DC Glow Discharge Plasma Research Articles

Dust-acoustic soliton breaking and the associated acceleration of charged particles.

The breaking of a plane self-excited dust-acoustic soliton in a dust cloud formed in stratified dc glow discharge plasma is studied. Both macroscopic and kinetic parameters of the dust component near the soliton are experimentally obtained. It is shown that the breaking of a soliton can accelerate charged particles to supersonic speeds. The theoretical interpretation of the experimental results is performed in the framework of the hydrodynamic plasma approach, as well as the single-particle approximation. Both dissipative and nondissipative cases are considered.

Analysis of antibacterial activity and cytotoxicity of silver oxide doped hydroxyapatite exposed to DC glow discharge plasma

The present work investigated the possibility of enhancing hydroxyapatite (HAp) bioactivity by substituting silver oxide. Ag2O-HAp nanoparticles were synthesized by using the wet precipitation process with exposure to DC glow discharge non thermal plasma. The phase purity, elemental composition and morphology were analyzed by XRD, FTIR, SEM and EDX. MTT assay for Silver oxide doped hydroxyapatite (Ag2O HAP) nanopowders (NPs) have been carried out for MCF-7 breast cancer cell line and the cyototoxicity effect were analysed. The biocompatibility of the synthesized silver oxide doped HAp proves it as promising candidate for upcoming biomedical applications.

Corrosion Behavior Evaluation in Simulated Body Fluid of a Modified Ti–6Al–4V Alloy by DC Glow Plasma Nitriding

DC glow discharge plasma nitriding is the process of surface hardening through the spread of nitrogen atoms to the metal surface under special conditions of the plasma nitriding. Titanium and titanium alloys are the most common alloys used in medical applications. Titanium and its alloys are lightweight, corrosion resistant, and have good fatigue properties but lack wear resistance under aggressive environments. The plasma nitriding process was used for a titanium alloy (Ti–6Al–4V) rod with different parameters at a vacuum chamber of air (2 mbar), 680 volts and 30 mA. The plasma nitriding process was performed at different nitriding times (5, 10, and 15 h), and the effect of plasma nitriding was examined on the chemical compassion of Ti–6Al–4V alloy and the appearance of phases was studied by optical microscopy (OM), scanning electron microscopy and field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Tafel potential polarization, and cyclic polarization. The results indicate that the formation of layers and phases Ti2N and Ti2N3−x on a surface of the alloy were achieved, which would improve the surface characteristics of chemical corrosion in simulated body fluid.

Melting transition of two-dimensional complex plasma crystal in the DC glow discharge

The formation of self-consistent dust crystal and its melting is a well- known phenomenon in rf generated plasmas but remains challenging in DC glow discharge plasmas. Here, we report the melting of a two- dimensional dusty plasma crystal, suspended in the cathode sheath of a DC glow discharge plasma. The experiments are carried out in a Dusty Plasma Experimental (DPEx) device which consists of a circular powered electrode and an extended grounded cathode tray. A stationary crystal of melamine formaldehyde particles is formed in a background of Argon plasma between a pair of confining strips that are placed on the cathode. The stable structure breaks and transition to a fluid state when the neutral pressure is reduced. The neutral pressure range where this melting transition is observed is an order of magnitude less than what is typically reported in rf discharge plasma. The transition is confirmed by evaluating the variation in different characteristic parameters such as the pair correlation function, Voronoi diagram, local bond order parameter, defect fraction and dust kinetic temperature as a function of background neutral pressure. For instance, the average bond order parameter (Ψ6) reduces from 0.87 to 0.4 when the neutral pressure is reduced from 15 to 11 Pa. The asymmetry of the electrode is a special feature that is believed to enable the formation of the plasma crystal.

PLASMA PRETREATMENT ON TASAR SILK FABRICS COATED WITH ZnO NANOPARTICLES AGAINST ANTIBACTERIAL ACTIVITY

Plasma pretreatment is an eco-friendly process employed to modify the surface properties and improve the adhesion properties of tasar silk fabrics. The plasma pretreatment has been carried out in DC glow discharge plasma at constant power and for different treatment durations (5, 10 and 30[Formula: see text]min). ZnO nanoparticles (ZnO NPs) play a significant role in antibacterial, cleaning and UV protection. ZnO NPs have been synthesized by the wet chemical method and the average crystallite size of the same is found to be 49[Formula: see text]nm using X-ray diffraction (XRD). Plasma treated silk fabrics are coated with ZnO NPs using vacuum thermal evaporation technique. Structural and chemical change of raw, untreated and plasma treated silk fabrics coated with ZnO NPs are analyzed by XRD and attenuated total reflection Fourier transform infrared (ATR-FTIR) studies. The surface morphologies of all the fabrics are analyzed by using scanning electron microscope (SEM), which confirms the adherence of ZnO NPs on the surface of the fabrics. Elemental analysis is carried out using energy dispersive spectroscopy, which confirms the presence of ZnO NPs on the surface of the fabrics. The improved surface property in terms of hydrophobicity is analyzed by using a contact angle test. It is found that the plasma pretreated silk fabrics coated with ZnO NPs have better antibacterial activities against Escherichia Coli bacteria.

