- Email: [email protected]
(10−4–10−3)CH4 plasma
Surface and Coatings Technology 112 (1999) 38–42
Measurements by optical and mass spectrometry of the density of active species in the flowing afterglow of a N /(10−4–10−3)CH plasma 2 4 A.-M. Diamy a,*, J.-C. Legrand a, A. Moritts a, A. Ricard b a Laboratoire de Chimie des Surfaces, CNRS URA 1428, Universite´ Pierre et Marie Curie, Case 196, 4 place Jussieu, 75252 Paris, Cedex 05, France b Centre Plasmas et Applications, CNRS ESA 5002, Universite´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, Cedex, France
Abstract The influence of small quantities of methane on the behaviour of the active species N, N (A) and N+ (B) has been studied by 2 2 emission and mass spectrometry. The nitrogen atom concentration [N ] is in the (0.1–4)×1015 particles cm−3 range under the experimental conditions investigated. For a N –0.01%CH mixture, [N ] is twice as high as for pure N . The metastable N (A) 2 4 2 2 concentration is approximately 1011 particles cm−3, i.e. it varies from 3 to 6 times lower than in pure N as the pressure decreases 2 from 25 to 12.5 mbar, and the excited ion density [N+ (B)] is 5×104–2×106 particles cm−3, i.e. 100–1000 times lower than in 2 pure N . © 1999 Elsevier Science S.A. All rights reserved. 2 Keywords: Emission spectroscopy; Mass spectrometry; Methane plasma; Nitrogen plasma
1. Introduction For a long time, the decomposition of methane in dinitrogen discharges has been the subject of numerous studies in different fields, such as detoxification, atmospheric chemistry, synthesis, metal nitriding, etc. [1–5]. To improve such applications, it is interesting to know the influence of methane addition on active species produced in the discharge and responsible for the chemistry in this medium. Such information can be obtained by means of the mass spectrometry of N atoms, and by the spectroscopic emission study of the first positive and second positive dinitrogen bands, and the first negative bands of N+. 2 2. Experimental set-up The experimental set-up is illustrated in Fig. 1. The plasma is produced in a silica tube (12 mm o.d., 10 mm i.d.) crossing a cylindrical resonant cavity connected to a microwave generator (2.45 GHz, adjustable power up to 2 kW ). The gas pressure and the gas flow rate are measured by means of a baratron gauge (MKS, 122A) and mass flow meters (Alfagaz, RDM 280), respectively. Optical emission of the following bands is analysed * Corresponding author. Tel.: +33 1 44275523; Fax: +33 1 44275525; e-mail: [email protected]
by means of a monochromator (Jobin-Yvon, HRS1, 1220 lines mm−1) and a photomultiplier (Hamamatsu, R928): 580.4 nm (B,11A,7), 380.5 nm (C,0B,2) of N and 391.4 nm (B,0X,0) of N+. Mass spectrometry 2 2 is performed with a Riber QMM17 quadripolar spectrometer with mass detection from 1 to 300 m.a.u. The species in the post-discharge are taken from a hole 56 mm in diameter and 1.5 mm long. Measurements are carried out along the post-discharge tube, from the end of the discharge to approximately 60 cm downstream (i.e. from 0 to 110 ms). For optical measurements, an optical fibre is moved along the tube to obtain the intensities I across the diameter of the reactor. For l mass spectrometry, the extraction hole being at a fixed position, it is the microwave cavity which is moved along the tube. The experimental conditions are the following: flow rate Q=1 SL min−1 (S, i.e. 298 K and 1 bar), pressure P=12.5–70 mbar, absorbed microwave power estimated at 180 W, and methane concentration in the mixture from 0.01 to 0.075%.
3. Results 3.1. N-atom concentrations For pure dinitrogen, the variation of the N-atom density, as measured by the mass spectrometer versus
0257-8972/98/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved. PII S 02 5 7 -8 9 7 2 ( 9 8 ) 0 0 61 2 - 4
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
39
Fig. 1. Experimental set-up.
afterglow time, is shown in Fig. 2. The afterglow time is deduced from the distance along the post-discharge by taking into account the temperature variation from 1500 K at the end of the discharge to 300 K in the late afterglow [6,7]. The N-atom concentrations, determined by NO titration, are also shown in Fig. 2. In the late afterglow (i.e. for times over 40 ms), satisfactory agreement is found between mass spectrometry and NO titration measurements. At a time of approximately 5 ms, a maximum in the N-atom density is observed in the pink afterglow part of the post-discharge.
