Positive Oxygen Ions Research Articles

Flux of High-Energy Positive Oxygen Ions from Plasma to a Substrate in a Pulsed Magnetron Discharge with a Hot Target

Flux of High-Energy Positive Oxygen Ions from Plasma to a Substrate in a Pulsed Magnetron Discharge with a Hot Target

Flow of high-energy positive oxygen ions from plasma onto the substrate in a pulsed magnetron discharge with a hot target.

A group of high-energy positive O^+ ions was detected in a plasma flowhigh-current pulsed magnetron discharge with a hot target in an Ar/O_2 gas mixture. The mechanism for the formation of accelerated O^+ ions may be the conversion of accelerated ones in the cathode layer of negative ions O^– → O^+ in the processes of charge exchange or ionization by electron impact.

Evidence of 1000 eV positive oxygen ion flux generated in reactive HiPIMS plasma

The arrival of highly energetic (near 1000 eV) positive atomic oxygen ions at the substrate region has been detected in a unipolar reactive high-power impulse magnetron sputtering process operated with an uncooled copper target in argon–oxygen mixtures. Examination of the ion fluxes from discharge plasma was performed with a magnetic sector mass-spectrometer and an electrostatic energy analyzer. The energy of fast positive O+ ions is close to the value of eV d (e—elementary charge, V d—discharge voltage), which indicates their connection to the well-studied fraction of negative O− ions, which undergo acceleration in the cathode sheath. After switching the oxygen gas supply off, the flux of energetic O+ species decreases gradually as the poisoned target surface layers become depleted of oxygen due to sputtering in pure argon. Presumably, the observed energetic O+ ions originate as a result of low-angle scattering of fast negative O− ions from other charged or neutral species in the plasma followed by electron detachment, ionization, or charge exchange.

Reducing the Effectiveness of Ward Particulate Matter, Bacteria and Influenza Virus by Combining Two Complementary Air Purifiers.

Air purifiers should pay much attention to hospital-associated infections, but the role of a single air purifier is limited. The goal of this study was to evaluate the effectiveness of the combined application of the nonequilibrium positive and negative oxygen ion purifier (PNOI) and the high-efficiency particulate air filter (HEPA) on a complex, polluted environment. Two of the better performing purifiers were selected before the study. The efficacy of their use alone and in combination for purification of cigarette particulate matter (PM), Staphylococcus albicans, and influenza virus were then evaluated under a simulated contaminated ward. PNAI and HEPA alone are deficient. However, when they were combined, they achieved 98.44%, 99.75%, and 100% 30 min purification rates for cigarette PM, S. albus, and influenza virus, respectively. The purification of pollution of various particle sizes and positions was optimized and reduced differentials, and a subset of airborne influenza viruses is inactivated. Furthermore, they were superior to ultraviolet disinfection for microbial purification in air. This work demonstrates the strong purification capability of the combined application of these two air purifiers for complex air pollution, which provides a new idea for infection control in medical institutions.

Study of He + 0.2% O2 plasma jet impinging on liquid surface from He(23S1) metastable atoms density measurements

This work presents spatial variations of the helium He(23S1) metastable atom absolute densities in a plasma jet at atmospheric pressure in He + 0.2% O2 gas mixture impinging on a liquid target. The plasma jet is ignited with 6 kV pulses of 2.5 μs duration and 8 ns rise and fall times at 20 kHz repetition rate. Streamers are created in both rising and falling fronts of the high voltage (HV). From Abel inversion of the line averaged absorbance of 1083 nm helium line, measured by laser absorption spectroscopy, the radial profiles of He(23S1) density along the plasma jet are deduced in two sources with different residence time of the gas within the discharge volume, having three different outlet tube diameters and with two gas flow rates. The metastable densities up to ∼3 × 1013 cm−3 have been measured. The radial profile remained always axially centered for the 1.5 mm outlet tube and with 0.5 slm for the larger diameter tubes. But in this later tubes and with 2 slm gas flow rate, the profile changed from a ring shape at the tube exit to axially centered when increasing the distance from the tube edge. In the rising front of the HV, the ring profile of He(23S1) density in the tube exit is attributed to the shape of the electric field, produced by the applied HV to the electrode wrapped around the dielectric tube. In the falling front of the HV, the electric field results from electrons deposited on the inner surface of the dielectric tube and positive ions accumulated on the surface of liquid during the 2.5 μs duration of the HV pulse. The influence of oxygen by-products formed in the plasma volume (O, O2(Δ), O3, positive and negative oxygen ions) on the dynamic of the plasma jet are analyzed.

