CVD catalytic growth of single-walled carbon nanotubes with a selective diameter distribution

Thermal pyrolysis chemical vapor deposition growth of single-walled carbon nanotubes (SWNTs) was demonstrated by using catalytic pads of nickel (3∼4 nm) and SiO2 (100 nm) deposited by electron-beam evaporation in sequence on the thermal silicon oxide substrate. The diameters of SWNTs on the samples with upper SiO2 layer of different deposition rates were characterized by atomic force microscopy (AFM) and micro-Raman spectroscopy. It was observed that the average diameter and density of SWNTs increased as the deposition rate of upper SiO2 layer increased. The differences of the SWNTs diameter distribution were attributed to the differences in the curvature of the SiO2 porous structure deposited with different deposition rates. The high-resolution transmission electron micrographs and the corresponding diffractogram showed that SWNTs with diameter as low as 0.51 nm could be found and the AFM measurements revealed that a high percentage (∼ 70%) of SWNTs of diameters lower than 1.0 nm was achieved by upper SiO2 layer deposition rate of 0.5 Å/s, whereas bundles of SWNTs were found with higher SiO2 deposition rates.