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7thInternational Workshop on Plasma Science & Entrepreneurship, p. 24, Bochum, Germany

International audience; http://ocs.ciemat.es/EPS2015PAP/pdf/P4.305.pdf

References [59-61] were incorrectly cited in Falchetto G.L. et al 2014 (Nucl. Fusion 54 043018), the corresponding paragraphs on page 14-15 should be replaced ...

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)

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)

This paper studies the modifications induced in low-pressure radio-frequency (rf) capacitively coupled nitrogen plasmas, by the addition of a few amount of hydrogen (up to 5%). The work is an intermediate step towards the study of N2-CH4 plasmas, for the simulation of the ionospheric chemistry of Saturn's satellite Titan. The plasmas are studied using both experiments and simulations. The experimental setup is a parallel-plate reactor (driven at 13.56 MHz frequency), surrounded by a cylindrical metallic grid to confine the discharge [1]. Electrical diagnostics allow measuring: (i) the electron density, by using a resonant cavity method; (ii) the effective rf power coupled to the plasma, by using the subtractive method [2]. Optical emission spectroscopy diagnostics are used to study the evolution, with the working conditions, of: (i) the First Negative System with the N2+ band; (ii) the atomic hydrogen Hβ line at 486.1 nm; (iii) the atomic argon line at 811.5 nm. Simulations use a hybrid code that couples a 2D (r, z) time-dependent fluid-type module, describing the transport of the charged particles, to a very complete 0D kinetic module, for the nitrogen-hydrogen mixture. Results reveal that the electron density increases with the amount of injected H2, at constant coupled power. References [1] G. Alcouffe et al, Plasma Sources Sci. Technol. 19, 015008 (2010) [2] L.L. Alves et al, Plasma Sources Sci. Technol. (submitted, 2012), Fundação para a Ciência e a Tecnologia (FCT) - PICS Cooperation Program, CNRS - ANR program (ANR-09-JCJC-0038)

Comunicação em Poster, This paper studies the modifications induced in low-pressure radio-frequency capacitively coupled nitrogen plasmas, by the addition of a few amount of hydrogen (up to 5%). The plasmas are studied using both experiments (electrical and optical emission spectroscopy measurements) and simulations (using a fluid+kinetic code). Results reveal that the electron density increases with the amount of injected H2, at constant coupled power., Work supported by a PICS Cooperation Program, financed by the Portuguese FCT and the French (CNRS). A. Mahjoub thanks the ANR program (ANR-09-JCJC-0038 contract) for a post-doctoral position.

We have performed extensive measurements in capacitively coupled radio-frequency discharges, producing N2-CH4 plasmas for methane concentrations between 0% and 10%. These dusty plasmas are well characterized by monitoring the evolution, with the methane concentration, of the electron density, the self-bias voltage, the coupled power, and the spectral line intensity of a number of optical transitions. The plasma properties exhibit drastic changes that are found correlated with the dust production regime., Fundação para a Ciência e a Tecnologia (FCT) - PICS Cooperation Program, financed by the Portuguese FCT and the French CNRS. A. Mahjoub thanks the ANR program (ANR-09-JCJC-0038 contract) for a post-doctoral position., CNRS - ANR program (ANR-09-JCJC-0038 contract)

