Ar Plasma Discharge Research Articles

Interaction of a precursor soliton with wake structure in a flowing dusty plasma

We report experimental observations on the interaction of a precursor soliton with a wake structure in a flowing dusty plasma system. The experiments are carried out in an inverted ∏-shaped experimental device in which a dusty plasma is created in a direct current glow discharge Ar plasma using micrometer sized Kaolin particles. Two copper wires installed radially on the cathode serve as charged objects in the plasma environment. Precursor solitons and wake structures are excited by each of the charged objects when the dust fluid flows supersonically over both the objects. In the frame of the fluid, the solitons propagate in the upstream direction, whereas the smaller amplitude wake structures propagate in the downstream direction. A soliton, excited by one of the objects, interacts with the wake structure generated by the other object in the region between the two charged objects. After the interaction, the amplitude and velocity of the soliton increase whereas its width decreases. The results are explained theoretically using numerical solutions of a model forced Korteweg-de Vries equation driven by two source terms.

Effects of amplitude modulated capacitively coupled discharge Ar plasma on kinetic energy and angular distribution function of ions impinging on electrodes: particle-in-cell/Monte Carlo collision model simulation

We investigated the effects of amplitude modulated (AM) capacitively coupled Ar discharge plasma on the ion energy distribution function (IEDF) and the ion angular distribution function (IADF) incident on electrodes using the particle-in-cell/Monte Carlo collision model. For AM discharge, the electron density and electron temperature and the kinetic energy and angle of ions incident on the ground electrode change periodically with AM frequency, whereas ones for continuous wave discharge are almost constant. For AM discharge, the plasma had hysteresis characteristics. The peak energy of IEDF varies from 53 to 135 eV and the FWHM of IADF varies from 1.82 to 3.34 degrees for gas pressure 10mTorr, the peak-to-peak input voltage 400 V and AM level of 50%. The variation width of the peak energy of IEDF and FWHM of IADF increases with the AM level. These effects of AM method discharge are more noticeable at lower pressures. Thus, the AM discharge offers a way to control simultaneously IEDF and IADF, which opens a new avenue for plasma processes such as an ALD-like PECVD.

Experimental observation of pinned solitons in a flowing dusty plasma

Pinned solitons are a special class of nonlinear solutions created by a supersonically moving object in a fluid. They move with the same velocity as the moving object and thereby remain pinned to the object. A well-known hydrodynamical phenomenon, they have been shown to exist in numerical simulation studies but to date have not been observed experimentally in a plasma. In this paper we report the first experimental excitation of pinned solitons in a dusty (complex) plasma flowing over a charged obstacle. The experiments are performed in a Π shaped dusty plasma experimental (DPEx) device in which a dusty plasma is created in the background of a DC glow discharge Ar plasma using micron sized kaolin dust particles. A biased copper wire creates a potential structure that acts as a stationary charged object over which the dust fluid is made to flow at a highly supersonic speed. Under appropriate conditions nonlinear stationary structures are observed in the laboratory frame that correspond to pinned structures moving with the speed of the obstacle in the frame of the moving fluid. A systematic study is made of the propagation characteristics of these solitons by carefully tuning the flow velocity of the dust fluid by changing the height of the potential structure. It is found that the nature of the pinned solitons changes from a single-humped one to a multihumped one and their amplitudes increase with an increase of the flow velocity of the dust fluid. The experimental findings are then qualitatively compared with the numerical solutions of a model forced Korteweg de Vries (fKdV) equation.

PLLA Honeycomb-Like Pattern on Fluorinated Ethylene Propylene as a Substrate for Fibroblast Growth.

