Showing papers on "Argon published in 2015"

Identification of the biologically active liquid chemistry induced by a nonthermal atmospheric pressure plasma jet.

Abstract: The mechanism of interaction of cold nonequilibrium plasma jets with mammalian cells in physiologic liquid is reported. The major biological active species produced by an argon RF plasma jet responsible for cell viability reduction are analyzed by experimental results obtained through physical, biological, and chemical diagnostics. This is complemented with chemical kinetics modeling of the plasma source to assess the dominant reactive gas phase species. Different plasma chemistries are obtained by changing the feed gas composition of the cold argon based RF plasma jet from argon, humidified argon (0.27%), to argon/oxygen (1%) and argon/air (1%) at constant power. A minimal consensus physiologic liquid was used, providing isotonic and isohydric conditions and nutrients but is devoid of scavengers or serum constituents. While argon and humidified argon plasma led to the creation of hydrogen peroxide dominated action on the mammalian cells, argon-oxygen and argon-air plasma created a very different biological action and was characterized by trace amounts of hydrogen peroxide only. In particular, for the argon-oxygen (1%), the authors observed a strong negative effect on mammalian cell proliferation and metabolism. This effect was distance dependent and showed a half life time of 30 min in a scavenger free physiologic buffer. Neither catalase and mannitol nor superoxide dismutase could rescue the cell proliferation rate. The strong distance dependency of the effect as well as the low water solubility rules out a major role for ozone and singlet oxygen but suggests a dominant role of atomic oxygen. Experimental results suggest that O reacts with chloride, yielding Cl2(-) or ClO(-). These chlorine species have a limited lifetime under physiologic conditions and therefore show a strong time dependent biological activity. The outcomes are compared with an argon MHz plasma jet (kinpen) to assess the differences between these (at least seemingly) similar plasma sources.

Low Radioactivity Argon Dark Matter Search Results from the DarkSide-50 Experiment

Abstract: The DarkSide-50 dark matter search reports the first results obtained using a target of low-radioactivity argon extracted from underground sources. The experiment is located at the Laboratori Nazionali del Gran Sasso and uses a two-phase time projection chamber as a detector. A total of 155 kg of low radioactivity argon has been obtained, and we have determined that underground argon is depleted in Ar-39 by a factor (1.4 +- 0.2) x 10^3 relative to atmospheric argon. The underground argon is also found to contain (2.05 +- 0.13) mBq/kg of Kr-85. We find no evidence for dark matter in the form of WIMPs in 70.9 live-days of data with a fiducial mass of (36.9 +- 0.6) kg. When combined with our preceding search with an atmospheric argon target, we set a 90 % C.L. upper limit on the WIMP-nucleon spin-independent cross section of 2.0 x 10^-44 cm^2 (8.6 x 10^-44 cm^2, 8.0 x 10^-43 cm^2) for a WIMP mass of 100 GeV/c^2 (1 TeV/c^2 , 10 TeV/c^2).

The effect of the driving frequency on the confinement of beam electrons and plasma density in low-pressure capacitive discharges

Abstract: The effect of changing the driving frequency on the plasma density and the electron dynamics in a capacitive radio-frequency argon plasma operated at low pressures of a few Pa is investigated by particle-in-cell/Monte-Carlo collision simulations and analytical modeling. In contrast to previous assumptions, the plasma density does not follow a quadratic dependence on the driving frequency in this non-local collisionless regime. Instead, a step-like increase at a distinct driving frequency is observed. Based on an analytical power balance model, in combination with a detailed analysis of the electron kinetics, the density jump is found to be caused by an electron heating mode transition from the classical α-mode into a low-density resonant heating mode characterized by the generation of two energetic electron beams at each electrode per sheath expansion phase. These electron beams propagate through the bulk without collisions and interact with the opposing sheath. In the low-density mode, the second beam is found to hit the opposing sheath during its collapse. Consequently, a large number of energetic electrons is lost at the electrodes resulting in a poor confinement of beam electrons in contrast to the classical α-mode observed at higher driving frequencies. Based on the analytical model this modulated confinement quality and the related modulation of the energy lost per electron lost at the electrodes is demonstrated to cause the step-like change of the plasma density. The effects of a variation of the electrode gap, the neutral gas pressure, the electron sticking and secondary electron emission coefficients of the electrodes on this step-like increase of the plasma density are analyzed based on the simulation results.

