Neutral Oxygen Research Articles

Accumulation of oxygen interstitial-vacancy pairs under irradiation of corundum single crystals with energetic xenon ions

Single crystals of α-Al2O3 with broad sides oriented perpendicular to the c crystal axis have been irradiated by 231-MeV xenon ions with fluence varying from 5×1011 to 1014 ions/cm2. The spectra of radiation-induced optical absorption (absorption of a pristine crystal is subtracted) have been decomposed into Gaussians serving as a measure of oxygen-related Frenkel defects (vacancy-interstitial pairs). The concentration of all structural defects considered – vacancy-type F and F+ centers as well as oxygen interstitials – continuously increases with ion fluence. Therefore, radiation-induced origin of elementary absorption bands at 5.6 and 6.6 eV tentatively ascribed earlier to charged and neutral oxygen interstitials has been proved for the first time. The concentrations of charged interstitials (in the form of superoxide ions) have been directly determined by the EPR method. The evolution of cathodoluminescence bands typical of self-trapped excitons (VUV band at 7.6 eV) and F-type defects (bands peaked around 3.0 and 3.8 eV) with the rise of Xe-ion-irradiation fluence has been measured and analyzed.

DFT modeling of reaction of H2 with O2 pre-adsorbed on In2O3(011) surface

The DFT approach is used for the first time to model the reaction of hydrogen with oxygen molecule adsorbed on the defective surface of In2O3(011). This reaction is crucial for hydrogen detection by In2O3 sensor. The activation energies are calculated using two mechanisms involving the formation of both an adsorbed water molecule and hydroxyl groups on the In2O3(011) surface. One hydroxyl group is formed due to the bonding of OH with the surface metal atom, and the other due to the bonding of hydrogen with oxygen of the lattice. Both reactions are characterized by the presence of a potential barrier and are exothermic. The activation energies of the two reactions are calculated by the climbing-image nudged elastic band method to be 0.99 eV and 0.98 eV. The results of the calculations are compared with available experimental data. It is also shown that the presence of a surface neutral oxygen vacancy leads to the formation of a vacancy state below the Fermi level, and the electron density is concentrated on the fourfold coordinated indium atom.

From surface activation to microfluidic heat pipes: An innovative in-situ wafer level heterogenous bonding method

There has been considerable interest in low-temperature in-situ integration techniques for the fabrication of hetero-structured substrates and micro/nanosystems. This study presents a novel bonding approach that uses a water vapor-assisted surface activation strategy with neutral oxygen species (NOS). This method enables of highly efficient in-situ bonding process that utilizes the controllable and flexible environment to meet specific integration needs without exposure to the unstable ambient air. The NOS and water vapor increases hydroxyl groups, leading to smoother and more hydrophilic surfaces. The combined effects of NOS and the water vapor result in a larger bonded area ratio and significantly higher bonding energy compared to those activated by NOS alone. Meanwhile, the silicon oxide and quartz glass surfaces avoid being heavily electrically charged. This process thus achieved flawless silicon/quartz glass wafer bonding at 150 °C with a high bonding energy (∼4 J/m2) and Si/Si bonding pairs without any subsequent annealing voids. Then, the bonding pairs have been verified to have high reliability in extreme environments from −65 °C to 200 °C with no thermal-shocked cracks. The high-quality heterointerfaces could also withstand subsequent mechanical grinding and polishing for silicon-on-quartz glass (SOQ) fabrication. Moreover, a SOQ structured microfluidic heat pipe device was successfully fabricated based on the low-temperature in-situ heterogenous bonding. The robust heterointerfaces ensured non-leakage working during the heat dissipation. This facile and cost-effective bonding method is suitable for damage-free heterogeneous integration of active devices, micro/nanofluidic chips, and M/NEMS packaging. It has of great potential in fields such as biochemical analysis, quantum computing, and thermal sensing.