In this study, we present the surface patterning of a biopolymer poly(l-lactide) (PLLA) for fibroblast growth enhancement. The patterning is based on a self-organized pore arrangement directly fabricated from a ternary system of a solvent-nonsolvent biopolymer. We successfully created a porous honeycomb-like pattern (HCP) on a thermally resistant polymer—fluorinated ethylene propylene (FEP). An important preparation step for HCP is activation of the substrate in Ar plasma discharge. The polymer activation leads to changes in the surface chemistry, which corresponds to an increase in the substrate surface wettability. The aim of this study was to evaluate the influence of the PLLA concentration in solution on the surface morphology, roughness, wettability, and chemistry, and subsequently, also on fibroblast proliferation. We confirmed that the amount of PLLA in solution significantly affects the material surface properties. The pore size of the prepared layers, the surface wettability, and the surface oxygen content increased with an increasing amount of biopolymer in the coating solution. The optimal amount was 1 g of PLLA, which resulted in the highest number of cells after 6 days from seeding; however, all three biopolymer concentrations exhibited significantly better results compared to pristine FEP. The cytocompatibility tests showed that the HCP promoted the attachment of cell filopodia to the underlying substrate and, thus, significantly improved the cell–material interactions. We prepared a honeycomb biodegradable support for enhanced cell growth, so the surface properties of perfluoroethylenepropylene were significantly enhanced.

Effect of size and shape of a moving charged object on the propagation characteristics of precursor solitons

We report on experimental observations of the modifications in the propagation characteristics of precursor solitons due to the different shapes and sizes of the object over which the dust fluid flows. The experiments have been performed in a Π shaped Dusty Plasma Experimental device where dusty plasma is created in a DC glow discharge Ar plasma using kaolin particles. A floating copper wire installed radially on the cathode acts as a charged object in the plasma environment. The flow on the dust fluid is initiated by suddenly lowering the potential of the charged object from grounded potential to close to floating potential. The size (height and width) of the potential hill is then varied by drawing current from the wire through a variable resistance. With a decrease in the height of the potential hill, the amplitude, velocity, and number of excited precursor solitons are found to decrease, whereas the widths of the solitons are seen to increase. It is found that below a threshold value, these solitary waves are not excited, and the dust fluid simply flows over the hill. To examine the effect due to the shape of the potential profiles, the wire is replaced by a triangular object. Only trailing wakes are seen to be excited when the dust fluid faces the linearly increasing slope of the potential profile, whereas both solitons and wakes get excited when the object is placed with the sharp edge facing the flow. All the experimental findings qualitatively agree with numerical solutions obtained with different source terms in the forced-Korteweg–de Vries model equation.

Diagnostics of low-pressure capacitively coupled RF discharge argon plasma

Low-pressure capacitively coupled RF discharge Ar plasma has been studied using Langmuir probe. The electron temperature, electron density and Debay length were calculated under different pressures and electrode gap. In this work the RF Langmuir probe is designed using 4MHz filter as compensation circuit and I-V probe characteristic have been investigated. The pressure varied from 0.07 mbar to 0.1 mbar while electrode gap varied from 2-5 cm. The plasma was generated using power supply at 4MHz frequency with power 300 W. The flowmeter is used to control Argon gas flow in the range of 600 standard cubic centimeters per minute (sccm). The electron temperature drops slowly with pressure and it's gradually decreased when expanding the electrode gap. As the gas pressure increases, the plasma density rises slightly at low gas pressure while it drops little at higher gas pressure. The electron density decreases rapidly with expand distances between electrodes.

Influence of admixing oxygen on Ar plasma discharge for organic pollutant degradation in wastewater treatment

In previous study, non-thermal plasma system with addition of O2 gas was proven to accelerate the decolorization process of dye solution, resulting in faster treatment of the synthetic wastewater. The present study deals with the influence of variation of O2 gas admixing to the Ar plasma discharge to examine the decolorization of methylene blue solution underwater through measurement of absorbance value of the plasma-treated solution by UV/VIS measurement. From the experiments it was found that the best result of methylene blue solution decomposition was obtained from the application of Ar 0.3 lpm with the admixing of O2 gas 0.3 lpm in an underwater plasma system generated at 1.56 kV. Modelling the decomposition process of methylene blue by using Ar+O2 plasma with variation of O2 flow rate, it was found that the system was confirmed to follow the first order kinetics equation. From this study it could be said that the plasma-based oxidation process is promising for the application in the decomposition of textile wastewater to support sustainable industry with environmentally friendly orientation.

