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M.g. Kong - One of the best experts on this subject based on the ideXlab platform.

  • contrasting characteristics of sub microsecond pulsed atmospheric air and atmospheric pressure helium oxygen Glow Discharges
    Journal of Physics D, 2010
    Co-Authors: James L Walsh, F Iza, Dingxin Liu, Mingzhe Rong, M.g. Kong
    Abstract:

    Glow Discharges in air are often considered to be the ultimate low-temperature atmospheric pressure plasmas for numerous chamber-free applications. This is due to the ubiquitous presence of air and the perceived abundance of reactive oxygen and nitrogen species in air plasmas. In this paper, sub-microsecond pulsed atmospheric air plasmas are shown to produce a low concentration of excited oxygen atoms but an abundance of excited nitrogen species, UV photons and ozone molecules. This contrasts sharply with the efficient production of excited oxygen atoms in comparable helium–oxygen Discharges. Relevant reaction chemistry analysed with a global model suggests that collisional excitation of O2 by helium metastables is significantly more efficient than electron dissociative excitation of O2, electron excitation of O and ion–ion recombination. These results suggest different practical uses of the two oxygen-containing atmospheric Discharges, with air plasmas being well suited for nitrogen and UV based chemistry and He–O2 plasmas for excited atomic oxygen based chemistry.

  • Contrasting characteristics of sub-microsecond pulsed atmospheric air and atmospheric pressure heliumoxygen Glow Discharges
    Journal of Physics D: Applied Physics, 2010
    Co-Authors: J L Walsh, D X Liu, F Iza, M Z Rong, M.g. Kong
    Abstract:

    Glow Discharges in air are often considered to be the ultimate low-temperature atmospheric pressure plasmas for numerous chamber-free applications. This is due to the ubiquitous presence of air and the perceived abundance of reactive oxygen and nitrogen species in air plasmas. In this paper, sub-microsecond pulsed atmospheric air plasmas are shown to produce a low concentration of excited oxygen atoms but an abundance of excited nitrogen species, UV photons and ozone molecules. This contrasts sharply with efficient production of excited oxygen atoms in comparable helium-oxygen Discharges. Relevant reaction chemistry analyzed with a global model suggests that collisional excitation of O 2 by helium metastables is significantly more efficient than electron dissociative excitation of O 2, electron excitation of O, and ion-ion recombination. These results suggest different practical uses of the two oxygen-containing atmospheric Discharges, with air plasmas being well suited for nitrogen and UV based chemistry and He-O 2 plasmas for excited atomic oxygen based chemistry.

  • effects of dielectric barriers in radio frequency atmospheric Glow Discharges
    International Conference on Plasma Science, 2007
    Co-Authors: J J Shi, Dawei Liu, M.g. Kong
    Abstract:

    This paper reports the effects of introducing dielectric barriers to radio-frequency (RF) atmospheric pressure Glow Discharges (APGD) that have hitherto employed bare electrodes. The resulting atmospheric RF dielectric barrier Discharges (DBD) are experimentally shown to retain their large volume without constriction at very large currents, well above the maximum current at which conventional RF APGD with bare electrodes can maintain their plasma stability. Optical emission spectroscopy is used to demonstrate that larger discharge currents lead to more active plasma chemistry. A complementary computational study is then presented on the dynamics and structures of the RF DBD under different operation conditions. While the RF DBD and conventional RF APGD may present very different electrical signatures in the external circuit, it is shown that their discharge properties, particularly the sheath characteristics, are very similar. Finally, it is demonstrated that thinner dielectric barriers or/and larger excitation frequencies are desirable to maximize the largest permissible discharge current without compromising the plasma stability

  • radio frequency dielectric barrier Glow Discharges in atmospheric argon
    Applied Physics Letters, 2007
    Co-Authors: J J Shi, M.g. Kong
    Abstract:

    In this letter, an experimental investigation is presented to characterize the properties and benefits of radio-frequency (rf) dielectric-barrier Discharges (DBDs) in atmospheric argon. Compared to rf atmospheric Glow Discharges generated with bare electrodes, atmospheric argon rf DBDs are shown to remain stable and uniform over a large current range from the α and the γ modes. Optical emission spectroscopy is used to show an active underpinning plasma chemistry and a gas temperature range of 461–562K. These highlight the advantages of argon rf DBD as a surface processing technique over more expensive helium-based rf atmospheric Glow Discharges.