Effect of additive oxygen gas on cellular response of lung cancer cells induced by atmospheric pressure helium plasma jet.

Abstract: The atmospheric pressure helium plasma jet driven by pulsed dc voltage was utilized to treat human lung cancer cells in vitro. The properties of plasma plume were adjusted by the injection type and flow rate of additive oxygen gas in atmospheric pressure helium plasma jet. The plasma characteristics such as plume length, electric current and optical emission spectra (OES) were measured at different flow rates of additive oxygen to helium. The plasma plume length and total current decreased with an increase in the additive oxygen flow rate. The electron excitation temperature estimated by the Boltzmann plot from several excited helium emission lines increased slightly with the additive oxygen flow. The oxygen atom density in the gas phase estimated by actinometry utilizing argon was observed to increase with the additive oxygen flow. The concentration of intracellular reactive oxygen species (ROS) measured by fluorescence assay was found to be not exactly proportional to that of extracellular ROS (measured by OES), but both correlated considerably. It was also observed that the expression levels of p53 and the phospho-p53 were enhanced in the presence of additive oxygen flow compared with those from the pure helium plasma treatment.

CO2-CH4 conversion and syngas formation at atmospheric pressure using a multi-electrode dielectric barrier discharge

Abstract: The conversion of CO2 and CH4 into value-added chemicals is studied in a new geometry of a dielectric barrier discharge (DBD) with multi-electrodes, dedicated to the treatment of high gas flow rates. Gas chromatography is used to define the CO2 and CH4 conversion as well as the yields of the products of decomposition (CO, O2 and H2) and of recombination (C2H4, C2H6 and CH2O). The influence of three parameters is investigated on the conversion: the CO2 and CH4 flow rates, the plasma power and the nature of the carrier gas (argon or helium). The energy efficiency of the CO2 conversion is estimated and compared with those of similar atmospheric plasma sources. Our DBD reactor shows a good compromise between a good energy efficiency and the treatment of a large CO2 flow rate.

Enhancing ion yields in time-of-flight-secondary ion mass spectrometry: a comparative study of argon and water cluster primary beams.

Abstract: Following from our previous Letter on this topic, this Article reports a detailed study of time-of-flight-secondary ion mass spectrometry (TOF-SIMS) positive ion spectra generated from a set of model biocompounds (arginine, trehalose, DPPC, and angiotensin II) by water cluster primary ion beams in comparison to argon cluster beams over a range of cluster sizes and energies. Sputter yield studies using argon and water beams on arginine and Irganox 1010 have confirmed that the sputter yields using water cluster beams lie on the same universal sputtering curve derived by Seah for argon cluster beams. Thus, increased ion yield using water cluster beams must arise from increased ionization. The spectra and positive ion signals observed using cluster beams in the size range from 1 000 to 10 000 and the energy range 5–20 keV are reported. It is confirmed that water cluster beams enhance proton related ionization over against argon beams to a significant degree such that enhanced detection sensitivities from 1 μm...

Characteristics of DC Gas-Liquid Phase Atmospheric-Pressure Plasma and Bacteria Inactivation Mechanism

Abstract: A direct current (DC) gas-liquid phase atmospheric-pressure argon (Ar) plasma is used to inactivate Staphylococcus aureus suspended in the liquid The characteristics of the gas-liquid plasma such as gas temperature, electron excitation temperature, and electron density are investigated by optical emission spectroscopy (OES) Direct plasma treatment for 40 min results in more than 20-log cell reduction The emission spectra obtained from the gas-liquid phase plasma show the presence of hydroxyl radicals and atomic oxygen which give rise to effective inactivation of microorganisms The energetic particles generated from the plasma tend to induce chemical effects such as formation of hydroxyl and hydrogen peroxide and reduced pH The water sample after plasma treatment retains the inactivation ability for a long time and the germicidal effects arise from residual H2O2 and acidic pH These effects have potential applications in plasma biomedicine and water purification

