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A one-dimensional (1D) fluid model is developed to investigate the effect of multi-frequency excitation consisting of consecutive harmonics on the charge of a single dust grain in a weakly collisional capacitively coupled plasma discharge. The spatial distributions of the electron density, the electrons temperature, and the charged particle flux are obtained and analyzed under the effects of the number of harmonics. It is shown that the number of harmonics considerably affects the discharge properties and the sheath thickness. In order to analyze the charge of an injected dust particle under the effect of different operating parameters, the model takes into account the electron and ion currents, as well as the effect of collisions between ions and neutral atoms. The results showed that as the number of harmonics increases, the particle charge increases in the powered sheath region while it decreases in the grounded sheath due to the electrical asymmetry effect. However, the charge remains constant in the central region where the electron temperature is constant. The present study further shows that the gas pressure and the driving frequency affect the dust charge oppositely, where an increase in pressure leads to a decrease in the dust charge, especially in the sheath regions, while the particle charge negatively increases as the driving frequency increases for all excitation waveforms. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the initiation, development and maintenance of a plasma surface discharge initiated by microwave (microwave) radiation of a gyrotron (75 GHz, 300 kW, 6 ms) in air under normal conditions on the surface of a quartz substrate with metal inclusions are presented. It is shown that the velocity of the propagation of the discharge ionization front reaches 40 m/s, which corresponds to the thermal conduction propagation mechanism. In this case, the maximum calculated gas temperature of the plasma reaches 5500 K, which leads to the sublimation of metal inclusions. For the first time, the plasma parameters of a surface microwave discharge on metal-dielectric targets, which have been used in various aeroplasma and plasma-chemical applications, are presented. [ABSTRACT FROM AUTHOR]

The effect of driving frequency in the range of 13.56–73 MHz on electron energy distribution and electron heating modes in a 50 mTorr capacitively coupled argon plasma discharge is studied using 1D-3V particle-in-cell simulations. Calculated electron energy probability functions exhibit three distinct "temperatures" for low-, mid-, and high-energy electrons at all the studied driving frequencies. When compared to published experimental data, the calculated probability functions show a reasonable agreement for the energy range resolved in the measurements (about 2–10 eV). Discrepancies due to limitations in experimental energy resolution outside this range lead to differences between computational and experimental values of the electron number density determined from the distribution functions, and the predicted effective electron temperature is within 25% of experimental values. The impedance of the discharge is interpreted in terms of a homogeneous equivalent circuit model, and the driving frequency dependence of the inferred combined sheath thickness is found to obey a known, theoretically derived, power law. The average power transferred from the field to the electrons (electron heating) is computed, and a region of negative heating near the sheath edge, particularly at higher driving frequencies, is identified. Analysis of the electron momentum equation shows that electron inertia, which on temporal averaging would be zero in a linear regime, is responsible for negative values of power deposition near the sheath edge at high driving frequencies due to the highly nonlinear behavior of the discharge. [ABSTRACT FROM AUTHOR]

Plasma asymmetry generation in capacitively coupled plasma (CCP) discharges provides control over vital parameters that are useful in many plasma processing applications. In this article, using the particle-in-cell simulation technique, we investigated the spatial plasma asymmetry creation by a temporally asymmetric (sawtooth) waveform by varying its number of harmonics (N). The simulation results predict a non-linear increase in the plasma density and ion flux with an increase in N, i.e., it first decreases, reaching to a minimum value for a critical value of N and then increases almost linearly with a further rise in N. The ionization asymmetry increases with N, and higher harmonics on the instantaneous sheath position are observed for higher values of N. These higher harmonics generate multiple ionization beams that are generated near the expanding sheath edge and are responsible for an enhanced plasma density. The ion energy distribution function (IEDF) depicts a bi-modal shape for different values of N. DC self-bias is observed on the powered electrode, its magnitude with respect to the plasma potential decreases with increasing N, and therefore, the corresponding ion energy on the powered electrode decreases. The results conclude that by changing N of a sawtooth waveform in a collisionless CCP system, the ion flux asymmetry is not altered, whereas sheath symmetry could be significantly affected causing a systematic variation in the ion energy asymmetry. Due to an increase in the higher harmonic contents in the sawtooth waveform, a transition from broad bi-modal to narrow-shaped IEDFs is found. [ABSTRACT FROM AUTHOR]