  • period multiplication and chaotic phenomena in atmospheric dielectric barrier Glow Discharges
    Applied Physics Letters, 2007
    Co-Authors: Yang Wang, Yuantao Zhang, Dezhen Wang, M.g. Kong
    Abstract:

    In this letter, evidence of temporal plasma nonlinearity in which atmospheric dielectric-barrier Discharges undergo period multiplication and chaos using a one-dimensional fluid model is reported. Under the conditions conducive for chaotic states, several frequency windows are identified in which period multiplication and secondary bifurcations are observed. Such time-domain nonlinearity is important for controlling instabilities in atmospheric Glow Discharges.

J J Shi - One of the best experts on this subject based on the ideXlab platform.

  • an experimental study on discharge mechanism of pulsed atmospheric pressure Glow Discharges
    Physics of Plasmas, 2011
    Co-Authors: Xiaojiang Huang, Liqun Sun, Yun Bao, Jing Zhang, J J Shi
    Abstract:

    The discharge mechanism of pulsed atmospheric pressure Glow Discharges excited by the unipolar positive voltage pulses between two parallel plate electrodes with or without one dielectric barrier on the ground electrode in flowing helium has been characterized by nanosecond time resolved optical and electrical measurements. The uniform Glow Discharges can only be achieved when the voltage pulse duration is less than 1 μs with bare electrodes. With introducing a dielectric barrier on the ground electrode, a model of electrons traveling on the background ions between two discharge events is proposed to explain the discharge mechanism and characteristics in terms of discharge ignition, discharge spatial profile and discharge current amplitude.

  • effects of dielectric barriers in radio frequency atmospheric Glow Discharges
    International Conference on Plasma Science, 2007
    Co-Authors: J J Shi, Dawei Liu, M.g. Kong
    Abstract:

    This paper reports the effects of introducing dielectric barriers to radio-frequency (RF) atmospheric pressure Glow Discharges (APGD) that have hitherto employed bare electrodes. The resulting atmospheric RF dielectric barrier Discharges (DBD) are experimentally shown to retain their large volume without constriction at very large currents, well above the maximum current at which conventional RF APGD with bare electrodes can maintain their plasma stability. Optical emission spectroscopy is used to demonstrate that larger discharge currents lead to more active plasma chemistry. A complementary computational study is then presented on the dynamics and structures of the RF DBD under different operation conditions. While the RF DBD and conventional RF APGD may present very different electrical signatures in the external circuit, it is shown that their discharge properties, particularly the sheath characteristics, are very similar. Finally, it is demonstrated that thinner dielectric barriers or/and larger excitation frequencies are desirable to maximize the largest permissible discharge current without compromising the plasma stability

  • radio frequency dielectric barrier Glow Discharges in atmospheric argon
    Applied Physics Letters, 2007
    Co-Authors: J J Shi, M.g. Kong
    Abstract:

    In this letter, an experimental investigation is presented to characterize the properties and benefits of radio-frequency (rf) dielectric-barrier Discharges (DBDs) in atmospheric argon. Compared to rf atmospheric Glow Discharges generated with bare electrodes, atmospheric argon rf DBDs are shown to remain stable and uniform over a large current range from the α and the γ modes. Optical emission spectroscopy is used to show an active underpinning plasma chemistry and a gas temperature range of 461–562K. These highlight the advantages of argon rf DBD as a surface processing technique over more expensive helium-based rf atmospheric Glow Discharges.

