Atomic Oxygen Research Papers - Academia.edu (original) (raw)

2025

Suprathermal O, C, and H atoms produced by means of photochemical reactions in planetary thermospheres can play an important role for the escape of atmospheric species by direct or indirect processes. In either case the non-thermal energy distribution functions at the exobase must be known in order to estimate the hot exosphere density profiles. For this purpose hot particles generated via photochemical processes are traced along their stochastic way through the thermosphere of Venus by using a 3D Monte-Carlo model and the kinetics and transport characteristics of these particles are determined. The simulation includes the collision of the suprathermal particles with the background gas, the energy transfer, and the tracing of secondary and cascaded hot atoms, which are generated in collisions of the hot particles with ambient constituents. A non-linear electron dissociative recombination coefficient as well as energy and mass dependent collision cross sections and their corresponding scattering angles are also taken into account. The exosphere density is obtained from the corresponding energy density and angular distribution at the exobase altitude by using a test particle model which traces the ballistic trajectories of hot O, C, and H atoms in the exosphere.

2025, MRS Proceedings

The effects of the space environment on polytetrafluorethylene and some fluorinated polymers, copolymers, and blends are critically reviewed. It is shown that in low altitude orbits such as Low Earth Orbit and Geostationary Orbit the presence of both ionizing radiation and atomic oxygen triggers a synergetic degradation of materials based on fluorinated polymers. The behavior is due to the lability of the in-chain alkyl radical to oxygen attack. It is concluded that fluorinated polymers should not be used as materials for space applications, as long as the mission implies low Earth orbits.

2025, Atmospheric Chemistry and Physics

Except for a few reactions involving electronically excited molecular or atomic oxygen or nitrogen, atmospheric chemistry modelling usually assumes that the temperature dependence of reaction rates is characterized by Arrhenius' law involving kinetic temperatures. It is known, however, that in the upper atmosphere the vibrational temperatures may exceed the kinetic temperatures by several hundreds of Kelvins. This excess energy has an impact on the reaction rates. We have used upper atmospheric OH populations and reaction rate coefficients for OH(v = 0...9)+O 3 and OH(v = 0...9)+O to estimate the effective (i.e. population weighted) reaction rates for various atmospheric conditions. We have found that the effective rate coefficient for OH(v = 0...9)+O 3 can be larger by a factor of up to 1470 than that involving OH in its vibrational ground state only. At altitudes where vibrationally excited states of OH are highly populated, the OH reaction is a minor sink of O x and O 3 compared to other reactions involving, e.g., atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or O x sink remains small. Among quiescent atmospheres under investigation, the largest while still small (less than 0.1%) effect was found for the polar winter upper stratosphere and mesosphere. The contribution of the reaction of vibrationally excited OH with ozone to the OH sink is largest in the upper polar winter stratosphere (up to 4%), while its effect on the HO 2 source is larger in the lower thermosphere (up to 1.5% for polar winter and 2.5% for midlatitude night conditions). For OH(v = 0...9)+O the effective rate coefficients are

2025

Ionospheric response to geomagnetic storms is determined by the efficiency of the solar wind-magnetosphere-ionosphere coupling that underlies the transfer of tremendous amount of mass and energy. The response of the equatorial and low latitude ionosphere to the moderate geomagnetic storm of 14 November 2012 is investigated. This study is carried out using vertical total electron content (VTEC) measured by Global Positioning System (GPS) receivers along the ~ 115°-121°E longitude. The GPS TEC observations show pronounced positive storm effects in the Asian sector (~115°-121°E) during the main phase of the storm for the low latitude and crest of anomaly stations. During the main phase of the storm the interplanetary electric field (IEF) penetrated to the equatorial ionosphere and caused significant density changes in the equatorial ionization anomaly (EIA) region. The eastward prompt penetration electric field associated with southward interplanetary magnetic field (IMF) augmented the...

2025, Journal of Computational Chemistry

The reaction mechanism for the styrene selective oxidation on the oxygen preadsorbed Au(111) surface has been studied by the density functional theory calculation with the periodic slab model. The calculated results showed that the process of reaction includes two steps: forming the oxametallacycle intermediate (OMME) and then producing the products. It was found that the second step, from OMME to product is the rate‐controlling step, which is similar to ethylene selective oxidation on Ag. Importantly, the present density‐functional‐theory calculation results suggested that the mechanism via the OMME (2) (i.e. the preadsorbed atomic oxygen bound to the CH2 group involved in C6H5CHCH2) to produce styrene epoxide is kinetically favored than that of OMME (1). © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009

2025, IEEE Transactions on Plasma Science

Chemical activation of the high voltage pulsed, cold atmospheric plasma jets is performed by introducing a low quantity of oxygen into the main flow of helium or argon. This article presents the influence of the oxygen over the intensity of the plasma jet current. Using optical emission spectroscopy we can demonstrate that there is an optimal value of the oxygen concentration that maximizes the plasma chemical activity.

