Abstract
The chemkin suite of computer programs has been used to model the concentration profiles of diVerent hydrocarbon species present within a hot filament CVD reactor during diamond growth, and the calculated values are compared with those obtained by direct measurements using an in situ molecular beam mass spectrometer. DiVerent hydrocarbon gases (CH 4 ,C 2 H 2 ,C 2 H 4 and C 2 H 6 ) were used as the carbon source in the input gas mixture, ensuring that the ratio of C:H 2 remained constant at 1%. Calculations for when C 2 H 6 is used as the precursor gas, after reaction and thermal equilibrium is realised, yield similar CH 4 :C 2 H 2 mole fraction ratios in the reactor under growth conditions to those obtained using CH 4 , and to those measured experimentally. However, simulations using C 2 H 4 or C 2 H 2 as input gases do not reproduce the experimentally observed ratio of CH 4 :C 2 H 2 mole fractions. This suggests that the conversion of unsaturated C 2 species to C 1 species is not a straightforward gas phase process, and there must be one or more reactions occurring within the chamber that are not present in the standard models for hydrocarbon reactions. We suggest that these neglected reaction(s) probably involve surface-catalysed hydrogenation, which in this case, is most likely occurring on the surface of the filament. © 1999 Elsevier Science S.A. All rights reserved.
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