Argon Dielectric Barrier Discharge Research Articles

Plasma Catalytic Synthesis of Silver Nanoparticles

We present the experimental results of plasma catalytic synthesis of colloidal silver nanoparticles, using AgNO3 as the precursor, ethanol as the solvent and reducing agent, and poly vinyl pyrrolidone (PVP) as the macromolecular surfactant. The plasma is generated by an atmospheric argon dielectric barrier discharge jet. Silver nanoparticles are produced instantly once the plasma is ignited. The system is not heated so it is necessary to use traditional chemical methods. The samples are characterized by UV-visible absorbance and transmission electron microscopy. For glow discharge mode no obvious silver nanoparticles are observed. For low voltage filamentary streamer discharge mode a lot of silver nanoparticles with the mean diameter of ∼3.5 nm are generated and a further increase of the voltage causes the occurrence of agglomeration.

Target patterns obtained by suddenly increasing applied voltage in dielectric barrier discharge

Stable target patterns are produced by suddenly increasing the applied voltage in argon dielectric barrier discharge at atmospheric pressure for the first time. The stability and wavelength selection of target patterns obtained by gradually increasing applied voltage after suddenly increasing applied voltage and by directly suddenly increasing applied voltage are studied respectively. It is found that the target patterns obtained by gradually increasing applied voltage are unstable. There is mutual transformation between target pattern and spiral, in which the target pattern can only survive for several tens milliseconds. The target patterns obtained by directly suddenly increasing applied voltage are much more stable, which can survive for more than 5min. The wavelength selections of target patterns obtained by above two methods are studied. It is found that the wavelength of target patterns obtained by directly suddenly increasing applied voltage decreases more quickly as the applied voltage increases. The results show that the applied voltage increasing way in which the target patterns are obtained plays an important role in the stability and wavelength selection of target pattern.

The effects of normal current density and the plasma spatial structuring in argon DBDs

This paper presents the results of theoretical studies of high-pressure dielectric barrier discharges (DBD) in argon. Two different DBDs at the megahertz and the kilohertz power frequency range were simulated. The effect of normal current density was obtained in the numerical model for both types of the discharge. The discharge of megahertz range was uniform over the radius. The increase in the discharge current is accompanied by increase in the discharge area. The discharge of kilohertz range is not uniform over the radius. The concentric ring formation was observed during calculations. The increase in the discharge current occurs due to increase in the number of rings and as a result in the discharge area. The developed 2D model is able to describe only the first stage of the filament formation – the formation of concentric plasma rings. The filament formation starts at the edge of the current channel and spreads to its centre. Both the effect of normal current density and the filaments formation are caused by the nonstationarity at the current channel boundary.

Surface modification of acrylate intraocular lenses with dielectric barrier discharge plasma at atmospheric pressure

Surface modification with dielectric barrier discharge (DBD) plasma was carried out at atmospheric pressure (argon as the discharge gas) to improve the biocompatibility of hydrophobic acrylate intraocular lens (IOL). Changes of the plasma-treated IOL surface in chemical composition, morphology and hydrophilicity were comprehensively evaluated by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and water contact angle (WCA) measurements. The surface biocompatibility of the untreated and plasma-treated IOLs was compared with the adhesion behavior of platelets, macrophages and lens epithelial cells (LECs) in vitro. After DBD plasma treatment, the hydrophilicity of the IOL surface was obviously improved. The changes in WCA with treatment extension may be attributed to both the introduction of oxygen or/and nitrogen-containing polar groups and the increase of surface roughness induced by plasma etching effect. The existence of low molecular weight oxidized material (LMWOM) was proved on the plasmatreated IOL which was caused by the chain scission effect of the plasma treatment. The plasma-treated IOLs resisted the adhesion of platelets and macrophages significantly. The LECs spreading and proliferation were postponed on the IOLs plasma-treated for more than 180 s, with a well maintained epithelial phenotype of LECs. The IOL biocompatibility was improved after the DBD plasma treatment. We speculate that slighter foreign-body reaction and later incidence of anterior capsule opacification (ACO) may be expected after implantation of the argon DBD plasma-treated IOL.

