Gas Discharge Plasma Research Articles

Effect of oxygen plasma treatment on the properties of ALD hafnium oxide films

In this work, we studied the effect of processing hafnium oxide samples prepared by atomic layer deposition in a gas discharge plasma of a mixture of argon and oxygen in a ratio of 1:10. It has been shown that such treatment preserves the amorphous structure of the film and reduces the content of oxygen vacancies in the film. This is important for the use of the film in the gate dielectric of a transistor. Processing in plasma leads to a change in its properties, namely: an increase in density and refractive index, as well as a decrease in the intensity of emission bands that are associated with an oxygen vacancy. The plasma temperature and ion energy were determined from the argon emission spectra. The activation energy for the diffusion of oxygen ions in hafnium oxide films has been calculated to be 0.43 eV.

Development and Diagnostic Study of the RF nitrogen Atom Source

With the development of thin film technology, particularly the increasing demand for research on group III nitride materials, the need for N ions has significantly increased. A wider and more efficient RF nitrogen atom source specifically designed for nitride film growth has been developed. To evaluate the nitrogen atom density from the RF nitrogen source, a global model of RF nitrogen gas discharge plasma was created. This model was calibrated by measuring the emission spectrum of RF nitrogen gas discharge, and the relationships between nitrogen atom density and actual working pressure, power, and discharge chamber size were determined. It was found that the nitrogen atom density increases with increasing power and initially increases with pressure before decreasing. Finally, the nitrogen atom density was determined, achieving an 18% nitrogen atom dissociation rate and a nitrogen atom density of 5×1012/cm³ at an RF power of 400 W. This density is significantly higher than that of nitrogen ions, indicating that this is a nitrogen atom source with high purity.

Methodology for measuring the energy characteristics of two-electrode gas discharge plasma switches in the picosecond range using the reflectometry method

This research proposes a new technique for measuring the energy characteristics (losses of energy in the spark gap, related to light radiation, ionization, excitation, and heating of the working gas during the development of plasma; discharge power) of two-electrode gas dischargers in the subnanosecond range. The work examines the voltage waveforms across the discharge gas gap and the discharge current waveform obtained by the reflectometry method in the subnanosecond range. To do this, the traditional technique for measuring such characteristics was modified. This allows us to restore the back edge of the voltage pulse across the discharge gap at the breakdown delay and the breakdown stages, which is usually lost in the subnanosecond range when measuring such waveforms. For modification, calculated data on the ionization frequency were used. This allows us to replace the plasma of the discharge gap with a constant resistor in those sections of the voltage waveform where the characteristic ionization time is more than an order of magnitude longer than the duration of the voltage pulse applied to the gap. The waveforms of the voltage across the discharge gap and the discharge current obtained in this way allowed us to calculate the power dynamics and total energy introduced into the gas discharge plasma. These parameters are important both for calculating the efficiency of gas switches and for other applications of gas discharge plasma, in particular laser pumping.

The effect of a constant electric field in an undisturbed plasma on the stability of the electron beam–gas discharge collisional plasma system

This work is devoted to the study of a fast non-relativistic electron beam–gas discharge plasma system within the framework of the kinetic theory of stability. The influence of a constant electric field, collinear beam velocity, on the stability of the system in an undisturbed plasma is studied. It is shown that even a relatively small electric field, which does not significantly affect the energy of the electron beam, can lead to significant changes in the parameters of harmonic disturbances propagating in the electron beam–plasma system in the region of its instability. It was found that the reason for such changes is the drift of plasma electrons, which, as a consequence, leads to a change in the frequency of disturbances in the coordinate system associated with the plasma due to the Doppler effect. The results obtained are demonstrated by calculations based on the kinetic theory of perturbation parameters in a low-voltage beam discharge in rare gases, which is used in the development of plasma electronics devices. The effect of electron-atomic collisions on the stability of the electron beam–plasma system is investigated and compared with the results of other authors' works.

Observation of Le Sage gravity analog in complex plasma.

