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In this study, the influence of ceramic shield characteristics, including thickness and geometry, on the transmission spectrum and electron density measurements of a ceramic shield cutoff probe (CSC) was investigated to measure high-density or process plasma. Through electromagnetic simulations and circuit modeling, we examined the measurement characteristics of the CSC based on different ceramic shield geometries. When the ceramic shield is sufficiently thin, it does not affect the CSC wave transmission characteristics. However, for a thick ceramic shield, a cutoff frequency shift of up to 3% toward the lower side can occur. This shift is attributed to the electrical properties of the ceramic material, which can function as a parasitic capacitor. In addition, when fabricating a CSC, depending on the shape of the ceramic shield or the method used to couple it with the CSC body, a cutoff frequency shift can occur toward the lower side. The simulation results were validated through experiments, revealing a cutoff frequency shift toward the lower side of up to 18.0% in the simulations and up to 11.6% in the experiments. The findings of this study could assist in high-density or processing plasma measurements using cutoff probes. [ABSTRACT FROM AUTHOR]

Defect generation and recovery at the interface of a silicon dioxide/silicon ( SiO 2 /Si) stack are studied in oxygen ( O 2) or argon (Ar) plasma processing and post-annealing. Defect generation is recognized to be dependent on the processing gas and the SiO 2 layer thickness. O 2 plasma processing shows a strong incident-ion energy dependence, where ion's implantation, diffusion, and reactions in the SiO 2 layer play important roles in defect generation. A similar dependence is observed for Ar plasma processing; however, it also shows the photon effects in defect generation for a thick SiO 2 layer. Defect recovery is demonstrated by annealing, where recovery depends on the annealing temperature as well as the amount of defects generated at the interface. [ABSTRACT FROM AUTHOR]

The dynamics of the neutral atoms in Hall thrusters affects several plasma processes, from ionization to electrons' mobility. In the context of Hall thruster's particle-in-cell (PIC) modeling, the neutrals are often treated kinetically, similar to the plasma species, and their interactions with themselves and the ions are resolved using the direct-simulation Monte–Carlo (DSMC) algorithm. However, the DSMC approach is computationally resource demanding. Therefore, modeling the neutrals as a 1D fluid has been also pursued in simulations that do not involve the radial coordinate and, hence, do not resolve the neutrals' radial expansion. In this article, we present an extensive study on the sensitivity of the PIC simulations of Hall thruster discharge to the model used for the neutral dynamics. We carried out 1D axial PIC simulations with various fluid and kinetic models of the neutrals as well as self-consistent quasi-2D axial-azimuthal simulations with different neutrals' fluid descriptions. Our results show that the predictions of the simulations in either 1D or 2D configurations are highly sensitive to the neutrals' model, and that different treatments of the neutrals change the spatiotemporal evolution of the discharge. Moreover, we observed that considering the ion-neutral collisions causes a significant variation in the neutral temperature, thus requiring that the neutrals' energy equation to be included as well in their fluid system of equations. Finally, the self-consistent axial-azimuthal simulations highlighted that a neutrals' model based on the continuity conservation equation only is not an appropriate choice and leads to physically unexpected high-frequency global discharge oscillations. [ABSTRACT FROM AUTHOR]

In recent decades, interest in simulation modeling of plasma processing under atmospheric pressure has been growing because of its appealing advantages across various domains. These advantages encompass the provision of diverse data types for evaluating processing states, the capability to predict processing outcomes from current operating conditions, and cost-effectiveness in comparison to experimental methods. This paper endeavors to offer a concise review of the evolution of simulation modeling of atmospheric plasma processing. This review encompasses foundational concepts and methodologies of plasma generation modeling of both thermal and nonthermal plasmas, progressing to discuss the framework and challenges of plasma processing modeling. In addition, a brief overview of contemporary challenges in modeling, such as simplifying complex physics, designing computational domains, and optimizing the balance between computational precision and cost, is provided to foster the advancement of atmospheric plasma processing modeling. Highlights: Classification and simulation modeling methodology of well-known atmospheric pressure plasma generation methods. Features and current challenges of some widely applied plasma processing techniques. Framework of current plasma processing simulation models and clarification of existing challenges and related solutions. [ABSTRACT FROM AUTHOR]

A promising pollution control technology is cold plasma driven chemical processing. The plasma is a pulsed electric gas discharge inside a near atmospheric-pressure-temperature reactor. The system is energized by a continuous stream of very short high-voltage pulses. The exhaust gas to be treated flows through the reactor. The methods applied involve the development of robust cold plasma systems, industrial applications and measuring technologies. Tests of the systems were performed at many industrial sites and involved control of airborne VOC (volatile organic compound) and odor. Electrical, chemical and odor measuring data were collected with state-of-the-art methods. To explain the test data an approximate solution of global reaction kinetics of pulsed plasma chemistry was developed. It involves the Lambert function and, for convenience, a simple approximation of it. The latter shows that the amount of removal, in good approximation, is a function of a single variable. This variable is electric plasma power divided by gas flow divided by input concentration. In the results sections we show that in some cases up to 99% of volatile pollution can be removed at an acceptable energy requirement. In the final sections we look into future efficiency enhancements by implementation of (sub)nanosecond pulsed plasma and solid state high-voltage technology and by integration with catalyst technology. [ABSTRACT FROM AUTHOR]

