Abstract
Methane, mixed with argon, has been polymerized by means of a hollow-cathode discharge system. Two types of cathodes were studied; one was made of a solid solution of 81% tungsten and 19% platinum, while the other was of pure tungsten. Under identical operating conditions, a higher polymer yield was found in the case of the platinum cathode (90% against 70% for tungsten). The work function of the solid solution was estimated to be 6.3 eV, compared with 4.4 eV for tungsten. In terms of the data available, the thermionic current, which is the main source of energetic electrons, is about one order of magnitude lower for the solid solution cathode when compared with the tungsten cathode thermionic current. However, the polymer yield observed is higher in the former case. The concentration of the CH• species in the hollow cathode was found to differ greatly for the cathodes tested and was about 5 times higher in the case of tungsten-platinum cathodes. Since no excited platinum vapor could be detected in the gas phase, the increase in CH• concentration was attributed to a catalytic effect of the cathode inside surface. An evaluation of the plasma polymer deposition rate yields 70 nm·s−1 for the platinum-tungsten type hollow cathode and 42 nm·s−1 for the tungsten one. In both cases, the deposition rate is much higher than those obtained from the most widely used methods for plasma polymer deposition (0.10–1.0 nm·s−1) implying methane-argon mixtures, and is comparable to the results obtained with a new type of plasma polymer deposition reactor described in the literature.
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Meubus, P., Lange, H. & Jean, G. Methane polymerization with a hollow cathode: Influence of the cathode metal. Plasma Chem Plasma Process 9, 527–543 (1989). https://doi.org/10.1007/BF01023918
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DOI: https://doi.org/10.1007/BF01023918