Fragmentation of a suspension of micron-sized plastic microparticles and their contraction into dense globules was experimentally obtained in a gas discharge plasma, when the plasma density was deliberately and abruptly increased. The globules took up spherical shapes 0.14-1.1mm in diameters and contained from tens to thousands microparticles. The fragmentation and globule formation appears to be similar to the development of gravitational instability. This process is attributed to the Le Sage's like attraction among microparticles in a dense plasma due to the plasma losses inside a globule hypothesized theoretically in the middle of the 1990s. The key role of plasma flows in the attraction was prominently demonstrated in the same experiment by the distinctly visible disintegration of the globules when we reduced the density of the surrounding plasma to the initial one. Also molecular dynamics simulations of fragmentation of microparticle clouds and globules formation qualitatively resemble typical patterns of the fragmentation and collapse of interstellar nebulae.

Non-thermal atmospheric pressure gas discharge plasma enhances tendon-to-bone junction repair in a rabbit model

Non-thermal atmospheric pressure gas discharge plasma enhances tendon-to-bone junction repair in a rabbit model

Electric Discharge Between a Metal Cathode and a Liquid Non-Metal Anode

Gas-discharge plasma generated between a metal cathode and a liquid non-metallic anode at atmospheric pressure has been studied. The discharge is ignited by immersing the metal electrode in the electrolyte. The types and shapes of plasma structures generated in the interelectrode gap and their electrical parameters are considered. The results of thermographic analysis of the electrode surface under discharge conditions are presented. Using emission spectroscopy, the plasma composition, electron concentration and temperature of the heavy component were studied.

Analyses of nonequilibrium transport in atmospheric-pressure direct-current argon discharge under different modes

Abstract The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow, arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current (DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath (P c) was used as a key parameter for judging different discharge modes, and the range of (0.28–1.2) × 1012 W m−3 was determined as a critical window of P c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.

Structuring of the Surface of Thin Carbon Films During Activation by Microsecond Current Pulses

The influence of current activation by electric pulse breakdown on changes in surface morphology and emission characteristics of a field emission cathode made on the basis of carbon films obtained by deposition in a microwave gas discharge plasma was studied. Current activation of these films was carried out by applying voltage pulses of microsecond duration until an electrical breakdown occurred. It is shown that during activation, the morphology of the film surface in the breakdown region changes with the formation of a micro-sized emitting structure, which significantly improves the field emission characteristics of cathodes based on carbon films.

On fundamental inconsistencies in a commonly used modification of a fluid model for glow discharge

This work considers the fundamental contradictions in the concept of one of the most well-known and widely used modifications of the fluid model for simulation of a glow discharge (GD), the ‘local mean energy approximation’ (LMEA). In this model, it is proposed to determine the kinetic coefficients in the electron particle and energy balance equations as functions of the electron mean energy (temperature) rather than local electric field, using a one-to-one correspondence between these parameters through the electron Boltzmann equation. It is shown that the scope of applicability of this model, like any other modification of the fluid model, is limited by the local mode of formation of the electron energy distribution function (EEDF). Therefore, as demonstrated by the examples of typical 1D and 2D problems for a GD in argon, its extension to the region of nonlocal EEDF is in no way justified and leads not only to serious errors in the results, but also to a logically intractable situation in attempts to apply the main postulate of the LMEA model to the region of a weak (or even reverse) electric field in a negative glow plasma. At the same time, the apparent reliability of calculations within the framework of the LMEA model for a number of parameters, in our opinion, only slows down progress in modeling of gas discharge plasma.

