Influence of the RF Excitation of the Catalyst System on the Morphology of Multiwalled Carbon Nanotubes

Multiwalled carbon nanotubes were synthesized by catalytic chemical vapor deposition using two different methods of heating. By one method, an external resistive tube furnace was used, whereas the other method involved heating with radio frequency excitation by induction coil. A comprehensive comparison was made between these two methods with regards to feed gas utilization, nanotube growth efficiency, nanotube product characterization and morphology, and the formation of amorphous carbon and gaseous byproducts. The carbon nanotubes synthesized using radio frequency excitation exhibited smaller outer diameters, fewer carbon layers, less amorphous carbon, and superior crystalline properties than those produced by external tube furnace. The radio frequency process resulted in more rapid and sustained growth rates of the nanotubes and more efficient use of the carbon source. The reason for these enhanced effects by inductive heating may be due not only to the internally produced thermodynamic heat flow characteristics but perhaps also to induced electron currents generated within the magnetic and metallic catalytic clusters due to RF.