Radio Frequency Dielectric Barrier Discharge Research Articles

Characteristics of Radio Frequency Dielectric Barrier Discharge Using Argon Doped with Nitrogen at Atmospheric Pressure

In order to study the characteristics of radio frequency dielectric barrier discharge (RF-DBD) using argon doped with nitrogen at atmospheric pressure, electrical and optical diagnoses of the discharge with different nitrogen ratios from 1% to 100% were carried out, and the self-organizing form of the filamentous plasma was studied through a transparent water electrode. At the same time, an ICCD camera was used to study the spatiotemporal evolution filamentous discharge during one cycle. Different from discharge using pure argon, using argon doped with nitrogen made the discharge change from glow discharge to filamentous discharge when the voltage increased to a certain value, and a higher nitrogen ratio made the filaments thicker and more sparsely arranged. Under different input power and nitrogen content conditions, several forms of glow discharge, hexagonal/irregularly arranged filamentous discharge and local filamentous discharge were obtained, all of which have potential applications to reduce the high cost of using inert gases.

Non-Thermal Plasma Characteristics and Ignition Behavior of Lean Mixture with Radio Frequency Dielectric Barrier Discharge at High Pressure

Non-Thermal Plasma Characteristics and Ignition Behavior of Lean Mixture with Radio Frequency Dielectric Barrier Discharge at High Pressure

Steady-State Model of an Argon–Helium High-Pressure Radio Frequency Dielectric Barrier Discharge

A steady-state kinetic model of argon–helium high-pressure radio frequency dielectric barrier discharge is developed using a simplified reaction rate package appropriate for pressures ranging from 200 to 500 torr. Electron production and loss rates are analyzed as a function of pressure and Ar–He mixture, highlighting the importance of the Ar2* dimer for higher pressures and Ar rich mixtures. As pressure increases, the primary ionization mechanism shifts between ionization of ground state Ar to dimer ionization, which affects the steady-state reduced electric field due to the electron energy required for the two dominant ionization mechanisms. The resulting reduced electric field profile controls the metastable Ar(1s5) production, which, combined with the Ar(1s5) loss rates, reveals the metastable density as a function of pressure and Ar-fraction. This simplified 0-D steady-state model shows close agreement with previous time-dependent simulations using a robust reaction rate package.

On the electron density of atmospheric pressure radio frequency dielectric barrier discharge and discharge with bare electrode

Atmospheric pressure radio frequency helium plasma with two different designs: dielectric barrier discharge (DBD) and discharge with bare electrode (DBE) were investigated by means of optical emission spectroscopy. Both DBD and DBE can work at relatively low temperature and produce abundant electrons facilitating production of reactive species through electron-impact reactions. Stark broadening method of Hydrogen Balmer beta (Hβ) line was employed to analyze the electron density. When electron density is below 1020 m−3, fine-structure fitting was used to improve the accuracy of electron density estimation. At power ranged 4–20 W, DBD and DBE showed electron density 4.1–6.1 × 1019 m−3, and 3.6–8.6 × 1019 m−3, respectively. The DBD is more suitable than DBE for biomedical applications due to the wider working power range and lower gas temperature in the range of 316–344 K, depending on the power.

Effect of Ar(3p54p; 2p)+M → Ar(3p54s; 1s)+M branching ratio on optically pumped rare gas laser performance

Optically pumped rare gas laser performance is analyzed as a function of the Ar(3p54p; 2p) + M → Ar(3p54s; 1s) + M branching ratios. Due to the uncertainty in the branching ratios, a sensitivity study is performed to determine the effect on output and absorbed pump laser intensities. The analysis is performed using a radio frequency dielectric barrier discharge as the source of metastable production for a variety of Argon in Helium mixtures over pressures ranging from 200 to 500 Torr. Peak output laser intensities show a factor of 7 increase as the branching ratio is increased from 0.25 to 1.00. The collection of Ar* in Ar(1s4) is inversely proportional to the branching ratio and decreases output laser intensity by reducing the density of species directly involved with lasing.