Plasma-solution synthesis of cobalt oxides

The production of nanosized oxide materials is an important practical problem. This is due to the fact that many of these substances are intensively used as catalysts, microelectronic devices, medical applications, etc. Among the various methods for their production, methods based on the use of gas-discharge plasma are the least studied. But these methods, compared to others, have a number of significant advantages. Among them, the main ones are high process rates and the absence of additional reagents. Therefore, in this work the regularities of the processes of formation of insoluble compounds under the action of a direct current discharge of atmospheric pressure in air on aqueous solutions of cobalt (II) nitrate have been studied. The solutions served as the cathode and anode of the discharge. The discharge was excited by applying a high voltage to two pointed titanium electrodes placed above the liquid anode and liquid cathode in the H-shaped cell. The range of discharge currents was (20–80) mA, and the range of concentrations was (20–60) mmol l−1. It was discovered that when a discharge acts on a liquid anode, a colloidal solution is formed in it, the destruction of which leads to the formation of precipitates. Based on measurements of the kinetics of consumption of Co2+ ions (spectrophotometric method) and the power inputted in the discharge, the rates of this process, effective rate constants, as well as the degree of conversion of Co2+ ions and energy yields of conversion were determined. These parameters depended on the discharge current and the initial concentration of the solution. The values of the constants were ∼(0.2–6) × 10−1 s−1, the energy yields were ∼(0.2–0.5) ions per 100 eV, and the degrees of conversion were ∼(0.1–0.5). The resulting powders were analyzed by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and energy-dispersive x-ray spectroscopy (EDS). The sizes of the powder aggregates were estimated from the results of scanning electron microscopy (SEM), transmission electron microscope (TEM) and Scherrer’s relation. It turned out that the resulting precipitates were a mixture of amorphous Co2+ and Co3+ hydroxides. Their calcination in air led, depending on the temperature, to the formation of predominantly cubic either CoO or Co3O4. The size of the aggregates of the calcined samples was ∼500 nm. The specific surface area of the powders, determined by the Brunauer–Emmett–Teller (BET) method, was ∼53 m2 g−1. The average pore volume and their size was ∼17 cm3 g−1 and ∼240 Å. The advantages of the proposed method over other methods are high process rates (process time ∼10 min) and the absence of any additional reagents.

Parameters of dust particle chains levitated vertically in a gas discharge plasma

The structural parameters of the dust particle chains suspended vertically in the electric field of a gas discharge are studied here. The investigations are performed by a numerical multi-block model based on a mean field approximation. The model describes the movement of ions and dust particles under the action of an external electric field, the electric field (Coulomb) of each charged dust particle, and the field of bulk plasma charge (ions and electrons) that screens the charges of dust particles. The gravity and the ion drag forces acting on the dust particles are also taken into account. Self-consistent chain parameters are calculated and compared for different number (1, 3, 5, and 7) and two different diameters (3.4 and 8.94 mcm) of dust particles in the chains. It is shown that an “ion wake” is formed behind the dust structures, and it grows with the number of dust particles and their size. With an increase in the number of dust particles in the chain, the charge of the first (top) dust particle increases. In the case of small dust particles, with an addition of new particles into the chain, the centers of the chains almost remain at the position of a single particle in the vertical direction. The chains of big dust particles move as a whole down in the direction of gravity with an increase in the number of particles.

INFLUENCE OF THE NANOSTRUCTURE OF TANTALUM OXIDE ON THE FLARE CHARACTER OF ITS ELECTROLUMINESCENCEWITH ANODIC-ELECTROLYSIS FORMATION IN CHEMICALLY PURE WATER

Theoretical and experimental studies were carried out to identify the reasons for the flash nature of the combustion of electroluminescence (EL) of tantalum oxide (Ta2O5), formed in chemically pure (distilled) water during high-voltage anodization of 1700 s. Nonlinear growth of the Ta2O5 film during this time was established, and a polychrome effect was discovered for its thicknesses from 150 ± 28 nm to 820 ± 80 nm. At the same time, EL ignition begins at an oxide thickness of 390 ± 74 nm, which corresponds to an anodization time of 78 ± 15 s, and from 968 ± 185 s until the end of this process, bright EL flashes are observed. Their luminosity can reach 2.8·10–3 lm/m2. It is shown that the cause of the outbreaks is explosive processes in dynamically changing Ta2O5 pores ranging in size from tens of nanometers to several micrometers and containing gas-discharge plasma from various products of electro- and plasma-chemical reactions with a temperature of the order of 12000 K, created due to Joule heating by the flowing current. It has been established that the formation of the plasma itself occurs as a result of electrical breakdown in pores, the field strength in which can reach the order of 3·108 V/m or more.

