Discussion of important factors in deposition of carbon nanotubes by atmospheric pressure microwave plasma torch

Deposition of carbon nanotubes in microwave plasma torch at atmospheric pressure is discussed in terms of factors influencing the deposition uniformity and amorphous carbon overlayer formation. The depositions were carried out on silicon substrates with a thin iron catalyst layer from the mixture of argon, methane and hydrogen. Samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Substrate temperature gradients and a size distribution of catalytic particles were main reasons for a deposit non-uniformity. The uniformity was improved by a substrate heating in Ar/H2 discharge before the deposition. The catalyst poisoning with a subsequent amorphous carbon deposition was responsible for the formation of amorphous carbon overlayer containing catalytic particles. Shorter deposition time and optimization of carbon feedstock dilution in hydrogen were suggested for a minimization of this effect.