The synthesis of high-quality diamond in combustion flames

High-quality diamond with good crystallinity has been successfully synthesized on a substrate using an oxy-acetylene combustion flame in the atmosphere. The crystal grains under some conditions have good optical transparency. The deposition rate of transparent diamond depended strongly on substrate temperatures and the O2/C2H2 ratio and averaged ∼30 μm/h. The substrate temperature for the growth of optically transparent crystals was 500–750 °C, which is relatively low compared with other chemical vapor deposition methods. The optical transparency is attributed to the low defect densities in the crystals, as determined by transmission electron microscope, which results from the low substrate temperatures and moderate growth rates. Raman spectroscopy and x-ray diffraction data on the synthesized crystals were comparable with that of natural diamond. The synthesis conditions and corresponding diamond quality as well as emission spectrum analysis of the combustion flame during diamond synthesis are described.