Low-pressure Dc Glow Discharge Research Articles

Theoretical comparison of effects of different cross fields on low pressure DC glow discharge

the mathematical models of glow discharge in transverse (y-direction) and axial (z-direction) magnetic fields are established in this paper. Firstly, Paschen's law is modified for different cross fields. The results show that the breakdown voltage first decreases and then increases with the increase of y-direction magnetic field at the same pressure. The breakdown voltage of glow discharge in z-direction magnetic field increases with the increase of magnetic field. Secondly, the effects of y-magnetic field and z-magnetic field on glow discharge are compared and analyzed by using the modified ionization coefficient. The results show that the plasma density has an extreme value under the combined action of y-direction magnetic field and air pressure. At the same pressure, the plasma density first increases and then decreases with the increase of magnetic field. The larger the magnetic field, the more obvious the plasma attenuation. In the z-direction magnetic field, the plasma density increases with the increase of air pressure or magnetic field.

Chemical constitution of coatings deposited remotely by activation of hexamethyldisiloxane in positive column plasma of glow discharge in argon flow

The present work deals with the chemical constitution of coatings deposited by plasma activation of hexamethyldisiloxane in positive column plasma of a low-pressure DC glow discharge in an argon flow (mass flow rate 230 mg/min). X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) are used to analyze deposit chemistry. The substance is complex and consists of many constitutional units forming branched and cross-linked irregular macromolecules. Chemical constitution depends on both discharge current (10–60 mA) and monomer flow rate (1–10 mg/min). Using the specific energy (SE) and Arrhenius-like approach, the threshold energy for the plasma polymerization of HMDSO has been estimated to be 12 ± 1 eV. Two regimes of the plasma chemical system have been identified. At SE near the threshold energy (from 5 to 40 eV/molecule), polymethylsiloxane-like coatings are deposited and variation of SE practically does not lead to changes in chemical constitution, but significantly affects the mass yield of deposit. At specific energies much higher than threshold energy, polymethylhydroxysiloxane-like coatings are formed; the coating structure is strongly SE-dependent, while the mass yield of the deposit does not change.

Experimental investigation of the period-adding bifurcation route to chaos in plasma.

Since the characteristic timescales of the various transport processes inside the discharge plasma span several orders of magnitude, it can be regarded as a typical fast-slow system. Interestingly, in this work, a special kind of complex oscillatory dynamics composed of a series of large-amplitude relaxation oscillations and small-amplitude near-harmonic oscillations, namely, mixed-mode oscillations (MMOs), was observed. By using the ballast resistance as the control parameter, a period-adding bifurcation sequence of the MMOs, i.e., from L^{s} to L^{s+1}, was obtained in a low-pressure DC glow discharge system. Meanwhile, a series of intermittently chaotic regions caused by inverse saddle-node bifurcation was embedded between the two adjacent periodic windows. The formation mechanism of MMOs was analyzed, and the results indicated that the competition between electron production and electron loss plays an important role. Meanwhile, the nonlinear time series analysis technique was used to study the dynamic behavior quantitatively. The attractor in the reconstructed phase space indicated the existence of the homoclinic orbits of type Γ^{-}. In addition, by calculating the largest Lyapunov exponent (LLE), the chaotic nature of these states was confirmed and quantitatively characterized. With the decrease in the ballast resistance, the return map of the chaotic state gradually changed from the nearly one-dimensional single-peak structure to the multibranch structure, which indicates that the dissipation of the system decreased. By further calculating the correlation dimension, it was shown that the complexity of the strange attractors increased for higher-order chaotic states.

