The Growth Mechanism of Diamond Crystals in Acetylene Flames

Abstract

To discuss the diamond growth mechanism in acetylene flames, numerical calculations are carried out, including both gaseous reactions in the boundary layer near a water-cooled substrate and overall surface reactions on a growing crystal. It is shown that stable species such as CH₄ and C₂H₄ are rapidly produced in the layer, followed by the methyl radical formation according to the fast partial equilibrium of the reaction, CH₄+H\rightleftarrowsCH₃+H₂. The comparison between the calculated and the measured CH₄ concentrations upon the substrate has revealed that C-radicals adsorbed on the diamond surface are etched by H-atoms to form CH₄, though the surface reactions do not have a significant effect on the gaseous concentrations. The dependences of the growth rate both on the substrate temperature and on the C₂H₂/O₂ ratio are shown to be explainable by the CH₃-precursor model.