DC Glow Discharge Plasma Research Articles

Experimental observation of phase-flip transitions in two inductively coupled glow discharge plasmas.

We report an experimental observation of a phase-flip transition in the frequency synchronization of two dc glow discharge plasma sources that are coupled in a noninvasive fashion. When the fundamental oscillation frequency of the potential fluctuations of one of the sources is progressively increased, by raising its discharge voltage, a frequency pulling regime is observed, followed by a synchronized regime that shows a frequency jump phenomenon. The jump is associated with a phase-flip transition that takes the synchronized state from an in-phase to an antiphase state. When the process is reversed, the transition takes place at a different frequency, thereby exhibiting a hysteresis effect. A heuristic model, consisting of two van der Pol oscillators that are coupled to each other through a dynamic common medium, eminently captures the essential features of our experimental observations.

Synthesis and characterisation study on polyaniline-SFA-Ag nanocomposite with plasma surface treatment

In-situ polymerisation of aniline was carried out in the presence of Sintered Fly Ash to synthesise polyaniline-SFA-Ag (IPANI-SFA-Ag) nanocomposite by chemical oxidation method with various compositions (5, 10, 15, 20 and 25 wt %) of fly ash in polyaniline. The synthesised composite film was surface modified by DC glow discharge plasma to improve the surface properties of IPANISFA-Ag nanocomposite. The prepared composite films were characterised by FTIR, XRD, SEM, UV and DC conductivity analysis. From FTIR analysis, some new bonds, like C=O, C-H., were observed in the plasma-treated samples. An XRD analysis report shows that the Ag nanoparticles were in good agreement with IPANI and the intensity of the composite has increased after plasma treatment. The calculated average grain size of the composite was 38 nm; also the specific surface area of both samples was (SSA) 26 m2 g-1.

Effect of Nitriding Time on the Structural Evolution and Properties of Austenitic Stainless Steel Nitrided Using High Power Pulsed DC Glow Discharge Ar/N2 Plasma

A high power pulsed DC glow discharge plasma (HPPGDP) system was employed to perform fast nitriding of AISI 316 austenitic stainless steel in Ar and N2 atmosphere. In-situ optical emission spectroscopy and Infrared pyrometer measurements were used during the plasma nitriding to investigate the effect of dynamic plasma on the nitriding behaviour. SEM and EDX, XRD, Knoop indentation, and tribo-tests were used to characterise microstructures and properties of the nitrided austenitic stainless steel samples. HPPGDP produced high ionization of both Ar and N2 in the plasma that corresponded to dense ion bombardment on the biased steel samples to induce effective plasma surface heating and to form high nitrogen concentration on the biased steel surfaces, and therefore fast nitriding (> 10µm/hour) was achieved. Various phases were identified on the nitrided stainless steel samples formed from a predominantly a single phase of nitrogen supersaturated austenite to a multi-phase structure comprising chromium nitride, iron nitride and ferrite dependent on the nitriding time. All the nitrided AISI 316 austenitic stainless steel samples were evaluated with high hardness (up to 17.3 GPa) and exceptional sliding wear resistance against hardened steel balls and tungsten carbide balls.

Sol-gel synthesis and antibacterial study on BC/ZnO/TiO2 nanocomposite treated by DC glow discharge plasma

Nanocomposite material of bamboo charcoal (BC), zinc oxide (ZnO), and titanium dioxide (TiO2) has prepared via sol–gel method. The synthesized nanocomposite surface was modified by a DC glow discharge plasma treatment. Characterization methods such as BET, SEM, XRD, FTIR, UV, and EDAX are utilized to examine the presence of all the three materials and their combination structure. The combined and plasma-modified surface structure of the bamboo charcoal/zinc oxide/titanium dioxide (BC/ZnO/TiO2) nanocomposite has shown by microscopic images in step by step. The phase structure of the prepared nanocomposite has been identified by X-ray diffraction and the crystalline size of the composite falls between 20 and 30 nm. The antibacterial behavior of the prepared nanocomposite was assessed through disk diffusion plate method and best antibacterial performance was observed. The metal oxides and plasma treatment increased the property of the synthesized nanocomposite and also the results gave extended results compared to BC/ZnO and BC/TiO2 in all formats.

