Densities of Active species in N2/H2 RF and HF afterglows: application to surface nitriding of TiO2 nanocrystals

N 2 /0–5% H 2 flowing afterglows from Radio Frequency (RF) and High Frequency (HF) sources have been analyzed by optical emission spectroscopy. In similar conditions (pressure 5–6 Torr, flow rate 0.5 slm and power 100 W), it is found in pure N 2 a nearly constant N-atom density from the pink to the late afterglow, which is higher in HF than in RF: (1–2) and 0.4 × 10 15  cm −3 , respectively. With a N 2 /2% H 2 gas mixture, the early afterglows is changed to a late afterglow with about the same N-atom density for both RF and HF cases: (8–9) × 10 14  cm −3 . Anatase TiO 2 nanocrystals and Atomic Layer Deposition-grown films were exposed to the RF afterglows at room temperature. XPS analysis of the samples has shown that the highest N/Ti ratio of 0.24 can be achieved with the pure N 2 late afterglow. In the HF pure N 2 late afterglow, however, the N/Ti coverage was limited to 0.04 in spite of higher N-atom density. Such differences in the N content between the two RF and HF cases are attributed to the presence of a high O-atom impurity of 2 × 10 13  cm −3 in HF as compared to that (8 × 10 11  cm −3 ) in RF.