AVS 47th International Symposium
    Nanotubes - Science and Applications Tuesday Sessions
       Session NM+NS-TuM

Paper NM+NS-TuM6
Time-Resolved Diagnostic Investigations of Carbon Nanotube Synthesis

Tuesday, October 3, 2000, 10:00 am, Room 309

Session: Carbon Nanotubes: Synthesis
Presenter: D.B. Geohegan, Oak Ridge National Laboratory
Authors: D.B. Geohegan, Oak Ridge National Laboratory
A.A. Puretzky, Oak Ridge National Laboratory
X. Fan, Oak Ridge National Laboratory
M.A. Guillorn, Oak Ridge National Laboratory
D.C. Joy, Oak Ridge National Laboratory
M.L. Simpson, Oak Ridge National Laboratory
V.I. Merkulov, Oak Ridge National Laboratory
S.J. Pennycook, Oak Ridge National Laboratory
Correspondent: Click to Email
Time-resolved imaging and spectroscopy measurements are applied in conjunction with ex situ TEM and FESEM investigations to understand the growth rate and mechanisms of carbon nanotube growth during laser vaporization synthesis inside a hot oven. Condensation times of atomic and molecular species in the plume are estimated using population densities of ground state species as measured by laser-induced fluorescence. Rayleigh scattering, induced blackbody emission, and real-time video techniques are used to measure the dynamics and annealing time of these condensed aggregates of clusters, nanoparticles, and nanotubes as they propagate inside the oven. By varying the growth time with these diagnostics, we have explored the rate and mechanism of single-wall carbon nanotube growth by laser vaporization through the use of high-resolution transmission electron microscopy and field emission scanning electron microscopy of deposits collected for various growth times. Z-contrast STEM combined with EELS is used to investigate the effects of size and composition of metal catalyst nanoparticles through the ability to compositionally profile individual catalyst nanoparticles. FESEM imaging in bright and backscatter modes is also used to provide a three-dimensional perspective of nanotube growth. We conclude that nanotube growth during the laser vaporization process occurs over seconds of time by the condensed phase conversion of nanoparticle feedstock by the metal catalyst nanoparticles. Ex situ annealing experiments of incompletely-converted, short nanotube 'seeds' are described which show that nanotube growth can occur outside the hot oven, supporting the condensed phase conversion growth mechanism. The possibility of varying the growth conditions to enable economically viable scale-up of nanotubes by this technique will be discussed. Research sponsored by the Laboratory Directed Research and Development program at Oak Ridge National Laboratory.