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

Diamond films were deposited in an atmospheric-pressure radio-frequenc y plasma reactor. Hydrogen and methane were injected coaxially into th e plasma as a high-velocity jet which impinged on the molybdenum subst rate. In some cases argon was added to the reactant jet to increase it s momentum, thereby reducing the boundary layer thickness. In most cas es argon addition substantially improved diamond growth. A numerical m odel was developed, which calculated two-dimensional reactor temperatu re and velocity distributions, and the chemical kinetics in the bounda ry, layer. The calculations indicate that under the experimental condi tions argon addition reduced the thickness of the hydrogen nonequilibr ium boundary layer from 3.5 to 1.0 mm. In addition, the calculations s uggest that monatomic carbon may, be a key diamond growth species unde r thermal plasma conditions.