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International audience; Tunable diode laser absorption spectroscopy is used for recording the spectrally mixed profiles of argon 772.376 nm (2p 7-1s 5) and 772.421 nm (2p 2-1s 3) lines at different argon background pressures between 0.3 and 1 atmosphere. The absorbing atoms in the Ar*(1s 5) and Ar*(1s 3) metastable states are produced in a plane-to-plane dielectric barrier glow discharge operating at 20 kHz. The pressure broadening coefficient w and wavelength shift, s of the lines, deduced from the analysis of their variation versus pressure of recorded profiles, are w 1 =28.3±2.0 pm (14.2±1.0 GHz) and s 1 =11.5±0.8 pm (-5.8±0.4 GHz) for 772.376 nm line and w 2 =36.3±0.5 pm (18.2±0.3 GHz) and s 2 =12.8±0.7 pm (-6.4±0.4 GHz) for 772.4207 nm line, at 1 bar and 300 K. The progressive enhancement with argon pressure of the peak densities ratio [Ar*(1s 3)]/[Ar*(1s 5)], reaching 0.3 at 1 bar, reveals the importance of Arinduced collisions for the population transfer from resonant 1s 2 to the metastable 1s 3 state. Also, the time variation of Ar*(1s) densities indicates the presence of a weak excitation channel outside the discharge current pulse initiated by the breakdown. This channel results from the heating of electrons by the electric field seen by the gas in the DBD gap.

National audience; Le présent bilan de mandature 2016-2021 de la CPCN (Conférence des présidentes et présidents de sections et de commissions interdisciplinaires du Comité national de la recherche scientifique) a une triple finalité. Il constitue d’abord une forme d’autoévaluation de l’action de la CPCN et, à travers elle, de l’action coordonnée des sections et commissions interdisciplinaires (CID), au cours de cette mandature, en rappelant autant que de besoin le contexte dans lequel cette action s’est inscrite. Il vise également à rendre compte de cette action auprès de la communauté scientifique française à travers une diffusion la plus large possible. Il doit enfin permettre un passage de relais avec les sections et CID et avec la CPCN qui seront mises en place à l’automne 2021.

This work demonstrates the efficient optical and passivation properties provided by hydrogenated silicon nitride (SiNx:H) layers deposited in a lab‐scale atmospheric pressure plasma enhanced chemical vapor deposition (AP‐PECVD) reactor. By applying modulated low‐frequency plasma (200 kHz), homogeneous SiNx:H layers, with small variances in thickness w and refractive index n (Dw < 2 nm; Dn < 0.02), were achieved on a surface area of 45 × 55 mm2. The use of voltage amplitude modulation enabled discharge optimization and led to greatly enhanced SiNx:H film homogeneity and conformity in comparison with continuous plasma discharge conditions. Additionally, AP‐PECVD SiNx:H showed good thermal stability (Dw < 1 nm; Dn < −0.02) with low absorption coefficients (k < 0.1 at 275 nm), demonstrating that such layers could act as efficient antireflective coatings. Furthermore, outstanding surface passivation properties were achieved after firing, both on n‐type FZ c‐Si substrates of standard 2.8 O.cm doping (teff = 1.45 ms) and on highly doped 85 O/sq n+ emitters (j0e = 74 ± 2 fA.cm−2). Finally, AP‐PECVD SiNx:H thin films were tested on industrial passivated emitter and rear solar cell (PERC) architectures, where the potential of applying these layers both as efficient rear‐side capping layer and front‐side antireflective coating was demonstrated. The first lab‐scale 40 × 40 mm2 PERC solar cells featuring AP‐PECVD SiNx:H layers led to conversion efficiencies of up to 20.6%. These results pave the way for upscaling the dielectric barrier discharge lab‐scale reactor in an industrial in‐line process, which could provide low‐cost and high‐throughput SiNx:H capping and antireflective layers.

Tunable diode laser absorption spectroscopy was used to record the space-and time-resolved number density of argon metastable atoms, Ar(1s3) (Paschen notation), in plane-to-plane dielectric barrier discharges (DBDs) operated in a Penning Ar–NH3 mixture at atmospheric pressure. In both low-frequency (LF 650 V, 50 kHz) discharges and dual LF–radiofrequency (RF 190 V, 5 MHz) discharges operated in α–γ mode, the density of Ar(1s3) revealed a single peak per half-period of the LF voltage, with rise and decay times in the sub-microsecond time scale. These results were compared to the predictions of a 1D fluid model based on continuity and momentum equations for electrons, argon ions (Ar+ and Ar2 +) and excited argon 1s atoms as well electron energy balance equation. Using the scheme commonly reported for Ar-based DBDs in the homogeneous regime, the Ar metastable kinetics exhibited much slower rise and decay times than the ones seen in the experiments. The model was improved by considering the fast creation of Ar2 * excimers through three-body reactions involving Ar(1s) atoms and the rapid loss of Ar2 * by vacuum ultraviolet light emission. In optically thin media for such photons, they can readily reach the dielectric barriers of the DBD electrodes and induce secondary electron emission. It is shown that Ar2 * and photoemission play a significant role not only on the Ar metastable kinetics, but also on the dominant ionization pathways and possible α–γ transition in dual frequency RF–LF discharges.

The proof of the concept of a new, onestep and safe by design process to synthesize metal-polymer nanocomposites thin films on a large surface is presented. It is based on the injection of an aerosol of a solution of metal (gold) salts dissolved in a polymerizable solvent (isopropanol) into an argon atmospheric pressure dielectric barrier discharge. The main novelty of this method resides in the fact that the nanoparticles are formed in situ, inside the plasma reactor, in the gas phase. Consequently, the nanoparticle synthesis and deposition are concomitant with the solvent polymerization used to produce the matrix, which makes it possible to obtain homogeneous layers of non-agglomerated nanoparticles (NPs) with high NPs density. By toggling between low and high-frequency discharges, gold/polymer nanocomposites with different morphologies and optical properties are synthesized. The effect of the concentration of gold in the aerosol and the gas residence time in the plasma as well as the ratio of high and low-frequency discharge and their repetition rate are presented. The thin films are systematically characterized by AFM and UV–visible spectroscopy to analyze their morphologies along with their plasmonic resonances.

