Gas-phase kinetics during microwave plasma-assisted diamond deposition: Is the hydrocarbon product distribution dictated by neutral-neutral interactions
- Sandia National Laboratories, Livermore, California 94550 (United States)
The mole fractions of H, H{sub 2}, CH{sub 3}, CH{sub 4}, and C{sub 2}H{sub 2} that were generated in a microwave plasma under conditions typical for diamond deposition are reported. When the methane percentage in the feed gas was {lt}1%, the measured concentrations were surprisingly similar to those reported for a hot-filament system operated under nearly identical conditions. However, as the methane percentage was increased beyond 1%, a noticeable deviation from the hot-filament results became apparent. In the hot-filament case, surface-induced dissociation of hydrogen on the filament surface was significantly inhibited at this high methane level and lead to a pronounced reduction of the H-atom concentration. But, in the microwave system where dissociation is a homogeneous process, no such reduction was observed. Other observations were: (i) The acetylene concentration scaled as the square of the methyl concentration; (ii) The CH{sub 4}+H{leftrightarrow}CH{sub 3}+H{sub 2} reaction was found to be at the same level of nonequilibrium as in the hot-filament case. These results, plus arguments based on general principles of plasma chemistry, are taken as indications that the hydrocarbon chemistry in the microwave system is as strongly dictated by neutral-neutral reactions as in a thermal system. The primary effect of the plasma is perhaps its role in dissociating hydrogen molecules to H atoms without having to raise the gas temperature significantly.
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 7266350
- Journal Information:
- Journal of Applied Physics; (United States), Journal Name: Journal of Applied Physics; (United States) Vol. 72:7; ISSN 0021-8979; ISSN JAPIA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360601* -- Other Materials-- Preparation & Manufacture
ALKANES
CARBON
CHEMICAL COATING
CHEMICAL REACTIONS
CHEMICAL VAPOR DEPOSITION
DEPOSITION
DIAMONDS
DISSOCIATION
ELECTROMAGNETIC RADIATION
ELEMENTAL MINERALS
ELEMENTS
HYDROCARBONS
HYDROGEN
METHANE
MICROWAVE RADIATION
MINERALS
NONMETALS
ORGANIC COMPOUNDS
PLASMA
RADIATIONS
SURFACE COATING