Improved DC arc-jet diamond deposition with a secondary downstream discharge

The efficiency of a polycrystalline diamond coating in a DC are-jet setup w ith a power of 5-10 kW was enhanced by extension of a high temperature jet core. Two approaches were investigated. First, an expansion of the plasma j et anode channel was employed. It allowed us to increase the process effici ency from 5.5 to 10 mg/h/kW by optimizing values of pressure and CH4 conten t in a reactionary Ar/H-2/CH4 mixture. In the second approach, the extensio n of the hot jet core was achieved by an additional downstream discharge wi th a power of 2.5 kW. The secondary discharge was initiated between a posit ively biased auxiliary electrode and the are-jet nozzle. This method allowe d us to obtain a growth rate of 40 mu m/h on an area of 12 cm(2) which corr esponds to an efficiency of 16 mg/h/kW. (C) 2000 Elsevier Science S.A. All rights reserved.