RF Plasma Discharge Research Articles

Reaction Mechanisms and Plasma-Catalyst Interaction in Plasma-Assisted Oxidation of n-Butane: A Data-Driven Approach

Experimental investigations of n-butane oxidation under atmospheric-pressure plasma conditions and in He-dilution have provided detailed information on the power-dependence of the conversion of C4H10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {C}_{4}\ ext {H}_{10}$$\\end{document} into CO and CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {CO}_{2}$$\\end{document} at 450 K surface temperature. The rf-plasma discharge has been equipped with a MnO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {MnO}_{2}$$\\end{document}-catalyst, and a significant impact on the reaction chain due to the presence of the catalyst surface could be observed. We report on ongoing data-based model development. Recently, a reaction kinetic model has been published, which agrees well with the experimental data (Stewig et al. in Plasma Sources Sci Technol 32:105006, 2023). However, that model could not clearly identify the main mechanisms in the interaction of plasma and catalyst. We show that various models can be found that explain the data similarly well. Detailed sensitivity analysis shows that only a maximum of three parameters can be identified in all the models considered for the currently limited data. Despite this limitation, we intend to continue the data analysis using more general models and introduce possible surface effects. Such unified models simultaneously describe the experimental data from both measurements with and without catalyst using a single set of physical parameters. To evaluate the hypotheses, we present numerical results for certain ranges of experimental parameters, which, in a subsequent experimental verification, allows to exclude or confirm one or another model.

THE Formation of chondrule-like particles in RF discharge plasma

THE Formation of chondrule-like particles in RF discharge plasma

Plasma-Enhanced Chemical Vapor Deposition of Thin GaS Films on Various Types of Substrates

Gallium monosulfide (GaS), a representative of Group III monochalcogenide layered materials, is a wide-bandgap semiconductor. It is considered an ideal material for light detectors in the blue and near ultraviolet ranges of the spectrum. In this work, for the first time, the method of plasma-enhanced chemical vapor deposition (PECVD) was applied to obtain thin GaS films on various substrates, where high-purity gallium and sulfur served as starting materials. To initiate the interaction between the reactants, a nonequilibrium RF discharge (40.68 MHz) plasma at a pressure of 0.1 torr was used. The influence of the substrate nature on the stoichiometry, structure, and surface morphology of GaS films has been studied. The plasmachemical process was monitored using optical emission spectroscopy.

Investigation of the Plasma-Chemical Synthesis of Thin Ga2O3 Films Doped with Zn in One Step in Plasma

A process for fabricating Zn-doped (up to 10 at %) β-Ga2O3 thin films by plasma-enhanced chemical vapor deposition has been studied. High-purity gallium, zinc, and oxygen were used as starting materials, and hydrogen was chosen as the carrier and plasma gas. A low-temperature nonequilibrium RF (40.68 MHz) discharge plasma at a reduced pressure (0.01 torr) was used to initiate chemical reactions of precursors. Theplasma-chemical process was monitored using optical emission spectroscopy. Structural properties and morphology of the deposited β-Ga2O3 films were studied by various methods.

Isotropic and Anisotropic Monolayer Structures in RF Discharge Plasma

We present the results of an experimental and analytical study of the structural and dynamic properties of a monolayer consisting of dust grains in an electrostatic trap in an RF discharge plasma. The possibility of forming a monolayer with an isotropic distribution for interparticle distance and kinetic energy of particles in the structure has been experimentally shown. Isotropy has crucial importance for the study of various processes in such systems, including the kinetics of phase transitions, the formation of directed flows, wave propagation, and others.

Dynamic Entropy of Two-Dimensional Active Brownian Systems in Colloidal Plasmas.

We analyze the experimental data on the motion of active Brownian micrograins in RF discharge plasmas. In the experiments, two types of microparticles were used: first—plastic grains fully covered with metal, and second—Janus particles with a thin metal cap. We have tracked the trajectories of the separate grains and plotted the pair correlation functions of the observed structures. To examine the motion of the grains, we studied the dependencies of the MFPT dynamic entropy on the coarsening parameter, the fractal dimension of the system on its mean kinetic temperature, and the mean localization area of the grain on its mean kinetic temperature. Based on the obtained results, we conclude that the character of motion of our active Brownian systems changes as the power of an illuminating laser (and, therefore, the mean kinetic temperature of the grains) increases. Janus particles change their trajectories from more chaotic to spiral-like ones; in the case of fully covered particles, we observe the dynamical phase transition from the more ordered structure to the less ordered one.