  • electron trapping in radio frequency atmospheric pressure Glow Discharges
    Applied Physics Letters, 2007
    Co-Authors: D W Liu, J J Shi, M.g. Kong
    Abstract:

    In this letter, the authors present experimental evidence of electron trapping in radio-frequency (rf) atmospheric-pressure Glow Discharges. By linking electron density to nanosecond plasma images and optical emission spectroscopy, they show that electron trapping occurs under most discharge conditions. The level of electron trapping increases with increasing discharge current or/and increasing excitation frequency, and manifests itself in the change of the differential conductivity at the point of the gas breakdown. Finally, they demonstrate that electron trapping is largely related to whether the half rf period is shorter than the electron transition time across the electrode gap.

  • mitigating plasma constriction using dielectric barriers in radio frequency atmospheric pressure Glow Discharges
    Applied Physics Letters, 2007
    Co-Authors: J J Shi, D W Liu, M.g. Kong
    Abstract:

    It is known that radio-frequency (rf) atmospheric Glow Discharges with bare electrodes are susceptible to plasma constriction at large discharge currents. This is undesirable for large-scale applications, even though large currents usually lead to abundant plasma reactive species and high application efficiency. In this letter, an experimental investigation is presented to demonstrate that plasma constriction can be mitigated by introducing dielectric barriers to the electrodes. The resulting atmospheric rf dielectric-barrier discharge is shown to operate in the γ mode of large discharge current while maintaining its discharge volume. This improves significantly plasma stability and the application potential.

Chengyu Bao - One of the best experts on this subject based on the ideXlab platform.

  • genetic effects of radio frequency atmospheric pressure Glow Discharges with helium
    Applied Physics Letters, 2008
    Co-Authors: Liyan Wang, Wenting Sun, Sen Wang, Hongxin Zhao, Xinhui Xing, Chengyu Bao
    Abstract:

    Due to low gas temperatures and high densities of active species, atmospheric-pressure Glow Discharges (APGDs) would have potential applications in the fields of plasma-based sterilization, gene mutation, etc. In this letter, the genetic effects of helium radio-frequency APGD plasmas with the plasmid DNA and oligonucleotide as the treated biomaterials are presented. The experimental results show that it is the chemically active species, instead of heat, ultraviolet radiation, intense electric field, and/or charged particles, that break the double chains of the plasmid DNA. The genetic effects depend on the plasma operating parameters, e.g., power input, helium flow rate, processing distance, time, etc.

  • electrical features of radio frequency atmospheric pressure bare metallic electrode Glow Discharges
    Plasma Chemistry and Plasma Processing, 2007
    Co-Authors: Wenting Sun, Huabo Wang, Chengyu Bao
    Abstract:

    Radio-frequency (RF), atmospheric-pressure Glow discharge (APGD) plasmas with bare metallic electrodes have promising prospects in the fields of plasma-aided etching, deposition, disinfection and sterilization, etc. In this paper, an induced gas discharge approach is proposed for obtaining the RF, atmospheric-pressure, γ-mode, Glow Discharges with pure nitrogen or air as the primary plasma-working gas using bare metallic electrodes. The discharge characteristics, including the discharge mode, the breakdown voltage and discharge voltage for sustaining α mode and/or γ mode Discharges, of the RF APGD plasmas of helium, argon, nitrogen, air or their mixtures using a planar-type plasma generator are presented in this study. The uniformity (no filaments) of the Discharges is confirmed by the images taken by an iCCD with a short exposure time (10 ns). The effects of different gap spacings and electrode materials on the discharge characteristics, the variations of the sheath thickness and the electron number density are also studied in this paper.

  • discharge characteristics of atmospheric pressure radio frequency Glow Discharges with argon nitrogen
    Applied Physics Letters, 2006
    Co-Authors: Huabo Wang, Wenting Sun, Chengyu Bao, Xing Gao, Huiying Luo
    Abstract:

    In this letter, atmospheric-pressure Glow Discharges in γ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the α-γ coexisting mode or γ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable γ mode radio-frequency, atmospheric-pressure Glow Discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.