2025

The thermal arc generator RB3 flows were characterized by laser absorption spectroscopy and Pitot probe measurement. Firstly, translational temperature and flow velocity distributions in an argon flow were deduced from measured absorption profile of ArI 772.42 nm. The averaged specific enthalpy and plasma power for TPS test region was estimated as 3.72±0.48 MJ/kg, 1.77±0.68 kW, respectively. Next, an air flow was diagnosed using OI 777.19 nm line. The specific enthalpy on the axis was estimated from the deduced temperature, Mach number and thermo-chemical equilibrium assumption in the plenum. As a result, the specific enthalpy, the degree of dissociation in oxygen and nitrogen were estimated as 11. 1±1.8 MJ/kg, 88.5 % and 3.8 %, respectively.

2025, Surface Science

The chemisorbed states of atomic oxygen and the subsequent replacement of the adsorbed O atoms by atomic hydrogen on the C(100) surface have been studied by electron energy loss spectroscopy (EELS ), thermal desorption spectroscopy ( TDS ) and low-energy electron diffraction (LEED). EELS spectra of the O-adsorbed C(100) surface at 300 K show losses at 113, 150, 215 and 261 meV. The 113 and 215 meV losses are assigned as the bending and stretching modes of the surface carbonyl (vCȎO) species (on-top O), respectively, which is formed by the dimer pand s-bond breaking. The 150 meV loss is attributed to the surface ether (CMOMC ) species (bridging O) which is also formed by the dimer bond breaking. These species are desorbed as CO at ~1100 K. The 261 meV loss indicates the existence of minority O atoms nearly triple-bonded to the substrate (which is decomposed by heating up to 800 K ). When the O-preadsorbed C(100) surface is exposed to an increasing amount of H, the 215 meV loss disappears and losses appear at 104, 152 and 362 meV which are associated with the surface hydride species. No CO and CO 2 desorptions are observed. These results suggest that the surface O atoms are replaced by atomic H completely and hydride species are formed. A model for the replacement is proposed.

2025

Eighteen Fe ablation trails were observed during the 17/18 Nov 1998 Leonid meteor shower with an airborne Fe lidar aboard the NSF/NCAR Electra aircraftover Okinawa. The average altitudeof the 18 trails from the high velocity(72 kin/s)Leonid meteors, 95.674-0.93 kin, is approximately 6.7 km higher than previouslyobserved forslower (---30 kin/s)sporadicmeteors. This height differenceisconsistentwith the assumption that meteors ablate when the kineticenergy imparted to the atmosphere reaches a critical threshold. The average age of the Fe trails, determined by a diffusionmodel, is 10.1 rain. The youngest ages were observed below 92 km and above 98 km where chemistry and diffusiondominate, respectively.The average abundance of the trails is10% of the abundance of the background Fe layer.Observationssuggest that the 1998 Leonid shower did not have a significant impact on the abundance of the background Fe layer.

2025, Pure and Applied Chemistry

The operating parameters of a miniature atmospheric pressure glow discharge torch (APGD-t) are optimized for the production of excited atomic oxygen, and the effect of the plasma jet on endothelial cells grown in Petri dishes is studied. We first demonstrate the importance of accounting for the effect of the voltage probe used to measure the electrical parameters of the torch on its ignition and operation characteristics. When operated with a main plasma gas flow rate of 1 SLM He and a power level of ~1 W, the torch shows an optimum in the production of excited atomic oxygen for a O2 flow of ~3.5 SCCM injected downstream from the plasma-forming region through a capillary electrode (i.e., 0.35 v/v % O2/He). It is shown that endothelial cells are detached from the Petri dishes surface under the action of the optimized plasma jet and that this effect does not originate from heating and fluid shearing effects. It is postulated that the cell detachment is caused solely by plasma-induced ...

2025, Journal of Electronic Materials

Molecular beam epitaxy (MBE) of ZnO on both sapphire and SiC sub strates has been demonstrated. ZnO was used as a buffer layer for the epitaxial growth of GaN. ZnO is a wfirtzite crystal with a close lattice match (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SiC, and high electron conductivity. ZnO is relatively soft compared to the nitride semiconductors and is expected to act as a compliant buffer layer. Inductively coupled radio frequency plasma sources were used to generate active beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O~ into atomic oxygen. Reflected high energy electron diffraction (RHEED) of the ZnO growth surface showed a two-dimensional growth. ZnO layers had n-type carrier concentration of 9 • 1018 cm -3 with an electron mobility of 260 cm2/V-s. Initial I-V measurements displayed ohmic behavior across the SiC/ZnO and the ZnO/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer layers also exhibited a two-dimensional growth. We have demonstrated the viability of using ZnO as a buffer layer for the MBE growth of GaN.

