Journal of Electron Microscopy Advance Access originally published online on August 25, 2005
Journal of Electron Microscopy 2005 54(3):231-237; doi:10.1093/jmicro/dfi037
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
In situ observation of the growth mechanisms of carbon nanotubes under diverse reaction conditions
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 and 3 Department of Chemistry, Clemson University, Clemson, SC 29634, USA
* To whom correspondence should be addressed. E-mail: renu.Sharma{at}asu.edu
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
Received 4 January 2005, accepted 21 February 2005