Annemie Bogaerts - One of the best experts on this subject based on the ideXlab platform.

  • effects of oxygen addition to argon Glow Discharges a hybrid monte carlo fluid modeling investigation
    Spectrochimica Acta Part B: Atomic Spectroscopy, 2009
    Co-Authors: Annemie Bogaerts
    Abstract:

    Abstract A hybrid model is developed for describing the effects of oxygen addition to argon Glow Discharges. The species taken into account in the model include Ar atoms in the ground state and the metastable level, O 2 gas molecules in the ground state and two metastable levels, O atoms in the ground state and one metastable level, O 3 molecules, Ar + , O + , O 2 + and O − ions, as well as the electrons. The hybrid model consists of a Monte Carlo model for electrons and fluid models for the other plasma species. In total, 87 different reactions between the various plasma species are taken into account. Calculation results include the species densities and the importance of their production and loss processes, as well as the dissociation degree of oxygen. The effect of different O 2 additions on these calculation results, as well as on the sputtering rates, is discussed.

  • hybrid monte carlo fluid model for studying the effects of nitrogen addition to argon Glow Discharges
    Spectrochimica Acta Part B: Atomic Spectroscopy, 2009
    Co-Authors: Annemie Bogaerts
    Abstract:

    Abstract A computer model is developed for describing argon/nitrogen Glow Discharges. The species taken into account in the model include electrons, Ar atoms in the ground state and in the 4s metastable levels, N2 molecules in the ground state and in six different electronically excited levels, N atoms, Ar+ ions, N+, N2+, N3+ and N4+ ions. The fast electrons are simulated with a Monte Carlo model, whereas all other species are treated in a fluid model. 74 different chemical reactions are considered in the model. The calculation results include the densities of all the different plasma species, as well as information on their production and loss processes. The effect of different N2 additions, in the range between 0.1 and 10%, is investigated.

  • the afterGlow mystery of pulsed Glow Discharges and the role of dissociative electron ion recombination
    Journal of Analytical Atomic Spectrometry, 2007
    Co-Authors: Annemie Bogaerts
    Abstract:

    It is generally recognized that excited level populations and, hence, optical emission intensities in pulsed Glow Discharges exhibit a peak upon pulse termination, i.e., in the so-called afterGlow. This afterpeak formation is attributed in many papers to electron–ion recombination, but up to now this hypothesis could not be confirmed quantitatively by numerical modelling, because of too low electron and ion number densities and recombination rate coefficients. In the present paper, we show the calculation results of a model, which includes also Ar2+ ions, beside the Ar+ ions, and which takes into account the thermalization of the electrons upon pulse termination, yielding higher recombination rate coefficients. The role of electron–Ar2+ dissociative recombination and electron–Ar+ three-body recombination as afterpeak formation mechanisms is investigated. Our study clearly shows the important role of Ar2+ ions and dissociative recombination in the afterpeak formation in the afterGlow of pulsed Discharges.

  • Plasma diagnostics and numerical simulations: insight into the heart of analytical Glow Discharges
    Journal of Analytical Atomic Spectrometry, 2006
    Co-Authors: Annemie Bogaerts
    Abstract:

    This review paper gives an overview of the fundamental studies, both by plasma diagnostics and numerical modelling, that have been carried out for analytical Glow Discharges. After some introduction about the basic aspects of a Glow discharge, the various plasma diagnostic techniques that have been described in the literature for analytical Glow Discharges will be outlined, including a discussion on their strong and weak points, and a presentation of some characteristic results. The major part of the paper, however, focuses on modelling activities for a better description of Glow Discharges. An overview is given of possible modelling approaches for Glow Discharges in general, as a means to point out why we have chosen to describe analytical Glow Discharges by a hybrid modelling network, consisting of various sub-models. The latter will be briefly described, and typical calculation results will be outlined, mainly for Glow Discharges in direct current (dc) mode, which are nowadays well described by numerical modelling. The modelling of radiofrequency (rf) Glow Discharges was found to be more complicated, as described in this review, but we believe that the most important aspects of the rf Glow discharge are also correctly predicted. For pulsed Discharges, on the other hand, some unanswered questions remain, mainly related to the so-called afterpeak behaviour. Hence, this will need further attention in the future, by modelling and/or plasma diagnostic measurements.

