nested nanotubes may oscillate
Technology Research News
Oscillators are the critical component
of many timers and sensors, and, as electronic devices continue to shrink,
researchers are looking for ways to make ever smaller oscillators.
Mechanical oscillators that are hundreds of times smaller than the head
of a pin and vibrate as fast as several million times a second function
as precision timers and sensors in systems ranging from automobiles to
satellites. Oscillators are used to trigger automobile airbags by sensing
A major goal of nanotechnology is making much smaller oscillators that
vibrate billions of times a second and can therefore make more precise
Researchers from the University of California at Riverside and Tsinghua
University in China have proposed a way to do this using multiwalled carbon
nanotubes that are thousands of times narrower than a human hair. Multiwalled
carbon nanotubes are typically 10 to 50 nanometers in diameter. A nanometer
is one millionth of a millimeter.
The atomic forces that hold nested sets of carbon nanotubes together cause
inner nanotubes to snap back into place after they are pulled partly out
of the outer tubes and released. The researchers calculated that if both
ends of a multiwalled nanotube were removed and the inner nanotubes partly
pulled out, they should slingshot through to extend partially out the
other side, then retract.
The slingshot action should go on for a period of time, allowing the core
nanotubes to slide back and forth faster than one billion times per second,
said Qing Jiang, a professor of mechanical engineering at the University
of California at Riverside.
The oscillator is not a microscopic perpetual motion machine, however.
The oscillation produces lateral vibrations in the carbon atoms of both
the inner and outer nanotubes, said Jiang's colleague, Quanshui Zheng,
a professor of engineering mechanics at Tsinghua University in China.
"Such vibration will induce... energy dissipation. Therefore, the oscillating
cannot be endless. To maintain a constant oscillation requires energy
input," he said.
Imperfections in the nanotubes could interfere with the action of the
oscillator, though any effect is probably too small to be detected by
even the most sensitive instruments available, said Jiang.
The key to the oscillator is the interplay between the atomic forces that
hold the tubes together and the kinetic energy imparted to the inner tubes
when they are set in motion. The Van der Waals force is the sum of the
attractive and repulsive forces between atoms. It draws atoms together,
but only to a point, also keeping them from coming into contact with each
other. This makes the sliding action of devices as small as nanotubes
According to the researchers' calculations, when the inner nanotubes are
fully extended, their kinetic energy is at a minimum and the Van der Waals
force is at a maximum, which will cause the inner tubes to slide back
inside the outer tubes. When the inner tubes slide back inside, the Van
der Waals force is at a minimum and the kinetic energy is at a maximum,
causing them to continue through to the other end.
The researchers calculate that a 100-nanometer-long, 4-nanometer-diameter
set of inner nanotubes pulled out one quarter of their length should oscillate
at about 1.39 gigahertz, or 1,390,000,000 times a second.
The two main challenges to implementing the researchers' proposed oscillator
are finding a method to set the nanotubes in motion, and connecting the
nanotubes to devices in order to use that motion, said Jiang.
"The [researchers] have proposed an imaginative geometry for a nano-mechanical
oscillator," said Vincent Crespi, an associate professor of physics at
Pennsylvania State University. However, it will pose "rigorous challenges"
for anyone attempting to build and test it experimentally, he said.
The researchers' next steps are to test their proposal experimentally
and explore applications for the oscillator. Nanotube oscillators could
be made practical in two to five years, said Jiang.
The researchers published their research in the January 28, 2002 issue
of the journal Physical Review Letters. The research was funded by the
Chinese National Science Foundation, Tsinghua University, the Office of
Naval Research and the University of California.
Timeline: 2-5 years
Funding: Government; University
TRN Categories: Nanotechnology
Story Type: News
Related Elements: Technical paper, "Multiwalled Carbon Nanotubes
as Gigahertz Oscillators," Physical Review Letters, January 28, 2002
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