Analysis of dissociative excitation reactions of CH3CN with the ECR plasmas of Ar and He

The dissociative excitation reactions of CH3CN with the electron-cyclotron resonance (ECR) plasma flows of Ar and He were studied based on the electrostatic-probe measurements and on the optical emission spectra of the CN(B2Σ+ − X2Σ+) transition. The density and the temperature of free electrons and the CN(B2Σ+ − X2Σ+) emission intensity in these plasmas are varied by adding a trace amount of H2O. From the correlation between the CN(B2Σ+ − X2Σ+) emission intensity and the electron density contributing to the dissociation process upon the addition of H2O, the formation of the CN(B2Σ+) state from the decomposition of CH3CN proceeds, predominantly, via the electron impact in the Ar plasma and via the electron impact and/or the ion–electron recombination in the He plasma. These results are found to be consistent with the evaluation of the number densities of CN(B2Σ+) using the steady-state method. In addition, hydrogenated amorphous carbon nitride films were prepared under the desiccated condition, and the compositional analysis was carried out, yielding the [N]/([N] + [C]) ratio of 0.22 and 0.25 for the Ar and He plasmas, respectively.

► The mechanism of decomposition of CH3CN in the electron cyclotron resonance plasmas of Ar and He was elucidated. ► A trace amount of H2O vapor was introduced into the reaction system to compare the dependencies of the CN(B2Σ+ − X2Σ+) emission intensity and the density and the temperature of electrons. ► The decomposition was found to proceed via the impact of energetic electrons in the Ar plasma and via the electron impact and/or the ion–electron recombination in the He plasma. ► This reaction was applied to form hydrogenated amorphous carbon nitride films with [N]/([N] + [C]) = 0.22 and 0.25 for the Ar and He plasmas, respectively.