The effect of an ionic core on the temperature relaxation in dense hot plasma of beryllium is studied using the pseudpotential model by Gericke et al [Phys. Rev. E 2010, 81, 065401(R)]. Employing the screened version of the ion pseudpotential [by Ramazanov et al, Phys. Plasmas 2021, 28 (9), 092702], we computed the quantum transport cross section for the electron‐ion collisions in dense beryllium plasma, where screening is taking into account using the density response function in the long‐wavelength regime. The results for the transport cross section are used to compute a generalised Coulomb logarithm and electron‐ion collision frequency. Utilizing the latter, we show the effect of the ionic core on the temperature relaxation. To understand the role of the ionic core, we compare the results with the data computed considering ions as point‐like charges. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, we address challenges in the biocompatibility of nickel‐based (NiCr) alloys, prevalent in the dental industry, due to toxic metal ion release impacting corrosion resistance and cytotoxicity. Employing magnetron sputtering and cathodic cage plasma nitriding (CCPN), a duplex plasma treatment (DPT) is introduced to the NiCr alloy. The novel approach enhances surface morphology, notably reducing ion leakage compared with untreated samples. Specifically, the CCPN‐TiN‐treated sample significantly improves corrosion resistance and minimizes metal ion leakage. This transformative DPT emerges as a promising solution for surface modification, particularly mitigating toxic ion leaching in aggressive electrolytes. This research demonstrates a major stride in enhancing NiCr alloy biocompatibility, emphasizing the vital role of innovative surface modification techniques for biomedical applications and challenges. [ABSTRACT FROM AUTHOR]

An original plasma chemical process initiated by microwave discharge in a mixture of metal and dielectric powders was applied to prepare specific materials, which consisted of microsized spherical particles of aluminum oxide covered with silver nanoparticles. The prepared materials are highly uniform in shape, size distribution, and composition. Their cytotoxicity was investigated using the human cell lines MCF7, HEK293T, A549, and VA-13 and the bacterial strains E. coli JW5503 (ΔtolC) and E. coli K12. Their cytotoxicity was found not to exceed the cytotoxicity of the starting materials. Thus, the prepared materials can be considered highly promising for catalysis and biotechnology applications. [ABSTRACT FROM AUTHOR]

The fault detection and classification (FDC) modeling proposed in this study is a research approach that is intended to improve the performance of plasma process models by leveraging optical emission spectroscopy (OES) data containing plasma information (PI) and enhancing model interpretability using explainable artificial intelligence (XAI) algorithms. Status variable identification data that included normal and abnormal states of bias power, pressure, SF6 gas flow, and O2 gas flow were collected during a silicon etching process with SF6, O2 gas plasma. Additional variables were derived from the OES data and included additional PI, such as O and F radicals, which were computed using actinometry, and electron temperature and electron density computed using the line ratio method. By building a high-performance FDC model and interpreting its results using XAI algorithms, we propose solutions to the limitations of the FDC model in semiconductor plasma processes. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD) plasma has several applications in different fields. One of these fundamental applications is medical usages, where various methods are employed to improve the plasma treatment process. The combination of different gases is one of the important strategies to improve the performance of plasma in treatment. In this paper, the optimized plasma parameters for one-dimensional radiofrequency discharge produced at low pressures in a helium gas combination is studied. In this research, the optimal combination of H2O and He is identified to attain the highest amount of reactive oxygen species (ROS). Considered mixture are 5, 10, 15 and 20 precent of H2O for one dimensional helium gas discharge. The results show that the parameters of the output plasma are highly dependent on the composition of the input gases. It is found that the greatest concentrations of H+, H+, Hes (excited helium), and OH densities are observed when the H2O percentage was at 10%. Moreover, the density distributions of various species and the temperatures of electrons are numerically calculated during the electrical discharge process. These findings provide useful knowledge on how to optimize plasma parameters for biomedical applications, which may lead to improved treatment results in several therapeutic areas. [ABSTRACT FROM AUTHOR]

The effect of the spatial distribution of electric potential on the separating properties of the plasma mass separator that operates in a configuration with crossed radial electric and longitudinal magnetic fields is studied. The single-particle approximation is used to obtain analytical expressions that connect the electric potential distribution and the angular mass spectrum. A mathematical algorithm is described that allows one to recover the distribution of electric potential from the given shape of the mass spectrum. It is shown that the local inhomogeneity of the electric potential profile allows one to achieve the deposition of mass groups in the diametrically opposite regions of the separator. Data is presented that confirms the possibility of creating experimentally both the positive and the negative local inhomogeneity of the potential. The results of this work can be used to increase the efficiency of the process of plasma mass separation of ions of different elements. [ABSTRACT FROM AUTHOR]

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages. [ABSTRACT FROM AUTHOR]

