Smalley's `atomic wire' may aid electron microscopy
Dry nanotechnology focuses on non-biological science and engineering in the range of one nanometer, or a billionth of a meter.
About a year ago, Smalley and his associates began work on an article entitled, "Unraveling Nanotubes: Field Emission from an Atomic Wire."
The team includes Peter Norlander, an associate professor of physics, Andrew Rinzler and Dan Colbert, post-doctoral students Jason Hafner and Pavel Nikoleav, graduate students Liang Lou of Wavefunction Corporation and Song Gong Kim and David Tomanek of Michigan State University.
They began by studying the growth of carbon nanotubes, which are comprised of hollow cylinders of carbon fullerenes, more commonly known as buckyballs.
The nanotube cylinders resemble rolls of chicken wire. The tubes can have from one to 10 layers of thickness and are very strong.
The nanotubes interest scientists because of their extraordinary strength. According to Colbert, this strength comes from the special properties of carbon-to-carbon bonds as well as their relatively few defects compared to larger fibers.
The possible applications include airplane part construction and atomic probes.
The group devised a method of growing nanotubes, using a metal alloy to keep the ends of the tubes from closing.
Growth is much easier with the ragged tips since there is an open site for new atoms to bond. Carbon atoms attach themselves to the open sites, thereby lengthening the nanotubes.
Some unusual results were found when testing the field emissions of these open-tipped tubes.
Under normal conditions, when the end of a wire is heated with a laser, the voltage increases. However, the group found that the open-tipped tubes actually reached levels 200 times higher when at room temperature.
"It was such an incredible conclusion that we had be very sure we were right," Smalley said.
"We built various versions of this aparatus, we talked and walked and we screamed and shouted at each other until we finally convinced ourselves because it was one of these advances with a bizarre result."
He said that his team used an elimination strategy to reach their conclusion.
"Of course, the weakness to the Sherlock Homes strategy is that you're never quite sure that you've thought of everything. That's really one of the fundamental reasons why we can never prove anything," he said.
An atomic wire is a chain of single carbon atoms and can be 10 to 100 atoms long. It is formed when an electric current forces the atoms to unravel from the open nanotube tip, much like a sweater sleeve coming apart.
The atomic wire conducts and emits a high electrical current using low voltage at room temperature.
Rinzler said that the main impetus for the research came early on from Smalley. "Two weeks into it, [Smalley] hypothesized the atomic wire," he said.
This research could be the first step in improving electron microscopes.
However, due to the thickness of the probes used to emit electrons in the microscope, the picture is unclear.
The group suspects that by using atomic wires the energy and angular distribution for the electrons would be smaller, thus concentrating the image.
"We feel this [atomic wire] could be the ultimate field emitter," Smalley said.
In addition to the electron microscopes, atomic wires could be applied anywhere that field emitters are used, including televisions. According to Colbert, the discovery may bring about a new generation of high-resolution television, holography and lithography.
In spite of the current degree of uncertainty of future applications, the group's discovery has helped the nanotechnological community. They can now learn more about how the tubes are bonded while also enabling a greater study of one-dimensional objects.
When Smalley was asked how he felt being back on top of the science world, he said, "I didn't know I left."
-- Asst. News Editor Felisa Yang and Photography Editor Joel Hardi contributed to this story.
This item appeared in the News section of the September 22, 1995 issue.
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