Effect of sliding discharge on proliferation and death of brain microvessel endothelial cells in vitro

The dose-dependent effects of plasma exposure to a unipolar nanosecond sliding discharge over the surface of the culture medium in a closed plate on the cells of cerebral endothelium in vitro were studied. Using a 24-well plate, the surface plasma energy density of one pulse was 360 μJ/cm2 at a pulse frequency of 100 Hz. It has been shown that in the creeping discharge plasma there is an active excitation of air molecules, the formation of positive nitrogen and oxygen ions, and the formation of carbon monoxide. In the dose density range of 0-32 J/cm2, the dose-dependent effects were assessed in the 4-12 h post-radiation period. Cell death was analyzed with an assessment of the total number of cells, necrotic cells, cells in apoptosis (phosphatidylserine externalization, internucleosomal DNA fragmentation) and their proliferative activity (Ki67-immunopositive cells). A preliminary assessment of subtle dose-dependent effects indicates the peculiarities of the effect of small doses.

О расчете сечений упругого рассеяния электронов на положительных ионах азота и кислорода

О расчете сечений упругого рассеяния электронов на положительных ионах азота и кислорода

Transition mechanism of negative DC corona modes in atmospheric air: from Trichel pulses to pulseless glow

Corona discharge in high voltage power transmission lines can generate audible noise and radio inference, causing environmental problems in daily life. There are three different discharge modes of negative corona depending on DC voltage amplitude, namely, Trichel pulses, stable glow and negative streamers. A 2D fluid model, incorporating three species (electrons, positive oxygen ions and negative oxygen ions), was successfully built to simulate the formation of repetitive Trichel pulses in air. However, this simplified model cannot correctly predict the transition to pulseless glow. The calculated transition voltage is higher than experimental results. In this work the gas dynamics and a detachment reaction are taken into account in the model. Gas heating due to the deposited discharge energy will influence the chemical reaction rates and reduce the gas density. Besides the mobility of charged particles, the ionization and attachment coefficients are determined by the reduced electric field. The calculation results of the gas density from the gas dynamics model are coupled back to the discharge model. The corona discharge in a needle-cylinder electrode configuration is simulated and the results show that the mode transitions at a lower voltage, which agrees well with the experimental data. The ionization rate is greatly enhanced around the needle because of the gas density reduction. Therefore, the reduced electric field will not easily be decreased by the generation and accumulation of negative ions. A higher detachment rate also causes the Trichel pulses to disappear. The simulation results suggest that gas heating is more important for the mode transition of negative coronas from Trichel pulses to pulseless glow than was previously expected.

Experimental visualization of the cathode layer in AC surface dielectric barrier discharge

A narrow etched polyimide line at the bottom edge of a biased electrode (BE) and a non-etched dielectric surface near the biased electrode were observed in an atmospheric AC flexible surface dielectric barrier discharge of polyimide dielectric. These findings are attributed to the bombardment of positive oxygen ions on the bottom edge of the BE and the electron breakdown trajectory not contacting the polyimide surface following the electric field lines formed between the BE edge and the surface charge layer on the dielectric. The length of the non-etched dielectric surface during the first micro-discharge was observed as 22 μm. This occurred, regardless of three different operating durations, which is in good agreement with the length of the cathode layer according to Paschen's law.

