Direct Current Glow Discharge Plasma Research Articles

Characterization of a Glow Discharge in a Tripped Hypersonic Boundary Layer

A direct current glow discharge plasma was generated on a canonical 2.75° half-angle wedge test article. Experiments were conducted in the Texas A&M University Actively Controlled Expansion Tunnel at M=5.7 and Re=6×106/m. The effects of Reynolds number, polarity, and upstream perturbation were all independently studied via imaging, power measurements, and optical emission spectroscopy (OES). These measurements are the first to be conducted in a tripped hypersonic boundary layer and allow a deeper understanding of the interplay between the plasma and tripped flow. The plasma, formally characterized as a normal glow discharge, had negligible Joule and cathode heating effects on the boundary layer. Analogously, the installation of trips upstream of the electrodes changed only the appearance of the plasma, creating periodic streaks corresponding to the wakes and vortices produced by each trip but not altering the power across the electrodes. The OES indicates generation of nitric oxide (NO) in both the positive column and, mainly, at the cathode at the relatively low plasma power of ∼47W.

Iron-Oxide-Nanoparticles-Doped Polyaniline Composite Thin Films.

Iron-oxide-doped polyaniline (PANI-IO) thin films were obtained by the polymerization of aniline monomers and iron oxide solutions in direct current glow discharge plasma in the absence of a buffer gas for the first time. The PANI-IO thin films were deposited on optical polished Si wafers in order to study surface morphology and evaluate their in vitro biocompatibility. The characterization of the coatings was accomplished using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), metallographic microscopy (MM), and X-ray photoelectron spectroscopy (XPS). In vitro biocompatibility assessments were also conducted on the PANI-IO thin films. It was observed that a uniform distribution of iron oxide particles inside the PANI layers was obtained. The constituent elements of the coatings were uniformly distributed. The Fe-O bonds were associated with magnetite in the XPS studies. The surface morphology of the PANI-IO thin films was assessed by atomic force microscopy (AFM). The AFM topographies revealed that PANI-IO exhibited the morphology of a uniformly distributed and continuous layer. The viability of Caco-2 cells cultured on the Si substrate and PANI-IO coating was not significantly modified compared to control cells. Moreover, after 24 h of incubation, we observed no increase in LDH activity in media in comparison to the control. In addition, our results revealed that the NO levels for the Si substrate and PANI-IO coating were similar to those found in the control sample.

Plasma pressure sensor based on direct current glow discharge

This paper describes a recently developed pressure-measuring technique based on direct current glow discharge plasma. The operation principle, characteristics and design of this plasma pressure sensor are introduced and investigated. The development of the plasma pressure sensor was motivated by the need to document the high-frequency internal information more clearly in the harsh environment of turbomachines or hypersonic flows. The electrode spacing and current were two main factors that influenced the sensor's monotonic response characteristic and static sensitivity to the pressure fluctuation. Three typical electrode spacings—50 μm, 100 μm and 220 μm—were tested for the static calibration. The results revealed that the optimal electrode spacing was 220 μm, which showed a monotonically increasing trend and had the highest sensitivity for a pressure range from 0.5 atm to 5.0 atm. The dynamic response of the sensor was calibrated with a sinusoidal-wave pressure generator and a shock tube as the step-function pressure generator. The results showed that the natural frequency of the plasma pressure sensor, including its high-voltage power supply and electronic circuit, was 146.6 kHz.

Glow Discharge Plasma as a Cause of Changes in Aqueous Solutions: The Mass Spectrometry Study of Solvation Processes of Ions

A new apparatus for inducing changes in the properties of water in closed dielectric vessel by subjecting it to pulsed direct current glow discharge plasma is designed and constructed. It has been hypothesized that the action of plasma on the structure of water consists in resonance excitation of water aggregates. As a result of resonance excitation, aggregates of high molar masses are broken down into low molecular mass aggregates. Analysis of the ESI MS spectra revealed that in all tested aqueous solutions after exposure to plasma, the concentration of low-molecular solvated ions [M(H2O)]+ and [M(H2O)2]+ significantly increased, while the concentration of the ions of high molecular masses [M(H2O)6-10]+ solvated by water aggregates decreased, relative to their concentrations in the water solutions not subjected to plasma irradiation. According to our measurements also a significant change in pH occurs. The presented results clearly show that it is possible to process a liquid that changes its structure without involving high processing energy and, unexpectedly, the obtained change of parameters is significant and stable over time.

