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Spatially Resolved Optical Emission and Modeling Studies of Microwave-Activated Hydrogen Plasmas Operating under Conditions Relevant for Diamond Chemical Vapor Deposition

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journal contribution
posted on 25.09.2018, 00:00 by Edward J. D. Mahoney, Benjamin S. Truscott, Sohail Mushtaq, Michael N. R. Ashfold, Yuri A. Mankelevich
A microwave (MW) activated hydrogen plasma operating under conditions relevant to contemporary diamond chemical vapor deposition reactors has been investigated using a combination of experiment and self-consistent 2-D modeling. The experimental study returns spatially and wavelength resolved optical emission spectra of the d → a (Fulcher), G → B, and e → a emissions of molecular hydrogen and of the Balmer-α emission of atomic hydrogen as functions of pressure, applied MW power, and substrate diameter. The modeling contains specific blocks devoted to calculating (i) the MW electromagnetic fields (using Maxwell’s equations) self-consistently with (ii) the plasma chemistry and electron kinetics, (iii) heat and species transfer, and (iv) gas–surface interactions. Comparing the experimental and model outputs allows characterization of the dominant plasma (and plasma emission) generation mechanisms, identifies important coupling reactions between hydrogen atoms and molecules (e.g., the quenching of H­(n > 2) atoms and electronically excited H2 molecules (H2*) by the alternate ground-state species and H3+ ion formation by the associative ionization reaction of H­(n = 2) atoms with H2), and illustrates how spatially resolved H2* (and Hα) emission measurements offer a detailed and sensitive probe of the hyperthermal component of the electron energy distribution function.