Diamond Synthesis and Deposition

Several researchers have synthesized diamonds using either dc or RF thermal plasma jets (Ref 35, 36, 37) and have shown

that generation of ^ 3 radicals and ionic hydrogen, which typically occurs under many plasma jet conditions, leads to the formation of diamond films. In these cases, precursor gases such as methane and hydrogen were injected into the plasma jets, where the high temperatures (>10,000 K) produced the required ionic concentrations such that on collision with a heated surface at —1000 °C amorphous carbon and diamond phases were formed. It is generally accepted that the ionic hydrogen assists in preferentially etching away the amorphous carbon phase, leaving diamond as the surface film. High growth rates (>1 /'m/min) can be achieved; however, the exact morphology and bonding of the deposited diamond films varies and can be a limiting factor. A wide range of thermal plasma processing conditions with a wide range of environments have now been used to produce diamonds. The critical elements of diamond growth clearly occur in the thin, plasma-enhanced, reaction zone created immediately above the substrate surface when the thermal plasma jet impinges on the substrate surface. The precise formation mechanisms are not yet completely understood, but research is now showing that it is the thermal plasma jet conditions that are primarily responsible for producing diamonds at high rates.

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