A Study of Interstellar Medium in the Line of Sight of Transient Neutron Star Low-Mass X-ray Binary, MXB 1659-298, by Timing and Spectral Analysis

This work is dedicated to the study of interstellar medium (ISM) along the line of sight (LOS) of the transient low-mass X-ray binary, MXB 1659-298, capitalizing the high resolving power of XMM-Newton in the soft energy range. We emphasized the analysis of reflection grating spectrometer (RGS) data in the energy range 0.5–2.15 keV, suitable for the study of ISM. The paper includes an explanation of why, in the soft X-ray energy range, only two observations (out of seven) were deemed eligible for analysis. Three absorption lines associated with highly ionized Fe XX (1s22p2-2p2 (3p) 4d), Si XIV (1s2-1s2p), and Mg XI (1s2-1s6p) were identified in the observations, with IDs of 8620701(2001) and 748391601(2015). These new absorption lines and the absorption edge due to the neutral oxygen K edge seen in the spectra validate the multiphase structure of ISM. The predominance of interstellar medium over the ionized absorber is established along the direction of the source. The equivalent hydrogen column density measured is nearly equal to the galactic HI value derived previously. The small value of the ionic column density of Fe, Si, and Mg in the site of the high-temperature region resembles previous findings.

First-principles investigation of positively charged and neutral oxygen vacancies in amorphous silica.

The structural parameters, electron localization functions, electron paramagnetic resonance (EPR) parameters, formation energies, and thermodynamic transition levels of various oxygen vacancy defects in amorphous silica are comprehensively and integrally investigated by using density functional theory. The trends of changes in the oxygen vacancy defect structure and electron localization induced by the increase in distance between defective silicon atoms are clearly identified. It is shown that the dimer configuration may be the potential structure of the Eδ' center. For the back-projected unpuckered configuration and the puckered configuration, whose EPR parameters are more consistent with the experimental values of the Eγ' center, the unpaired electron localized on the sp3 hybridized silicon atom is a common feature. Due to the three-coordinated oxygen atom in the forward-oriented configuration, the EPR parameters are closest to those of the Eα' center. Transformations of oxygen vacancy defects under different charge states are studied by sequentially adding and removing electrons. The thermodynamic transition level analysis reveals that the dimer and forward configurations may behave as deep traps for electron accumulation. The back-projected puckered fourfold-coordinated and fivefold-coordinated configurations are comparatively stable and may be able to function as shallow traps for electron transport. The neutral double unpuckered, neutral back-projected puckered fourfold-coordinated, and neutral back-projected unpuckered configurations are more likely to lose electrons during hole trapping. As the bias voltage is repeatedly changed, the defect density of the puckered configuration may reduce, while that of the dimer and unpuckered configuration may take an opposite trend.

Spectral evolution and photo-ionization analysis of Nova Cas 2020 (V1391 Cas)

We present spectroscopic observations of Nova Cas 2020 (V1391 Cas) obtained using the Russian Turkish Telescope during different stages of its 2020 outburst. We followed the spectral evolution of the nova until it entered the nebular phase. The expansion velocity of the ejecta reached ∼780km s−1. The fluxes of the neutral [O I] lines at wavelengths 6300, 6364, and 5577 ̊A were used to calculate the electron temperature and the mass of neutral oxygen in the ejecta. We found average values Te=4890K, MOI=2.54×10−5M⊙ which are consistent with the values calculated for other novae. We modeled the nova’s ejected envelope 515 days after its discovery and found that the log elemental abundances by number relative to Hydrogen of the envelope are He = −0.7, C = −5.5, O = −2.5, N = −2.0 and Ne = −4.0.

Simulations of nozzle gas flow and gas-puff Z-pinch implosions on the Weizmann Z-pinch

We present simulations of an oxygen gas puff Z-pinch on a University scale generator at the Weizmann Institute of Science. The work accounts for the detailed geometry of the nozzle, the initial neutral gas density distribution, and the subsequent implosion. The modeling results show significant improvement with data for the current at the time of stagnation in comparison with a previous effort [Rosenzweig et al., Phys. Plasmas 27, 022705 (2020)]. As a first step, we performed simulations of the flow of neutral diatomic oxygen from a plenum through a nozzle within a recessed cathode, across a gap, and into the anode with a recessed grounded honeycomb. These simulations show an agreement with the measured initial gas density profiles within the region not blocked by the recesses and accessible to visible measurements. The computed neutral gas flow profile serves as the initial condition for a radiation magnetohydrodynamic simulation of the implosion using the MACH2-TCRE code. By considering the specific details of the nozzle and chamber geometry, we find agreement with the measured current profile, including the inductive notch. The simulations predict that the plasma undergoes a strong pinch within the hidden anode recess. The simulations also predict the strongest radiation pulse occurs within the anode recess and at the time of the observed inductive notch.

