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Nano Gems

Carbon nanotubes are sometimes described as, basically, soot. In fact, they can be found among the deposits formed when electricity arcs between two carbon electrodes. But describing nanotubes as soot is like saying diamonds are nothing more than compressed coal. Each carbon atom in a nanotube is naturally positioned in a chicken-wire lattice that wraps into a hollow pipe. This molecular perfection gives nanotubes their long list of unusual-and potentially useful-properties.

Knowledge of the carbon structure dates back to 1985, when researchers at Rice University in Houston discovered soccer-ball-shaped carbon molecules called fullerenes. Following the discovery, theoretical physicists predicted that tubular versions of this same carbon structure could exist and that such molecules would have a number of enticing properties, such as excellent electrical conductivity. Mildred Dresselhaus, a physicist at MIT, recalls calculating the likely properties of what she called carbon “nanotubules.” “We didn’t have them yet,” she says, but it was still possible to speculate on “what they might be like.”

Spurred by the growing excitement over the new form of carbon, Sumio Iijima, a physicist at NEC Research in Tsukuba, Japan, went hunting for carbon nanotubes in late 1990. Trained in electron microscopy, Iijima says he was used to “looking at all kinds of graphite and small diamonds.” Iijima also says he was “quite lucky” in being experienced in observing needlelike microscopic shapes; his PhD had been on microscopic whiskers of silver. Several months after beginning his search, Iijima hit pay dirt. “When I saw all these needles of carbon, immediately I came to the right answer,” he remembers.

What Iijima was peering at were “multiwall” nanotubes-long carbon molecules stuffed one within another like nested Russian Matryoshka dolls. In 1993, Iijima and his NEC coworkers, and another group at IBM Research in San Jose, CA, separately produced an even more exquisite version: nanotubes whose walls were only a single atom thick.

The new structures didn’t disappoint. One early research finding was that in the presence of an electric field nanotubes emit electrons from their extremely fine tips. Any number of electrically conductive materials will, when a high enough voltage is applied, spit out electrons. Nanotubes can do this at remarkably low voltages because of their extreme sharpness. So carbon nanotubes are almost perfect for building tiny, efficient electron emitters. They can direct focused electron beams at very small targets-say, a pixel of a display.
As many as two dozen electronics firms, including Samsung and Motorola, are now racing to develop flat-panel displays that use nanotubes. TV screens and the computer displays that sit on most desktops are holdovers of the vacuum-tube era. These clear and relatively cheap displays use cathode-ray tubes, in which electrically heated wires shoot electron beams onto a phosphor-coated screen, which in turn lights up. The problem is that the picture tube uses a lot of power, and it must be deep enough to allow the electron guns to project to the whole screen-hence the fat bulge in back of most TVs. In contrast, screens using an array of nanotubes can put tiny electron emitters behind each pixel and therefore can be far thinner.

At first glance, the prototype 13-centimeter screen made at the Samsung Advanced Institute of Technology in Suwon, South Korea, doesn’t look much different than any other small TV. Smiling actors flash across its face in a slickly made promo. But that similarity is exactly the point. If Samsung researchers can turn this prototype-which uses nanotubes to bombard the phosphor screen with electrons-into a TV as bright and clear as the one in your living room, they could capture the best of both display worlds: cheap as cathode-ray tubes and thin as far more expensive liquid-crystal or plasma display TVs.

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Tagged: Computing

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