The active-particle number density is a key parameter for plasma material processing, space propulsion, and plasma-assisted combustion. The traditional actinometry method focuses on measuring the density of the atoms in the ground state, but there is a lack of an effective optical emission spectroscopy method to measure intra-shell excited-state densities. The latter atoms have chemical selectivity and higher energy, and they can easily change the material morphology as well as the ionization and combustion paths. In this work, we present a novel state-resolved actinometry (SRA) method, supported by a krypton line-ratio method for the electron temperature and density, to measure the number densities of nitrogen atoms in the ground and intra-shell excited states. The SRA method is based on a collisional-radiative model, considering the kinetics of atomic nitrogen and krypton including their excited states. The densities measured by our method are compared with those obtained from a dissociative model in a miniature electron cyclotron resonance (ECR) plasma source. Furthermore, the saturation effect, in which the electron density remains constant due to the microwave propagation in an ECR plasma once the power reaches a certain value, is used to verify the electron density measured by the line-ratio method. An ionization balance model is also presented to examine the measured electron temperature. All the values obtained with the different methods are in good agreement with each other, and hence a set of verified rate coefficient data used in our method can be provided. A novel concept, the 'excited-state system', is presented to quickly build an optical diagnostic method based on the analysis of quantum number propensity and selection rules. [ABSTRACT FROM AUTHOR]

Tungsten diboride ceramics with a relative density higher than 90 % without addition of sintering aid can be prepared by boron/carbothermal reduction method combined with spark plasma sintering. Among the raw materials,WO 3 , B 4 C, and C, C content is of vital importance to obtain WB 2 bulk samples with high density and good mechanical properties. In the present work, we investigated the effects of C content in powder synthesis, as well as SPS sintering rate on phase composition, microstructure, and Vickers hardness of WB 2 bulk samples.WB 2 bulk sample with a relative density as high as ∼94 % was obtained with the optimal raw material ratio of WO 3 :B 4 C:C=2:1.075:4.8, which was then increased to ∼96 % with the decrease of sintering rate from 100 °C/min to 50 ℃/min. This represents the highest relative density of the pure WB 2 ceramic publicly reported in the literatures. [ABSTRACT FROM AUTHOR]

MgAgSb alloy has attracted wide attention due to its inherent low thermal conductivity, excellent thermoelectric (TE) properties, and environmental friendliness. Although the TE performance has been deeply investigated for the temperature range over 300–700 K, while cryogenic range has seldom report. In this study, a systematic investigation on cryogenic TE performance of α-MgAgSb has been performed. α-MgAgSb alloy has been synthesized by ordinary ball milling followed spark plasma sintering process and then further regulated by heat treatment. The power factor of MgAgSb alloy after 10 days of heat-treating increased by 230%, which is attributed to the reduction of the impurity phase and the improvement of the crystallinity achieved by the optimization of heat treatment. The total thermal conductivity decreased by 18% to 1.15 W m−1 K−1, and the maximum ZT reached 0.264 at 173 K, which is 300% enhancement to untreated one. The ZTavg reached to 0.45 over 173–298 K, located at the pinnacle among cryogenic TE materials. In addition, the ZTeng value of 0.23 related to the highest device conversion efficiency of 5.2% demonstrates good device potential. This work reveals that the purity and the cryogenic TE properties of α-MgAgSb alloy can be effectively improved by heat-treating, and demonstrates the greatly potential of MgAgSb materials in the field of liquefied natural gas's cold energy recovery. [ABSTRACT FROM AUTHOR]

The spatial and temporal dependencies of the characteristics of the hydrogen plasma flow generated in quasi-stationary plasma accelerator were investigated. The spatiotemporal structure of discharge radiation in the interelectrode gap was studied. The range of changes in the length of the plasma glowing region in the interelectrode gap during the discharge pulse was determined. The region with bright plasma radiation located in the output face of the accelerator electrode system was observed. The presence of impurities and increased electron concentration values were observed in this region. Fluctuations in the radiation intensity of the plasma flow were detected along the entire length of its propagation. The spatial and temporal characteristics of these fluctuations were determined. The electron concentration values near the output face of the electrode system were obtained by measuring the Stark broadening of the H β line. For the first time, the time dependence of the electron concentration of free plasma flow was obtained using two methods simultaneously. The measurements were conducted at a distance, which significantly exceeds the characteristic size of the electrode system and where the influence of interelectrode processes of plasma flow generation is reduced. The first is based on measuring the Stark broadening of H β . As a second method, heterodyne interferometry was used. [ABSTRACT FROM AUTHOR]

The double-cone ignition scheme is a novel approach with the potential to achieve a high gain fusion with a relatively smaller drive laser energy. To optimize the colliding process of the plasma jets formed by the CHCl/CD shells embedded in the gold cones, an x-ray streak camera was used to capture the spontaneous x-ray emission from the CHCl and CD plasma jets. High-density plasma jets with a velocity of 220 ± 25 km/s are observed to collide and stagnate, forming an isochoric plasma with sharp ends. During the head-on colliding process, the self-emission intensity nonlinearly increases because of the rapid increase in the density and temperature of the plasma jets. The CD colliding plasma exhibited stronger self-emission due to its faster implosion process. These experimental findings effectively agree with the two-dimensional fluid simulations. [ABSTRACT FROM AUTHOR]

