Simulations of the hot-filament diamond CVD gas-phase environment: direct comparison with experimental measurements

The CHEMKIN suite of computer programs (Sandia Labs) has been used to simulate the mole fractions of the important gas phase species within a hot filament CVD diamond reactor. These simulations have been compared to data measured using an in-situ molecular beam mass spectrometer. Excellent agreement between simulation and experiment was obtained by using just two fitting parameters. The first of these, the local gas temperature, was found to be a relatively insensitive parameter, and values could be varied by several hundred degrees centigrade with no appreciable effect on the results of the calculation. However, the second parameter, the mole fraction of hydrogen atoms, was found to be very important since it controlled the whole gas-phase chemistry. Comparison of experimental data with simulations, therefore, has allowed us to derive absolute mole fractions of not only the stable hydrocarbon species, but also the methyl radicals and the hydrogen atoms, simultaneously, during a typical CVD process. These results are presented as a function of filament temperature. (C) 1999 Elsevier Science S.A. All rights reserved.