Apresentação em poster, The present work involves the study of Capacitively Coupled Plasmas (CCPs) produced at 13.56 MHz radio-frequency (RF) and 0.2 to 1.2 mbar pressures. The main characteristics of the CCP source, which is described with more detail in reference [1], are the following: (i) the discharge is confined laterally by a grounded cylindrical metallic grid; (ii) the gas is continuously injected into the chamber through the driven electrode, ensuring a uniform gas flow; and (iii) gases are pumped by a rotary-vane vacuum pump. In a parent abstract [2] we study CCPs produced in pure N2. Here we analyse the effect (upon both the electrical discharge and the plasma) of adding a small amount of H2 (up to 5%) to the RF nitrogen plasma. The measured discharge parameters are: (i) the applied voltage Vrf (which is kept constant as we vary the pressure and the concentration of H2); (ii) the self-bias potential Vdc of the polarized electrode; and (iii) the absorbed RF power. We observe that, for the same Vrf value, the effective RF absorbed power depends on both the pressure and the gas mixture composition. The plasma is studied by Optical Emission Spectroscopy (OES) from UV to near Infra-Red. The bands of the nitrogen second positive system (SPS), the nitrogen ionic first negative system (FNS) and the hydrogen line Hβ (486.1 nm) are recorded as a function of the H2 concentration, for different pressures. A small amount of argon is added to the gas mixture to act as an actinometer. For OES measurements, the 811.5nm Ar line is chosen because it doesn’t overlap with the nitrogen first positive system and because its excitation energy (13.07 eV) is close to the 12.74 eV of Hβ. For a given value of Vrf, our measurements show variations of the argon line intensity for different initial hydrogen concentrations. This behaviour reveals that the addition of H2 into N2 may affect the plasma chemistry. We will present the changes, for different plasma conditions, of the SPS bands of N2 and the FNS bands of N2+, the latter allowing to monitor the influence of H2 on the plasma ionisation. The variation of the H2 dissociation degree, for various work conditions, will also be presented., PICS Cooperation Program - Portuguese Foundation for Science and Technology and the French CNRS.

Apresentação em poster, This paper studies ccrf discharges (at f=13.56 MHz frequency) in pure nitrogen, produced within cylindrical parallel-plate reactors similar to GEC reference cells [1] (associated with the GREMI and the LATMOS setups, the latter corresponding to the PAMPRE experiment [2]), at 100-300 V applied voltages and 0.1-1 mbar pressures. Under these conditions, the neutral gas is found close to room temperature (~350 K) [3]. The discharges are studied using both experiments and simulations. Experiments include the measurement of the following quantities: (i) the applied voltage, using a high-voltage probe; (ii) the self-bias voltage; (iii) the effective power coupled to the plasma, taking into account circuit losses; (iv) the average electron density, using a resonant-cavity technique; (v) the intensities of radiative transitions with the nitrogen second-positive system and first-negative system, and with the 881.5 nm atomic line of argon, using optical emission spectroscopy diagnostics. The comparison between model results and measurements shows the influence in results of the nitrogen kinetics, particularly via the interaction of species with the reactor walls. Simulations use an hybrid code that couples a 2D time-dependent fluid module [4], describing the dynamics of charged particles (electrons and positive ions N2+ and N4+), and a homogeneous (0D) kinetic module, describing the production and destruction of nitrogen (atomic and molecular) neutral species. The coupling between these modules adopts the local mean energy approximation [4] to define space-time dependent electron parameters for the fluid module and to work-out space-time average rates for the kinetic module. Model results yield the self-consistent dc-bias voltage, the effective power coupled to the plasma, and the 2D spatial distributions for (i) the densities and fluxes with the charged particles and the electron mean energy, (ii) the densities of the most relevant nitrogen species, and (iii) the rf plasma potential., PICS Cooperation Program, financed by the Portuguese Foundation for Science and Technology and the Centre National de la Recherche Scientifique.

Apresentação em poster, Capacitively coupled radio-frequency (ccrf) discharges in N2-H2 mixtures are becoming increasingly popular. Discharges operated in mixtures of hydrogen and nitrogen are nowadays used as a source of active species for various kinds of applications from etching of low-k materials to modifications of polymer surfaces for biomedical applications. Moreover, these discharges are also being used for studies of planetary atmospheres. This work presents the modelling of 13.56 MHz ccrf discharges in N2 -H2 mixtures, produced within a cylindrical parallel-plate reactor (with 69 mm radius and 33 mm inter-electrode distance), similar to a GEC reference cell surrounded by a lateral grounded grid, for pressures from 0.2 to 1.5 mbar and RF coupled powers up to 30 W. Simulations use a 2D (r, z) time-dependent fluid-type code to describe the transport of electrons and positive ions in the reactor under study, coupled to a very complete 0D kinetic code for the nitrogen-hydrogen mixture. The fluid code solves the charged particle continuity and momentum transfer equations, the electron mean energy transport equations, and Poisson's equation for the rf electric potential. The kinetic code solves the electron Boltzmann equation and the rate balance equations of vibrational excited states and electronic excited states of the N2 and H2 molecules, yielding a set of electron transport parameters and rate coefficients for the processes involved in the charged particle production and destruction. The latter include (i) electron-impact ionisation from ground-state; (ii) electron-impact ionisation and associative ionisation involving excited states; (iii) ion conversion; and (iv) electron recombination with ions. The electron parameters are used within the fluid code, allowing for a self-consistent solution to the charged particle transport model by adopting the local mean energy approximation. Model results are systematically compared to measurements of the self-bias potential, the effective rf power (accounting for circuit losses), the average electron density (obtained by resonant-cavity measurements), and the intensities of radiative transitions with the nitrogen SPS and with atomic lines emitted by argon traces (obtained by Optical Emission Spectroscopy diagnostics).

