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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.

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 kinds of discharges can provide information relevant for studies of planetary atmospheres. The present work involves the study of a low pressure capacitively coupled RF discharge operated in variable mixtures of N2 and H2 at variable pressures and powers. The systematic measurements of electron density, RF voltage, self bias and the observation of several molecular bands by means of optical emission spectroscopy gave us important information about basic processes relevant for the understanding and application of such kind of discharges. The experimental results are interpreted by means of a hybrid model, namely the effect of admixing hydrogen into a N2 discharge.

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).

International audience; Dust particle nucleation and growth has been widely studied these last 15 years in different chemistries and experimental conditions. This phenomenon is correlated with various electrical changes at electrodes, including self-bias voltage and amplitudes of the various harmonics of current and voltage. Some of these changes, such as the appearance of more resistive plasma impedance, are correctly attributed to loss of electrons in the bulk plasma to form negative molecular ions and more precisely charged nanoparticles. These changes were studied and correlated to the different phases on the dust particle formation. It is well known now that, in silane argon gas mixture discharges, in the first step of this particle formation we have formation of nanometer sized crystallites. These small entities accumulate and when their number density reaches a critical value, they start to aggregate to form bigger particles. The different phases are well defined and determined thanks to the time evolution of the different electrical parameter changes. The purpose of this contribution is to compare different chemistries to highlight similarities and/or differences in order to establish possible universal dust particle growth mechanisms. The chemistries we studied concern SiH4-Ar, CH4, CH4-N2 and Sn(CH3)4. We also refer to works performed in other laboratories in different discharge configurations.

International audience; The aim of this paper is to contribute to improve the knowledge concerning the growth steps of hydrocarbon dust particles in Ar-CH4 plasma. To achieve this aim, we monitored the plasma impedance modification, due to the particle formation, by measuring the time-evolution of the self bias voltage, the current third harmonic and the electron density. Emission Spectroscopy turns out to be a good tool for estimating the electron temperature. While, Transmission and Scanning Electron Microscopy are used to characterize the morphology and the size of collected powders.

International audience; This paper deals with the study of the growth kinetics of hydrocarbon dust particles in low pressure N2-CH4 gas mixture radio frequency discharges. The partial pressure of CH4 is about 2% of the gas mixture total pressure (0.9 mbar), and the power varies from 20 to 40 W. The initiation and growth of hydrocarbon particles are followed thanks to the measurement of the self bias voltage, the amplitude of the third harmonic of the discharge current, the electron density and the electron temperature. The microwave resonant cavity technique is used to measure the time evolution of the electron density, while the morphology and the size of the collected powders are studied by the means of Transmission and Scanning Electron Microscopy.