Ball lightning dynamics and stability at moderate ion densities

A general mechanism is presented for the dynamics and structure of ball lightning and for the maintenance of the ball lightning structure for several seconds. Results are obtained using a spherical geometry for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions and negative ions coupled with Poisson’s equation. A lightning strike can generate conditions in the lightning channel with a majority of positive nitrogen ions, and a minority of negative oxygen ions and electrons. The calculations are initiated with electrons included; however, at the moderate ion densities chosen the electrons are rapidly lost to form negative ions, and after 1 µs their influence on the ion dynamics is negligible. Further development after 1 µs is followed using a simpler set of equations involving only positive ions and negative ions, but including ion diffusion. The space-charge electric field generated by the majority positive ions drives them from the centre of the distribution and drives the minority negative ions and electrons towards the centre of the distribution. In the central region the positive and negative ion distributions eventually overlap exactly and their space-charge fields cancel resulting in zero electric field, and the plasma ball formed is quite stable for a number of seconds. The formation of such plasma balls is not critically dependent on the initial diameter of the ion distributions, or the initial density of minority negative ions. The ion densities decrease relatively slowly due to mutual neutralization of positive and negative ions. The radiation from this neutralization process involving positive nitrogen ions and negative oxygen ions is not sufficient to account for the reported luminosity of ball lightning and some other source of luminosity is shown to be required; the plasma ball model used could readily incorporate other ions in order to account for the luminosity and range of colours reported for ball lightning. Additionally, ‘phantom plasma balls’ may well be generated and go unnoticed due to very low luminosity; luminous ball lightning may be the exception. Finally, the mechanism described here may also be active in the dynamics of bead lightning.

The bidirectional character of O2 concentration in pulsed dielectric barrier discharges in O2/N2 gas mixtures

This paper presents experimental results on the influence of O2 on the characteristics of dielectric barrier discharges (DBDs) at one and at half atmospheric pressure. Gas mixtures of 0.1–10 vol % O2 in N2 were investigated, as well as in virtually pure N2. Electrical data, simultaneous streak and intensified charge-coupled device images were recorded in pulsed driven dielectric barrier discharges of 0.8 mm gap in a single filament arrangement. The O2 concentration is shown to have a significant impact on the electrical characteristics, the temporal DBD development and its breakdown inception. Higher O2 concentrations (above 0.1 vol %) led to an ignition delay, a shorter discharge duration, increased discharge radius, higher discharge current maxima and larger velocities of the cathode directed streamers. For O2 concentrations below 0.01 vol %—i.e. nearly pure nitrogen—some of these effects were reversed. Moreover, the effects were more pronounced at a pressure of 0.5 bar compared to 1 bar. This result can be explained by the pressure dependent decay and recombination processes of positive nitrogen and oxygen ions.

Passivation of a-Si:H-based structures in KCN and HCN solutions and its application on p-i-n solar cell

Dominant aim of the contribution is focused on investigation of very thin SiO2/a-Si:H interface properties. After PECVD deposition, surface of a-Si:H is not covered by reproducibly defined insulating layer. Therefore, three basic types of oxygen plasma sources were used for treatments of a-Si:H surfaces. Electrically well defined SiO2 very thin film layers are formed by (i) inductively coupled plasma in connection with its applying at plasma anodic oxidation, (ii) RF plasma as the source of positive oxygen ions for plasma immersion ion implantation process, and (iii) dielectric barrier discharge ignited at high pressures. In addition, chemical oxidation of a-Si:H surface was performed in boiling azeotropic HNO3 solutions. Electrical properties of SiO2/semiconductor interface of both a-Si:H- and Si-based structures were improved by treatments in KCN and/or HCN solutions. Positive passivation influence of last mentioned solutions is presented on p-i-n a-Si-H solar cell parameters.

K-shell Photodetachment from O−

The K-shell photodetachment spectrum of O- has been investigated using the merged ion-photon beam photo-detachment technique. O- ions were produced in a Cs sputtered ion source on a new Movable Ion Photon Beamline (MIPB) while the photons were produced at the Advanced Light Source Beamline 8.0.1. Positive oxygen ions formed by multiple detachment were detected as a function of photon energy. Photoexcitation of a 1s electron leads to a short-lived Feshbach resonance ~3 eV below the 1s detachment threshold due to the extra stability of the now full 2p6 shell.

Numerical Simulation of Trichel Pulses in a Negative Corona Discharge in Air

In this paper, a new 2-D model is presented for numerical simulation of Trichel pulses in a point-plane configuration. Both radial and axial components of the electric field are considered and it is assumed that three ionic species exist in the air gap: electrons, and positive and negative oxygen ions. The Poisson equation is solved for electric field calculations and three continuity equations for modeling the transport of charge densities in the air gap. The finite element method (FEM) is used for solving the Poisson equation and a combined Flux Corrected Transport-FEM is used for the charge transport equations. Trichel pulses for different applied voltages are shown and the characteristics of these pulses at different voltages are compared with experimental results reported in the literature. The time variation of the electric field on the corona electrode at different stages of one Trichel pulse is also presented. Moreover, the distributions of electron, positive ion and negative ion densities at different stages of the Trichel pulse are discussed.