Electrophoretic deposition (EPD) is a versatile fabrication method allowing the deposition of coatings on substrates with complicated shapes. The main disadvantage of this method, especially in relation to bio applications, lies in hazardous stabilisers frequently used to optimise suspension parameters. This work deals with the plasma treatment of hydroxyapatite (HA) powder for stabilising the suspension without any additives. This approach was already successfully used for alumina powder. EPD of untreated and plasma treated HA powder is performed to compare the final deposits' microstructure. Besides this primary goal, the powder and suspension characteristics are monitored to clarify the effect of plasma treatment on processing and final properties. Moreover, the impact of the rapid sintering approach on deposits' densification is tested. Finally, the suitability of EPD of plasma treated powder for the preparation of homogeneous coating on the orthopaedic screw is manifested. • Electrophoretic deposition of ceramics usually requires physical, environmental, or health hazardous additives. • Atmospheric plasma treatment changes the powder's surface properties. • Homogeneous and uniform hydroxyapatite coatings are obtained without additives. • Rapid pressureless sintering leads to quick and sufficient densification in a fraction of the time. • Orthopaedic screws are uniformly coated. [ABSTRACT FROM AUTHOR]

Electromagnetic fundamental and harmonic emission is ubiquitously observed throughout the heliosphere, and in particular it is commonly associated with the occurrence of type II and III solar radio bursts. Classical analytic calculations for the plasma-emission process, though useful, are limited to idealized situations; a conclusive numerical verification of this theory is still lacking, with earlier studies often providing contradicting results on e.g. the precise parameter space in which fundamental and harmonic emission can be produced. To accurately capture the chain of mechanisms underlying plasma emission – from precursor plasma processes to the generation of electromagnetic waves over long times – we perform large scale, first-principles simulations of beam–plasma instabilities. By employing a very large number of computational particles we achieve very low numerical noise, and explore (with an array of simulations) a wide parameter space determined by the beam–plasma density ratio and the ion-to-electron temperature ratio. In particular, we observe direct evidence of both fundamental and harmonic plasma emission when the beam-to-background density ratio ≤0.005 (with beam-to-background energy ratio ∼0.5), tightly constraining this threshold. We observe that, asymptotically, in this regime |$\sim 0.1~{{\ \rm per\ cent}}$| of the initial beam energy is converted into harmonic emission, and |$\sim 0.001~{{\ \rm per\ cent}}$| into fundamental emission. In contrast with previous studies, we also find that this emission is independent of the ion-to-electron temperature ratio. In addition, we report the direct detection of third-harmonic emission in all of our simulations, at power levels compatible with observations. Our findings have important consequences for understanding the viable conditions leading to plasma emission in space systems, and for the interpretation of observed electromagnetic signals throughout the heliosphere. [ABSTRACT FROM AUTHOR]

On 2021 September 28, a C1.6 class flare occurred in active region NOAA 12871, located approximately at 27°S and 51°W on the solar disk with respect to Earth's point of view. This event was followed by a partial halo coronal mass ejection (CME) that caused the deflection of preexisting coronal streamer structures, as observed in visible-light coronagraphic images. An associated type II radio burst was also detected by both space- and ground-based instruments, indicating the presence of a coronal shock propagating into interplanetary space. By using H i Ly α (121.6 nm) observations from the Metis coronagraph on board the Solar Orbiter mission, we demonstrate for the first time the capability of UV imaging to provide, via a Doppler dimming technique, an upper limit estimate of the evolution of the 2D proton kinetic temperature in the CME-driven shock sheath as it passes through the field of view of the instrument. Our results suggest that over the 22 minutes of observations, the shock propagated with a speed decreasing from about 740 ± 110 km s−1 to 400 ± 60 km s−1. At the same time, the postshock proton temperatures peaked at latitudes around the shock nose and decreased with time from about 6.8 ± 1.01 MK to 3.1 ± 0.47 MK. The application of the Rankine–Hugoniot jump conditions demonstrates that these temperatures are higher by a factor of about 2–5 than those expected from simple adiabatic compression, implying that significant shock heating is still going on at these distances. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) centers in diamond are a promising platform for nanoscale NMR sensing. Despite significant progress toward using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. Such sensing requires that target molecules are immobilized within nanometers of NV centers with long spin coherence. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C--H bonds on single-crystal diamond surfaces under ambient conditions using visible light, forming C--F, C--Cl, C--S, and C--N bonds at the surface. This method is compatible with NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof-of-principle demonstration, we use shallow ensembles of NV centers to detect nuclear spins from surface-bound functional groups. Our approach to surface functionalization opens the door to deploying NV centers as a tool for chemical sensing and single-molecule spectroscopy. [ABSTRACT FROM AUTHOR]

Particle contamination due to plasma processing motivates the design of a method of electrically lifting particles in a time interval after a plasma's power is turned off. Small solid dust particles have electric charges that are not frozen until a late stage of the plasma afterglow. Beyond that time, before they fall to a surface below and cause defects, particles can be lifted in a controlled manner by applying an appropriate direct-current (DC) electric field, as we demonstrate experimentally. A few milliseconds after an argon plasma's capacitively coupled radio-frequency power is switched off, a vertical DC electric field is applied. Thereafter, video imaging shows that the falling of the particles is slowed or stopped altogether, depending on the magnitude of the upward electric force. [ABSTRACT FROM AUTHOR]