Deactivation of yeast by dielectric barrier discharge

Saccharomyces Cerevisiae (S. Cerevisiae) and Mrakia Frigida (M. Frigida) were deactivated using alternative current dielectric barrier discharge (DBD). The deactivation was done in argon and oxygen plasma under different discharge currents. It has been found that ozone and atomic oxygen play a significant role in the deactivation of S. Cerevisiae and M. Frigida when using DBD discharge, while argon ions are less important in the deactivation of the same microorganisms in argon DBD.

Plasma‐Polymerization of HMDSO Using an Atmospheric Pressure Dielectric Barrier Discharge

AbstractIn this work, an atmospheric pressure glow‐like dielectric barrier discharge in argon with small admixtures of hexamethyldisiloxane (HMDSO) is employed for the deposition of thin polydimethylsiloxane (PDMS) films. The effect of discharge power and feed composition (monomer concentration) on film properties has been investigated by means of contact angle measurements, Fourier‐Transform Infrared Spectroscopy (FT‐IR), and Atomic Force Microscopy (AFM). The results are described by defining a W/FM value, where W is the discharge power, F the monomer flow rate, and M is the molecular weight of the monomer. This paper shows that the deposition rate and the chemical composition of the deposited films are strongly affected by the W/FM value at which plasma‐polymerization is performed.

Electron density of an individual microdischarge channel in patterns in a dielectric barrier discharge at atmospheric pressure

The electron density of an individual microdischarge channel in different stable patterns including a square and a hexagon pattern in a dielectric barrier discharge in argon at atmospheric pressure is investigated using a spectral line profile method. The procedure for deconvolution of the asymmetric convolution integral is used to obtain the Stark broadening and shift of Ar I 696.54 nm for the calculation of electron density. The broadening parameters such as electron impact width ωe and ion impact width α can also be obtained from the procedure. By comparing ωe with the theoretical values at different electron temperatures given by Griem, the electron temperature can be reasonably estimated. It is found that the electron density in an individual microdischarge channel increases with increasing voltage.

Influence of dielectric parameters on temporal behavior of dielectric barrier discharge

The Influences of different temperature and materials of dielectrics on temporal behavior of dielectric barrier discharge in argon at atmospheric pressure are studied by using a device with asymmetric dielectric parameters. It is found that the temporal waveform of discharge current in each half cycle is almost the same at lower applied voltage, whereas the number of discharge current pulses is different in half cycles of different polarity at higher applied voltage. The analysis shows that both temperature and material of dielectrics affect the accumulation of wall charges, resulting in the change of temporal behavior of discharge.

Excitation temperatures of atmospheric argon in dielectric barrier discharges

A method for the determination of excitation temperatures based on optical emission spectroscopy and Fermi–Dirac distribution was set up and experiments were performed on atmospheric argon dielectric barrier discharges. Local thermodynamic equilibrium was proved to exist in the discharge and the validity of Boltzmann distribution is discussed. The main aim of this paper is to obtain the temperatures of atmospheric Ar II as a function of the discharge voltage, discharge frequency, argon flow rate and the argon fraction. It was found that the excitation temperatures are in the range 3800–4950 K. Besides, an increase in the argon flow rate resulting in a slight growth of the temperature and the add-in of air leading to the decrease in temperature was observed.

Square and hexagon pattern formation in dielectric barrier discharge in argon at atmospheric pressure

Pattern formations in dielectric barrier discharge in argon at atmospheric pressure under different discharge conditions are investigated. Patterns undergo the transition sevies of hexagonal-square-square with glow background-hexagonal with glow background as the applied voltage is increased, and the spatial wavelength and the filament density change also. When the glow background appears under a certain discharge condition, the spatial wavelength and the filaments density remain constant and the number of discharge pulses of each filament in half cycle changes from one to two.

