A Revolution in Energy Transmission

‘Armchair quantum wire’ (AQW) is the name for a weave of metallic nanotubes that
can carry electricity with negligible losses, even over long distances. “It will be an ideal
replacement for the nation’s copper-based grid, which leaks electricity at an estimated 5
percent per 100 miles of transmission” said Rice chemist Andrew R. Barron, author of a
paper published online by the American Chemical Society journal Nano Letters.

“A prime technical hurdle in the development of this ‘miracle’ cable,” Barron
continued, “is the manufacture of massive amounts of metallic single-walled carbon
nanotubes, dubbed armchairs for their unique shape. Armchairs are best for carrying
current, but can’t yet be made alone. They grow in batches with other kinds of nanotubes
and have to be separated out, which is a difficult process, given that a human hair is
50,000 times larger than a single nanotube!”

Barron’s lab has demonstrated a way to take small batches of individual nanotubes
and make them dramatically longer. Ideally, long armchair nanotubes could be cut, re-
seeded with catalyst and re-grown indefinitely.

The paper was written by graduate student and first author Alvin Orbaek, undergraduate
student Andrew Owens and Barron, the Charles W. Duncan Jr.-Welch Professor of
Chemistry and a professor of materials science. Amplification of nanotubes was seen
as a key step toward the practical manufacture of AQW by the late Rice professor,
nanotechnology pioneer and Nobel laureate Richard Smalley, who worked closely with
Barron and Rice chemist James Tour, the T.T. and W.F. Chao Chair in Chemistry and
others, to lay out a path for its development.

Barron charged Orbaek with the task of following the concept through when he joined
the lab five years ago. “When I first heard about Rice University, it was because of Rick
Smalley and carbon nanotubes,” said Orbaek, a native of Ireland. “He had a large global
presence with regard to nanotechnology, and that reached me. “So I was delighted to
come here and find I’d be working on nanotube growth that was related to Smalley’s
work.” Orbaek said he hasn’t strayed far from Barron’s original direction, which involved
chemically attaching an iron/cobalt catalyst to the ends of nanotubes and then fine-
tuning the temperature and environment in which amplification could occur.

“My group, with Smalley and Tour’s group, demonstrated you could do this — but in the
first demonstration, we got only one tube to grow out of hundreds or thousands,” Barron
said. Subsequent experiments raised the yield, but tube growth was minimal. In other

attempts, the catalyst would literally eat — or “etch” – the nanotubes, he said.

Refining the process has taken years, but the payoff is clear because up to 90 percent
of the nanotubes in a batch can now be amplified to significant lengths, Barron said.
The latest experiments focused on single-walled carbon nanotubes of various chiralities,
but the researchers feel the results would be as great, and probably even better, with a
batch of pristine armchairs.
The key was finding the right balance of temperatures, pressures, reaction times and
catalyst ratios to promote growth and retard etching, Barron said. While initial growth
took place at 1,000 degrees Celsius, the researchers found the amplification step
required lowering the temperature by 200 degrees, in addition to adjusting the chemistry
to maximize the yield.

“What we’re getting to is that sweet spot where most of the nanotubes grow and none of
them etch,” Barron said. Wade Adams, director of Rice’s Richard E. Smalley Institute
for Nanoscale Science and Technology and principal investigator on the AQW project,
compared the technique to making sourdough bread. “You make a little batch of pure
metallics and then amplify that tremendously to make a large amount. This is an
important increment in developing the science”.

Adams noted eight Rice professors and dozens of their students are working on aspects
of AQW. “We know how to spin nanotubes into fibers, and their properties are improving
rapidly too,” he said. “All this now has to come together in a grand program to turn
quantum wires into a product that will carry vast amounts of electricity around the world.”

Barron and his team are continuing to fine tune their process and hope that by summer’s
end they can begin amplifying armchair nanotubes with the goal of making large
quantities of pure metallics. “We’re always learning more about the mechanisms by
which nanotubes grow,” he said. Orbaek, who sees the end game as the development
of a single furnace to grow nanotubes from scratch, cap them with new catalyst, amplify
them and put out a steady stream of fiber for cables. “What we’ve achieved is the first
baby step,” he said. “But it verifies that, in the big picture, armchair quantum wire is
technically feasible.”

Orbaek said he is thrilled to play a role in achieving amplification, which Smalley
recognized as necessary to his dream of an efficient energy grid that would catalyze
solutions to many of the world’s problems. “I’d love to meet him now to say, ‘Hey, man,
you were right”. The Robert A. Welch Foundation and the Air Force Office of Scientific
Research funded the research. The Air Force Research Laboratory is primary funding
agency for the AQW project.

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