Physical and mechanical properties of surface modified poly ethylene terephthalate films through low pressure plasma and ultra-violet light

The present work focussed on the effect of UV light radiation and Direct current glow Discharge Plasma (DC) on Polyethylene Terephthalate (PET) surface for food packaging applications. The PET was treated by three different plasma such as air, argon, and oxygen with a treatment time of 5–25 min and pressure kept as 3 Pa. The PET film was exposed by UV radiation using the wavelength between 200–400 nm UV light Lamp with a treatment time of 5–25 min. And also we measured the electron temperature (Te) and electron density (Ne) of the three different plasmas by Single Langmuir probe method. The surface properties of UV light radiated and plasma treated PET films were characterized by static contact angle, x-ray diffraction, Optical analysis (UV–vis), ATR-FTIR, Structural analysis (AFM)) and the results were compared. We observed that the bulk properties of the treated materials remained unchanged. This was confirmed by x-ray diffraction results. The new polar functional groups were also detected on the treated films by FTIR spectrum analysis. The surface roughness was calculated from AFM analysis for both untreated and treated PET films. The oxygen plasma treated sample showed higher roughness, which indicated that a large amount of oxygen containing polar groups appeared on the surface of the PET film. The obtained results reveal that the plasma treated PET films were more effective than the Ultra-violet (UV) light radiated film.

Optical and electrical properties of plasma surface treated polymethylmethacrylate films

Abstract In the present study, the optical and electrical properties of Polymethylmethacrylate (PMMA) films have been investigated under the effect of direct current (DC) glow discharge plasma. PMMA films have been prepared and treated with low-pressure DC glow discharge plasma at different plasma conditions; mainly various working gas and plasma treatment time. The optical and electrical properties of the treated PMMA samples were measured and compared to the untreated one. Nitrogen, argon, and nitrogen-argon mixture have been used as working gases. Plasma parameters, such as the electron density, the ion density, and electron temperature, were measured, at the position of the PMMA films, using Langmuir probe. The results reveal that, the optical properties of PMMA were found to be more sensitive to N2- plasma treatment than Ar and N2-Ar gas mixture. The optical energy gap showed a decreasing behavior with increasing the treatment time of N2 plasma however, the band tail width and the electrical resistivity increased.

Dust vortices in a direct current glow discharge plasma: a delicate balance between ion drag and Coulomb force

Dust vortices with a void at the centre are reported in this paper. The role of the spatial variation of the plasma potential in the rotation of dust particles is studied in a parallel plate glow discharge plasma. Probe measurements reveal the existence of a local potential minimum in the region of formation of the dust vortex. The minimum in the potential well attracts positively charged ions, while it repels the negatively charged dust particles. Dust rotation is caused by the interplay of the two oppositely directed ion drag and Coulomb forces. The balance between these two forces is found to play a major role in the radial confinement of the dust particles above the cathode surface. Evolution of the dust vortex is studied by increasing the discharge current from 15 to 20 mA. The local minimum of the potential profile is found to coincide with the location of the dust vortex for both values of discharge currents. Additionally, it is found that the size of the dust vortex as well as the void at the centre increases with the discharge current.

Synthesis of multiple single crystal diamonds by DC-GD-CVD

ABSTRACTMultiple single crystal diamonds (SCDs) were first synthesised on 24 high pressure high temperature (HPHT) synthetic type Ib (100) SCD seeds by direct current glow discharge plasma chemical vapour deposition (DC-GD-CVD) system with gas mixture of CH4–H2–Ar. Owing to the increase of the formed plasma density and temperature caused by the addition of 1.2 vol.-% Ar gas, a high growth rate of 22.2 µm h−1 for diamonds deposition was achieved by the plasma with diameter of 2 inches at 900–950°C. After deposition for 50 h, diamond material with a thickness of about 1 mm was uniformly deposited on each seed. The average FWHM value, hardness and transmittance of as-obtained SCDs were 3.2 cm−1, 105 GPa and 69.4%, revealing the high quality of multiple SCDs fabricated by the DC-GD-CVD method.

Hydrogen Evolution Reaction in an Alkaline Solution via ε-Fe3N Phase Formation on AISI 316 Stainless Steel by Plasma Treatment

Surface modification techniques can be used to enhance the use of low-cost materials in water electrolysis applications, improving their hydrogen evolution efficiency and life. In this work, a well-known AISI 316 stainless steel was treated with nitrogen direct current glow discharge plasma for the periods of 2, 3, 4, and 5 hours. The e-Fe3N phase was created from the first plasma treatment period, as detected by the X-ray powder diffraction and X-ray photo-electron spectroscopy investigations. To understand the effect of the e-Fe3N phase formation and growth on the hydrogen evolution rate and mechanism both the electrochemical and electro-chemical impedance spectroscopy measurements were done. Advanced plasma treatment over time and enhanced e-Fe3N phase growth were found to decrease the Tafel slope, over-potential, and polarization resistance, which contributes to improving the hydrogen evolution reaction properties of AISI 316 stainless steel. A lab scale electrolyzer equipped with a distilled water displacement attachment was prepared to evaluate the HER practically. The contact angle was measured to find an evidence on the effect of the advanced plasma treatment on the surface hydrophilicity.

