Atomic Oxygen Flux Research Articles

Blood Clotting by Low-Temperature Air Plasma

In this paper, the feasibility and effectiveness of using an air-plasma torch to clot blood are studied. The emission spectroscopy and temperature measurement of the torch show that the torch produces abundant atomic oxygen in the plasma effluent. Anticoagulated whole-blood samples (10 mulscr ) were tested for two cases: 1) sample exposed to the plasma effluent and 2) sample exposed to a heated airflow; in both cases, the increase of the sample temperature was controlled to be about the same. No indication of blood coagulation was observed in the second case; on the other hand, in the first case when the blood sample was exposed directly to the plasma effluent, a shell was formed on the surface of the blood sample. The experimental results demonstrated that this plasma torch could clot a blood sample via a nonthermal mechanism. The dependence of the degree of blood clotting on the atomic-oxygen flux was demonstrated by varying the exposure distance. Experimental results also showed that blood coagulation was seen in the treated platelet-rich plasma sample but not in the treated platelet-poor plasma sample. Moreover, plasma treatment with multiple short exposures was shown as more effective in clotting blood than that of applying a continuous exposure with the same total exposure time.

A reaction-diffusion model for atomic oxygen interacting with spacecraft surface protective materials in low earth orbit environment

When hyperthermal atomic oxygen collides with a silicon surface, an ultrathin oxidation regime characterized by fractional atomic-oxygen anions having low diffusive and reactive barriers, along with their enhanced diffusion due to both the electric field and image potential, will form on the surface. In accordance with these properties, an attempt was made in the present study to modify the Almeida-Goncalves-Baumvol (AGB) model by setting the diffusivity and reaction rate constant to be diffusion-length dependence. According to the modified model, numerical parametric studies for oxidation thin growth were performed. The dependencies of the diffusion coefficient, the reaction rate constant, the attenuation length, and the adjustable parameter upon the translational kinetic energy, flux, temperature, and tangential flux of atomic oxygen were analyzed briefly via the fitting of the experimental data given by Tagawa et al. The numerical results confirmed the rationality of the modified diffusion-reaction model. The model together with the computer code developed in this study would be a useful tool for thickness evaluation of the protective film against the oxidation of atomic oxygen toward spacecraft surface materials in LEO environment.

Ultrahigh-frequency microplasma jet as a low-power, high-density, and localized ions/radicals source

An ultrahigh-frequency (450 MHz) microplasma jet was stably generated at a chamber pressure as low as 10−3 Pa. Electron and gas temperatures of this microplasma as estimated by optical-emission spectroscopy measurements were ∼7000 and 1000 K, respectively. The atomic oxygen flux at the torch exit was revealed to be of the order of 1019 atoms/cm2 s, which is 102–104 times higher than that obtained by other conventional plasma sources. This microplasma jet was also applied as an ion source for in situ neutralization of electron charging-up effects in a scanning-electron microscopy observation of insulating materials.

Reactive oxygen plasma-enabled synthesis of nanostructured CdO: tailoring nanostructuresthrough plasma–surface interactions

Plasma-assisted synthesis of nanostructures is one of the most precise and effectiveapproaches used in nanodevice fabrication. Here we report on the innovative approach ofsynthesizing nanostructured cadmium oxide films on Cd substrates using a reactive oxygenplasma-based process. Under certain conditions, the surface morphology featuresarrays of crystalline CdO nano/micropyramids. These nanostructures grow viaunconventional plasma-assisted oxidation of a cadmium foil exposed to inductivelycoupled plasmas with a narrow range of process parameters. The growth of theCdO pyramidal nanostructures takes place in the solid–liquid–solid phase, withthe rates determined by the interaction of plasma-produced oxygen atoms andions with the surface. It is shown that the size of the pyramidal structures canbe effectively controlled by the fluxes of oxygen atoms and ions impinging onthe cadmium surface. The unique role of the reactive plasma environment inthe controlled synthesis of CdO nanopyramidal structures is discussed as well.

Lateral Distribution of Atomic Oxygen Flux Produced by an Array of Three Fan-Shaped Plasma Torches

An array of three fan-shaped plasma torches is designed to be a source of atomic oxygen flux for biological decontamination applications. A narrowband-filtered CCD camera is used to record the intensities of 777.4-nm emissions from the torches and reveal the lateral distribution of the atomic oxygen flux produced in the plasma effluent of the torches.

