FLUID BOUNDARY-LAYER EFFECTS IN ATMOSPHERIC-PRESSURE PLASMA DIAMOND FILM DEPOSITION

Diamond films were deposited in an atmospheric-pressure radio-frequency plasma reactor. Hydrogen and methane were injected coaxially into the plasma as a high-velocity jet which impinged on the molybdenum substrate. In some cases argon was added to the reactant jet to increase its momentum, thereby reducing the boundary layer thickness. In most cases argon addition substantially improved diamond growth. A numerical model was developed, which calculated two-dimensional reactor temperature and velocity distributions, and the chemical kinetics in the boundary, layer. The calculations indicate that under the experimental conditions argon addition reduced the thickness of the hydrogen nonequilibrium boundary layer from 3.5 to 1.0 mm. In addition, the calculations suggest that monatomic carbon may, be a key diamond growth species under thermal plasma conditions.