This paper investigates the transition from α to α–γ-mode of a dual frequency (5 MHz/50 kHz) dielectric barrier discharge (DBD) at atmospheric pressure. The study is based on both experiments and modeling of a plane/plane DBD in a Penning mixture (Ar–NH3). The discharge is in the α-RF mode with three different voltage amplitudes (250, 300 and 350 V) and biased by a low-frequency (LF) voltage with an amplitude varying from 0 to 1300 V. At a given threshold of LF voltage amplitude (of about 400 V for a 2 mm gap and 133 ppm of NH3), a transition from α to α–γ-mode occurs. It is characterized by a drastic increase of both the argon and NH emissions. Increasing the NH3 concentration leads to a decrease of the LF voltage amplitude required to reach the α–γ-mode (experiment). The transition from α to α–γ-mode is initiated when the ionization in the sheath increases and the α–γ-mode is established when this ionization becomes higher than the self-sustainment criterion (1/γ). The transition from α to α–γ-mode results in an increase of the particle densities and a stabilization of the gas voltage independently of the LF voltage amplitude. Without secondary electron emission there is no transition. In the model, increasing the secondary emission coefficient from 0.05 to 0.15 leads to a decrease of the LF voltage amplitude required to switch from α to α–γ-mode from 700 to 550 V.

International audience; Glow and filamentary regimes of Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition (AP-PECVD) in a planar Dielectric Barrier Discharge (DBD) configuration were compared for thin film deposition from ethyl lactate (EL) as a precursor. Space-resolved Fourier Transform Infrared Spectroscopy (FTIR) was used to study both the EL decomposition in the plasma phase and the composition of the thin film. EL chemical bonds concentration along the gas flow decreases progressively in the GDBD while it drastically oscillates in the FDBD, with values higher than that of the initial mixture. EL decomposition route depends on the discharge regime as the decrease of the concentration of the different investigated bonds are not the same for an identical amount of energy provided to the EL molecules. CO2 is systematically formed in the plasma reaching a maximum concentration of 25 ppm in the FDBD and 40 ppm in the GDBD mode.

International audience; An aerosol-assisted plasma process was used to deposit, at low temperature and atmospheric pressure, photocatalytic hydrocarbon polymer/TiO2 nanoparticles nanocomposite coatings onto both flat glass slides and open-cell polyurethane foams. Various characterization techniques were used to demonstrate the potential of the developed process for the controlled deposition of TiO2-based coatings on the different supporting substrates, with special attention to the foams due to their complex three-dimensional porous structure.The photocatalytic activity of the plasma-coated materials was evaluated by the decomposition of methyl orange in aqueous solution under UV irradiation, using a purposely designed recirculating batch photoreactor. The comparative study revealed that greater photocatalytic activity can be achieved with the open-cell foams, pointing to the beneficial properties of macroporous photocatalyst supports in comparison with conventional flat ones.The prepared photocatalytic materials presented remarkable reusability and maintained good activity after prolonged operation (40 h) corresponding to 20 consecutive reaction runs. Results on the evolution of the photocatalytic performance of the plasma-coated samples over multiple runs were correlated with those obtained from the detailed characterization of their surface chemical composition, morphology and wettability as a function of the operation time in photocatalytic water treatment.

Radio-frequency (RF) homogeneous dielectric barrier discharge (DBD) is compared to low frequency glow DBD to make silicon oxide from Ar/NH3/SiH4. RF-DBD is a more powerful discharge, and the growth rate is not limited by precursor dissociation rate but by powder formation. Powders are not deposited in the plasma zone but in the post-discharge due to their trapping by the electric field. Modulation of the RF-DBD is a useful solution to avoid powder formation. Powders are systematically avoided if the plasma energy during time on stays below 750 µJ. RF-DBD modulation also increases the growth rate twofold compare to continuous RF. The optimum growth rate without powder corresponds to a short Ton to limit precursor dissociation, a long Toff to enhance diffusion and a fast repeat frequency to increase deposition rate.

Christian Mayoux passed away on the 29th of October, 2020, at the age of 84, in Muret, a small town near Toulouse in the south of France, where he used to live since ten years. Christian was born in Pamiers, France, in 1936. He received the Doctorate degree (PhD) in 1961 from the University of Toulouse from which Paul Sabatier University was established in 1969. From 1963 to 1966, he was lecturer at the University before joining the French National Center for Scientific Research (CNRS) and the new born “Laboratoire de Genie Electrique de Toulouse” (LGET). The new lab was under the supervision of Professor R. Lacoste and focused its research on dielectrics and electrical insulation in the context of Electrical Engineering. The LGET researchers were fighting within the French research landscape to launch and organize the new domain of “engineering sciences”. Christian Mayoux investigated the effects of electrical discharges on dielectric surfaces, trying to understand the chemical and physical processes at play at different stages of the interaction. Transformation of the surface for short interaction time with the emergence of specific surface properties, but also surface degradation for longer interaction time, with deleterious effects for the material withstanding were put forward. Following this, a new approach where the surface of a polymer was exposed to different species -electrons, ions, metastables, UV, etc. was brought about with the objective to understand the individual and synergetic effects of each of the energy sources present in a partial discharge. Christian was quickly recognized by the international community for this pioneering work then developed internationally. Later on, starting in 1976, he began to focus on electrical treeing phenomena, and later on water treeing, following at the same time the ideas that emerged from his initial work on partial discharges. On top of that, Christian Mayoux was at the origin of several research areas that are still very active in LAPLACE (the successor of LGET), among them the dielectric barrier discharges at atmospheric pressure that become homogeneous under given circumstances, the luminescence phenomena occurring when an electric field is applied to a dielectric, or the mechanical deformation of a polymer under high electric field. Christian Mayoux received many invitations for giving invited lectures either at international conferences or during seminars. He was awarded the Whitehead Memorial Lecture at the Conference on Electrical Insulation and Dielectric Phenomena (CEIDP) in 2000.

International audience; Nanocomposite coatings are made by Atmospheric Pressure PECVD from ethyl lactate (EL) and silica nanoparticles (NPs) in a Dielectric Barrier Discharge (DBD) using Frequency Shift Keying (FSK) to alternate between 1 and 15 kHz voltages. In-situ plasma FTIR and thin film FTIR, SEM, AFM and profilometry show that (i) 1 kHz DBD mainly deposits NPs, 15 kHz only polymerizes EL (ii) the EL polymerization rate is the same in FSK and continuous modes (iii) despite the 50/50 contribution of both frequencies, the NPs deposit is 3 times faster in FSK mode than in 1 kHz DBD and compared to 1 and 15 kHz coatings, in the nanocomposite, NPs Si-O-Si and EL C=O bonds per unit length are equal to 68 and 34% respectively. In-situ FTIR 2 detects SiO2 NPs, their functionalization, and the formation of CO2.

