Chemical vapour deposition, developed in the mid 1980’s is a process by which incredibly thin films of diamond (a few microns thick) can be generated and deposited on a base. The process involves high temperatures (over 2000°C) and lower pressures than involved in HPHT. Mixtures of hydrogen and hydrocarbon gases are energised with heat or electrical energy in a deposition reactor. The carbon molecules are deposited on a substrate as a thin film of polycrystalline material.
Quality and purity are very high and particular diamond properties can be selected. Boron added to the growth gases, for example, will produce an electrically conducting diamond. When the diamond layer has reached the correct thickness the reactor is shut down and the CVD wafers can be removed. Single crystal diamonds can also be grown, but sizeable gem quality is proving difficult. All CVD diamonds are believed to be Type IIa diamonds as no nitrogen is present.
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