During reentry, the high temperatures experienced by near-space hypersonic vehicles result in surface ablation, generating ablative particles. These particles become part of a plasma, commonly referred to as a "dusty plasma sheath" in radar remote sensing. The dusty plasma model, integral in radar studies, involves extensive charge and dynamic interactions among dust particles. Previous derivations assumed that the dust particle radius significantly surpassed the Debye radius, leading to the neglect of dust radius effects. This study, however, explores scenarios where the dust particle radius is not markedly smaller than the Debye radius, thereby deducing the charging process of dusty plasma. The derived equations encompass the Debye radius, charging process, surface potential, and charging frequency, particularly considering larger dust particle radii. Comparative analysis of the dusty plasma model, both before and after modification, reveals improvements when dust particles approach or exceed the Debye length. In essence, our study provides essential equations for understanding dusty plasma under realistic conditions, offering potential advancements in predicting electromagnetic properties and behaviors, especially in scenarios where dust particles closely align with or surpass the Debye radius. [ABSTRACT FROM AUTHOR]

The intermittent discharge that filament only discharges once in a cycle rather than once every half-cycle is observed in all the three substructures of the (bright spots)–(dark spots)-halo stripe pattern (BDHSP) in dielectric barrier discharge. The discharge characteristics are investigated by a high-speed video camera, an intensified charge-coupled device camera, and two photomultiplier tubes. It is found that the direction of the stripe choose to form in BDHSP is determined by the direction in which the surface discharge is stronger in the square pattern. The spatiotemporal dynamics results of BDHSP suggest that bright spot (B) discharges in this half-cycle, and the dark spot (D) and the halo (H) discharge in the next half-cycle of the applied voltage, which is intermittent discharge. Combined with the analysis in the electric field simulation, it can be concluded that the intermittent discharge is the result of the mutual influence between the directional selective surface discharge induced by bright spots and dark spots. Overall, the BDHSP is formed by the self-organization of the wall charge under the interaction between the plasma physical processes and the spatial distribution. The discovery of the intermittent discharge provides insight and enlightenment for the study of plasma physics. [ABSTRACT FROM AUTHOR]

The effects of magnetic field intensity on the properties of the plasma discharge and on the underlying phenomena are studied for different propellants' ion mass. The plasma setup represents a 2D radial–azimuthal configuration with perpendicular electric and magnetic fields. The electric field is along the axial direction, and the magnetic field is along the radial direction. The magnetic field intensity is changed from 5 to 30 mT, with 5 mT increments. The studied propellant gases are xenon, krypton, and argon. The simulations are carried out using a reduced-order particle-in-cell code. It is shown that, for all the propellants, the change in the magnetic field intensity yields two distinct plasma regimes, where either the modified two-stream instability (MTSI) or the electron cyclotron drift instability (ECDI) are dominant. A third plasma regime is also observed for cases with moderate values of the magnetic field (15 and 20 mT), where the ECDI and the MTSI co-exist with comparable amplitudes. This described variation of plasma regime becomes clearly reflected in the radial distribution of the axial electron current density and the electron temperature anisotropy. At the relatively low-magnetic-field intensities (5 and 10 mT), the MTSI is mitigated. At relatively high magnitudes of the magnetic field (25 and 30 mT), the MTSI becomes strongly present, a long-wavelength wave mode develops, and the ECDI becomes suppressed. An exception to this latter observation was noticed for xenon, for which the ECDI was observed to be detectable with a notable strength up to the magnetic field value of 25 mT. [ABSTRACT FROM AUTHOR]

We present an extensive study into the influences that the magnitudes of the applied electric (E) and magnetic (B) fields have on collisionless plasma discharges of xenon, krypton, and argon. The studies are performed in a two-dimensional radial-azimuthal configuration with perpendicular fields' orientation. The dependency of the dynamics of E × B discharges on the strength of electromagnetic field and ion mass has not yet been studied in a manner that distinguishes the role of individual factors. This has been, in part, due to significant computational cost of conventional high-fidelity particle-in-cell (PIC) codes that do not allow for practical extensive simulations over broad parameter spaces. Also, the experimental efforts have been limited by aspects such as the measurements' spatiotemporal resolution and the inability to independently control individual discharge parameters. The computationally efficient reduced-order PIC scheme allows to numerically cast light on the parametric variations of various aspects of the physics of E × B discharges, such as high-resolution spatial-temporal mappings of plasma instabilities. In this part I, we focus on the effects of the E -field intensity. We demonstrate that, across all the studied propellants, the E -field intensity determines two distinct plasma regimes characterized by different dominant instability modes. At relatively low E -field magnitudes, the modified two stream instability (MTSI) is dominant. At relatively high E -field magnitudes, the MTSI is mitigated, and the electron cyclotron drift instability becomes dominant. Consequent to the change in the plasma regime, the radial distribution of the axial electron current density and the electron temperature anisotropy vary. [ABSTRACT FROM AUTHOR]