Study on structural, morphological and thermal properties of surface modified polyvinylchloride (PVC) film under air, argon and oxygen discharge plasma

The effect of air, argon, oxygen DC glow discharge plasma on the polyvinylchloride (PVC) film synthesized by solution casting technique, were evaluated via changes in physio-chemical properties such as structural, morphological, crystalline, thermal properties. The PVC film was plasma treated as a function of exposure time and different plasma forming gases, while other operating parameters such as power and pressure remained constant at 100 W and 2 Pa respectively. The plasma treated PVC were characterized by static contact angle, ATR-FTIR, XPS, AFM and T-peel analysis. It was found that various gaseous plasma treatments have improved the polar components, surface roughness on the surface of PVC which was confirmed by XPS, AFM, resulting in highly enhanced wettability and adhesion. X-ray diffraction study showed that plasma treatment does not persuade considerable change, even though it vaguely induces the crystallinity. The thermal properties of plasma treated PVC were evaluated by Differential Scanning Calorimetry and it was observed that O2 plasma treatment gives higher glass transition temperature of 87.21 °C compared with the untreated one. The glass transition temperature slightly increased for Oxygen plasma treated material due to the presence of higher concentration of the polar functional groups on the PVC surface due to strong intramolecular bonding.

A Study of Ion Drag for Ground and Microgravity Dusty Plasma Experiments

This paper presents the results of a recent study of the interaction between charged dust particles and plasma ions through the electrostatic and ion drag forces in a dc glow discharge plasma. Measurements of the dust particles motion are carried out using particle image velocimetry (PIV). When an electrostatic perturbation is applied to the dust cloud, the particle motion, in response to the perturbation, is shown to reverse direction as the gas pressure is increased. An analysis of the dust particle motion and background plasma parameters suggests that there is a change in the equilibrium position and competition between the electrostatic force and the ion drag force on the particles that lead to the asymmetric motion of the cloud. The ion drag and electric forces on the dust particles are calculated at each pressure using detailed measurements of the plasma parameters, as measured by a single Langmuir probe. The analysis of these measurements suggests that the reversal of direction is a result of the change in the electric field in the plasma, but that the effectiveness of the perturbation at displacing the dust cloud is controlled by the ion drag force.

Synthesis and conductivity study on polyaniline/BaFe/silver (PANI+BaFe+Ag) nanocomposite with plasma treatment

Polyaniline/fly ash/silver (IPANI+BaFe+Ag) composite films were prepared in different concentrations of BaFe and surface modified by DC glow discharge plasma. The prepared composite films were characterised by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV and DC conductivity analysis. From FTIR analysis, some new bonds like C = O and C–H were observed in the plasma treated samples. An XRD analysis report shows that the Ag nanoparticles were in good agreement with IPANI, and the intensity of the composite has increased after plasma treatment. The calculated average grain size of untreated Ag is 38 nm and plasma treated is 35 nm, and also, the specific surface area of both samples is 24 m2 g− 1. SEM analysis showed the Ag particles were well distributed on IPANI and also had a small amount of surface roughness after plasma treatment. The UV–Vis absorption spectroscopy indicates the characteristics of absorption spectra of IPANI. The DC conductivity of pure PANI/BaFe+Ag nanocomposites clearly indicated that the Ag nanoparticles increased the electrical conductivity of PANI nanocomposites as compared to pure aniline.

Voids in Dusty Plasma of a Stratified DC Glow Discharge in Noble Gases

AbstractExperimental investigations of dusty plasma parameters of a DC glow discharge were performed in helium and argon. In the discharge in helium, at high discharge current dust‐free regions (voids) were formed in the center of the dust particles clouds that levitated in the strong electric field of a stratified positive column. In experiments with argon, the dust particles were moved from the center of the discharge tube to the periphery at high discharge current. The behavior of voids formation was investigated for different discharge conditions (sort of gas, discharge pressure and discharge current) and dust particles parameters (particles radii and particles total number). It was shown that it is the ion drag force radial component that leads to the formation of voids in helium and moves the particles to the tube periphery in argon discharge. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of glow discharge plasma on step index polymer optical fiber parameters

DC glow discharge plasma of power 40 W was applied to step index polymer optical fibers for different exposure times. Nitrogen, oxygen, and hydrogen gases were used to obtain the glow discharge. The fiber core material was poly methyl methacrylate and the cladding was fluorinated polymer. The effect of plasma on the optical parameters, such as core index profile, cladding index, and the numerical aperture, was studied by multiple beam interference fringes and Fourier transformation of infrared spectroscopy spectra. It was found that the plasma treatment affected the optical parameters of both the cladding and the core regions of optical fibers. The optical parameters also changed with the treatment time. The hydrogen plasma had effects greater than those of nitrogen and oxygen plasma. These observed results can be explained by the effect of the electric field during plasma treatment. The studied optical fibers after plasma treatment can be used as inverted-graded index with its important applications.

