Experiments and modelling in N2-H2 capacitively coupled radio-frequency discharges at low pressure

This work uses experiments and simulations to analyze the modifications induced in pure N2 capacitively coupled radio-frequency discharges, running at low pressure (0.6–1.2 mbar) and low power (5–20 W), by the addition of small amounts of H2 (up to 5%). Simulations use a hybrid code coupling a two-dimensional time-dependent fluid module, describing the dynamics of the charged particles, to a zero-dimensional kinetic module, describing the production and destruction of nitrogen and hydrogen neutral species. The discussion is particularly focused on the results obtained for the electron density and the radiative transition intensities with nitrogen species. Model predictions are in qualitative agreement with measurements, for the evolution of these quantities with changes in both the gas pressure and the hydrogen percentage in the gas mixture.Fundação para a Ciência e a Tecnologia (FCT

Modelling of a CCP-RF discharge used for the simulation of Titan’s chemistry

This paper reports the modelling of CCP-RF discharges (13.56 MHz) in pure nitrogen, produced within a cylindrical parallel-plate reactor, similar to a GEC reference cell surrounded by a lateral grounded grid, at 0.1-2 mbar pressures and 10-50 W coupled powers. This study is a first step in simulating Titan’s chemistry at laboratory scale, using the PAMPRE experiment. Modelling results are compared with experimental measurements of the average electrondensity, and the self-bias potential at the polarized electrode

Capacitively coupled radio-frequency N2 discharges at low pressures

Capacitively coupled radio-frequency discharges (ccrf) in nitrogen mixtures are frequently used for the processing, modification and functionalization of different kinds of materials. Although nitrogen plasmas have been studied for many years, and despite their growing interest in applications, there is only partial knowledge about ccrf nitrogen plasmas. This paper uses experiments and modelling to study ccrf discharges in pure nitrogen, at 13.56 MHz frequency, 0.1–1 mbar pressures and 2–30 W coupled powers [1]. Experiments performed on two similar (not twin) setups, existing in the LATMOS and the GREMI laboratories, include electrical and optical emission spectroscopy (OES) measurements. Electrical measurements give the rf-applied and the direct-current-self-bias voltages, the effective power coupled to the plasma and the average electron density. OES diagnostics measure the intensities of radiative transitions with the nitrogen second-positive and first-negative systems, and with the 811.5 nm atomic line of argon (present as an actinometer). In the particular case of non-equilibrium ccrf discharges in nitrogen, a self-consistent modeling strategy must account for the interplay between the transport of particles, in the presence of density gradients and the rf field, and their production/destruction due to kinetic mechanisms involving both electrons and heavy species. Simulations use a hybrid code that couples a two-dimensional timedependent fluid module [2], describing the dynamics of the charged particles (electrons and positive ions N2 + and N4 +), and a zero-dimensional kinetic module, describing the production and destruction of nitrogen (atomic and molecular) neutral species [3]. The coupling between these modules adopts the local mean energy approximation to define space–time-dependent electron parameters for the fluid module and to work out space–time-averaged rates for the kinetic module. The model gives general good predictions for the self-bias voltage and for the intensities of radiative transitions (both average and spatially resolved), underestimating the electron density by a factor of 3–4.Fundação para a Ciência e a Tecnologia (FCT

Use of the linear absorption coefficient for absolute comparison of plasma films in the mid-IR range

In this work, we present the mid-infrared analysis of analogues of Titan's aerosols produced in a radio frequency capacitively coupled plasma (RF-CCP). The influence of the gas mixture on aerosols spectra is also studied through the analysis of the carbonaceous bands of the spectra, and its Gaussian deconvolution.Представлен анализ в среднем инфракрасном диапазоне аналогов титановых аэрозолей, которые производятся в радиочастотных источниках плазмы с емкостной связью (РЧ-ЕСС). Также изучено влияние газовой смеси на спектры аэрозолей с помощью анализа углеродсодержащих полос спектра и ее гауссовой деконволюции (обратная свертка).Представлено аналіз у середньому інфрачервоному діапазоні аналогів титанових аерозолів, які проводяться в радіочастотних джерелах плазми з ємнісним зв'язком (РЧ-ЕСС). Також вивчено вплив газової суміші на спектри аерозолів за допомогою аналізу вуглецевмісних смуг спектра і її гауссової деконволюції (зворотня згортка)