Gigantic Coaxial Line for Experimental Studies of the Interaction of Nanosecond Electromagnetic Pulses with an Ionized Gas Medium

A large-scale coaxial line filled with the plasma of RF discharge has been developed for laboratory modeling of the effects of the interaction of ultrashort electromagnetic pulses (EMPs) with the atmosphere and the ionosphere in the KROT facility. The oversized coaxial line ensures pulse transmission through an ionized medium in the TEM mode, which corresponds to the polarization of the transverse electromagnetic wave in free space, and in uniform isotropic plasma. The coaxial line has a length of 10 m and a diameter of 140 cm. The processes of propagation of the nanosecond and subnanosecond pulses in this line, in vacuum and with plasma, have been simulated numerically.

Generalizing Similarity Laws for Radio-Frequency Discharge Plasmas across Nonlinear Transition Regimes

We generalize similarity theory based on the scaling and solution invariance of the Boltzmann equation, coupled with the Poisson equation, and demonstrate similarity laws for radio-frequency (rf) discharge plasmas across three nonlinear transitional regimes, namely, the alpha-gamma mode transition, the stochastic-Ohmic-heating mode transition, and the bounce-resonance-heating mode transition. Fundamental plasma parameters, e.g., the electron power absorption, under similar discharge conditions are examined via fully kinetic particle-in-cell simulations, and electron-kinetic invariance is exemplified in similar rf discharge plasmas. The results unambiguously confirm the applicability of similarity laws for rf plasmas in extended operating regimes, and strengthen the foundations and framework of similarity physics with universality.

Gallium oxide thin films synthesis in different phase composition by gallium interaction with oxygen in oxygen-hydrogen plasma on silicon substrates

A modern synthesis method by plasma-chemical deposition of gallium oxide layers was developed. High-purity gallium was utilized as the source of gallium for moving by hydrogen flow into the reaction zone for interaction with oxygen in plasma discharge. Low temperature non-equilibrium RF (40MHz) plasma discharge was utilized for initiation interactions between precursors at a pressure of 0.1 Torr. The optical emission spectroscopy was used to assess the main excited particles formed in the gas phase. The paper researches the dependence of properties of the solid phase, grown on the silicon substrate, on the experimental parameters.

Obtaining of carbon nanoparticles in pulsed modulated RF discharge plasma

Carbon nanoparticles were synthesized using a 13.56 MHz RF discharge plasma in pulsed mode to control the size of the nanoparticles. An Ar/CH4 gas mixture was injected into the chamber to create capacitive coupled plasma medium, the main part of which is an electrode connected to the RF generator and a grounded electrode arranged in parallel. The synthesis experiments were carried out at room temperature and under the following conditions: pressure in the working chamber 0.99 Torr; concentration of Ar(96%)+CH4(4%) gas mixture; synthesis time 5 seconds; at discharge power 10 W. The frequency of the RF discharge plasma pulse during modulation was varied from 10 Hz to 10 kHz, also the duty-cycle was 50% for each performed experiment. Experimental observations have revealed that the size of carbon nanoparticles increases with the frequency of the pulse signal. It has also been determined that by using a frequency of the modulated pulsed RF signal it is possible to control the size of carbon nanoparticles in the range of 40-70 nm. The synthesized nanoparticles were collected directly on a copper mesh for TEM microscopy, which was placed on the surface of the bottom electrode. TEM image analysis showed two types of nanoparticles, some of which are an agglomerate of nanoparticles with an amorphous structure, while the others are nanometer-sized with crystalline structures.

RF discharge diagnostics: Some problems and their resolution

In this paper, we discuss a number of problems found in the literature related to experimental measurements of rf discharge electrical and plasma parameters with different electromagnetic probes. Incorrect evaluations of discharge power and the inaccurate measurement of basic plasma parameters with electrical (Langmuir), magnetic (B-dot), and microwave probes are among the troubling issues found in many recent publications on rf plasma. The purpose of this review is to show the origination of errors and ways to their mitigation based on the three-decade development of contemporary rf discharge diagnostics.

Plasma-engineered bifunctional cobalt-metal organic framework derivatives for high-performance complete water electrolysis.