Comparative investigation of the emission characteristics between 6.78-MHz radio-frequency and direct-current glow discharge plasmas for atomic emission spectrometry

This paper focused on the characteristics of emission spectra excited by a Grimm-style glow discharge plasma source in a 6.78-MHz radio-frequency (RF) power mode, in comparison to a conventional direct-current (DC) power mode. For this purpose, Boltzmann plots for atomic emission lines of iron were analyzed in detail, when the RF forward power and argon pressure in the discharge chamber were selected as the experimental parameters. The Boltzmann plot for low-lying excited levels of iron atom (3.4–4.8 eV) was on a linear relationship to provide an excitation temperature, whereas emission lines having larger excitation energies (more than 5 eV) generally deviated upwards from the linear relation. Any systematic dependence on the spin multiplicity was not found among the high-lying excited levels in the Boltzmann plot. The reason for the phenomenon was considered as follows: (1) the excitation for the low-lying emission lines would be caused by a dominant thermal collision process and (2) any non-thermal process also contributed to excitations for the high-lying emission lines to cause their over-population as a whole. The resultant excitation temperature was obtained in a narrow range of 3400–3600 K, which was hardly affected by the discharge power and the argon pressure, and further, the excitation temperature was very similar to that of a DC plasma that we had already reported. This result suggested that the glow discharge plasma could be supported by a self-stabilized negative glow region, where the kinetic energy distribution of the particles would be changed to a lesser extent as far as a stable discharge could be maintained.

Morphological and Structural Analysis of Polyaniline and Poly(o-anisidine) Layers Generated in a DC Glow Discharge Plasma by Using an Oblique Angle Electrode Deposition Configuration.

This work is focused on the structural and morphological investigations of polyaniline and poly(o-anisidine) polymers generated in a direct current glow discharge plasma, in the vapors of the monomers, without a buffer gas, using an oblique angle-positioned substrate configuration. By atomic force microscopy and scanning electron microscopy we identified the formation of worm-like interlinked structures on the surface of the polyaniline layers, the layers being compact in the bulk. The poly(o-anisidine) layers are flat with no kind of structures on their surfaces. By Fourier transform infrared spectroscopy we identified the main IR bands characteristic of polyaniline and poly(o-anisidine), confirming that the polyaniline chemical structure is in the emeraldine form. The IR band from 1070 cm−1 was attributed to the emeraldine salt form of polyaniline as an indication of its doping with H+. The appearance of the IR band at 1155 cm−1 also indicates the conducting protonated of polyaniline. The X-ray diffraction revealed the formation of crystalline domains embedded in an amorphous matrix within the polyaniline layers. The interchain separation length of 3.59 Å is also an indicator of the conductive character of the polymers. The X-ray diffraction pattern of poly(o-anisidine) highlights the semi-crystalline nature of the layers. The electrical conductivities of polyaniline and poly(o-anisidine) layers and their dependence with temperature are also investigated.

Development of soft ionization using direct current pulse glow discharge plasma source in mass spectrometry for volatile organic compounds analysis

This study describes an ionization source for mass analysis, consisting of glow discharge plasma driven by a pulsed direct-current voltage for soft plasma ionization, to detect toxic volatile organic compounds (VOCs) rapidly and easily. The novelty of this work is that a molecular adduct ion, in which the parent molecule attaches with an NO+ radical, [M+NO]+, can be dominantly detected as a base peak with little or no fragmentation of them in an ambient air plasma at a pressure of several kPa. Use of ambient air as the discharge plasma gas is suitable for practical applications. The higher pressure in an ambient air discharge provided a stable glow discharge plasma, contributing to the soft ionization of organic molecules. Typical mass spectra of VOCs toluene, benzene, o-xylene, chlorobenzene and n-hexane were observed as [M+NO]+ adduct ion whose peaks were detected at m/z 122, 108, 136, 142 and 116, respectively. The NO generation was also confirmed by emission bands of NO γ-system. The ionization reactions were suggested, such that NO+ radical formed in an ambient air discharge could attach with the analyte molecule.