Magnetic field enhanced cold plasma sterilization

Cold plasma sterilization offers an efficient way to sterilize medical components and instruments. This paper reports using a magnetized plasma to realize low-temperature sterilization. A radio frequency dielectric barrier discharge is created in a quartz tube using a mixture of argon and oxygen gas. A uniform amount of Escherichia coli is applied onto glass slides and exposed to the plasma afterglow at different pressures with and without a magnetic field. Optical emission spectroscopy is used to identify the plasma species present. The magnetic field significantly promotes the intensity of the plasma and the sterilization efficiency. A process gas pressure of 100 mTorr presents the most effective treatment with a sterilization time less than one minute and sample temperature below 32 °C.

Metastable Ar(1s5) density dependence on pressure and argon-helium mixture in a high pressure radio frequency dielectric barrier discharge

Simulations of an α-mode radio frequency dielectric barrier discharge are performed for varying mixtures of argon and helium at pressures ranging from 200 to 500 Torr using both zero and one-dimensional models. Metastable densities are analyzed as a function of argon-helium mixture and pressure to determine the optimal conditions, maximizing metastable density for use in an optically pumped rare gas laser. Argon fractions corresponding to the peak metastable densities are found to be pressure dependent, shifting from approximately 15% Ar in He at 200 Torr to 10% at 500 Torr. A decrease in metastable density is observed as pressure is increased due to a diminution in the reduced electric field and a quadratic increase in metastable loss rates through Ar2* formation. A zero-dimensional effective direct current model of the dielectric barrier discharge is implemented, showing agreement with the trends predicted by the one-dimensional fluid model in the bulk plasma.

Oxygen functionalization of MWCNTs in RF-dielectric barrier discharge Ar/O2 plasma

The oxygenation of multi-wall carbon nanotubes (MWCNTs) was performed via a radio frequency dielectric barrier discharge (RF-DBD) in an Ar/ plasma mixture. The relative intensity of the Ar/ plasma species was characterized by optical emission spectroscopy (OES). The effects of treatment time, RF power and oxygen gas percentage on the chemical composition and surface morphology of MWCNTs were investigated by means of x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). The results of FTIR and XPS revealed the presence of oxygen-containing functional groups on the MWCNTs treated in an Ar/ plasma at an RF power of 50 W and pressure of 400 Pa. The amount of oxygen functional groups (C=O, C–O, and O–COO) also increased by increasing treatment time up to 6 min, but slightly decreased when treatment time was increased by 10 min. The increase of oxygen gas percentage in the plasma mixture does not affect the oxygen content in the treated MWCNTs. Meanwhile, MWCNTs treated at high power (80 W) showed a reduction in oxygen functional groups in comparison with low RF power conditions. The Raman analysis was consistent with the XPS and FTIR results. The integrity of the nanotube patterns also remained damaged as observed by FE-SEM images. The MWCNTs treated in RF-DBD using the Ar/ plasma mixture showed improved dispersibility in deionized water. A correlation between the OES data and the observed surface characterization for an improved understanding of the functionalization of MWCNTs in Ar/ plasma was presented.

Formation and characteristics of patterns in atmospheric-pressure radio-frequency dielectric barrier discharge plasma

The patterns in radio-frequency dielectric barrier discharge (RF DBD) are studied at atmospheric pressure of argon (Ar) or helium (He) mixed with nitrogen (N2) gas. When a small amount of N2 is mixed with He or Ar gas, discharge patterns are formed. In a N2/He gas mixture, besides the filament discharge that forms patterns, a glow background discharge is also observed, whereas only the filament discharge forms patterns in a N2/Ar gas mixture. The resolution of the hexagonal pattern as a function of applied power and gas flow rate is then explored. On the basis of spatial–temporal images taken using an intensified charge-coupled device (ICCD), we find that there is no interleaving of two transient hexagon sublattices in N2/Ar or N2/He plasma in RF DBD patterns, which are totally different from those in which surface charges dominated in the mid-frequency DBD plasma. This supports our hypothesis that the bulk charges dominate the pattern formation in RF DBD.

