Activity of tungsten and rhenium filaments in CH sub 4 /H sub 2 and C sub 2 H sub 2 /H sub 2 mixtures: Importance for diamond CVD
- Department of Physics, The City College of the City University of New York, New York, NY (USA)
The resistance R, spectral emissivity {epsilon}, and power consumption of W and Re filaments heated to 2500 {degree}C in mixtures of CH{sub 4} or C{sub 2}H{sub 2} in H{sub 2} 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 CH{sub 4} and C{sub 2}H{sub 2} in the reaction chamber, depend critically on both the filament temperature and the reactant ratio, e.g., C{sub 2}H{sub 2}/H{sub 2}. 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 non-reactive 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.
- DOE Contract Number:
- FG02-87ER45317
- OSTI ID:
- 6331439
- Journal Information:
- Journal of Materials Research; (USA), Journal Name: Journal of Materials Research; (USA) Vol. 5:11; ISSN JMREE; ISSN 0884-2914
- Country of Publication:
- United States
- Language:
- English
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360601 -- Other Materials-- Preparation & Manufacture
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
ABSORPTION
CARBON
CHEMICAL COATING
CHEMICAL VAPOR DEPOSITION
DEPOSITION
DIAMONDS
DISPERSIONS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTAL MINERALS
ELEMENTS
EMISSIVITY
ENERGY ABSORPTION
FILAMENTS
FILMS
FLUIDS
GASES
HEATING
HYDROCARBONS
HYDROGEN
METALS
MINERALS
MIXTURES
NONMETALS
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
RHENIUM
SURFACE COATING
SURFACE PROPERTIES
THIN FILMS
TRANSITION ELEMENTS
TUNGSTEN
VERY HIGH TEMPERATURE