Synthesis, structure, and electronic properties of single-walled carbon nanotubes

Single-walled nanotubes are of great scientific interest because of the remarkable dependence their electronic properties have on their structure. Most efforts in synthesis are therefore directed at gaining control over the structure of the nanotubes, and also at scaling up the production volume to industrial levels. Pure materials with uniform properties (e.g. a single chirality) are the ultimate goal, and synthesis appears more promising than post-processing or separation techniques because of the small size and high aspect ratio of nanotubes.; Pulsed laser vaporization synthesis (PLV), while incapable of producing large amounts of material, affords a high degree of control over SWNT growth conditions. In this work we have systematically studied the structure and bulk electronic properties of SWNTs produced under a variety of conditions and with a range of catalyst compositions. RhPd catalyst combinations were given special attention because they are known to generate smaller nanotubes than more commonly used NiCo alloys, and because we have found that they can produce materials containing a larger fraction of metallic nanotubes. Transmission electron microscopy was used to investigate changes in the composition, morphology, and SWNT yield of the carbon materials as the catalyst composition was changed.; The diameter distributions of the SWNTs in the materials were characterized mainly by resonance Raman spectroscopy. Nanotubes made with RhPd catalyst were determined to grow in a range of sizes from about 0.9 nm to 1.7 nm. Some degree of control over the diameter of the tubes was achieved using the RhPd catalyst system alone, but with a broad overlap in the size distributions from sample to sample. Nuclear magnetic resonance spectroscopy revealed that in two of the samples the percentage of metallic nanotubes was enhanced to 87%, compared with 33% for NiCo-catalyzed samples, a value consistent with a random distribution of chiralities. While the reason for this enhancement and the exact role of the catalyst in SWNT growth is still not fully understood, the result is promising and shows that the bulk electronic properties of SWNT materials depend on the selection of the catalyst.