Scientists team up for nanotube breakthrough

Researchers at Stanford and UC Berkeley have come up with a way to grow carbon nanotubes on silicon wafers and to test the nanotubes, which could help pave the way for carbon chips.

Researchers at Stanford University and the University of California at Berkeley have come up with a way to grow carbon nanotubes on silicon wafers and to test the nanotubes--two significant steps that could help pave the way for carbon chips.

Carbon nanotubes have been touted as a miracle material that could revolutionize computers, textiles and other products because of their unusual properties. The tubes, which are made up of carbon atoms arranged in a coil that looks like a spool of chicken wire, conduct electricity better than metal, are stronger than steel and can even conduct light.

How to manufacture nanotubes--which measure about 5 nanometers (5 billionths of a meter) thick--and incorporate them into workable products, though, has always been a major challenge. Different nanotubes from the same manufacturing batches exhibit different properties. They also get produced by heating hydrocarbons such as methane in environments that can exceed 800 degrees Celsius.

Organizing these tiny structures into circuit arrays has been a problem that has occupied researchers at IBM Research and other laboratories.

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Some researchers have performed work showing that the tubes can be arranged by applying magnetic or electrical fields. Growing them directly on silicon has been proposed as a solution, but this is the first project in which researchers accomplished that, according to scientists at Stanford and UC Berkeley.

Chips made of nanotubes are still years away, if they ever emerge, but the universities' results bring the possibility slightly closer to becoming reality.

"We first envisioned a patterned growth of carbon nanotubes on silicon wafers five years ago, but it wasn't clear at that time whether that approach would work as an integrated nanotube-silicon hybrid circuit," Hongjie Dai, an associate professor of chemistry at Stanford and one of the co-leaders of the project, said in a prepared statement.

In the Berkeley-Stanford project, researchers created a chip, called the random access nanotube test (RANT) chip, which served as a substrate for growing the tubes and also testing them. To withstand the high temperatures, the silicon transistors on the RANT were connected with molybdenum rather than copper or aluminum, which is used on ordinary chips.

Once in place, the thousands of tubes on the RANT were tested by sending signals to them. If they flipped on and off, the tubes were deemed semiconductors. If they didn't flip off, the tubes were deemed metallic.

In a final chip, the metallic tubes would be rendered inert, because they couldn't be controlled by electrical impulses. Controlling how and when transistors flip on and off is how chips work.

Stanford's Dai specializes in issues surrounding the carbon nanotubes, while the Berkeley researchers mostly worked on developing the RANT.

The research results are detailed in the January 2004 issue of Nano Letters, a publication of the American Chemical Society.

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