Numerical simulation of the hysteresis of the transition from the stationary to oscillatory regime in the low-pressure DC glow discharge

As a typical highly nonlinear medium, laboratory plasmas can exhibit abundant nonlinear phenomena. It is well known that the presence of negative differential conductivity can cause the system to exhibit temporal chaotic oscillations when a DC glow discharge is operated in the subnormal glow discharge regime. In addition, for a nonlinear system, the hysteresis often occurs due to the coexistence of multiple attractors. In this work, a two-dimensional plasma fluid model based on the drift-diffusion approximation is developed to study the hysteresis phenomenon of the nonlinear dynamical behaviors of the low-pressure DC glow discharge. The results demonstrate that the initial discharge conditions selected in calculations will influence the nonlinear dynamical behaviors significantly that the system exhibits. Hysteresis can be observed from the voltage waveform when the applied voltage is altered to allow the system to work between the stationary discharge regime and the oscillatory discharge regime. In the hysteresis region, the system exhibits bi-stable characteristics. Near the critical point, the dynamical behaviors of the system will jump from the stationary state to the oscillatory state under small perturbations and the reverse adjustment of control parameters will not immediately restore the original stationary state, which is a typical characteristic of the subcritical Hopf bifurcation.

Comparison between 1D radial and 0D global models for low-pressure oxygen DC glow discharges

This work focuses on the comparison between a zero-dimensional (0D) global model (LoKI) and a one-dimensional (1D) radial fluid model for the positive column of oxygen DC glow discharges in a tube of 1 cm inner radius at pressures between 0.5 Torr and 10 Torr. The data used in the two models are the same, so that the difference between the models is reduced to dimensionality. A good agreement is found between the two models on the main discharge parameters (gas temperature, electron density, reduced electric field and dissociation fraction), with relative differences below 5%. The agreement on other species average number densities, charged and neutral, is slightly worse, with relative differences increasing with pressure from 11% at 0.5 Torr to 57% at 10 Torr. The success of the 0D global model in describing these plasmas through volume averaged quantities decreases with pressure, due to pressure-driven narrowing of radial profiles. Hence, in the studied conditions, we recommend the use of volume-averaged models only in the pressure range up to 10 Torr.

Effect of O2, N2, Ar, and Ar/O2 Plasma Treatment on Optical Properties of Polyaniline Films

In the current work, improvement of the optical properties of Polyaniline (PAni) films was investigated using cold plasma technique. Samples were treated with different gases including argon (Ar), oxygen (O2), nitrogen (N2) and Ar/O2 mixture using low-pressure dc glow discharge. Films of about 300 nm were fabricated by simple deposition of polyaniline suspension in toluene on glass slides. UV-Vis spectrophotometric measurements of the prepared films showed that plasma treatment resulted in a significant increase in the optical band gap of the films. Plasma treatment was found to increase the band gap energies range from (1.7–1.98 eV) of the untreated films to 1.8-2.42 eV of the treated ones. Exposure to oxygen plasma was found to alter the chemical composition of the films and thus, resulting in a high transmission (over 85%) of the peak centred at 550 nm. This increases the photoelectric performance of the plasma treated polyaniline films

Positive column of a glow discharge in neon with charged dust grains (a review)

The effect of charged micron-size dust grains (microparticles) on the electric parameters of the positive column of a low-pressure dc glow discharge in neon has been studied experimentally and numerically. Numerical analysis is carried out in the diffusion-drift approximation with allowance for the interaction of dust grains with metastable neon atoms. In a discharge with a dust grain cloud, the longitudinal electric field increases. As the number density of dust grains in an axisymmetric cylindrical dust cloud rises, the growth of the electric field saturates. It is shown that the contribution of metastable atoms to ionization is higher in a discharge with dust grains, in spite of the quenching of metastable atoms on dust grains. The processes of charging of dust grains and the dust cloud are considered. As the number density of dust grains rises, their charge decreases, while the space charge of the dust cloud increases. The results obtained can be used in plasma technologies involving microparticles.

An effective approach for designing a low pressure DC glow discharge plasma reactor

Most plasma reactors are designed for research purposes and they are less appropriate for industry. To facilitate the engineering of an industrial reactor, an effective approach based only on the calculated Paschen curve, the simulation of the electric field and the breakdown reduced field is proposed. The results show that the experimental Paschen curve is different from the theoretical one; consequently the recalculation of the electric parameters is discussed. The experimental voltage/Current characteristic is used to identify the abnormal glow discharge regime and also to correlate the visual aspect of the discharge with its regimes.

