Active Screen Caging Effect on the Plasma Parameters in Helium–Nitrogen Gas Mixture

Cold atmospheric pressure plasma treatment is currently being explored as an alternative way to improve the germination and growing parameters of plant seeds. However, it is important to pay attention to the effect of plasma treatment on DNA damage of the seeds as well as detailed characteristics of plasma composition and parameters. The aim of this work was to study the DNA damage of plasma-treated pea seeds (Pisum sativum L.) and plasma parameters such as the chemical composition of plasma gaseous compounds and plasma radiation. Seeds were treated with plasma using the diffuse coplanar surface barrier discharge generated in different working gases (ambient air, nitrogen, oxygen and different mixtures of oxygen and nitrogen) at atmospheric pressure and at 60 s, 180 s and 300 s exposure times. DNA damage was studied using the single cell-gel electrophoresis called the comet assay and the plasma parameters were investigated by Fourier transform infrared spectroscopy and optical emission spectroscopy. Experiments in different ratios of oxygen and nitrogen were realized in order to understand the reaction mechanism between the ambient air plasma and the treated seeds. Based on our results, ambient air plasma appears to be the most advantageous for the plasma treatment due to no significant DNA damage because of the proper combination of plasma composition in combination with water vapor present in ambient air.

In plasma nitriding, local plasma diagnostics are used to obtain information on the plasma distribution and parameters during the nitriding process. Since the plasma parameters have direct influence on the quality of the formed nitride layer, it is important to study the plasma in different nitriding scenarios. The goal of the paper is to present our measurements' results obtained in the Direct Current Plasma Nitriding setup (DCPN) and the Hollow Cathode Anodic Plasma Nitriding Setup (HCAPN), and to analyze the plasma parameters for different process parameters (gas mixtures, reactive gas pressure, applied voltage, etc.)

Наведено результати дослідження спектральних, інтегральних і ресурсних характеристик випромінювання газорозрядної плазми атмосферного тиску на багатокомпонентних сумішах дийодиду кадмію з гелієм і малої добавки молекулярного азоту. Створення газорозрядної плазми і збудження компонент робочої суміші здійснювалося імпульсно-періодичним (частота проходження імпульсів 18–20 кГц, тривалість імпульсів 150 нс) бар’єрним розрядом. Виявлено випромінювання у видимій області спектру ексиплексних молекул монойодиду кадмію, атомів кадмію. Встановлено закономірності в змінах оптичних характеристик плазми в залежності від частоти проходження імпульсів накачки, компонентного і кількісного складу сумішей. Представлено обговорення результатів досліджень. Дані досліджень представляють інтерес для створення ексиплексних газорозрядних джерел видимого випромінювання з максимумом випромінювання на довжині хвилі λ=650 нм.

We investigated the effect of various plasma parameters (relative density of atomic N and H, plasma temperature, and vibrational temperature) and process conditions (pressure and H2/(N2 + H2) ratio) on the chemical composition of modified poly(tetrafluoroethylene) (PTFE). The plasma parameters were measured by means of near-infrared (NIR) and UV-visible emission spectroscopy with and without actinometry. The process conditions of the N2-H2 microwave discharges were set at various pressures ranging from 100 to 2000 mTorr and H2/(N2+H2) gas mixture ratios between 0 and 0.4. The surface chemical composition of the modified polymers was determined by X-ray photoelectron spectroscopy (XPS). A mathematical model was constructed using the partial least-squares regression algorithm to correlate the plasma information (process condition and plasma parameters as determined by emission spectroscopy) with the modified surface characteristics. To construct the model, a set of data input variables containing process conditions and plasma parameters were generated, as well as a response matrix containing the surface composition of the polymer. This model was used to predict the composition of PTFE surfaces subjected to N2-H2 plasma treatment. Contrary to what is generally accepted in the literature, the present data demonstrate that hydrogen is not directly involved in the defluorination of the surface but rather produces atomic nitrogen and/or NH radicals that are shown to be at the origin of fluorine atom removal from the polymer surface. The results show that process conditions alone do not suffice in predicting the surface chemical composition and that the plasma characteristics, which cannot be easily correlated with these conditions, should be considered. Process optimization and control would benefit from plasma diagnostics, particularly infrared emission spectroscopy.

