DC Plasma Research Articles

Lithium Demand and Cyclability Trade‐Off in Conductive Nanostructure Scaffolds in Terms of Different Tortuosity Parameters

AbstractThrough alteration of the polarity of DC plasma during the growth of carbon nanotubes in a PECVD reactor, significantly different morphologies of such species have been achieved. By using this approach, for the first time, both Half‐aligned and Entangled structures were synthesized, along with Full‐aligned carbon nanotubes, introducing three binder‐free electrodes with various levels of tortuosity. The crucial parameter and influential effect of tortuosity in these three‐dimensional nanostructure scaffolds for application in lithium‐ion batteries were investigated. Previous research findings suggested that increasing the tortuosity of the conductive scaffolds leads to preferential accumulation of lithium at the top surface and causes the loss of capacity in subsequent charge‐discharge cycles. Our finding reveals that there exists a trade‐off between lithium‐demand, capacity, and preferential accumulation of lithium at the top surface. Among the presented scaffolds, the Half‐aligned MWCNTs was able to maintain a high capacity of 876.9 mAh/g over more than 300 cycles, and demonstrate capacity improvement during this period and excellent rate capability, even at a rate of 5 C. This capacity is almost three times that can be achieved with graphite, showcasing promising and outstanding results for carbon nanotubes.

Self-consistent modelling of radio frequency sheath in 3D with realistic ICRF antennas

Abstract Ion Cyclotron Resonant Frequency (ICRF) induced impurity production has raised many concerns since ITER proposed to change the first wall material from beryllium to tungsten. Enhanced DC plasma potential (VDC) due to RF sheath rectification is well known as one of the most important mechanisms behind the RF induced impurities. Our previous work (L. Lu et.al, Plasma Phys. Control. Fusion 60 (2018) 035003) considered the impact of both the slow wave and the fast wave on the RF sheath rectification in a 2D geometry. It can barely recover the double-hump structure of the VDC poloidal distribution observed in various machines when only the slow wave is modelled using the multi-2D approach which intrinsically assumes the poloidal wavenumber kz is zero. The fast wave on the other hand is found to be more sensitive to a finite kz and may need to be tackled in 3D. This work reports our recent progress on the 3D RF sheath modelling. In this new code, the latest RF sheath boundary conditions (J. R. Myra, J. Plasma Phys. 87 (2021) 905870504) and the realistic 3D ICRF antennas are implemented. Compared to the 2D results, the 3D code could well recover the double-hump poloidal distribution of VDC even with the fast wave included, which confirms our speculation on the necessity of treating the fast wave in 3D. While the double-hump pattern is robust in the simulation, the amplitude of VDC is found to be affected by the magnetic tilt angle and the antenna geometry. This emphasizes the importance of adopting a realistic antenna geometry in the RF sheath modelling. The double-hump VDC poloidal structure breaks as the magnetic tilt angle increases. This is explained by the gyrotropic property of the cold plasma dielectric tensor. The spatial proximity effect we identified in the previous 2D simulations is still valid in 3D. Finally, simulation shows the slow wave dominates the RF sheath excitation in the private SOL, while the fast wave gradually takes over when moving to the far SOL region. This code could be a new tool to provide numerical support for ITER impurity assessment and ICRF antenna design.

Synthesizing, characterizing, and cold plasma treating of Cr2O3/CuO nanomaterials doped PMMA/PEO for flexible optoelectronic applications

Polymeric nanocomposites are attracting significant attention due to their ability to facilitate innovative uses. This work investigated the possibility of improving performance by examining the impact of dispersing copper oxide (CuO) and chromium (III) oxide (Cr2O3) nanoparticles in a blend of poly (methyl methacrylate) and polyethylene oxide (PEO) on several properties. UV–visible and photoluminescence spectroscopies were used for optical properties, and FE-SEM was used for surface morphology analysis. The results showed that as the CuO–Cr2O3 percentage increased, the extinction coefficient increased, and indirect band gaps decreased. The photoluminescence properties showed two distinct peaks (dual emission). We measured the AC electrical properties with frequencies ranging from 100 Hz to 5 MHz. The composite's AC conductivity and dielectric loss increased significantly at high frequencies (higher than 2 MHz). The dielectric constant is nearly frequency-independent and increases as the concentration of nanoparticles increases. We used a DC plasma sputtering facility to treat the nanocomposites with argon plasma at a pressure of 0.12 mBar for 7 min. We analyzed the films' properties before and after plasma treatment, observing a significant impact on nanocomposite-incorporated nanoparticles. After plasma treatment, the band gap decreased from 5.05 eV to 4.8 eV for the lowest concentration of CuO + Cr2O3 (1.5 wt%) and from 3.55 eV to 2.47 eV for the highest concentration of CuO + Cr2O3 (6 wt%). The changes ranged from 0.25 to 1.08 eV. The films possess features that render them suitable for high-frequency optoelectronic devices as well as optical applications such as emission filters and UV shielding.