Discharge structure on the dielectric surface of a pin-to-plane DBD in argon at atmospheric pressure

The experimental results on the surface structure of the dielectric barrier discharge (DBD) excited in pin-to-plane geometry in argon at atmospheric pressure are presented. It has been found that the DBD exhibits on the surface of dielectric three different spatial modes replacing one another with an increase in amplitude of the applied voltage. A correlation between the surface structure of discharge in each DBD mode and peculiarities of the current waveform was established.

Study on the electrical characteristic of different modes of dielectric barrier discharge in argon

Three modes of discharges, including diffuse, streamer, and patterned discharges , are achieved in dielectric barrier discharge in argon at 40 kPa gas pressure b y using a dielectric barrier discharge device with water electrodes. The electri cal and optical characteristics of the discharges are investigated. The voltage drop across discharge gap is obtained by measuring the voltage drop across the t est capacitor. Results show that the moment of discharge initiation is shifted e arlier and duty ratio of the discharge increases as the applied voltage increase s. At the moment of discharge initiation, the voltage drop across the discharge gap decreases and the transported charges abruptly increase. So the waveforms of the voltage drop across the discharge gap and the transported charges deviate from sinusoidal. The relationship between the voltage drops across the discharg e gap and the transported charges is nonlinear. Also the relationship between th e voltage drops across the discharge gap corresponding to zero applied voltage a nd the applied voltage is given. The function of wall charges and the influence of them on the voltage drops across the discharge gap and the transported charge s are discussed.

Square pattern formation in a gas discharge system

The square pattern is observed in dielectric barrier discharge in argon for the first time. The hexagon pattern and the mixture of hexagon and square structure are also observed. The square pattern can remain stable for several tens of minutes. The spatio-temporal dynamics of square pattern formation is investigated by optical method. The measurement results show that the square pattern is an interleaving of two square patterns, which is the reason of the stability of square pattern.

Pattern formation in the dielectric barrier discharge in argon at atmospheric pressure

The hexagon and square gridding patterns were observed in Ar（0.5％Air） at atmospheric pressure by using a dielectric barrier discharge set-up with double water electrodes. The temporal behaviour of an individual filament in square gridding was measured. The experimental results show that the time interval between two adjacent discharges are changed between long and short alternately. The influence of the charges deposited on dielectric surface on the self-organized filament pattern has been discussed.

Optical emission kinetics of argon inductively coupled plasma and argon dielectric barrier discharge

An experimental setup has been built up to create radio frequency (RF) inductively coupled plasma (ICP) and dielectric barrier discharge (DBD), and to investigate the kinetics of the deposition of diamond like carbon films. Optical emission spectra in visible and near ultraviolet region from argon ICP and DBD plasmas created in the machine were measured to analyze their optical emission kinetics. For ICP plasma of argon, the higher RF power input (higher than 500 W for our machine), the stronger ion optical emission strength. But the atom optical emission strength does not get higher the increase of the power input. On the otherwise, the optical emission kinetics of argon DBD discharge behaves in manner of unipolar pulsed discharge. DBD current is composed of a series of breakdown pulses equally spaced in temporal domain. The kinetics of DBD optical emission strength is mainly governed by the DC breakdown voltage of the used gas and therefore by the density of the breakdown current pulse.

Diagnostics of Argon Inductively Coupled Plasma and Dielectric Barrier Discharge Plasma by Optical Emission Spectroscopy

An experimental setup was built up to carry out radio frequency (RF) inductively coupled plasma (ICP) and dielectric barrier discharge (DBD), and to depict the optical emission spectra (OES) of the discharges. OES from argon ICP and DBD plasmas in visible and near ultraviolet region were measured. For argon ICP, the higher RF power input (higher than 500 W for our machine), the higher degree of argon plasma ionization. But that doesn't mean a higher mean electron energy. With the increase in the power input, the mean electron energy increases slightly, whereas the density of electron increases apparently. Or, the contrary, argon DBD discharge behaves in the manner of a pulsed DC discharge on optical emission spectroscopy and V-I characteristics. DBD current is composed of a series of pulses equally spaced in temporal domain. The kinetics of DBD emission strength is mainly governed by the frequency of the current pulse.