Plasma sterilization using the RF glow discharge

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30 s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40 W and gas flux was 20 cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.     

The low-temperature afterglow in N2–ε·CH4 gas mixtures

The influence of the small methane impurities on the pure nitrogen afterglow was studied in DC flowing plasma reactor in wide range of methane concentrations (0.01–400 ppm) at different wall temperatures of the reactor observation part (77–300 K). The relative vibrational distributions of states have been calculated from the recorded spectra in pure nitrogen. We observed strong quenching of the nitrogen pink afterglow at methane concentrations of a few ppm, however the pink afterglow intensity was growing up at the methane concentrations under 1 ppm. Simultaneously, the maximum pink afterglow intensity was observable at later decay times with the increase of the methane concentration. At low wall temperatures, especially at later decay times, we observed extremely high sensitivity of the pure nitrogen to the methane pretence in the discharge. Thus we are able to detect the methane concentrations in order of 0.01 ppm. We also observed the higher transitions of the CN violet system which are usually observed in the spectra of space emission sources. The method detecting hydrocarbon and fluorocarbon impurities in pure nitrogen is based on the results of the above mentioned experiments. We present first results of some experiments studying the polyhydrocarbon destruction rates measured by this new sensitive method. Finally, we designed also the simple kinetic model describing the processes during the afterglow in the N₂–·CH₄ mixture.     

Reaction Kinetics and Chemical Quasi-Equilibria of the Ozone Synthesis in Oxygen DC Discharges

The spatial distribution of ozone and of oxygen atoms was studied along the active and the passive zone of a dc discharge (positive column, pressure: p = (4 … 10) · 10² Pa, current: I = 2 … 50 mA, flow rate: F = 5 … 100 sccm) in flowing oxygen. The composition of the final output O₂/O₃-mixture is controlled by relaxation processes in the passive reactor zone. It is affected sensitively by the total number density and the gas temperature in the afterglow. Steady states meaning reversible chemical quasi-equilibria were observed and analysed extensively. Within a detailed kinetic model the formation of these equilibria can be explained quantitatively. The synthesis to ozone is controlled above all by the metastable O₂ (a¹Δg) species, which modify drastically the results for the basic mechanism, considering the O atoms in the ³P and ¹D states.     

Recombination in Dense Ion Plasmas

A theory is developed to treat ion recombination in dense ion plasmas. Numerical results are obtained with the method of molecular dynamics. Exponential suppression of recombination is found for the discharge afterglow plasma in sulfur hexafluoride at strong Coulomb nonideality Γ. The reason for suppression is an increase of the recombination activation energy ΔE with increase of Γ. The range ΔE corresponds to the multiparticle fluctuations. Ion solvation is another suppression factor. Its importance is demonstrated for the discharge afterglow plasma in fluorine at weak Coulomb nonideality. The theory developed agrees with the experimental data available. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low temperature argon plasma sterilization effect on Pseudomonas aeruginosa and its mechanisms

In the present work, low temperature argon plasma was used to sterilize Pseudomonas aeruginosa on PET sheets. The discharge conditions were as follows: power of 30 W and gas flux of 20 cm³/min, and the pressure in the reaction chamber was 6.2 Pa. In a self-designed plasma reaction equipment, active species (electron, ion, radical and UV light, etc.) were separated effectively, and the discharge zone, afterglow zone and remote zone were plotted out in the plasma field. For a treatment time of 60 s, the germicidal effects were 3.94, 3.86 and 2.93 respectively in the three zones. The results show that argon plasma can effectively sterilize P. aeruginosa in a short time. Before and after plasma treatment, cell morphology was studied via scanning electron microscopy (SEM). Cell wall or cell membrane cracking was tested to determine the content of nucleic acid in the bacteria suspensions using ultraviolet spectroscopy. To test the content of protein, a coomassie light blue technique was used. The results show that plasma activity cracks the cell wall and cell membrane, resulting in cellular content leakage. In addition, the results from electron spin resonance (ESR) spectroscopy and double Langmuir electron probe show that electrons, ions and argon free radicals play important roles in sterilization in the discharge zone, but only argon free radicals act to sterilize bacteria in the afterglow zone and the remote zone.     