Non-invasive assessment of the plasma parameters is a useful tool for a reliable characterization of many electric thrusters for space applications. Due to high costs, limited availability, and growing use of electric propulsion in spaceflight, alternatives to Xe as a propellant are becoming increasingly important. One option is to use the lighter noble gas krypton or xenon/krypton gas mixtures as a propellant. We propose a versatile analytical approach for establishing empirical correlations between plasma parameters and optical emission (OE) spectroscopy utilizing principal component analysis (PCA). Our approach allows us to establish a surjective mapping of individual OE spectra via their PCA scores onto the corresponding plasma parameters. We prove the feasibility of this approach for Xe, Kr, and Xe/Kr mixed plasmas demonstrating that it is applicable for a wide range of propellant candidates. A major advantage is that the approach does not rely on any microscopic modeling of the OE spectra of the plasma. After having established corresponding reference mappings, the approach can be explored for determining non-invasively and spatially resolved plasma parameters of the propellant plasma of various kinds of operating ion thrusters, which operate in the same plasma regime as the reference plasma. Thus, this method may contribute to shorter qualification and testing times of ion thrusters.

Active screen plasma nitriding (ASPN) is a relatively recent and promising technique for the enhancement of surface properties of steel and other metal alloys. The ASPN system is usually powered by a pulsed DC power supply. Therefore, the plasma parameters in an ASPN should be measured as a function of time. In this work, the measurement of time resolved plasma parameters in such system has been demonstrated using a Triple Langmuir probe (TLP) diagnostic. The TLP technique allows quick calculation of fundamental plasma parameters such as the floating potential and electron temperature [Te]. The influence of input pulse current and frequency have been studied in a low pressure H2-N2 mixture plasma generated by 40-60 kHz pulsed D.C. power supply. The plasma parameters have been correlated with the input voltage and current. The preliminary work reveals the changes in the discharge characteristics as a function of input current and thus it’s influence on time resolved plasma parameters.

In this research, the plasma parameters were determined each of electron temperature (Te), electron density (ne), plasma frequency (fp), Debye length (λD). The plasma jet operates with argon gas at atmospheric pressure. It is equipped with an alternating AC high voltage power supply of 12 kilovolts and a frequency of 20 kilohertz. Plasma parameters were calculated from the emission spectrum using an optical emission spectrometer (OES) which captured the spectrum resulting from the plasma at various flow rates of argon gas from 0.5 to 5 L/min. Several peaks of argon gas (ArI) and nitrogen gas (N2) were appeared, where the results showed that the highest peak of argon gas was at 763.51 nm for the fifth flow of argon gas. The results indicated the electron temperature (Te) decrease with increased flow rate and ranged (1.296–0.645) ev, while the electron density (ne) increased with flow rate and ranged were (4.054-5.068x1017) cm-3, respectively. In contrast an increase in the intensity of spectral lines was observed.

For citation:Efremov A.M., Kwon K.-H. Plasma parameters and composition in CF4/O2/Ar gas mixture. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 50-55.The effects of O2/Ar mixing ratio in CF4/O2/Ar mixture on both plasma parameters and fluxes of active species determining the dry etching kinetics in this gas system were analyzed. The investigation combined plasma diagnostics by Langmuir probes and zero-dimensional plasma modeling. It was found that the substitution of Ar with O2 at constant fraction of CF4 in a feed gas does not result in the non-monotonic change in F atom density, as it was repeatedly reported for the binary CF4/O2 gas mixtures. The mechanisms of this phenomenon as well as its possible impact on the etching/polymerization kinetics were discussed in details.

