Simultaneous Observation of Single-Walled Carbon Nanotubes and Catalyst Particles on SiO2 Substrate by Transmission Electron Microscopy

Abstract

Single-walled carbon nanotubes (SWNTs) were grown by catalytic chemical vapor deposition on SiO2 substrates. By thinning the substrate before growth, the morphologies of the SWNTs and their seed catalyst particles were simultaneously observed in the as-grown state by plan-view transmission electron microscopy (TEM). Analysis over a wide area of the substrate showed that the diameters of the SWNTs d and those of the catalyst particles D had different distributions. The catalytic activity was size-dependent: fine particles (D\\lesssim4 nm) yielded the same diameter SWNTs (d∼D), and intermediate sizes (∼4 < D\\lesssim6 nm) yielded finer tubes (d < D), while larger particles (D\\gtrsim6 nm) had no catalytic activity. We also found that the small catalyst particles with D of less than 5 nm that appeared during the growth process by chemical reactions with the carbon source mainly contributed to the growth of SWNTs.