2025, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Pre-irradiation defects in insulators may be activated or decorated through the effects of ionizing radiation. In order to understand these reactions it is important to have a detailed understanding of the nature of the defects which existed prior to the exposure. We shall take a close lock at defects which are introduced by omnipresent trace impurities such as Hz0 and CO, in a model-type oxide structure like MgO. Dissolved Hz0 not only forms OH-ions but also H, molecules and peroxy ions, O;-. The Hz molecules may diffuse away leaving excess 0, *-ions behind. Above 800 K the Oi-dissociate into two paramagnetic defects: V-centers (O-state bound to a cation vacancy) and unbound positive holes, i.e. O-states free to move through the 02-sublattice. If two unbound holes recombine at the surface, atomic oxygen is released. In the bulk the unbound holes cause redox reactions with transition metal impurities. Dissolved CO, does not form carbonate ions, CO:-, but Ot-plus CO;-both of which are diamagnetic. The C atoms can either occupy cation vacancy sites (at low temperatures) or enter interstitial sites (above 800 K) where they are very mobile and subject to subsurface segregation. Above 800 K the CO;-configuration dissociates into the V-center and the equally paramagnetic COspecies. Between 500-800 K a transient paramagnetism is observed probably caused by the carbon atoms of the COf-configuration fluctuating between the cation vacancy sites and the next-nearest interstitial sites.

2025, Plasma Sources Science and Technology

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2025, arXiv (Cornell University)

Our ability to design and fabricate electronic devices with reproducible properties using complex oxides is critically dependent on our ability to controllably synthesize these materials in thin-film form. Structure-property relationships are intimately tied to film and interface composition. Here we report on the effects of cation stoichiometry in LaCrO 3 heteroepitaxial films prepared using molecular beam epitaxy. We show that LaCrO 3 films grow pseudomorphically on SrTiO 3 (001) over a wide range of La-to-Cr atom ratios. However, the growth mode and structural quality are sensitive to the La-to-Cr ratio, with La-rich films being of considerably lower structural quality than Cr-rich films. Cation mixing occurs at the interface for all La-to-Cr ratios investigated, and is not quenched by deposition at ambient temperature. Indiffused La atoms occupy Sr sites in the substrate. The presence of defects in the SrTiO 3 substrate is implicated in promoting La indiffusion by comparing the properties of LaCrO 3 /SrTiO 3 with those of LaCrO 3 /Si, both prepared at ambient temperature. Additionally, pulsed laser deposition is shown to result in more extensive interfacial mixing than molecular beam epitaxy for deposition at ambient temperature on Si.

2025, Applied Physics Letters

Stoichiometric, epitaxial LaCrO3 films have been grown on SrTiO3(001) by molecular beam epitaxy using O2 as the oxidant. Films grew in a layer-by-layer fashion, giving rise to coherently strained, structurally excellent films and surfaces which preserve the step-terrace structure of the substrate. The critical thickness is in excess of 500 Å. Cr(III) near the surface is easily oxidized to Cr(V) upon exposure to atomic oxygen and reduction back to Cr(III) is readily achieved by vacuum annealing, resulting in tunability of the charge state at the B-site cation.

2025, Colloids and Surfaces A: Physicochemical and Engineering Aspects

The first detailed study of molecular ozone adsorption by means of FT-IR spectroscopy at low temperatures (77 K) is reported. The spectra of 1603, 1803 and mixed isotopic modifications adsorbed on silica and titania were observed. Ozone molecules reveal basic properties, forming hydrogen bonds with acidic surface OH groups via one of the terminal oxygen atoms. Fundamental frequencies of hydrogen-bonded ozone, calculated from the combination bands or measured directly, are close to those of physisorbed, liquid or dissolved molecules. Ozone adsorption on a titania surface dehydrated at different temperatures, or pre-exposed to pyridine, acetonitrile, CO2 and CO, illustrates its interaction with Lewis acid sites of different strength. With weaker sites, ozone molecules form a coordination complex bound via one of the terminal oxygen atoms. The observed frequency values (about 1145 and 990 cm-1), as well as isotopic shifts observed for ozone enriched with 180, reveal a strong distortion of this molecule in the complex. The same form of ozone adsorption was found also for ZrO2, MgO and CeO2. No molecular adsorption of ozone on strong Lewis sites of TiO2, A1203 or ZnO was detected. The data obtained provide evidence for ozone dissociation on these sites, resulting in the formation of atomic oxygen, which participate in the catalytic reactions of ozone decomposition or oxidation of CO on the oxide surfaces.