Superhydrophilic TiO2 thin film by nanometer scale surface roughness and dangling bonds

A remarkable enhancement in the hydrophilic nature of titanium dioxide (TiO2) films is obtained by surface modification in DC-glow discharge plasma. Thin transparent TiO2 films were coated on glass substrate by sol–gel dip coating method, and exposed in DC-glow discharge plasma. The plasma exposed TiO2 film exhibited a significant change in its wetting property contact angle, which is a representative of wetting property, has reduced to considerable limits 3.02° and 1.85° from its initial value 54.40° and 48.82° for deionized water and ethylene glycol, respectively. It is elucidated that the hydrophilic property of plasma exposed TiO2 films dependent mainly upon nanometer scale surface roughness. Variation, from 4.6nm to 19.8nm, in the film surface roughness with exposure time was observed by atomic force microscopy (AFM). Analysis of variation in the values of contact angle and surface roughness with increasing plasma exposure time reveal that the surface roughness is the main factor which makes the modified TiO2 film superhydrophilic. However, a contribution of change in the surface states, to the hydrophilic property, is also observed for small values of the plasma exposure time. Based upon nanometer scale surface roughness and dangling bonds, a variation in the surface energy of TiO2 film from 49.38 to 88.92mJ/m2 is also observed. X-ray photoelectron spectroscopy (XPS) results show change in the surface states of titanium and oxygen. The observed antifogging properties are the direct results of the development of the superhydrophilic wetting characteristics to TiO2 films.

Multi-scale dynamics in externally excited glow discharge plasma

Time series analysis of fluctuations excited due to external perturbation in a dc glow discharge plasma system is presented. Analysis shows that the observed data is non-Gaussian in nature and has purely deterministic behavior. The oscillations are bi-periodic in nature without any occurrence of chaos with increasing discharge voltage. Two dominant frequencies 100 KHz and 200 KHz with background noise are observed. The Hurst coefficient is also evaluated for the data sets and is seen to be greater than 0.5 for all the cases. The observed bi-periodic oscillations have their origin due to some nonlinearities in the system. The observed frequencies are found to be due to ionization instability and ion acoustic instability.

Dusty Plasma Experimental (DPEx) device for complex plasma experiments with flow.

A versatile table-top dusty plasma experimental device to study flow induced excitations of linear and nonlinear waves/structures in a complex plasma is presented. In this Π-shaped apparatus, a DC glow discharge plasma is produced between a disc shaped anode and a grounded long cathode tray by applying a high voltage DC in the background of a neutral gas (argon) and subsequently a dusty plasma is created by introducing micron sized dust particles that get charged and levitated in the sheath region. A flow of the dust particles is induced in a controlled manner by adjusting the pumping speed and the gas flow rate into the device. A full characterisation of the plasma, using Langmuir and emissive probe data, and that of the dusty plasma using particle tracking data with the help of an idl based (super) Particle Identification and Tracking (sPIT) code is reported. Experimental results on the variation of the dust flow velocity as a function of the neutral pressure and the gas flow rate are given. The neutral drag force acting on the particles and the Epstein coefficient are estimated from the initial acceleration of the particles. The potential experimental capabilities of the device for conducting fundamental studies of flow induced instabilities are discussed.

Generation of multiple toroidal dust vortices by a non-monotonic density gradient in a direct current glow discharge plasma

Observation of two well-separated dust vortices in an unmagnetized parallel plate DC glow discharge plasma is reported in this paper. A non-monotonic radial density profile, achieved by an especially designed cathode structure using a concentric metallic disk and ring of different radii, is observed to produce double dust tori between cathode and anode. PIV analysis of the still images of the double tori shows oppositely rotating dust structures between the central disk and the ring. Langmuir probe measurements of background plasma shows a non-uniform plasma density profile between the disk and the ring. Location and sense of rotation of the dust vortices coincides with the location and direction of the radial gradient in the ion drag force caused by the radial density gradient. The experimentally observed dust vorticity matches well with the calculated one using hydrodynamic formulations with shear in ion drag dominating over the dust charge gradient. These results corroborate that a radial gradient in the ion drag force directed towards cathode is the principal cause of dust rotation.