Surface modification of polyethylene in an argon atmospheric pressure plasma jet

Abstract: The surface properties of polyethylene can successfully be altered using argon plasmas. In this work, the surface modification of low density polyethylene (LDPE) using an argon atmospheric pressure plasma jet (APPJ) is profoundly investigated. The surface modification is examined using different analysing techniques namely, water contact angle (WCA) measurements for the wettability and X-ray photoelectron spectroscopy (XPS) for the chemical composition. Particular attention is paid to the treatment distance between the plasma jet capillary and the LDPE foil and the applied treatment time. At treatment distances between 5 and 15 mm, the WCA can be reduced with more than 70% within a treatment time of a few ms. XPS measurements reveal that this is due to the incorporation of oxygen containing groups and especially the increased implementation of the O–C O group has a big influence. At treatment distances above 15 mm, the wettability decreases with increasing treatment distance. The wettability can however be enhanced by increasing the treatment time. Ageing considerations show that the loss in treatment efficiency is restricted to only 25%, meaning that even after 14 days of ageing the WCA reduction upon plasma treatment is still more than 40%. Based on the above mentioned results, the most appropriate parameters can thus be selected to provide an efficient plasma treatment of LDPE using the argon APPJ.

Gas flow characteristics of a time modulated APPJ: The effect of gas heating on flow dynamics

Abstract: This work investigates the flow dynamics of a radio-frequency (RF) non-equilibrium argon atmospheric pressure plasma jet. The RF power is at a frequency of 50 Hz or 20 kHz. Combined flow pattern visualizations (obtained by shadowgraphy) and gas temperature distributions (obtained by Rayleigh scattering) are used to study the formation of transient vortex structures in initial flow field shortly after the plasma is switched on and off in the case of 50 Hz modulation. The transient vortex structures correlate well with observed temperature differences. Experimental results of the fast modulated (20 kHz) plasma jet that does not induce changes of the gas temperature are also presented. The latter result suggests that momentum transfer by ions does not have dominant effect on the flow pattern close to the tube. It is argued that the increased gas temperature and corresponding gas velocity increase at the tube exit due to the plasma heating increases the admixing of surrounding air and reduces the effective potential core length. With increasing plasma power a reduction of the effective potential core length is observed with a minimum length for 5.6 W after which the length extends again. Possible mechanisms related to viscosity effects and ionic momentum transfer are discussed.

The effect of air on solvated electron chemistry at a plasma/liquid interface

Abstract: Plasmas in contact with liquids initiate complex chemistry that leads to the generation of a wide range of reactive species. For example, in an electrolytic configuration with a cathodic plasma electrode, electrons from the plasma are injected into the solution, leading to solvation and ensuing reactions. If the gas contains oxygen, electronegative oxygen molecules may react with the plasma electrons via attachment to reduce the electron flux to the solution reducing the production of solvated electrons or produce reactive oxygen species that quickly scavenge solvated electrons in solution. Here, we applied a total internal reflection absorption spectroscopy technique to compare the concentration of solvated electrons produced in solution by an argon plasma containing various amounts of oxygen, nitrogen, and air. Our measurements indicate that in oxygen or air ambients, electron attachment in the plasma phase greatly attenuates the electron flux incident on the liquid surface. The remaining electrons then solvate but are quickly scavenged by reactive oxygen species in the liquid phase.