Metal-organic framework (MOF) derivatives are among the most promising catalysts for the hydrogen evolution reaction (HER) for clean hydrogen energy production. Herein, we report the in situ synthesized MOF-derived CoPO hollow polyhedron nanostructures by simultaneous high temperature annealing and Ar-N2 radio frequency plasma treatment in the presence of a P precursor and subsequent oxygen incorporation from open air at lower temperature. The optimum Ar-N2 gas flow rates are used to precisely tune the P/O ratio, cut Co bonds within the MOFs and reconnect Co with P. Consequently, both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance are enhanced. Meanwhile, the filling of P elements can effectively change the electronic structure around the catalyst to ensure the uniform distribution of catalytically active sites. The resultant CoPO hollow nanocages with large specific surface areas show excellent bifunctional electrocatalytic activity towards both HER and OER with a low overpotential of 105 and 275 mV and a small Tafel slope of 48 and 52 mV dec-1, respectively. Our results open a new avenue for precise plasma-assisted engineering of MOF-derived hybrid hetero-structured electrocatalysts with rich oxygen vacancies and P dopants to simultaneously boost both half reactions in water electrolysis.

Preparation of gallium of the special purity for semiconductors and optoelectronics

This work is devoted to the development of a novel method of gallium purification especially designed for the fabrication of semiconductors and optical materials of UV–Visible-Mid IR range. For the first time gallium was purified by distillation in complex oxygen-hydrogen plasma. The process of purification including both oxidation and reduction stages was carried out at the low pressure (1∙10−3 Torr) in inductively coupled non-equilibrium RF (40.68 MHz) plasma discharge. In situ Optical Emission Spectroscopy (OES) was also used to determine the intermediate excited species forming in the process of plasma-chemical purification. The novel technological approach is aiming to diminish content as metal as carbon-containing impurities that behaviour was also investigated. A possible mechanism of impurities conversion during the process was discussed.

Mechanisms of Resonant Power Input into a Magnetoactive RF Discharge Plasma

We consider the excitation and absorption of waves in a magnetoactive rf discharge plasma in the conditions when the generator frequency is lower than the electron cyclotron frequency. We consider the cases of unconfined and confined plasmas in the cylindrical geometry and different regimes of excitation of plasma waves with different dispersion relations and field polarizations. The power input to the plasma depends on the distribution of external-source currents initiating the discharge and on the density parameter characterizing the plasma density and transverse sizes of the system. In the case of a plasma cylinder with a free surface or a plasma cylinder in a large conducting casing, which is most interesting for applications, plasma contains only potential and nonpotential E-type oblique Langmuir waves as well as a strongly nonpotential surface wave. The latter wave is practically not excited by external currents flowing over the cylinder surface for real parameters of the system. For high values of the density parameter, the effective resistance of the plasma with inducting excitation of the discharge is predominant. For moderate and low values of this parameter, capacitive excitation of the wave by the current on the plasma cylinder surface is found to be most effective.

Plasma-Chemical Synthesis of Lead Sulphide Thin Films for Near-IR Photodetectors

Lead sulfide (PbS) thin films of different morphology were synthesized via direct interaction of lead and sulfur vapors. Low temperature nonequilibrium RF (40.68 MHz) plasma discharge at low pressure ((3–5) × 10–3 Torr) was used for the initiation of chemical interaction between precursors in the gas phase. The in-situ Optical Emission Spectroscopy (OES) was utilized to determine the exited reactive species existing in plasma discharge and possible mechanism of plasma-chemical reactions resulting in the formation of the solid phase. The chemical composition, structure and morphology of the surface of the as-deposited materials in dependence of parameters of the plasma process such as stoichiometry of the precursors in the gas phase, power of the plasma discharge and substrate temperature were characterized by SEM, XRD and AFM analytical techniques. The optical properties and electrophysical parameters of the samples were studied as well.

Steel Wire Cleaning using Cold Plasma

Current galvanizing process used hydrochloric acid to remove oxide layer and mild acidic bath to remove oil on metal wire surface. These cleaning processes are compulsory before steel wire coated with zinc. These chemicals cleaning technique cause ecological harm and produce toxic waste. To consider of minimizing these problems, cold plasma was introduced for metal wire cleaning. Previous research already proves that cold plasma capable to remove oil by using dielectric barrier discharge (DBD) and remove oxide layer on copper by using RF plasma discharge. Therefore, in this research, the same plasma discharge system that is DBD was used to remove oil and oxide layer on steel wire. 8kV of voltage and air was used to generate plasma. By using copper and steel wire as electrode, it can remove oil around 82% and oxide layer around 54%.

