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

Abstract

Abstract. 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 Â 10 15 cm À3 , 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) Â 10 14 cm À3 . 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 Â 10 13 cm À3 in HF as compared to that (8 Â 10 11 cm À3 ) in RF.