cvd synthesis

Another way to make synthetic diamond was developed by the Union Carbide Corporation in 1952. With this method, diamond is created from gas by means of Chemical Vapor Deposition (CVD).

A diamond substrate is exposed to a mixture of hydrocarbon gas (methane, CH4) and hydrogen (H2). This mixture is heated up using a microwave beam or a hot filament. At temperatures over 1000°C every atomic bond is broken and even electrons are separated from the nuclei. In other words a plasma is created in which all atoms are free.

The carbon atoms will precipitate onto the substrate forming diamond layer after layer. At the moment, the growth rate of this process is very slow: less than half a millimeter per day.

Hydrogen gas is used to remove (etch away) all traces of non-diamond that is formed. Atomic hydrogen is very reactive and will dissolve everything that is not diamond. The diamond will also be corroded, but at a much slower rate than, for example, graphite.

In the mid 1970's, researchers from the Japanese Institute for Research in Inorganic Materials (NIRIM) made a breakthrough by finding a fast and economic viable method for growing CVD diamond films. Unfortunately, the diamond film is composed of small diamonds with different crystallographic orientation (a so called polycrystalline film).The problem has been that no-one could figure out how to grow a single crystal with this method.

Apollo Diamond, made a breakthrough by discovering the ‘sweet point'. This is an exact combination of temperature, gas mixture and pressure at which the carbon atoms are arranged in a large single crystal and not in multiple small crystals. The CVD-technology was as such turned into a new method of growing gem-quality diamonds. The actual chemical process for diamond growth is still under study and is complicated by the extremely wide variety of diamond growth processes used.


The inside of a CVD diamond chamber.