  • The Glow discharge: an exciting plasma!
    Journal of Analytical Atomic Spectrometry, 1999
    Co-Authors: Annemie Bogaerts
    Abstract:

    Glow Discharges are used in a large number of application fields. Their use as a spectroscopic source for analytical chemistry is only one application; they are much more widely used for other purposes, such as in the micro-electronics industry and in materials technology, and also as lasers, various kinds of light sources, and in the new upcoming plasma displays. In this review we will give a brief overview of these applications. In order to improve the results in these application fields and, in general, to obtain a better understanding of the plasma processes, various modeling approaches for Glow Discharges, mainly for the non-analytical applications, have been described in the literature, of which a brief overview will be given here. Finally, our own modeling network, which is specifically applied to analytical Glow Discharges, will be briefly described and some typical results will be shown.

Karl H. Schoenbach - One of the best experts on this subject based on the ideXlab platform.

  • removal of volatile organic compounds in atmospheric pressure air by means of direct current Glow Discharges
    IEEE Transactions on Plasma Science, 2005
    Co-Authors: Chunqi Jiang, R H Stark, Abdelaleam H Mohamed, J H Yuan, Karl H. Schoenbach
    Abstract:

    A nonthermal plasma with an electron density on the order of 10/sup 12/ cm/sup -3/ and a gas temperature of 2000 K was generated in atmospheric pressure air, using a microhollow cathode discharge as plasma cathode. The plasma was sustained in a /spl sim/1 mm/sup 3/ micro reactor, by a voltage of 470 V between the plasma cathode and a planar anode, and at currents ranging from 12 to 22 mA. This direct current Glow discharge has been used to study the remediation of methane and benzene, two of the most stable volatile organic compounds (VOCs). The removal fraction for 300-ppm methane in atmospheric pressure air, flowing through the 0.5-mm thick plasma layer, with a residence time of the gas in the plasma of less than 0.5 ms, was measured at 80% with an energy density of 4 kJ/L. For benzene, the remediation rate is as high as 90%, comparable to results obtained with low pressure Glow Discharges. The energy efficiency for benzene remediation is 0.9 g/kWh, higher than that obtained for benzene remediation in low pressure Glow Discharges in noble gases. However, the VOC fraction remaining was found to be limited to values of approximately 0.1 and 0.05 for methane and benzene, respectively. In addition to experimental studies, the VOC dissociation mechanism in a VOC/dry air mixture plasma was modeled using a zero-dimensional plasma chemistry code. The modeling results have shown that atomic oxygen impact reactions are the dominant dissociation reactions for VOC destruction in this kind of Glow discharge. Diffusion of atomic oxygen to the dielectric walls of the reactor is assumed to cause the observed limitation in the VOC destruction rate and efficiency.

  • direct current Glow Discharges in atmospheric air
    IEEE Transactions on Plasma Science, 2002
    Co-Authors: Abdelaleam H Mohamed, R Block, Karl H. Schoenbach
    Abstract:

    A microhollow cathode discharge was used as plasma cathode to sustain a stable direct current Glow discharge in atmospheric pressure air. The length of the Glow discharge column was varied from 1 mm to 2 cm, with the sustaining voltage increasing linearly with length. For Glow Discharges with currents on the order of 10 mA, the electron density in the air plasmas exceeded 10/sup 11/ cm/sup -3/, with highest values of almost 10/sup 13/ cm/sup -3/ close to the plasma cathode. When two 8.5-mA Discharges were operated in parallel, at a distance of 0.4 cm, the discharge plasmas were found to merge for electrode gaps exceeding 0.5 cm, an effect that can be used to generate large volume, homogenous air plasmas.

