C2(a 3 Πu) radicals were produced using the dissociative excitation reaction of C2H2 with the microwave discharge flow of Ar. The mechanism of the production of these radicals was investigated by a combined analysis of the laser-induced fluorescence spectroscopy of the C2(d 3 Πg−a 3 Πu) (Swan band) and Ar( 3 P1− 3 P0) transitions and the electrostatic-probe measurements. From the dependences of these LIF intensities and the kinetic-energy distribution of free electrons on the pressure of Ar, it was concluded that the mechanism of the production of C2(a 3 Πu) was the collisional energy transfer from the metastable state of Ar, Ar( 3 P0,2). This conclusion was supported by a chemical-kinetic analysis.
Optical emission spectra of the CH(A2Δ–X2Π) transition were observed using the dissociative excitation reaction of C2H2 with the microwave discharge flow of Ar at the pressure of Ar, PAr, in the range of 0.20–0.40 Torr. The mechanism of the production of the CH(A2Δ) state was investigated by the following two methods. The first is the comparison of the PAr dependences of the emission intensity, of the intensity of the laser-induced fluorescence spectra of the 3P1–3P0 transition of Ar, and of the density and temperature of free electrons. The second is the steady-state chemical kinetic analysis with several assumptions of the relevant reaction rate constants. It was concluded that CH(A2Δ) radicals were formed by charge transfer from Ar+ followed by ion–electron recombination with the significant contribution of the impact of free electrons. Energetic considerations revealed that the ions participating in the recombination reaction are excited vibrational levels of C2H2+.
Hydrogenated amorphous carbon nitride films with the [N]/([N] + [C]) ratios of 0.29–0.44 were formed from the microwave discharge of the gas mixture of C2H2 with an excess amount of N2. The ratio of the fluxes, s = Φa-CN/ΦCN(X), was evaluated in this study, where Φa-CN was the flux of N atoms incorporated into the films and ΦCN(X) was that of CN radicals in the gas phase. ΦCN(X) was evaluated from the density of CN radicals using the A2Πi–X2Σ+ laser-induced fluorescence spectra and from the flow speed using the time-resolved emission, and Φa-CN from the film mass calibrated against atomic compositions. The s value was in the range of 0.22–0.78, being 1.2–1.7 times the sticking probability of CN radicals corrected in this study, 0.19–0.45. Then, the contribution of CN radicals was evaluated to be 60–80% of the N source of the films. The chemical structure and mechanical property of the films were analyzed in terms of Raman scattering, IR absorption, and nanoindentation measurements.
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