Effects of Atomic Oxygen Irradiation on Transparent Conductive Oxide Thin Films

Transparent conductive oxide （TCO） thin film is a kind of functional material which has potential applications in solar cells and atomic oxygen （AO） resisting systems in spacecrafts. Of TCO, ZnO：Al （ZAO） and In2O3：Sn （ITO） thin films have been widely used and investigated. In this study, ZAO and ITO thin films were irradiated by AO with different amounts of fluence. The as-deposited samples and irradiated ones were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Hall-effect measurement to investigate the dependence of the structure, morphology and electrical properties of ZAO or ITO on the amount of fluence of AO irradiation. It is noticed that AO has erosion effects on the surface of ZAO without evident influences upon its structure and conductive properties. Moreover, as the amount of AO fluence rises, the carrier concentration of ITO decreases causing the resistivity to increase by at most 21.7%.

A Simulator for Producing of High Flux Atomic Oxygen Beam by Using ECR Plasma Source

In order to study the atomic oxygen corrosion of spacecraft materials in low earth orbit environment, an atomic oxygen simulator was established. In the simulator, a 2.45 GHz microwave source with maximum power of 600 W was launched into the circular cavity to generate ECR (electron cyclotron resonance) plasma. The oxygen ion beam moved onto a negatively biased Mo plate under the condition of symmetry magnetic mirror field confine, then was neutralized and reflected to form oxygen atom beam. The properties of plasma density, electron temperature, plasma space potential and ion incident energy were characterized. The atomic oxygen beam flux was calibrated by measuring the mass loss rate of Kapton during the atomic oxygen exposure. The test results show that the atomic oxygen beam with flux of 1016-1017 atoms-cm-2·s-1 and energy of 5-30 eV and a cross section of φ80 mm could be obtained under the operating pressure of 10-1-10-3 Pa. Such a high flux source can provide accelerated simulation tests of materials and coatings for space applications.

Experimental Study of Vacuum Ultraviolet Radiation Effects and Its Synergistic Effects with Atomic Oxygen on a Spacecraft Material-Polytetrafluoroethylene

Polytetrafluoroethylene (Teflon), a widely used spacecraft material, isstudied to investigate the vacuum ultraviolet (VUV) effects and its synergistic effects with atomicoxygen (AO) in a ground-based simulation facility. The samples before and after the experiments arecompared in appearance, mass, optical properties and surface composition. The reactioncharacteristics of Teflon are summarized and the reaction mechanisms are analyzed. The followingconclusion can be drawn: at the action of VUV the Teflon sample surface is darkened for theaccumulation of carbon; and when the sample is exposed to AO, the carbon is oxidized and thedarkening surface is bleached; the synergistic effects of VUV and AO may cause the erosion of Teflonmore severe.

Oxygen Atom Exchange Mechanism in Reaction of OH Radical with AsO

Oxygen atom exchange reaction mechanism in the reaction of OH radicals with AsO was investigated by means of the density functional theory (DFT) with 6 311++G( 3df,3pd ) and 6 311++G( d,p ) basis sets. The calculated results suggest that the reaction between OH and AsO should make the oxygen atoms exchange rapidly because the barrier to isomerization is significantly less than the HO-AsO bond dissociation energy.

Atmospheric Pressure Cold Argon/Oxygen Plasma Jet Assisted by Preionization of Syringe Needle Electrode

An atmospheric pressure nonequilibrium argon/oxygen plasma jet assisted by the preionization of syringe needle electrode discharge is reported. With the syringe needle plasma as its pre-ionization source, the hybrid barrier-jet was shown to generate uniform discharge with a lower breakdown voltage and a relatively low gas temperature varying from 390 K to 440 K, even when the vol.% oxygen in argon was up to 6%. Utilizing the actinometry method, the concentration of atomic oxygen was estimated to be about in an orders of magnitude of 10^17 cm^-3. The argon/oxygen plasma jet was then employed to clean out heat transfer oil, with a maximum cleaning rate of 0.1 mm/s achieved.

Ground-based Investigations of Atomic Oxygen Erosion Behaviors of Silver and Ion-implanted Silver

Silver foils and ion-implanted silver foils exposed to atomic oxygen （AO） generated in a ground simulation facility were investigated by the quartz crystal microbalance （QCM）, the scanning electron microscopy （SEM） and the X-ray photoelectron spectroscopy （XPS）. The experimental results show the presence of Ag2O and AgO in an oxidation process of the silver foil having exposure to AO. As soon as silver comes under the bombardment of atomic oxygen, the oxidation process starts with a thick film forming on the silver surface. Because of the development of stresses, the oxide layer gets cracked and spalled, which leads to appearance of a new silver surface intensifying further oxidation. At last, AgO begins to form on the outer surface of the oxide film. The analytical results of the XPS and the AES attest to formation of a continuous high-quality protective oxide-based layer on the surface of ion-implanted silver films after exposure to AO. This layer can well protect materials in question from erosion.

