Low-temperature Argon Plasma Research Articles

Advanced Thomson scattering system for high-flux linear plasma generator

An advanced Thomson scattering system has been built for a linear plasma generator for plasma surface interaction studies. The Thomson scattering system is based on a Nd:YAG laser operating at the second harmonic and a detection branch featuring a high etendue (f/3) transmission grating spectrometer equipped with an intensified charged coupled device camera. The system is able to measure electron density (n(e)) and temperature (T(e)) profiles close to the output of the plasma source and, at a distance of 1.25 m, just in front of a target. The detection system enables to measure 50 spatial channels of about 2 mm each, along a laser chord of 95 mm. By summing a total of 30 laser pulses (0.6 J, 10 Hz), an observational error of 3% in n(e) and 6% in T(e) (at n(e) = 9.4 × 10(18) m(-3)) can be obtained. Single pulse Thomson scattering measurements can be performed with the same accuracy for n(e) > 2.8 × 10(20) m(-3). The minimum measurable density and temperature are n(e) < 1 × 10(17) m(-3) and T(e) < 0.07 eV, respectively. In addition, using the Rayleigh peak, superimposed on the Thomson scattered spectrum, the neutral density (n(0)) of the plasma can be measured with an accuracy of 25% (at n(0) = 1 × 10(20) m(-3)). In this report, the performance of the Thomson scattering system will be shown along with unprecedented accurate Thomson-Rayleigh scattering measurements on a low-temperature argon plasma expansion into a low-pressure background.

Low-temperature atmospheric pressure argon plasma treatment and hybrid laser-plasma ablation of barite crown and heavy flint glass

We report on atmospheric pressure argon plasma-based surface treatment and hybrid laser-plasma ablation of barite crown glass N-BaK4 and heavy flint glass SF5. By pure plasma treatment, a significant surface smoothing, as well as an increase in both the surface energy and the strength of the investigated glass surfaces, was achieved. It was shown that for both glasses, hybrid laser plasma ablation allows an increase in the ablation depth by a factor of 2.1 with respect to pure laser ablation. The ablated volume was increased by an averaged factor of 1.5 for N-BaK4 and 3.7 for SF5.

Atmospheric pressure argon plasma-assisted enhancement of laser ablation of aluminum

In this paper, we present a hybrid laser-plasma ablation method for material processing applications. For this purpose, a coaxial configuration consisting of a low-temperature atmospheric pressure argon plasma beam and a Nd:YAG-laser at a wavelength of 355 nm was used. Both pure laser ablation and hybrid laser-plasma ablation experiments were performed on aluminum at different laser energies and numbers of laser pulses. In the case of hybrid ablation, both the depth and volume ablation rates were increased significantly in comparison to pure laser ablation. This effect is described by a linear interrelationship of both the ablation rate and the particularly applied laser energy and is thus due to energetic synergies. Such behavior can be explained by the de-excitation of argon plasma species and an accompanying energy deposition at the generated debris and the sample surface. The energetic effect was found to abate with increasing ablation depth. However, considerable improvements in terms of ablation rate are achieved in the near-surface depth range of approx. 500 microns.

Surface Properties of UHMWPE Fiber after Low Temperature Argon-Plasma Treatment

To improve the adhesion between ultra-high-molecular-weight polyethylene (UHMWPE) fibers and matrix, the UHMWPE fibers were treated by low temperature argon-plasma. The effects of argon-plasma treatment on the properties of UHMWPE have been investigated. The roughness and wetting ability were all found to increase significantly after modifications. The tensile strength of UHMWE fibers were decreased with the plasma treatment time. The optimum plasma treatment is 2min.The increasing of roughness and wetting ability of UHMWPE fiber are beneficial to the improvement the adhesion between UHMWPE fiber and matrix.

Argon plasma modeling with detailed fine-structure cross sections

Our recently reported fully relativistic distorted-wave electron-impact cross sections from the ground and metastable states of argon to various excited fine-structure levels are incorporated in a collisional-radiative model to obtain the population densities for the 3p54s and 3p54p (1s and 2p) fine-structure manifolds for low temperature argon plasmas. Excitation cross sections from the two 3p54s J = 1 resonance levels, 1s2 and 1s4, to the higher lying 2p fine-structure manifold as well as for transitions among individual levels of the 1s and 2p manifolds are also calculated and included in the present model which were not fully considered in any earlier model. Our results for the population densities of the 1s and 2p levels show good agreement with recent measurements. The variation of population densities of all the 1s and 2p levels with electron temperature and density are presented. We have also calculated and compared the intensities for the 750.38 nm (2p1 → 1s2) and 696.54 nm (2p2 → 1s5) lines with recently reported experimental results. The present work suggests that the inclusion of a complete fine-structure description of the electronic processes occurring in the plasma is important for a collisional radiative model, which includes separate 1s and 2p levels.