To study dual frequency Townsend glow and radio frequency DBDs in an Ar/NH3 Penning mixture, different voltages are applied on each electrode of a plane/plane DBD. The one which has the higher amplitude and frequency, V H, determines the discharge regime. The other one, which has a lower amplitude and frequency, V L, is more similar to a bias voltage. V H frequency ranges from 50 kHz to 13.56 MHz and V L frequency from 1 kHz to 2 MHz. The amplitude of V L is always kept lower than the breakdown voltage. The discharge behavior is characterized by space and phase resolved optical emission spectroscopy and Fourier transform of the plasma induced light intensity. When the frequencies of two voltages are close to each other, V L higher than 150 V increases the discharge light intensity. In glow and Townsend discharges, this increase is attributed to the enhancement of the plasma density, due to the ions drift from the plasma bulk to the cathode, which produces a higher secondary electron emission. For the radiofrequency discharge, the enhancement of the light intensity is attributed to an enhancement of the positive space charge due to the higher voltage amplitude. When the frequencies of two voltages are very different, e.g. for V L between 1 and 100 kHz and a 5.5 MHz α-RF discharge, the behavior largely depends on V L amplitude. Above some low frequency (LF), the discharge tends to extinguish when V L amplitude is at its maximum. This is explained by a diminution of the plasma density resulting from the ion drift to the cathode due to V L. When V L is very high, it enhances the discharge intensity. This discharge amplification is associated with a transition from α to γ RF mode, which only occurs when the two voltages have the same polarity. Whatever the RF discharge mode, γ or α, the discharge is diffuse. To determine the interest of LF-RF dual frequency DBD for the PECVD, SiOx coatings, made with a single and a dual LF-RF frequency DBDs, are compared. It is concluded that the ɣ dual frequency removes OH functions from the material lattice and densifies the layer.

International audience; This article describes the occurrence of a phenomenon that is observed while recording mid-infrared (4000–700 cm−1) absorption spectra of dielectric barrier discharges sustained at frequencies ranging from 300 Hz to 15 kHz. This phenomenon is observed as the presence of very sharp spikes in the spectrum, for which the wavenumber depends on both the high voltage frequency used to generate the discharge and the velocity of the moving mirror of the interferometer (which in turn determines the interferogram sampling frequency). While it is well known that the consumption of gas precursor within plasmas can be followed, we demonstrate that Fourier transform infrared spectroscopy also makes it possible to monitor frequencies and coupling of excitation mechanisms occurring in the plasma.

Dense hydrogenated silicon nitride (SiNx:H) layers for photovoltaics are made by Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition (AP-PECVD). The dependence of morphology, chemical, optical and passivation properties of the thin films on the plasma reactor configuration, the mode of homogeneous DBD (glow, Townsend, RF, nano pulsed) and the SiH4/NH3 gas flow ratio are investigated. Avoiding gas recirculation, improving thin film homogeneity through the electrode length and the plasma modulation appear as key points. Silicon solar cells made with AP-PECVD SiN antireflective coating have the same efficiency as standard low pressure PECVD cells, showing the great potential of AP-PECVD.

Nanocomposite thin films of TiO2 in a polymer-like matrix are grown in a filamentary argon (Ar) dielectric barrier discharge (DBD) from a suspension of TiO2 nanoparticles in isopropanol (IPA). The sinusoidal voltage producing the plasma is designed to independently control the matrix growth rate and the transport of nanoparticle (NP) aggregates to the surface. The useful FSK (frequency shift keying) modulation mode is chosen to successively generate two sinusoidal voltages: a high frequency of 15 kHz and a low frequency ranging from 0.5 to 3 kHz. The coating surface coverage by the NPs and the thickness of the matrix are measured as a function of the FSK parameters. The duty cycle between these two signals is varied from 0 to 100%. It is observed that the matrix thickness is mainly controlled by the power of the discharge, which largely depends on the high-frequency value. The quantity of NPs deposited in the composite thin film is proportional to the duration of the low frequency applied. The FSK wavefor...

This work is a contribution to a better understanding of dual frequency discharge at atmospheric pressure. Based on experiments and numerical modeling, it is focused on radio frequency (5 MHz) – low frequency (50 kHz) plane/plane dielectric barrier discharge in a Penning mixture (Ar-NH3). The discharge is in the α-RF mode, biased by a LF voltage having an amplitude ranging from 0 to 1300 V. When the LF amplitude increases, there is a threshold (around 600 V for a 2 mm gap) from which the light intensity (experiment) and the ionization level (modelling) drastically increase. In this work the physics of the RF-LF DBD below and above this threshold is studied. Depending on the respective RF and LF polarity, the net voltage applied to the gas is alternatively enhanced or reduced which induces an increase or a decrease of the ionization level. In all cases the ion drift to the cathode due to the LF voltage results in an ion loss and a production of secondary electrons. For a LF voltage amplitude lower than 600 V, the ions loss to the cathode is higher than the ions creation related to the secondary electrons. The consequence is a decrease of the plasma density. This density oscillates at a frequency equal to 2LF: it is maximum each time the LF voltage amplitude is equal to 0 and minimum when the LF voltage amplitude is maximum. For a LF voltage amplitude higher than 600 V, when the LF and RF polarity are the same, the secondary electrons emission is high enough to counterbalance the ion loss, to enhance the bulk ionization and the discharge becomes a γ-RF. The gas voltage is controlled by the dielectric charge like a low frequency DBD. Around the gas voltage maximum, on each RF cycle, the discharge is alternatively an α-RF and a γ-RF discharge. When the discharge is in the γ mode, the ions flux at the cathode is increased by a factor 40.