A Community Ionosphere‐Thermosphere Observing System Simulation Experiment (OSSE) Tool: Geospace Dynamics Constellation Example

AbstractObserving System Simulation Experiments (OSSEs) provide an effective way to evaluate the impact of assimilating data from a specific observing system on hindcasting, nowcasting, and forecasting of environmental systems. The NSF NCAR's Data Assimilation (DA) Research Testbed/Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (DART/TIEGCM) tool, to be hosted at the NASA Community Coordinated Modeling Center, serves as a valuable and accessible community resource for quantitatively evaluating the impact of observations from both current and future ionosphere‐thermosphere (IT) observing systems. This study demonstrates the utility of DART/TIEGCM as an IT OSSE tool, using synthetic observations simulated using a currently planned NASA Geospace Dynamics Constellation (GDC) observing system design. Five sets of OSSEs are carried out to compare the effects of assimilating various combinations of prospective GDC observations (e.g., neutral temperature, neutral wind, neutral composition, atomic oxygen ion density, and ion and electron temperature) during a major geomagnetic storm period of the St Patrick's Day Storm on 17 March 2013. The maximum error reduction in neutral temperature and atomic ion oxygen density is 24.6% and 43.3% compared to the control experiment. These OSSEs indicate the benefits of coupled IT DA approaches implemented in DART/TIEGCM to maximize the impact of multi‐parameter IT observations, such as those expected from the GDC mission. Although more work is required to draw any definitive conclusion on the GDC data impact, the study provides an illustrative example of how the DART/TIEGCM community tool can be used to evaluate observational impacts of planned or existing missions for geospace research and applications.

Evidence of Pop III stars’ chemical signature in neutral gas at z ∼ 6

Aims. This study explores the metal enrichment signatures attributed to the first generation of stars (Pop III) in the Universe, focusing on the E-XQR-30 sample – a collection of 42 high signal-to-noise ratio spectra of quasi-stellar objects (QSOs) with emission redshifts ranging from 5.8 to 6.6. We aim to identify traces of Pop III metal enrichment by analyzing neutral gas in the interstellar medium of primordial galaxies and their satellite clumps, detected in absorption. Methods. To chase the chemical signature of Pop III stars, we studied metal absorption systems in the E-XQR-30 sample, selected through the detection of the neutral oxygen absorption line at 1302 Å. The O I line is a reliable tracer of neutral hydrogen and allowed us to overcome the challenges posed by the Lyman-α forest’s increasing saturation at redshifts above ∼5 to identify damped Lyman-α systems (DLAs). We detected and analyzed 29 O I systems at z ≥ 5.4, differentiating between proximate DLAs (PDLAs) and intervening DLAs. Voigt function fits were applied to obtain ionic column densities, and relative chemical abundances were determined for 28 systems. These were then compared with the predictions of theoretical models. Results. Our findings expand the study of O I systems at z ≥ 5.4 fourfold. No systematic differences were observed in the average chemical abundances between PDLAs and intervening DLAs. The chemical abundances in our sample align with literature systems at z > 4.5, suggesting a similar enrichment pattern for this class of absorption systems. A comparison between these DLA-analogs at 4.5 < z < 6.5 with a sample of very metal-poor DLAs at 2 < z < 4.5 shows in general similar average values for the relative abundances, with the exception of [C/O], [Si/Fe] and [Si/O] which are significantly larger for the high-z sample. Furthermore, the dispersion of the measurements significantly increases in the high-redshift bin. This increase is predicted by the theoretical models and indicates a potential retention of Pop III signatures in the probed gas. Conclusions. This work represents a significant advancement in the study of the chemical properties of highly neutral gas at z ≥ 5.4, shedding light on its potential association with the metal enrichment from Pop III stars. Future advancements in observational capabilities, specifically high-resolution spectrographs, are crucial for refining measurements and addressing current limitations in the study of these distant absorption systems.

Kinetics of Surface Wettability of Aromatic Polymers (PET, PS, PEEK, and PPS) upon Treatment with Neutral Oxygen Atoms from Non-Equilibrium Oxygen Plasma.

