Dimensional control of multi-walled carbon nanotubes in floating-catalyst CVD synthesis

Dimensional control in CVD synthesis of MWNT’s is significant and critical to a number of different applications. This study examines the dimensional effect of a number of synthesis variables on the products of floating-catalyst CVD, including catalyst concentration in the feedstock, nanotube growth time, and deposition substrate selection. Extensive diameter surveys are performed by TEM and compared with results from thermo-gravimetric analyses to Raman spectroscopy, offering a novel dimensional analysis of nanotubes grown by FC-CVD methods. CNT diameters are inversely proportional to the catalyst concentration with weak correlation over the range examined and are directly proportional to growth time. Results are combined with prior art to develop a new theory regarding catalyst particle formation over a range of catalyst concentrations. Carbon deposition occurs in two stages, the first characterized by accelerating deposition and increases in CNT diameter and length, the second by etching of the array and carbon deposition at a constant rate. Deposition substrates interact directly with the catalysts to strongly influence the resulting nanotube diameters, based upon the mobility of the catalysts on the substrate surface.