DIAMOND GROWTH IN A DIRECT-CURRENT LOW-PRESSURE SUPERSONIC PLASMAJET

A direct-current, water-cooled hydrogen plasmajet was designed and bui lt, The are burning between a thoriated tungsten cathode and a Laval n ozzle acting as anode was operated at a power level of 4 kW. The plasm ajet expands supersonically into a vacuum vessel in which a pressure o f a few millibars is sustained, Methane as carbon-containing species i s mixed into the decaying plasma close to the exit of the Laval nozzle . Molybdenum plates were used as substrates for diamond deposition. Th e substrates were placed on a water-cooled movable substrate holder, w hich allowed depositions at distances ranging rom 2 to 30 cm, The bull ; temperature of the substrate was monitored by a thermocouple. The de posited coatings were analysed by Raman spectroscopy for diamond phase purity and by scanning electron microscopy for morphology. The film t hickness was determined by a Talley Surf profilometer and by optical t hickness analysis. At the conditions investigated, a maximum growth ra te of about 6 mu m h(-1) was observed. The growth rate showed a maximu m at a distance of 6-10 cm from the nozzle, With increasing distance f rom the nozzle the growth rate as well as the crystallite size decreas es and the diamond phase purity as reflected in the Raman spectra dete riorates. An alteration of arcjet power had only little effect on grow th rate and no effect on film quality, (C) 1997 Elsevier Science S.A.