Investigation of catalytic properties of Al2O3 particles in the growth of single-walled carbon nanotubes.

We systematically investigate the catalytic properties of Al2O3 particles in the growth of carbon nanotubes (CNTs) in chemical vapor deposition (CVD). Compared with the conventional metal catalysts, the particle size of Al2O3 catalyst has no influence on the number of nanotube walls because only single-walled carbon nanotubes (SWCNTs) are produced. Interestingly, one large Al2O3 particle can usually nucleate several SWCNTs. However, statistical analysis reveals that the average growth rate of SWCNTs from Al2O3 catalyst is about 200 nm/min, which is much lower than that of CNTs grown from Fe catalyst under the same conditions. Additionally, a low gas pressure is found to be important for the growth of SWCNTs from Al2O3 catalyst. These results reflect that Al2O3 catalyst has different catalytic properties from the conventional metal catalysts, which will be helpful for the elucidation of the nanotube growth mechanism.