New CVD Synthetics Hit Market
Gemologists research ways to distinguish them from
natural diamonds and other synthetics
In a dramatic new wrinkle in diamond synthesis, Apollo Diamond Inc. announced in August it has patented a system to produce single crystals via chemical vapor deposition and that the crystals are now thick enough to be fabricated into gem-sized crystals (U.S. Patent 6,582,513). The company says it can control the role of diamond impurities such as nitrogen, phosphorous or boron to tailor-make different diamond types for different applications.
In a sense, the advancement is no surprise. Chemical vapor deposition of pure crystallized diamond layers may have existed long before humans. Meteorites contain evidence of nano-diamonds so minuscule that scientists propose they were formed by CVD processes, fed by methane and carbon-rich gases following the deaths of supernova stars.
Here on earth, human-inspired CVD diamond research has been ongoing since the 1950s. Diamonds produced by CVD have been synthesized for decades, but always in the form of thin polycrystalline coatings and films, often over substrate materials. In early 1993, De Beers announced the production of Diafilm, a synthetic polycrystalline diamond grown by CVD. Those inventions heralded new developments in heat-resistant CVD synthetics for use in the computer and space travel industries. However, the development of larger, single-crystal diamonds, in layer upon layer of vapor deposition, has been elusive until now.
Relevance to the Jewelry Industry
We knew this would become a problem for the jewelry industry if it wasnt handled properly, says Brian Linares, CEO of Apollo Diamond. Linares says his company patented the process as a control mechanism and has introduced and fully disclosed the products to EGL USA and the Gemological Institute of Americas Gem Trade Laboratory in the United States by way of preparing the public. We are in favor of full disclosure about this product, says Linares. He adds his company is leaning toward calling the synthetic diamonds cultured, for reasons similar to those cited for cultured pearls. [Editors note: Some gemologists and the FTC may disagree. While cultured pearls and CVD diamonds may start out with seed material, the mollusk in which a pearl grows is a natural environment. CVD processes take place in a laboratory.]
The cut CVD diamonds that Apollo has shown labs are well under a carat, but Linares expects quarter-carats, half-carats and 1-plus carat stones to be available in commercial quantities late next year. Linares says the companys gem division expects to produce 50-100 carats a week in the first quarter of 2004. That will be enough to start test-marketing. We are building up our production for now.
Because these diamonds are not produced through high-pressure/high-temperature techniques, producers say they are of superb crystal structure. For now stones submitted to the labs are almost all Type IIa (rare, with negligible or no trace of nitrogen or boron), fancy light brown to better colors in the H-J category and in clarities between SI and VVS. EGL USA says it has seen only fancy-shaped stones so far.
Linares says the future is bright for CVD, and he discredits a September 2003 Wired article that implies CVD gem diamonds will sell for as low as $5 per carat. The operating range for large CVD diamonds is very narrow and very difficult to achieve, he says. Costs will soon fall dramatically for thin-film CVD for electronics applications. Thats where the $5 figure comes in, certainly not for jewelry-quality CVD diamonds!
Linares says his companys goal is to offer the most perfect crystals possible. We are literally wringing out the impurities and perfecting the product, he says. In semiconductors alone, diamonds need to be perfect, more even than what is offered by nature.
For now, its the impurities that are providing the best clues for identification, says Branko Deljanin, EGL USAs director of Canadian operations. He says three early indicators that separate CVD diamonds have emerged so far:
u Shortwave fluorescence appears 1&Mac251; to 2&Mac251; stronger than longwave UV fluorescence in CVD diamonds. (As a rule longwave is always stronger in natural diamonds).
u CVD samples show clouds of white microscopic particles, mostly confined to distinct layers in the stones. In natural diamonds, similar looking particles tend to be more widely dispersed. (Linares says Apollo is working on eliminating the particles altogether.)
u Exposing CVD diamonds to strong electron beams results in cathodoluminescence, where the viewer sees unique colors. CVD diamonds turn orangy gold (see photo on page 24), while natural diamonds tend to turn blue and HPHT synthetic diamonds tend to turn green.
Future CVD experiments may even include submitting brownish Type IIa diamonds to HPHT treatments, says Deljanin. From what we already know about how Type IIa diamonds respond [to HPHT], its likely that colors could be improved. That, of course, is yet another wrinkle.
- Apollo Diamond Inc., Medfield, MA; (617) 742-5661.
- EGL USA, Vancouver, BC, Canada; (604) 630-0464.
by Robert Weldon, G.G.
||This princess-cut synthetic diamond was made by chemical vapor deposition. Under strong electron beams, the diamond exhibits orangy cathodoluminescence, a detection clue. Courtesy of EGL USA and University of British Columbia.
||An article in Wired implied gem-size CVD synthetic diamonds would soon be available for $5 a carat. The maker says thats wrong.