Photoelectrochemical performance of N-doped ZnO branched nanowire photoanodes.

A ZnO branched-nanowire (BNW) photoanode was doped with N for use in a photoelectrochemical cell (PEC) to generate H2 from water splitting. First, ZnO BNWs were synthesized by chemical bath deposition method. Two experimental methods were used for N-doping: the time-controlled direct-current glow discharge plasma (DCGDP) and the DC magnetron plasma (DCMP) methods, to optimize N-doping of the NW structure. X-ray photoelectron spectroscopy (XPS) provided the N distribution and atomic percentage in the BNWs. The XPS results confirmed that N distribution into ZnO BNWs occurred by N substitution of O sites in the ZnO structure and through well-screened molecular N2. The morphologies and structures of the fabricated nanostructures were investigated by field-emission scanning electron microscopy and X-ray diffraction respectively. The photoanode performance was demonstrated in photoelectrochemical studies at various power densities under both dark and illuminated conditions. Increasing the N amount in the ZnO BNWs increased the photocurrent in the PEC.

Study on plasma pre-functionalized PVC film grafted with TiO2/PVP to improve blood compatible and antibacterial properties

Research into the design of new biopolymers/polymer functionalized with nanoparticles is of tremendous interest to the medical sector, particularly with regard to blood-contacting devices. In this present study, a steady blood compatible and active antibacterial coating was fabricated by the grafting of titanium dioxide (TiO2)/polyvinylpyyrolidone (PVP) onto a polyvinyl chloride (PVC) film surface via the direct-current glow discharge plasma method. To enhance the chemical interaction between TiO2/PVP and PVC, the surfaces of the PVC films were functionalized by different plasmas (air, argon, and oxygen) before coating. In this study, the plasma parameters were varied, such as treatment time of about 5–20 min for a constant power of 100 W, potential 300 V, and a constant gas pressure of 2 Pa for air, argon, and oxygen gas environment. Then, the different plasma treatments on the PVC films, TiO2/PVP were grafted using a simple dip-coating method. In addition, the TiO2/PVP-grafted PVC films were characterized by contact angle, attenuated total reflectance Fourier transform infrared spectroscopy, field-emission scanning electron microscope, and x-ray photo electron spectroscopy. Importantly, TiO2/PVP is grafted onto the PVC surface due to the plasma-based retained functionality and demonstrates adhesive efficiency, which was observed by XPS. The bio-stability of the TiO2/PVP-modified PVC film was evaluated by in vitro platelet activation analysis and protein adsorption analysis. Then, the antibacterial properties were evaluated by the agar diffusion method against Escherichia coli. The result reveals that the grafting of TiO2/PVP was slightly higher for the 15 min oxygen plasma-functionalized PVC, which significantly decreases the platelet adhesion and protein adsorption. Moreover, the antibacterial properties of the 15 min oxygen plasma-functionalized PVC with TiO2/PVP-grafted film is also greatly improved compared with an air- and argon-functionalized surface. Our present study demonstrates that the plasma treatment is a beneficial and eco-friendly method to achieve higher hydrophilicity. Furthermore, our results indicated that the plasma-modified PVC exhibits appropriate anti-fouling performance.

Battery-Operated Atomic Emission Analyzer for Waterborne Arsenic Based on Atmospheric Pressure Glow Discharge Excitation Source.

In this paper, a sensitive atomic emission spectrometer (AES) based on a new low power and low argon consumption (<8 W, 100 mL min-1) miniature direct current (dc) atmospheric pressure glow discharge (APGD) plasma (3 mm × 5 mm) excitation source was developed for the determination of arsenic in water samples. In this method, arsenic in water was reduced to AsH3 by hydride generation (HG), which was then transported to the APGD source for excitation and detected by a compact CCD (charge-coupled device) microspectrometer. Different parameters affecting the APGD and the hydride generation reactions were investigated. The detection limit for arsenic with the proposed APGD-AES was 0.25 μg L-1, and the calibration curves were found to be linear up to 3 orders of magnitude. The proposed method was successfully applied to the determination of certified reference material (GBW08605), tap water, pond water, groundwater, and hot spring samples. Measurements from the APGD analyzer showed good agreement with the certified value/values obtained with well-established hydride generation atomic fluorescence spectrometry (HG-AFS). These results suggest that the developed robust, cost-effective, and fast analyzer can be used for field based arsenic determination and may provide an important tool for arsenic contamination and remediation programs.

