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Optical Emission from C2 Anions in Microwave-Activated CH4/H2 Plasmas for Chemical Vapor Deposition of Diamond

Research output: Research - peer-reviewArticle

Original languageEnglish
Pages (from-to)2760−2772
Number of pages13
JournalJournal of Physical Chemistry A
Issue number14
Early online date20 Mar 2017
StatePublished - 13 Apr 2017


Visible emission from C2(B2Σu+) anions has been identified underlying the much strongerSwan band emission from neutral C2(d3Πg) radicals (henceforth C2* and C2*, respectively) in MW-activated C/H/(Ar) plasmas operating under conditions appropriate for the chemical vapour deposition (CVD) of diamond. Spatially resolved measurements of the C2* and C2* emissions as functions of the C/H/(Ar) ratio in the input gas mixture, the total pressure, and the applied MW power, together with complementary 2-D(r, z) plasma modelling, identifies dissociative electron attachment (DEA) to C2H radicals in the hot plasma as the dominant source of the observed C2* emission. Modelling indicates substantially higher concentrations of C2H anions (from analogous DEA to C2H2) in the near-substrate region, but also suggests that the anion number densities will typically be 3–4 orders of magnitude lower than those of the electrons and partner cations, i.e. mainly C2H2+ and C2H3+. The identification of negatively charged carbon-containing species in diamond CVD plasmas offers a possible rationale for previous reports that nucleation densities and growth rates can be enhanced by applying a positive bias to the substrate.

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