Transition from Townsend to radio-frequency homogeneous dielectric barrier discharge in a roll-to-roll configuration

The aim of this paper is to better understand the transition from Townsend to radio-frequency homogeneous dielectric barrier discharge (DBD) at atmospheric pressure. The study is done in an Ar/NH3 Penning mixture for an electrode configuration adapted to roll-to-roll plasma surface treatment. The study was led in a frequency range running from 50 kHz up to 8.3 MHz leading to different DBD modes with a 1 mm gas gap: Glow (GDBD), Townsend (TDBD), and Radio-frequency (RF-DBD). In the frequency range between TDBD and RF-DBD, from 250 kHz to 2.3 MHz, additional discharges are observed outside the inter-electrode gas gap. Because each high voltage electrode are inside a dielectric barrel, these additional discharges occur on the side of the barrel where the gap is larger. They disappear when the RF-DBD mode is attained in the 1 mm inter-electrode gas gap, i.e., for frequencies equal or higher than 3 MHz. Fast imaging and optical emission spectroscopy show that the additional discharges are radio-frequency DBDs while the inter-electrode discharge is a TDBD. The RF-DBD discharge mode is attained when electrons drift becomes low enough compared to the voltage oscillation frequency to limit electron loss at the anode. To check that the additional discharges are due to a larger gas gap and a lower voltage amplitude, the TDBD/RF-DBD transition is investigated as a function of the gas gap and the applied voltage frequency and amplitude. Results show that the increase in the frequency at constant gas gap or in the gas gap at constant frequency allows to obtain RF-DBD instead of TDBD. At low frequency and large gap, the increase in the applied voltage allows RF-DBD/TDBD transition. As a consequence, an electrode configuration allowing different gap values is a solution to successively have different discharge modes with the same applied voltage.

Contrasting Characteristics of Radio-Frequency Atmospheric Argon Discharges With and Without Dielectric Barriers

In this paper, the fundamental characteristics of glow discharge operation modes in radio frequency (RF) atmospheric argon discharges with and without dielectric barriers were studied by experiments. It is found that the RF dielectric-barrier discharge (DBD) in atmospheric argon operates more stable in alpha mode than RF atmospheric pressure glow discharge in argon. The ratios of oxygen and nitrogen to argon are achieved to be 9.5% and 6% in stable RF DBD in atmospheric argon, respectively. The plasmas chemistry, measured by optical emission spectra and intensity, explains that the stable alpha mode discharge range is larger with mixture of oxygen than nitrogen.

Spectroscopic Study of a Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge with Anodic Alumina as the Dielectric

This paper presents the fabrication and a spectroscopic study of a stable radio-frequency dielectric barrier discharge (RF DBD) in Ar with a novel dielectric, anodic alumina, at atmospheric pressure. Dielectric electrodes are fabricated from commercially available low cost impure aluminum strips by a two-step anodization process in 0.3 M solution of oxalic acid. The discharge is found to be stable with excellent spatial uniformity for the RF input power range of 30∼80 W. Excitation and rotational temperatures measured in the experiment range of 1472∼3255 K and 434∼484 K, respectively, as the input power changes from 30 W to 80 W. These temperature ranges are suitable for surface modification applications.

Synthesis of full-visible-spectrum luminescent silicon nanocrystals and the origin of the luminescence

An efficient synthesis route for highly luminescent silicon nanocrystal (Si-nc) films is presented. Si-ncs in the films are synthesized in the gas phase by using an argon-silane radio-frequency dielectric-barrier discharge (RF-DBD) plasma. The size of Si-ncs is well tunable by changing the resident time. The resulting Si-nc films with different oxidation degree exhibit emission across the full visible spectrum. Structural and optical characterization indicates that the red-to-green luminescence from big particles show quantum confinement effect (QCE), while this effect disappears in blue luminescence from small ones. A model is presented to explain this result. In this model, the radiative process in big particles is Band-to-Band recombination, in which surface states have a negligible impact on the QCE, while the blue emission from small Si-ncs is due to the Band-to-Bound recombination, in which surface state plays an important role, resulting in the disappearance of QCE. Additionally, obvious double-exponential decay from midsize particles is observed, in which the two kinds of recombination may coexist.

Two-dimensional simulation of an atmospheric-pressure RF DBD in a H2 : O2 mixture: discharge structures and plasma chemistry

The results of two-dimensional modelling of a radio-frequency dielectric barrier discharge (RF DBD) in a hydrogen–oxygen stoichiometric mixture under atmospheric pressure are presented. The production of active species and the possibility of ignition of the mixture are studied. It is shown that the production of active species in the discharge is enough to reduce the ignition temperature significantly. A detailed description of the ion production and loss is presented. The processes of electron attachment are very fast, while the detachment processes depend on the type of ion. The electron detachment, charge recombination, and conversion of negative and positive ions are very important here. The current discharge consists of breakdowns that occur in each half-period, and it resembles the standard DBDs of kilohertz frequency. The surface charge is not uniform over the electrode area and the RF DBD consists of micro-discharges, which are not so pronounced as in the DBDs of kilohertz frequency. Two additional types of RF DBDs, the dual-frequency RF DBD and frequency-modulated RF DBD, are simulated for the purpose of controlling the ratio between the input power absorbed by electrons and ions in this discharge.