Micro-dynamics of neutral flow induced dusty plasma flow

We present a detailed experimental study of gas flow induced motion of dust particles in a DC glow discharge plasma. The characteristics of the dust dynamics are investigated as a function of the differential gas flow rate, the background neutral pressure, the dust particle size, and the neutral species of the gas. The experiments have been carried out in the table top Dusty Plasma Experimental (DPEx) device in which a plasma is created between a disk shaped anode and a grounded cathode in a Π-shaped Pyrex glass tube. The asymptotic steady state flow velocity of the injected micron sized dust particles is found to increase with an increase in neutral flow velocity and decrease with an increase in the background pressure. Furthermore, this velocity is seen to be independent of the size of the dust particles, but decreases with an increase in the mass of the background gas. A simple theoretical model, based on estimates of the various forces acting on the dust particles, is used to elucidate the role of neutrals in the flow dynamics of the dust particles. Our experiments thus provide a detailed microscopic understanding of some of the past phenomenological observations of dust flows in the DPEx device and can prove useful in future experimental implementations of dust flow experiments.

A Comparative Study of Surface Modification of PS Films Using DC Glow Discharge Plasma in N2 and Ar

In this paper, the polystyrene (PS) film surface was treated using DC glow discharge nitrogen (N2) and argon (Ar) plasma to improve the wettability and antibacterial properties. The untreated and plasma treated surfaces were characterized by contact angle, FTIR, XRD and SEM analysis. The antibacterial activity of untreated and plasma treated PS films was evaluated using optical density (OD) technique against Staphylococcus aureus bacteria. The results of the PS film surface treated in both N2 and Ar showed a noticeable increase in the wettability due to the increase in the roughness and the introduction of oxygen-containing polar groups as corroborated with SEM, weight loss calculations and FTIR spectra. The results of antibacterial activity showed that the treated samples inhibit the bacterial growth. The Ar treatment created more oxygen-containing polar groups and increase roughness on the PS film surface and extensively modified the polymer surface than the N2 treatment.

Experimental observation of a dusty plasma crystal in the cathode sheath of a DC glow discharge plasma

Dusty plasma crystals have traditionally been observed and studied in radio frequency discharge plasmas, and their formation in a DC glow discharge plasma remains experimentally challenging. We report the first ever observation of a stable dusty plasma Coulomb crystal in the cathode sheath region of a DC glow discharge plasma. The observations are made in the dusty plasma experimental (DPEx) device where crystals of mono-disperse melamine formaldehyde grains are produced in the background of an Argon plasma. The crystalline nature of the structure is confirmed through a host of characteristic parameter estimations which includes the radial pair correlation function, Voronoi diagram, Delaunay Triangulation, the structural order parameter, the dust temperature, and the Coulomb coupling parameter. The special features of the DPEx device which permit such a crystal formation are delineated, and some principal physical features of the crystal are discussed.

Determining the spectrum of penning electrons by current to a wall probe in nonlocal negative glow plasma

It was shown that the spectrum of Penning electrons in a nonlocal equipotential plasma is associated with the second derivative of their current to a wall electrode (sensor). Analytical calculations are confirmed by experimental studies in a negative glow plasma of short DC glow discharge at moderate and high pressures (up to 150 Torr).

Modification of Asymmetric Polysulfone Membrane Surfaces using Mixed Ar/O2 Plasma Technique

Asymmetric polysulfone (PSF) membranes for gas separation were prepared via dry-wet phase inversion technique at different conditions such as coagulation bath temperature (CBT) and evaporation time (ET). The thickness of the dense layer that plays an important role on gas selectivity has been investigated by adjusting CBT and ET. Additionally, membranes were treated with mixed Ar/O2 DC glow discharge plasma in order to modify membrane wettability, surface roughness, and functional groups on the membrane surface. Scanning electron microscopy (SEM) was used to illustrate a cross sectional structure of PSF membranes. Hydrophilic properties of the membrane surfaces were analyzed via water contact angle (WCA) and surface energy measurements. Morphological structures of membrane surfaces, roughness and creation of functional groups were analyzed both before and after plasma treatment by atomic force microscopy and Fourier transform infrared spectroscopy, respectively. Experimental results show that CBT and ET can change porous voids size of the supporting layer and the dense layer thickness underneath of the membrane surface, while a mixed Ar/O2 gas plasma treatment can enhance hydrophilic properties of the asymmetric PSF membrane surfaces.

