High H-atom Density in R(He,Ar)/x%(N2–5%H2) Early Afterglows

Abstract

Absolute densities of N atoms and N2(A) molecules and estimated densities of H atoms and N2(X,v > 13) and NH molecules are determined in R(He,Ar)/x%(N2–5%H2) flowing microwave discharges by a band intensity ratio method after calibration of the N atom density by NO titration. By varying the plasma parameters: pressure of 8 and 4 Torr, flow rates of 0.5, 1.0 and 2.0 slpm, HF power up to 150 W, a high N + N recombination fraction (> 80%) has been observed with He dilution in the early afterglow (t = 5 × 10–3 s). A maximum value of the H-atom density has been found in the He/2%(N2–5%H2) gas mixture at 8 Torr, 0.5 slpm and 150 W, with a [H]/[N] ratio of 0.3. With Ar dilution, it is found that the Ar/5%(N2–5%H2) gas mixture at 4 Torr, 0.5 slpm, 100 W brought a high H2 dissociation (80%), with a [H]/[N] ratio of about 0.6. From the variation of the H-atom density along the quartz tube, the wall destruction probability of the H-atoms was calculated to be $${\gamma }_{H}^{He}$$ = $${\gamma }_{H}^{Ar}$$ = (1–4) × 10–3 in helium and argon mixtures. Such results are of interest for the enhancement of surface nitriding by the combined effects of N and H atoms inclusion inside a TiO2 surface.