B 2Σ u + excited states of the N + 2 ion and the electron temperature in the discharge afterglow of an Ar-N2 mixture

The electron energy distribution function in the afterglow of a low-pressure discharge in an Ar-N₂ mixture was experimentally found. The values of electron temperature were determined. At the initial stage of plasma decay, the electron temperature was shown to be close to the nitrogen vibrational temperature. A study was made of the afterglow observed in the bands of the first negative system of N ₊ ² , and it is shown that this afterglow may be attributed to collisions of argon ions with nitrogen molecules found on higher vibrational levels.     

Measurement of Excited States Density and the VUV-Radiation in the Pulsed Xenon Medium Pressure Discharge

Time resolved absolute density measurements of the 1s5 (metastable) and 1s4 (resonance) level in the positive column of a pulsed xenon gas discharge for gas pressures between 1 and 40 Torr and currents between 100 and 300 mA are presented. The densities ranged from 1 × 10¹¹ to 5 × 10¹² cm^?3 and were found to be ten times larger in the afterglow than in the active part of the discharge. The enhanced radiation obtained in the afterglow in the near infrared regions as well as in the VUV region is caused by a dissociative recombination and formation of excimer states.     

Molecular Emission Spectrohetry ih a Low Pressure Electrical Discharge

A low pressure electrical discharge for excitation of polycyclic aromatic hydrocarbons, PAHs, without fragmentation is described. The discharge characteristics as well as the plasma background spectra are given. The application of the discharge for the excitation of molecular spectra of PAHs is described. Difficulties with correction of the analyte emission spectrum for the background emission spectrum of the gas (He) are mentioned. Analytical use of the discharge for detection of PAH3 introduced by gas chromatography is described and is shown to be of marginal analytical use because of the rather poor detection limits of about 1 μg.

Jurgensen and Winefordner¹ have reviewed both reduced pressure and atmospheric pressure nitrogen discharges for detection of atomic and molecular species. The same authors² have also described an active nitrogen-induced chemiluminescence system for detection of polycyclic aromatic hydrocarbons, PAHs, and achieved detection limits in the range of 0.01 - 2000 ng. The intriguing aspect of the active nitrogen—induced chemiluminescence approach² for detection of PAHs was that the discharge was gentle resulting in little fragmentation of the PAHs and in the appearance of emission spectra characteristic of the parent molecules. Because of the poor understanding of the mechanism of excitation of the large organic molecules and the minimal fragmentation and because of the lack of control of the direct discharge as opposed to the afterglow in the studies of Jurgensen and Winefordner², the present authors began a careful study of the physical and analytical characteristics of this discharge in the fall of 1984. The physical characteristics were reported by Yu and Winefordner³ and indicated that the previous workers², were using the direct discharge plasma as a result of llpoorlv grounding. In addition, the same workers³ showed that the active nitrogen afterglow was not capable of exciting PAHs. In this note, we report on the analytical capabilities of an improved active gas (nitrogen or helium) electrical discharge system for gaseous PAHs.     

Recombination population of excited states of the hydrogen atom in an He-H<Subscript>2</Subscript> plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H₂] ≈ 10¹² cm^?3) has been studied spectroscopically. The contribution from electron-ion recombination Γ ₃ ^rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ ₃ ^rec (T _e ～ T _e ^?(0.9–1.0) has been obtained in the region kT _e = 0.026–0.064 eV.     

Investigations on Afterglows of Neon Gas Discharges

We report on the experimental and numerical investigations on afterglows of neon gas discharges, which are performed at the Eindhoven University of Technology. The studied gas pressure range extends from 1 to 100 torr, the discharge current from 1 to 100 mA. The densities of the 1s-levels are measured with the help of the selective excitation spectroscopy (fluorescence technique). In this way a great number of decay curves of the 1s-densities have been measured in the afterglow of neon gas discharges. From these curves the diffusion coefficient of the metastable 1s-atoms, the coefficients of atomic collisional transfer between the 1s₅- and 1s₄-level, as well as the three body collision coefficient between metastable 1s₅-atoms and neon ground state atoms have been determined. Besides these experiments a numerical model of the neon afterglows has been developed. With this model the afterglow phenomena can be simulated and the influence of the particular processes on the whole afterglow can be studied conveniently. Comparison is made between the experimentally and numerically obtained decay curves. For the application of the numerical model a number of starting conditions, such as radial density profiles, gas temperature, (relative) densities of the 1s-levels, have been measured. Results of these measurements are presented. Also with the help of the selective excitation spectroscopy the coefficients of atomic collisional transfer between the 2p-levels have been measured in the afterglow. From these results, together with the measured (relative) intensities of the neon spectral lines in the afterglow the partial recombination coefficients for the 2p-levels were calculated.     