2025, arXiv (Cornell University)

The solar photospheric oxygen abundance has been determined from [O ], O , OH vibration-rotation and OH pure rotation lines by means of a realistic time-dependent, 3D, hydrodynamical model of the solar atmosphere. In the case of the O  lines, 3D non-LTE calculations have been performed, revealing significant departures from LTE as a result of photon losses in the lines. We derive a solar oxygen abundance of log O = 8.66 ± 0.05. All oxygen diagnostics yield highly consistent abundances, in sharp contrast with the results of classical 1D model atmospheres. This low value is in good agreement with measurements of the local interstellar medium and nearby B stars. This low abundance is also supported by the excellent correspondence between lines of very different line formation sensitivities, and between the observed and predicted line shapes and center-to-limb variations. Together with the corresponding down-ward revisions of the solar carbon, nitrogen and neon abundances, the resulting significant decrease in solar metal mass fraction to Z = 0.0126 can, however, potentially spoil the impressive agreement between predicted and observed sound speed in the solar interior determined from helioseismology.

2025, Physical Review B

Up to 30 nm thick Fe 2 O 3 /Pt͑111͒ layers were prepared by atomic-oxygen-assisted molecular beam epitaxy. The structure, morphology, composition and magnetic properties of the films were investigated. The growth becomes 3D above 2 nm and after 3 nm the epitaxial ␥-Fe 2 O 3 ͑111͒ phase fully transforms into a ␣ -Fe 2 O 3 ͑0001͒ layer along with a ferrimagnetic to antiferromagnetic transition and a progressive structural relaxation. It is shown that the apparent surface lattice parameter is not simply related to the chemical phase up to 20 nm.

2025, Review of Scientific Instruments

Low reflectivity (“black”) surface treatments for space-borne infrared systems are reviewed. The uses of black surfaces in general, as well as for specific space-borne applications are discussed. Compositions of a wide variety of surface treatments with examples of experimental data to characterize performances are provided. Specific treatments included are: Ames 24E paint; AZKO 463 (Sikkens, Cat-A-Lac) paint; Ball IR black paint; Chemglaze (Aeroglaze) Z306 and Z302 paints; Eccosorb 268E paint; Parsons Black paint; black anodize; black Hardlub; black Hardcoat; Martin Black; InfraBlack; Enhanced Martin Black; Ebonal C; Teflon; ion beam textured; appliqués; black chrome; black etched beryllium on beryllium; plasma sprayed boron on beryllium; plasma sprayed beryllium on beryllium; boron carbide on POCO graphite; and Kapton. Data presented for some but not all of the surfaces include: spectrally integrated, 5–25 μm hemispherical-directional reflectance; spectral reflectance at wavelengt...

2025

Doppler temperatures from O(1D) airglow in the daytime thermosphere as observed by the Wind Imaging Interferometer (WINDII) on the UARS satellite

2025, Journal of Physics D

In a recent rewiew article we have reported-among other things-on preliminary computational studies regarding the effect of nitridation on the SiC/SiO 2 interface, in case of ntype doping. We have since discovered a few numerical errors in the paper, which also influence some of our statements. Here we present the correct results and their consequences.

2025, Journal of Physics D: Applied Physics

2025

Pentlandite (Co,Fe,Ni)9S8 is the most abundant iron-nickel sulphide ore containing mineral and has a wide range of applications in industries. The mineral is of commercial importance and can be extracted using floatation processes; one of the processes is by oxidation. This process plays a significant role in forming air bubbles that float the pentlandite mineral. Despite reports that oxidation tend to depress the sulphide minerals, it however, increases the pulp potential during flotation. The present study investigate the clean and oxidised nickel-rich {110} pentlandite surface using ab-initio density functional theory (DFT). The Bader analysis have been used to evaluate clean and oxidised surface and suggests that Fe and Ni have 3+ and 2+ (clean) and 4+ and 3+ (oxidised) oxidation state, respectively. Furthermore, when oxygen is adsorbed on the (fcc hollow site or on Fe-top site) and on Ni-top site, it was found that the surface oxidises as Fe-O-Fe and Ni-O-O, respectively. Oxida...

2025, esmat.esa.int

Polymers in space may be subjected to a barrage of incident atoms, photons, and/or ions. Atomic layer deposition (ALD) techniques can provide films that mitigate many of the current challenges for space polymers. ALD is a gas-phase technique based on two sequential, self-limiting surface reactions as illustrated in the Figure below. These sequential surface reactions allow conformal, pinhole free films to be deposited with atomic layer thickness control. ALD provides significant advantages over more conventional polymer coating technologies. ALD can deposit nanometer thin ultra-barrier films on thermally fragile polymer substrates. ALD films grow conformally on three-dimensional substrates and the films are strongly adhered to the surface. ALD can also be scaled up to coat very large substrates and can coat multiple substrates in parallel, resulting in reasonable throughput and economics. We have studied the efficacy of various ALD coatings to protect Kapton polyimide, FEP Teflon, and poly(methyl methacrylate) films from atomicoxygen and VUV attack. Atomic-oxygen and VUV studies were conducted with the use of a laserbreakdown source for hyperthermal O atoms and a D 2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al 2 O 3 ALD coatings protected the underlying substrates from atomic-oxygen attack, and the addition of TiO 2 coatings protected the substrates from VUV-induced damage. The results indicate that ALD coatings can simultaneously protect polymers from oxygen-atom erosion and VUV radiation damage.

