It is presently compared to the afterglows after microwave plasmas in Toulouse Univ. and after RF plasmas in Ajou Univ. The synthesis of results after a microwave plasma is detailed in where the densities of N, H and C‐ atoms are reported in N2 − H2 and N2 − CH4. The applications of the HF and RF afterglows are for TiO2 surface nitriding. We report a detailed comparison between RF and microwave (HF) plasmas of N2 as well as N2 − H2 and N2 − CH4 in the corresponding afterglows by comparing densities of active species at nearly the same discharge conditions of tube diameter (5-6 mm), gas pressure (6-8 Torr), flow rate (0.6-1.0 slpm) and applied power (50-150 W). The analysis reveals an interesting difference between the two cases; the length of the RF plasma (25 cm) is measured to be much longer than that of HF (6 cm). In RF, with a N2 flow rate Q = 1 slpm, a pressure p = 8 Torr and an incident power of 100 Watt, a pink afterglow extends on 15 cm in the 21 mm i.d. tube (from z = 32 cm to z = 47 cm), followed by a late afterglow (after z = 48 cm). In HF, a pink afterglow is observed in the bent part of the 18 mm tube with an N2 flow rate of 0.5 slpm, a pressure p = 5 Torr and an incident power of 100 Watt. The late afterglow extends up to the 5 liter reactor with a characteristic yellow color. This yellow color is the signature of N-atom recombination on the N2(B,11) radiative state as described in the following. This ensures a much longer residence time (10−2s) of the active species in the N2 RF plasma [compared to that (10−3s) of HF], providing a condition for an efficient vibrational excitation of N2(X, v), making the RF plasma more vibrationally excited than the HF one. As a result of high VV plasma excitation in RF, the densities of the vibrationally excited N2(X, v > 13) molecules are higher in the RF afterglow than in the HF afterglow. Destruction of N2(X, v) on the quartz tube wall is estimated to be very similar between the two systems as can be inferred from the γv destruction probability of N2(X, v > 13) on the tube wall: (2- 3) 10−3 for both cases, obtained from a comparison between the density of N2(X, v > 13) along the afterglows. Interestingly enough, densities of N‐atoms and N2(A) metastable molecules in the afterglow regions, however, are measured to be very similar to each other. The measured lower density of N2+ ions than expected in the HF afterglow is rationalized from a high oxygen impurity in the HF setup since N2+ ions are very sensitive to oxygen impurity. In the N2 − H2 studied gas mixtures, the N2(X, v > 13) molecules were more destroyed in RF than in HF and inversely, the NH radicals and H atoms are more populated.
The H-atom density was corrected from the N+H+N2 rate
coefficient as determined in Chapter 13: k=10-33cm6s-1.
The TiO2 surface nitriding in RF was compared to
HF at room gas temperature (RT). First, it produced the most rich nitriding
layers with a ratio N/Ti of 0.24 in the RF N2 late afterglow which was
attributed to a low O‐impurity in RF (a few ppm), compared to several 102 ppm in
HF. Second, in the N2 − H2 studied gas mixtures, the high
H‐atoms density appeared to be at the detriment of the nitriding layer with a
N/Ti ratio reduced to a few percent in RF as for the HF case. In both RF and HF
afterglows, the NH inclusion came with that of N.
In progress, a new HF reactor in Toulouse with reduced
O‐atom impurity (a few ppm) to increase the N/Ti ratio as for the RF Ajou
reactor.
Author (s) Details
André Ricard
LAPLACE, Université de
Toulouse, CNRS, INPT, UPS, 118 route de Narbonne, 31062 Toulouse Cedex 9,
France.
Jean-Philippe
Sarrette
LAPLACE, Université de Toulouse, CNRS, INPT, UPS, 118 route de Narbonne,
31062 Toulouse Cedex 9, France.
Soo-Ghee Oh
Department of Energy Systems Research, Ajou University, Suwon 16499, Korea
and Department of Chemistry, Ajou
University, Suwon 16499, Korea.
Yu-Kwon Kim
Department of Energy Systems Research, Ajou University, Suwon 16499, Korea
and Department of Chemistry, Ajou University, Suwon 16499, Korea.
Please see the book here:- https://doi.org/10.9734/bpi/mono/978-93-49473-93-5/CH23
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