Ozone Synthesis in an Electric Discharge between Ferroelectric Electrodes at Atmospheric Pressure

This paper deals with studies of the ozone synthesis by means of an ac discharge (50 Hz) between two parallel ferroelectric plates under radial oxygen flow conditions at atmospheric pressure. Bariumtitanate based ceramic with ? ∽ 6000 was used as ferroelectric material. An important feature of this kind of the discharge is the fact that the operating voltage is well one order of magnitude smaller than that of the silent discharge usually used for the O₃ production. Examples of I — U characteristics are discussed. The absorption of light at 253.7 nm wavelength was used to determine [O₃] within and downstream of the discharge as function of the O₂ flow rate. These results have been examined in terms of a kinetic investigation of the O₃ synthesis based on the so-called plug flow model including the particle balance equations of electrons, O atoms, O₂ and O₃ molecules, respectively. Thus, the measured decrease of [O₃] with increasing flow rate can be explained by the increasing influence of the loss of O₃ by convection on the particle balance of O₃. Furthermore it is shown that inside the plasma reactor [O₃] increases with the radius r. Therefore the data for measured spatial average of [O₃] inside the discharge are lower than that of [O₃] in the flowing afterglow. The last values are identical with that of [O₃] at the exit of the discharge.     

CARS study of the vibrational kinetics of nitrogen molecules in the burning and afterglow stages of a pulsed discharge

The vibrational kinetics of the nitrogen molecule in the ground state X ¹Σ _g ⁺ in the burning and afterglow stages of a pulsed discharge are investigated by coherent anti-Stokes Raman spectroscopy (CARS). The total cross section for vibrational excitation of the nitrogen molecule by electron impact to the first eight vibrational levels is determined. The rate constant for the associative ionization reaction involving nitrogen atoms in the metastable states ² P and ² D is estimated. It is found that the best agreement between the calculated and measured populations of the nitrogen molecules in the ground state X ¹Σ _g ⁺ in the afterglow stage of a pulsed discharge is obtained when the rate constant for VV exchange K ₀₁ ¹⁰ has the value predicted by the quantum-classical Billing-Fisher model. Zh. Tekh. Fiz. 67, 34–42 (May 1997)     

Elektronenverluste in einem abklingenden Wasserstoffplasma

The time dependence of the electron density in the afterglow period of an electrodeless discharge in hydrogen was measured by means of 4- and 8-mm microwave interferometry. An exponential decay was observed in the late afterglow permitting the evaluation of a time constant in the density range from 10¹²–10¹⁰ electrons per cm³. The decay time of the plasma was influenced by the discharge conditions. Electron losses could be explained by ambipolar diffusion and attachment to impurities. Two diffusion coefficients were found correlated to the discharge duration. The mobility value H₀=10.1±1.0 cm²/V · sec calculated from the diffusion coefficient found for short discharge pulses agrees with Saporoschenkos mobility value μ₀=10.2 cm²/V · sec for the H ₃ ⁺ -ion. A second mobility value μ₀=14.8±1.2cm²/V · sec found for longer discharge pulses might refer to the H⁺-ion.     

An optical emission spectroscopy study of the plasma generated in the DC HF CVD nucleation of diamond

Optical emission spectroscopy (OES) was used to study the plasma generated by the activation of the gas phase CH₄ + H₂ both by hot filaments and by a plasma discharge (DC HF CVD) during the nucleation of CVD diamond. The effects of nucleation parameters, such as methane concentration and extraction potential, on the plasma chemistry near the surface were investigated. The density of the diamond nucleation and the quality of the diamond films were studied by scanning electron microscopy (SEM) and Raman scattering, respectively. The OES results showed that the methane concentration influenced strongly the intensity ratio of H_β-H_α implying an increase of electron mean energy, as well as CH, CH⁺, C₂. A correlation between the relative increase of CH⁺ and the diamond nucleation density was found, conversely the increase of C₂ contributed to the introduction of defects in the diamond nuclei.     

