In 1994, Thomas R. Anthony et al. of GE filed U.S. Patent 5,437,891 (issued in 1995) stating that the growth rate of cubic facets (100) of polycrystalline diamonds can be increased by chemical vapor deposition (CVD). In particular, if a small amount (e.g., 1%) of air (78% nitrogen, 21% oxygen, 1% argon) is added to the gas stream (e.g., 98% hydrogen + 1% methane), the growth rate will increase even more.
In 1996, Anthony et al. also invented a method for treating CVD-grown polycrystalline diamond films at high temperatures (e.g., 1300°C) at high pressures (> 3 Kb) to reduce defects (U.S. Patent 5,672,395, issued in 1997). In 2004, Robert H. Frushour filed a similar U.S. Patent 6,811,610, but the heat-treated diamond is a monocrystalline diamond film. In 2004, Suresh S. Vagarali et al. were awarded U.S. Patent 6,692,714 for a high-pressure and high-temperature method of changing colored diamond monocrystals into light or colorless ones.
H.K. Mao and Russell Hemley, members of the Academia Sinica in Taiwan (also members of the Academies of Sciences in the U.S. and China), are scientists in the Geophysical Lab of the Carnegie Institute of Washington (CIW) in the U.S.In 1998, Chih-Hsuey Yen of Taiwan grew CVD diamond monocrystals in a program they funded. chemical vapor deposition is based on natural or man-made diamond monocrystals as crystalline species, and then on its homo-epitaxial growth of epitaxial. To accelerate the growth rate, not only is the temperature of the seed greatly increased, but the methane content is also appropriately increased, and nitrogen and oxygen are added to the gas, so that nitrogen-containing yellow diamonds can be grown at a rate of more than 15 micrometers (µm) per hour. According to Example 1 of U.S. Patent 6,858,078, filed by Hemley et al. in 2002, CVD uses microwave plasma as the heat source at a pressure of 160 torr, with a gas composition of 3% N2: 97% CH4: 12% CH4: 88% H2. The gas flow rates are 1.8 sccm N2, 60 sccm CH4 and 500 sccm H2. The size of the grown diamond species is 3.5 × 3.5 × 1.6 mm3, and its front surface is (100). Diamonds grow at a temperature of 1220°C ± 10°C. The size after 12 hours of growth was 4.2 × 4.2 × 2.3 mm3 and the calculated growth rate was 58 µm per hour.
In 2005, Chih-Hsuey Yen produced a 10-carat diamond, a milestone in the synthesis of CVD diamonds. The cost of growing this diamond is said to be only 5,000 dollars, which is only 5% of the value of a natural diamond gemstone of the same weight. CVD-grown diamonds are not dense on the inside, but the hardness of CIW CVD-grown diamonds can be significantly increased after 10 minutes of high-pressure (6 GPa) and high-temperature (nearly 2000 degrees Celsius) treatment, and the hardness of work-hardened diamonds may even exceed that of natural diamonds. However, the U.S. Patent (U.S. Patent 6,811,610, filed 2002, issued 2004) for the use of high pressure heat treatment to improve the properties (e.g., transparency) of CVD diamond films is owned by Robert H. Frushour. Frushour was the manager of GE’s Specialty Materials Department (the predecessor of GE Superabrasives) in the 1970s. Later he founded Valdiamant in Valenite, GTE, to compete with GE for PCD customers. Later GE merged with him and took away the presses, and Frushour founded Phoenix Crystal to sell the high-pressure technology. GE Superabrasives was sold to Littlejohn in 2003. By that time, GE’s “old guard” had dispersed, and to avoid a break in technology transfer, Diamond Innovations hired Frushour, a former “rebel,” as a consultant. Not only that, GE Superabrasives has also been a result of the support of Song’s technology for Iljin Diamond in Korea and Asian Diamonds in China. Since 2004, Diamond Innovations has also been receiving technical support from K.M. Soong to improve its high-pressure synthesis process.
Mr. Yen uses the ASTeX AX5250 growth diamond manufactured by Seki in Japan. The power of the machine is 5 Kw and the microwave frequency is 2.45 GHz. Yellow diamonds are produced at a rate of 15 microns or 1/3 carat per hour. If colorless and transparent diamonds are grown, the velocity drops to less than 5 microns. However, during the growth process, the (100) facets will accumulate small pyramids on the (111) facets, which reduces the growth rate. Therefore, it is often necessary to interrupt the growth process by removing the diamonds and grinding them, and then putting them back in to thicken them by grafting them together.
Grow up to 100 square centimeters at 5 Kw. The temperature of monocrystalline diamond deposition is about 1200°C, so its growth efficiency can be as high as 3 cc per 100 kWh (100 KwH), which is 10 times higher than that of conventional CVD, which grows polycrystalline diamond films at a lower temperature (900°C). In comparison, the direct cost of chemical vapor deposition of diamonds is approximately $10 per hour or $100 per carat.
chemical vapor deposition (CVD) is used to grow mesostable diamonds in the graphite-stabilized zone, so a great deal of energy must be used to dissociate the hydrogen molecules to protect the diamond bonds (sp3). Even so, since gas molecules are nearly a thousand times thinner than liquids, it is difficult to increase the rate of diamond growth. In addition to the fact that CVD is a two-dimensional growth technique, it must be deposited on a large area to be valuable for the mass production of gem-quality diamonds, and the high-pressure liquid-phase deposition method should still be used. Epitaxy of CVD diamonds is an effective method for making semiconductor films in the future.
On July 7, 2006, Mr. Mao and Mr. Yen gave speeches on the topics of “The New Diamond Era” and “High Speed Growth of Large Monocrystalline Diamonds” at the Taipei International Convention Center, and on the topic “Catalyzing Taiwan’s Synthetic Diamond Industry”. Mr. Mao presented his vision of growing a 4-inch diamond plate, while Mr. Yen presented the possibility of growing it by 0.1 mm per hour. Henderson Lee of Jiaotong University once visited Mao Heguang’s laboratory to inquire about technology transfer, but the price could not be agreed upon, so Henderson Lee set up Genesis Materials Technology Inc. in 2007 to research and develop related technologies.
