Sticking probability of CN radicals

The sticking probability, s, of CN(X2Σ+) radicals which were the precursor of the formation of amorphous carbon nitride films with high [N]/([N]+[C]) ratios (≤ 0.5) was re-evaluated. CN(X2Σ+) radicals were generated from the decomposition of BrCN with the microwave discharge flow of Ar of the pressure of 0.2–0.4 Torr. The number density of CN(X2Σ+), nCN(X), was evaluated from the intensity of the CN(A2Πi–X2Σ+) laser-induced fluorescence spectrum calibrated against Rayleigh scattering intensity of Ar. The weight of the C and N components of films, w, was evaluated from the compositional analysis for the deposited films using Rutherford back scattering and elastic recoil detection analysis. The [N]/([N]+[C]) ratios of films were 0.4–0.5. Based on nCN(X), w, and the flow speed measured by a time-resolved emission, s was evaluated both under the desiccated and H2O-added conditions as (8.5 ± 2.1) × 10− 2 − (6.1 ± 1.2) × 10− 2 and (11.4 ± 1.3) × 10− 2 − (7.4 ± 1.8) × 10− 2, respectively. The variation of s under various experimental conditions was discussed based on the electron densities in the reaction region.

Research Highlights
► Thin films of amorphous carbon nitride (a-CNx) with high [N]/([N] + [C]) ratios of 0.4 – 0.5 were fabricated.
► The precursor of the film formation was specifically the ground-state CN radicals.
► The sticking probability of CN radicals was evaluated with higher precision than the previous studies.