Single-walled carbon nanotubes synthesis: a direct comparison of laser ablation and carbon arc routes

Carbon arc and chemical vapor deposition are at present the most efficient methods for mass production of single-walled carbon nanotubes. However, laser ablation is renowned for high quality nanotubes with narrow diameter distributions and hence is also of great interest. The aim of this work was to compare both the carbon arc and laser ablation techniques with respect to the quality--and relative yield of the produced SWCNTs. For this comparative study we used Fe as the catalyst, which is known not to be very active in laser ablation. However, we show this is not the case when H2 is included in the reaction. The reactions for both synthesis routes were carried out in a N2-H2 (95-5% vol.) atmosphere. The same homogenous carbon rods with different iron contents, between 1 and 5 at.% were used as the carbon feedstock and catalyst supply in both synthesis routes. Additionally, two types of carbon rods containing 1 at.% Fe with different graphitization degrees were also investigated. In the arc-discharge case, the low-graphitized electrode produced a web-like product rich in SWCNTs, while the high-graphitized carbon rods yielded soot containing carbon-encapsulated iron nanocrystallites, amorphous carbon nanoparticles, and surprisingly a small fraction of SWCNTs. With laser ablation synthesis, the Fe content and the reactor temperature significantly influenced the SWCNTs yield. Carbon arc plasma diagnostics were also performed. By using optical emission and Absorption spectroscopy the plasma temperature, C2 and CN radical content in the arc zone were determined.