Single-walled Carbon Nanotube Generation by Laser-heated ACCVD Method

Abstract

Single-walled carbon nanotubes (SWNTs) were synthesized by the laser-heated ACCVD method on the sample stage of an environmental AFM with Raman scattering measurement capabilities. Fe/Co or Co/Mo metal particles, which were supported on zeolite particles or silicon substrates, were used as catalyst, and ethanol vapor was used as the carbon source. The catalysts on the AFM sample stage were heated (to about 800°C) in ethanol vapor (0.01∼1 Torr) by Ar-ion laser irradiation, and SWNTs grew from the catalyst particles. Though this laser-heated ACCVD method was simple, Raman scattering spectra, AFM images, and SEM images showed that high-quality SWNTs were generated. By using the laser-heated ACCVD method, in-situ Raman scattering, which was caused by the heating laser irradiation, was measured during the entire CVD process. The G-band from SWNTs and the silicon peak appeared in in-situ Raman scattering spectra. The intensity of the G-band showed the growth of SWNTs, and the temperature dependence of the Raman shift of the silicon peak was used to determine the sample temperature. In-situ Raman scattering elucidated the lifetime of the catalyst and the existence of an incubation time before the onset of SWNT growth. SWNTs started to grow rapidly after the incubation time and the growth rate gradually decreased. The incubation time was strongly dependent on the pressure of the ethanol gas.