P2-56; The present work is part of an endeavour to perform laboratory simulations of the chemistry of Titan, satellite of Saturn. In the atmosphere of Titan, composed of N2 and CH4, solid particles are produced by photochemistry and charged particles from Saturn's magnetosphere. We mimic this chemistry using a low-pressure capacitively coupled plasma (CCP), produced in a gas mixture representative of Titan's atmosphere. The production of solid particles in these discharges has already been observed, together with the delay in their formation and their effect upon the electron density. Here, we present a first contribution to this global task, by characterizing pure nitrogen CCPs (with a simpler chemistry) RF discharges. The study involves both modelling and diagnostics of the discharge plasma, aiming to compare simulations and measurements.

CTP.00151; This paper uses simulations and measurements to study capacitively coupled rf discharges (13.56 MHz) in pure nitrogen, produced within a cylindrical parallel-plate reactor, at 0.2-2 mbar pressures and 20-30 W coupled powers. The reactor is similar to a GEC reference cell surrounded by a lateral grounded grid. Simulations use an hybrid code that couples a 2D (r,z) time-dependent fluid module, describing the dynamics of charged particles, and a 0D kinetic module, describing the production and destruction of nitrogen (atomic and molecular) neutral species. The coupling between these modules adopts the local mean energy approximation to define space-time dependent electron parameters for the fluid code and to work-out space-time average rates for the kinetic code. Model results are compared to measurements of the self-bias potential, the effective rf power (accounting for circuit losses), the average electron density (obtained by resonant-cavity measurements), and the intensities of radiative transitions with the nitrogen SPS and with atomic lines emitted by argon traces (obtained by OES diagnostics).

KTP.029; This paper reports the modeling of capacitively coupled radio-frequency 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 0.2-3 mbar pressures and 5 -30 W coupled powers. This reactor is used to simulate, at laboratory scale, the N2/CH4 chemistry of Titan's atmosphere. We have used a 2D, time-dependent fluid-type code to describe the transport of electrons and positive ions N+2 and N+4 in the reactor, coupled to a 0D kinetic code for N2. The fluid code solves the charged particle and the electron mean energy transport equations, coupled to Poisson's equation for the RF electric potential. The kinetic code solves the electron Boltzmann equation and the rate balance equations of 45 vibrationally excited states and 7 electronically excited states of the N2 molecule, yielding a set of electron transport parameters and rate coefficients for the charged particle production and destruction. Model results are compared to measurements of the self- bias potential, the average electron density, and the line intensities of the FNS(0-0) [N+2 (B,0)-N+2 (X,0)] and of the SPS(0-2) [(N2(C,0)-N2(B,2)].

This paper presents a systematic characterization of a pure hydrogen capacitively coupled radio frequency discharge, produced in a parallel plate cylindrical setup, comparing experimental measurements obtained for such discharge with numerical simulations. A good agreement is found between simulation results and experimental measurements for the discharge main electrical parameters. A comparison of H atom absolute density LIF measurements with simulation results will also be presented.

In this paper we present the self consistent coupling of a 2D model of a parallel plate radio frequency discharge in pure hydrogen with a homogeneous chemical kinetics model including H2(X1Σg+,v=0..14) molecules and hydrogen atoms H(n=1-5). The model can estimate the ground state atomic hydrogen density and it was found that the vibrational kinetics changes the H3+ ion density and coupled power to the discharge about 40% when comparing with previous estimates using a simplified kinetics.