Effect of Duty Cycle on the Characteristics of Pulse-Modulated Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge

Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.

A cryogenic circulating advective multi-pass absorption cell

A novel absorption cell has been developed to enable a spectroscopic survey of a broad range of polycyclic aromatic hydrocarbons (PAH) under astrophysically relevant conditions and utilizing a synchrotron radiation continuum to test the still controversial hypothesis that these molecules or their ions could be carriers of the diffuse interstellar bands. The cryogenic circulating advective multi-pass absorption cell resembles a wind tunnel; molecules evaporated from a crucible or injected using a custom gas feedthrough are entrained in a laminar flow of cryogenically cooled buffer gas and advected into the path of the synchrotron beam. This system includes a multi-pass optical White cell enabling absorption path lengths of hundreds of meters and a detection sensitivity to molecular densities on the order of 10(7) cm(-3). A capacitively coupled radio frequency dielectric barrier discharge provides ionized and metastable buffer gas atoms for ionizing the candidate molecules via charge exchange and the Penning effect. Stronger than expected clustering of PAH molecules has slowed efforts to record gas phase PAH spectra at cryogenic temperatures, though such clusters may play a role in other interstellar phenomena.

Characterization of argon/air atmospheric pressure capacitively coupled radio frequency dielectric barrier discharge regarding parasitic capacitor at 13.56 MHz

In this paper, uniform argon glow discharge at atmospheric pressure in a diffuse mode driven by a 300-W radio-frequency (13.56 MHz) power supply based on dielectric barrier discharge was investigated. In this work, the effect of the parasitic capacitor on the electrical characteristics of the capacitively coupled atmospheric pressure plasma was investigated. It was revealed that more than half of the RF current is parasitic in our system as a characteristic of the capacitively coupled plasma. It was also proved that the discharge resistance and sheath capacitance increase at higher input powers while the impedance decreases. In order to recognize plasma, optical emission spectroscopy apparatus was used. Argon, oxygen, copper, and nitrogen spectrum lines were diagnosed. The plasma gas temperature and electronic excitation temperature were investigated showing a non-equilibrium discharge.

The Spatiotemporal Pattern Formed in an Atmospheric-Pressure Radio-Frequency Dielectric-Barrier-Discharge Oxygen Plasma

In this paper, we developed a radio-frequency (RF) dielectric barrier oxygen discharge, which consists of a powered brass electrode covered by fused silica as a dielectric layer and a grounded liquid electrode. The self-organized patterns in the RF dielectric barrier discharge at atmospheric pressure are investigated. With increasing the input power, the plasma patterns transform from the ring to the netlike structure.

A Large Gap of Atmospheric Pressure RF-DBD Glow Discharges in Ar and Mixed Gases

A large gap (up to 5.5 mm) between electrodes is acquired at Ar atmospheric pressure glow discharge (APGD) in radio frequency dielectric barrier discharge (RF-DBD). The characteristics of I–V in single barrier Ar RF-DBD mixed with different ratios of O2 (0–100%) is studied in detail.

A large gap of radio frequency dielectric barrier atmospheric pressure glow discharge

A large gap was acquired between electrodes (up to 5.5 mm) of Ar atmospheric pressure glow discharge in radio frequency dielectric barrier discharge (rf-DBD). The discharge of Ar plasma was characterized by I-V curve and Lissajous plot, and the effective power of the discharge was calculated based on the measured Lissajous plot and found to be higher than 90% of the input power. To gain a thorough understanding of the mechanism, the rf-DBD with a single dielectric barrier layer operating in γ mode glow discharge of N2 plasma was diagnosed in spatial resolution through optical emission spectroscopy. It was concluded that secondary electron emission might be responsible for the sustainable glow discharge in the large gap rf-DBD plasma.