Atmospheric Ar/NH3 dielectric barrier discharge (DBD) is a type of uniform dielectric barrier discharge that has potential applications in surface treatment, thin film surface deposition, hydrogen storage, etc. The characteristics and the application effects of Ar/NH3 DBD are strongly dependent on dielectric materials, electrode structures, and gas atmospheres. In this paper, a one-dimensional fluid numerical simulation model was established to investigate the effects of dielectric constant and secondary electron emission coefficient (SEEC) of the barrier dielectric material on the discharge characteristics and product distributions in Ar/NH3 gas mixture. The results show that increasing dielectric constant makes the discharge moment slightly earlier (discharge phase 17.5°–5°) and has a greater effect on the discharge intensity (discharge current), plasma parameters, and discharge products as well as their yields. While increasing SEEC makes the discharge moment significantly earlier (discharge phase 27.5° to −5°), it has less influence on the discharge intensity (discharge current), plasma parameters, and discharge products and their yields. On this basis, a possible strategy was proposed to describe the effect of the two dielectric parameters on the discharge characteristics and products.

In this work, we investigated the influence of fluorocarbon component ratio in the CF4 + C4F8 + O2 gas mixture on electro-physical plasma parameters, steady-state densities of active species and silicon etching kinetics under typical reactive-ion process conditions. The combination of plasma diagnostics (double Langmuir probes, optical emission spectroscopy) and plasma modeling confirmed known peculiarities of plasma chemistry of individual fluorocarbons in the presence of oxygen as well as provided an extended analysis of both fluorine and oxygen atom kinetics in the three-component gas mixture. It was shown that the substitution of CF4 by C4F8 at the constant fraction of O2 a) causes the weak disturbance in electrons- and ions-related plasma parameters (electron temperature, electron density, ion energy flux); b) provides drastically increasing density of polymerizing CFx (x = 1, 2) radicals; and c) results in monotonically decreasing F atoms density. The latter is due to simultaneous changes in both F atom formation rate and their loss frequency, especially in C4F8-rich plasmas. From experiments, it was found that Si etching rate is by more than 85% controlled by its chemical component (in a form of ion-stimulated heterogeneous reaction Si + xF → SiFx) and decreases with increasing C4F8 fraction in a feed gas. The change in effective reaction probability contradicts with the growth of polymer deposition rate and film thickness (as it follows from changes in gas-phase plasma characteristics) but may reflect the weakening of surface passivation by oxygen atoms. For citation: Efremov A.M., Bobylev A.V., Kwon K.-H. Plasma parametrs and silicon etching kinetics in CF4 + C4F8 + O2 mixture: effect of CF4/C4F8 mixing ratio. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 6. P. 29-37. DOI: 10.6060/ivkkt.20246706.6982.

In this work, we carried out the study of CF4 + O2 + X (X = C4F8 or CF2Br2) gas chemistries in respect to the SiOxNy reactive-ion etching process in a low power regime. The interest in the liquid CF2Br2 as an additive component is motivated by its generally unknown plasma etching performance. The combination of various diagnostic tools (double Langmuir probe, quadrupole mass-spectrometry, X-ray photoelectron spectroscopy) allowed us to compare the effects of CF4/X mixing ratio, input power and gas pressure on gas-phase plasma characteristics as well as to analyze the SiOxNy etching kinetics in terms of process-condition-dependent effective reaction probability. It was found that the given gas systems are characterized by: (1) similar changes in plasma parameters (electron temperature, ion current density) and fluxes of active species with variations in processing conditions; (2) identical behaviors of SiOxNy etching rates, as determined by the neutral-flux-limited process regime; and (3) non-constant SiOxNy + F reaction probabilities due to changes in the polymer deposition/removal balance. The features of CF4 + CF2Br2 + O2 plasma are lower polymerization ability (due to the lower flux of CFx radicals) and a bit more vertical etching profile (due to the lower neutral/charged ratio).

