Characterization of Carbon Nanotubes Deposited in Microwave Torch at Atmospheric Pressure

Abstract

Carbon nanotubes (CNTs) were prepared in microwave plasma torch at atmospheric pressure on the Si/SiO2 substrates with iron catalytic layer from the mixture of CH4/H2/Ar. The pretreatment phase for production of Fe nanoparticles was an integral part of the deposition. It took only few seconds and the substrate temperature reached 1 020–1 170 K. The stable temperature of the deposition was 870–950 K. Due to a spatial non-uniformity of the discharge, the prepared samples exhibited several different regions of CNTs. A blackish transition region close to the iron margins contained thin CNTs with the average diameter below 18 nm and much larger Fe particles. Most of the black deposit was a continuous film of straight standing CNTs with an average diameter of 38 nm. Iron particles of the approximately the same size were found at the nanotube tips. HRTEM showed the presence of triple-walled nanotubes with outer diameter below 5 nm. Raman spectra in the low frequency region consisted of several weak peaks assigned to RBM of thin MWNTs whereas first-order Raman peaks in the high frequency region were attributed to D, G, and D′ bands.