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Conventional Method: Chemical Vapor Deposition

Chemical vapor deposition (CVD) has been widely used to grow diamond films for about 20 years. The conventional method begins with a gaseous mixture of 1 percent methane and 99 percent hydrogen. The hydrogen gas reacts with the methane—chemical formula CH4—to strip off hydrogen and expose the carbon atom so it can bond to other carbon atoms to grow diamond crystals on a substrate, such as silicon.

The large crystal size of these conventionally grown films is caused by the high hydrogen concentrations.

"When there's a lot of hydrogen," Gruen says, "most of the smallest diamond crystals will re-gasify. Only the largest crystals survive and grow, making the surface rough."

So rough, in fact, that they must be polished for some applications. For example, diamond film is a key component in "surface acoustic wave" (SAW) devices used in high-frequency cell phones. But conventional diamond films have to be polished before they are smooth enough for a SAW device, Gruen says, and the polishing accounts for about half the device's cost.


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