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Activity of tungsten and rhenium filaments in CH4/H2 and C2H2/H2 mixtures: Importance for diamond CVD

Published online by Cambridge University Press:  31 January 2011

M. Sommer  and
F. W. Smith
M. Sommer
Affiliation:
Department of Physics, The City College of the City University of New York, New York, New York 10031
F. W. Smith
Affiliation:
Department of Physics, The City College of the City University of New York, New York, New York 10031
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Abstract

The resistance R, spectral emissivity ∊, and power consumption of W and Re filaments heated to 2500 °C in mixtures of CH4 or C2H2 in H2 have been measured in a series of experiments focusing on the state of the filament activity, i.e., its ability to dissociate the reactant gases. It has been found that these properties of the filaments, as well as the partial pressures of CH4 and C2H2 in the reaction chamber, depend critically on both the filament temperature and the reactant ratio, e.g., C2H2/H2. Specifically, both W and Re filaments show sharp jumps in power consumption at essentially the same temperature, signaling strong increases in filament activity and, hence, production of atomic hydrogen. These results are proposed to be due to the removal of nonreactive carbon from the surface of the filament via etching by atomic hydrogen and are consistent with the predictions of our thermodynamic model for the C–H system. Evidence for gas phase reactions is presented and the role of thermal diffusion is discussed. The emissivities of the W and Re filaments are observed to have significantly different temperature dependences which are attributed to differences in the phase diagrams for the W–C and Re–C systems. The implications of these results for hot-filament diamond CVD are discussed.

Type
Diamond and Diamond-Like Materials
Information
Journal of Materials Research , Volume 5 , Issue 11 , November 1990 , pp. 2433 - 2440
Copyright
Copyright © Materials Research Society 1990

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References

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