Mixture Plasma Research Articles

Role of sulfur in catalyzing fluorine atom fast etching of silicon with smooth surface morphology

Chemical reaction probabilities, defined as the number of silicon atoms removed per incident fluorine atom, have been investigated in mixtures of NF3 and SF6 plasmas in an inductively-coupled plasma reactor. Fluorine atom densities were measured by optical emission actinometry, and isotropic etching rates were measured by the degree of undercutting of SiO2-masked silicon by cross-sectional scanning electron microscopy. In addition, atomic force microscopy was used to examine surface morphology of etched Si surfaces. The F atom reaction probabilities derived from isotropic etching rates indicate an ∼30-fold higher reaction probability in SF6 plasmas compared with values in NF3 plasmas. Surfaces etched in SF6 plasmas were much smoother than those etched in NF3 plasmas. The addition of only 10% SF6 to an NF3 plasma produced a much higher reaction probability (∼5-fold) than in a pure NF3 plasma. This surprising enhancement of reaction probabilities for F with Si in SF6 plasmas is further investigated, based on the mechanism of adsorbed sulfur acting as a catalyst to greatly enhance the etching rate of Si. Dilute sulfur solutions in isopropyl alcohol were allowed to evaporate on the masked Si samples, depositing sulfur in relatively high concentrations near mask edges in ∼2 μm diameter periodic “strings of beads.” The sulfur-dosed sample etched several times faster at the center of each bead than a sample not exposed to sulfur that was placed side by side. The catalytic effect of sulfur is ascribed to an enhanced F sticking coefficient and/or decreased desorption rate on a surface covered with sulfur.

Improvement of efficiency of the use of pulsed corona discharge energy during the conversion of volatile organic compounds

The effect of electronegative additives on the conversion of volatile organic compounds in plasma of air mixtures has been studied. It was shown that during the conversion of trichloroethylene C2HCl3 and perchloroethylene C2Cl4 in air under the action of pulsed corona discharge of nanosecond duration, the addition of carbon tetrachloride CCl4 to the mixture leads not only to a decrease in the discharge current, but also to an increase in energy efficiency of the conversion of toxic impurity. To explain the results obtained, the estimation of parameters of non-equilibrium non-thermal plasma and the analysis of processes in various regions of pulsed corona discharge have been carried out.

Thermodynamic properties of He/Ar/N2/C/Ni/Co thermal plasmas used in carbon nanotube synthesis

This work aims to study thermodynamic properties of Ar/He/N2/C/Ni/Co plasma mixtures used in carbon nanotubes (CNTs) synthesis. Assuming a local thermodynamic equilibrium (LTE) and based on the composition results, calculated values are obtained for a temperature range of 1000–30 000 K and pressure in the range of 3–100 kPa. We have examined the influences of the chamber volume (60, 25 and 18 l) and plasmagen gases on the thermodynamic properties. We have also investigated the influence of metal/carbon vapors, which form part of the plasma gas mixture from approximately 2500 K. In this paper, many thermodynamic properties, mainly mass density, specific enthalpy and specific heat at constant pressure, are presented in detail through figures and tables. In total, we have considered 25 plasma configurations. In addition to the customary used description, each studied configuration is described through constituent elements proportion in order to standardize these data to be appropriate to a wide range of studies and setups other than the arc plasma reactor.

Analysis of radiative opacities for optically thin and thick astrophysical plasmas

The resolution of the radiative transfer equation in radiation-hydrodynamic simulations of astrophysical plasmas require radiative opacities. In this work, an analysis of the monochromatic and multigroup opacities of an astrophysical plasma mixture has been carried out. The study has been made in ranges of electron temperatures and densities of 1−1000 eV and 1011−1020 cm−3, respectively, a wide range of plasma conditions that can be found in several astrophysical scenarios where local and non-local thermodynamic regimes are attained. Collisional-radiative calculations were performed to obtain the plasma level populations and the monochromatic opacities in that range of plasma conditions, covering both thermodynamic regimes. Since the astrophysical mixture includes chemical elements from hydrogen to iron, their contribution to the total opacity will depend on the plasma conditions and we have made a characterization of their contribution as a function of the electron density and temperature and also of the photon frequency. Multigroup and gray approaches are commonly used in the radiative transfer equation in radiation-hydrodynamic calculations. We have analyzed the influence of the number of the groups in the accuracy of the multigroup opacities and we have showed that, for a given plasma condition, the opacity of the multicomponent plasma in the gray approach may be considerably influenced by only some of the contributing elements, due to the influence of the weighting function in the mean, which can lead to great differences with respect to the monochromatic opacity. Finally, since there are situations in which the self-absorption of the plasma radiation becomes relevant due to the dimensions of the plasma, we have performed an analysis of the influence of the radiation trapping in the monochromatic and multigroup opacities in terms of the plasma conditions and the width of the plasma slab, assuming the plasma with planar geometry and we have also studied the departures of the local thermodynamic regime.

