Carbon Nanotubes Grown by RF Heating and Their Morphological and Structural Properties

Multiwall and single-wall carbon nanotubes were synthesized on Fe-Co/CaCO3 and a Fe-Co/MgO catalyst system, respectively, by using two different catalytic chemical vapor deposition methods, external furnace (EF) heating and radio frequency (RF) excitation. The carbon nanotubes synthesized with radio frequency excitation have a smaller outer diameter, fewer layers (smaller outer/inner diameter ratio), and better crystalline properties than the nanotubes grown with external furnace heating. The radio frequency process was found to be responsible for a faster growth rate of the carbon nanotubes over longer periods of time due to a higher localized heating. These findings can be explained by the skin currents induced in the metallic catalytic clusters, which keep the catalysts active for longer periods of time and diminish the amount of noncrystalline carbon formed in the synthesis process