In the pink afterglow, a new ionisation is produced by vibrationally excited dinitrogen molecules, as discussed below. It can be seen in Fig. 2 that the N-atom density, as determined by NO titration in the early afterglow, is approximately 50% higher than the values obtained by mass spectrometry, because the NO molecules can be consumed not only by N atoms but also by N+ ions. 2 The pink afterglow disappears as methane is added to dinitrogen. Variations of the N-atom concentration versus added CH are shown in Fig. 3. It can be seen 4
Fig. 2. N atom density versus time in the afterglow of pure dinitrogen for different pressures, measured by mass spectrometry and by NO titration (&).
40
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
that the N-atom concentration increases by a factor of approximately 2 when 0.01% CH is introduced into 4 N. 2
sities are reduced in the N –CH mixtures. The intensity 2 4 maximum in the N pink afterglow is no longer 2 observed.
3.2. Radiative N species 2 3.2.1. 580.4 nm band emission The N (B,11A,7) l=580.4 nm band intensity is 2 reproduced on a logarithmic scale versus time in Fig. 4, for conditions of pure N and of N –0.015%CH dis2 2 4 charges (180 W ), at pressures of 12.5, 18, 25 and 40 mbar. It has been reported previously [8] that at time t 10 ms, the production of the N (B,11) state is mainly 2 by N-atom recombination, and the intensity of the 580.4 nm band is related as follows: =Q ×[N ]2, 580.4 580.4 where I is the intensity of the 580.4 nm band and 580.4 Q is a function of the K spectral response of the 580.4 580.4 spectrometer and of the kinetic rate constants [6,7]. In Fig. 4, the maxima of I in pure N at time t 10 ms 580.4 2 results from energy transfers from excited N states 2 occurring in the pink afterglow [6–8]. By introducing 0.015% CH into N , the maximum of I is flattened. 4 2 580.4 It increases with gas pressure and is observed for longer times than in pure N . 2 I
3.2.2. 380.5 and 391.4 nm band emissions The N (C,0–B,2) l=380.5 nm and N+ (B,0−X,0) 2 2 l=391.4 nm band intensities are shown in Fig. 5 for the same conditions as in Fig. 4. Clearly, these band inten-
4. Kinetic reactions The pink afterglow is produced after the discharge as the gas temperature is sufficiently low (approximately 500 K ) to inhibit the quenching of N ( X,v) vibrational 2 levels (v–T processes). Consequently, the vibrational excitation of N ( X,v) increases again by vibrational 2 interchanges (v–v processes). This results in a new ionisation process in the post-discharge (Penning ionisation): N (a∞)+N (a∞)e+N+ +N (or N+ ), (1) 2 2 2 2 4 where N (a∞) is a metastable molecule which is produced 2 by the following reaction: N ( X,v≥16)+N ( X,v≥16)N +N (a∞). (2) 2 2 2 2 Other metastable molecules such as N (A) are also 2 excited by N ( X,v) and N ( X,v) collisions, leading to 2 2 N-atom production in the pink afterglow by the following reactions: N (A)+N (A)N (B,v=13–15)+N N+N+N , 2 2 2 2 2 (3) N (A)+N ( X,v≥13)N (B,v=13−15)+N 2 2 2 2 N+N+N . 2
(4)
Fig. 3. [N ]/[N ] ratio in the near afterglow (10 cm: &, 0, +) and in the late afterglow (50 cm: $, n) at three pressures, i.e. 66.7 (&, $), 50 (0) 2 and 13.3 mbar (+, n), versus methane concentration (%) in the mixture.
