I. Jauberteau

NH3 and NHx<3 radicals synthesis downstream a microwave discharge sustained in an Ar-N2-H2 gas mixture. Study of surface reactive processes and determination of rate constants

NH3 and NHx<3 radicals are produced downstream a microwave discharge containing Ar-N2-H2 gas mixture. The chemical mechanism under investigation consists of heterogenous reactions between adsorbed species NH or NH2 (denoted NHs and NH2s) and H or H2 flowing downstream the discharge. NHs is adsorbed on the stainless steel reactor wall and reacts with H or H2 producing NH2s or . Then, part of NH2s produced reacts with H atoms producing ; another part is desorbed from the tube wall: . We assume that NH3 is spontaneously and totally desorbed. From the balance equations, we determine analytical relations for NH2s, NH2 and NH3 concentrations. We then measure values of reaction rate constants and compare the numerical results to measurements performed in the afterglow by means of mass spectrometer versus the %H2 injected in the discharge. We measure values in two different initial gas mixtures, 98.7% Ar-1.3% N2 and 66.6% Ar-33.3% N2. In the first gas mixture, k1, k2(NHs), k3(NHs) and ksg range between 1×10-17 and 2×10-17 m3 s-1, 0.035 and 0.045 m s-1, 9 and 11 m s-1, and 0.30 and 0.35 m-1 s-1, respectively. In the second gas mixture, as expected, similar values are found for k1 and ksg but the other two values increase by a factor of 5. Such an increase for k2(NHs) and k3(NHs) is probably due to the increase of the (NHs) concentration on the reactor wall. The recombination coefficient γ is deduced from the previous rate constant values. We find γ1 = 4.12×10-4, γ2 = 4.91×10-6 and γ3 = 7.93×10-4, using the mean values of reaction rate constants determined for k1, k2 and k3, respectively, in the first gas mixture. To our knowledge, these results have never been published before. They are in good agreement with values given in the literature for other similar mechanisms. Finally, we conclude that the loss of H atoms on the reactor wall mainly results in producing NH2s and NH3.

Characterization of an argon-hydrogen microwave discharge used as an atomic hydrogen source. Effect of hydrogen dilution on the atomic hydrogen production

This work is devoted to the study of an argon-hydrogen microwave plasma used as an atomic hydrogen source. Our attention has focused on the effect of the hydrogen dilution in argon on atomic hydrogen production. Diagnostics are performed either in the discharge or in the post-discharge using emission spectroscopy (actinometry) and mass spectrometry. The agreement between actinometry and mass spectrometry diagnostics proves that actinometry on the Ha(656.3 nm) and Hβ(486.1 nm) hydrogen Balmer lines can be used to measure the relative atomic hydrogen density within the microwave discharge. Results show that the atomic hydrogen density is maximum for a gas mixture corresponding to the partial pressure ratioPH2/PAr range between 1.5 and 2. The variation of atomic hydrogen density can be explained by a change of the dominant reactive mechanisms. At a low hydrogen partial pressure the dominant processes are the charge transfers with recombinations between Ar+ and H2 which lead to ArH+ and H2+ ion formation. Both ions are dissociated in dissociative electron attachment processes. At a low argon partial pressure the electron temperature and the electron density decrease with increasing partial pressure ratio. The dominant mechanisms become direct reactions between charged particles (e, H+, H2+, and H3+) or excited species H(n=2) with H2 producing H atoms.

HIGH REACTIVITY OF CH2 RADICAL IN AN AR-CH4 POST-DISCHARGE

AbstractThis work is devoted to the study of the reactivity of CH2radical in the post-discharge of an Ar–CH4microwave plasma. These radicals are selectively produced using the energy transfer reaction between argon metastable Ar(3P2) and CH4, This paper consists of three parts. The first part is the characterization of the argon metastable source. We measure the absolute argon metastable density within the argon microwave post-discharge, then we select the best discharge parameters in order to obtain the best conditions to produce Ar(3P2) species. The second part is related to the mass spectrometry study of species observed within the post-discharge and produced when methane is injected in an argon microwave post-discharge. We measure the absolute densities of the hydrocarbon species. Results show that the main species observed in the post-discharge are CH4, C2H2then C2H6, C2H4and the radical CH3. However, the radical CH2is only detectable for a low CH4density injected. The third part is related to the study of the methylene radical (CH2) reactivity in an Ar–CH4post-discharge. We measure the reaction rate constant of Ar(3P2) energy transfer to

Nitrogen ion beam-assisted pulsed laser deposition of boron nitride films

CH_4 ;Ar(^3 P_2 ) + CH_4 \underset{\raise0.3em\hbox{

Plasma nitriding of thin molybdenum layers at low temperature

\smash{\scriptscriptstyle\rightarrow}

Plasma chemistry and diagnostic in an Ar–N2–H2 microwave expanding plasma used for nitriding treatments

}}{k} _1 CH_2 + 2H + Ar

CHARACTERIZATION OF AN AR-TMS MICROWAVE DISCHARGE USING MASS SPECTROMETRY : EFFECT OF THE REACTOR DESIGN ON FREE-RADICAL CONTENTS

we find a value k1ranging from 5.7×10−16to 1.2×10−16m3/s. This value is in good agreement with the results proposed in the literature. Then we use this first reaction to produce CH2and to study in post-discharge the reaction