Parametric study and nonlinear dynamical analysis of the discharge parameter variations are presented here for a hollow cathode source in the glow discharge regime and later in the radio frequency (RF) discharge regime. A plasma source consisting of a semi‐transparent hollow cathode leads to the generation of nonthermal energetic charged particles and the formation of multiple potential regimes in the plasma column during both the glow discharge as well as the RF discharge regimes. The hollow cathode discharge obtained using this single plasma source exhibits significant mixed‐mode oscillations (MMOs) during the glow discharge regime. Various regular and irregular sequences of MMOs evolved during the progressive change of discharge voltage in the glow discharge regime. During the RF power application across the hollow cathode source, the charged particles oscillate and appear in bursts in the time series. The present study investigates energy distribution among the coherent modes of discharge through the application of the Empirical Mode Decomposition technique. Multiple coherent modes are identified during both discharge regimes that carry most of the discharge energy. [ABSTRACT FROM AUTHOR]

Despite the progress made in the treatment of nephrolithiasis, the existing methods of renal calculi destruction are not ideal and have both advantages and disadvantages. Considering the process of high-frequency glow discharge formation on the surface of an electrode and in an electrolyte solution, we obtained the results on the destruction of renal calculi in vitro. It was shown that the destruction of kidney stones by glow discharge plasma was caused by several processes—the plasma induced effect of hydrated electrons and shock wave effect of the electrolyte stimulated by electrical breakdowns in the plasma. The plasma generation modes were configured by estimating the thickness of the vapor–gas layer in which the plasma burns. Thus, the average rate of contact destruction of renal calculi was measured depending on the plasma generator input power and time of plasma exposure. We conclude that the method of stone fragmentation by high-frequency electrolyte plasma is rather perspective and can be used in endoscopic urology for percutaneous and transurethral lithotripsy. [ABSTRACT FROM AUTHOR]

Results of optical and gas-dynamic investigations of the microwave discharge plasma under conditions of gas-jet synthesis of diamond are reported. The data are analyzed for determining the temperature and composition of the mixture in the discharge chamber for the purpose of further optimization of the method. The influence of the flow rate of the injected gas mixture on the macroparameters of the gas mixture flow at the exit of the discharge chamber is studied. The temperature and pressure measured in the discharge chamber are used for the numerical analysis of the mixture composition depending on the injected gas flow rate. It is demonstrated that the mixture composition at the exit of the discharge chamber correlates with the rate of diamond synthesis. [ABSTRACT FROM AUTHOR]

Chlorine-containing plasma and its mixtures with molecular and inert gases, as well as plasmas of complex polyatomic gases, such as freons, are often used to form the topology on the surface of semiconductors. This article examines the surface quality (based on the roughness data) of the semiconductor structure of GaAs after plasma-chemical etching in the plasma of mixtures of HCl/Ar, HCl/Cl2, and HCl/H2, as well as R-12 freon and its mixture with argon. Freon R-12 is often used for etching Si, Ge, and a number of other materials (GaAs, GaP, InP), providing technologically acceptable interaction rates, and also meets the requirements for anisotropy and selectivity. Also, mixtures of active gases with inert (He, Ar) gases have become widespread, which can act both as simply diluent gases and as sources of ions for the ion bombardment of the sample for the further ionic stimulation of the desorption of the interaction products, which improves the functional properties surface, with a slight decrease in the speed of interaction. Nevertheless, controlling the surface quality of samples remains an urgent task in modern electronics. [ABSTRACT FROM AUTHOR]

