New Ccvd Generation and Characterization of Single-walled Carbon Nanotubes

Bulk amount of single-walled carbon nanotubes (SWNTs) have been generated by laser-oven or arc-discharge techniques, and recently by catalytic chemical vapor deposition (CCVD) technique. CCVD technique is being intensively developed for the possibility of larger-scale production of high quality SWNTs at a low cost. We have demonstrated the high-quality generation of SWNTs by utilizing gas phase alcohols (methanol and ethanol) over iron and cobalt catalytic metal particles supported with zeolite. Compared with conventional CCVD techniques, using hydrocarbons or carbon monoxide over metal catalysts, our products were much purer at low reaction temperature. The product was observed by scanning electron microscope (SEM), transmission electron microscope (TEM) and analyzed by Raman spectroscopy. Figure A-1 shows SWNTs generated from ethanol at 800°C. There were many bundles of SWNTs tangling from the zeolite surface and bundles were made of a few hundred high quality (highly graphitized) SWNTs without any by-products (amorphous carbons, multi-walled carbon nanotubes (MWNTs) and nanoparticles). Raman spectra revealed that tube diameter decreased with lower temperature, and depended on gas flow rate. The relatively low temperature generation was possible with the minimum temperature of about 550°C with methanol. It seems that hydroxyl radicals, which come from reacting alcohol on catalytic metal particles, remove carbon atoms with a dangling bond, which are the obstacles of high-purity SWNTs. This alcohol CCVD (ACCVD) technique would promote the realization of SWNTs in application devices, and promise the direct growth of SWNTs on conventional semiconductor devices already pattered with aluminum. In order to create nanotube devices, we tried to generate SWNTs on a silicon wafer. Very small amount of Fe/Co supported with zeolite was located on a silicon wafer, and SWNTs were generated by ACCVD technique from ethanol at 900°C (Fig. A-2). The bundles of SWNTs were growing from the surface of zeolite particles and running on a silicon wafer, because of van der Waals attraction. This is the demonstration of the first step to grow SWNTs on patterned silicon surface.