Measurements of radial profile of hydrogen and deuterium density in isotope mixture plasmas using bulk charge exchange spectroscopy.

A bulk charge exchange spectroscopy system has been applied to measure the radial profiles of the hydrogen (H) and deuterium (D) density ratio in the isotope mixture plasma in a large helical device. Charge exchange lines of Hα and Dα are fitted by 4 Gaussian of H and D cold components and H and D hot components with 5 parameters by combining the measurement of plasma toroidal rotation velocity with carbon charge exchange spectroscopy. The radial profiles of the relative density of hydrogen and deuterium ions are derived from H and D hot components measured and the beam density calculated from beam attenuation calculation. A proof-of-principle experiment is performed by the H pellet and the D pellet injections into the H-D mixture plasma.

P‐13.12: The Lifetime and Yield Improvement by Plasma Treatment to Anode Surface in Active Matrix Organic Light Emitting Diode Display

The active matrix organic light emitting diode (AMOLED) display industry has been undergoing rapid development and increasing competition as heavy investment enters the industry continuously. The performance and yield of one company’s products, closely related to OLED device fabrication process, are the critical factors to its core competence [1]. Here, the lifetime and Mura defects could be improved simultaneously by introducing plasma treatment to anode surface of array driver circuit were proved. The lifetime was increased at least 50% and the Mura defects caused by residue on anode surface were decreased at least 75%. Also, the effects of different kinds of plasma gas, pure O2 and mixture of SF6 and O2 were compared and the mechanism was discussed. Our work demonstrated that the plasma treatment to anode surface before organic materials evaporated was beneficial and necessary to enhance the product performance of AMOLED display.

Increase of space width roughness in directed self-assembly patterning arising from shrinking stress in the remaining poly(methyl methacrylate)

The mechanism for the increase in space width roughness (SWR) after selective poly(methyl methacrylate) (PMMA) etching to polystyrene (PS) is investigated for directed self-assembly patterning. Considering the cross-sectional image obtained from field-emission scanning electron microscopy, the authors propose a physical model where the shrinking stress in the remaining PMMA with thickness variation induces PS-line collapse and this collapse increases SWR. Linear finite-element calculations show that this proposed model can explain two experimental results; namely, the SWR exhibits a peak that depends on the thickness of the remaining PMMA and the low-frequency component of SWR becomes larger after etching. To prove our model more directly, PMMA was shrunk by electron beam (EB) irradiation and the change in SWR was examined. SWR with residual PMMA increased with an increasing EB-dose amount, while SWR without residual PMMA did not show a clear increasing trend. These results clearly show the shrinking stress in the remaining PMMA with thickness variation increases SWR. To suppress the SWR increase during etching, the etching condition was also modified based on our model. Intrinsic-shrinking stress in PMMA was reduced by a carbon-oxygen mixture plasma. In addition, the thickness variation of the remaining PMMA was suppressed by the reduction of the reactive ion etching lag with a dual-time modulated (DTM) plasma. Eventually, an SWR less than the incoming value was realized by using a carbon-oxygen mixture plasma with DTM.

