December 19, 2003 8:22 AM PST

Nanotubes break semiconducting record

Semiconducting carbon nanotubes are significantly better at conducting electricity at room temperature than any other known material, according to recent tests at the University of Maryland.

The findings are the latest evidence that nanotubes could form the basis for future generations of powerful electronics.

The electrical conductivity properties of nanotubes--a synthetic material with the potential to revolutionize industries from plastics to computer chips--have been well known for some time. But the results from the university's Center for Superconductivity Research indicate that carbon nanotubes may make even better semiconductors than previously thought.

A team of researchers, led by Michael Fuhrer, head of the university's Nanoelectronics Research Group, were able to fabricate a semiconducting nanotube transistor with mobility almost 25 percent higher than any previous semiconducting material, and more than 70 times higher than the mobility of computer chip silicon, the university said. Mobility is a measurement of how well a semiconductor conducts electricity.

The previous record was measured in indium antimonide in 1955.

"This is the first measurement of the intrinsic conduction properties of semiconducting nanotubes," Fuhrer said in a statement. "It is an important step forward in efforts to develop nanotubes into the building blocks of a new generation of smaller, more powerful electronics."

The findings were published in the journal Nano Letters and publicized earlier this month.

The team said it had to use (relatively) extremely long nanotubes for the experiment, using lengths of up to 0.03 centimeters, about 100 times longer than nanotubes previously used in semiconducting experiments.

Within a decade, nanotubes could replace silicon as the transistors inside processors and memory chips. Tubes could also be used to convey light through optical fibers and, further out, to deliver medicines to specific cells inside a body or even restructure the nation's power grid.

Mass production of nanotubes, however, remains a challenge and is currently a slow and costly process. Because of this, some researchers say that silicon nanowires--solid microscopic strands of silicon--could prove to be a more practical alternative.

A carbon nanotube is essentially a sheet of carbon atoms--arranged in hexagons--that curls up in a tube. It comes in two basic varieties: a single-walled nanotube, which is a single coil of carbon hexagons; and a multiwalled version, wherein a single tube is encased in a wider tube, which itself is inside other tubes. Most of today's research is concentrated on single-walled tubes.

The tubes' properties are significant because of two factors: their size, which allows them to function as one-dimensional objects, and the intrinsic nature of carbon.

Because one-dimensional nanotubes have essentially no height or width, electrons can travel ballistically on them. That is, barring obstacles or flaws in the material, electrons don't get scattered or lost.

Matthew Broersma of ZDNet UK reported from London. CNET News.com's Michael Kanellos contributed to this report.

 

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