High temperature oxidation of stainless steel AISI316L in air plasma

A study on surface oxidation of AISI316L stainless steel surface was performed. Stainless steel was oxidized in air plasma with a high degree of dissociation of oxygen molecules of about 70%. The resultant flux of oxygen atoms to the surface was about 1 × 10 24 m −2 s −1. The oxidation was performed at high temperatures ranging up to 1250 K. The oxidation time was 5 min. After oxidation the surface of the samples was analyzed by different methods including Auger electron depth profiling (AES), X-ray photoelectron spectroscopy (XPS), scanning electron spectroscopy (SEM) and X-ray diffraction (XRD). The microstructure and composition of the surface were temperature dependent. In all cases high Cr concentration was observed on the surface after oxidation at a temperature above 600 K. With increasing temperature Mn concentration at the surface increased as well. Below 1000 K the oxide film was uniform, while above 1000 K islands with large spinel particles were observed to appear.

Oxidation of Ni(Pt)Si by molecular vs. atomic oxygen

X-ray photoelectron spectroscopy (XPS) has been used to characterize the oxidation of a clean Ni(Pt)Si surface under two distinct conditions: exposure to a mixed flux of atomic and molecular oxygen (O + O 2; P O + O 2 = 5 × 10 −6 Torr) and pure molecular oxygen (O 2; P O 2 = 10 −5 Torr) at ambient temperatures. Formation of the clean, stoichiometric (nickel monosilicide) phase under vacuum conditions results in the formation of a surface layer enriched in PtSi. Oxidation of this surface in the presence of atomic oxygen initially results in formation of a silicon oxide overlayer. At higher exposures, kinetically limited oxidation of Pt results in Pt silicate formation. No passivation of oxygen uptake of the sample is observed for total O + O 2 exposure <8 × 10 4 L, at which point the average oxide/silicate overlayer thickness is 23 (3) Å (uncertainty in the last digit in parentheses). In contrast, exposure of the clean Ni(Pt)Si surface to molecular oxygen only (maximum exposure: 5 × 10 5 L) results in slow growth of a silicon oxide overlayer, without silicate formation, and eventual passivation at a total average oxide thickness of 8(1) Å, compared to a oxide average thickness of 17(2) Å (no silicate formation) for the as-received sample (i.e., exposed to ambient.) The aggressive silicon oxidation by atomic oxygen, results in Ni-rich silicide formation in the substrate and the kinetically limited oxidation of the Pt.

Lateral Distribution of Atomic Oxygen Flux Produced by an Array of Three Fan-Shaped Plasma Torches

Lateral Distribution of Atomic Oxygen Flux Produced by an Array of Three Fan-Shaped Plasma Torches

Study of one-side aluminized polyimide films exposed on the Mir orbital space station

During exposure on the Mir space station, external polyimide films aluminized on one side substantially lost mass and mechanical strength and their outer surfaces became hydrophilic. The surface tension and polar plots of brightness of the exposed films acquired an anisotropic character. Spatially-oriented nano- and microsized entities, whose size and shape depend on the time of exposure, were detected by the scanning electron and atomic-force microscopy techniques on the outer surfaces of external films. The orientation axes of drops on the surface of the films, polar plots of brightness, and spatially oriented structures coincided with the direction of the station movement. It was assumed that one of the main factors of outer space responsible for mass loss and the formation of the anisotropic nano- and microsized structures is the impact of a flux of oxygen atoms onto the surface of the external film. The efficiency of the reaction of atomic oxygen with polyimides was estimated. A possible (photoelectron) mechanism of the influence of the metal on polyimide degradation is discussed.

A ground-based radio frequency inductively coupled plasma apparatus for atomic oxygen simulation in low Earth orbit

A radio frequency (rf) inductively coupled plasma apparatus has been developed to simulate the atomic oxygen environment encountered in low Earth orbit (LEO). Basing on the novel design, the apparatus can achieve stable, long lasting operation, pure and high density oxygen plasma beam. Furthermore, the effective atomic oxygen flux can be regulated. The equivalent effective atomic oxygen flux may reach (2.289-2.984) x 10(16) at.cm(2) s at an oxygen pressure of 1.5 Pa and rf power of 400 W. The equivalent atomic oxygen flux is about 100 times than that in the LEO environment. The mass loss measured from the polyimide sample changes linearly with the exposure time, while the density of the eroded holes becomes smaller. The erosion mechanism of the polymeric materials by atomic oxygen is complex and involves initial reactions at the gas-surface interface as well as steady-state material removal.

AES investigation of the stainless steel surface oxidized in plasma

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 10 24 m −2 s −1. A set of samples was oxidized 4 min at different temperatures up to 1300 K during plasma treatment. AES measurements showed that the oxide film thickness increased with the increasing temperature. The thickness of the oxide film on the samples oxidized in plasma at 300 K was nearly the same as for the untreated sample. The thickness of the oxide film of the samples which were oxidized at 1000 K was about 170 nm and it consisted of iron oxide. The thickest oxide film of about 350 nm was found on the samples heated in oxygen plasma to 1300 K. Depth profiling showed the uppermost layer of manganese oxide, followed by a mixture of chromium oxide and iron oxide. The scanning electron microscope analyses showed a dramatic increase of the surface roughness.