2025, IEEE Transactions on Plasma Science

2025

Radiation can create atomic-scale defect states in polymers, leading to changes in their optical, electrical and mechanical properties. Recent studies of polymers have shown that these defect states are sensitive to oxygen or air exposure. It is believed that air cause the number of defect states to decrease and the polymers to revert to their original states. However, the time scale of this regression is not known. This experiment quantified the time that it takes one polymer to recover and the extent of said recovery; polymide (PI). In order to study the regression, optical transmission data were taken using a StellarNet UV/VIS Spectrometer. Optical data were collected at different intervals of time and then compared in order to quantify the time frame of the regression. Failure to account for this time-dependent recovery in radiation studies may result in inaccurate results and has called into question previous studies involving radiation effects in polymers where exposure times were not recorded.

2025, Physical Review E

An efficient method predicting the electron density N, and temperature T, in partially ionized plasmas with a fraction of atomic oxygen greater than about 10% of all heavy particles of the plasma is presented. The method is valid in plasmas where 10' cm &N, &10' cm and 8000 K & T, &15000 K [X, =2(X, +X, ), and N, is the density of the oxygen atotns].

2025

A summary of the Low Earth Orbital Environment, its impact on the Photovoltaic Power systems of the space station and the solutions implemented to resolve the environmental concerns or issues are described. Low Earth Orbital Environment (LEO) presents several concerns to the Photovoltaic power systems of the space station. These concerns include atomic oxygen interaction with the polymeric substrate of the solar arrays, ionized environment effects on the array operating voltage, the effects of the meteoroids and debris impacts and penetration through the different layers of the solar cells and their circuits, and the high energy particle and radiation effects on the overall solar array performance. Potential solutions to some of the degrading environmental interactions that will provide the photovoltaic power system of the space station with the desired life are also summarized.

2025, Carbon

The interaction of graphite with plasmas of pure gases (O 2 , N 2 or H 2 O), air or mixtures of gases containing NO has been studied by XPS ''in situ'' analysis. Depending on the type of plasma, different species of nitrogen, oxygen and carbon have been detected on the surface of graphite. The nitrogen containing species have been attributed to pyridinic, pyrrol, quartenary and oxidized groups adsorbed on the surface. The evolution with the treatment time of the relative intensity of the different nitrogen bands for Ar + NO, N 2 + NO, air or N 2 plasmas has served to propose a model accounting for the reactions of graphite with plasmas of NO containing gases. The model explains why carbon materials (in the form of graphite, soot particles, etc.) can be very effective for the removal of the NO present in exhaust combustion gases excited by a plasma. The analysis of the C1s and O1s photoemission peaks reveals the formation of C/O adsorbed species up to a maximum concentration on the surface of around 10% atomic oxygen. A general evolution is the progressive formation of C/O species where the carbon is sp 3 hybridized. This tendency is enhanced when graphite is treated with the plasma of water.

2025, Monthly Notices of the Royal Astronomical Society: Letters

Some 16 transitions in atomic oxygen originating from its 3 P ground state were measured using a tunable narrow-band extreme-ultraviolet laser source, with an unprecedented accuracy of λ/λ = 8 × 10 -8 . The results are relevant for comparisons with spectral absorption features observed in the line of sight of quasars, in order to test a possible variation of the fine-structure constant α on a cosmological time-scale.

2025

Accurate modeling of planetary atmospheres requires the knowledge of a series of chemical parameters, possibly determined in laboratory experiments. In particular, for gas-phase bimolecular reactions the kinetic rate constants and product branching ratios are desired. In our laboratory we have undertaken a systematic investigation of some bimolecular reactions, which are believed to form key steps in the models, with the aim of characterizing the reaction mechanism and product branching ratio. We have employed the crossed molecular beam scattering method with mass-spectrometric detection to study reactions involving atomic nitrogen in the first electronically excited state, N( 2 D), and ground state atomic oxygen, O( 3 P), with species relatively abundant in the atmospheres of Titan (as well as Mars and Triton). Results have been obtained for the reactions of N( 2 D) with H 2 and the hydrocarbons CH 4 , C 2 H 2 and C 2 H 4 , which are amongst the most abundant minor components of the atmosphere of Titan. In the cases of the reactions with hydrocarbons, molecular products containing a novel CN bond are formed, thus suggesting possible routes towards the production of gas-phase nitriles. Interestingly, most of the observed nitriles are either cyclic or unsaturated and could, therefore, be responsible for the building-up of the nitrogen-rich atmospheric aerosols of Titan. We have also investigated the reactions between O( 3 P) and unsaturated hydrocarbons, which might play a role in the conversion of oxygen to CO. Finally, we have extended the same approach to the study of radical-radical reactions, namely O( 3 P)+CH 3 and C 3 H 5 . Molecular products other than those already considered in the modeling of planetary atmospheres have been identified and new routes of formation of CO can be envisaged.