Investigation of Surface Reaction and Degradation Mechanism of Kapton during Atomic Oxygen Exposure

The erosion behavior of Kapton when exposed to atomic oxygen (AO) environment in the ground-based simulation facility was studied. The chemical and physical changes of sample surfaces after exposed to AO fluxes were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results indicated that Kapton underwent dramatically degradation, including much mass loss and change of surface morphologies; vacuum outgassing effect of Kapton was the key factor for initial mass loss in the course of atomic oxygen beam exposures. XPS analysis showed that the carbonyl group in Kapton reacted with oxygen atoms to generate CO2, then CO2 desorbed from Kapton surface. In addition, PMDA in the polyimide structure degraded due to the reaction with atomic oxygen of 5 eV.

Preparation and anti atomic oxygen erosion properties of OPPOSS/PI composites

Atomic oxygen （AO） found in low earth orbit can cause serious erosion to polyimide （PI） materials, which greatly limits their lifetime. 8-phenyl silsesquioxane （OPPOSS） was synthesized, and OPPOSS/PI composites were pre- pared by physical blending, followed by thermal imidization to enhance the AO erosion resistance of PI materials. The morphology, composition, and structure of the composites were analyzed before and after AO exposure in a ground sim- ulated facility of atomic oxygen. After 16 h AO exposure, the OPPOSS/PI composite with 5wt% OPPOSS addition shows an erosion rate of about 1.4×10-24 cm3/atom with only 48% mass loss of that of PI without OPPOSS addition. The mixture of OPPOSS nano molecules is assembled into a kind of regular square structure and distributed evenly in OPPOSS/PI composites. Some SiO2 particles are formed in the composites during AO exposure, which can act as ＂inert points＂ to reduce the AO erosion rate of OPPOSS/PI composites.

Effectiveness of oxygen nebulization at preventing radiotherapy-induced mucositis in patients with nasopharyngeal cancer

Purpose:To evaluate the effectiveness of oxygen nebulization at preventing radiotherapyinduced mucositis in patients with nasopharyngeal cancer.Methods:Sixty patients with nasopharyngeal cancer treated with simultaneous integrated boost intensity-modulated radiotherapy were randomly assigned to oxygen nebulization or ultrasonic nebulization groups;treatment was once daily for 20 minutes.All patients received routine oral care.We compared saliva pH and volume,food intake,and change in oral mucosa during radiotherapy,and dry mouth and sore throat after radiotherapy between the two groups.Results:There were significant differences in the incidence of grade III or IV mucositis,saliva volume and pH,and dry mouth and sore throat between the two groups when the total dose was 33 Gy(p<0.05 or p<0.01).Conclusion:Oxygen nebulization reduces radiotherapy-induced mucositis and relieves symptoms such as dry mouth and sore throat in patients with nasopharyngeal cancer.

Effects of Vacuum Ultraviolet Radiation on Atomic Oxygen Erosion of Polysiloxane/SiO_2 Hybrid Coatings

Polysiloxane/SiO2 hybrid coatings have been prepared on Kapton films by a sol-gel process. The erosion resistance of polysiloxane/Si02 （20 wt pct） coating was evaluated by exposure tests of vacuum ultraviolet radiation （VUV） and atomic oxygen beam （AO） in a ground-based simulation facility. The experimental results indicate that this coating exhibits better AO resistance than pure polysiloxane coating. The erosion yield （Ey） of the polysiloxane/Si02 （20 wt pct） hybrid coating is about 10-27 cm3/atom, being one or two orders of magnitude lower than that of polysiloxane. VUV radiation can affect the erosion process greatly. Under simultaneous AO and VUV exposure, the value of Ey of the polysiloxane/5iO2 （20 wt pct） hybrid coating increases by 3g% compared with that under single AO exposure.

Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave （MW） resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence （TALIF） using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy （OES）. In this case, we compared the spectra intensities of a specific atomic oxygen line （844 nm） and the closest wavelength xenon line （823 nm）. The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon （1% Xe） of this chemically inert gas inside the air while a further small quantity of H2 （2~） is also added in the mixture in order to collect OH（A- X） and NH（A-X） spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09× 1017＋ 0.2×1017 cm-3. This is in very good agreement with the TALIF measurement, which is equal to 2.0×101T cm-3.

Exploring the Interactions of Atomic Oxygen on Silver Clusters with Hydrogen

The interactions between AgnO- （n=1-8） and H2 （or D2） were explored by combination of the mass spectroscopy experiments and density function theory （DFT） calculations. The experiments found that all oxygen atoms in AgnO- （n--1-8） are inert in the interactions with H2 or D2 at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation （PROX） of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between AgnO- （n=1-8） and H2 were explored using DFT calculations. The results indicated that adsorption of H2 on any site of AgnO- （n=1-8） is extremely weak, and oxidation of H2 by any kind of oxygen in AgnO- （n=1-8） has an apparent barrier strongly dependent on the adsorption style of the ＂O＂. These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.

Roll-to-roll fabrication of large-scale polyorgansiloxane thin film with high flexibility and ultra-efficient atomic oxygen resistance

One of the most widely used and well-established atomic oxygen(AO)protection solutions for low Earth orbit(LEO)satellites is the deposition of protective coatings on polymeric materials.However,manufacturing extensive expanses of these coating materials with good transparency,flexibility,smoothness,ultra-thinness,and exceptional AO resistance remains a critical issue.Herein,we successfully deposited a 400 nm thick polyorgansiloxane(SiO_(x)C_(y)H_(z))coating with high optical transparency and uniform good adherence on to a 1.2 m wide polyimide surface,by optimizing the distribution of hexamethyldisiloxane and oxygen as precursors in the roll-to-roll compatible plasmaenhanced chemical vapor deposition process.After AO irradiation with the fluence of 7.9×10^(20)atoms·cm^(–2),the erosion yield of the SiO_(x)C_(y)H_(z)-coated Kapton was less than 2.30×10^(–26)cm^3·atom^(–1),which was less than 0.77%of that of the Kapton.It indicates that the SiO_(x)C_(y)H_(z)coating can well prevent the erosion of Kapton by AO.In addition,it was also clarified that a SiO_(2) passivation layer was formed on the surface of the SiO_(x)C_(y)H_(z)coating during AO irradiation,which exhibited a‘self-reinforcing’defense mechanism.The entire preparation process of the SiO_(x)C_(y)H_(z)coating was highly efficient and low-cost,and it has shown great potential for applications in LEO.

The Erosion Effect of Kapton Film in a Ground-based Atomic Oxygen Irradiation Simulator

In order to investigate the effect of space environmental factors on spacecraft materials, a ground-based simulation facility for space atomic oxygen（AO） irradiation was developed in our laboratory. Some Kapton film samples were subjected to AO beam generated by this facility. The Kapton films before and after AO exposure were analyzed comparatively using optical microscopy, scanning electronic microscopy, atomic force microscopy, high-precision microbalance, and X-ray photoelectron spectroscopy. The experimental results indicate that the transmittance of Kapton film will be reduced by AO irradiation notably, and its color deepens from pale yellow to brown. Surface roughness of the AO-treated sample is already increased obviously after AO irradiation for 5 hours, and exhibits a flannel-like appearance after 15 hours’ exposure in AO beam. The imide rings and benzene rings in kapton molecule are partially decomposed, and some new bonds form during AO irradiation. The mass loss of kapton film increases linearly with the increase of AO fluence, which is resulted from the formation of volatile products, such as CO, CO2 and NOx. The breakage in structure and degradation in properties of AO-treated Kapton film can be attributed to the integrated effect ofimpaction and oxidization of AO beam. The test results agree well with the space flight experimental data.

Inactivation of Bacillus Subtilis by Atomic Oxygen Radical Anion

UAtomic oxygen radical anion （O-） is one of the most active oxygen species, and has extremely high oxidation ability toward small-molecules of hydrocarbons. However, to our knowledge, little is known about the effects of O- on cells of micro-organisms. This work showed that O- could quickly react with the Bacillus subtilis cells and seriously damage the cell walls a s well as their other contents, leading to a fast and irreversible inactivation. SEM micrographs revealed that the cell structures were dramatically destroyed by their exposure to O-. The inactivation efficiencies of B. subtilis depend on the O- intensity, the initial population of cells and the treatment temperature, but not on the pH in the range of our investigation. For a cell concentration of 10^6 cfu/ml, the number of survived cells dropped from 10^6 cfu/ml to 10^3 cfu/ml after about five-minute irradiation by an O- flux in an intensity of 233 nA/cm^2 under a dry argon environment （30 ℃, 1 atm, exposed size： 1.8 cm^2）. The inactivation mechanism of micro-organisms induced by O- is also discussed.