XPS study of oxygen plasma activated PET

A study on oxygen plasma functionalization of polyethyleneterephthalate (PET) is presented. Samples were exposed to a weakly ionized, highly dissociated RF oxygen plasma with an electron temperature of 5 eV, a density of positive ions of 8×10 15 m −3 and a density of neutral oxygen atoms of 4×10 21 m −3. The oxygen pressure was 75 Pa and the discharge power was 200 W. The wettability of plasma-modified samples was determined by measuring the contact angle of a water drop, while the appearance of the functional groups on the sample surface was determined by using a high-resolution X-ray photoelectron spectrometer (XPS). Already in the order of seconds of the plasma treatment the samples were covered by the surface functional groups. These results were explained by the high flux of oxygen atoms onto the sample surface. The stability of functional groups on the plasma-modified PET surface stored in a dry plastic box was monitored by using XPS as a function of the ageing time. After 1 day of ageing, the concentration of newly formed functional groups decreased by about 15%.

Changes of properties of the materials of spacecraft solar arrays under the action of atomic oxygen

A procedure is developed for physical and chemical modeling and investigation of the weight, geometrical, and thermo-optical characteristics of polymer paneling materials of solar arrays and of the electric power of solar cells under the prolonged action of supersonic fluxes of atomic oxygen in orbit. The behavior of changes in the material characteristics as a function of the integral fluence of atomic oxygen is found. It is established that the electric power of solar cells is virtually invariable within the errors of measurements under irradiation by atomic oxygen flux with a fluence of no higher than 5 · 1021 cm−2.

Rapid surface functionalization of poly(ethersulphone) foils using a highly reactive oxygen‐plasma treatment

AbstractWe present a study of the oxygen‐plasma functionalization of polyethersulphone (PES). PES samples were exposed to a weakly ionized, highly dissociated oxygen plasma, with an electron temperature of 5 eV and a positive ion density of 8 × 1015 m−3, and its afterglow, in which the density of charged particles was negligibly low and the density of neutral oxygen atoms was 4 × 1021 m−3. The wettability of the samples was determined by measuring the contact angle of a water drop, while the appearance of the functional groups on the surface of the samples was determined using high‐resolution conventional XPS. The samples were saturated with surface functional groups, both in the plasma and in the afterglow region, after 1 s of treatment time. The results are explained by the high flux of oxygen atoms on the sample surface and the characteristics of the oxygen plasma. Copyright © 2007 John Wiley &amp; Sons, Ltd.

On the latitudinal variations of the non-periodic response of minor species induced by a dissipative gravity-wave packet in the MLT region

A spectral full-wave model and a two dimensional (2-D), time dependent, fully nonlinear chemistry model were used to investigate the latitudinal variations of the wave effects on the minor species in the OH chemistry in the mesosphere/lower thermosphere region. A dissipative gravity-wave packet is launched at three different latitudes propagating upward through the OH nightglow emission layer in the northern hemisphere. In addition to causing the minor species densities to fluctuate, the wave packet also causes non-periodic secular variations of the minor species densities as a consequence of violation of the non-acceleration conditions due to wave transience and dissipation. The associated fluxes of minor species are downward, and consequently minor species densities typically decrease at higher altitudes and increase at lower altitudes. The downward flux and subsequent chemical recombination of atomic oxygen is particularly important and can itself cause large secular variations of other less abundant minor species. Our studies indicate that the wave-induced non-periodic, secular variations are largest at high latitudes, second largest at low latitudes, and smallest at mid-latitudes.

Energetic oxygen atoms in the polar geocorona

[1] The role of the auroral sources induced by the electron and proton precipitation in the formation of the hot oxygen corona in the polar upper atmosphere is studied. It is found that both electron precipitation through exothermic chemistry and proton precipitation through atmospheric sputtering significantly contribute to the population of the hot oxygen geocorona. It is also found that only atmospheric sputtering results in the formation of the escape flux of energetic oxygen atoms, providing an important source of heavy atoms for the magnetosphere. The exothermic chemistry induced by the electron precipitation and/or by the absorption of the solar UV radiation is operating continuously in the polar upper atmosphere and results in a steady population of the very near-Earth environment by suprathermal oxygen atoms with energies below a few eV. By contrast, atmospheric sputtering by magnetospheric protons provides a more variable contribution, strongly coupled with the cusp region. It produces the more energetic oxygen atoms that populate the external regions of the hot oxygen geocorona. The results of calculations are in a good agreement with the analysis of the low-latitude perigee Low Energy Neutral Atom (LENA) images showing that the instrument signal consists of low to medium energy (5–30 eV) oxygen atoms produced in and near the cusp region. The more energetic (>30 eV) fraction of energetic oxygen atoms produced by the ioninduced atmospheric sputtering could be responsible for the energetic neutrals observed by the instrument far away from the cusp or oval regions. The total escape flux of oxygen atoms associated with atmospheric sputtering by protons is found about 8 � 10 23 s � 1 ; therefore this mechanism may provide a substantial contribution to the magnetospheric oxygen population.

