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Microwave plasma-activated chemical vapour deposition of nitrogen-doped diamond, II: CH4/N2/H2 plasmas

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)8537-8549
Number of pages13
JournalJournal of Physical Chemistry A
Volume120
Issue number43
Early online date8 Oct 2016
DOIs
DateAccepted/In press - 8 Oct 2016
DateE-pub ahead of print - 8 Oct 2016
DatePublished (current) - 3 Nov 2016

Abstract

We report a combined experimental and modelling study of microwave-activated dilute CH4/N2/H2 plasmas, as used for chemical vapour deposition (CVD) of diamond, under very similar conditions to previous studies of CH4/H2, CH4/H2/Ar and N2/H2 gas mixtures. Using cavity ring-down spectroscopy, absolute column densities of CH(X, v=0), CN(X, v=0) and NH(X, v=0) radicals in the hot plasma have been determined as functions of height, z, source gas mixing ratio, total gas pressure, p, and input power, P. Optical emission spectroscopy has been used to investigate, with respect to the same variables, the relative number densities of electronically excited species, namely H atoms, CH, C2, CN and NH radicals, and triplet N2 molecules. The measurements have been reproduced and rationalised from first principles by 2-D (r, z) coupled kinetic and transport modelling, and comparison between experiment and simulation has afforded a detailed understanding of C/N/H plasma-chemical reactivity and variations with process conditions and with location within the reactor. The experimentally-validated simulations have been extended to much lower N2 input fractions and higher microwave powers than were probed experimentally, providing predictions for the gas-phase chemistry adjacent to the diamond surface and its variation across a wide range of conditions employed in practical diamond-growing CVD processes. The strongly bound N2