Time-Resolved Observation of Carbon Nanotube Growth by Using an Environmental TEM

Abstract

We report in-situ observations of the growth of carbon nanotubes (CNTs) by using an environmental transmission electron microscope (E-TEM). E-TEM is a specially designed transmission electron microscope (TEM) with a dierential pumping system where gas can be flowed into the specimen whilst keeping a high vacuum level in the remainder of the TEM column. In order to grow CNTs, Ni nanoparticles as a catalyst were deposited on holey SiOx-TEM mesh grids by using a solution phase catalyst deposition method. Chemical vapor deposition (CVD) was carried out inside the TEM column by flowing acetylene gas ( 10 mTorr) over the Ni catalyst heated to 600 C. At a given growth condition, the CNTs grew with a serpentine morphology with the growing apex frequently returning to the substrate to become anchored at both ends. The growth durations were observed to be quite short, and the growth rate was estimated to be 0.2 mm/sec, which is relatively fast, at low C2H2 pressures of <10 mTorr. Growth was confirmed to occur at the tip where the nickel catalyst particle is located, rather than at the base of the tube, as suggested in the tip growth model. Both multi-walled CNT and single-walled CNT were synthesized simultaneously under the same reaction conditions. This suggests that the nature of the catalyst still plays an important role in determining the characteristics of the CNT even though these characteristics can be controlled by altering either the reaction temperature or pressure.