Filamentary Dielectric Barrier Discharge Research Articles

Electric and spectroscopic analysis of a pure nitrogen mono-filamentary dielectric barrier discharge (MF-DBD) at 760 Torr

Mono-filamentary dielectric barrier discharge (MF-DBD), occurring within 1 mm gap of atmospheric pressure pure nitrogen and operating with a sinusoidal electric supply at about 8 kHz, is studied in this paper. A thorough electrical analysis allows experimental determination of the ignition and extinction voltages, respectively (15 750 ± 50) V and (2097 ± 7) V, the injected energy (158 ± 2) J and charge (17.22 ± 0.22) nC in a single filament. The mean axial reduced electric field is equal to (644 ± 2) Td at ignition. An empirical technique is proposed to evaluate these discharge parameters by avoiding bulky calculations. Optical emission spectroscopic measurements of the vacuum ultraviolet (VUV), ultraviolet (UV), visible and near infrared (IR) emissions are presented and discussed. Two atomic nitrogen lines attributed to the decay of the N[2s2p23s 2P] triplet towards N[2s22p3 2D°] level are observed at 150 and 175 nm, together with the Lyman–Birge–Hopfield system in the VUV range. The second positive system (N2[C 3Πu] → N 2[B 3Πg]) dominates the UV and visible-blue spectra. The (0–0) transition of the first negative system peaking at 391.4 nm, the first positive system and the Herman IR transitions are also present. Both our VUV and near IR spectra are consistent with recently reported results in hollow cathode and cylindrical DBDs. The electrical and spectroscopic experimental results reported here are useful for ongoing and forthcoming modelling of filamentary nitrogen dielectric barrier discharges.

Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: I. Flat surfaces

Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: I. Flat surfaces

Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: II. Particles

Ion energy and angular distributions onto polymer surfaces delivered by dielectric barrier discharge filaments in air: II. Particles

Phase resolved optical emission spectroscopy of coaxial microplasma jet operated with He and Ar

Atmospheric pressure plasma jet sources are currently in the focus of many researchers for their promising applications in medical industry (e.g. treatment of living tissues), surface modification or material etching or synthesis. Here we report on the study of excitation mechanisms of a coaxial microplasma jet with a hollow capillary as an inner electrode and a ceramic tube with metal ring as outer electrode. This microplasma jet is operated in He and Ar gas and it is investigated by means of electrical measurements, optical emission spectroscopy and space and phase resolved wavelength integrated optical spectroscopy. Measurements of a microscale atmospheric pressure plasma jet with parallel metal electrodes operated in He are shown for comparison as well. Four different modes are distinguished with He as plasma forming gas. The α discharge in annular space between the electrodes, observed at low applied voltages, is very similar to the discharge in the jet with parallel electrodes. As the voltage increases a γ discharge appears, first localized at the tip of the capillary. As the voltage increases further the γ discharge appears in the annular space as well. A hollow cathode plasma is observed at any voltage used on the symmetry axis of the jet. Only one mode of plasma operation is observed in argon gas with distinctively different behavior. We hypothesize that it is comparable to a single microdischarge of a filamentary dielectric barrier discharge.

Temperature profiles in filamentary dielectric barrier discharges at atmospheric pressure

Physico-chemical properties of atmospheric pressure filamentary dielectric barrier discharges (f-DBD) depend on coupled electrical characteristics and thermal profiles. In this paper, a method for studying thermal and electrical effects is developed. Therefore, thermal profiles of f-DBD are studied for well-defined electrical characteristics of quasi-identical filaments with controlled distribution in time and space. The temperatures of gas, dielectric surface and plasma depend on the surface density and on the temporal frequency of filaments, defining the input power, and can be tuned by controlling heat transfers. Different methods to control these temperatures are depicted. Moreover, heat transfer through conduction and convection from dielectric surface is shown to be the dominant heating mechanism of the flowing gas in the reactor. Finally, experimental results show that the local temperature gradient around each filament can be controlled by the frequency of the applied voltage. Actually, the temperature difference between the filament and the surrounding gas is constant below 10 kHz but increases linearly with the frequency above 10 kHz. At high frequency, the time between two successive filaments occurring at the same position becomes smaller than the relaxation time constant of thermal exchanges (∼0.1 ms). Hence, this rise in local temperature can be attributed to time-limited heat transfers from the filament axis.