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
41
Fig. 4. 580.4 nm emission intensity, N (B,v=11A,v=7), versus time. 2 +, pure N ; $, N –0.015%CH . 2 2 4
Fig. 5. 380.5 [N (C,v=0B,v=2)] and 391.4 nm [N+(B, v=0X,v= 2 2 0)] emission intensity versus time. +, pure N ; $, N –0.015%CH . 2 2 4
Eqs. (3) and (4) could explain the increase in N atoms (Fig. 2). They also contribute to the N (B,v=11) excita2 tion observed in the pink afterglow at time t 10 ms in pure N ( Fig. 4). The N (C,0) and N+ (B,0) excitation 2 2 2 in the pink afterglow is produced by the following reactions:
CH mixture, where a sharp decrease is observed behind 4 the end of the discharge. At time t10 ms, the N (A) 2 density is about one order of magnitude lower in the N –CH mixture than in pure N . 2 4 2 Again, the excited N+ (B,0) ion density can be deter2 mined from the 391.4 nm band intensity [6,7]:
N (A)+N (A)N (C )+N , (5) 2 2 2 2 N+ +N ( X,v=12)N+ (B)+N . (6) 2 2 2 2 Eqs. (5) and (6) are at the origin of the 380.5 and 391.4 nm band emissions (Fig. 5). A rough estimation of the N (A) density can be 2 deduced from the intensity of N (C,0B,2) [6,7]: 2 I =Q ×[N (A)]2, (7) 380.5 380.5 2 where Q is a function of K , the pressure and rate 380.5 380.5 constants. Results are displayed in Fig. 6 for two pressures in pure N and in the N –0.015%CH mixture. A 2 2 4 N (A) density maximum is detected in the N pink 2 2 afterglow. Such a maximum disappears in the 0.015%
I
=K ×[N+ (B,0)]. (8) 391.4 391.4 2 [N+ (B,0)] is in the range 5×104−2×106 2 particles cm−3 in the N –CH mixture, i.e. 102–103 lower 2 4 than in pure N . This result shows that the ion density 2 decreases with the addition of methane. This is in good agreement with the results obtained in previous work [9], where the ion concentrations were measured by Langmuir probes.
5. Conclusion The densities of the active species N and N (A) have 2 been determined in N and N –0.015%CH flowing 2 2 4
42
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
Fig. 6. N (A) density versus time. +, pure N ; $, N –0.015%CH . 2 2 2 4
post-discharges. The early afterglow is characterised by a new ionisation process with strong emission from excited N+ (B) ions, giving it the name ‘‘pink afterglow’’. 2 By mass and optical spectrometry, an increase in N-atom densities has been found in the pure N pink afterglow 2 as a result of production by N ( X,v) and N ( X,v) 2 2 pooling reactions. The pink afterglow disappears with CH addition as a consequence of the efficient quenching 4 of active N (a∞) species by methane and its radicals. 2 However, an increase in the N-atom concentration with the introduction of CH into N was observed. 4 2 Such an increase can in part be attributed to an electricfield increase in the discharge, as demonstrated previously in N –H DC discharge [10], and also to a 2 2 modification of the surface of the tube by the products of methane decomposition (particularly H atoms). The decrease in the metastable N (A) state density (Fig. 6) 2 could also be due to the increase in nitrogen atom concentration, because N quenches N (A) very easily 2 [11].
References [1] D.E. Tevault, Plasma Chem. Plasma Process. 5 (1985) 369–390. [2] P. Capezzuto, F. Cramarossa, G. Ferraro, P. Maione, E. Molinari, Gazz. Chim. Ital. 103 (1973) 1153–1188. [3] F. Raulin, D. Mourey, G. Toupance, Origins Life 12 (1982) 267–279. [4] A. Ricard, J. Oseguera, L. Falk, H. Michel, M. Gantois, IEEE Trans. Plasma Sci. 18 (1990) 940. [5] A. Oumghar, J.C. Legrand, A.M. Diamy, N. Turillon, R.I. Ben-Aim, Plasma Chem. Plasma Process. 14 (1994) 229–249. [6 ] J. Al Andari, A.-M. Diamy, L. Hochard, J.-C. Legrand, A. Ricard, in: J. Harry ( Ed.), Proc. ISPC 11, vol. 4, Loughborough, 1993, pp. 1344–1349. [7] J. Al Andari, A.-M. Diamy, L. Hochard, J.-C. Legrand, A. Ricard, in: J.V. Herberlein, D.W. Ernie, J.T. Roberts ( Eds.), Proc. ISPC 12, vol. 1, Minneapolis, MN, 1995, pp. 373–378. [8] S. Bockel, A.M. Diamy, A. Ricard, Surf. Coat. Technol. 7475 (1995) 474–478. [9] A.M. Diamy, J.C. Legrand, V. Hrachova´, J. Phys. III 5 (1995) 435–445. [10] A. Garscadden, R. Nagpal, Plasma Sources Sci. Technol. 4 (1995) 268. [11] M.F. Golde, Int. J. Chem. Kinet. 20 (1988) 75–92.
