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Journal of Electron Microscopy Advance Access published online on August 25, 2005
Journal of Electron Microscopy, doi:10.1093/jmicro/dfi037
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© The Author 2005. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org

Article

In situ observation of the growth mechanisms of carbon nanotubes under diverse reaction conditions

Renu Sharma 1*, Peter Rez 2, Michael M. J. Treacy 2, and Steven J. Stuart 3

1 Center for Solid State Science, Arizona State University, Tempe, AZ 85287-1704, USA
2 Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA
3 Department of Chemistry, Clemson University, Clemson, SC 29634, USA

* To whom correspondence should be addressed.
Renu Sharma, E-mail: renu.Sharma{at}asu.edu


  Abstract

We report in situ environmental transmission electron microscope observations of the nucleation and growth of multi-wall and single-wall carbon nanotubes formed by the catalytic decomposition of acetylene (C2H2) on Ni/SiO2 catalyst. The growth rate, structure and morphology of the carbon nanotubes formed depended upon reaction temperature and pressure. Under 20-100 mTorr of gas pressures at 480°C, serpentine-shaped or zigzag, multi-wall carbon nanotubes grew at an average rate of 35-40 nm sec-1. At pressures <10 mTorr at the same temperature, straight single-wall carbon nanotubes with nearly uniform diameters (~3.5 nm) formed at average growth rates of 6-9 nm sec-1. The growth of both straight and serpentine carbon nanotubes tends to proceed at non-uniform rates, with frequent pauses followed by growth spurts. The nanotubes frequently contained sharp bends that turned the nanotube axis by ~60° and ~120°. We conjecture that the bends are related to the change in growth direction that is dictated by the crystallographic orientation of the catalyst particle. The rotations of the nanometer-sized catalyst particle may be caused by transient melting-recrystallization events caused by local thermal variations. The nanotube attempts to follow the preferred growth direction, while simultaneously attempting to maintain a seamless 3-coordinated graphene wall. This latter condition is most easily satisfied by the introduction of pentagon-heptagon defect pairs dissociated to the opposite sides of the nanotube creating the 60° bend.

Keywords: Carbon nanotubes; chemical vapor deposition; in situ; environmental transmission electron microscope; catalyst; growth mechanisms.
Dedicated to the memory of the Late Prof. John M. Cowley.
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