Mechanisms Involved in the Conversion of ppHMDSO Films into SiO2‐Like by Oxygen Plasma Treatment

AbstractSummary: Thin ppHMDSO plasma polymer films deposited in a low pressure hexamethyldisiloxane plasma have been exposed to oxygen plasmas ignited in the same reactor at different pressures. The time evolution of the ppHMDSO film during the oxygen plasma treatment (30 s to one hour) was monitored in situ by multi‐wavelength ellipsometry. The treated films were analysed ex situ by X‐ray reflectometry, spectroscopic ellipsometry and infrared spectroscopy. On the other hand, the oxygen atom density as well as the oxygen ion density and energy were measured by actinometry and Langmuir probe measurements, respectively. For all the investigated oxygen plasma conditions, the film thickness and extinction coefficient significantly decrease. If the O ion energy is low enough (typically less than 10 eV) the 65nm ppHMDSO can even be transformed into a 45 nm‐thick carbon free SiO2‐like film. In contrast, if the ion energy is higher than 10 eV, the ppHMDSO is only partially oxidised. Based on the oxygen atom flux measurement, it is concluded that the number of oxygen atoms impinging on the ppHMDSO film is not the only parameter which governs the treatment. The oxygen ion energy appears to have a key role as far as energetic ions are likely to induce the formation of a dense superficial SiO2 layer which prevents the diffusion of O atoms in the film and the out diffusion of volatile oxidation products. magnified image

Photopolymerisation of composite material in simulated free space environment at low Earth orbital flight

Inflatable Gossamer’s structures which can be deployed in Earth orbit have great prospects in the future. Material for use in inflatable structures must be soft before and during unfolding and harden after unfolding. The best way for solidification of Gossamer’s structures is by chemical polymerisation of a composite material in space environment. The polymerisation processes of liquid polymer matrix in a free space environment are sensitive to microgravitation, temperature variations (−150 to +150 °C), high vacuum (10 −3 to 10 −7 Pa), atomic oxygen flux (in LEO), UV and VUV irradiations, X-ray and γ-irradiations, high energy electron and ion fluxes. In this paper experiments of the photopolymerisation processes under simulated free space conditions were carried out. The influences of high vacuum, temperature variations, high energy ion beam, radio-frequency and microwave plasma on polymerisation of UV-curing resin were observed. The effects of low molecular components evaporations, acceleration of curing kinetics, additional chemical reactions and mixing processes during polymerisation were observed. The photopolymerisation of inflatable structure was carried out under simulated temperature conditions of space flight in low Earth orbit. The results indicate a technology for large-size inflatable constructions in Earth orbit, in far space and on space bodies as for deployed antennas, solar sail stringers, solar shield stringers, frames for large-size space stations, frames for Moon, Mars, asteroids bases and frames for space plant on Earth orbit and other celestial bodies.

Measurement of 5-eV atomic oxygen using carbon based films: preliminary results

Carbon-based sensors have been developed to measure the atmospheric neutral atomic oxygen (AO) flux experienced by spacecraft in low Earth orbit. Thin- and thick-film carbon sensor elements were deposited onto an alumina substrate between thick-film gold tracks and silver palladium solder pads. AO flux is deduced by measuring resistance changes as the carbon film erodes and applying a simple theory. A wide range of responses were observed that are dependent on the deposition process and post deposition annealing. The deposition methods used were dc magnetron sputtering, e-beam evaporation, and screen-printing. The sensors tested compare favorably with similar silver-based sensors that have been flown previously on small satellite missions with significant mass/power constraints.

Two-dimensional calculation of spatial distribution of neutral atoms for a planar inductively coupled oxygen discharge

Two-dimensional self-consistent fluid simulation of inductively coupled oxygen plasma is presented. The model equations include continuity equations for charged species and neutral oxygen atom, the Poisson equation, and the electron energy balance equation. The drift–diffusion approximation is employed. From the Maxwell equations, the induced electric field and absorbed power are calculated. The two-dimensional spatial distributions of charged species densities, charged species flux, density and flux of atomic oxygen, electric potential, and electron temperature are calculated. The effect of the gas pressure on the plasma uniformity is investigated. As the pressure increases, the spatial distributions of charged species and neutral atom have their peak values in the toroidal region where a large amount of the input power is absorbed by the plasma.