Basic model for calculating the macroscopic temperature of plasma plume and comparison with electron excitation temperature by optical spectroscopy method for non-transferred DC plasma torch

Basic model for calculating the macroscopic temperature of plasma plume and comparison with electron excitation temperature by optical spectroscopy method for non-transferred DC plasma torch

Determination of the electron energy distribution function in weakly ionized plasma by means of a Langmuir probe and numerical methods

Numerical methods are used to determine the Electron Energy Distribution Function (EEDF) from I(V) probe characteristics, which are measured using a cylindrical Langmuir probe in the case of weakly ionized plasmas. This task becomes difficult when measurement is complicated by the presence of an external magnetic field or in high pressure plasma because of collision between electrons and heavy particles within the sheath formed around the probe tip. In this case, the electron current must be calculated using the Swift law instead of the Langmuir law. The numerical methods consist of determining the derivative functions of the I(V) probe characteristics in the case of a noisy signal and correcting the EEDF taking into account the electron diffusion coefficient within the sheath formed around the probe collector. Algorithms are given to detail the methods step by step, which can be used to write homemade codes. The methods are tested in the case of different plasma reactors described in the literature, such as microwave plasma and rf (radio-frequency) and dc (direct current) plasma reactors working at different pressures with or without magnetic field. The results show the effect of pressure or magnetic field on the I(V) probe characteristics because of the change in the electron diffusion coefficient.

Evolution of hard carbon layers on Ti-45Al-2Nb-2Mn-1B by plasma enhanced chemical vapor deposition of hydrocarbons and hydrogen

Extension of pulsed DC plasma enhanced CVD (PECVD) of carbon from hydrocarbons resulted in thick hard carbon layers on Ti-45Al-2Nb-2Mn-1B. PECVD for less than 2 h led to the formation of surface interlayers of TiC and Ti2AlC compounds under the hard carbon layer. After 5 h until 20 h, the formation of carbons layers surpassed the growth of TiC and Ti2AlC layers and resulted in a thicker hard carbon layer. This can be explained with the deceleration of carbon diffusion into the base alloy that resulted in the accumulation of a hard structure of carbon on the outer surface. The thickness of the hard carbon layers reached up to ∼40 μm, which were revealed using SEM microcopy. The hardness on the outer surface of hard carbon layer was around 600–1500 HV0.5 (5.88–14.71 GPa). EDX analysis across the surface layers showed ∼50–100 at. % carbon on the outermost layers. Raman spectroscopy of carbon layers showed sp3 (D) and sp2 (G) peaks of carbon at ∼1330 and ∼1560 cm−1 and peaks of TiC at ∼200 cm−1 peaks.

Effects of Gas Components on the Jet Characteristics of a DC Plasma Torch by Using Orthogonal Test Method

Effects of Gas Components on the Jet Characteristics of a DC Plasma Torch by Using Orthogonal Test Method

A reactor for generating DC plasma inside a liquid

A reactor for generating DC plasma inside a liquid

Comparison between the optical properties of TiO2 and ZnO thin films deposited using Dc plasma sputtering and pulsed laser deposition

Comparison between the optical properties of TiO2 and ZnO thin films deposited using Dc plasma sputtering and pulsed laser deposition

Novel high-efficiency plasma nitriding process utilizing a high power impulse magnetron sputtering discharge