Formation of Black Silicon in a Process of Plasma Etching with Passivation in a SF6/O2 Gas Mixture.

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from -20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters-the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface-photovoltaics, supercapacitors, catalysts, and antibacterial surfaces.

Determination of gas discharge plasma potential by Langmuir probe using different methods

In a hollow cathode discharge in helium at reduced pressure, the profile of the plasma potential Up in the cathode-anode region was measured with a single Langmuir probe. A digital technique was used to control and analyze the experimental results. The probe current-voltage characteristic was generated by applying a voltage with a spectrum with an equal probability distribution in the measured voltage range. Three methods were compared: (1) differentiation of the probe current-voltage characteristic (IVC) by the Langmuir-Druyvesteyn (LD) method with the Savitsky-Golay (SG) filter; (2) definition of the position of the noise maximum in the experimental IVC; (3) determination of the voltage corresponding to the intersection of the asymptotes of different range of the IVC. Methods (2) and (3) were used both as alternatives to method (1) for measuring the potential Up and as additional ones when choosing free parameters of the SG filter for plasma diagnostics by method (1).

Surface air gas discharge plasma: An ecofriendly virus inactivation approach to enhance CPRRs mediated antiviral genes expression against airborne bio-contaminant (human Coronavirus-229E)

Emerging bio-contaminants (airborne viruses) exploits and manipulate host (human) metabolism to produce new viral particles, evading the host's immune defences and leading to infections. Non-thermal plasma, operating at atmospheric pressure and ambient temperature, is explored for virus inactivation, generating RONS that interact and denatures viral proteins. However, various factors affecting virus survival influence the efficacy of non-thermal plasma. Glucose analogue 2-DG, a metabolic modifier used in this study, disrupts the glycolysis pathway viruses rely on, creating an unfavourable environment for replication. Here, airborne HCoV-229E bio-contaminant was treated with plasma for inactivation, and the presence of RONS was analysed. Metabolically altered lung cells were subsequently exposed to the treated airborne viruses. Cytopathic effect, spike protein, and cell death were evaluated via flow cytometry and confocal microscopy, and CPRRs mediated antiviral gene expression was evaluated using PCR. Gas plasma-treated viruses led to reduced virus proliferation in unaltered lung cells, although few virus particles survived the exposure, as confirmed by biological assessment (cytopathic effects and live/dead staining). A combination approach of gas plasma-treated viruses and altered lung cells displayed drastic virus reduction compared to the control group, established through confocal microscopy and flow cytometry. Furthermore, altered lung cell enhances gene transcription responsible for innate immunity when exposed to the gas plasma-treated virus, thereby impeding airborne virus propagation. This study demonstrates the significance of a surface air gas plasma and metabolic alteration approach in enhancing genes targeted towards antiviral innate immunity and tackling outbreaks of emerging bio-contaminants of concerns (airborne viruses).

Impact of motile microorganisms on a Sutterby nanofluid flow over a rotating disk with Hall current and ion slip

The dynamics of partly ionized fluid flow, when subjected to a magnetic field, differ considerably from that of typical fluid flow. The main applications of the partially ionized fluids including thermal arc plasma cutting, gas discharge lamps, lighting, and plasma medicine have made them vital when discussed under the effects of the applied magnetic field. This study discusses the flow of the Sutterby nanofluid over a stretching disk with Hall and ion slip effects amalgamated with Cattaneo–Christov double diffusion. The uniqueness of the envisaged model is enriched by considering the gyrotactic microorganisms. The system of governing equations is normalized and addressed numerically by applying the bvp4c package of MATLAB software. The outcomes are depicted via graphs and in tabularized form. It is perceived that fluid velocity is affected by the Hall current parameter. For the bioconvection Lewis number, a decline in the microorganism distribution is also observed. In addition, it is also perceived that the fluid concentration is enhanced against mass diffusion relaxation stress. The validity of the envisioned model by comparing it with a published study is also a part of this exploration.

