The field-effect transistors that underlie
electronics are made from semiconducting materials rather than conductors
like metals because it is possible to use an electric field to block or
allow the flow electricity in semiconductors, and thus turn the transistor
on or off.
It's difficult to make tiny semiconductor devices that conduct
efficiently, however. Metals are much more efficient at conducting electricity
but the flow of electricity through a metal is not easy to shut off because
the flow is not ordinarily sensitive to electric fields.
Researchers from the University of Illinois at Urbana-Champaign
have found a way to produce a field effect in a metallic single-wall carbon
nanotube that conducts electricity 40 times more efficiently than copper.
Carbon nanotubes are rolled-up sheets of carbon atoms that can be smaller
than a single nanometer in diameter and are either metallic or semiconducting.
A nanometer is the span of 10 hydrogen atoms.
The metal field effect transistor has the potential to consume
less energy, operate at higher frequencies, and dissipate heat more readily
than traditional semiconducting field effect transistors, according to
The researchers took advantage of the nanotubes' small size and
a special type of electric field to produce the effect. They made the
electric field highly irregular, which breaks the nanotube's molecular
symmetry, thereby changing the tube from conducting to semiconducting.
The metal transistor could be used in practical applications in
five to ten years, according to the researchers. The work appeared in
the April 19, 2004 issue of Applied Physics Letters.
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