Preparation and characterisation of bamboo charcoal/titanium dioxide (BC/TiO2) nanocomposite with plasma surface treatment

In this present work, the bamboo charcoal/titanium dioxide (BC/TiO2) nanocomposite was synthesised by sol–gel method; consequently, the surface was modified by DC glow discharge plasma. The observed new functional groups were studied by Fourier transform infrared spectroscopy. The phase structure, crystalline size, specific surface area and morphology index were obtained by X-ray powder diffraction analysis. Surface morphology and elemental composition were determined by scanning electron microscopy and energy dispersive spectrum. The antibacterial property was evaluated by disc diffusion method, and the result indicated antibacterial activity of the prepared sample.

Polarity functions’ characterization and the mechanism of starch modification by DC glow discharge plasma

The wheat starch was investigated, before and after exposure to the argon and oxygen glow discharge plasma, without any added chemical reagents, using a novel media polarity functions method. The mechanisms of modification of starch in plasma discharge irradiation were explained using some methods such as; NMR, IR spectroscopy, Kamlet–Abboud–Taft polarity functions (specific and nonspecific interaction) of modified starch. The starch modification, by plasma treatment, shows valuable changes with plasma gas and relative ionized or active species. Characterizations indicate that argon glow discharge plasma increases crosslink in C-2 site of starch. Also, oxygen plasma discharge irradiation tends to oxidize the OH group in C-6 site of carbonyl group. Furthermore, the reported mechanisms show the highest efficiency, because of the stereo-chemical orientation of active sites of starch and plasma potential of wall in plasma media.

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.

Influence of the initial composition of a methane-argon mixture on the electricophysical parameters and plasma composition of DC glow discharge

The stationary parameters and composition of DC glow discharge plasma (p = 40–200 Pa, i = 30–70 mA) in CH4-Ar mixtures of different compositions have been studied by probe diagnostics and mathematical simulation. Data on the influence of the initial composition of the plasma-forming mixture on the reduced electric field strength, energy electron distribution, rate constants of processes under electron impact, stationary concentrations, and flux densities of neutral and charged particles have been obtained.

Observation of dust torus with poloidal rotation in direct current glow discharge plasma

Observation of dust cloud rotation in parallel-plate DC glow discharge plasma is reported here. The experiments are carried out at high pressures (∼130 Pa) with a metallic ring placed on the lower electrode (cathode). The dust cloud rotates poloidally in the vertical plane near the cathode surface. This structure is continuous toroidally. Absence of magnetic field rules out the possibility of E × B induced ion flow as the cause of dust rotation. The dust rotational structures exist even with water cooled cathode. Therefore, temperature gradient driven mechanisms, such as thermophoretic force, thermal creep flow, and free convection cannot be causing the observed dust rotation. Langmuir probe measurement reveals the existence of a sharp density gradient near the location of the rotating dust cloud. The gradient in the density, giving rise to a gradient in the ion drag force, has been identified as the principal cause behind the rotation of dust particles.

Investigation and quantification of nonlinearity using surrogate data in a glow discharge plasma

Detection of nonlinearity has been carried out in periodic and aperiodic floating potential fluctuations of DC glow discharge plasma by generating surrogate data using iterative amplitude adjusted Fourier transform method. We introduce “delay vector variance” analysis (DVV) for the first time, which allows reliable detection of nonlinearity and provides some easy to interpret diagram conveying information about the nature of the experimental floating potential fluctuations (FPF). The method of false nearest neighbourhood is deployed on the FPF's to find a good embedding so as to be acquainted with the precise knowledge of m, which is desirable for carrying out DVV analysis. The emergence of nonlinearity with increase in discharge voltage has been ensured by taking into consideration the total energy present in different band of frequencies excited due to nonlinear processes. Rejection of null hypothesis has been verified by performing the rank test method that confirms the presence of nonlinearity quantitatively.

Hysteresis in amplitudes of self-excited oscillations for co-axial electrode-geometry DC glow discharge plasma

Hysteresis in amplitudes of the self-excited oscillations of the floating potential and discharge current is observed in an unmagnetized co-axial electrode-geometry DC glow discharge plasma system. The nonlinearities of these oscillations are studied using standard dynamical analysis tools. The characterization revealed the transition of low-amplitude high-frequency period-n oscillations to a large amplitude low frequency period-1 oscillations through a chaotic intermediate route. The transition of the low amplitude, high frequency period-n oscillations to chaotic type is observed to be linked to the dynamical change in the plasma system, i.e., after a negative differential resistance (NDR) region, whereas the transition from chaotic to period-1 is observed to be linked to a discharge current threshold.