Characterization of the large area plane-symmetric low-pressure DC glow discharge

Electron density and temperature as well as nitrogen dissociation degree in the low-pressure (10–50mTorr) large area plane–symmetric DC glow discharge in Ar-N2 mixtures are studied by probes and spectral methods. Electron density measured by a hairpin probe is in good agreement with that derived from the intensity ratio of the N2 2nd positive system bands IC,1−3/IC,0−2 and from the intensity ratio of argon ions and atom lines IArII/IArI, while Langmuir probe data provides slightly higher values of electron density. Electron density in the low-pressure DC glow discharge varies with the discharge conditions in the limits of ~108–1010cm−3. The concept of electron temperature can be used in low-pressure glow discharges with reservations. The intensity ratio of (0–0) vibrational bands of N2 1st negative and 2nd positive systems I391.4/I337.1 exhibits the electron temperature of 1.5–2.5eV when argon fraction in the mixture is higher than nitrogen fraction and this ratio quickly increases with nitrogen fraction up to 10eV in pure nitrogen. The electron temperature calculated from Langmuir probe I-V characteristics assuming a Maxwellian EEDF, gives Te~0.3–0.4eV. In-depth analysis of the EEDF using the second derivative of Langmuir probe I-V characteristics shows that in a low-pressure glow discharge the EEDF is non-Maxwellian. The EEDF has two populations of electrons: the main background non-Maxwellian population of “cold” electrons with the mean electron energy of ~0.3–0.4eV and the small Maxwellian population of “hot” electrons with the mean electron energy of ~1.0–2.5eV. Estimations show that with electron temperature lower than 1eV the rate of the direct electron impact ionization of N2 is low and the main mechanism of N2 ionization becomes most likely Penning and associative ionization. In this case, assumptions of the intensity ratio IN2+,391/IN2,337 method are violated.In the glow discharge, N2 dissociation degree reaches about 7% with the argon fraction in the Ar-N2 mixture<10% and decreases afterwards approaching to ~1–2% when the argon percentage becomes 90% and higher. The atomic nitrogen species is produced by electron-impact processes such as, collisions between electrons and nitrogen molecules or between electrons and N2+ ions. At small Ar fraction in Ar-N2 mixtures, the atomic nitrogen species is most likely produced by the collisions between electrons and N2+ ions.

Asymmetric polysulfone gas separation membranes treated by low pressure DC glow discharge plasmas

ABSTRACTAsymmetric polysulfone (PSF) gas separation membranes were prepared at different conditions such as non‐solvent concentration, evaporation time (ET) and coagulation bath temperature (CBT). In addition, effects of low‐pressure DC glow discharge plasma on the characteristics of PSF membranes were investigated. PSF membranes both before and after plasma treatment were characterized by several techniques, including contact angle measurement, scanning electron microscope (SEM), dynamic mechanical thermal analysis (DMTA), and atomic force microscopy (AFM). Furthermore, the performance of membranes was evaluated in terms of permeability of CO2, CH4, O2, and N2 gases. The ideal selectivity of CO2/CH4 and O2/N2 and surface free energy was calculated. Results showed that the EtOH concentration, ET and CBT affect the morphology of PSF membranes. For membranes prepared from a casting solution consisting of PSF 26.0, NMP 28.0, THF 28.0, and EtOH 18.0 wt % and ET for 3 min, the maximum selectivity of untreated membrane is about 69.76 and 12.59 for CO2/CH4 and O2/N2, respectively. After plasma treatment, the ideal selectivity is receded; however, the CO2/CH4 is still higher than 40.41 at pressure of 5 bars. Finally, preparation conditions and DC glow discharge plasmas have significant effects on the characteristics of the PSF membranes and result in an increase of the gas permeation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42116.

Characterization of suprathermal electron population in He dc glow discharges by optical emission and probe diagnostics

Evidence of the strong contribution of electrons with energies up to the cathode fall potential was found in low-pressure He dc glow discharge plasmas (3–8 mTorr), in agreement with expectations from the estimates of the mean free path of electron–neutral inelastic collisions. A simple gridded probe, of the retarding field analyzer type, was applied to the characterization of the full electron energy distribution function (EEDF) in He plasmas with significant contribution from suprathermal electrons (up to 3.5%). The inferred EEDFs were cross-checked with results from the He line ratio diagnostic and good agreement was found at several values of pressure and plasma current.

