Synthesis of single-walled carbon nanotubes (C-SWNTs) with a plasma torch: a parametric study

In this study, we examine, in detail, the synthesis of single wall carbon nanotubes (C-SWNTs) with a plasma torch, using molecular sources for both carbon and catalyst (typically a carbon-containing gas such as ethylene and ferrocene for the metal catalyst). A comparison of the results obtained by Raman spectroscopy, using two different excitation wavelengths, permitted us to evaluate the importance of certain experimental parameters affecting the quality of the samples; these include the growth temperature of the nanotubes, and the temperature gradient between the flame and the oven. We have found that our method provides results that are qualitatively similar to those obtained using arc and laser techniques: C-SWNTs mixed with catalyst nanoparticles and amorphous carbon. Although the yields of C-SWNTs in the experiments reported here are somewhat lower than other approaches, our method avoids the inconveniences related to the solid phase of the initial material. Observations from scanning electron micrographs (SEM) and transmission electron micrographs (TEM) suggest that the mechanisms involved in the synthesis of the C-SWNTs by our plasma torch are similar to these latter techniques. An industrial-scale process based on a plasma torch could produce large amounts of C-SWNTs with good efficiency, since the present set-up produces continuously 1.5 g/h of deposit while using only 1 kW of power.