Collective dynamics of large aspect ratio dusty plasma in an inhomogeneous plasma background: Formation of the co-rotating vortex series

In this paper, the collective dynamics of large aspect ratio dusty plasma is studied over a wide range of discharge parameters. An inductively coupled diffused plasma, which creates an electrostatic trap to confine the negatively charged grains, is used to form a large volume (or large aspect ratio) dusty plasma at low pressure. For introducing the dust grains into the potential well, a unique technique using secondary DC glow discharge plasma is employed. The dust dynamics is recorded in a two-dimension (2D) plane at a given axial location. The dust fluid exhibits wave-like behavior at low pressure (p < 0.06 mbar) and high rf power (P > 3 W). The mixed motion, waves and vortices, is observed at an intermediate gas pressure (p ∼ 0.08 mbar) and low power (P < 3 W). Above the threshold value of gas pressure (p > 0.1 mbar), the clockwise and anti-clockwise co-rotating vortex series are observed on edges of the dust cloud, whereas the particles in the central region show random motion. These vortices are only observed above the threshold width of the dust cloud. The occurrence of the co-rotating vortices is understood on the basis of the charge gradient of dust particles, which is orthogonal to the gravity. The charge gradient is a consequence of the plasma inhomogeneity from the central region to the outer edge of the dust fluid. Since a vortex has the characteristic size in the dissipative medium; therefore, a series of the co-rotating vortex on both sides of dusty plasma is observed. The experimental results on the vortex formation and its multiplicity are compared to an available theoretical model and are found to be in close agreement.

Influence of dust particles on DC glow discharge plasma

The effect of dust particles on DC glow discharge plasma parameters is studied numerically through the development of a self-consistent model based on the extended fluid approach. The orbital motion limited theory and collision enhanced collection approximation are employed to describe the charging processes of dust particles with various sizes and densities. The uniform distribution of dust particles in plasma and the instantaneous charging process were assumed during simulations. The influence of dust particle size rd and density Nd on gas discharge and dust particle parameters is investigated systematically. It is shown that the plasma parameters can be affected obviously by the dust particles. The increase in the values of rd and Nd leads to the decrease in the dust particle charge number, electron, and ion density. Meanwhile, the appearance of dust particles leads to an obvious increase in the averaged plasma electric field and electron temperature to sustain the discharge in the dust region. The dust particles are proven to be a very efficient way to artificially manipulate gas discharge parameters.

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.

Investigation and quantification of Phase coherence index for different types of forcing in DC glow discharge plasma

The evidence of finite nonlinear interaction in a DC glow discharge plasma has been demonstrated by estimating phase coherence index for different types external forcing techniques likewise noise, sinusoidal, square etc. The existence of finite phase coherence index i.e finite correlation prompts us to carry out nonlinearity analysis using delay vector variance (DVV). Finite nonlinear interaction obtained from phase coherence index values is observed to be predominant at a particular amplitude of square forcing which corroborates our nonlinearity analysis using DVV. Existence of phase coherence index has been demonstrated introducing continuous wavelet transform (CWT). Characterization of the difference in the phase distribution by the difference in the waveform in real space instead of dealing in Fourier space has been facilitated by introducing structure function or path length for different orders to study and identify the dynamical system. The expression of path length eventually enables us to evaluate the phase coherence index. The transition in the dynamics is observed through recurrence plot techniques which is an efficient method to observe the critical regime transitions in dynamics.

Quantification of scaling exponent with Crossover type phenomena for different types of forcing in DC glow discharge plasma

We have carried out a detailed study of scaling region using detrended fractal analysis test by applying different forcing likewise noise, sinusoidal, square on the floating potential fluctuations acquired under different pressures in a DC glow discharge plasma. The transition in the dynamics is observed through recurrence plot techniques which is an efficient method to observe the critical regime transitions in dynamics. The complexity of the nonlinear fluctuation has been revealed with the help of recurrence quantification analysis which is a suitable tool for investigating recurrence, an ubiquitous feature providing a deep insight into the dynamics of real dynamical system. An informal test for stationarity which checks for the compatibility of nonlinear approximations to the dynamics made in different segments in a time series has been proposed. In case of sinusoidal, noise, square forcing applied on fluctuation acquired at P=0.12 mbar only one dominant scaling region is observed whereas the forcing applied on fluctuation (P=0.04 mbar) two prominent scaling regions have been explored reliably using different forcing amplitudes indicating the signature of crossover phenomena. Furthermore a persistence long range behavior has been observed in one of these scaling regions. A comprehensive study of the quantification of scaling exponents has been carried out with the increase in amplitude and frequency of sinusoidal, square type of forcings. The scalings exponent is envisaged to be the roughness of the time series. The method provides a single quantitative idea of the scaling exponent to quantify the correlation properties of a signal.