A new method to obtain antireflective and passivation layers for p-type silicon solar cells is presented. Hydrogenated silicon carbon nitride (SiCxNy:H) films are obtained by low frequency plasma enhanced chemical vapor deposition (PECVD), using ammonia (NH3) and tetramethylsilane (TMS) as precursors; the influence of the deposition temperature and gas ratio on the film composition and properties is studied. It can be observed that the chemical composition of the film as well as its optical and passivation properties vary strongly with the gas ratio and temperature used. The optimal conditions with respect to the refractive index, the absorption coefficient and the minority carrier lifetime after rapid thermal annealing are determined. These conditions lead to an approximate stoichiometry of SiC0.6N0.8:H thin film including nearly 5 × 1021 cm− 3 hydrogen bonds.

International audience; The cost of industrial silicon solar cells could be greatly reduced by the implementation of PECVD at atmospheric pressure for the deposition of the silicon nitride (SiN) antireflective coating. For a successful development of this vacuum-free process tool, a deep understanding of the plasma discharge mode has to be undertaken. This work focuses on the control of a wide range of plasma excitation conditions in order to obtain homogeneous dielectric barrier discharges (DBD) at atmospheric pressure, and thus dense and uniform SiN layers. The influence of the discharge mode is then studied in order to optimize the optical and passivation properties of the SiN thin films, showing good antireflective properties as well as surface recombination velocities as low as 15 cm.s-1.

International audience; The aim of this paper is to better understand the transition from Townsend to radio-frequency homogeneous dielectric barrier discharge (DBD) at atmospheric pressure. The study is done in an Ar/NH3 Penning mixture for an electrode configuration adapted to roll-to-roll plasma surface treatment. The study was led in a frequency range running from 50 kHz up to 8.3 MHz leading to different DBD modes with a 1 mm gas gap: Glow (GDBD), Townsend (TDBD), and Radio-frequency (RF-DBD). In the frequency range between TDBD and RF-DBD, from 250 kHz to 2.3 MHz, additional discharges are observed outside the inter-electrode gas gap. Because each high voltage electrode are inside a dielectric barrel, these additional discharges occur on the side of the barrel where the gap is larger. They disappear when the RF-DBD mode is attained in the 1 mm inter-electrode gas gap, i.e., for frequencies equal or higher than 3 MHz. Fast imaging and optical emission spectroscopy show that the additional discharges are radio-frequency DBDs while the inter-electrode discharge is a TDBD. The RF-DBD discharge mode is attained when electrons drift becomes low enough compared to the voltage oscillation frequency to limit electron loss at the anode. To check that the additional discharges are due to a larger gas gap and a lower voltage amplitude, the TDBD/RF-DBD transition is investigated as a function of the gas gap and the applied voltage frequency and amplitude. Results show that the increase in the frequency at constant gas gap or in the gas gap at constant frequency allows to obtain RF-DBD instead of TDBD. At low frequency and large gap, the increase in the applied voltage allows RF-DBD/TDBD transition. As a consequence, an electrode configuration allowing different gap values is a solution to successively have different discharge modes with the same applied voltage.

In the present publication, the effect of the addition of H 2 in an atmospheric pressure Townsend Dielectric Barrier Discharge in an atmosphere of N 2 –C 2 H 4 is examined with an emphasis put on the evaluation of the surface chemistry and growth mechanisms. Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and Fourier Transform Infrared Spectroscopy were used to characterize the coatings. For all H 2 concentrations, films obtained present high N/C ratio (∼ 0.8) with high NH x and nitrile content. However, when H 2 is added in the discharge, nanoparticles/nanorods are formed imbedded in a smooth film. The average size of the nanorods is 100–200 nm in diameter with length from 1 to 10 μm. A growth mechanism is proposed to explain the formation of the nanorods on the surface of the coating in the presence of H 2 .

The goal of this study was to investigate the properties and growth mechanisms of nitrogen-containing carbon-based coatings obtained with an atmospheric pressure dielectric barrier discharge in an N2-C2H4 atmosphere. Radically different chemical compositions were observed depending on C2H4/N2 ratio. With a low C2H4 concentration ( 0.8) and low hydrogen content. At the short residence time, growth was due to mobile small radicals that procured a smooth yet soluble coating, while at the longer residence time, diffusion-limited aggregation of high sticking N-containing radicals produced a cauliflower-like structure. With a high C2H4 concentration (≥2,000 ppm), a polymer-like coating with relatively lower nitrogen content (N/C ~ 0.2) was observed with a cauliflower morphology for the entire coating. Nanoindentation measurements revealed very different physical properties in the two types of coatings.

Functionalized plasma polymer thin films were obtained in a dielectric barrier discharge at atmospheric pressure in an atmosphere of N2 and C2H4. The coatings were hydrophilic, adherent, chemically stable and presented a surface concentration of NH2 suitable for further biomolecule conjugation. Covalent grafting of a linking arm (glutaric anhydride) and subsequent conjugation of fibronectin, a protein of the extracellular matrix, were successful. Finally, endothelial cell adhesion experiments were performed directly on the functionalized thin films as well as on the conjugated coatings. Effects on cell adhesion were observed as a function of the plasma thin film deposition parameters.

In this paper, homogeneous and dense silicon-based coatings have been deposited from hexamethyldisiloxane (HMDSO: Si2O(CH3)6) on patterned silicium in a Townsend dielectric barrier discharge operating at atmospheric pressure. A brief description of the physical mechanisms ruling the step coverage is first described, followed by a description of the atmospheric pressure plasma process used. The step coverage is discussed with regard to the aspect ratio of the patterned wafers. Coatings deposited in and after the discharge region have also been characterized to understand the influence of plasma activation. In order to understand the experimental results, numerical simulations have been performed using a simplified reactive transport model. These results provide information and first general insight on the physical mechanisms ruling the conformity of silicon-based films deposited with this technique.

International audience; Optical emission spectroscopy (OES) measurements coupled with a collisional-radiative model were used to characterize a plane-to-plane dielectric barrier discharge at atmospheric pressure operated in nominally pure helium. The model predicts the population densities for the n = 3 levels of He excited by electron impact processes from either ground or metastable states and takes into account excitation transfer processes between He n = 3 levels as well as all relevant radiative decays and quenching reactions. Time-resolved OES measurements indicate that line ratios from He n = 3 triplet states (for example, 587.5 nm-to-706.5 nm) and singlet states (for example, 667.8 nm-to-728.1 nm) first sharply rise as the discharge ignites and then slowly decrease as it extinguishes. Assuming that n = 3 levels are first populated only by electron impact on ground state He atoms and then only by electron impact on metastable He atoms as the discharge current and thus the metastable number density rise, triplet and singlet line ratios predicted by the model become in each opposite case solely dependent on the electron temperature T e (assuming Maxwellian electron energy distribution function). The values of T e deduced from the analysis of both ratios were relatively high early in the discharge cycle (around 1.0–1.4 eV) and then much lower near discharge extinction (around 0.15 eV). For analysis of time-integrated (or cycle-averaged) OES measurements, the electron temperatures were closer to the 0.15 eV values near the end of the discharge cycle, in good agreement with the values expected from theoretical predictions in the positive columns of He glow discharges at atmospheric pressure.