Use of the linear absorption coefficient for absolute comparison of plasma films in the mid-IR range

In this work, we present the mid-infrared analysis of analogues of Titan's aerosols produced in a radio frequency capacitively coupled plasma (RF-CCP). The influence of the gas mixture on aerosols spectra is also studied through the analysis of the carbonaceous bands of the spectra, and its Gaussian deconvolution.Представлен анализ в среднем инфракрасном диапазоне аналогов титановых аэрозолей, которые производятся в радиочастотных источниках плазмы с емкостной связью (РЧ-ЕСС). Также изучено влияние газовой смеси на спектры аэрозолей с помощью анализа углеродсодержащих полос спектра и ее гауссовой деконволюции (обратная свертка).Представлено аналіз у середньому інфрачервоному діапазоні аналогів титанових аерозолів, які проводяться в радіочастотних джерелах плазми з ємнісним зв'язком (РЧ-ЕСС). Також вивчено вплив газової суміші на спектри аерозолів за допомогою аналізу вуглецевмісних смуг спектра і її гауссової деконволюції (зворотня згортка)

N2-H2 capacitively coupled radio-frequency discharges at low pressure. Part I. Experimental results: Effect of the H2 amount on electrons, positive ions and ammonia formation

The mixing of N2 with H2 leads to very different plasmas from pure N2 and H2 plasma discharges. Numerous issues are therefore raised involving the processes leading to ammonia (NH3) formation. The aim of this work is to better characterize capacitively-coupled radiofrequency plasma discharges in N2 with few percents of H2 (up to 5%), at low pressure (0.3-1 mbar) and low coupled power (3-13 W). Both experimental measurements and numerical simulations are performed. For clarity, we separated the results in two complementary parts. The actual one (first part), presents the details on the experimental measurements, while the second focuses on the simulation, a hybrid model combining a 2D fluid module and a 0D kinetic module. Electron density is measured by a resonant cavity method. It varies from 0.4 to 5 109 cm-3, corresponding to ionization degrees from 2 10-8 to 4 10-7. Ammonia density is quantified by combining IR absorption and mass spectrometry. It increases linearly with the amount of H2 (up to 3 1013 cm-3 at 5% H2). On the contrary, it is constant with pressure, which suggests the dominance of surface processes on the formation of ammonia. Positive ions are measured by mass spectrometry. Nitrogen-bearing ions are hydrogenated by the injection of H2, N2H+ being the major ion as soon as the amount of H2 is >1%. The increase of pressure leads to an increase of secondary ions formed by ion/radical-neutral collisions (ex: N2H+, NH4 +, H3 +), while an increase of the coupled power favours ions formed by direct ionization (ex: N2 +, NH3 +, H2 +).N. Carrasco acknowledges the financial support of the European Research Council (ERC Starting Grant PRIMCHEM, Grant agreement no. 636829). A. Chatain acknowledges ENS Paris-Saclay Doctoral Program. A. Chatain is grateful to Gilles Cartry and Thomas Gautier for fruitful discussions on the MS calibration. L.L. Alves acknowledges the financial support of the Portuguese Foundation for Science and Technology (FCT) through the project UID/FIS/50010/2019. L. Marques and M. J. Redondo acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2019

N(2D) and N(2P) metastable production by electron collisions in a D.C. glow discharge