Lifetime and biocompatibility of orthopedic implants are crucial in meeting the new challenges brought about by the fall in the patient age and the aging population. The high-load surfaces in contact with the biological environment must display enhanced tribological properties, biocompatibility, and reduced metal ion release in long-term clinical performance. Surface modification techniques such as nitriding can significantly improve the in-service behavior of the medical-grade alloys in current use. We report on a novel approach for nitriding of CoCrMo alloys using high power impulse magnetron sputtering (HIPIMS) discharge. The new nitriding process has been successfully carried out at the National HIPIMS Technology Centre at Sheffield Hallam University, UK, in an industrial size Hauzer 1000-4 system enabled with HIPIMS technology. While the nitriding ion flux is controlled by the HIPIMS magnetron plasma source, the ion energy can be independently set via the substrate bias. Implementing the HIPIMS source allows reducing the operational pressure by one order of magnitude compared to conventional dc plasma nitriding (DCPN). Plasma analyses have identified significantly enhanced production of ions of molecular nitrogen (N2+), atomic nitrogen (N+), and N2H+ radicals in the HIPIMS discharge compared to DCPN. Because of the low pressure of operation of the HIPIMS process, the energy of ions is similar to the bias voltage, whereas the high pressures used in DCPN cause severe losses in ion energy due to scattering collisions within the sheath. The high flux and high ion energy are primarily responsible for achieving a fourfold increase in process productivity as compared to state-of-the-art plasma nitriding processes. The nitrided surface layers exhibit excellent mechanical and tribological properties, which bring about significant improvements in hardness, fracture toughness, and wear. The protective function of the nitrided layer against corrosion in the aggressive environments of simulated body fluid is remarkably augmented. The barrier properties of the nitrided layer have been demonstrated through a reduction in metal ion release by as much as a factor of 2, 4, and 10 for Co, Cr, and Mo, respectively.

Review of DC and AC Arc Plasma at High Pressures Above Atmospheric Pressure

Review of DC and AC Arc Plasma at High Pressures Above Atmospheric Pressure

Experimental quantification of ion flux reduction at the sheath edge due to ion–neutral collisions in low temperature plasmas

Reduction of the ion flux at the sheath edge due to ion–neutral collisions in low temperature DC plasmas is experimentally quantified for low to intermediate neutral gas pressures (<102 mTorr). The reduction factor is defined as a ratio of the ion flux at the sheath edge in a collisional plasma to that in a collisionless limit in this work. Its quantification as a function of the collisionality with a Langmuir probe has been hindered since the measured data contain two intermingled effects, namely, the flux reduction and the sheath expansion, which are difficult to isolate one from the other. The sheath expansion effect with and without the flux reduction effect are analyzed, and by comparing the two, the reduction factor as a function of the collisionality has been estimated with Langmuir probe data from approximately 1000 systematic scans of the plasma conditions. Neutral gas pressures ranging from 0.2–30.0 mTorr for Ar and 1.0–65.0 mTorr for He discharges are generated in a multidipole chamber with hot filaments. The estimated reduction factors are found to agree with the results from the particle-in-cell simulations for He discharges [Beving et al., Plasma Sources Sci. Technol. 31, 084009 (2022)]. The estimated reduction factors for Ar discharges are larger than those for He discharges, and the dependence of the reduction factor on species is discussed. Reduction of the ion flux at the sheath edge at intermediate gas pressures highlights the importance of taking into account ion–neutral collisions in many plasma applications.

Modelling of thermal plasma-assisted carbon tetrafluoride abatement

This study focuses on the numerical modelling of the decomposition process of carbon tetrafluoride (CF4, Freon R-14), the most stable perfluorinated gas with a significant global warming potential, as experimentally carried out using a thermal argon/steam plasma in a plasma-chemical reactor. The numerical modelling approach incorporates advanced computational fluid dynamics (CFD) techniques and the kinetics of a complex chemical reaction mechanism. A two-dimensional axisymmetric model, incorporating the conservation of mass, momentum, energy and chemical balances, has been developed to simulate the species distribution under the assumption of steady flow, including turbulence effects. In order to compare the species distributions and destruction efficiencies, two chemical reaction mechanism models of different complexity were implemented: a simplified model A with 196 reactions and a model B with 258 reactions. The simulations were performed for plasma generated by steam and argon stabilized DC plasma torch under three operating conditions for arc currents of 120, 150 and 200 A. The destruction and removal efficiency (DRE) of CF4 decomposition at a high feed rate was computed by both models, with an error of less than 6% compared to the experimental data. It can be concluded that both models accurately predict the residual CF4 concentration trends depending on the feed per input torch power. While model A overestimates process efficiency, model B, with a more balanced reaction mechanism, more closely aligns with experimental results. Model B provides an accurate prediction of the DRE and captures trends as a function of input parameters. Importantly and innovatively, the model presented in this study, unlike previous models, allows for the first time the inclusion of both high concentrations and a sufficiently large reaction mechanism for CF4 abatement. This model presents a novel opportunity to perform trend simulations of operating characteristics for the CF4 abatement problem at a quantitative level, allowing experimental design to be evaluated and optimised.