低温等离子体活化转化煤层甲烷机理的光谱诊断

为了探究低温等离子体活化转化煤层甲烷的机理,采用自制的介质阻挡放电实验系统对体积组成为CH440%、O212%、N248%的模拟煤层甲烷进行等离子体活化转化。采用色谱分析方法对煤层甲烷介质阻挡放电稳定产物进行分析,结果表明低温等离子体活化煤层甲烷的主要产物为CH3OH、CO和CO_2。采用发射光谱原位诊断技术在200~700 nm波长范围内研究了放电气体的发射光谱,检测到O·、CH·、C·、Hα、N2(A3Σ+U)等激发态物种。基于发射光谱原位诊断和气相色谱分析结果,对煤层甲烷活化转化的自由基反应过程进行了推断。同时,明晰了反应气中N2对煤层甲烷活化和主要产物的生成具有促进作用,即N2产生了存活时间更长的亚稳态离子,该亚稳态离子将能量传递给反应气中的O2和CH4,进而加速了煤层甲烷的活化和稳定产物的生成。     

The dissociative recombination of HeNe+ ions with electrons: The partial rate constants for the formation of atoms in the 2p 53p configuration

A simple experiment transparent for interpretation is presented in which afterglow of a discharge in helium with a small admixture of neon was studied. The intensities of the spectral lines of the Ne* atom at the stage of plasma decay were analyzed to find the conditions under which the dissociative recombination of heteronuclear ions HeNe⁺ + e ?? He + Ne* played a predominant role in the formation of part of the after-glow spectrum. The absolute values of partial coefficients responsible for the formation of excited neon atoms in the 2p ⁵3p configuration were determined.     

氦-氧等离子体针灭活肺癌A549细胞

研究了介质阻挡放电等离子体针对肺癌A549细胞的灭活机制, 探讨从不锈钢管注入到氦等离子体尾流区域的氧气含量对杀灭肺癌细胞A549的影响. 利用中性红吸收测试法定性观察了等离子体处理后死亡的细胞和活着的细胞的形态区别, 并且定量测定了不同条件下的细胞存活率. 在固定功率24 W的处理过程中, 氦-氧等离子体的灭活效率主要取决于等离子体曝光时间以及氦气中添加氧气的百分含量. 实验结果显示最好的处理参数为: 处理时间150 s, 800 mL/min的氦气添加3%氧气, 保持针距样品的距离为3 mm. 根据氦-氧等离子体发射光谱, 可以推断在细胞灭活过程中, 氦-氧等离子体中的活性粒子(如羟基和氧自由基)起主要作用.     

Relaxation of the electron temperature in an inert-gas afterglow plasma at elevated pressures

The relaxation of the electron temperature T _e in helium and neon afterglow at elevated pressures is studied theoretically and experimentally. It is shown that the processes in which fast electrons are produced are accompanied by the heating of thermal electrons. The high-energy part of the electron energy distribution function is studied in the intermediate regime (between the local and nonlocal regimes) of its formation. It is shown that, in this case, the calculated effective energy transferred from the fast electrons to the thermal electrons depends substantially on the wall potential of the discharge tube. Comparison of these calculations with experiments testifies to the reliability of the probe technique for measuring T _e in an afterglow at elevated pressures.     

Role of neon in a decaying high-purity helium plasma

The evolution of the electron and atomic and molecular metastable densities and the radiation of the decaying plasma of helium with a 10^–5-fraction of neon additive is experimentally studied. A model of elementary processes in He–Ne plasma is constructed, which describes the formation and destruction of HeNe⁺ and Ne₂ ⁺ molecular ions and their contribution to the formation of the afterglow spectrum by the electronion recombination. The various criteria influence of neon on the parameters of the decaying plasma are studied. The possibility of determining the amount of neon in helium by measuring the relative intensities of helium molecular bands and neon spectral lines in the afterglow is considered.     

On the mechanisms of formation of excited hydrogen atoms in a decaying helium-hydrogen plasma

We spectroscopically studied the population of the excited hydrogen atomic states with the principal quantum numbers n=3 and 4 in a decaying plasma produced by a pulsed discharge in a mixture of helium (p=40.4 Torr) with a small amount of hydrogen ([H₂]≈10¹² cm^?3). Experiments on recording the response of the spectral line intensities to a short-duration electron temperature perturbation revealed the contribution of electron-ion recombination to the population of the H*(n=3) states in the early afterglow. The ions produced by collisions of hydrogen molecules with metastable He(2³ S ₁) atoms, whose density decreases relatively rapidly with time in the decaying plasma, were assumed to be involved in this process. No population of the H*(n=4) atomic levels due to electron-ion recombination was found. Our experimental results are consistent with the conclusions of previous studies that excitation transfer during collisions of metastable helium molecules with hydrogen molecules plays a major role in the population of the excited hydrogen atomic states both with n=3 and with n=4 during most of the afterglow.