This paper comprises two main parts: a review of the literature on atmospheric-pressure discharges used for micro-organism inactivation, focused on the inactivation mechanisms, and a presentation of our research results showing, in particular, that UV photons can be the dominant species in the inactivation process.The possibility of achieving spore inactivation through UV radiation using an atmospheric-pressure discharge or its flowing afterglow is the object of a continuing controversy. In fact, the review of the literature that we present shows that a majority of researchers have come to the conclusion that, at atmospheric pressure, chemically reactive species such as free radicals, metastable atoms and molecules always control the inactivation process, while UV photons play only a minor role or no role at all. In contrast, only a few articles suggest or claim that UV photons coming from atmospheric-pressure discharges can, in some cases, inactivate micro-organisms, but the experimental data presented and the supporting arguments brought forward in that respect are relatively incomplete.Using a dielectric-barrier discharge operated at atmospheric pressure in an N2–N2O mixture, we present, for the first time, experiments where micro-organisms are subjected to plasma conditions such that, on the one hand, UV radiation is strong or, on the other hand, there is no UV radiation, the two different situations being obtained with the same experimental arrangement, including the same gas mixture, N2–N2O. To achieve maximum UV radiation, the concentration of the oxidant molecule (N2O) added to N2 needs to be tuned carefully, resulting then in the fastest inactivation rate. The concentration range of the oxidant molecule in the mixture for which the UV intensity is significant is extremely narrow, a fact that possibly explains why such a mode of plasma sterilization was not readily observed. The survival curves obtained under dominant UV radiation conditions are, as we show, akin to those recorded at reduced pressure. Relatively fast spore inactivation can also be obtained under no UV radiation as a result of radicals diffusing deeply inside the spores, leading to oxidative lethal damage.

This work is a contribution to the understanding of mechanisms controlling the Atmospheric Pressure Glow Discharge (APGD). The approach consists in developing an electrical model of the discharge based on electrical circuit compounds. This model takes into account the main phenomena of the discharge including the memory effect and the creation of the cathode fall. It allows to have a general view of the process and can be easily associated to the power supply with short computational duration; it is also an interesting tool for the optimization of the whole process.

The electrical characteristics of homogeneous dielectric barrier discharges in helium, argon and nitrogen are presented and discussed. From the evolution of the discharge current as a function of the voltage applied to the gas it is shown that (i) in helium and argon, during the current increase, the discharge transits from a non-self-sustained discharge to a Townsend discharge and then a subnormal glow discharge (atmospheric pressure glow discharge) (ii) in nitrogen the ionization level is too low to induce a localization of the electrical field and the glow regime cannot be achieved. The discharge is a Townsend discharge (atmospheric pressure Townsend discharge). The characteristics of this specific discharge are described including the time variation of the density of electron, ion, metastable state and electrical field.

The aim of this study is to contribute to the understanding of the thin film growth mechanism using an Atmospheric Pressure Townsend-like Discharge (APTD). Films obtained in dielectric barrier discharges fed with N2 and small admixtures of hexamethyldisiloxane (HMDSO) and nitrous oxide (N2O) as oxidizer gas have been investigated. Results are compared to those obtained with SiH4, in similar conditions. The discharge dissipated power and the feed composition ([N2O]/[HMDSO] ratio) on film properties have been investigated by means of Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Ellipsometry. The film thickness homogeneity and deposition rate have been measured by means of a profilometer and an ellipsometer at the same time. Then silicon oxide thin film properties obtained with SiH4 and HMDSO containing APTD are compared. Concerning chemical composition results are similar. In the two cases, a rather low adding of N2O allows to get SiOx layer without N and C incorporation. Si–OH bounds are always observed. The relative contribution of homogeneous and heterogeneous growth mechanisms is very dependent on the nature of the precursor. Because of its high reactivity, SiH4 induces particles formation in the plasma. These particles are efficiently included in the coating, decreasing drastically the layer density. Thin films made with HMDSO are always dense.

This work is a contribution to the understanding of the mechanisms controlling the transition from a Townsend to a filamentary dielectric barrier discharge when the power increases. The approach consists in developing an electrical model of the discharge and the power supply to study the interaction between these two elements. The main components of the discharge model are (i) two Zener diodes whose characteristics depend on the power to take into account the effect of the gas density variation induced by the temperature variation and (ii) a RC circuit describing the memory effect from one discharge to the following one which is due to the metastables and the electrons trapped on the surface of the solid dielectrics. The calculated and measured currents are very similar over all the range of amplitude and frequency allowing to get an atmospheric pressure Townsend discharge. The model also describes the transition to filamentary discharge observed when the excitation frequency increases too much showing that it is due to a very fast variation of the load connected to the power supply. From this understanding, a solution is deduced to increase the maximum power dissipated in the discharge which consists in decreasing the solid dielectric capacitance.

The aim of this paper is the modeling of a dielectric barrier discharge at atmospheric pressure, in the Townsend regime. This model is based on an equivalent electrical circuit. It takes into account the main physical phenomena of the discharge. This model allows to have a general view of the process and to study the influence of the power supply on the discharge. It is also an interesting tool for the power supply design and the process optimization.