Cold sintering process (CSP) developed recently has attracted much attention due to the ultralow sintering temperatures and high efficiencies with the assist of transient liquid phase (TLP). Based on CSP, we have further established a protocol for low‐temperature sintering processes by combining TLP with other sintering technologies, including hybrid sintering process with microwave and TLP (MW‐TLP), and hybrid sintering process with spark plasma sintering and TLP (SPS‐TLP). Three typical electro‐ceramics (TiO2, CaWO4, and ZnO) are selected, which are highly densified (>97%) with excellent electrical properties at reduced sintering temperatures, applied pressures or holding times, demonstrating the feasibility of MW‐TLP and SPS‐TLP in fabricating electro‐ceramics. Especially, the Q × f value of TiO2 ceramics (38,020 GHz) prepared by MW‐TLP at 1000°C is 46.2% and 23.4% higher than that of microwave and spark plasma sintered samples, respectively, and comparable to traditional thermal sintered (TTS) samples at 1300–1400°C. The dielectric properties of MW‐TLP CaWO4 ceramics sintered at 900°C for 2 h are comparable to TTS samples sintered at 1000–1300°C for 2–5 h. ZnO ceramics can be highly densified (∼98%) by SPS‐TLP with mild sintering conditions (200–300°C and 3.8–50 MPa) compared to SPS (>500°C) and CSP (>100 MPa). The frameworks of fundamental mechanisms are outlined together with the experimental data. It is expected that this work will provide promising sintering methods to fabricate electro‐ceramics and offer inspirations on sintering combinations to develop low‐temperature sintering processes with high efficiencies. [ABSTRACT FROM AUTHOR]

Micro-cathode arc thrusters (μCATs) are space propulsion options suitable for microspacecraft, and have recently attracted much attention because of their low electrical power requirements and simple, compact propellant systems. The plasma ionization process, however, is not currently well understood. In this study, a μCAT prototype was designed with the use of different specific materials for each component, enabling the study of the ionization process from the emissive light of excited and ionized states from different elements. ICCD emission spectroscopy and scanning monochromator measurements are conducted inside the electrode channel of a μCAT with a coaxial configuration. The excited state atomic spectral results and ionization state spectral results give us a comprehensive understanding of the behavior of neutral particles and ions during the discharge process of the μCAT. The ionization sequence follows in the order of C+, Al+, Ti+, Cu+, and Ti2+. From the duration of the spectral lines, C I has the shortest duration (16.9 μs), which shows that the ablation of the conductive film is mainly concentrated during the first half of the discharge, while anode and cathode ionization occur over the entire discharge duration. Additionally, Al+ ionization is observed during the discharge process, showing that part of the discharge energy is expended in ionizing the thruster outer shell, resulting in efficiency loss. An ionization ratio of k is proposed in this work to represent the relative ionization of the conductive film and cathode material, aiding us in determining the optimal operation conditions for lifetime extension. • A μCAT prototype with different materials of each component is designed. • ICCD emission spectroscopy and scanning monochromator measurements are conducted inside a μCAT. • The impact of discharge energy and magnetic field strength on the ionization process is investigated. • An ionization ratio k is proposed to represent the relative ionization of the conductive film and cathode material. [ABSTRACT FROM AUTHOR]

Plasma, owing to its reactivity and nonequilibrium properties, is a unique field commonly used in material processing. In recent years, plasma processing with a liquid phase has attracted considerable attention owing to its important advantages, such as high electron density and the availability of a wide variety of reactions in solutions. However, plasma‐in‐liquid material synthesis is occasionally difficult to control and guidelines are lacking. In this study, we investigated whether the hard‐soft acid–base (HSAB) principle, which is often applied in material synthesis, is applicable to the plasma‐in‐liquid process and demonstrated that organic solvent‐derived substances produced by plasma‐in‐liquid processing reacted with solutes according to the HSAB principle. These results suggest that the HSAB principle may apply to plasma‐in‐liquid processing. [ABSTRACT FROM AUTHOR]

In this work, a system of kinetic equations is constructed to study the processes in a three-component plasma. It is an analogue of the Krook model, which is widely used in the dynamics of rarefied gases. The model is supposed to be used to study the processes in the channels of rocket electric thrusters. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of helium (He) plasma irradiation and thermal treatment on the morphology, the surface characteristics, and the photoelectrochemical performance of bulk iron (Fe) sheets. After processing, all samples consisted mainly of an α -Fe 2 O 3 surface. Helium plasma irradiation resulted in a cathodic shift in the onset potential of the photocurrent from 1.16 V RHE (no pretreatment) to 0.57 V RHE (plasma exposure at 660 ° C), where V RHE represents the potential versus reversible hydrogen electrode (RHE). An increase in the surface roughness and a smaller amount of hydroxyl or oxygen vacancies at the surface after photoelectrochemical measurement are related to the decrease of the onset potential. The results show that He plasma irradiation does not only modify the surface morphology, but also affects the functional properties of the materials. • The photoelectrochemical performance of α -Fe 2 O 3 is investigated. • Helium plasma irradiation resulted in a cathodic shift in the onset potential. • The onset potential shifted from 1.16 to 0.57 V RHE. • A small amount of hydroxyl or oxygen vacancies are likely to be the most influential. [ABSTRACT FROM AUTHOR]