Measurements by optical and mass spectrometry of the density of active species in the flowing afterglow of a N /(10−4–10−3)CH plasma 2 4 A.-M. Diamy a,*, J.-C. Legrand a, A. Moritts a, A. Ricard b a Laboratoire de Chimie des Surfaces, CNRS URA 1428, Universite´ Pierre et Marie Curie, Case 196, 4 place Jussieu, 75252 Paris, Cedex 05, France b Centre Plasmas et Applications, CNRS ESA 5002, Universite´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, Cedex, France
Abstract The influence of small quantities of methane on the behaviour of the active species N, N (A) and N+ (B) has been studied by 2 2 emission and mass spectrometry. The nitrogen atom concentration [N ] is in the (0.1–4)×1015 particles cm−3 range under the experimental conditions investigated. For a N –0.01%CH mixture, [N ] is twice as high as for pure N . The metastable N (A) 2 4 2 2 concentration is approximately 1011 particles cm−3, i.e. it varies from 3 to 6 times lower than in pure N as the pressure decreases 2 from 25 to 12.5 mbar, and the excited ion density [N+ (B)] is 5×104–2×106 particles cm−3, i.e. 100–1000 times lower than in 2 pure N . © 1999 Elsevier Science S.A. All rights reserved. 2 Keywords: Emission spectroscopy; Mass spectrometry; Methane plasma; Nitrogen plasma
1. Introduction For a long time, the decomposition of methane in dinitrogen discharges has been the subject of numerous studies in different fields, such as detoxification, atmospheric chemistry, synthesis, metal nitriding, etc. [1–5]. To improve such applications, it is interesting to know the influence of methane addition on active species produced in the discharge and responsible for the chemistry in this medium. Such information can be obtained by means of the mass spectrometry of N atoms, and by the spectroscopic emission study of the first positive and second positive dinitrogen bands, and the first negative bands of N+. 2 2. Experimental set-up The experimental set-up is illustrated in Fig. 1. The plasma is produced in a silica tube (12 mm o.d., 10 mm i.d.) crossing a cylindrical resonant cavity connected to a microwave generator (2.45 GHz, adjustable power up to 2 kW ). The gas pressure and the gas flow rate are measured by means of a baratron gauge (MKS, 122A) and mass flow meters (Alfagaz, RDM 280), respectively. Optical emission of the following bands is analysed * Corresponding author. Tel.: +33 1 44275523; Fax: +33 1 44275525; e-mail: [email protected]
by means of a monochromator (Jobin-Yvon, HRS1, 1220 lines mm−1) and a photomultiplier (Hamamatsu, R928): 580.4 nm (B,11A,7), 380.5 nm (C,0B,2) of N and 391.4 nm (B,0X,0) of N+. Mass spectrometry 2 2 is performed with a Riber QMM17 quadripolar spectrometer with mass detection from 1 to 300 m.a.u. The species in the post-discharge are taken from a hole 56 mm in diameter and 1.5 mm long. Measurements are carried out along the post-discharge tube, from the end of the discharge to approximately 60 cm downstream (i.e. from 0 to 110 ms). For optical measurements, an optical fibre is moved along the tube to obtain the intensities I across the diameter of the reactor. For l mass spectrometry, the extraction hole being at a fixed position, it is the microwave cavity which is moved along the tube. The experimental conditions are the following: flow rate Q=1 SL min−1 (S, i.e. 298 K and 1 bar), pressure P=12.5–70 mbar, absorbed microwave power estimated at 180 W, and methane concentration in the mixture from 0.01 to 0.075%.
3. Results 3.1. N-atom concentrations For pure dinitrogen, the variation of the N-atom density, as measured by the mass spectrometer versus
0257-8972/98/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved. PII S 02 5 7 -8 9 7 2 ( 9 8 ) 0 0 61 2 - 4
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
39
Fig. 1. Experimental set-up.
afterglow time, is shown in Fig. 2. The afterglow time is deduced from the distance along the post-discharge by taking into account the temperature variation from 1500 K at the end of the discharge to 300 K in the late afterglow [6,7]. The N-atom concentrations, determined by NO titration, are also shown in Fig. 2. In the late afterglow (i.e. for times over 40 ms), satisfactory agreement is found between mass spectrometry and NO titration measurements. At a time of approximately 5 ms, a maximum in the N-atom density is observed in the pink afterglow part of the post-discharge.