The aim of this work is to determine the properties and to understand the growth mechanisms of silicon-based coatings realised with an atmospheric pressure glow dielectric barrier discharge. Mixtures of SiH 4 and N 2 O, diluted in N 2 to reach the atmospheric pressure are used to obtain silicon oxide thin films. A longitudinal gas injection allows to study the coating properties as a function of the reactive gas decomposition and transformations level. The other parameters of this study are the silane rate and the plasma power. The thickness profile as a function of the gas residence time in the discharge clearly shows two maxima. SEM observations, ellipsometry and infrared results show that the first maximum which typically corresponds to a 400 μs residence time is due to radicals directly interacting with the surface while the second one observed for 10 ms residence time is due to the accumulation of aggregates formed in the gas phase following the interaction of radicals in the gas bulk. The first mechanism leads to dense silicon oxide coatings. Higher is the plasma power, denser is the coating: values of 98% of SiO 2 are reached. The growth rate increases with the silane concentration and the plasma power but saturation is observed around some tens of nanometers per minute. The second mechanism leads to porous deposit typically made of 30% of SiO 2 and 70% of void. The growth rate is proportional to the power and increases as the square of the silane concentration. The maximum coating roughness is observed when the two mechanisms significantly contribute to the film growth leading to the formation of ‘cauliflower’ type structure.

Glow dielectric barrier discharge (GDBD) appears as an attractive solution to realise an atmospheric pressure cold plasma process suitable for all the surface treatments including thin film coatings. Such a development requires a large understanding of the GDBD physics and chemistry. The objective of this work is to contribute to that understanding. From the analysis of electrical measurements, time resolved emission spectroscopy, short exposure time pictures and numerical model results, it is shown that GDBD which are discharges due to a Townsend initiation and not to a streamer coupling, transit from Townsend to subnormal glow discharge during the current increase. Depending on the maximum current density, they can be considered as a glow or a Townsend discharge. In a glow discharge, the memory effect from one discharge to the following one is based on electrons and ions trapped in the positive column while in a Townsend discharge, it is metastables which stay in the gas and create electrons through cathode secondary emission. In all the cases, the ionisation has to be slowed down by a significant contribution of Penning ionisation.

The synthesis of composites thin films made by injecting an aerosol suspension of 20 nm-size TiO2 nanoparticles (NPs) and isopropanol (IPA) in a filamentary argon Dielectric Barrier Discharge (DBD) is studied as a function of the DBD frequency from 1 to 50 kHz. The plasma is modulated to get homogeneous coatings. The deposition rate and morphology of the composite thin films are determined from SEM images of both surface and cross section. Their chemical composition is investigated by XPS, Raman spectroscopy and FTIR measurements. The structural composition of the NPs is examined by XRD. All the deposited composites show the chemical signature of the NPs as well as of the polymer-like coating resulting from the plasma polymerization of IPA. No mixed phase is observed and the sizes of the NPs as well as of their aggregates are not affected by the plasma. With this method aerosol droplets are evaporated before entering the plasma and the NPs inside a same droplet are aggregated. Results show that the DBD frequency controls the composite composition by independently influencing the NPs transport and the matrix growth rate. At 1 kHz, the coating is essentially made of NPs with a low carbon coating. From 1 to 50 kHz, the Ti/C ratio is divided by two orders of magnitude. As the frequency increases the quantity of NPs decreases and since 10 kHz the matrix thickness increases. The decrease of the NPs is explained by the numerical modeling of the NPs trajectory. It is found that from 10 to 1 kHz, the lower is the frequency, the higher is the transport of the NPs to the surface due to the electrostatic force. On the other hand the matrix growth rate increases from almost zero at 10 kHz up to 19 nm · min−1 at 50 kHz because of the linear increases of the DBD power with the frequency.

This paper reports on the study of confined jets and jets interaction in terms of increasing chemical transport. The context of this study is the atmospheric pressure plasma-enhanced chemical vapor deposition, higher thin film growth rate being desired, while maintaining total flow rate as low as possible. Turbulence mixing and enhanced heat transfer are the physical mechanisms identified as being capable of increasing the growth rate at atmospheric pressure. A numerical study of jets impinging on a heated substrate was carried out using quasicompressible Reynolds-Averaged Navier–Stokes (RANS) equations. Abe–Kondoh–Nagano (AKN) low-Reynolds k-ε and standard k-ε models were tested using an unconfined impinging jet at Reynolds number Re = 23,750 for jet diameter to plate-spacing ratios of H/d = 2 and H/d = 6. Results were compared with experimental data from the literature. Based on numerical results and in accordance with existing findings, the AKN low-Reynolds k-ε was shown to be reasonably accurate and was thus chosen for the numerical study. The effects of flow rate, hole diameter and length, jet-to-jet spacing, confinement width, and jet number were investigated numerically for inline jets confined between two vertical planes for jet Reynolds numbers between 810 and 5060. The configurations with the greatest turbulent intensity were studied, with the addition of diluted species transport and consumption. A laminar flow setup with a slot jet (Re = 79.5) was compared to two injection designs consisting of a simple set of 12 impinging gas jets (Rej = 2530; H/d = 3) with and without the adjunction of a wire to break the jets (Rej = 1687; H/d = 2). The two turbulent injection methods improved growth rate by 15%, which mainly resulted from a larger gas heating by the surface due to turbulent heat exchange in the jet impact zone.

International audience; In recent years, atmospheric pressure plasma-enhanced chemical vapour deposition has been identified as a convenient way to deposit good quality thin films. With this type of process, where the gas mixture is injected on one side of the electrodes, the chemical composition of the gas evolves with the gas residence time in the plasma. The consequence is a possible gradient in the chemical composition over the thickness of in-line coatings. The present work shows that the modulation of the plasma with a square signal significantly reduces this gradient while the drawback of low growth rate is avoided by increasing the discharge power. This study deals with plane/plane glow dielectric barrier discharges (DBDs) in an Ar/NH3/SiH4 gas mixture to make thin films. The 50 kHz discharge power of the glow DBD was varied by increasing voltage and modulating excitation. The impact on (i) the plasma development was observed through emission spectroscopy and (ii) the thin film coating through Fourier transform infrared measurements. It is shown that the modulation significantly decreases the time and the energy needed to achieve stable chemistry, enhances secondary chemistry and limits disturbance induced by impurities because of a slower decrease of SiH4 concentration and thus a higher ratio of SiH4/impurities, all very important points for in-line AP-PECVD development. When the growth rate is limited by diffusion, coating growth continues when the discharge is off, so long as there is a precursor gradient between the surface and the gas bulk. A higher discharge power steepens this gradient, which enhances diffusion from the bulk and thus growth rate.