Time-dependent effects of low-temperature atmospheric-pressure argon plasma on epithelial cell attachment, viability and tight junction formation in vitro

The application of physical plasma to living tissues is expected to promote wound healing by plasma disinfection and stimulation of tissue regeneration. However, the effects of plasma on healthy cells must be studied and understood. In our experiments we used an argon plasma jet (kINPen®09) to gain insights into time-dependent plasma effects on cell attachment, viability and tight junction formation in vitro. Murine epithelial cells mHepR1 were suspended in complete cell culture medium and were irradiated with argon plasma (direct approach) for 30, 60 and 120 s. Suspecting that physical plasma may exert its effect via the medium, cell culture medium alone was first treated with argon plasma (indirect approach) and immediately afterwards, cells were added and also cultured for 24 h. Cell morphology and vitality were verified using light microscopy and an enzyme-linked immunosorbent assay. Already after 30 s of treatment the mHepR1 cells lost their capability to adhere and the cell vitality decreased with increasing treatment time. Interestingly, the same inhibitory effect was observed in the indirect approach. Furthermore, the argon plasma-treated culture medium-induced large openings of the cell's tight junctions, were verified by the zonula occludens protein ZO-1, which we observed for the first time in confluently grown epithelial cells.

Improvement in micro-structural and mechanical properties of zinc film by surface treatment with low temperature argon plasma

Nanocrystalline zinc films were deposited on gold coated borosilicate glass substrates by thermal evaporation method using zinc powders as the source material and then treated with argon plasma at various temperatures. From X-ray diffraction study, the as-deposited films are found to be metallic Zn and polycrystalline in nature. The crystalline nature improves with the increase of temperature up to 200°C and decreases with the further increase of temperature to 300°C. The binding energy observed for Zn 2p3/2, and the binding energy separation between Zn 2p3/2 and Zn 2p1/2 in the X-ray photoelectron spectrum indicate that the films are metallic zinc films. Transmission electron microscopic study shows hexagonal shaped grains having size ∼58nm upon treatment with Ar plasma. It is clearly shown the grain growth and distinct grain boundary with the increase in temperature. The average Young's modulus (E) and hardness (H) are measured to be 84GPa and 4.0GPa for as-deposited film, whereas 98GPa and 5.8GPa for plasma treated film at 200°C. The enhancement in mechanical properties is attributed to improvement in crystalline nature of the film and better interlinking between grains and boundaries.

A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere

A 2.54 cm diameter conducting electrically isolated Copper sphere is suspended in a low density (104 cm−3), low temperature (Te = 0.5 eV) Argon plasma, which mimics a spacecraft in an ionospheric plasma. An electron beam with current density of approximately 10−10 A/cm2 and beam spot of 10.2 cm diameter, which mimics an auroral electron beam, is fired at the sphere while varying the beam energy from 100 eV to 2 keV. The plasma potential in the sheath around the sphere is measured using an emissive probe as the electron beam energy is varied. To observe the effects of the electron beam, the experimental sheath potential profiles are compared to a model of the plasma potential around a spherically symmetric charge distribution in the absence of electron beams. Comparison between the experimental data and the model shows that the sphere is less negative than the model predicts by up to half a volt for beam energies that produce high secondary electron emission from the surface of the sphere. It is shown that this secondary emission can account for changes in potential of spacecraft in the ionosphere as they pass through auroral beams and thus helps to improve interpretations of ionospheric thermal ion distributions.

Vapor generation in dielectric barrier discharge for sensitive detection of mercury by inductively coupled plasma optical emission spectrometry

Mercury solution without or with formic acid was introduced into a low temperature argon plasma from dielectric barrier discharge (DBD). Mercury vapor generated in the DBD was separated from the liquid phase and finally swept into an inductively coupled plasma optical emission spectrometer (ICP-OES) for determination. The optimum conditions for the proposed technique and operation of the ICP-OES, as well as interferences from concomitants, were investigated in detail. It was found that the vapor generation efficiency of mercury could be significantly enhanced with the addition of formic acid. However, the efficiency was reduced sharply in the presence of chloride ions or oxidizing substances of high concentration. Under the optimized conditions, a limit of detection of 0.090 μg L−1 and a precision of 2.1% RSD at a concentration of 10 μg L−1 were achieved by the proposed method. The new DBD-induced mercury vapor generation provides several advantages including low power consumption (<25 W), green analytical chemistry, cost-effectiveness, smaller size, long operation lifetime, and ease of on-line operation. The methodology has been successfully applied to the determination of mercury in a certified reference water sample and mineral water samples.