In the pink afterglow, a new ionisation is produced by vibrationally excited dinitrogen molecules, as discussed below. It can be seen in Fig. 2 that the N-atom density, as determined by NO titration in the early afterglow, is approximately 50% higher than the values obtained by mass spectrometry, because the NO molecules can be consumed not only by N atoms but also by N+ ions. 2 The pink afterglow disappears as methane is added to dinitrogen. Variations of the N-atom concentration versus added CH are shown in Fig. 3. It can be seen 4
Fig. 2. N atom density versus time in the afterglow of pure dinitrogen for different pressures, measured by mass spectrometry and by NO titration (&).
40
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
that the N-atom concentration increases by a factor of approximately 2 when 0.01% CH is introduced into 4 N. 2
sities are reduced in the N –CH mixtures. The intensity 2 4 maximum in the N pink afterglow is no longer 2 observed.
3.2. Radiative N species 2 3.2.1. 580.4 nm band emission The N (B,11A,7) l=580.4 nm band intensity is 2 reproduced on a logarithmic scale versus time in Fig. 4, for conditions of pure N and of N –0.015%CH dis2 2 4 charges (180 W ), at pressures of 12.5, 18, 25 and 40 mbar. It has been reported previously [8] that at time t 10 ms, the production of the N (B,11) state is mainly 2 by N-atom recombination, and the intensity of the 580.4 nm band is related as follows: =Q ×[N ]2, 580.4 580.4 where I is the intensity of the 580.4 nm band and 580.4 Q is a function of the K spectral response of the 580.4 580.4 spectrometer and of the kinetic rate constants [6,7]. In Fig. 4, the maxima of I in pure N at time t 10 ms 580.4 2 results from energy transfers from excited N states 2 occurring in the pink afterglow [6–8]. By introducing 0.015% CH into N , the maximum of I is flattened. 4 2 580.4 It increases with gas pressure and is observed for longer times than in pure N . 2 I
3.2.2. 380.5 and 391.4 nm band emissions The N (C,0–B,2) l=380.5 nm and N+ (B,0−X,0) 2 2 l=391.4 nm band intensities are shown in Fig. 5 for the same conditions as in Fig. 4. Clearly, these band inten-
4. Kinetic reactions The pink afterglow is produced after the discharge as the gas temperature is sufficiently low (approximately 500 K ) to inhibit the quenching of N ( X,v) vibrational 2 levels (v–T processes). Consequently, the vibrational excitation of N ( X,v) increases again by vibrational 2 interchanges (v–v processes). This results in a new ionisation process in the post-discharge (Penning ionisation): N (a∞)+N (a∞)e+N+ +N (or N+ ), (1) 2 2 2 2 4 where N (a∞) is a metastable molecule which is produced 2 by the following reaction: N ( X,v≥16)+N ( X,v≥16)N +N (a∞). (2) 2 2 2 2 Other metastable molecules such as N (A) are also 2 excited by N ( X,v) and N ( X,v) collisions, leading to 2 2 N-atom production in the pink afterglow by the following reactions: N (A)+N (A)N (B,v=13–15)+N N+N+N , 2 2 2 2 2 (3) N (A)+N ( X,v≥13)N (B,v=13−15)+N 2 2 2 2 N+N+N . 2
(4)
Fig. 3. [N ]/[N ] ratio in the near afterglow (10 cm: &, 0, +) and in the late afterglow (50 cm: $, n) at three pressures, i.e. 66.7 (&, $), 50 (0) 2 and 13.3 mbar (+, n), versus methane concentration (%) in the mixture.