  • direct current Glow Discharges in atmospheric air
    International Conference on Plasma Science, 2001
    Co-Authors: Abdelaleam H Mohamed, R Block, Karl H. Schoenbach
    Abstract:

    Summary form only given, as follows. Research on atmospheric pressure Glow Discharges in air is motivated by applications such as instantly activated reflectors and absorbers for electromagnetic radiation, remediation and detoxification of gaseous pollution, and surface treatment. One of the major obstacles in obtaining stable Glow Discharges at high electron densities (> 10/sup 11/ cm/sup -3/) is the Glow-to-arc-transition, which develops generally in the cathode fall region. The use of a microhollow cathode discharge as independent electron emitter, has been shown to reduce the cathode fall drastically, and has therefore allowed us to generate direct current, atmospheric-pressure air Glow Discharges. The millimeter size plasmas, studied in earlier experiments, have been scaled to centimeter dimensions by operating MHCD sustained air Glows in parallel and extending the electrode distance up to 2 cm. The electric field in these discharge plasmas, varies between 1.2 kV/cm, for a discharge current of 13 mA, to 2 kV/cm at 5 mA. The current density varies between 50 mA/cm/sup 2/ for high currents (13 mA) and 500 mA/cm/sup 2/ for low currents (5 mA), corresponding to electron densities between 10/sup 11/ cm/sup -3/ and 10/sup 12/ cm/sup -3/. The MHCD supported air Glow discharge has a negative differential resistance. Parallel operation of the individual Discharges therefore requires individual ballast. Two parallel Discharges were generated, with their axes 0.4 cm apart. It was found that for this configuration the positive columns merged for currents exceeding 10 mA, creating a homogeneous plasma. The required electrical power density for electron densities of 1.5 /spl times/ 10/sup 11/ cm/sup -3/ was measured as 100 W/cm/sup 3/. By pulsing the plasma this power dissipation can be reduced considerably without sacrificing on the time-average value of the electron density.

  • electron heating in atmospheric pressure Glow Discharges
    Journal of Applied Physics, 2001
    Co-Authors: R H Stark, Karl H. Schoenbach
    Abstract:

    The application of nanosecond voltage pulses to weakly ionized atmospheric pressure plasmas allows heating the electrons without considerably increasing the gas temperature, provided that the duration of the pulses is less than the critical time for the development of Glow-to-arc transitions. The shift in the electron energy distribution towards higher energies causes a temporary increase in the ionization rate, and consequently a strong rise in electron density. This increase in electron density is reflected in an increased decay time of the plasma after the pulse application. Experiments in atmospheric pressure air Glow Discharges with gas temperatures of approximately 2000 K have been performed to explore the electron heating effect. Measurements of the temporal development of the voltage across the discharge and the optical emission in the visible after applying a 10 ns high voltage pulse to a weakly ionized steady state plasma demonstrated increasing plasma decay times from tens of nanoseconds to mic...

  • Direct current Glow Discharges in atmospheric air
    Applied Physics Letters, 1999
    Co-Authors: R H Stark, Karl H. Schoenbach
    Abstract:

    Direct current Glow Discharges have been operated in atmospheric air by using 100 μm microhollow cathode Discharges as plasma cathodes. The Glow Discharges were operated at currents of up to 22 mA, corresponding to current densities of 3.8 A/cm2 and at average electric fields of 1.2 kV/cm. Electron densities in the Glow are in the range from 1012 to 1013 cm−3. Varying the current of the microhollow cathode discharge allows us to control the current in the atmospheric pressure Glow discharge. Large volume atmospheric pressure air plasmas can be generated by operating microhollow cathode Discharges in parallel.