8 at % by EELS. The C-13 NMR chemical shift of SWNT nuclei is affected by boron doping by shifting to higher frequency, as expected for p-type doping. The EELS and NMR data exclude the possibility of B and N codoping. Aspects of the growth mechanism are discussed.