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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.
Alternative Excitation Mechanisms Occurring within Microwave-activated Plasmas under Conditions Relevant to the Chemical Vapour Deposition of DiamondAuthor: Mahoney, E. J. D., 1 Oct 2019
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)
Mahoney, E. J. D., Truscott, B. S., Ashfold, M. N. R., & Mankelevich, Y. A. (2017). Optical Emission from C2– Anions in Microwave-Activated CH4/H2 Plasmas for Chemical Vapor Deposition of Diamond. Journal of Physical Chemistry A, 121(14), 2760−2772. https://doi.org/10.1021/acs.jpca.7b00814