Hybrid Computer Simulation Scheme for Computational Study of Low-Temperature Plasma Containing Micrometer-Sized Dust Particles

In this paper, an algorithm for the computational study of low-temperature argon plasma containing small micrometer-sized solid dust particulates is presented. In the first section, the numerical and computational approaches that are most frequently used in this area of research are summarized, and the references on some theoretical and experimental works are given. Consequently, we describe a hybrid model that is capable to express physical quantities depending on the electron energy distribution function (like reaction rates, diffusion coefficients, coefficients of mobility, etc.) as functions of space coordinates (x, y, z) and given time <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> . This way, the precision of calculation is increased in comparison with fluid modeling techniques. Some results of illustrative calculations are presented and discussed in the last section.

Core magnetic islands and plasma confinement in the H-1NF heliac

Plasma confinement in the vicinity of vacuum magnetic islands near the magnetic axis in the H-1NF heliac [S. M. Hamberger et al., Fusion Technol. 17, 123 (1990)] has been experimentally studied in a low temperature argon plasma. Experimental results indicate that, under favorable conditions, these low order (m=2) islands near the core of the plasma serve as “pockets” of higher electron density. This results in significant profile modifications including enhancement of the core radial electric field to a large positive value, possibly through an electron-root ambipolar condition. The characteristics of islands are found to be dependent on the plasma collisionality and island width.

Nanodispersed powders: Synthesis methods and practical applications

A comparative analysis of the methods and technologies used to produce nanopowders is performed. The fundamentals of both the traditional technology for chemically synthesizing inorganic nanocrystalline particles of metal oxides by the crystallization of precursors (amorphous metal hydroxides obtained by chemical coprecipitation from salts) and the most promising methods for producing nanopowders and materials on their basis (including the dispersion of monodisperse flows of liquids and solutions in an electrical field and a plasma technology that involves electrical arc recondensation of substances) are considered. The studies performed at the State Research Institute of Organoelemental Compound Chemistry and Technology (SRIOCCT) are taken as examples to describe methods for the recondensation of coarse powders of silicon, silicon carbide, and aluminum oxide in low-temperature argon plasma. The most efficient regimes of the process, difficulties, and unresolved problems are analyzed. Results of the physicochemical investigations and tests of the synthesized pilot samples are described.

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 cm 3/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.

Hybrid computer simulations: electrical charging of dust particles in low-temperature plasma

This paper is focused on the study of the electrical charging process of micron-sized particles immersed into low-temperature argon plasma by the methods of computer modelling. The hybrid computer simulations are performed for a set of particles with the radius up to \(20~{\rm \mu m}\) in order to determine the dependence of the electric charge on the surface of the particulate on its radius. This dependence seems to be linear. The distribution of the electric potential in the vicinity of the particulate is obtained from the fluid model. Afterwards, the non self-consistent particle simulation is performed in order to determine both the reaction rates and the electric charge on the surface of the particulate. The most important collision processes of charged particles in plasma and the appropriate dependence of the collision cross-section on the particle energy are considered (elastic scattering of electrons on neutrals, excitation of neutrals into all important energetic states, ionisation of Argon atoms by fast electrons, elastic scattering of positively charged ions etc.). The presented algorithm provides an effective way, how the key quantity in dusty plasma physics – electric charge on the surface of the particulate – can be determined.

Emissive Probe Diagnostics in Low Temperature Plasma – Effect of Space Charge and Variations of Electron Saturation Current

AbstractWe report a study of electron saturation current variations at varying probe heating that were found to be closely related to probe wire contamination. The study was performed in three types of low temperature argon plasma – the weakly magnetized plasma of a cylindrical magnetron, the non‐magnetized plasma of a double plasma machine and a hollow cathode plasma jet, showing different trends. In the present work the effect of overestimation of the plasma potential by a strongly emitting probe is discussed and experimental data are compared with a theoretical model. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Liquid crystal alignment on a-C:H films by an argon plasma jet at atmospheric pressure

A novel liquid crystal alignment method has been successfully developed. The alignment layer was made of a hydrogenated amorphous carbon film (a-C:H). At atmospheric pressure, the surface of the film was treated by a low temperature argon plasma jet. Experimental results showed that uniform alignment of the liquid crystal (ZLI-2293) has been achieved with a pretilt angle of 2.32° in a twist nematic cell. The alignment effects by this method are attributed to the directional scanning treatment by the plasma jet and C O and C O bonds formed on the surface of the alignment layer. Compared with the ion beam and plasma beam methods, this novel technique provides a more simple and continuous in-line plasma process for the LC alignment.