Structural-elastic relationships of Zr-TL (TL = Cu, Co, Ni) thin films metallic glasses

Abstract In this study, we investigated the structural and elastic properties of Zr-TL (late transition metal TL = Cu, Co, Ni) thin films metallic glasses (TFMG) deposited by dc magnetron co-sputtering from pure TL targets in Ar plasma discharge. The influence of the deposition parameters on the microstructure, chemical composition and elastic properties of the thin films has been explored. Advanced non-destructive techniques such as the picosecond ultrasonics and the Brillouin light scattering were employed to selectively measure the longitudinal V L and the transversal V T sound velocities, leading to the determination of the elastic constants C 11 , C 44 , respectively. From these data sets, the elastic constants of metastable amorphous single elements a -Zr, a -Cu, a -Co and a -Ni have been extrapolated. Some relationships between elastic moduli (Young's modulus E and shear modulus G = C 44 ) and the structural state either crystalline or amorphous are established. Predicted ductility/brittleness character was emphasized based on the Blackman's diagram, Pugh's ratio and the Pettifor criteria. Equivalently, the newly introduced δ parameter termed as ‘the cooperation parameter’ and related uniquely to the Poisson's ratio ν , confirmed the improvement of ductility with TL alloying.

Observation of dust acoustic multi-solitons in a strongly coupled dusty plasma

The excitation and propagation of low frequency dust acoustic multi-solitons are investigated in an unmagnetized strongly coupled dusty plasma. A floating 2D dusty medium is produced in an RF discharge Ar plasma with silica micro-particles. Dust acoustic perturbations are excited by applying a negative sinusoidal pulse of frequency 1–2 Hz and amplitude 4–20 V to an exciter grid. An initial large amplitude dust density compression breaks into a number of solitary pulses which are identified as dust acoustic solitons. The observed multi-soliton evolution is compared with numerical simulations of modified Korteweg de Vries (KdV)-Burger equation. The characteristics of the generated solitons are in good agreement with the theory.

An experimental study on discharge characteristics in a pulsed-dc atmospheric pressure CH3OH/Ar plasma jet

Recently, C/H/Ar plasma discharges found enormous potential and possibility in carbonaceous compounds conversion and production. In this work, a pulsed-dc CH3OH/Ar plasma jet generated at atmospheric pressure is investigated by means of optical and electrical diagnosis concerning the variation of its basic parameters, absolute concentration of OH radicals, and plasma temperature with different CH3OH/Ar volume ratios, in the core region of discharge with needle-to-ring electrode configuration. The voltage–current characteristics are also measured at different CH3OH/Ar ratios. Laser-induced fluorescence (LIF) results here show that only small amounts of added methanol vapor to argon plasma (about 0.05% CH3OH/Ar volume ratio) is favorable for the production of OH radicals. The optical emission lines of CH, CN, and C2 radicals have been detected in the CH3OH/Ar plasma. And, the plasma temperatures increase with successive amount of added methanol vapor to the growth plasma. Moreover, qualitative discussions are presented regarding the mechanisms for methanol dissociation and effect of the CH3OH component on the Ar plasma discharge at atmospheric pressure.

Preconcentration and Atomization of Arsane in a Dielectric Barrier Discharge with Detection by Atomic Absorption Spectrometry.

Atomization of arsane in a 17 W planar quartz dielectric barrier discharge (DBD) atomizer was optimized, and its performance was compared to that of a multiple microflame quartz tube atomizer (MMQTA) for atomic absorption spectrometry (AAS). Argon, at a flow rate of 60 mL min(-1), was the best DBD discharge gas. Free As atoms were also observed in the DBD with nitrogen, hydrogen, and helium discharge gases but not in air. A dryer tube filled with NaOH beads placed downstream from the gas-liquid separator to prevent residual aerosol and moisture transport to the atomizer was found to improve the response by 25%. Analytical figures of merit were comparable, reaching an identical sensitivity of 0.48 s ng (-1) As in both atomizers and limits of detection (LOD) of 0.15 ng mL(-1) As in MMQTA and 0.16 ng mL(-1) As in DBD, respectively. Compared to MMQTA, DBD provided 1 order of magnitude better resistance to interference from other hydride-forming elements (Sb, Se, and Bi). Atomization efficiency in DBD was estimated to be 100% of that reached in the MMQTA. A simple procedure of lossless in situ preconcentration of arsane was developed. Addition of 7 mL min(-1) O2 to the Ar plasma discharge resulted in a quantitative retention of arsane in the optical arm of the DBD atomizer. Complete analyte release and atomization was reached as soon as oxygen was switched off. Preconcentration efficiency of 100% was observed, allowing a decrease of the LOD to 0.01 ng mL(-1) As employing a 300 s preconcentration period.