Моделирование мультикасповой магнитной системы источника ускоренных нейтральных частиц

The article considers the solution of an important technological problem of cleaning dielectric surfaces, during which the formation of a surface potential is eliminated, requiring the development of specialized sources of accelerated neutral particles integrated into ion-plasma installations. A significant disadvantage of these sources is the low density and poor uniformity of the output flow, which leads to an increase in the time of the technological operation and deterioration in the quality of surface treatment. To eliminate these disadvantages, a multicusp magnetic field system can be integrated into the device to reduce the plasma load on the anode, reduce the effective area of the anode and increase the density of the vapor-plasma flow. To optimize the design of the source, a simulation of the magnetic system was carried out and the calculation of the distribution of the magnetic field in the working area was conducted. For optimal operation of the source, it is necessary to achieve the largest possible magnitude of magnetic field induction at the walls of the working volume and as small as possible in the central region in which the vapor-plasma flow moves. The simulation results show that there is an optimal solution when choosing the number of permanent magnets holding the gas-discharge plasma. The retention effect increases with an increase in the number of permanent magnets, while the output of electrons from the loss cone becomes more frequent, which leads to a deterioration in the quality of the output flow. The optimal number of magnets is selected from the condition of balancing these two competitive effects.

Determination of the kinetic parameters of a supersonic plasma flow of a gas-discharge source from the current measured by an insulated probe system

The aim of this work is to develop a procedure for determining the kinetic parameters of charged particles in a supersonic jet of a gas-discharge source of collisionless plasma by measuring the current collected by an insulated probe system of cylindrical electrodes placed transversely to the jet. Based on the authors’ mathematical model of current collection by the above-mentioned probe system and asymptotic solution for the probe current in the electron saturation region, the ion temperature and directed velocity and the electron temperature are related to the measured probe current. The effect of the probe system parameters and the current and voltage measurment error on the reliability of diagnostics of a diatomic gas-discharge plasma is studied. Within the framework of the probe current collection model for the electron saturation region, numerical and analytical estimates of the errors in determining the kinetic plasma parameters are obtained as a function of the geometric parameters of the probe system, the accuracy of probe current measurement, and the bias potential of the probe relative to the potential of the reference electrode. The measuring-to-reference electrode area ratio and the probe current measurement conditions optimal for adequate estimation of the average kinetic energy and the directed velocity of ions in a supersonic gas-discharge plasma jet are determined. A priori quantitative characteristics of the effect of the probe measurement errors on the reliability of the determination of the charged particle kinetic parameters are given. The reported procedure and estimates of the error in kinetic plasma parameter determination allow one to choose the probe system parameters and estimate the required measurement accuracy when planning and conducting experiments on laboratory plasma diagnostics.

Simulation of filamentation dynamics of microwave discharge in nitrogen

The present study deals with numerical simulations of microwave (MW) discharges in nitrogen based on extended fluid-dynamic model. The set of governing equations for non-equilibrium gas-discharge plasma includes conservation equations for species number densities, electron energy density, Poisson equation for the electric field coupled to the multi-temperature Navier–Stokes fluid-dynamic equations taking into account thermal nonequilibrium; the power transmitted from MW radiation to electrons is determined from the Helmholtz equation. The kinetic scheme includes 61 reactions involving neutral molecules and atoms in the ground and electronically excited states, ions and electrons. The set of equations is solved for a two-dimensional problem under conditions of experiments at a pressure of 40 and 50 Torr and different electromagnetic wave frequencies and pulse duration. The dynamics of discharge formation and transition from the diffuse to the filament form is studied. The results are compared with experimental data, and a good agreement is shown for the time larger than 10 µs. The possible reasons for discrepancies at a shorter time are discussed and the effect of small oxygen impurities on the quantitative characteristics of the discharge are evaluated. The presence of a small oxygen impurity and seed electrons in the region of discharge formation yields a better agreement between numerical and experimental data.