The atomic nitrogen metastable densities of N(2D) and N( 2P) have been measured by optical absorption in a continuous glow dis harge. Electronic densities have been measured with a microwave resonant cavity. The evolution of N( 2D) and N(2P) densities as a function of electronic density allows the estimation of the overall creation coefficient by electronic collisions CeM : e + N2 →eCM e + N(2D, 2P) + N. This coefficient is of the same order of magnitude for N( 2D) and N(2P) and lies between 1.5 x 10-10 and 4 x 10-11 cm3 s-1 for a pressure range between 0.5 and 1.5 torr (tube radius R = 1 cm). For currents higher than 20 mA the density of N(2P) is larger than the N(2D) density (approximately a factor of two at 50 mA).Les densités des atomes métastables d'azote atomique N(2D) et N(2P) ont été mesurées par absorption optique dans une décharge luminescente continue. La densité électronique a été mesurée à l'aide d'une cavité hyperfréquence. L'évolution des densités des deux états N(2D) et N(2P) en fonction de la densité électronique permet d'estimer le coefficient de création global CeM des niveaux métastables par collisions électroniques : e + N2 →eCM e + N(2D, 2P) + N . Ce coefficient est du même ordre de grandeur pour N(2D) et N(2P). Il est compris entre 1,5 x 10-10 et 4 x 10-11 cm3 s -1 pour des pressions variant de 0,5 à 1,5 torr (rayon du tube R = 1 cm). Pour des courants supérieurs à 20 mA, la densité du niveau N(2P) est plus élevée que celle du niveau N(2D) (environ le double à 50 mA)

N(2D, 2P) METASTABLE ATOMS PRODUCTION IN A N2 D.C. GLOW DISCHARGE.

No abstract availabl

Nitrogen Atoms and Triplet States N2(B3Πg),N2(C3Πu)\mathsf{N_{2}(B^{3}}\Pi_\mathsf{g}), \mathsf{N_{2}(C^{3}}\Pi_\mathsf{u}) in Nitrogen Afterglow

The fluorescence of N$_{2}$(B$^{3}\Pi_{\rm g}$) and N$_{2}$(C$^{3}\Pi_{\rm u}$) states is observed in a time afterglow. This fluorescence is due to repopulation via pooling reaction of N$_{2}$(A$^{3}\Sigma^{+}_{\rm u}$) state. From a kinetic model, it is shown that the N$_{2}$(C$^{3}\Pi_{\rm u}$) characteristic decay time depends on the atomic nitrogen density. Atomic density is deduced from the observed fluorescence of N$_{2}$(C$^{3}\Pi_{\rm u}$) for density higher than $5\times10^{13}$ cm$^{-3}$. This density increases with pulse duration and current intensity.La fluorescence des états N$_{2}$(B$^{3}\Pi_{\rm g}$) et N$_{2}$(C$^{3}\Pi_{\rm u}$) est observée dans une post-décharge temporelle. Ces fluorescences sont dues à un repeuplement par la réation de pooling entre états N$_{2}$(A$^{3}\Sigma^{+}_{\rm u}$). A partir d'un modèle cinétique, il est montré que le temps caractéristique de décroissance de l'état N$_{2}$(C$^{3}\Pi_{\rm u}$) dépend de la densité d'azote atomique. La densité d'atomes est déduite de la fluorescence observée pour des densités supérieures à $5\times10^{13}$ cm$^{-3}$. La densité atomique augmente avec la durée et l'intensité de l'impulsion

Atomic oxygen recombination on fused silica: modelling and comparison to low-temperature experiments (300 K)

International audienceThis work is devoted to the study of atomic oxygen recombination on a glass surface, mainly in connection with atomic sources development. In this paper we present a non-stationary model for atomic oxygen recombination on a fused silica surface. Kinetics equations for oxygen atoms, taking into account heterogeneous reactions between gaseous atoms and the surface (Eley-Rideal mechanisms), as well as homogeneous processes involving surface migration of adsorbed species (Langmuir-Hinshelwood mechanisms), are solved. Surface reaction coefficients are calculated, and the choice of numerical values for surface parameters is discussed. The solution to the equations is compared to our previous experiments concerning the influence of the surface state on atomic recombination. An estimation is made of surface reaction coefficient values