Manufactured diamonds move closer to nature

Researchers at the Carnegie Institute have come up with a way to produce 10-carat diamonds measuring a half-inch thick that are also colorless, an attribute that has bedeviled diamond makers until now.

Manufactured diamonds--which some believe could play a large part in the industrial and jewelry market--are generally produced through the so-called high pressure/high temperature (HPHT) method, similar to how diamonds are created in nature.

By contrast, the Carnegie team employed chemical vapor deposition (CVD) in which hot vapors are condensed into a solid. Semiconductor manufacturers use CVD to apply thin, uniform metal layers on silicon wafers.

At 10 carats, the Carnegie diamonds are roughly five times the size of diamonds produced through the HPHT method. Just as important, they are transparent from the ultraviolet to infrared wavelengths, making them colorless to humans. Most HPHT diamonds are yellow in color. Earlier attempts at CVD diamonds have mostly turned up brown, not exactly the sort of thing Liz Taylor would name a perfume after. And up to this point, colorless diamonds produced by either of these methods have been relatively small.

"High-quality crystals over 3 carats are very difficult to produce using the conventional approach," Russell Hemley, who leads the diamond effort at Carnegie, said in a prepared statement.

The Carnegie team managed to grow the diamonds at about 100 microns (a millionth of a meter) per hour, but at one time hit speeds of 300 microns per hour.

Industrially, diamonds are used in e-beam lithography systems. Others have also proposed using diamonds to deliver electrons to the screen in televisions and, instead of silicon, as a substrate for semiconductors.

Diamonds are three-dimensional crystals of pure carbon. Two-dimensional carbon is graphite, while nanotubes are considered a one-dimensional form of pure carbon. (Technically, graphite and nanotubes have three dimensions, but the Z axis on graphite and the Z,Y axes on nanotubes are so small that they become irrelevant.) Eliminating a dimension alters the property of these materials, even though all are made entirely of carbon atoms. Zero-dimensional carbon is a quantum dot.

The results were reported at the 10th International Conference on New Diamond Science and Technology in Tsukuba, Japan, last week. Further discussion of the group's techniques will be reported Wednesday at the Applied Diamond Congress in Argonne, Illinois.