Low-pressure plasma processes are routinely used to grow, functionalize or etch materials, and thanks to some of its unique attributes, plasma has become a major player for some applications such as microelectronics. Plasma processes are however still at a research level when it comes to the synthesis and functionalization of nanoparticles. Yet plasma processes can offer a particularly suitable solution to produce nanoparticles having very peculiar features since they enable to: (i) reach particle with a variety of chemical compositions, (ii) tune the size and density of the particle cloud by acting on the transport dynamics of neutral or charged particles through a convenient setting of the thermal gradients or the electric field topology in the reactor chamber and (iii) manipulate nanoparticles and deposit them directly onto a substrate, or codeposit them along with a continuous film to produce nanocomposites or (iv) use them as a template to produce 1D materials. In this article, we present an experimental investigation of nanoparticles synthesis and dynamics in low-pressure microwave plasmas by combining time-resolved and in-situ laser extinction and scattering diagnostics, QCL absorption spectroscopy, mass spectrometry, optical emission spectroscopy and SEM along with a particle transport model. We showed for the first time the thermophoresis-driven dynamic of particle cloud in electrodless microwave plasmas. We showed that this effect is linked to particular fluctuations in the plasma composition and results in the formation of a void region in the bulk of the plasma surrounded by a particle cloud in the peripherical post-discharge. We also reveals and analyze the kinetics of precursor dissociation and molecular growth that result in the observed nanoparticle nucleation. [ABSTRACT FROM AUTHOR]

Low-pressure plasma processes are routinely used to grow, functionalize or etch materials, and thanks to some of its unique attributes, plasma has become a major player for some applications such as microelectronics. Plasma processes are however still at a research level when it comes to the synthesis and functionalization of nanoparticles. Yet plasma processes can offer a particularly suitable solution to produce nanoparticles having very peculiar features since they enable to: (i) reach particle with a variety of chemical compositions, (ii) tune the size and density of the particle cloud by acting on the transport dynamics of neutral or charged particles through a convenient setting of the thermal gradients or the electric field topology in the reactor chamber and (iii) manipulate nanoparticles and deposit them directly onto a substrate, or codeposit them along with a continuous film to produce nanocomposites or (iv) use them as a template to produce 1D materials. In this article, we present an experimental investigation of nanoparticles synthesis and dynamics in low-pressure microwave plasmas by combining time-resolved and in-situ laser extinction and scattering diagnostics, QCL absorption spectroscopy, mass spectrometry, optical emission spectroscopy and SEM along with a particle transport model. We showed for the first time the thermophoresis-driven dynamic of particle cloud in electrodless microwave plasmas. We showed that this effect is linked to particular fluctuations in the plasma composition and results in the formation of a void region in the bulk of the plasma surrounded by a particle cloud in the peripherical post-discharge. We also reveals and analyze the kinetics of precursor dissociation and molecular growth that result in the observed nanoparticle nucleation. [ABSTRACT FROM AUTHOR]

The excellent mechanical stability and electrochemical reactivity of activated carbon nanostructures has resulted in their wide use as an electrode material for the energy storage device. The method of activation generally uses a solution process using a strong acid or a strong base, which makes it difficult to control the degree of activation, and has limitations in using harmful chemicals. In this work, a method of fabricating activated carbon nanotubes in which heterogeneous element-based functional groups are finely controlled in a carbon structure using a vacuum plasma process is proposed. The type of functional group introduced into the carbon structure was adjusted by varying the type of plasma gas (O2, NH3, or C4F8), while the amount of functional group was changed through the exposure power. Carbon nanotubes with oxygen-related functional groups showed a large active surface area (141.66 m2 g−1) and volume of micropores than in the other cases (NH3 and C4F8), to promote the rapid adsorption/desorption of ions, thereby offering excellent energy storage performance. The carbon nanotube into which oxygen is introduced was applied as an electrode material for a symmetrical two-electrode supercapacitor device to have a specific capacitance of 284 F g−1, and excellent rate capability and cycle stability of 95.1% after 5000 cycles. Activated carbon nanotubes in which the degree and type of the functional group is finely adjusted by the vacuum plasma process exhibit high energy storage capacity. [ABSTRACT FROM AUTHOR]

The deposition of multilayer coating of NiTi is carried out by a thermal plasma spraying process on a stainless steel substrate. The deposition of melted NiTi particles creates an adhesion layer on the substrate with the subsequent formation of multilayer coating with a certain thickness. Six layers of coating are created to achieve a certain thickness in terms of the sprayed sample. This paper aims to investigate multilayer NiTi coatings created through a thermal plasma process. The key variable feed rate was considered, as well as its effect on the microstructure characteristics. The shape memory effect associated with the coating properties was analyzed in detail. The variable feed rate was considered one of the most important parameters in the thermal plasma spraying process due to its ability to control the quality and compactness of the coating structure. The coatings were characterized by examining their microstructure, thermal, chemical, and microhardness. The indent marks were made/realized along the cross-section surface for the analysis of crack propagation resistance and wear properties. The coating's surface did not display segmentation crack lines. Nevertheless, the cross-sectional surfaces showed evidence of crack lines. There were eutectic zones of the interlamellar structure observed in the structure of the coating. The plasma-sprayed samples from thermo-mechanical analysis of the hysteresis curve provide strong confirmation of the shape memory effect. [ABSTRACT FROM AUTHOR]

