Helical carbon nanotubes: catalytic particle size-dependent growth and magnetic properties.

The exact knowledge of helical carbon nanotube (HCNT) growth mechanism has not yet been completely clarified, and effective synthesis of high-purity helical carbon nanotubes in high yield still remains a tremendous challenge. In this study, HCNTs were synthesized via a catalytic chemical vapor deposition method using Fe nanoparticles as catalysts. We performed systematic experiments to investigate the specific effect of catalytic particle size (CPS) on the selective growth of HCNTs, such as on the morphology, yield, mobility of carbon atoms, and HCNT purity of carbon products. Our study showed that the CPS plays a key role in the selectivity to HCNTs, yield, and morphology of the carbon products, and a small catalytic particle is favorable to HCNT formation. We hope that this result may give a beneficial suggestion to obtain highly pure HCNTs. A CPS-dependent growth mechanism for HCNTs was finally proposed. Magnetic measurements demonstrated that the HCNTs are ferromagnetic properties and show high magnetization at room temperature.

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