High-Quality Double-Walled Carbon Nanotubes Grown by a Cold-Walled Radio Frequency Chemical Vapor Deposition Process

Abstract

High-quality double-walled carbon nanotubes were synthesized by radio frequency (cold-walled) catalytic chemical vapor deposition from methane on a novel Fe-Mo/MgO catalyst obtained by coprecipitation. Transmission electron microscopy observations provided compelling evidence for the formation of double-walled carbon nanotubes, while the Raman results supported the overall quality of the samples and showed clearly defined radial breathing mode signals corresponding to tubes with diameters ranging between 0.72 and 2.42 nm. The second-order Raman (2D) band was found to be composed of two overlapping peaks corresponding to the inner and outer nanotubes. Thermogravimetric analysis showed a 95% purity for the as-grown material corresponding solely to nanotubes. It was found that inductive heating by a radio frequency source considerably suppressed the deposition of amorphous carbon, leading to very pure samples suitable for further investigations.