Low Pressure DC Glow Discharge Air Plasma Surface Treatment of Polyethylene (PE) Film for Improvement of Adhesive Properties

The present work deals with the change in surface properties of polyethylene (PE) film using DC low pressure glow discharge air plasma and makes it useful for technical applications. The change in hydrophilicity of the modified PE film surface was investigated by measuring contact angle and surface energy as a function of exposure time. Changes in the morphological and chemical composition of PE films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap-shear strength. The results show that the wettability and surface energy of the PE film has been improved due to the introduction of oxygen-containing polar groups and an increase in surface roughness. The XPS result clearly shows the increase in concentration of oxygen content and the formation of polar groups on the polymer surface. The AFM observation on PE film shows that the roughness of the surface increased due to plasma treatment. The above morphological and chemical changes enhanced the adhesive properties of the PE film surfaces, which was confirmed by T-peel and lap-shear tests.

Laser absorption spectroscopy for xenon monitoring in the cover gas of sodium cooled fast reactors

Xenon is a fission product of uranium that must be monitored on line and in real time in the cover gas of a sodium cooled fast neutron reactor (SFR) for safety reasons. In this paper, tunable diode laser absorption spectroscopy is applied to quantify low concentrations of natural xenon in argon. Optical detection is carried out at 12 145 cm−1 (823 nm) from the 6s[3/2]02 Xe electronic metastable state, populated in a low pressure DC glow discharge. Optimal discharge parameters (110 Pa, 1.3 W) were experimentally determined to maximize the laser absorption signal. Measurement stability, argon pressure spectral broadening, isotope quantification, and linearity of the optical measurement with respect to the xenon concentration in the gas sample were carefully investigated. Under optimized experimental conditions, the detection limit of xenon over argon molar ratio is estimated as 60 ± 10 parts per billion at 1 Hz, corresponding to a xenon number density of 1.6 × 109 atoms.cm−3 along the laser beam.

Chemical and physical changes in surface of Argon plasma treated cotton fabrics

Hydrophilic cotton fabrics were exposed by low-pressure DC glow discharge plasma in argon atmosphere. The influence of different operating parameters such as treatment time, discharge potential, and operating pressure on the chemical and physical properties of the cotton fabrics is studied. Surface analysis and characterization of the plasma-treated cotton fabrics is performed using vertical wicking experiments, X-ray photoelectron spectroscopy, scanning electron microscopy, and weight loss measurements. The cotton fabrics show a significant increase in wicking behavior, an effect that increases with increasing treatment time. Results also show that low-pressure DC glow treatment leads to surface attrition of the cellulose fibers, accompanied by an incorporation of oxygen-containing groups (C–O, C=O, O–C–O, and O–C=O) on the cotton fibers.

Comparison of low-pressure DC glow discharge and dielectric barrier discharge in CO2-laser mixture by optical emission spectroscopy

Nowadays the CO2 lasers are used in many technologies, including medicine and material processing industry. Besides original low-pressure low-power lasers pumped by DC glow discharge, the attention is focused on the high power atmospheric pressure lasers. We use optical emission spectroscopy to study both low pressure (from 266 Pa to 1330 Pa) DC glow discharge (DC GD) and the dielectric barrier discharge (DBD) (from 5 kPa to 100 kPa) in mixtures of helium, nitrogen and carbon dioxide used in CO2 lasers.Considering the emission spectrum of the discharges mentioned above, we can find bands of the first and the second positive systems of the nitrogen molecule. From these bands it is possible to deduce energetic balance and the vibrational temperature [1].In our contribution, the vibrational temperature of nitrogen is determined by means of optical emission spectroscopy from the second positive system band of the nitrogen molecule for various discharge currents in DC glow discharge and for various gap widths in DBD. Using these two discharges we covered the whole pressure range from 266 Pa up to atmospheric pressure. The dependence of the vibrational temperature on N2 content in the mixture is also investigated. The vibrational temperature showed a steady decrease with increasing pressure in whole pressure range. It was found, that the vibrational temperature of nitrogen in the DC GD is twice as high as in the DBD, which was attributed to the different nature of discharges.Spectroscopic measurements were complemented with measurements of electric properties of discharges: the longitudinal electric field strength for DC glow discharge and Lissajous' figures for DBD [1,2].