Point defects assisted NH3 gas sensing properties in ZnO nanostructures

Abstract: In this report, the NH 3 gas sensing properties of ZnO nanostructures fabricated by radio frequency magnetron sputtering under various argon sputtering pressures have been investigated under various temperatures. The morphological transitions occur from vertical standing nanorods to inclined and tapered nanostructures with increasing the argon sputtering pressure. The dominant green emission at around 2.28 eV in the photoluminescence spectra signifies the presence of oxygen vacancies in the ZnO nanostructures which increases as a function of argon sputtering pressure. Despite low surface area, the nanostructures grown under higher argon sputtering pressure of 10 Pa exhibit excellent NH 3 gas response magnitude since it is exhibiting more oxygen vacancies as compared to other counterparts. For 25 ppm NH 3 gas at room temperature, a response time of 49 s and a fast recovery time of 19 s are attributed to the modification in the intermediate defect states induced by the oxygen vacancies through the adsorption and desorption of gas molecules on the surface of ZnO nanostructures.

The impact of different process gas compositions on the inactivation effect of an atmospheric pressure plasma jet on Bacillus spores

Abstract: Atmospheric plasma provides the advantages of high microbial inactivation that can be performed under ambient conditions. It is consequently regarded as potential alternative to traditional food preservation methods. In this study we systematically tested the influence of argon as plasma carrier gas with admixtures of oxygen (0–0.34 vol.%) and nitrogen (0–0.3 vol.%) towards its emission intensity of UV-C light, excited OH and N 2 -species and atomic oxygen. A mixture of argon, 0.135 vol.% oxygen and 0.2 vol.% nitrogen emitted four fold more UV photons than pure argon. However, sporicidal effects on Bacillus atrophaeus (3.1 log 10 ) and Bacillus subtilis spores (2.4 log 10 ) were found for pure argon plasma, which were similar as compared to the sporicidal effect of the plasma with highest UV-emission. To distinguish lethal effects caused by emitted UV-light and reactive species, UV-sensitive mutant spore strains (PS578 and FB122) were exposed to plasmas with different UV-emission intensities and a significant impact of UV-light on the first phase of spore inactivation was confirmed. Industrial relevance As an efficient method for the inactivation of microorganisms at low temperatures and atmospheric pressure, plasma is already commercially used for the sterilization of medical devices. The results presented in this study could be useful for a process optimization regardless if the plasma is applied for food preservation or surface decontamination. Especially the impact of emitted UV photons from the plasma on the first inactivation phase of endospores attached to surfaces, depicts a high potential of such plasmas for a rapid spore inactivation.

Quantitative schlieren diagnostics for the determination of ambient species density, gas temperature and calorimetric power of cold atmospheric plasma jets

Abstract: A measurement and evaluation technique for performing quantitative Schlieren diagnostics on an argon-operated cold atmospheric plasma jet is presented. Combined with computational fluid dynamics simulations, the method not only yields the temporally averaged ambient air density and temperature in the effluent of the fully turbulent jet, but also allows for an estimation of the calorimetric power deposited by the plasma.The change of the refractive index due to mixing of argon and air is in the same range as caused by the temperature increase of less than 35 K in the effluent of the plasma jet. The Schlieren contrast therefore needs to be corrected for the contribution from ambient air diffusion. The Schlieren system can be calibrated accurately using the signal obtained from the argon flow when the plasma is turned off. The temperature measured in this way is compared to the value obtained using a fibre-optics temperature probe and shows excellent agreement. By fitting a heat source in a fluid dynamics simulation to match the measured temperature field, the calorimetric power deposited by the plasma jet can be estimated as 1.1 W.

Experimental and Theoretical Studies of the Infrared Spectra and Bonding Properties of NgBeCO3 and a Comparison with NgBeO (Ng = He, Ne, Ar, Kr, Xe)

Abstract: The novel neon complex NeBeCO3 has been prepared in a low-temperature neon matrix via codeposition of laser-evaporated beryllium atoms with O2 + CO/Ne. Doping by the heavier noble gas atoms argon, krypton and xenon yielded the associated adducts NgBeCO3 (Ng = Ar, Kr, Xe). The noble gas complexes have been identified via infrared spectroscopy. Quantum chemical calculations of NgBeCO3 and NgBeO (Ng = He, Ne, Ar, Kr, Xe) using ab initio methods and density functional theory show that the Ng–BeCO3 bonds are slightly longer and weaker than the Ng–BeO bonds. The energy decomposition analysis of the Ng–Be bonds suggests that the attractive interactions come mainly from the Ng → BeCO3 and Ng → BeO σ donation.