Investigation of the Measured and Computed Neutron Yield From the PF-24 Device Operated With D2-$x$ %Ar Admixture

Many experiments have been carried out on the (16.8 kJ, 17 kV) dense plasma focus PF-24 device operated with pure deuterium and deuterium-argon admixture. The main purpose of the work was to investigate the influence of the doping argon on the average total neutron yields experimentally and numerically. The 103 discharges (34 for D2, 69 for D2- $x$ %Ar, where $x = 3, 5, 10, 15, 22, 25, 30, 45, 60$ ) were performed in four experimental sessions under constant total initial optimum pressure of about 2.2 torr. The total current and its time derivative traces, as well as the total neutron yield values, were recorded, and the electro-kinetic plasma parameters were estimated for each shot. The Lee model has also been adapted for gas mixture plasma focus modeling, and then the enhanced code was used for simulation of each of the PF-24 discharge with D2 and D2- $x$ %Ar. The fitting parameters for each shot are found and discussed. The measured and computed values of the neutron yield and the electro-kinetic plasma parameters are in good agreement. The obtained results showed that there is no neutron yield enhancement with argon seeding. The scaling law of the neutron yield $Y_{n}$ against argon fraction has been deduced. Additionally, our results illustrate that the PF-24 plasma focus device has an optimized configuration for the DD fusion neutron emission.

Laser monitor for imaging single crystal diamond growth in H2-CH4 microwave plasma

We used an active optical system referred to as ‘laser monitor’ based on a copper bromide vapor brightness amplifier for imaging a diamond crystal surface during its synthesis in a microwave plasma in CH4-H2 gas mixture. The approach allows observation of an entire crystal without interrupting the chemical vapor deposition process. It is demonstrated that the broadband plasma background radiation with the brightness temperature of about 3000 K does not interfere with object real-time monitoring at the laser wavelength of 510.6 nm. High quality images obtained using both passive (laser illumination) and active (laser monitor) methods provide information about the surface relief of the growing crystal with resolution of a few tens of micrometer. Each frame is formed through one pulse (about 30 ns), with the maximum frame rate being 20,000 frames/sec.

The role of SiHn radicals generation in the mechanisms of formation of thin films of amorphous silicon

In this research, we studied the processes of configuration changes to the structural elements of amorphous silicon thin films created by the decomposition of reacting gas mixture (silane and argon) in low-frequency glow discharge plasma. We analyzed how concentrations of various local atomic groups and their links depend on deposition parameters. We also defined phase composition and the role of SiHn radicals generation in the mechanisms of formation of hydrogenated amorphous silicon thin films deposited on glass and Sitall substrates.

Erosion, screening, and migration of tungsten in the JET divertor

The erosion of tungsten (W), induced by the bombardment of plasma and impurity particles, determines the lifetime of plasma-facing components as well as impacting on plasma performance by the influx of W into the confined region. The screening of W by the divertor and the transport of W in the plasma determines largely the W content in the plasma core, but the W source strength itself has a vital impact on this process. The JET tokamak experiment provides access to a large set of W erosion-determining parameters and permits a detailed description of the W source in the divertor closest to the ITER one: (i) effective sputtering yields and fluxes as function of impact energy of intrinsic (Be, C) and extrinsic (Ne, N) impurities as well as hydrogenic isotopes (H, D) are determined and predictions for the tritium (T) isotope are made. This includes the quantification of intra- and inter-edge localised mode (ELM) contributions to the total W source in H-mode plasmas which vary owing to the complex flux compositions and energy distributions in the corresponding phases. The sputtering threshold behaviour and the spectroscopic composition analysis provides an insight in the dominating species and plasma phases causing W erosion. (ii) The interplay between the net and gross W erosion source is discussed considering (prompt) re-deposition, thus, the immediate return of W ions back to the surface due to their large Larmor radius, and surface roughness, thus, the difference between smooth bulk-W and rough W-coating components used in the JET divertor. Both effects impact on the balance equation of local W erosion and deposition. (iii) Post-mortem analysis reveals the net erosion/deposition pattern and the W migration paths over long periods of plasma operation identifying the net W transport to remote areas. This W transport is related to the divertor plasma regime, e.g. attached operation with high impact energies of impinging particles or detached operation, as well as to the applied magnetic configuration in the divertor, e.g. close divertor with good geometrical screening of W or open divertor configuration with poor screening.JET equipped with the ITER-like wall (ILW) provided unique access to the net W erosion rate within a series of 151 subsequent H-mode discharges (magnetic field: T, plasma current: MA, auxiliary power MW) in one magnetic configuration accumulating 900 s of plasma with particle fluences in the range of 5– in the semi-detached inner and attached outer divertor leg. The comparison of W spectroscopy in the intra-ELM and inter-ELM phases with post-mortem analysis of W marker tiles provides a set of gross and net W erosion values at the outer target plate. ERO code simulations are applied to both divertor leg conditions and reproduce the erosion/deposition pattern as well as confirm the high experimentally observed prompt W re-deposition factors of more than 95% in the intra- and inter-ELM phase of the unseeded deuterium H-mode plasma. Conclusions to the expected divertor conditions in ITER as well as to the JET operation in the DT plasma mixture are drawn on basis of this unique benchmark experiment.