Behavior of pure and modified carbon/carbon composites in atomic oxygen environment

Atomic oxygen （AO） is considered the most erosive particle to spacecraft materials in low earth orbit （LEO）. Carbon fiber, car-bon/carbon （C/C）, and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO. Scanning electron microscopy （SEM）, AO erosion rate calculation, and mechanical property testing were used to characterize the material properties. Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing. According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C, a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation.

Generation and Applications of a Broad Atomic Oxygen Beam with a High Flux-Density via Collision-lnduced Dissociation of O_(2)

We detail the generation of a pulsed atomic oxygen(AO)broad beam with a high flux-density via collision-induced dissociation of O_(2) to support practical industrial exploitation of AOs,particularly for facilitating 2-dimenstional oxidation/etching at a fast rate of one-monolayer per second in an area≥1000 cm².This innovation fuses the following interdisciplinary concepts:(a)a high density of O^(*) can be produced in an electron-cyclotron-resonance(ECR)O2 plasma;(b)o^(*) can be extracted and accelerated with an aperture-electrode in the plasma.

Mechanistic Investigation on the Reaction of O- with CH3CN Using Density Functional Theory

The potential energy profile of the reaction between the atomic oxygen radical anion and acetonitrile has been mapped at the G3MP2B3 level of theory. Geometries of the reactants, products, intermediate complexes, and transition states involved in this reaction have been optimized at the （U）B3LYP/6-31＋G（d,p） level, and then their accurate relative energies have been improved using the G3MP2B3 method. The potential energy profile is confirmed via intrinsic reaction coordinate calculations of transition states. Four possible production channels are examined respectively, as H＋ transfer, H-atom transfer, H2＋ transfer, and bi- molecular nucleophilic substitution （SN2） reaction pathways. Based on present calculations, the H2＋ transfer reaction is major among these four channels, which agrees with previous experimental conclusions.

Preparation and Characterization of Storage and Emission Functional Material of Cs2O-doped 12CaO.7Al2O3

We provides a novel approach to generate low-temperature atomic oxygen anions （O-） emission using the cesium oxide-doped 12CaO.7Al2O3 （Cs2O-doped C12A7）. The maximal emission intensity of O- from the Cs2O-doped C12A7 at 700℃ and 800 V/cm reached about 0.54μA/cm2, which was about two times as strong as that from the un-doped C12A7 （0.23 μA/cm2） under the same condition. The initiative temperature of the O- emission from the Cs2O-doped C12A7 was about 500 ℃, which was also much lower than the initiative temperature from the un-doped C12A7 （570 ℃） in the given field of 800 V/cm. High pure O- emission close to 100% could be obtained from the Cs2O-doped C12A7 under the lower temperature （〈550℃）. The emission features of the Cs2O-doped C12A7, including the emission distribution, temperature effect, and emission branching ratio have been investigated in detail and compared with the un-doped C12A7. The structure and storage characteristics of the resulting material were also investigated via X-ray diffraction and electron paramagnetic resonance. It was found that doping Cs2Oto C12A7 will lower the initiative emission temperature and enhance the emission intensity

Discharge Characteristics of an Atmospheric Pressure Argon Plasma Jet Generated with Screw Ring-Ring Electrodes in Surface Dielectric Barrier Discharge

An atmospheric-pressure argon plasma jet with screw ring-ring electrodes in surface dielectric barrier discharge is generated by a sinusoidal excitation voltage at 8 kHz. The discharge characteristics, such as rotational and vibrational temperature of nitrogen, electronic excitation temperature, oxygen atomic density, nitrogen molecular density, and average electron density, are estimated. It is found that the rotational temperature of nitrogen is in the range of 352 ～ 392 K by comparing the simulated spectrum with the measured spectrum at the C3Πu → B3Πg （△ν = 2） band transition, the electronic excitation temperature is found to be in the range of 3127 ～ 3230 K by using the Boltzmann plot method, the oxygen atomic and nitrogen molecular density are of the order of magnitude of 1016 cm-3 by the actinometry method, and the average electron density is of the order of magnitude of 1012 cm-3 by the energy balance equation. Besides, the effective power, conduction, and displacement current are measured during the discharge.