Surface Treatment of Polyethylene Terephthalate Films Using DBD Excited by Repetitive Unipolar Nanosecond Pulses in Air at Atmospheric Pressure

Dielectric barrier discharge (DBD) is proved to be an effective method for surface treatment of polymers over the past 20 years and is now widely used in the fields of surface modification. In this paper, surface treatment of polyethylene terephthalate (PET) films for improving the hydrophilicity using DBD excited by unipolar nanosecond pulses is presented. Two typical discharges exhibiting homogeneous and filamentary modes are obtained under certain experimental conditions, and then, they are used to modify the surface of PET films. The microstructure and properties of the film surface before and after treatment are characterized with water contact angle measurement, scanning electron microscope, atomic force microscope, and X-ray photoelectron spectroscope. The results show that, with the treatment power density of 192 and 158 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in filamentary and homogeneous modes, respectively, surface morphology and property after treatment are significantly changed, and the physical etching and introduction of oxygen-containing polar functional groups account for the decease of surface contact angle and the increase of surface roughness. Compared with the filamentary DBD treatment, the homogeneous DBD (HDBD) is more effective in surface treatment, such as lower contact angle, higher roughness, and more oxygen-containing function groups after treatment. It is attributed to the fact that the HDBD can achieve a uniform treatment and can make the physical and chemical interaction much sufficient.

Polymer Surface Processing by Atmospheric Pressure DBD for Post-Discharge Grafting of Washing-Resistant Functional Coatings

We present a process for rapid post-discharge deposition of liquid monomer to form functional coatings at atmospheric pressure. The post-discharge polymerization of dense polyacid and polyether coatings is first depicted versus the energy density deposited by the preliminary surface treatment of polyethylene and polystyrene substrates in air Dielectric Barrier Discharge (DBD) with respect to SEM, to XPS and FTIR-ATR analysis and to polymerization yield determined by mass measurements. The paper focuses on the effect of the filamentary air DBD on surface of the polymer substrates and on post-discharge polymerization mechanism. Indeed, the grafting yield is shown to depend on the energy density deposited by DBD and on the time exposure to air between DBD and monomer deposition, controlling respectively the surface density of radicals and labile peroxides, both triggering the polymerization of vinyl precursors. Then, the effect of deposition conditions on the polymerization yield and related thickness of the functional polymer coatings is shown and special attention is paid to the stability of the coating upon washing.

大气压下氮气介质阻挡微放电中分子振动温度的时间分辨

大气压下氮气介质阻挡微放电中分子振动温度的时间分辨

Deposition and etching of fluorocarbon thin films in atmospheric pressure DBDs fed with Ar–CF 4–H 2 and Ar–CF 4–O 2 mixtures

The deposition and etching of plasma-polymerized fluorocarbon thin films were studied in filamentary dielectric barrier discharges (FDBDs) fed with Ar–CF 4–H 2 and Ar–CF 4–O 2 mixtures, respectively. The etching/polymerization competition was investigated as a function of the feed composition. Hydrogen addition to CF 4 promotes thin films deposition, with a maximum deposition rate at 20% H 2, and reduces the F/C ratio of the deposit, while the oxygen addition promotes the etching of the plasma-deposited film. It is demonstrated that fluorine atoms can perform the etching of the fluoropolymer also without ion bombardment. The correlation between the trend of the etch rate and the trend of the surface chemical composition of fluoropolymers etched in Ar–CF 4–O 2 mixtures allows to enhance hypotheses on the reaction mechanism and on the role of the different active species involved in plasma–surface interactions.

Interaction of current filaments in dielectric barrier discharges with relation to surface charge distributions

In a planar, laterally extended dielectric barrier discharge (DBD) system operated in glow mode, a filamentary discharge is observed. The filaments tend to move laterally and hence tend to cause collisions. Thereby, usually one collision partner becomes destroyed. In this paper, the collision process and especially the preceding time period is investigated. Beside the luminescence density of the filaments, the surface charge density accumulated between the single breakdowns of the DBD is observed via an optical measurement technique based on the linear electro-optical effect (pockels effect). A ring-like substructure of the surface charge distribution of a single filament is found, which correlates to the filament interaction behaviour. Furthermore, a preferred filament distance is found, suggesting the formation of a filamentary quasi-molecule.

Optical Emission Spectroscopy of Argon-Fluorocarbon-Oxygen Fed Atmospheric Pressure Dielectric Barrier Discharges

Atmospheric pressure filamentary dielectric barrier discharges (FDBDs) fed with argon, a fluorocarbon compound (i.e. CF 4 , C 3 F 8 , C 3 F 6 and c-C 4 F 8 ) and O 2 were investigated by optical emission spectroscopy (OES). The UV-Vis spectra of the plasma in argon-fluorocarbon mixtures are characterized by narrow signals from Ar atoms, CF 2 and CF fragments and by two continua due to CF + 2 and CF 3 . O 2 addition to the feed gas reduces the emissions of fluorocarbon fragments and results in the appearance of an intense narrow emission at 193 nm and of a broad continuum centred at 290 nm ascribed to ArF and Ar 2 F excimers, respectively. Any signal from F atoms was not detected under the experimental conditions investigated even though the plasma contains F atoms since the dry etching of silicon substrates, a typical process driven by F atoms, was observed. Some possible explanations of this phenomenon are presented.