International audience; The aim of this work was to identify the different diffuse dielectric barrier discharges (DBDs) obtained in the same electrode configuration and in the same gas for an excitation frequency ranging from 50 kHz to 9 MHz. The gas mixture was argon with 133 ppm of NH3. This Penning mixture is useful to obtain both low-frequency glow DBDs (GDBDs) and diffuse radio-frequency (RF) discharges. Electrical measurements and short exposure time photographs showed that whatever the frequency, a discharge free of micro-discharge was obtained. In the same configuration, the discharge was a GDBD up to 200 kHz. For frequencies higher than 250 kHz, the discharge behavior was that of a Townsend-like discharge associated with a maximum energy transfer close to the anode and a higher power (about twice that of the GDBD). The cathode fall formation was no longer observed during the discharge current increase because of ion trapping in the gas gap by the rapid electric field oscillations. In the same configuration, the alpha RF mode was observed from 1.3 MHz. Gamma secondary electron emission gave way to electron acceleration by the cathode sheath formation. Bulk ionization was important due to the high electron collision rate at atmospheric pressure. One consequence of the transition from low-frequency to high-frequency discharge was a significant increase in the power (factor ≈30), which reached 35 W cm−3, while the breakdown voltage decreased from 900 V to less than 200 V.

The aim of the present work is to detect the light emitted by a polypropylene film at ambient temperature once its surface has been subjected to a cold plasma, in other words plasma-induced luminescence (PIL). The general topics is to develop a tool for investigating surface polymer transformation. Kinetic and spectral features of PIL emission were recorded after discharge switch off, thanks to a photomultiplier and a liquid-nitrogen-cooled CCD camera. Three spectral components were clearly identified with their own excitation processes. The two fastest luminescence decay processes are due to radiative de-excitation of energy levels populated during plasma contact, termed as ‘direct excitation mechanisms’. They are related to the short wavelength range of the PIL spectrum which mainly characterizes chromophores initially present in the material. The third one, called a ‘carrier-recombination mechanism’, corresponds to a slow luminescence decay which becomes more and more dominant with the increase of the treatment duration.

Dielectric barrier discharge (DBD) is the discharge involved in corona treatment, widely used in industry to increase the wettability or the adhesion of polymer films or fibers. Usually DBD's are filamentary discharges but recently a homogeneous glow DBD has been obtained. The aim of this paper is to compare polypropylene surface transformations realized with filamentary and glow DBD in different atmospheres (He, N2, N2 + O2 mixtures) and to determine the relative influence of both the discharge regime and the gas nature, on the polypropylene surface transformations. From wettability and XPS results it is shown that the discharge regime can have a significant effect on the surface transformations, because it changes both the ratio of electrons to gas metastables, and the space distribution of the plasma active species. This last parameter is important at atmospheric pressure because the mean free paths are short (∼μm). These two points explain why in He, polypropylene wettability increase is greater by a glow DBD than by a filamentary DBD. In N2, no significant effect of the discharge regime is observed because electrons and metastables lead to the same active species throughout the gas bulk. The specificity of a DBD in N2 atmosphere compared to an atmosphere containing oxygen is that it allows very extensive surface transformations and a greater increase of the polypropylene surface wettability. Indeed, even in low concentration and independently of the discharge regime, when O2 is present in the plasma gas, it controls the surface chemistry and degradation occurs.

The aim of this work is to study the properties of a silicon-based deposit realized with a glow dielectric barrier discharge at atmospheric pressure in a nitrogen, silane and nitrous oxide mixture. It is shown that a continuous thin film can be realized. The chemical composition of the thin layer has been determined by x-ray photoelectron spectroscopy and static secondary ion mass spectrometry. The characteristics of the deposit are correlated to those of the discharge. The first steps of a chemical pathway leading to the precursors of the deposit are proposed from the analysis of the optical emission spectrum of the discharge. It appears that, unlike the low-pressure PECVD in a N2O-SiH4 mixture, in an atmospheric-pressure glow discharge NO is the main oxidizing species, due to the action of the metastable nitrogen molecules.

The aim of this paper is to show the possibility to synthesize silicon-based deposits on a polypropylene substrate, using a glow dielectric barrier discharge at atmospheric pressure, and to correlate the gas phase behavior with the properties of the thin film deposits. The discharge is generated in a mixture of nitrous oxide and silane, diluted in nitrogen. The influence of the [N2O]/[SiH4] ratio on the layer characteristics is mainly studied. Deposits are analyzed by XPS, SSIMS, AFM and wetting angle measurements. The discharges are also characterized by their optical emission spectra. Measurements are made as a function of the distance from the gas inlet, and they allow one to correlate these spectra with the film thickness and its chemical composition. Finally, chemical kinetics of the reactive gas decomposition reactions are proposed.

Several isotactic polypropylene samples have been thermally oxidised and their chemiluminescence recorded. The experimental device employed has allowed the simultaneous measurement of the integral and the spectral light emitted by the samples during oxidation. It has been found that the spectrum of chemiluminescence remains unchanged along the auto-acceleration stage of oxidation, while a gradual broadening and shift to longer wavelengths occurs as the kinetic curve approaches its intensity maximum, a shift which continues as long as oxidation does so. The shift to longer wavelengths originates in the disappearing of the low-wavelength emission (around 415 nm in isotactic polypropylene) which dominates the spectrum along the auto-acceleration stage, concomitant to a growing of longer wavelength components. Correlated stages exist in the kinetics and in the spectral evolution of the chemiluminescent emission along the thermal oxidation of polypropylene. ©

The quenching rates of N 2 (C, v ′) by N 2 and He, k C, v ′ N 2 and k He C, v ′ , have been determined for O v ′⩽3 in glow silent discharges at atmospheric pressure. First, the characteristic vibrational temperature of the N 2 (X, v ) ground state which is close to room temperature in the present low power (∼1 W) glow silent discharge has been calculated. Then, starting with the published quenching rates of N 2 (C,0), k C,0 N 2 =10 −11 cm 3 s −1 and k He C,0 =10 −12 cm 3 s −1 , the following values have been calculated: k C,1 N 2 =3.3(±0.4)×10 −11 cm 3 s −1 , k C,2 N 2 =6.3(±0.8)×10 −11 cm 3 s −1 , k C,3 N 2 =8(±2)×10 −11 cm 3 s −1 , k He C,1 ≅ k He C,2 =2(±0.3)×10 −12 cm 3 s −1 . Such data are useful in order to determine the N 2 vibrational distribution in high-power discharges at atmospheric pressure.

