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  News in Brief

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  Wow! Fermilab Confirms the Tau

  Superweld

  Working Science

  People

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  Subscribe Free

















This issue...

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  Wow! Fermilab Confirms the Tau

  Superweld

  Working Science

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Argonne Process: Ultra-nanocrystalline Diamonds

Carbon-60 buckminster fullereneThe key to Argonne's approach is the use of Buckeyballs (Buckminster Fullerenes) as the source of carbon, along with a minimal amount of hydrogen. Buckeyballs, technically "carbon-60," are pure carbon, each molecule containing 60 carbon atoms arranged in a soccer-ball-like configuration.

In 1990, Gruen's team discovered that when excited properly, Buckeyballs break up into a series of "dimers"—particles consisting of exactly two carbon atoms each. It took more than two years, however, for them to learn how to use dimers as building blocks for diamond films.

"This process is revolutionary," says Gruen. "Because there's a virtual absence of hydrogen, the small diamond crystals survive. Our average crystal is so small that about a million can fit in the same space occupied by a single conventionally grown crystal. The smaller crystals make the film so smooth you don't have to polish it. We call them 'ultra-nanocrystalline' diamonds."

The process takes place in a specially designed microwave discharge chamber filled with a gaseous mixture of 1 percent carbon-60, 98 percent argon, and 1 percent hydrogen. The microwave energy converts the argon into plasma, an electronic soup of ions and electrons. The small hydrogen concentration stabilizes the plasma, but the reaction will run without it.

The argon in the plasma collides with carbon-60 and knocks off an electron to create a C60+ ion. Electrons in the plasma react with the C60+ to initiate fragmentation, which produces a series of carbon dimers. The dimers emit a bright, emerald green glow in the reaction chamber.

"The dimers are so reactive that they insert themselves directly into carbon-carbon and carbon-hydrogen bonds," says Gruen. "This means they can react with one another to start new diamond crystals, or they can attach to existing crystals and enlarge them."

Argonne's diamond crystals range from 3 to 5 nanometers across, some 300 to 2,000 times smaller than the crystals that make up conventional diamond films. One nanometer is one-billionth of a meter, about the distance across five atoms.


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