Alchemist revival. Using particle beams, a "carbon onion," a structure consisting of nested fullerenelike balls, can be converted into a diamond. Here a growing diamond can be seen inside concentric graphitic layers.

Gems of the Nanoworld

Most diamonds are made with brute force. Extremely high pressures and temperatures inside Earth or in a laboratory, for example, can rearrange the carbon atoms of graphite into the crystalline structure of diamond. Now, researchers have used clever physics instead. They turned nested spheres of graphite into tiny pressure chambers by bombarding them with high-speed electrons and ions. Carbon in the interior of the spheres turned into tiny diamonds, the researchers report in the 6 October issue of Applied Physics Letters.

Florian Banhart and four colleagues at the Max Planck Institute for Metals Research in Stuttgart, Germany, began by creating "carbon onions." Sending intense beams of electrons or ions into a sample of graphite created tiny concentric spheres of graphite, like the layers of an onion. The researchers then bombarded the onions with neon ions accelerated to energies of 3 million electron volts. The beam knocked out some of the carbon atoms, forcing the shells to contract and leading to very high pressures at their center. And when Banhart monitored the carbon onions in an electron microscope, he could watch the diamond growing under the influence of an electron beam, at the expense of the surrounding graphite shells.

"What they see is a quite fascinating phenomenon," says Risto Nieminen from Helsinki University of Technology in Finland, who also researches diamond production with ion beams. In an upcoming paper in Physical Review Letters, Banhart and Michael Zaiser calculate that the spherical structures may not even be needed for electron or ion irradiation to transform graphite to diamond. "This is very intriguing and certainly will create a lot of excitement if it is true," says Nieminen. While the process won't yield diamonds in industrial quantities, it might help make diamond substrates to insulate microelectronics, says Banhart.

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