Generation of Positive and Negative Oxygen Ions in Magnetron Discharge During Reactive Sputtering of Alumina

At present, the reactive magnetron sputtering is a well-mastered process currently used for industrial productionof various thin films and coatings. Great attention wasdevoted particularly to: (i) elimination of hysteresisphenomenon, (ii) removal of arcing at the surface ofsputtered target during reactive sputtering of electricallyinsulatingcompoundsand(iii)stabilizationofsputteringinthetransitionmode.

Scattering of light molecules from thin Al 2O 3 films

Molecular oxygen and hydrogen ions were scattered at grazing incidence from various thin Al 2O 3 films. The energy of incident particles was varied from 390 to 1000 eV. For scattered positive oxygen ions, negative ion fractions of up to 17% were recorded. For scattered positive hydrogen ions, the negative ion fractions reached up to 2%. These findings qualify thin films of Al 2O 3 as possible candidates for use as charge state conversion surfaces in neutral particle sensing instruments, which will work in space.

Secondary-ion mass spectrometry of photoconducting targets

Secondary-ion mass spectrometry of photoconducting CdS-PbS films has revealed a change in the yield of positive secondary ions upon illumination. In the course of bombardment by positive oxygen ions, illu- mination of the samples by visible light decreases the yield of cadmium ions and increases that of lead ions. The observed phenomena suggest that the secondary-ion photoeffect takes place; these phenomena are called the normal and anomalous secondary-ion photoeffect, respectively. The phenomena observed are explained, and a preliminary quantitative description of these effects is proposed.

On interface properties of ultra-thin and very-thin oxide/a-Si:H structures prepared by oxygen based plasmas and chemical oxidation

Amorphous hydrogenated silicon (a-Si:H) belongs still to most promising types of semiconductors for its utilization in fabrication of TFTs and thin film solar cell technology due to corresponding cheap a-Si:H-based device production in comparison with, e.g. crystalline silicon (c-Si) technologies. The contribution deals with both two important modes of preparation of very-thin and ultra-thin silicon dioxide films in the surface region of a-Si:H semiconductor (oxygen plasma sources and liquid chemical methods) and electrical, optical and structural properties of produced oxide/semiconductor structures, respectively. Dominant aim is focused on investigation of oxide/semiconductor interface properties and their comparison and evaluation from view of utilization of used technological modes in the nanotechnological industry. Following three basic types of oxygen plasma sources were used for the first time in our laboratories for treatments of surfaces of a-Si:H substrates: (i) inductively coupled plasma in connection with its applying at plasma anodic oxidation; (ii) rf plasma as the source of positive oxygen ions for plasma immersion ion implantation process; (iii) dielectric barrier discharge ignited at high pressures.The liquid chemical manner of formation SiO2/a-Si:H structures uses 68wt% nitric acid aqueous solutions (i.e., azeotropic mixture with water). Their application in crystalline Si technologies has been presented with excellent results in the formation of ultra-thin SiO2/c-Si structures [H. Kobayashi, M. Asuha, H.I. Takahashi, J. Appl. Phys. 94 (2003) 7328].Passivation of surface and interface states by liquid cyanide treatment is additional original technique applied after (or before) formation of almost all formed thin film/a-Si:H structures. Passivation process should be used if high-quality electronical parameters of devices can be reached.

Scattering of light molecules from Al2O3 surfaces

Various light ions were scattered at grazing incidence from a highly polished Al2O3 single crystal and from a thin film of Al2O3 on graphite. The energy of incident particles was varied from 390eV to 1200eV. For scattered positive oxygen and carbon ions, negative ion fractions of up to 14% and 3%, respectively, were recorded. For scattered positive hydrogen ions, the negative ion fractions reached the percent level.

Pulsed population inversion in recombination of positive metal ions with negative oxygen ion

We discuss the ion-ion recombination of positive metal ions and negative oxygen ion in a pulsed gas discharge for realization of the pulsed inversion population mechanism. The metal atom energy levels most populated in this process are estimated. The energy level diagrams with probable transitions for several metal atoms are presented.