Effect of chamber pressure on the output characteristics of a low-pressure DC plasma torch

This study explores the effects of chamber pressure on the electrical and thermodynamic characteristics of a low-pressure thermal plasma jet. The investigation focuses on current–voltage characteristics, arc voltage fluctuations, plasma jet temperature, electron density, and velocity within the range of 100–500 A arc current, at chamber pressures of 100 Pa, 1 kPa, and 3 kPa. Spectral analysis of the arc voltage reveals the presence of distinct frequencies, including restrike, Helmholtz, and acoustic modes, which exhibit varying behavior under different chamber pressure conditions. Restrike frequency shows an increase with decreasing chamber pressure, while Helmholtz frequency remains unaffected, and the power density of the acoustic frequency diminishes, eventually disappearing from the spectrum. The transition of the plasma jet from a continuum regime to a frozen state with decreasing chamber pressure is observed along with its shock structures. Optical emission spectroscopy is utilized to map the excitation temperature and electron density profile along the jet axis, demonstrating that the jet temperature and density peaks at the compression zone. Furthermore, Mach probe measurements of the plasma jet velocity at different axial locations, under various chamber pressure conditions, illustrate that the plasma jet maintains a supersonic state, regardless of chamber pressure. However, after the formation of a Mach disk, the jet velocity becomes subsonic. The highest velocity is achieved at 100 Pa chamber pressure, reaching Mach 2.9 at 50 mm from the anode exit. This research enhances our understanding of thermal plasma jets under low-pressure conditions, contributing to the advancement of knowledge in their applications across various domains.

Optical roughness calculation for material structural analysis of energy structure applications under dc plasma processes

Surface qualities make aluminium a low-DC plasma interaction candidate. Aluminum for energy system structure building is studied experimentally, with observations obtained. Aluminum is cheap and frequently utilized in aerospace applications. The selection of materials for new applications of thermonuclear fusion energy, such as Tokamak reactor walls and fusion-based spaceship thrust structures, is important to decide in the design phase. In this study, an experimental setup application is created with low DC-type He plasma ions processed on aluminium pellet surfaces. The physical changes of the aluminium pellet material as an example of an energy structure surface are analysed under a scanned array microscope and 3D surface plots to detect optical roughness attributes.

Optical roughness calculation for material structural analysis of energy structure applications under dc plasma processes

Surface qualities make aluminium a low-DC plasma interaction candidate. Aluminum for energy system structure building is studied experimentally, with observations obtained. Aluminum is cheap and frequently utilized in aerospace applications. The selection of materials for new applications of thermonuclear fusion energy, such as Tokamak reactor walls and fusion-based spaceship thrust structures, is important to decide in the design phase. In this study, an experimental setup application is created with low DC-type He plasma ions processed on aluminium pellet surfaces. The physical changes of the aluminium pellet material as an example of an energy structure surface are analysed under a scanned array microscope and 3D surface plots to detect optical roughness attributes.

Decoration of Graphene in Plasma Jets of a DC Plasma Torch for 2D Printing

Decoration of Graphene in Plasma Jets of a DC Plasma Torch for 2D Printing

Discharge voltage’s effect on the optical and structural characteristics of CdS solar cell sputtered by DC plasma technique

Discharge voltage’s effect on the optical and structural characteristics of CdS solar cell sputtered by DC plasma technique

Synthesis of thermally stable carbon nanostructures via ethanol pyrolysis in DC plasma jets

Thermostable graphene and carbon nanotubes (CNTs) obtained by the plasma-chemical method were stable when heated to 1300 K. The peculiarity of the obtained materials is associated with the nature of the precursor (ethanol) containing oxygen. It is shown that the composition of the gas phase and the temperature interval for the formation of gaseous precursors depends on the plasma-forming gas used for the pyrolysis of ethanol in a plasma jet: helium, argon, or nitrogen. According to the results of plasma flow simulation, the temperatures of the onset of carbon condensation for helium plasma (2900–2950 K) and argon plasma (2980–3010 K) are quite close, and in the corresponding gas phase the main components are H, H2 and CO, and at lower concentrations there are radicals COOH and OH and HCO+. The nitrogen plasma contains well-represented cyanopolyins responsible for the rearrangement of the gas phase at lower temperatures of 2240–2250 K. It seems that these temperatures are too low for CNT synthesis, so only graphene is formed here. The influence of the combination of H and O in the high-temperature region of plasma flow on the mechanism of formation of precursors of carbon nanostructures has been found.

Application of similarity theory to predict operational characteristics of a DC plasma torch under low-pressure condition

Application of similarity theory to predict operational characteristics of a DC plasma torch under low-pressure condition