The present study describes the control characteristics of the gas temperature and velocity fields and also plasma parameters of RF induction argon nonequilibrium plasma by injecting a premixed cold helium gas axially at atmospheric pressure. The flow and the gas temperature fields and the plasma parameters in the RF induction mixed gas plasma are obtained by solving the axisymmetric turbulent 2D MHD equations taking account of the variable transport properties of gas mixtures and using two-temperature model coupled with 2D Maxwell's equations. The mixing rate of a secondary injected gas is also evaluated using the species conservation equation. It is examined how the thermofluid and diffusion characteristics, the plasma parameters and the nonequilibrium degree in the RF induction plasma are influenced by the positions and the inlet mass fractions of injected helium gas. Finally, the calculated gas temperature taking account of the nonequilibrium effect shows good agreement with the previously obtained experimental data.

A mercury-free and electrodeless discharge fluorescent lamp is expected for preserving the environment and a long lifetime. Influence of Xe gas concentration on plasma parameters such as density and temperature of electrons and luminance characteristics is investigated in a fluorescent lamp driven by inductively coupled radio frequency discharge using Ne / Xe mixture gases. It is found that the electron density has a peak value for a Xe gas concentration of 1 % and then decreases with increasing the Xe gas flow rate, whereas the electron temperature takes a minimum value for the Xe gas concentration of 1 % and then increases with increasing the Xe gas concentration. The luminance of the fluorescent lamp decreases remarkably with increasing Xe gas concentration up to 1% and then gradually decreases. The color of the fluorescent lamp changes from red to purple when the Xe gas concentration increases.

Summary form only given. SF6 gas is known as an effective insulator due to its high dielectric characteristics. Because of this property, it is widely used in the field of high voltage pulse systems and compact electrical distribution sites. But the phenomenon of breakdown between spark gaps according to SF6 ratio and mixture gas pressure is still unknown well. There are several parameters about breakdown phenomenon between the spark gap switches. Electron temperature is one of most important parameter in plasma. We have investigated the electron temperature according to the SF6 rate and pressure. We used the high power microwave generator named, “Chundoong”, which is a high-power pulse generator with maximum 600 kV, 88 kA, and 60 ns pulse duration. We installed the breakdown chamber in front of vacuum chamber. The material of electrode is copper-tungsten consisting of 70 % tungsten and 30 % copper. We have used nitrogen gas (N2), sulphur hexafluoride (SF6) and there mixture gases, respectively. The SF6 has been mixed from 1 % to 30 % to the N2 basis. Mixture pressure has been changed by 100 torr, 400 torr, 1 atm, 2 atm, 3 atm, and 4 atm. It is found that the electron temperatures are rapidly increased to 10 %, but beyond that those are saturated to be 17 eV. These electron temperatures above 10% mixture ratio of SF6 are not in big differences in accordance with gas pressures in this experiment.

Background: Cold plasma is shown to inhibit the cancer cell growth. Manipulation of different plasma parameters might have influence on the production of major reactive species which leads to killing of the cancer cells. Antiproliferative activity of cold atmospheric pressure plasma jet was investigated on small-cell lung carcinoma BHY cell line (squamous cell carcinoma) under different in vitro conditions. Methods: A homemade plasma jet was designed and created using pure helium gas. To identify the species created by the plasma jet, optical emission spectroscopy (OES) was employed. Next, the effect of plasma jet was examined on lung cancer cell survival by MTT assay and the effects of main parameters were evaluated on plasma performance. In this favor, various treatment times including 60, 90, 120, 180, and 300 s in combination with different voltages of 5, 11, and 14 kV were investigated, and the results were analyzed at 2, 24, and 48 h after exposure to plasma. Results: Predominant species of OES spectra were O, OH, N2+, and N2. Results of MTT assay indicated a dramatic reduction in cell viabilities in both dose- and time-dependent manners, and more than 75% of cancer cells were died after 48 h at 180 s of plasma treatment. Conclusion: The homemade plasma jet can chiefly contribute to the production of reactive oxygen and nitrogen species (reactive oxygen species and reactive nitrogen species) and can induce apoptosis in small-cell lung carcinoma BHY cell line.