Fast growth, purity may multiply uses. (Better-Built Diamonds).

Although researchers have been getting better at making artificial diamonds for a half century, they haven't yet made the crystals as big or as pure as some diamond visionaries would like. Yet large natural diamonds that make beautiful jewelry are neither pure enough nor cheap enough for the more demanding requirements of technology developers. Artificial diamonds may soon make the grade, two new studies suggest.

A Swedish-English research group has now fabricated the purest diamonds ever made or found, hastening the prospect of a new class of rugged and more capable microchips made from diamond. Another group, based in the United States, claims to have devised a way to grow high-quality diamonds up to 100 times faster than typical growth rates. The fast-growth technique promises to make large, high-quality diamonds affordable for certain uses in science and industry. Among those would be exceptionally large so-called diamond anvils for testing materials at ultrahigh pressures (SN: 6/2/01, p. 349).

Aside from their luster and hardness, diamonds boast other properties that make them desirable to industry. For instance, diamond is a semiconductor--the same type of material as silicon, upon which modern electronics is based.

Manufacturers have long made artificial diamonds by pressing graphite at high temperature and pressure. Although clear and hard, the resulting diamonds are typically not much bigger than sesame seeds and too riddled with impurities and crystalline defects for use in electronics.

In their new work, the two teams wedded the heat-and-press method with another well-established diamond-growing technique known as chemical-vapor deposition. In that low-pressure technique, hot, carbon-containing gases condense and react on a hard surface to form a thin coating of diamond. Both groups used diamonds created in presses as the deposition surface in the vapor chamber.

Combining the two methods has been done before. What's new, both groups claim, is the precision with which they've controlled the deposition process to achieve their ends.

In the Swedish-English experiments, the result is diamonds up to a few tenths of a carat, but so pure that they allow electrons and other electric-charge carriers to pass through with startling ease. The scientists, of the ABB Group Services Center in Vasteras, Sweden, and De Beers Industrial Diamonds in Ascot, England, report their accomplishment in the Sept. 6 Science.

"This paper is ... a major breakthrough," comments James E. Butler of the Naval Research Laboratory in Washington, D.C. "It says we're now making diamond better than nature," he adds.

To speed up crystal growth, Chih-shiue Yan of the Carnegie Institution of Washington (D.C.) and his colleagues boosted both the heat and pressure of the deposition process and pumped in nitrogen. Yan and his colleagues report their method in an upcoming issue of the Proceedings of the National Academy of Sciences.

The growth rate they attained "is a very big achievement," says Dennis D. Klug of the National Research Council of Canada in Ottawa, Ontario. The team already has grown flaw-riddled test diamonds up to 5 carats, but it is shooting to create top-notch diamonds on the scale of 100 carats.

However, says Steven E. Coe of De Beers, a coauthor of the Science report, the small diamonds already in hand from his team's new technique are sufficiently large for making electronic components for niche markets. He predicts that those would include high-power, high-voltage devices used in trains, radar systems, and electric-power-grid circuits.