Enhancement of O-atom density through collisions with Ne by laser-produced plasma in Ne–O2 gas mixtures and possible energy transfer mechanism

Laser-produced plasma in Ne and O2 gases and Ne–O2 gas mixture with different O2 fractions have been investigated. The plasma were produced by focusing a laser beam of 5 ns pulse duration from a Nd:YAG laser ([Formula: see text] = 1064 nm) through a lens of 5 cm focal length into the chamber filled with different gas species at different pressures. Possible enhancement in O-atom densities through collisions with metastable Ne atoms by the laser-created plasma in Ne–O2 gas mixtures and possible energy transfer mechanism was studied. Study of energy transfer through collisions was carried out by comparisons of the line intensities of the emitted spectra from laser-created plasma in gas mixtures and pure gases with the technique of optical emission spectroscopy (OES). Strong evidence of energy transfer from Ne to O was recorded. From the result, it was suggested that the high-lying metastable levels of Ne were responsible for enhancement of O-atoms density in gas mixture and Ne also play important role in energy transfer mechanism through collision. Also, behaviors of the line intensities under different laser energies were studied. Behaviors of line intensities and line widths were the main parameters measured. Stark broadening of lines in Ne with different laser energies was recorded. The electron temperature T[Formula: see text] and number density N[Formula: see text] were found to be 1.01 eV and 9.44 × 10[Formula: see text] cm[Formula: see text] in Ne at different laser energy/pulse with total pressure of 1000 mbar.

Gas mixture effects on ion‐beam flux characteristics from dense plasma focus device: Investigation by the Vlasov–Maxwell equations and experiments

The Vlasov–Maxwell equations were numerically solved to calculate the ion‐beam flux from the plasma of argon and the plasma of mixtures of argon and neon. Some experiments were performed to measure the ion beam from the Amirkabir plasma focus (APF) device. The calculations have shown that the argon ion‐beam flux peaked up to 1.928 × 1030 ions m−2 s−1 at the optimum pressure of 1.866 mbar while the neon‐argon mixture's ion‐beam flux reached a maximum of 4.301 × 1030 ions m−2 s−1 for 15% neon admixture at the optimum pressure of 1.866 mbar. The calculated kinetic energy of the ion beam has shown a maximum value of 708.7 J for the mixture of 85% argon‐15% neon at the mentioned optimum pressure.

Nitrogen doping of carbon nanoballoons by radiofrequency magnetron plasma and evaluation of their oxygen reduction reaction activity

AbstractNitrogen‐doped carbon materials exhibit a catalytic activity, such as an oxygen reduction reaction (ORR). In this study, we performed nitrogen doping on a carbon nanoballoon (CNB), which is a nanometer‐sized carbon particle in the form of a hollow sphere made of graphite by radiofrequency (RF) magnetron plasma in a gas mixture of nitrogen and helium. Nitrogen‐doped CNBs (N‐doped CNBs) were prepared by different plasma irradiation conditions: the sample installation positions, input powers, and irradiation times. The samples were examined for chemical state by X‐ray photoelectron spectroscopy (XPS). Hydrodynamic voltammetry was used for the evaluation of the catalytic activity of a N‐doped CNB with a pyridinic N concentration of 0.4‐1.0 at.%. As a result, the onset potential was measured to be 0.13 V versus RHE (reversible hydrogen electrode), which was close to the previously reported data of highly oriented pyrolytic graphite (HOPG) with a pyridinic N concentration of 0.57 at.%, which was prepared by annealing under NH3.