Structural and Characteristics Change of Water Hyacinth Fiber due to Combine Effect of Plasma and Nano-technology

Water hyacinth [Eichhornia crassipes] fiber has been treated using DC glow discharge plasma to make its surface more hydrophobic in nature for various applications. The plasma treated fibers have been coated with synthesized phase pure ZnO nano-particle at room temperature to enhance both hydrophobicity and Ultra Violet [UV] light protection rate. The behavioral changes of fibers and its characteristics have been studied using XRD, SEM, EDS, a ATR-FTIR and TGA. Surface chemistry of the treated fiber has been altered as depicted by ATR-FTIR studies, while the improve degree of crystallinity analysed by XRD shows the effects of molecular structure of the fibers. The hydrophobic nature of the fibers has been recognized by contact angle measurement using Goniometer and by water absorption processes. Moreover, moisture content of treated fiber has been measured quantitatively using TGA. Finally wavelet analysis has been applied to understand the surface characteristics of water hyacinth fiber and compare its surface roughness value was measured by SEM. Furthermore, entropy of the treated and untreated fibers has also been calculated.

Experimental observation of self excited co-rotating multiple vortices in a dusty plasma with inhomogeneous plasma background

We report an experimental observation of multiple co-rotating vortices in an extended dust column in the background of an inhomogeneous diffused plasma. An inductively coupled rf discharge is initiated in the background of argon gas in the source region. This plasma was later found to diffuse into the main experimental chamber. A secondary DC glow discharge plasma is produced to introduce dust particles into the plasma volume. These micron-sized poly-disperse dust particles get charged in the background of the DC plasma and are transported by the ambipolar electric field of the diffused plasma. These transported particles are found to be confined in an electrostatic potential well, where the resultant electric field due to the diffused plasma (ambipolar E–field) and glass wall charging (sheath E–field) holds the micron–sized particles against the gravity. Multiple co-rotating (anti–clockwise) dust vortices are observed in the dust cloud for a particular discharge condition. The transition from multiple vortices to a single dust vortex is observed when input rf power is lowered. The occurrence of these vortices is explained on the basis of the charge gradient of dust particles, which is orthogonal to the ion drag force. The charge gradient is a consequence of the plasma inhomogeneity along the dust cloud length. The detailed nature and the reason for multiple vortices are still under investigation through further experiments; however, preliminary qualitative understanding is discussed based on the characteristic scale length of the dust vortex. There is a characteristic size of the vortex in the dusty plasma; therefore, multiple vortices could possibly be formed in an extended dusty plasma with inhomogeneous plasma background. The experimental results on the vortex motion of particles are compared with a theoretical model and are found to be in close agreement.

Mixed mode oscillations in presence of inverted fireball in an excitable DC glow discharge magnetized plasma

The typical phenomena of mixed mode oscillations and their associated nonlinear behaviors have been investigated in collisionless magnetized plasma oscillations in a DC glow discharge plasma system. Plasma is produced between a cylindrical mesh grid and a constricted anode. A spherical mesh grid of 80% optical transparency is kept inside a cylindrical grid to produce an inverted fireball. Three Langmuir probes are kept in the ambient plasma to measure the floating potential fluctuations at different positions of the chamber. It has been observed that under certain conditions of discharge voltages and magnetic fields, the mixed mode oscillation phenomena (MMOs) appears, and it shows a sequential alteration with the variation of the magnetic fields and probe positions. Low frequency instability has been observed consistently in various experimental conditions. The mechanisms of the low frequency instabilities along with the origin of the MMOs have been qualitatively explained. Extensive linear and nonlinear analysis using techniques such as fast Fourier transform, recurrence quantification analysis, and the well-known statistical computing, skewness, and kurtosis are carried out to explore the complex dynamics of the MMO appearing in the plasma oscillations under various discharge conditions and external magnetic fields.

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.

DC Glow Discharge in Axial Magnetic Field at Low Pressures

On the basis of fluid approximation, an improved version of the model for the description of dc glow discharge plasma in the axial magnetic field was successfully developed. The model has yielded a set of analytic formulas for the physical quantities concerned from the electron and ion fluids equations and Poisson equation. The calculated results satisfy the practical boundary conditions. Results obtained from the model reveal that although the differential equations under the condition of axial magnetic field are consistent with the differential equations without considering the magnetic field, the solution of the equations is not completely consistent. The results show that the stronger the magnetic field, the greater the plasma density.