Assistance of A-plane sapphire substrate to the growth of single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWCNTs) were synthesized on A-plane sapphire and SiO2/Si substrates by thermal chemical vapor deposition (CVD) of methane at a temperature of 800 °C. The yield of SWCNTs on A-plane sapphire surface was always found to be much higher than that on silica surface after the same CVD process. A-plane sapphire substrate was discovered to remarkably catalyze the decomposition of methane at 900 °C and was believed to serve as an assistant catalyst to the pyrolysis of methane during the growth of SWCNTs at 800 °C. The higher yield of SWCNTs on A-plane sapphire surface could be attributed to a higher concentration of active carbon species around catalysts on the A-plane sapphire substrate than that on the silica surface due to the enhancement of methane decomposition achieved by the assistant catalysis of A-plane sapphire. However, the assistant catalysis of A-plane sapphire would provide too much carbon species on the surface and prohibit the growth of SWCNTs at 900 °C.