Control of diameter distribution of single-walled carbon nanotubes using the zeolite-CCVD method at atmospheric pressure

Single-walled carbon nanotubes (SWCNTs) have been synthesized on zeolite powder with Fe/Co catalysts by a catalytic chemical alcohol-vapor deposition (CCAVD). We have first used a cold wall reactor at the atmospheric pressure, the system having been modified for the zeolite-CCAVD specifications by the use of radio-frequency heating. The G/D ratio (∼25), estimated by analysis of Raman spectroscopy, obtained here is equivalent to that by the conventional CCAVD method under reduced pressure, indicating the high purity of the present specimen. The estimated diameter distributions of the SWCNTs obtained at synthesis temperatures of 900, 1000 °C and constant ethanol temperature of 0 °C are 0.9-1.8 and 1.2-2.2 nm, respectively, whereas that of synthesized at synthesis temperature of 900 °C and ethanol temperatures of 40 °C ranges form 0.8 to 1.4 nm. The diameter distribution shifts towards larger diameters as the synthesis temperature is increased and the carbon supply rate (ethanol temperature) decreases, from which we suggest a selective growth model due to a competition between deposition and etching of carbon atoms.