Recent Advances in the Atmospheric Pressure PE‐CVD of Fluorocarbon Films: Influence of Air and Water Vapour Impurities

AbstractThe influence of air and water vapour on the deposition process of fluoropolymers in argon‐hexafluoropropene (Ar‐C3F6) filamentary dielectric barrier discharges was investigated by adding known concentrations of these contaminants to the feed gas. The obtained results show that Ar‐C3F6 DBDs allow in depositing thin films with a XPS F/C ratio as high as 1.7. Under the experimental conditions investigated, contaminant addition slightly affects the F/C ratio of the coatings, and does not cause appreciable O‐ and N‐uptake, but induces a decrease of the deposition rate. Preliminary results from the OES investigation of the gas phase and the GC‐MS analysis of the gas effluent are also reported.

Atmospheric pressure plasmas for aerosols processes in materials and environment

The paper highlights applications of some atmospheric pressure plasmas (dc-corona, streamer and spark and ac-Dielectric Barrier Discharges) to aerosol processes for Materials and Environment (filtration, diagnostics). The production of vapor i.e. condensable gaseous species, leads to nano-sized particles by physical and chemical routes of nucleation in these AP plasmas: (i) when dc streamer and spark filamentary discharges as well as ac filamentary dielectric barrier discharges interact with metal or dielectric surfaces, and (ii) when discharges induce reactions with gaseous precursors in volume. It is shown how composition, size and structure of primary nano-particles are related to plasma parameters (energy, number per unit surface and time and thermal gradients). Then the growth by coagulation controls the final size of agglomerates versus plasma parameters and transit time in and after the plasma. Charging and electro-thermal collection are depicted to account for the related potential applications of controlled kinematics of charged aerosol.

Polyethylene Terephthalate Surface Modification by Filamentary and Homogeneous Dielectric Barrier Discharges in Air

In this paper, polyethylene terephthalate (PET) films are modified using nonequilibrium plasma generated by homogeneous dielectric barrier discharges (DBDs) in air at medium pressure, and the results are compared to those treated by using filamentary DBDs in air at atmospheric pressure. The characteristics of homogeneous DBDs are studied and compared with those of filamentary DBDs by measuring their electrical discharge parameters and observing their light-emission phenomena, and the surface properties of PET films before and after the treatments are studied using contact-angle and surface-energy measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. It is found that the homogeneous DBD is quite homogeneous and stable in the whole gas gap, which differs from the filamentary DBD, and the plasma treatments modify the PET surface in both morphology and composition. The PET films modified in both treatments show a remarkable decrease in water contact and a remarkable increase in surface energy due to both the introduction of oxygen-containing polar groups onto the surface and the improvement in surface roughness. It is found that the homogeneous DBD is more effective in PET surface modification than the filamentary DBD as it can make the contact angle decline to a lower level by introducing more oxygen-containing groups, and the possible reason for this effect is discussed.

Polytetrafluoroethylene surface modification by filamentary and homogeneous dielectric barrier discharges in air

In this paper, polytetrafluoroethylene (PTFE) films are modified using non-equilibrium plasma generated by homogeneous DBD in air at medium pressure, and the results are compared to those treated by using filamentary DBD in air at atmospheric pressure. The surface properties of PTFE films before and after the treatments are studied using contact angle and surface energy measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It is found that the plasma treatments modify the PTFE surface in both morphology and composition. The PTFE films modified in both treatments show a remarkable decrease in water contact and a remarkable increase in surface energy. XPS analysis reveals that oxygen-containing polar groups are introduced onto the PTFE surface, and SEM analysis shows that the surfaces of the films are etched after both the treatments. It is found that homogeneous DBD is more effective in PTFE surface modification than filamentary DBD as it can make the contact angle decline to a lower level by introducing more oxygen-containing groups, and the possible reason for this effect is discussed.

Comparison of surface modification of polypropylene film by filamentary DBD at atmospheric pressure and homogeneous DBD at medium pressure in air

