Kunio Komaki

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.

Rapid growth of diamond films by arc discharge plasma CVD

Diamond films have been synthsized by arc discharge plasma CVD in a hydrogen-argon-ethanol mixture gas. The arc discharge power is about 560 W and the typical gas flow rate is 500–2000 cm3/min, respectively. The growth rate of diamond films has been obtained about 200–250 µm/h which is higher than that of other CVD methods. The obtained diamond films are identified as natural cubic diamond by X-ray diffraction. It is found that graphitic and amorphous carbon are not contained in the diamond films by Raman spectra. Atomic hydrogen (H) plays important roles in the growth of high-quality diamonds.

Synthesis of Diamond in Combustion Flame under Low Pressures

The oxygen-acetylene combustion flame method has been investigated as to low pressure, gas ratio and substrate temperature effects, and flame emission spectral analysis. Non-diffusion of oxygen from ambient atmosphere enhanced expansion of the area and the amount of deposited diamond. H and OH radical emission have not been observed on combustion flames in a chamber. The reactions relating C2 and CH radicals have been revealed to have important roles in diamond synthesis.