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

Abstract

N2 /0–5% H2 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 N2 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 × 1015 cm−3 , respectively. With a N2 /2% H2 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) × 1014 cm−3 . Anatase TiO2 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 N2 late afterglow. In the HF pure N2 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 × 1013 cm−3 in HF as compared to that (8 × 1011 cm−3 ) in RF.