Enhanced adherence of mouse fibroblast and vascular cells to plasma modified polyethylene.

Since the last decade, tissue engineering has shown a sensational promise in providing more viable alternatives to surgical procedures for harvested tissues, implants and prostheses. Biomedical polymers, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE), were activated by Ar plasma discharge. Degradation of polymer chains was examined by determination of the thickness of ablated layer. The amount of an ablated polymer layer was measured by gravimetry. Contact angle, measured by goniometry, was studied as a function of plasma exposure and post-exposure aging times. Chemical structure of modified polymers was characterized by angle resolved X-ray photoelectron spectroscopy. Surface chemistry and polarity of the samples were investigated by electrokinetic analysis. Changes in surface morphology were followed using atomic force microscopy. Cytocompatibility of plasma activated polyethylene foils was studied using two distinct model cell lines; VSMCs (vascular smooth muscle cells) as a model for vascular graft testing and connective tissue cells L929 (mouse fibroblasts) approved for standardized material cytotoxicity testing. Specifically, the cell number, morphology, and metabolic activity of the adhered and proliferated cells on the polyethylene matrices were studied in vitro. It was found that the plasma treatment caused ablation of the polymers, resulting in dramatic changes in their surface morphology and roughness. ARXPS and electrokinetic measurements revealed oxidation of the polymer surface. It was found that plasma activation has a positive effect on the adhesion and proliferation of VSMCs and L929 cells.

Global Model of <formula formulatype="inline"><tex Notation="TeX">$\hbox{Cl}_{2}\hbox{/Ar}$</tex> </formula> High-Density Plasma Discharge and 2-D Monte-Carlo Etching Model of InP

A multiscale approach has been developed in order to simulate the etch process of InP in an inductive coupled plasma (ICP) Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma discharge. The model consists of three modules: a global kinetic model of the Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma discharge, a sheath model, and a 2-D Monte-Carlo etching model. The densities and the fluxes of all neutral and charged species considered in the reaction scheme as well as the electron temperature are calculated from the global model. The angular and energy distribution functions of ions are computed from the sheath model. The output parameters of both the global kinetic model and the sheath model in terms of particle fluxes, ion angular distribution function and ion energy distribution function are used as input parameters in the 2-D etching model. The latter allows tracking in time the evolution of the etched surface. The ultimate goal of the multiscale approach is to predict the etch rate, the etched surface chemical composition, and the etch profile as a function of the operating conditions (power, pressure, gas flow rates, etc). In this paper, the results from the global model are first compared to the measurements carried out in the ICP etching tool, showing a satisfactory agreement. The etching model is then used to simulate the etching of narrow trench and small-diameter hole in InP. The mechanisms involved in the development of undercut below the mask and in the bowing effect are analyzed. The comparison between simulated and experimental etch profiles evidences the important role of Cl adsorption probability on the development of the undercut, and the significant impact of the redeposition of the etched species on the etch rate variation and on the narrowing in the bottom of the etched hole/trench.

