Atomic Oxygen

An Ag(111) single crystal electrode emersed from NaF+NaOH electrolyte (pH 11) under anodic polarisation has been studied ex situ by means of X-ray photoelectron spectroscopy ( XPS). ''Underpotential'' oxidation has been found at +0.2 and 0.0 V vs. Hg/HgO, that is by 0.2-0.4 V more negative than the reversible potential of the Ag 2 O phase formation. The generation of a number of surface and bulk oxygen-containing species, including surface Ag 2 O-like species, surface and bulk OH groups (OH ads and OH bulk , respectively), surface and bulk atomic oxygen, has been observed on the emersed electrode. The present work provides the first direct evidence of the hydroxide incorporation in the bulk of an Ag(111) electrode in the course of underpotential oxidation. OH bulk is characterised by a O 1s peak at approximately 532.8 eV, while surface OH ads manifests itself as the peak at ca. 531.6 eV. The origin of the positive binding energy shift is discussed. Surface and bulk OH groups demonstrate substantially different thermal stability. Surface species desorb below 470 K, while dissolved OH groups exhibit high stability towards prolonged annealing in vacuum at temperatures up to 750 K; they remain in the near-surface region even after sputtering by Ar+ and He+ ions. The oxide-like species is characterised by the O 1s peak at 529.5 eV and decomposes after heating in vacuum at a temperature of about 470 K. The He(I ) and He(II ) UP spectra of the emersed electrode along with the XPS data provide evidence that the coverage with surface oxide is less than 1 ML. A tentative scheme of Ag(111) underpotential oxidation is discussed.

We report the detection of electrons due to photo-ionization of atomic oxygen and carbon dioxide in the Venus atmosphere by solar helium 30.4 nm photons. The detection was by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) on the Venus Express (VEx) European Space Agency (ESA) mission. Characteristic peaks in energy for such photoelectrons have been predicted by Venus atmosphere/ionosphere models. The ELS energy resolution (DE/E$7%) means that these are the first detailed measurements of such electrons. Considerations of ion production and transport in the atmosphere of Venus suggest that the observed photoelectron peaks are due primarily to ionization of atomic oxygen.

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.

A series of titanium compounds, Ti(NMe,),, t-BuTi(NMe,),, [Ti&-N-t-Bu)(-NMe,),],, Tie-BUDAD), and CpTiC7H7, have been screened in combination with NH, for their suitability as precursors for the CVD of titanium nitride films at substrate temperatures of 300-600°C and a system pressure of 1.5 Torr. The best TIN layers have been grown using t-BuTi(NMe,), and NH,, from which an 0.8 pm thick layer deposited at 400°C. showed a resistivity of 1.4.10.~ n -c m and contained 5 atom% carbon and 6 atom% oxygen.

We analyze significant increases in 630 nm atomic oxygen night emissions during very strong geomagnetic storms, using optical measurements, theoretical modeling, and magnetogram inversion technique (MIT) data. It is shown that during strong magnetic storms when electron precipitation equatorial boundary at the night sector expands up to ~40°, the interaction of energetic electron flux with thermospheric components may cause extreme increases in the 630 nm emission intensity. Model calculations of the red line intensity show good agreement with observational data. Using the November 20, 2003 magnetic storm as an example, we have found that oxygen atom collisions with thermal Maxwell and superthermal electrons make a major contribution to the integral emission intensity. Thermospheric density variations during the magnetic storm significantly affect the red line generation.

This research focuses on the synthesis and characterization of a piezoelectric (β-CN)-APB/ODPA polyimide. The remanent polarization and piezoelectric d 31 and g 33 coefficients are reported to assess the effect of synthesis variations. Each of the materials exhibits a level of piezoelectricity which increases with temperature. The remanent polarization is retained at temperatures close to the glass transition temperature of the polyimide.

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The Mars Global Surveyor (MGS) z -axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90°E and 90°W, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.

The adsorption of NH a on Rh(lll) has been investigated by temperature programmed desorption, work function measurements, low energy electron diffraction and secondary ion mass spectrometry. TPD indicates the existence of three distinct desorption states; el-, ~2-and 13-NHa with peak maxima at 320, 155 and 130 K, respectively. For the most strongly chemisorbed state, ~I-NH3, the desorption energy is 81.5 kJ mol-k A (2 x 2) LEED pattern is observed after complete filling of the ~1-and ~2-NH3 states, which is attributed to saturation of the first adsorption layer, corresponding to an NH3 coverage of 0.25 ML. The sticking coefficient for NH 3 adsorption at 120 K, is on the order of unity and independent of coverage during filling of the first adsorption layer. NH 3 adsorption causes a significant work function decrease of 2.4 eV below the value of clean Rh(lll). The initial work function decrease corresponds to an average dipole per NH 3 molecule of 1.9 D, i.e. higher than that of the NH3 molecule in the gas phase. SIMS spectra of NH a on Rh(lll) contain Rh(NH3) + as the predominant ammonia-derived duster ion. The intensity of the Rh(NH3) + duster ion behaves strongly non-linear with the NH3 coverage and indicates some changes in the NH3 adlayer at a coverage of ~0.12 ML.

A three-dimensional (3-D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O 2 + between 120 and 300 km and the sputtering of the Martian atmosphere by incident O + pickup ions. The reimpacting and escaping fluxes of pickup ions are derived from a 3-D hybrid model describing the interaction of the solar wind with our computed Martian oxygen exosphere. In this work it is shown that the role of the sputtering crucially depends on an accurate description of the Martian corona as well as of its interaction with the solar wind. The sputtering contribution to the total oxygen escape is smaller by one order of magnitude than the contribution due to the dissociative recombination. The neutral escape is dominant at both solar activities (1 Â 10 25 s À1 for low solar activity and 4 Â 10 25 s À1 for high solar activity), and the ion escape flux is estimated to be equal to 2 Â 10 23 s À1 at low solar activity and to 3.4 Â 10 24 s À1 at high solar activity. This work illustrates one more time the strong dependency of these loss rates on solar conditions. It underlines the difficulty of extrapolating the present measured loss rates to the past solar conditions without a better theoretical and observational knowledge of this dependency.

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.

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.

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

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...

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

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.

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.

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.

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 ...

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.

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.

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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.

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.

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.

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.

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.

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...

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...

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.

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.

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].

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.

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.

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.

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.

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.

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.

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.