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Linear
arrays of nanotubes offer path to high-performance electronics
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Click
photo to enlarge |
Photo
courtesy John A. Rogers |
Scanning
electron microscope image of a pattern of aligned,
linear
single-walled carbon nanotubes formed by chemical
vapor deposition
growth on a quartz substrate. The bright horizontal
stripes
correspond to the regions of iron catalyst. |
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James
E. Kloeppel, Physical Sciences Editor
217-244-1073; kloeppel@illinois.edu
Released
3/26/2007
CHAMPAIGN, Ill. —
Despite the attractive electrical properties and physical features of
single-walled carbon nanotubes, incorporating them into scalable integrated
circuits has proven to be a challenge because of difficulties in manipulating
and positioning these molecular scale objects and in achieving sufficient
current outputs.
Now, researchers at the University of Illinois, Lehigh University and
Purdue University have developed an approach that uses dense arrays
of aligned and linear nanotubes as a thin-film semiconductor material
suitable for integration into electronic devices.
The nanotube arrays can be transferred to plastic and other unusual
substrates for applications such as flexible displays, structural health
monitors and heads-up displays. The arrays also can be used to enhance
the performance of devices built with conventional silicon-based chip
technology.
“The aligned arrays represent an important step toward large-scale
integrated nanotube electronics,” said John A. Rogers, a Founder
Professor of Materials Science and
Engineering at Illinois, and corresponding author of a paper accepted
for publication in the journal Nature Nanotechnology, and posted on
its Web site.
To create nanotube arrays, the researchers begin with a wafer of single-crystal
quartz, on which they deposit thin strips of iron nanoparticles. The
iron acts as a catalyst for the growth of carbon nanotubes by chemical
vapor deposition. As the nanotubes grow past the iron strips, they lock
onto the quartz crystal, which then aligns their growth.
 |
Click
photo to enlarge |
University
of Illinois Photo |
| John
A. Rogers, a Founder Professor of Materials Science
and Engineering, says this is the "first study
that shows properties in scalable
device configurations that approach the intrinsic
properties of the tubes themselves, as inferred from
single-tube studies." |
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The resulting linear
arrays consist of hundreds of thousands of nanotubes, each approximately
1 nanometer in diameter (a nanometer is 1 billionth of a meter),
and up to 300 microns in length (a micron is 1 millionth of a meter).
The nanotubes are spaced approximately 100 nanometers apart.
The arrays function as an effective thin-film semiconductor material
in which charge moves independently through each of the nanotubes.
In this configuration, the nanotubes can be integrated into electronic
devices in a straightforward fashion by conventional chip-processing
techniques.
A typical device incorporates approximately 1,000 nanotubes, and can
produce current outputs 1,000 times higher than those of previously
reported devices that incorporate just a single nanotube. Many devices
can be built from each array, with good device-to-device uniformity.
Detailed theoretical analysis of these unusual devices reveals many
aspects of their operation.
Using the arrays, the researchers built and tested a number of transistors
and logic gates, and compared the properties of nanotube arrays with
those of individual nanotubes.
“This is the first study that shows properties in scalable device
configurations that approach the intrinsic properties of the tubes themselves,
as inferred from single-tube studies,” said Rogers, who also is
a researcher at the university’s Beckman
Institute.
Nanotube arrays aren’t likely to replace silicon, Rogers said,
but could be added to a silicon chip and exploited for particular purposes,
such as higher speed operation, higher power capacity and linear behavior
for enhanced functionality. They can also be used in applications such
as flexible devices, for which silicon is not well suited.
“Nanotubes have shown potential in the past, but there hasn’t
been a clear path from science to technology,” said Moonsub Shim,
a professor of materials science and engineering at Illinois, and a
co-author of the paper. “Our work seeks to bridge this gap.”
With Rogers and Shim, co-authors of the paper are postdoctoral research
associate Seong Jun Kang and graduate students Coskun Kocabas and Taner
Ozel, all at Illinois; electrical and computer engineering professor
Muhammad A. Alam and graduate student Ninad Pimparkar at Purdue, and
physics professor Slava V. Rotkin at Lehigh.
The National Science Foundation and the U.S. Department of Energy funded
the work.
Editor’s note: To reach John Rogers, call
217-244-4979; e-mail: jrogers@illinois.edu.