Enhancement of hydrophobicity and tensile strength of muga silk fiber by radiofrequency Ar plasma discharge

The hydrophobicity and tensile strength of muga silk fiber are investigated using radiofrequency (RF) Ar plasma treatment at various RF powers (10–30 W) and treatment times (5–20 min). The Ar plasma is characterized using self-compensated Langmuir and emissive probe. The ion energy is observed to play an important role in determining the tensile strength and hydrophobicity of the plasma treated fibers. The chemical compositions of the fibers are observed to be affected by the increase in RF power rather than treatment time. XPS study reveals that the ions that are impinging on the substrates are mainly responsible for the cleavage of peptide bond and side chain of amino acid groups at the surface of the fibers. The observed properties (tensile strength and hydrophobicity) of the treated fibers are found to be dependent on their variation in atomic concentration and functional composition at the surfaces. All the treated muga fibers exhibit almost similar thermal behavior as compared to the virgin one. At RF power of 10 W and treatment time range of 5–20 min, the treated fibers exhibit properties similar to that of the virgin one. Higher RF power (30 W) and the increase in treatment time deteriorate the properties of the fibers due to incorporation of more surface roughness caused by sufficiently high energetic ion bombardment. The properties of the plasma treated fibers are attempted to correlate with the XPS analysis and their surface morphologies.

Computation of the Net Emission Coefficient with the Overlapping Lines Consideration on the CH&lt;sub&gt;4&lt;/sub&gt;-Ar Plasma Discharge

Net emission coefficients of radiation were calculated for isothermal plasma of CH4 –Ar as a function of the plasma temperature 5,000–30,000 K and the arc radius (0–1 cm) at various plasma pressures. Calculations take into account continuum and line radiations. The line shapes in our calculations are given by convolution of Doppler and Lorentz profiles, resulting in a simplified Voigt profile. The overlapping lines have also been taken into account. In the case of hydrogen profile, we used the Vidal tables, and the four first Lyman lines and the four first Balmer lines have been considered in this work. Values of net emission coefficients calculated for various spectral regions were compared with others author’s works.

Irradiation Effects of Photoemission-Assisted Direct Current Discharge Plasma on Metal Surfaces

2″-size Al and Si substrates were treated by photoemission-assisted DC discharge Ar plasma, in which photoelectrons emitting from the negatively biased substrate surface under UV light irradiation are utilized as a trigger of discharge and therefore the substrate surface can be exposed to accelerated Ar+ ions. The surface morphology of Al surfaces, prepared by mechanical grinding, showed a significant decrease of arithmetical average roughness (Ra) from 341.9 nm to 260.2 nm due to Ar+ ion sputtering for an irradiation time of 100 min. The Si surface was also etched with maintaining surface flatness at Ra=1-2 nm, while protrusions grew, perhaps resulting from agglomeration of sputtered Si atoms and/or masking effects of dusts. These resulsts suggest that the photoemission-assisted DC discharge plasma is applicable as an ion source for improving surface roughness of substrates.

Post‐Plasma Grafting of AEMA as a Versatile Tool to Biofunctionalise Polyesters for Tissue Engineering

In the last decade, substantial research in the field of post-plasma grafting surface modification has focussed on the introduction of carboxylic acids on surfaces by grafting acrylic acid (AAc). In the present work, we report on an alternative approach for biomaterial surface functionalisation. Thin poly-ε-caprolactone (PCL) films were subjected to a dielectric barrier discharge Ar-plasma followed by the grafting of 2-aminoethyl methacrylate (AEMA) under UV-irradiation. X-ray photoelectron spectroscopy (XPS) confirmed the presence of nitrogen. The ninhydrin assay demonstrated, both quantitatively and qualitatively, the presence of free amines on the surface. Confocal fluorescence microscopy (CFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to visualise the grafted surfaces, indicating the presence of pAEMA. Static contact angle (SCA) measurements indicated a permanent increase in hydrophilicity. Furthermore, the AEMA grafted surfaces were applied for comparing the physisorption and covalent immobilisation of gelatin. CFM demonstrated that only the covalent immobilisation lead to a complete coverage of the surface. Those gelatin-coated surfaces obtained were further coated using fibronectin. Osteosarcoma cells demonstrated better cell-adhesion and cell-viability on the modified surfaces, compared to the pure PCL films.

