http://www.physorg.com/news98713032.html

Nanoscale pasta: Toward nanoscale electronics

Transmission electron microscope micrograph of a singly wound, coiled carbon
nanofiber synthesized through thermal chemical vapor deposition at high In
concentration (In/Fe ratio > 3). Credit: UCSD / Prab Bandaru

Pasta tastes like pasta - with or without a spiral. But when you jump to the
nanoscale, everything changes: carbon nanotubes and nanofibers that look
like nanoscale spiral pasta have completely different electronic properties
than their non-spiraling cousins. Engineers at UC San Diego, and Clemson
University are studying these differences in the hopes of creating new kinds
of components for nanoscale electronics.

"We are looking at spiraling, bent and helical carbon nanotubes from the
point of view of new functionality. Can we get something totally different
from these nonlinear nanotubes?" asked Prab School of Engineering.

For example, spiral shaped nanotubes could turn out to be important for new
kinds of nanoscale switching and memory storage devices.

      A mat of nanocoils. Scale bar = 2 micrometers. Credit: UCSD / Prab
Bandaru
Recently, Bandaru won a National Science Foundation CAREER award for the
study of nonlinear nanotubes. Bandaru's award carries with it a 5-year,
$400,000 grant to support research aimed at developing Bandaru, a mechanical
and aerospace engineering professor at the UC San Diego Jacobs new types of
nanoelectronic components including electrical switches, logic elements,
frequency mixers and nanoscale inductors. Such devices could some day
outperform conventional silicon technologies on a number of levels, such as
power consumption, radiation hardness, and heat dissipation.

Bandaru collaborates with Apparao Rao, of Clemson University, on the
controlled synthesis of carbon nanotubes with a variety of shapes, including
Y-junctions and nanohelices, through chemical vapor deposition processes.
Once they are grown, transmission electron microscopy is used to perform
structural analyses of the nonlinear nanotubes. The engineers are also
investigating nanotube growth mechanisms, defects, nanoscale electrical
conduction mechanisms and device modeling. In addition, they are exploring
both the layout of electrical and optoelectronic circuits, and the limits of
device operation through high frequency measurements.

"Because nanotubes are so small, you need to work at the atomic level to
understand and manipulate them," explained Bandaru. The presence or absence
of single carbon atoms at strategic locations within nanotubes determines
whether they have a linear or spiral shape.

Work on nonlinear nanowires is already well underway at UCSD and around the
world. Bandaru, for example, is the first author on a paper recently
published in the Journal of Applied Physics that outlines a mechanism for
how carbon nanotubes and nanofibers grow. In particular, the model predicts
conditions under which coiling will happen.

"Now that we know the exact conditions under which the helical
nanostructures grow, we can exert greater control over the electronic and
other properties of nonlinear nanotubes," said Bandaru.

Exactly where, when and how linear and nonlinear nanotubes will make the
leap from the laboratory to the real world is still unclear. Scientists have
more to learn about their basic properties, about how to control their
growth, and about how to integrate them into devices.

In August 2005, Bandaru made headlines around the world when his work on
Y-shaped nanotubes appeared in the journal Nature Materials. Bandaru and
colleagues at UCSD's Jacobs School and Clemson University demonstrated that
Y-shaped nanotubes can behave as electronic switches similar to conventional
transistors, which are the workhorses of modern microprocessors, digital
memory, and application-specific integrated circuits.

Nanotubes, of course, are not the only tiny spiraling structures. DNA and
proteins also have helical structures. "It's gratifying to encounter
connections at the nanoscale between biological structures and helices and
coils synthesized via chemical vapor deposition," said Bandaru. "Our future
work might improve our understanding of why helices abound in nature."

Reference: P.R. Bandaru et al, Journal of Applied Physics, vol. 101, no. 9,
p 094307, 2007

Source: University of California - San Diego
-- 

Ken

"Buddhism elucidates why we are sentient."
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