A mini-pig model for evaluating the efficacy of autologous platelet patches on induced acute full thickness wound healing

BackgroundAutologous platelet concentrates are currently widely used across different areas of regenerative medicine in order to enhance the wound healing process. Although several protocols for platelet concentrates are available, their application remains difficult due to different protocols leading to distinct products with vary potential biological uses. In this study, we attempted to make a platelet patch (PP) using mixtures of platelet rich plasma (PRP) injection and platelet rich fibrin (PRF) to promote wound repair and regeneration.ResultsExperiments were performed using a full-thickness wound model in mini-pigs. Autologous PRP, PRF and PP were prepared immediately before creating four full-thickness skin wounds in pigs. We quantified concentrations of platelets, thrombin and various growth factors to ensure that the desired effect can be produced. After surgery, hydrocolloid dressing, PRP injection, PRF and PP was applied to experimentally induced wounds. Application efficacy was evaluated by measurement of wound sizes and histological examination. The results indicated that all wounds showed a significant size reduction. Wound repair efficacy in response to PP treatment exhibited enhanced re-epithelialization compared to PRP and PRF (P < 0.05) and higher wound contraction than did PRF application (P < 0.05). Another aspect, experiment using DsRed transgenic pigs as blood donors demonstrated that leucocytes in PP were incorporated into the wound bed at the end of the study, suggesting that leucocytes activity is stimulated in response to PP application. Safety of the experimental processes was also confirmed by examination of organ biopsies.ConclusionsWe used a mini-pig model to evaluate the efficacy of lab-made PP on induced full-thickness wound healing. Results demonstrated that application of one piece of PP was enough to obtain comparable efficacy versus general utilization of PRP or PRF for wound care. We also demonstrated that leucocytes in PP were incorporated into the wound bed and no safety concerns have been found in the whole experiment. This study provides a novel and feasible method for veterinary or clinical wound care.

Study of wall ablation on low-voltage arc interruption: The effect of Stefan flow

Low-voltage circuit breakers provide essential protection for industrial and residential power installations, by taking advantage of the voltage drop at the electrode–plasma interface to force current zero. This is accomplished by using the magnetic force and unbalanced pressure on the arc as the contacts open to push the arc toward a stack of steel plates that break the arc into subarcs and thereby multiply the number of voltage drops. As the fault current can be high, substantial energy can be dissipated, which results in interactions among the arc and solid counterparts in terms of wall ablation and metal evaporation. In this study, ablation experiments are conducted to demonstrate its great influence on the arc voltage and on the pressure field. Significant progress has been accomplished in the computation of arc dynamics through the coupling of fluid motion with electromagnetics, although an important mechanism in arc breaking simulation, the effect of Stefan flow caused by species generation, has not been considered. We report out a numerical approach for taking into account the effect of Stefan flow, particularly for the breakers with high gasifying wall materials. This approach accounts for the diffusion induced convection due to added-in species from the evaporation surfaces, which will largely influence the flow field and the properties of the plasma mixture. Apart from the voltage drop, this mechanism plays an important role in simulating arc interruption. The ability of conducting Stefan flow computation further enhances the understanding of arc behaviors and improves the design of practically oriented low-voltage circuit breakers.

Computational study on silicon oxide plasma enhanced chemical vapor deposition (PECVD) process using tetraethoxysilane/oxygen/argon/ helium

Plasma enhanced chemical vapor deposition (PECVD) of silicon oxide (SiO2) using tetraethoxysilane (TEOS) was investigated theoretically by developing an unprecedented plasma chemistry model in TEOS/O2/Ar/He gas mixture. In the gas phase reactions, a TEOS molecule is decomposed by the electron impact reaction and/or chemically oxidative reaction, forming intermediate TEOS fragments, i.e., silicon complexes. In this study, we assume that SiO is the main precursor that contributes to SiO2 film growth under a particular process or simulation condition. The surface reaction was also investigated using quantum mechanical simulations with density functional theory. Based on the gas and surface reaction models, we constructed a computational plasma model for SiO2 film deposition in a PECVD process. The simulation results using CHEMKIN pro and CFD-ACE + have shown that the neutral atomic O and SiO as well as the charged O2+ are the dominant species to obtain a high deposition rate and uniformity. The spatial distributions of various species in the TEOS/O2/Ar/He gas mixture plasma were shown in the study. The uniformity of deposited film due to the change in the plasma bulk property was also discussed.