After treatment with cold He plasma at −180°C LDPE and PP films emit light. This Plasma Induced Luminescence (PIL) shows three components, one of which has been previously identified as chemiluminescence (PIL-CL). The chemiluminescence component in PIL of PP and LDPE is compared with isothermal chemiluminescence (CL) spectra obtained on heating PP in air at 165°C and strong similarities are found. Furthermore, increasing plasma treatment time or heating time brings a similar evolution in the PIL-CL and isothermal CL spectra, rendering spectra broader and shifted to higher wavelength.

Time variations of spectral line intensities of a helium dielectric discharge at atmospheric pressure have been analyzed by emission spectroscopy. A dielectric barrier controlled glow discharge with polymer films on the electrodes (O: 0.04 m, interelectrode distance: 0.005 m) is produced with a sinusoidal voltage of ca 800 Vr.m.s. The discharge is characterized by a current peak in each half cycle, its duration is of the order of 5×10 −6 s at 10 4 Hz. The radiative emission species are helium lines and mainly N 2 , N 2 + , CO + , CO 2 and OH bands coming from impurities which were in part desorbed from the polymer surfaces. From the time variations of band emissions, the main kinetic reactions at the origin of radiative species are discussed.

Preliminary results on the effect of polymer structure on the plasma-induced luminescence of polypropylene are reported. The spectral features of the light emission following plasma treatment at liquid nitrogen temperature have been analysed on commercial and laboratory-made polypropylene films of different structure. We observed that, for the less crystalline sample, the magnitude of the chemiluminescent component, which peaks at 400nm, was initially lower than for the others, but that it was less sensitive to the accumulation and the duration of the treatments. This feature has been explained by the formation of more isolated carbonyl groups in the case of this sample, which would result from a deeper penetration of active species created by the plasma discharge, or a larger fraction of amorphous regions associated with a larger proportion of oxygen in the bulk. A parallel effect was seen in the luminescent component ascribed to charge recombination on conjugated chromophores, with wavelength emission in the range 500–600nm. © 1998 SCI.

The aim of this paper is to confirm the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs, and numerical modeling were used to achieve this task. Experimental observations and numerical simulation are in good agreement. Therefore, the analysis of the calculated space and time variations of the electric field together with the ion and electron densities helps to explain the discharge mechanisms involved, showing the main role played by the electron as well as helium metastable density just before the discharge is turned on.

Light emission from electrically stressed polymers, so called electroluminescence, is a subject of great interest because it is associated with electrical aging and dielectric breakdown of highly insulating materials. Radiative recombination of charge carriers on luminescent centers generally is evoked as the main contribution to the emission, but this is difficult to assess in polyolefins since the spectral features associated with this mechanism are not known. The reason is twofold. First, there is a lack of knowledge on the nature of the luminescent centers in these materials, and second, it is difficult to get wavelength-resolved electroluminescence spectra due to the low light level. By using an alternative activation method, we have isolated the emission spectrum associated with isothermal charge recombination in polyethylene and polypropylene. Electrical charges of both polarities are brought to the surface of the samples by contact with a cold plasma powered at a frequency of /spl ap/5 kHz. The kinetic and spectral features of the recombination-induced emission are recorded after discharge switch off. The recombination mechanism is considered on the basis of the light decay kinetics whereas the chemical nature of the luminescent centers is discussed by a comparison with the photoluminescence spectrum of the polymer. It is shown that charges recombine by tunneling from traps to the luminescent centers which are unsaturated species. The chromophores involved in photo- and recombination-induced luminescence appear to be the same, but not the electronic transitions. Light emitted upon charge recombination has been assigned to transitions from the lowest lying triplet states of poly-enone sequences.

Recently, a glow like dielectric controlled barrier discharge (GDBD) working at atmospheric pressure has been observed. Such a discharge could replace a filamentary dielectric controlled barrier discharge (FDBD) used in corona treatment systems to improve the wettability or the adhesion of polymers. So it is of interest to compare these two types of discharges and their respective effect on a polymer surface. This is the aim of an extensive study we have undertaken. The first step presented here is the comparison of a filamentary discharge in air with a glow discharge in helium. Helium is the most appropriate gas to realize a glow discharge at atmospheric pressure. Air is the usual atmosphere for a corona treatment. The plasma was characterized by emission spectroscopy and current measurements. The surface transformations were indicated by the water contact angle, the leakage current measurement and the X-ray photoelectron spectroscopy. Results show that the helium GDBD is better than air FDBD to increase polypropylene wettability without decreasing the bulk electrical properties below a certain level. Contact angle scattering as well as leakage current measurements confirm that the GDBD clearly results in more reproducible and homogeneous treatment than the FDBD.

An innovative method to obtain antireflection and passivation coatings on p-type crystalline silicon solar cells is presented. The method consists in the growth of hydrogenated silicon nitride films (SiN x :H) by atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD). Compared to industrial process, using this kind of processing may allow an augmentation of the silicon solar cell production throughput and yield enabling a reduction of the cost of photovoltaic systems. The optical and passivation properties of the SiN x :H films grown by AP-PECVD are determined and compared with the standard low pressure plasma enhanced chemical vapor deposition (LP- PECVD) films. Minority carrier lifetime of 1 ms was reached. Solar cells coated with AP-PECVD SiN x :H films were made, and their performances were compared with standard SiN x :H coated cells. The same cell efficiency is obtained for the two groups of cells proving the interest of the AP-PECVD for the solar cell industry.

The light emitted by an insulating material once its surface has been submitted to a cold plasma, plasma-induced luminescence is investigated on polypropylene films at low temperature. An analysis of the integral and wavelength resolved light is carried out. The kinetical evolution of the spectrum after plasma interaction are reported and analyzed. Investigation of the photo- and chemiluminescence spectra of the material shows that plasma-induced luminescence has three spectral components, each having different excitation mechanisms and thus different kinetics. The fastest is due to the ultraviolet irradiation during plasma contact, the second is dominated by radical chemistry producing carbonyl groups, and the third, with the slowest kinetics, is due to carrier recombination on the most conjugated chromophores which are preferentially charged by the plasma. To confirm the interpretation of plasma induced luminescence spectrum, the first results concerning short and long plasma interaction are considered.