Numerical experiments on evaporation and explosive boiling of ultra-thin liquid argon film on aluminum nanostructure substrate

Abstract: Evaporation and explosive boiling of ultra-thin liquid film are of great significant fundamental importance for both science and engineering applications. The evaporation and explosive boiling of ultra-thin liquid film absorbed on an aluminum nanostructure solid wall are investigated by means of molecular dynamics simulations. The simulated system consists of three regions: liquid argon, vapor argon, and an aluminum substrate decorated with nanostructures of different heights. Those simulations begin with an initial configuration for the complex liquid-vapor-solid system, followed by an equilibrating system at 90 K, and conclude with two different jump temperatures, including 150 and 310 K which are far beyond the critical temperature. The space and time dependences of temperature, pressure, density number, and net evaporation rate are monitored to investigate the phase transition process on a flat surface with and without nanostructures. The simulation results reveal that the nanostructures are of great help to raise the heat transfer efficiency and that evaporation rate increases with the nanostructures’ height in a certain range.

Effect of secondary electron emission on the plasma sheath

Abstract: In this experiment, plasma sheath potential profiles are measured over boron nitride walls in argon plasma and the effect of secondary electron emission is observed. Results are compared to a kinetic model. Plasmas are generated with a number density of 3 × 1012 m−3 at a pressure of 10−4 Torr-Ar, with a 1%–16% fraction of energetic primary electrons. The sheath potential profile at the surface of each sample is measured with emissive probes. The electron number densities and temperatures are measured in the bulk plasma with a planar Langmuir probe. The plasma is non-Maxwellian, with isotropic and directed energetic electron populations from 50 to 200 eV and hot and cold Maxwellian populations from 3.6 to 6.4 eV and 0.3 to 1.3 eV, respectively. Plasma Debye lengths range from 4 to 7 mm and the ion-neutral mean free path is 0.8 m. Sheath thicknesses range from 20 to 50 mm, with the smaller thickness occurring near the critical secondary electron emission yield of the wall material. Measured floating potenti...

Simulation of emission spectra from nonuniform reactive laser-induced plasmas

Abstract: We demonstrate that chemical reactions leading to the formation of AlO radicals in plasmas produced by ablation of aluminum or Ti-sapphire with ultraviolet nanosecond laser pulses can be predicted by the model of local thermodynamic equilibrium. Therefore, emission spectra recorded with an echelle spectrometer and a gated detector were compared to the spectral radiance computed for uniform and nonuniform equilibrium plasmas. The calculations are based on analytical solutions of the radiation transfer equation. The simulations show that the plasmas produced in argon background gas are almost uniform, whereas temperature and density gradients are evidenced in air. Furthermore, chemical reactions exclusively occur in the cold plume periphery for ablation in air. The formation of AlO is negligible in argon as the plasma temperature is too large in the time interval of interest up to several microseconds. Finally, the validity of local thermodynamic equilibrium is shown to depend on time, space, and on the elemental composition. The presented conclusions are of interest for material analysis via laser-induced breakdown spectroscopy and for laser materials processing.

The spatio-temporal distribution of He (23S1) metastable atoms in a MHz-driven helium plasma jet is influenced by the oxygen/nitrogen ratio of the surrounding atmosphere