Structural analysis of hydrogenated nano-crystalline silicon suboxide (nc-SiOx:H, x < 1) thin films with SAXS for a potential application as phase change material

Hydrogenated nano-crystalline silicon suboxide (nc-SiOx:H; x < 1) is a two-phase material in which nanometer-sized silicon (nc-Si) region enclosed by hydrogenated amorphous silicon suboxide (a-SiOx:H) matrix. nc-SiOx:H thin films are produced by using highly hydrogen-diluted (dH ≥ 90%) plasma of silane and carbon-dioxide mixture, in a Plasma Enhanced Chemical Vapor Deposition (PECVD) system. The high concentration of the H-atoms in the plasma assist the silicon atoms on the growing film surface to crystallize. Small Angle X-Ray Scattering (SAXS) method was used to determine the nano-scale structures of nc-SiOx:H thin films, for varying hydrogen dilution ratios. The size, shape and the distribution of the nano-formations are found to depend strongly on the preparation conditions. From FTIR absorption and Raman scattering experiments, atomic oxygen and hydrogen contents and also the crystal ratio of the samples are evaluated. As results of nano-structural analyses, the morphologies, sizes and distributions of the nano-aggregations are found to be closely related to the crystallization of the films. From the SAXS results of the samples prepared at the hydrogen dilution ratio of 90%, the nano-aggregations are found to form in uniformly distributed core-shells. However, as the hydrogen dilution is increased to higher ratios to 95% and further to 99%, the nano-scaled fractals are deduced to form. The oxygen and hydrogen contents in nc-SiOx:H are strictly related to the crystal ratio of the samples. The crystal ratio is determined by the hydrogen dilution ratio during the deposition. The two-phase structure of nc-SiOx:H samples and the dependence on the hydrogen dilution ratio may suggest these materials are candidates for phase change materials. Depending on the deposition parameters, smaller nc-Si structures may be prepared which may have different (lower) electron densities required to melt the amorphous region and make the phase change possible due to explosive crystallization.

PLASMACHEMICAL GENERATION OF NITRIC OXIDES IN AIR PLASMAS FOR MEDICAL APPLICATIONS

Nitric oxide is well known as a poly functional regulator of different physiological processes in human body and therefore could be used for therapeutic purposes in different medical applications. In this review mechanism of nitric oxide generation in gas plasma and biological mechanisms of nitric oxide containing plasma gas treatment of tissues are described. In addition to nitric oxide the other biologically active species like hydrogen peroxide and nitrogen dioxide are formed in air plasma at atmospheric pressure. Synergetic action of molecules NO/H2O2 и NO/O2, generated in plasma gas results to manifold increase of sterilization activity of plasma mixture to bacteria and at the same time the toxicity of these species to living cells is low. Plasma gas exhibits therapeutic action on human tissues. On the one hand plasma gas contains molecules Н2О2, NO and NO2 acting as a antimicrobial agents and promoting sterilization, on the other hand the presence of significant concentration of NO leads to effective regeneration of damaged tissue. These processes are complementary and finally result to effective healing of diabetic trophic ulcer and other diseases in the oncology, ophthalmology, dentistry, purulent surgery, battlefield surgery and so on. Peculiarities of different discharges which could be used for generation of nitric oxide, like arc discharge, gliding arc discharge, microwave discharge, radiofrequency and pulsed discharges are discussed. The production of nitric oxide depending on type of discharge and plasma parameters like discharge power, gas flow rate and electrode configuration are analyzed. The efficacy of nitric oxide generation in different discharges is compared.

Modeling of Emission Spectra in Nonequilibrium Plasmas for Testing Pyrolyzing Ablators

Simulations are performed in collaboration with inductively coupled plasma torch experiments to investigate gas-phase chemical kinetics in the boundary layer of a pyrolyzing ablator. A gas injection probe delivers or into plasma mixtures of , and emission spectroscopy provides absolute, spatially, and spectrally resolved measurements of the radiative emission in the boundary layer. A computational model of the plasma flow in the Inductively Coupled Plasma facility was used with finite rate chemistry mechanisms, and line-of-sight emission spectra were computed from the results to assess the accuracy of the chemistry mechanisms. The –air and –air chemistries were examined, and CN emission levels were overpredicted by a factor of 3–4, whereas OH emission was underpredicted by a factor of 2. Sensitivity analyses show that uncertainty in the experimental temperature accounts for much of the discrepancy.