Other CVD Methods for Diamond Production

Low-pressure synthesis of diamond films from a gas medium has been accomplished by many techniques, such as hot-filament chemical vapor deposition (CVD), microwave-plasma and radio-frequency (rf) plasma, direct current (DC) and alternating current (AC) plasma jets, combustion flame and oxyacetylene torches, ion beams, and so on. CVD techniques provide the capability to coat various shapes and produce many forms of diamond, such as fine powders, protective coatings, epitaxial and whisker growth, and coating of particles. Although there are many ways to produce diamond films and many applications, much needs to be accomplished before the full potential of diamond CVD is realized. In these methods, the feed gases are exposed to high temperatures and/or some high-energy activation to initiate the reactions necessary for CVD. Usually, the substrates are maintained at temperatures greater than 700°C for good-quality deposits. Hydrogen atoms are usually considered essential in facilitating deposition of diamond under graphite stable conditions, so the production of hydrogen radicals is key for most of the above processes [7.1].