Non-equilibrium plasmas generated by a dielectric barrier discharge (DBD) are of great interest in material surface processing because of their convenience, effectiveness and low cost. In this paper, polypropylene (PP) films are modified using a non-equilibrium plasma generated by a DBD in air in homogeneous mode and in filamentary mode. The filamentary DBD is generated in ambient air, and the homogeneous DBD is generated at medium pressure with an operating pressure value of 3 kPa. The characteristics of homogeneous DBD are studied and compared with those of filamentary DBD by measuring their electrical discharge parameters and observing their light emission phenomena, and the surface properties of the PP films before and after the treatments are studied using contact angle and surface energy measurement, x-ray photoelectron spectroscopy and scanning electron microscopy. It is found that the homogeneous DBD is even and stable in the whole gas gap, which differs from the commonly filamentary DBD. The plasma treatments modify the PP surface in both morphology and composition. The PP films modified in both treatments show a remarkable decrease in the water contact angle and a remarkable increase in surface energy due to the introduction of oxygen-containing groups on the surface and the etching of the surface. The homogeneous DBD is more effective in PP surface modification than the filamentary DBD as it can make the contact angle decrease to a lower level by introducing more oxygen-containing groups. This effect could be explained by the evenly distributed plasma at a homogeneous DBD than at a filamentary DBD, and by the more efficient introduction of atomic oxygen to the PP surface in the case of homogeneous DBD.

VUV spectroscopy and post-discharge kinetic analysis of a pure xenon mono-filamentary dielectric barrier discharge (MF-DBD)

A spectroscopic and kinetic analysis of a pure xenon mono-filamentary dielectric barrier discharge (MF-DBD) is reported here. The MF-DBDs were achieved with a sinusoidal voltage supply at frequencies around tens of kilohertz, for pressures ranging from 25 to 550 Torr. The discharge emits the first (152 nm) and second (172 nm) continua of xenon. Between 25 and 75 Torr, these emissions have comparable peak values, whereas above 300 Torr, only the 2nd continuum is observed. These spectra are interpreted in the light of previously reported results obtained by selectively populating either the Xe(3P1) or the Xe(3P2) state, by using two-photon absorption laser induced fluorescence. The temporal analysis of both continua, in real operating conditions of the discharge, allowed in situ determination of its post-discharge kinetic scheme. Primary excitation of the lowest xenon atomic 6s and 6s′ states is practically achieved after an active phase of about 80 ns. We simultaneously estimated the three-body formation rate constants of the and Xe2[1 u (3P2)] excimers and the radiative lifetime of the lowest vibrational levels of the latter. We, respectively, found: (180 ± 29) Torr−2 s−1, (75.6 ± 4.2) Torr−2 s−1 and (96 ± 6) ns. The post-discharge kinetic model proposed here should contribute towards considerably improving the computing time when modelling filamentary xenon dielectric barrier discharges.

The Transition Between Different Discharge Regimes in Atmospheric Pressure Air Barrier Discharge

AbstractIn our previous work [1], we have demonstrated the possibility of observing the transition from a filamentary dielectric barrier discharge operation regime into the diffuse barrier discharge regime in air at atmospheric pressure. This work presents our attempt to reproduce the transition conditions in newly constructed transparent discharge reactor. The role of appropriate power supply and dielectric barrier to stabilize the discharge in a Townsend‐to‐glow discharge region is investigated and discussed. Unlike operating in nitrogen, a streamer mechanism is involved in the formation of the uniform air plasma. Nevertheless the electrical current waveform of a diffuse streamer pulse differs from the filamentary streamer pulse, as the diffuse mode pulse exhibits an extended tail part. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A study of atmospheric pressure plasma discharges for surface functionalization of PTFE used in biomedical applications

Plasma polymer surface modification is widely used in the biomedical field to tailor the surface properties of materials to improve their biocompatibility. Most of these treatments are performed using low pressure plasma systems but recently, filamentary dielectric barrier discharge (FDBD) and atmospheric pressure glow discharge (APGD) have appeared as interesting alternatives. The aim of this paper is to evaluate the potential of surface modifications realized with FDBD and APGD in different atmospheres (N2+ H2 and N2+ NH3 mixtures) on poly(tetrafluoroethylene) to determine the relative influence of both the discharge regime and the gas nature on the surface transformations. From XPS analysis, it is shown that the discharge regime can have a significant effect on the surface transformation; FDBDs operating in H2/N2 lead to a high concentration of amino-groups with high specificity but also important damaging on the surface. Glow discharges in both H2/N2 and NH3/N2 lead to lower concentrations of amino-groups with lower specificity but lower surface damaging. Therefore, this simple surface treatment seems to be an effective, low cost method for the production of uniform surface modification with amino-groups that can subsequently be used to graft various chemical functionalities used for biomaterial compatibility.

Measurement and 3D Simulation of Self-Organized Filaments in a Barrier Discharge

We report on pattern formation phenomena in the filamentary dielectric barrier discharge between plane glass electrodes. It is for the first time that a three-dimensional (3D) self-organized glow pattern was both observed in an actual experiment and directly calculated in a full 3D discharge simulation in a quantitative manner. Specifically, we investigate the genesis of periodic patterns during the first breakdowns. Despite our simple drift-diffusion discharge model, the correspondence of experimental and numerical findings is surprisingly good.