Abstract: The density of helium He (23S1) metastable atoms is measured in a 1.6 mm diameter MHz-driven atmospheric pressure helium plasma jet by laser absorption spectroscopy with spatial and temporal resolution. The surrounding atmosphere of the jet is varied from pure oxygen to pure nitrogen with a gas shielding device. The highest metastable density of 1.3 × 1013 cm−3 is obtained in the center of the jet close to the nozzle exit at normal atmospheric air conditions. Within 0.3 mm in the radial direction and 2 mm in the axial direction, the He metastable density drops below the detection limit. The obtained He metastable lifetime is almost independent of the shielding gas composition. By analyzing the diffusion of shielding gas species into the effluent it is concluded that their density is too low to explain the observed He metastable lifetime. Instead, impurities from the feed gas, especially water molecules, are more likely to be responsible. However, a drastic change in metastable He density is observed when decreasing the amount of oxygen in the shielding gas. The lower the oxygen amount, the lower the metastable He density. For pure nitrogen, no He metastables are detected at all. By exchanging nitrogen with argon, a similar behavior is observed. Thus, it is concluded that it is the absence of ambient oxygen rather than the elevated presence of nitrogen, which is responsible for the observed decrease in the He (23S1) density.

Numerical analysis of the effect of nitrogen and oxygen admixtures on the chemistry of an argon plasma jet operating at atmospheric pressure

Abstract: In this paper we study the cold atmospheric pressure plasma jet, called kinpen, operating in Ar with different admixture fractions up to 1% pure , and + . Moreover, the device is operating with a gas curtain of dry air. The absolute net production rates of the biologically active ozone () and nitrogen dioxide () species are measured in the far effluent by quantum cascade laser absorption spectroscopy in the mid-infrared. Additionally, a zero-dimensional semi-empirical reaction kinetics model is used to calculate the net production rates of these reactive molecules, which are compared to the experimental data. The latter model is applied throughout the entire plasma jet, starting already within the device itself. Very good qualitative and even quantitative agreement between the calculated and measured data is demonstrated. The numerical model thus yields very useful information about the chemical pathways of both the and the generation. It is shown that the production of these species can be manipulated by up to one order of magnitude by varying the amount of admixture or the admixture type, since this affects the electron kinetics significantly at these low concentration levels.

Optimized Mie potentials for phase equilibria: Application to noble gases and their mixtures with n-alkanes

Abstract: Transferrable force fields, based on n-6 Mie potentials, are presented for noble gases. By tuning the repulsive exponent, ni, it is possible to simultaneously reproduce experimental saturated liquid densities and vapor pressures with high accuracy, from the normal boiling point to the critical point. Vapor-liquid coexistence curves for pure fluids are calculated using histogram reweighting Monte Carlo simulations in the grand canonical ensemble. For all noble gases, saturated liquid densities and vapor pressures are reproduced to within 1% and 4% of experiment, respectively. Radial distribution functions, extracted from NVT and NPT Monte Carlo simulations, are in similarly excellent agreement with experimental data. The transferability of the optimized force fields is assessed through calculations of binary mixture vapor-liquid equilibria. These mixtures include argon + krypton, krypton + xenon, methane + krypton, methane + xenon, krypton + ethane, and xenon + ethane. For all mixtures, excellent agreement with experiment is achieved without the introduction of any binary interaction parameters or multi-body interactions.

Opacity and conductivity measurements in noble gases at conditions of planetary and stellar interiors

Abstract: The noble gases are elements of broad importance across science and technology and are primary constituents of planetary and stellar atmospheres, where they segregate into droplets or layers that affect the thermal, chemical, and structural evolution of their host body. We have measured the optical properties of noble gases at relevant high pressures and temperatures in the laser-heated diamond anvil cell, observing insulator-to-conductor transformations in dense helium, neon, argon, and xenon at 4,000–15,000 K and pressures of 15–52 GPa. The thermal activation and frequency dependence of conduction reveal an optical character dominated by electrons of low mobility, as in an amorphous semiconductor or poor metal, rather than free electrons as is often assumed for such wide band gap insulators at high temperatures. White dwarf stars having helium outer atmospheres cool slower and may have different color than if atmospheric opacity were controlled by free electrons. Helium rain in Jupiter and Saturn becomes conducting at conditions well correlated with its increased solubility in metallic hydrogen, whereas a deep layer of insulating neon may inhibit core erosion in Saturn.