2025, Journal of The Optical Society of America B-optical Physics

2025, Optics Communications

2025, Journal of the Optical Society of America B

2025

DOE Scientific and Technical Information. DOE Scientific and Technical Information. ...

2025, Excellent Publisherd

Cleaning and disinfection assessment is an important part of cGMP in any pharmaceutical industry. To validate the efficacy of disinfectants used in disinfection procedure, in order to reduce surface contaminations, we tested invitro the action of commercial disinfectants. The qualification of procedure was carried out on a screening test in order to measure effectiveness of the test disinfectants. A clean surface becomes easier to disinfect and so the cleaning and disinfection programs complement each other. Disinfection efficacy and validation studies has been carried in accordance with the United States Pharmacopeia <1072> Disinfectants and Antiseptics protocol. The test organisms used include standard strains mentioned in USP <1072>. Standard Use Dilution test protocol was followed, before and after disinfection and the microbial load was assessed to calculate the Log 10 reduction index. Subsequently, we developed and validated a disinfection procedure on using approximately 10 6-10 7 total colony forming units per test. Our results showed a bactericidal, fungicidal, and sporicidal efficacy coherent to the acceptance criteria suggested by United States Pharmacopeia <1072>. The correct implementation of our cleaning and disinfection procedure, respecting stipulated concentrations and contact times, led to a reduction of more than 4 Log 10 for all microorganisms used. The qualification of procedure was carried out on a screening test in order to measure effectiveness of the disinfectants, chosen according to their principle of action.

2025, Advances in Space Research

Detailed studies of preserved hypervelocity impact residues on spacecraft multi-layer insulation foils have yielded important information about the flux of small particles from different sources in low-Earth orbit. We have extended our earlier research on impacts occurring in LEO to design and testing of a compact capture device. MULPEX (MUlti-Layer Polymer EXperiment) is simple, cheap to build, lightweight, of no power demand, easy to deploy, and optimised for the efficient collection of impact residue for analysis on return to Earth. The capture medium is a stack of very thin (8 micron and 40 micron) polyimide foils, supported on poly-tetrafluoroethylene sheet frames, surrounded by a protective aluminium casing. The uppermost foil has a very thin metallic coating for thermal protection and resistance to atomic oxygen and ultra-violet exposure. The casing provides a simple detachable interface for deployment on the spacecraft, facing into the desired direction for particle collection. On return to the laboratory, the stacked foils are separated for examination in a variable pressure scanning electron microscope, without need for surface coating. Analysis of impact residue is performed using energy dispersive X-ray spectrometers. Our laboratory experiments, utilising buck-shot firings of analogues to micrometeoroids (35-38 micron olivine) and space debris (4 micron alumina and 1mm stainless steel) in a light gas gun, have shown that impact residue is abundant within the foil layers, and preserves a record of the impacting particle, whether of micrometer or millimetre dimensions. Penetrations of the top foil are easily recognised, and act as a proxy for dimensions of the penetrating particle. Impact may cause disruption and melting, but some residue retains sufficient crystallographic structure to show clear Raman lines, diagnostic of the original mineral.

2025, Journal of Materials Science

Atomic oxygen (AO) is a dominant component of the low earth orbit and can erode most spacecraft material. We demonstrated the application of graphene to enhance AO erosion resistance of spacecraft polymers. Graphene-reinforced epoxy resin nanocomposites were prepared by solidification of epoxy resin in solution with dispersed graphene flakes and their AO erosion resistance was investigated in a plasma-type ground-based AO effects simulation facility. The nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Results based on erosion kinetics revealed that a 46 % decrease in mass loss and a 47 % decrease in erosion yield were achieved by addition of only 0.5 wt% of graphene. Further analysis of the surface morphology and composition showed that the graphene nanoflakes could serve as barriers to protect underneath from AO erosion. Thus, this approach provides a novel route for improving durability and reliability of spacecraft material, especially polymers.