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
41
Fig. 4. 580.4 nm emission intensity, N (B,v=11A,v=7), versus time. 2 +, pure N ; $, N –0.015%CH . 2 2 4
Fig. 5. 380.5 [N (C,v=0B,v=2)] and 391.4 nm [N+(B, v=0X,v= 2 2 0)] emission intensity versus time. +, pure N ; $, N –0.015%CH . 2 2 4
Eqs. (3) and (4) could explain the increase in N atoms (Fig. 2). They also contribute to the N (B,v=11) excita2 tion observed in the pink afterglow at time t 10 ms in pure N ( Fig. 4). The N (C,0) and N+ (B,0) excitation 2 2 2 in the pink afterglow is produced by the following reactions:
CH mixture, where a sharp decrease is observed behind 4 the end of the discharge. At time t10 ms, the N (A) 2 density is about one order of magnitude lower in the N –CH mixture than in pure N . 2 4 2 Again, the excited N+ (B,0) ion density can be deter2 mined from the 391.4 nm band intensity [6,7]:
N (A)+N (A)N (C )+N , (5) 2 2 2 2 N+ +N ( X,v=12)N+ (B)+N . (6) 2 2 2 2 Eqs. (5) and (6) are at the origin of the 380.5 and 391.4 nm band emissions (Fig. 5). A rough estimation of the N (A) density can be 2 deduced from the intensity of N (C,0B,2) [6,7]: 2 I =Q ×[N (A)]2, (7) 380.5 380.5 2 where Q is a function of K , the pressure and rate 380.5 380.5 constants. Results are displayed in Fig. 6 for two pressures in pure N and in the N –0.015%CH mixture. A 2 2 4 N (A) density maximum is detected in the N pink 2 2 afterglow. Such a maximum disappears in the 0.015%
I
=K ×[N+ (B,0)]. (8) 391.4 391.4 2 [N+ (B,0)] is in the range 5×104−2×106 2 particles cm−3 in the N –CH mixture, i.e. 102–103 lower 2 4 than in pure N . This result shows that the ion density 2 decreases with the addition of methane. This is in good agreement with the results obtained in previous work [9], where the ion concentrations were measured by Langmuir probes.
5. Conclusion The densities of the active species N and N (A) have 2 been determined in N and N –0.015%CH flowing 2 2 4
42
A.-M. Diamy et al. / Surface and Coatings Technology 112 (1999) 38–42
Fig. 6. N (A) density versus time. +, pure N ; $, N –0.015%CH . 2 2 2 4
post-discharges. The early afterglow is characterised by a new ionisation process with strong emission from excited N+ (B) ions, giving it the name ‘‘pink afterglow’’. 2 By mass and optical spectrometry, an increase in N-atom densities has been found in the pure N pink afterglow 2 as a result of production by N ( X,v) and N ( X,v) 2 2 pooling reactions. The pink afterglow disappears with CH addition as a consequence of the efficient quenching 4 of active N (a∞) species by methane and its radicals. 2 However, an increase in the N-atom concentration with the introduction of CH into N was observed. 4 2 Such an increase can in part be attributed to an electricfield increase in the discharge, as demonstrated previously in N –H DC discharge [10], and also to a 2 2 modification of the surface of the tube by the products of methane decomposition (particularly H atoms). The decrease in the metastable N (A) state density (Fig. 6) 2 could also be due to the increase in nitrogen atom concentration, because N quenches N (A) very easily 2 [11].
References [1] D.E. Tevault, Plasma Chem. Plasma Process. 5 (1985) 369–390. [2] P. Capezzuto, F. Cramarossa, G. Ferraro, P. Maione, E. Molinari, Gazz. Chim. Ital. 103 (1973) 1153–1188. [3] F. Raulin, D. Mourey, G. Toupance, Origins Life 12 (1982) 267–279. [4] A. Ricard, J. Oseguera, L. Falk, H. Michel, M. Gantois, IEEE Trans. Plasma Sci. 18 (1990) 940. [5] A. Oumghar, J.C. Legrand, A.M. Diamy, N. Turillon, R.I. Ben-Aim, Plasma Chem. Plasma Process. 14 (1994) 229–249. [6 ] J. Al Andari, A.-M. Diamy, L. Hochard, J.-C. Legrand, A. Ricard, in: J. Harry ( Ed.), Proc. ISPC 11, vol. 4, Loughborough, 1993, pp. 1344–1349. [7] J. Al Andari, A.-M. Diamy, L. Hochard, J.-C. Legrand, A. Ricard, in: J.V. Herberlein, D.W. Ernie, J.T. Roberts ( Eds.), Proc. ISPC 12, vol. 1, Minneapolis, MN, 1995, pp. 373–378. [8] S. Bockel, A.M. Diamy, A. Ricard, Surf. Coat. Technol. 7475 (1995) 474–478. [9] A.M. Diamy, J.C. Legrand, V. Hrachova´, J. Phys. III 5 (1995) 435–445. [10] A. Garscadden, R. Nagpal, Plasma Sources Sci. Technol. 4 (1995) 268. [11] M.F. Golde, Int. J. Chem. Kinet. 20 (1988) 75–92.