On the Role of Oxygen and Hydrogen in Diamond-Forming Discharges.

Plasma emission actinometry has been used to study the mechanism by which small additions of oxygen (~0.5%) enhance the rate of diamond deposition in a dilute (4%) CH sub 4 /H sub 2 discharge at high temperature (900-1300 K). Increasing amounts of CH sub 4 in the feed depress [H], while increasing the O sub 2 concentration up to ~5% produces a 5-fold increase in atomic hydrogen in the discharge zone. Invoking a mechanism where diamond growth competes with the formation of an amorphous/graphitic inhibiting layer, these results and earlier studies suggest that oxygen (1) increase [H] which selectively etches amorphous/graphitic carbon, (2) accelerates reaction of this layer with molecular hydrogen, and (3) may itself act as a selective etchant of non-diamond carbon. As a result, the number of active diamond growth sites is increased and enhanced growth rates are observed.