`Crop Circles’ Appear in Nanotubes

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‘Crop Circles’ Appear in Nanotubes

The Rice University team of nanotube researchers has regularly observed
mysterious circular formations of single-walled carbon nanotubes in each
nanotube batch they create. They could be coils that circled around as the
nanotube grew, they thought, but they couldn’t see any overlap or step that
would come from the start or the end of the coil.

The researchers quickly dubbed them “crop circles” to reflect their
skepticism that what they were seeing in their microscope images were actually
seamless circular tubes, known as tori. A torus is a doughnutshaped figure or
object.

“We are now convinced some of them are perfect `doughnuts’,” says Daniel
Colbert, Welch Postdoctoral Fellow and co-author of a paper to appear in the
Feb. 27 issue of Nature describing the “crop circles.” “In those with
thicknesses that are extremely small, we see no evidence of any step along the
edge, indicating that these nanotubes are not coils, but perfectly seamless
tori.”

The group can find the doughnut-shaped nanotubes on a regular basis, but
Colbert says they exist in relatively low abundance.

Because nanotubes conduct electricity, the doughnut-shaped nanotubes are of
interest in studying basic fundamental issues of electron transport. This is the
first time scientists have had a metallic loop of wire just 300-500 nanometers
in diameter. This discovery gives scientists the opportunity to study how
electrons move in loops on the nanometer scale, and to understand the physics of
nanoscale conductivity. The nanoscale “crop circles” could someday prove to help
in designing electronic nano-machines.

Nanotubes, which look like rolled up chicken wire, are created when a laser
condenses carbon. In addition to conducting electricity, they have a diameter
about 100,000 times smaller than a human hair and are predicted to be 100 times
stronger than steel.

Authors on the Nature paper, titled “Fullerene Crop Circles,” are: Jie Liu,
Hongjie Dai, Jason Hafner, Daniel Colbert and Richard Smalley, all of Rice
University and Rice’s Center for Nanoscale Science and Technology.

Contact: Daniel Colbert, Welch Postdoctoral Fellow, at (713) 527-4688, or by
E-mail at colbert@rice.edu; or Lia Unrau,
science editor, at (713) 831-4793, or unrau@rice.edu. To view an on-line copy of the
paper and images go to: http://cnst.rice.edu/crop.html. For
more information about nanoscale science at Rice go to: http://cnst.rice.edu.

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