Neutral gas depletion mechanisms in dense low-temperature argon plasmas

Neutral gas depletion mechanisms are investigated in a dense low-temperature argon plasma—an inductively coupled magnetic neutral loop (NL) discharge. Gas temperatures are deduced from the Doppler profile of the 772.38 nm line absorbed by argon metastable atoms. Electron density and temperature measurements reveal that at pressures below 0.1 Pa, relatively high degrees of ionization (exceeding 1%) result in electron pressures, pe = kTene, exceeding the neutral gas pressure. In this regime, neutral dynamics has to be taken into account and depletion through comparatively high ionization rates becomes important. This additional depletion mechanism can be spatially separated due to non-uniform electron temperature and density profiles (non-uniform ionization rate), while the gas temperature is rather uniform within the discharge region. Spatial profiles of the depletion of metastable argon atoms in the NL region are observed by laser induced fluorescence spectroscopy. In this region, the depletion of ground state argon atoms is expected to be even more pronounced since in the investigated high electron density regime the ratio of metastable and ground state argon atom densities is governed by the electron temperature, which peaks in the NL region. This neutral gas depletion is attributed to a high ionization rate in the NL zone and fast ion loss through ambipolar diffusion along the magnetic field lines. This is totally different from what is observed at pressures above 10 Pa where the degree of ionization is relatively low (<10−3) and neutral gas depletion is dominated by gas heating.

Multidimensional fluid–particle modelling technique in low-temperature argon plasma at low pressure

In the contribution there is presented a new computer modelling technique, which can be used in multidimensional computer simulations of plasma at low pressure. The technique is based on the fluid–particle approach and can be used in the study of the range of physical phenomena, e.g. plasma behaviour in the vicinity of substrates, probe diagnostics, plasma technology, etc. The computer model is useable for the solution of three-dimensional problems and it minimizes the restrictions arising in complicated model geometry. The algorithm has been tested during the study of plasma sheath formation in the vicinity of probes with various geometries immersed into low-temperature argon plasma. Some results of these simulations are presented in the last section.

Bacterial Deactivation Using a Low Temperature Argon Atmospheric Plasma Brush with Oxygen Addition

AbstractThis study investigated the bacterial deactivation effects of a low temperature atmospheric argon plasma brush with oxygen addition. Two types of bacteria, Escherichia coli (E. coli) and Micrococcus luteus (M. luteus) seeded in various media were exposed to the oxygen enriched gas plasma and their survivability were thoroughly examined under various plasma conditions. It was found that the bacterial deactivation capability of the plasmas was highly dependent on the amount of oxygen addition and the type of supporting medium. With filter paper as the supporting medium, the addition of oxygen into the argon plasma system led to significant improvement in the bacterial killing efficacy, compared with an argon only plasma discharge. With oxygen addition, the plasma treatment time for a complete kill of the bacteria was 2 min for E. coli and 1 min for M. luteus. These are much shorter than the times required with argon only plasmas. When a nutrient broth or standard methods agar were used as the supporting medium, however, a longer plasma treatment time was necessary when using plasmas with the oxygen addition. The changes in bacterial cell structure after plasma exposure were examined using scanning electron microscopy. The change in plasma characteristics with oxygen addition was investigated using optical emission spectroscopy. The possible mechanism for bacterial inactivation of the plasmas is also discussed here. magnified image

The techniques of single probe and emission spectroscopy diagnostics in low temperature argon plasmas

Electric probe and analytical emission spectroscopy were used to acquire I-V curve and spectra of cylindrical plasmas produced by dc high-voltage discharge in the laboratory. The electron excitation temperature, electron temperature and electron density were obtained using respectively the electron energy probability function, Fermi-Dirac model and Schottky diffusion theory of low pressure discharge. The inherent relationships between the method of emission spectroscopy for determination of electron excitation temperatures, method of low-pressure discharge theory for estimation of electron density, and method of electric probe for calculation of electron temperature and density were explored. Further more, the spcial features of different diagnostic techniques were discussed. It was pointed out that the methods described in the article have preferential applications in plasma diagnostics under special environments.