Simultaneous interaction of methyl radicals and atomic hydrogen with amorphous hydrogenated carbon films, as investigated with optical in situ diagnostics |
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Authors: | A von Keudell M Meier T Schwarz-Selinger |
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Institution: | (1) Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748 Garching, Germany, DE |
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Abstract: | Methyl radicals (CH3) and atomic hydrogen (H) are dominant radicals in low-temperature plasmas from methane. The surface reactions of these radicals
are believed to be key steps leading to deposition of amorphous hydrogenated carbon (a-C:H) films or polycrystalline diamond
in these discharges. The underlying growth mechanism is studied, by exposing an a-C:H film to quantified radical beams of
H and CH3. The deposition or etching rate is monitored via ellipsometry and the variation of the stoichiometry is monitored via isotope
labeling and infrared spectroscopy. It was shown recently that, at 320 K, methyl radicals have a sticking coefficient of 10-4 on a-C:H films, which rises to 10-2 if an additional flux of atomic hydrogen is present. This represents a synergistic growth mechanism between H and CH3. From the interpretation of the infrared data, a reaction scheme for this type of film growth is developed: atomic hydrogen
creates dangling bonds by abstraction of bonded hydrogen within a surface layer corresponding to the range of H in a-C:H films.
These dangling bonds serve at the physical surface as adsorption sites for incoming methyl radicals and beneath the surface
as radicalic centers for polymerization reactions leading to carbon–carbon bonds and to the formation of a dense a-C:H film.
Received: 18 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001 |
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Keywords: | PACS: 81 15 Gh 82 65 My 81 15 Aa 52 40 Hf |
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