Retracted: Study of the wettability of ZnO nanofilms

This article was mistakenly published twice. For this reason this duplicate article has now been retracted. For citation purposes please cite the original: http://www.inljournal.com/?_action=articleInfo&article=21 Al-doped and un-doped ZnO thin films deposited on quartz substrates by the nebulized spray pyrolysis method were studied to investigate the wettability of the surface. The main objective of the present study was to investigate the wettability of ZnO thin film by changing the concentration of Al doping. Microstructure and water contact angles of the films were measured by scanning electron microscopy (SEM) and using a contact angle goniometer. SEM studies revealed that the grain size within the film increases with the doping concentration. The contact angles were studied to see the effect of aluminum doping on the hydrophilicity of the film. ZnO films were found to be hydrophobic in nature. A good correlation was observed between the SEM micrographs and contact angle results. The nature of the film was found to change from being hydrophobic to hydrophilic after the treatment in low-pressure DC glow discharge plasma, which, however, was reversible with the storage time.

Plasma Copolymerization of Thiophene and Pyrrole

The copolymerization of thiophene and pyrrole thin films synthesized by using a double discharge technique which has a fast filamentary discharge formed from the superposition of an ordinary low-pressure dc glow discharge and a high-current pulsed one is presented. Quartz glass substrates were coated at a pressure of 0.8 mbar and 19-kV pulsed and 2-kV dc potentials. The analysis of functional groups by FTIR spectrometry showed that the molecular structure of the copolymerized thin films with the filamentary discharge part almost preserves the conventional polymeric structure.

Decomposition Characteristics of an Artificial Biogas in a Low-Pressure DC Glow Discharge

SUMMARY The decomposition characteristics of an artificial biogas, which is a mixture of CH 4, CO 2, and H 2 S, using a low-pressure DC glow discharge have been investigated. It is found that H 2, CO, C 2 H 2, H 2 O, CS 2, and COS are produced from the artificial biogas in the glow discharge. About 65% of the hydrogen atoms in CH 4 are converted into H 2 at an input energy of 800 J, at which CH 4 is completely decomposed, and the decomposition characteristics of the artificial biogas are minimally dependent on the H 2 S additive. Further, H 2 S has a tendency to be decomposed earlier than the other components of the artificial biogas. When the glow discharge is generated in the artificial biogas with H 2 S, some of the carbon atoms are found to deposit on the electrodes and the wall of the discharge chamber. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 26–33, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22304

Decomposition Process of Benzene in a Low Pressure DC Glow Discharge

The variations in the partial pressures of gaseous molecules produced by the decomposition of C6H6 in a low pressure DC glow discharge in N2/C6H6 and Ar/C6H6 mixtures are measured by the mass spectrometry. Also, rate equations for the partial pressure variations, which consider possible reaction among the gaseous molecules in the low pressure DC glow discharge, with the electrical energy-input, are proposed, and rate constants are determined by fitting the calculated partial pressure variations to the measured partial pressure variations. The rate constants deduced here indicate that C6H6 is mainly decomposed into an intermediate, which is regarded as a fragment of C6H6, the intermediate is decomposed into mainly C2H2, and then C2H2 is converted into H2 and HCN (only in N2/C6H6).

Low-Pressure Dynamical Glow Discharge With Electrolytic Cathode in the Form of Aqueous Solution of $\hbox{NaHCO}_{3}$

Video images of a low-pressure dc glow discharge with an electrolytic cathode in the form of aqueous solution of sodium bicarbonate NaHCO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> are presented in this paper. Various forms of the discharge are observed. One of the discharge forms-a dc glow discharge with a foam cathode-was recorded for the first time. A space-time diagram of the discharge is drawn.