The process of numerical thermalization in particle-in-cell (PIC) simulations has been studied extensively. It is analogous to Coulomb collisions in real plasmas, causing particle velocity distributions (VDFs) to evolve toward a Maxwellian as macroparticles experience polarization drag and resonantly interact with the fluctuation spectrum. This paper presents a practical tutorial on the effects of numerical thermalization in 2D PIC applications. Scenarios of interest include simulations, which must be run for many thousands of plasma periods and contain a population of cold electrons that leave the simulation space very slowly. This is particularly relevant to many low-temperature plasma discharges and materials processing applications. We present numerical drag and diffusion coefficients and their associated timescales for a variety of grid resolutions, discussing the circumstances under which the electron VDF is modified by numerical thermalization. Though the effects described here have been known for many decades, direct comparison of analytically derived, velocity-dependent numerical relaxation timescales to those of other relevant processes has not often been applied in practice due to complications that arise in calculating thermalization rates in 1D simulations. Using these comparisons, we estimate the impact of numerical thermalization in several examples of low-temperature plasma applications including capacitively coupled plasma discharges, inductively coupled plasma discharges, beam plasmas, and hollow cathode discharges. Finally, we discuss possible strategies for mitigating numerical relaxation effects in 2D PIC simulations. [ABSTRACT FROM AUTHOR]

In recent years, plasma biomedicine has developed into a new interdisciplinary subject. The interaction between plasma and organisms involves three aspects: "gas–liquid–living organisms." Molecular dynamics (MD) simulation can simulate the interaction process between plasma and biological tissue with high temporal and spatial resolution. This article reviews the research on plasma biomedicine based on MD simulation and systematically summarizes the progress of MD simulation research on the interaction between plasma and water layer, cell membrane, intracellular substances, extracellular environment, and viruses. These simulations offer a unique opportunity to gain insights into the microscopic mechanisms of these interactions. This article also further looks forward to the opportunities and challenges of MD simulation research. [ABSTRACT FROM AUTHOR]

We present an experimental realization of virtual critical coupling in microwave, i.e., virtual perfect absorption of an incident wave by a resonant cavity, through transient time modulation of its amplitude. The design of a waveform matched to the ignition process of a plasma, characterized in a simplified way by two operating modes over time (plasma off/plasma on), motivates this first step in practical realization of virtual critical coupling in microwaves. We propose a time domain method for extracting necessary parameters for realization of virtual critical coupling, especially the complex frequency called zero of the S-matrix. To this end, we start from the experimental characterization of a single-mode and single-access microwave cavity including metal protrusions for future plasma ignition. Then, the method relies on the analysis of harmonic response of the overcoupled cavity during three time periods: the transient under excitation, the steady state under excitation, and the transient after excitation cutoff. Finally, an experimental demonstration of virtual critical coupling is performed. [ABSTRACT FROM AUTHOR]

Reflectron-type time-of-flight mass spectrometry was applied to the time-resolved component analysis of deep oscillation magnetron sputtering (DOMS), which has been developed as a technique of modulated pulsed magnetron sputtering. In the present study, the DOMS of a Ti target was performed under an Ar gas atmosphere by using a DOMS-specific control waveform consisting of 25 current and/or power pulses. The time evolution of the formation of ionized species (Ar+, Ar2+, Ti+, and Ti2+) after the application of the first discharge pulse was observed at the position corresponding to the deposition region. This study revealed that the plasma build-up process from non-metallic plasma to metallic plasma takes approximately two micropulses (around 100 μs from ignition) in DOMS discharge. In addition, we have found the possibility of studying sputtering processes, such as the rarefaction, and refilling processes of Ar as a function of pulse number through DOMS research. [ABSTRACT FROM AUTHOR]

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al–Ti–Cu–Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al–Ti–Cu–Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8–5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture. [ABSTRACT FROM AUTHOR]

Ethylenediamine is industrially used as an intermediate for the fabrication of many products. The development of new methodologies for synthesis compatible with the environment and sustainability, such as cold plasma processes, implicates reactions induced by nonthermal electrons. In this contribution, we study the interaction of low-energy (<10 eV) electrons with ethylenediamine. We show that electrons induce the fragmentation of the molecule into various anion fragments and associated neutral counterparts via dissociative electron attachment. The fragmentation mechanisms and energetics are discussed in the frame of DFT calculations. The fragmentation processes are quantified by the estimation of the cross sections and the branching ratios for competitive accessible dissociation routes. [ABSTRACT FROM AUTHOR]

The paper proposes the reduction of the surface roughness and improvement of its strength properties for metallic materials and products fabricated by additive manufacturing. The proposed technique implies the creation of a 2 µm thick metal film on the doped surface layer by the vacuum arc deposition and pulsed electron-beam processing of the film/substrate system. The proposed technique of the film (Zr)/substrate (VT6) system processing provides a 25 times reduction of the surface roughness and improves its strength properties by 1.5 times. [ABSTRACT FROM AUTHOR]

A thermodynamic analysis was performed using the universal TERRA program, which made it possible to determine the optimal parameters of the process of plasma ignition and stabilization of solid fuel combustion. Kinetic modeling of the process of plasma ignition and stabilization of solid fuel combustion was carried out using the PlasmaKinTherm program. Changes in temperatures, rates, and concentrations of high-temperature binary fuel components along the length of the plasma–fuel system were revealed. In experiments on plasma ignition of an air mixture of Ékibastuz coal, a stable torch was obtained, and its temperature, composition, and degree of carbon gasification were determined. A comparison of the experimental and calculated data showed their satisfactory agreement. [ABSTRACT FROM AUTHOR]