Growth of Single-Walled Carbon Nanotubes from Nonmagnetic Catalysts by Plasma Chemical Vapor Deposition

Single-walled carbon nanotubes (SWNTs) are firstly grown from nonmagnetic catalysts such as Au, Pt, and Ag by plasma chemical vapor deposition (PCVD). Through the systematical investigation of the SWNT growth by thermal CVD (TCVD) and PCVD utilizing nonmagnetic and magnetic catalysts, it was revealed that an obviously opposite dependence of the SWNT yield on the H₂ concentration exists between the growth experiments with the magnetic and nonmagnetic catalysts. This unique feature is explained by the difference of adsorption efficiency of hydrocarbon materials on the surface of catalysts. Optical emission spectra were also measured during the growth of SWNTs by PCVD. It was found that the intensity ratio of CH/H_α shows a tendency similar to the intensity ratio of G- and D-band (I_G/I_D) of SWNTs as a function of H₂ concentration. This indicates the CH/H_α can be available to optimize the growth condition of SWNTs by PCVD, especially for nonmagnetic catalysts, whose catalytic activity is much more sensitive to the etching element than magnetic catalysts.