Correction for Neutral Pressure-Driven Signal in Radiated Power Measurements on Proto-MPEX

A pinhole camera using four-channel resistive bolometers was designed and implemented on the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) to measure the plasma radiated power. Quantification of the radiated power is required for comprehensive power balance assessments but faces unique challenges on linear plasma devices due to weak absolute signal, compared to typical use in toroidal fusion plasmas, and high neutral pressure changes. Around 1 mTorr, the pressure-driven signal contribution was shown to overwhelm the radiated power signal in Proto-MPEX, found to be ~3 μW. Since the pressure-driven signals could not be predicted from first principle arguments, the signals were corrected using empirical models that take two experimental pressure measurements and the raw bolometer signal to reveal the radiated power signals. Four “gas-only” Proto-MPEX shots were taken, without the radio frequency (rf) plasma discharge, to train, optimize, and validate empirical models. The data included two pressure measurements at different locations along with the bolometer signal. Multiple models were tested; partial least-squares regression with a cross correlation method to account for the time offset in the pressure measurements provided the best combination of accuracy and stability. The model was validated to have a modeling error of 0.0036 V, which was lower than 10% of the expected radiated power signal. The model was tested on a different “gas-only” shot with a complete time-series data. For plasma operation shots, the corrected bolometer measurements were compared with an absolute extreme ultraviolet photodiode measurement and similarities and differences are discussed.

Superhydrophobic carbonous surfaces production by PECVD methods

The paper presents the results of a complex study of superhydrophobic surfaces obtained by PECVD methods in RF discharge plasma with gas mixtures (Ar/CH4 and Ar/C2H2) and by plasma jet (Ar/CH4). In both experiments hydrophobic surfaces were obtained by deposition of carbon nanoparticles on glass and silicon substrates by plasma of Ar (93%) + CH4 (7%) and Ar (93%) + C2H2 (7%) gas mixtures. To compare surfaces with high hydrophobicity produced by the above two methods their contact angles were studied. The dependence of changes in the contact angle on the storage time of the samples under normal conditions show that samples obtained in Ar/CH4 plasma and plasma jet at atmospheric pressure are much better preserved.

Hybrid Plasma – Prospects for Application in Medicine and Biology

Different schemes and designs of generators of low-temperature hybrid plasma produced by simultaneous ionization of plasma-generating medium by an electron beam with electron energy of 30 keV and an RF discharge (13.56 MHz) are considered. A plasma-chemical reactor designed for hybrid plasma generation is described, and results of spectrometric measurements of its reaction volume are presented. The reactor has been used to prepare biocompartible thin chitosan films. Experiments showed that modification of chitosan films in hybrid oxygen plasma improves their hydrophilic properties and has advantages over modification in RF-discharge or electron beam plasma when they are used separately. The bactericidal effect of the hybrid plasma was found in tests Escherichia coli cultures. Prospects for practical hybrid plasma applications in biology and medicine are discussed.

Study of Si and Ge Atoms Termination Using H-Dilution in SiGe:H Alloys Deposited by Radio Frequency (13.56 MHz) Plasma Discharge at Low Temperature.

In this work, we present the study of the atomic composition in amorphous SiXGeY:HZ films deposited by radio frequency (RF—13.56 MHz) plasma discharge at low deposition temperature. A study and control of Si and Ge atoms termination using H-dilution in SiGe:H alloys deposited by RF plasma discharge was conducted and we made a comparison with low-frequency plasma discharge studies. Solid contents of the main elements and contaminants were determined by SIMS technique. It was found that for low dilution rates from RH = 9 to 30, the germanium content in the solid phase strongly depends on the hydrogen dilution and varies from Y = 0.49 to 0.68. On the other hand, with a higher presence of hydrogen in the mixture, the germanium content does not change and remains close to the value of Y = 0.69. The coefficient of Ge preferential incorporation depended on RH and varied from PGe = 0.8 to 4.3. Also, the termination of Si and Ge atoms with hydrogen was studied using FTIR spectroscopy. Preferential termination of Si atoms was observed in the films deposited with low RH < 20, while preferential termination of Ge atoms was found in the films deposited with high RH > 40. In the range of 20 < RH < 40, hydrogen created chemical bonds with both Si and Ge atoms without preference.