Improved Adhesion, Growth and Maturation of Vascular Smooth Muscle Cells on Polyethylene Grafted with Bioactive Molecules and Carbon Particles

High-density polyethylene (PE) foils were modified by an Ar+ plasma discharge and subsequent grafting with biomolecules, namely glycine (Gly), polyethylene glycol (PEG), bovine serum albumin (BSA), colloidal carbon particles (C) or BSA and C (BSA + C). As revealed by atomic force microscopy (AFM), goniometry and Rutherford Backscattering Spectroscopy (RBS), the surface chemical structure and surface morphology of PE changed dramatically after plasma treatment. The contact angle decreased for the samples treated by plasma, mainly in relation to the formation of oxygen structures during plasma irradiation. A further decrease in the contact angle was obvious after glycine and PEG grafting. The increase in oxygen concentration after glycine and PEG grafting proved that the two molecules were chemically linked to the plasma-activated surface. Plasma treatment led to ablation of the PE surface layer, thus the surface morphology was changed and the surface roughness was increased. The materials were then seeded with vascular smooth muscle cells (VSMC) derived from rat aorta and incubated in a DMEM medium with fetal bovine serum. Generally, the cells adhered and grew better on modified rather than on unmodified PE samples. Immunofluorescence showed that focal adhesion plaques containing talin, vinculin and paxillin were most apparent in cells on PE grafted with PEG or BSA + C, and the fibres containing α-actin, β-actin or SM1 and SM2 myosins were thicker, more numerous and more brightly stained in the cells on all modified PE samples than on pristine PE. An enzyme-linked immunosorbent assay (ELISA) revealed increased concentrations of focal adhesion proteins talin and vinculin and also a cytoskeletal protein β-actin in cells on PE modified with BSA + C. A contractile protein α-actin was increased in cells on PE grafted with PEG or Gly. These results showed that PE activated with plasma and subsequently grafted with bioactive molecules and colloidal C particles, especially with PEG and BSA + C, promotes the adhesion, proliferation and phenotypic maturation of VSMC.

Deposition of gold nano-particles and nano-layers on polyethylene modified by plasma discharge and chemical treatment

Polyethylene (PE) was treated in Ar plasma discharge and then grafted from methanol solution of 1,2-ethanedithiol to enhance adhesion of gold nano-particles or sputtered gold layers. The modified PE samples were either immersed into freshly prepared colloid solution of Au nano-particles or covered by sputtered, 50 nm thick gold nano-layer. Properties of the plasma modified, dithiol grafted and gold coated PE were studied using XPS, UV–VIS, AFM, EPR, RBS methods and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain, creation of excessive free radicals and conjugated double bonds. After grafting with 1,2-ethanedithiol the concentration of free radicals declined but the concentration of double bonds remained unchanged. Plasma treatment changes PE surface morphology and increases surface roughness too. Another significant change in the surface morphology and roughness was observed after deposition of Au nano-particles. The presence of Au on the sample surface after the coating with Au nano-particles was proved by XPS and RBS methods. Nanoindentation measurements shown that the grafting of plasma activated PE surface with dithiol increases significantly adhesion of sputtered Au nano-layer.

Poly(N-isopropylacrylamide) Grafted on Plasma-Activated Poly(ethylene oxide): Thermal Response and Interaction With Proteins

Thermoresponsive polymer layers offer the possibility of preparing smart surfaces with properties that are switchable through a phase transition, usually close to the lower critical solution temperature of the polymer. In particular, poly( N-isopropylacrylamide) (pNIPAM) has gained a great deal of attention because it has such a phase transition in a physiologically interesting temperature range. We have prepared ultrathin thermoresponsive coatings by grafting pNIPAM on a plasma-CVD-deposited, poly(ethylene oxide)-like polymer substrate that was activated in an Ar plasma discharge to initiate the grafting. The presence and integrity of pNIPAM was verified by XPS and ToF-SIMS, and a dramatic change in the wettability during the phase transition was identified by temperature-dependent contact angle measurements. The transition from the hydrated to the collapsed conformation was analyzed by temperature-dependent QCM measurements and by AFM. An unusual, reversible behavior of the viscoelastic properties was seen directly at the phase transition from the swollen to the collapsed state. The phase transition leads to a switching from protein repulsion to a state that allows the adsorption of proteins.