2025, Surface Science

The adsorption of atomic oxygen and its inclusion into subsurface sites on Ag(210) and Ag(410) surfaces have been investigated using density functional theory. We find that-in the absence of adatoms on the first metal layer-subsurface adsorption results in strong lattice distortion which makes it energetically unfavoured. However subsurface sites are significantly stabilised when a sufficient amount of O adatoms is present on the surface. At high enough O coverage on the Ag(210) surface the mixed on-surface + subsurface O adsorption is energetically favoured with respect to the on-surface only adsorption. Instead, on the Ag(410) surface, at the coverage we have considered (3/8 ML), the existence of stable terrace sites makes the subsurface O incorporation less favourable. These findings are compatible with the results of recent HREEL experiments which have actually motivated this work.

2025, Physical Review B

The structure and dynamics of atomic oxygen adsorbed on Ag(410) and Ag(210) surfaces has been investigated using density functional theory. Our results show that the adsorption configuration in which O adatoms decorate the upper side of the (110) steps forming O-Ag-O rows is particularly stable for both surfaces. On Ag(210), this arrangement is more stable than other configurations at all the investigated coverages. On Ag(410), adsorption on the terrace and at the step edge are almost degenerate, the former being slightly preferred at low coverage while the latter is stabilized by increasing the coverage. These findings are substantiated by a comparison between the vibrational modes, calculated within density-functional perturbation theory, and the HREEL spectrum which has been recently measured in these systems.

2025, Journal of Chemical Sciences

The reaction of ground-state atomic oxygen [O( 3 P 2 )] with methyl, ethyl, n-propyl and isopropyl radicals has been studied using the density functional method and the complete basis set model. The energies of the reactants, products, reaction intermediates and various transition states as well as the reaction enthalpies have been computed. The possible product channels and the reaction pathways are identified in each case. In the case of methyl radical the minimum energy reaction pathway leads to the products CO + H 2 + H. In the case of ethyl radical the most facile pathway leads to the products, methanal + CH 3 radical. For propyl radical (n-and iso-), the minimum energy reaction pathway would lead to the channel containing ethanal + methyl radical.

2025, Journal of Geophysical Research

This paper compares the observed behavior of the Fe layer of the ionosphere at Millstone Hill and Hobart with calculations from the field line interhemispheric plasma (FLIP) model for solar maximum, solstice conditions in 1990. During the study period the daily F10.? index varied by more than a factor of 2 (123 to 280), but the 81-day mean F10.? (F10.?A) was almost constant near 190. Calculations were performed with and without the effects of vibrationally excited N2 (N]) which affects the loss rate of atomic oxygen ions. In the case without N] there is generally good agreement between the model and measurement for the daytime, peak density of the F region (NmFe). Both the model and the measurement show a strong seasonal anomaly with the winter noon densities a factor of 3 to 4 greater than the summer noon densities at Millstone Hill and a factor of 2 greater at Hobart. The seasonal anomaly in the model is caused by changes in the neutral composition as given by the mass spectrometer and incoherent scatter (MSIS) 86 neutral density model. There is generally little or no increase in the observed noon NmFe as a function of daily F10.7 except at Millstone Hill in winter. In May-July, where the measured NmFe shows least dependence on daily F10.?, there is excellent agreement between the model and data. The modeled NmFe is about 30% less than the measured values at Millstone Hill at the December solstice, but both model and data increase with increasing daily F10.? index. At Hobart, on the other hand, the model densities are greater than or comparable to the measured densities for the December solstice. This suggests that the differences between model and data are not due to the incorrect solar EUV flux. The effect of including N] is to worsen the agreement between model and data at Millstone Hill by reducing the summer densities from good agreement to 40% below the data. In winter the N• effects are much smaller, and the densities are reduced by only 10%. While N] worsens the model-data comparison at Millstone Hill, it does bring the model seasonal density ratio into better agreement with the data and also improves the agreement at Hobart. Although the 1990 daytime ionosphere can be well modeled without N], it may still be important for high levels of solar and magnetic activity. There is a very close relationship between the height at which peak density occurs hmFe variation and the NmFe variation with F10.? in summer at Millstone Hill. In contrast to the generally good agreement between model and data at noon, the model badly underestimates the density at night at Millstone Hill at all seasons. At Hobart the model reproduces the nighttime density variations well in both winter and summer. The international reference ionosphere (IRI) model generally provides a good representation of the average behavior of noon NmFe and hmFe but because the data show a lot of day-to-day variability, there are often large differences. The FLIP model is able to reproduce this variability when hmFe is specified. The IRI model peak densities are better than the FLIP densities at night, but the IRI model does not represent the Millstone Hill summer data very well at night in 1990.

