THERMODYNAMIC AND EXPERIMENTAL-STUDY OF DIAMOND DEPOSITION FROM A CH4-H2 GAS-MIXTURE

Abstract

The effects of deposition variables on the nucleation and growth of diamond particles were investigated using the tungsten-filament chemical vapor deposition method. Deposition was performed under the conditions of 0.3%-1.5% methane in hydrogen, 2000-2200-degrees-C filament temperature, 840-1040-degrees-C substrate temperature, 50-300 mbar reactor pressure, and 50-150 standard cm3 min-1 flow rate. The nucleation density and growth rate increased with increasing methane concentration, filament temperature, and flow rate. By increasing the substrate temperature, the nucleation density and growth rate increased first and showed maxima around 950-degrees-C. The free energy change, calculated under the assumption that diamond was deposited from the supercooled gas mixture with no solid to the equilibrium gas and solid mixture at the substrate temperature, agreed well with the experimental results.