Surface Modification of Asymmetric Polysulfone/Polyethylene Glycol Membranes by DC Ar-Glow Discharge Plasma

Polysulfone/polyethylene glycol (PSF/PEG) membranes were prepared by dry/wet phase inversion method. Effects of direct current glow discharge plasma using argon as working gas on morphological structures and gas separation properties of membranes were studied. Alteration of membrane characteristics were analyzed by various techniques like contact angle, scanning electron microscope, Fourier transform infrared spectroscopy, and dynamic mechanical thermal analysis. Gas separation properties were measured in terms of permeation and ideal O2/N2 selectivity. Results showed that hydrophilic and gas separation properties of PSF/PEG membranes increased by plasma surface modification. It was also shown that the dosage of PEG and plasma treatment affected the morphological structures and mechanical and gas separation properties. The macro voids and transmembrane structure disappeared with a little amount of PEG dosage. Pore size and mechanical strength tend to decrease with increasing PEG dosage up to 10 wt%. Glass transition temperature (Tg) receded from 201.8 to 143.7°C for pure PSF and PSF/PEG with PEG dosage of 10 wt%. O2 and N2 gases permeation through the 10-minute plasma treated membranes tend to increase. However, the permeation strongly dispersed when treatment time was more extended.

Effect of Pressure and Hot Filament Cathode on Some Plasma Parameters of Hollow Anode Argon Glow Discharge Plasma

The present study represents a review article and a complementary study to a published paper of direct current hot cathode and hollow anode argon glow discharge plasma at different pressures in the range 0.05 - 0.8 mbar. The glow discharge usually obtained by applying a high voltage between the electrodes sufficient to occurring breakdown of argon gas and sustaining the discharge. Additional estimation of some plasma parameters, ion temperature, degree of ionization and electron energy distribution function as well as some characteristics of glow discharge under the influence of pressure and filament current has been done. Plasma parameters have been calculated using single probe method at fixed discharge current Id=1.88mA and diameter of hollow anode. Furthermore a computer MATLAB program is applied for this purpose. Results show that the average discharge voltage increases while its average discharge current decreases according to the increasing of the filament current. On the Contrary the average discharge voltage decrease nearly exponentially whiles its average discharge current increases according to increasing of the gas pressure. Degree of ionization starts to increase from low pressure to medium and then tends to decrease toward high pressure investigated. However it starts to increase to maximum value at filament current 0.9A then tends to decrease at higher current and low pressure. While for high pressures there is no significance change. Ion temperature increases slowly with filament current up to 0.9A and then sharply increases to maximum value at 1.5A. But it decreases for pressures in the range 0.05 - 0.09 mbar and then increases with gas pressure. Electron energy distribution function (EEDFs) decrease according to increases filament current, however, it starts to increase from low pressure to maximum value at medium pressure then tends to increase according to further increases of pressure.

Parameters of plasma and mechanisms of etching of metals and semiconductors in HCl + Ar, H2, O2, and Cl2 mixtures

A comparative study of the effect of the initial composition of the HCl + Ar, H2, O2, and Cl2 binary mixtures on the steady-state physical parameters and composition of direct-current glow-discharge plasma was carried out. Information on the reduced electric field intensity, average energy and concentration of electrons, concentrations and densities of fluxes of atoms and ions were obtained. A simulation analysis of the effect of the initial composition of mixtures on the kinetics of the interaction between reactive species of plasma and the surface in the ion-stimulated chemical reaction mode is carried out.

Synchronization between two coupled direct current glow discharge plasma sources

Experimental results on the nonlinear dynamics of two coupled glow discharge plasma sources are presented. A variety of nonlinear phenomena including frequency synchronization and frequency pulling are observed as the coupling strength is varied. Numerical solutions of a model representation of the experiment consisting of two coupled asymmetric Van der Pol type equations are found to be in good agreement with the observed results.

Ammonia formation in N2/H2 plasmas on ITER-relevant plasma facing materials: Surface temperature and N2 plasma content effects

Ammonia production in N2/H2 direct current glow discharge plasmas, with nitrogen concentrations from 1.5% to 33%, different wall materials (tungsten, stainless steel and aluminium as a proxy for beryllium) and surface temperatures up to 350°C has been investigated. Ammonia yields on the exposed materials have been deduced, resulting in different values depending on the wall material, its temperature and N2 plasma content. The results indicate weak wall temperature dependence in tungsten and stainless steel. However, wall temperatures above 300°C have a very clear influence on aluminium walls, as almost all the molecular N2 depleted from the gas phase is converted into ammonia. The amount of implanted N seems to have a direct impact on the ammonia formation yield, pointing to the competition between N implantation and N/H–N/N recombination on the walls as the key mechanism of the ammonia formation.