2025, Chemical Vapor Deposition

The gas phase reactions of tetraethoxysilane in atomic oxygen‐induced chemical vapor deposition were investigated. A high‐resolution gas chromatography/mass spectrometry examination of the reaction products, collected in a cold trap, revealed the presence of linear and cyclic siloxane oligomers containing the ‐(EtO)2SiO‐ repeating unit. The structure of the identified oligomers and mechanisms of TEOS reactions with atomic oxygen suggest that diethoxysilanone plays a predominant role in the silica film growth process.

2025, Applied Surface Science

In this study, we prepared thin films by blending ethylene vinyl acetate copolymers (EVA) containing 12-33 (wt.%) vinyl acetate (VA) with polyvinyl acetate (PVAc) and high density polyethylene homopolymers. Large area micropatterns having controlled protrusion sizes were obtained by phase-separation especially for the PVAc/EVA-33 blends using dip coating. These surfaces were characterized by XPS and contact angle measurements. A reasonably linear relation was found between the VA content on the surface (wt.%) obtained from XPS analysis and the VA content in bulk especially for PVAc/EVA-33 blend surfaces. PE segments were more enriched on the surface than that of the bulk for pure EVA copolymer surfaces similar to previous reports and VA enrichment was found on the EVA/HDPE blend surfaces due to high molecular weight of HDPE. Water Â e decreased with the increase in the VA content on the blend surface due to the polarity of VA. A good agreement was obtained between - s and atomic oxygen surface concentration with the increase of VA content. The applicability of Cassie-Baxter equation was tested and found that it gave consistent results with the experimental water contact angles for the case where VA content was lower than 55 wt.% in the bulk composition.

2025, Scanning microscopy

We report unambiguous atomic scale evidence demonstrating that the atom density in the high temperature "lxl" phase of Si(lll) is -6% higher than the 7x7. Such evidence is provided by scanning tunneling microscopy (STM) observation of excess adatom density, and related island formation, on surfaces with very large terraces. The unusually large terraces were produced by heating the sample with DC current in the step-down direction at 1200°C. By trapping adatoms on the terraces through a quench, we have also created areas of metastable reconstructions, i.e., 9x9, 2x2, c2x4andV3xV3, much larger than previously reported. For the first time, we have demonstrated the existence of metastable llxll, 13x13 and c2x8 on Si(lll). We have found that the c2x8 reconstruction can be stabilized as well as other members of the 2x2/c2x4/c2x8 family of reconstructions. An energetic model, based on the idea of atomic conservation, is proposed for the formation of the observed high atom density metastable reconstructions.

2024, Physical Review Letters

Core-level photoelectron spectra, in excellent agreement with ab initio calculations, confirm that the stable wetting layer of water on Ru{0001} contains O-H and H 2 O in roughly 3:5 proportion, for OH x coverages between 0.25 and 0.7 ML, and T < 170 K. Proton disorder explains why the wetting structure looks to low energy electron diffraction (LEED) to be an ordered p 3 p 3 p R30 adlayer, even though 3 8 of its molecules are dissociated. Complete dissociation to atomic oxygen starts near 190 K. Low photon flux in the synchrotron experiments ensured that the diagnosis of the nature of the wetting structure quantified by LEED is free of beam-induced damage.

2024, Icarus

As a part of a global effort, the dynamics of energetic particles flowing through the martian upper atmosphere is studied. Most of the production of hot atomic oxygen occurs deep in the day-side thermosphere of Mars, where dissociative recombination (DR) of O þ 2 ion is the dominant source. The study of an upper atmosphere is complicated by the change in the flow regime from a thermospheric collisional to an exospheric collisionless domain. To understand the martian exosphere, it is then highly desirable to employ a global kinetic model that includes a self-consistent description of both thermospheric and exospheric regions. In this work, a combination of our Direct Simulation Monte Carlo (DSMC) model [Tenishev, V.,

2024

This paper reports the evidence for an enhanced gravity wave activity of 1-2 hour periodicity in the equatorial mesopause temperature during the counter electrojet (CEJ) events. The analysis based on the data from a unique dayglow photometer and Proton Precession Magnetometer over a dip equatorial station Trivandrum (8.5°N, 77°E, dip latitude 0.5°N) clearly indicates that in general, the wave activity is high during CEJ events compared to a normal day. It is very interesting to note that the wave activity at mesopause region fades out during the period of the occurrence of CEJ when the mesospheric zonal wind shows a reversal from west to east. This indicates a possible upward penetration of the gravity waves from mesosphere to lower thermosphere during such events, thereby, reversing the vertical polarization field and hence the generation of CEJ. This study presents first direct evidence for such an enhancement in the wave activity in the upper mesospheric region during CEJ events, supporting the gravity hypothesis of Raghavarao & Anandarao [Raghvarao R & Anandarao B G, Vertical winds as a plausible cause for equatorial counter electrojet, Geophys Res Lett (USA), 7 (1980) pp 357-360].