A microwave beam (wavelength 4 mm, power 150–300 kW) generates an ionization wave in air in the subthreshold field in the shape of a conglomerate of thread-like channels that moves toward the beam. The periphery of the beam refracts in the plasma of the non-self-sustained discharge in the UV halo of the thread-like discharges and self-focuses in the recombining plasma behind the front of the plasmoid that consists of thread-like channels. The self-focusing of the peripheral regions of the wave beam causes local bursts of ionization behind the front of the leading plasmoid. [ABSTRACT FROM AUTHOR]

Various dyeing techniques are utilised at dyeing different types of fabrics and current study discuss the possibility of using a single dye bath for the given purpose. The current study utilised a radio frequency glow discharge plasma source maintained at near atmospheric conditions (around 200 mbar) in nitrogen and air environments to treat cotton, nylon, and polyester fabrics. Similar surface modifications produced in all three types of fabrics by OH and O radicals tailoring them more sensitive to certain dyes and glues. SEM images verified that bulk material is well protected by plasma treatment and the presence of additional surface functionalities (hydroxyl, carboxylic, and carbon-nitrogen groups) on the treated fabric surfaces were determined by FTIR and XPS analysis. The plasma-treated samples were dyed in a single dye bath using a reactive dye under atmospheric neutral conditions and a significant enhancement in fabric dyeability (cotton- 124%, nylon- 61%, polyester- 38%) was observed. PVA glue was used for fastening the fabric samples and the adhesion was analysed through tensile measurement. Well improved adhesion capabilities (148%, 95%, and 57.3% respectively for cotton, nylon, and polyester) also confirm the advantages of RF glow discharge plasma treatment for unified fabric processing. • RF glow discharge plasma for unified fabric processing. • Fabric surface modification with O and N containing surface functionalities. • The enhancement in fabric dyeability with reactive dyes. • Enhanced adhesion capabilities with PVA based glues. [ABSTRACT FROM AUTHOR]

The present work aims to analyze the mutual influence of channels in a combined discharge based on the RF inductive and DC discharges and to find the conditions under which the gain in the plasma density can be obtained. A cylindrical plasma reactor with a diameter of 20 cm and a length of 20 cm has been used as an object of research. The measurements have been carried out in argon at pressures of 0.08 and 8 Pa, as well as in air at pressures of 8 and 18.7 Pa. The performed experiments have shown that the gain in plasma density in the combined discharge is possible under conditions when the plasma density in DC discharge overcomes that in the inductive one. As a rule, such situation occurs when inductive discharge is in a E-mode. Due to the higher value of the plasma density, provided by the DC channel, the RF power input through the inductive discharge increases. A synergistic effect appears, and the resulting plasma density exceeds the sum of the densities, specific to the inductive and DC discharges separately. • The gain in plasma density in the combined RF and DC discharge can be obtained. • A synergistic effect appears when the resulting plasma density exceeds the sum of the densities, characteristic of the inductive and DC discharges separately. • The DC channel can be locked in the combined discharge. • The properties of the combined discharge are close to that in the inductive one near antenna and to DC discharge near the cathode if the electron mean free path is smaller than the distance between antenna and electrodes. [ABSTRACT FROM AUTHOR]

The results of a study on particles' surfaces after being exposed to the near-electrode region of a radio frequency (RF) discharge are presented. It was experimentally displayed that metal starts being deposited on the surface of particles levitating above the lower electrode of the discharge chamber after switching the RF discharge on. For melamine-formaldehyde (MF) particles, the appearance of an island metal coating is observed after 30 min of plasma exposure. Eroded electrodes and elements of the gas discharge chamber may serve as a source of deposited material. In addition, an analysis of the surface and composition of particles placed on the upper electrode after 6 h of plasma exposure is presented. We reveal that the composition and structure of the particle coating changes during the experiment. The MF particles under exposure become eroded, and needle-like structures containing metals are formed on their surface. We also observe the formation of columnar structures from the products of erosion of electrodes on particles with a metal coating. [ABSTRACT FROM AUTHOR]