The wettability of polymers is usually inadequate to ensure the appropriate spreading of polar liquids and thus enable the required adhesion of coatings. A standard ecologically benign method for increasing the polymer wettability is a brief treatment with a non-equilibrium plasma rich in reactive oxygen species and predominantly neutral oxygen atoms in the ground electronic state. The evolution of the surface wettability of selected aromatic polymers was investigated by water droplet contact angles deposited immediately after exposing polymer samples to fluxes of oxygen atoms between 3 × 1020 and 1 × 1023 m-2s-1. The treatment time varied between 0.01 and 1000 s. The wettability evolution versus the O-atom fluence for all aromatic polymers followed similar behavior regardless of the flux of O atoms or the type of polymer. In the range of fluences between approximately 5 × 1020 and 5 × 1023 m-2, the water contact angle decreased exponentially with increasing fluence and dropped to 1/e of the initial value after receiving the fluence close to 5 × 1022 m-2.

Modified quantum defect theory: application to analysis of high-resolution Fourier transform spectra of neutral oxygen

Modified quantum defect theory: application to analysis of high-resolution Fourier transform spectra of neutral oxygen

Europa Modifies Jupiter's Plasma Sheet

AbstractJupiter's plasma sheet has been understood to be primarily composed of Io‐genic sulfur and oxygen, along with protons at lower mass density. These ions move radially away from Jupiter, filling its magnetosphere. The material in the plasma sheet interacts with Europa, which is also a source of magnetospheric pickup ions, primarily hydrogen and oxygen. Juno's thermal plasma instrument JADE, the Jovian Auroral Distributions Experiment, has provided comprehensive in situ observations of the composition of Jupiter's plasma sheet ions with its Time‐of‐Flight mass‐spectrometry capabilities. Here, we present observations of the magnetospheric composition in the Europa‐Ganymede region of Jupiter's magnetosphere. We find material from Europa is intermittently present at comparable densities to Io‐genic plasma. The intermittency of Europa‐genic signatures suggests Europa's neutral oxygen toroidal cloud is more localized to Europa's vicinity than its hydrogen cloud. These observations reveal a more complex and compositionally diverse magnetosphere than previously thought.

Direct in-situ insights into the asymmetric surface reconstruction of rutile TiO2 (110)

The reconstruction of rutile TiO2 (110) holds significant importance as it profoundly influences the surface chemistry and catalytic properties of this widely used material in various applications, from photocatalysis to solar energy conversion. Here, we directly observe the asymmetric surface reconstruction of rutile TiO2 (110)-(1×2) with atomic-resolution using in situ spherical aberration-corrected scanning transmission electron microscopy. Density functional theory calculations were employed to complement the experimental observations. Our findings highlight the pivotal role played by repulsive electrostatic interaction among the small polarons −formed by excess electrons following the removal of neutral oxygen atoms− and the subsequent surface relaxations induced by these polarons. The emergence and disappearance of these asymmetric structures can be controlled by adjusting the oxygen partial pressure. This research provides a deeper understanding, prediction, and manipulation of the surface reconstructions of rutile TiO2 (110), holding implications for a diverse range of applications and technological advancements involving rutile-based materials.

One hundred optical emission lines of molecular hydrogen from a low-metallicity photodissociation region

ABSTRACT We report the detection of a rich spectrum of more than one hundred optical emission lines of vibrationally hot molecular hydrogen (H2) from the photodissociation region (PDR) around the mini-starburst cluster NGC 346 in the Small Magellanic Cloud. The lines are concentrated in the spectral range $6000 \, {{\mathring{\rm A}}}$ to $9300 \, {{\mathring{\rm A}}}$ and have observed brightnesses ranging from 0.01 per cent to 0.4 per cent times that of the H β λ4861 hydrogen recombination line. Analysis of the spatial distribution of the H2 lines shows that they originate from a range of depths in the PDR, intermediate between the shallow layers probed by fluorescent lines of neutral nitrogen and oxygen, and the more shielded layers probed by neutral carbon recombination lines. Comparison with other PDRs shows that the relative strength of the H2 lines with respect to the [$\mathrm{C\, \scriptstyle I}$] λ8727 line increases rapidly with decreasing metallicity, being at least 40 times larger in NGC 346 than in the prototypical PDR of the Orion Bar. The internal PDR dust extinction is also found to be anomalously low in NGC 346. A separate result is the discovery of a high-ionization bow shock around the O2 star Walborn 3.

New insight into defect energy levels in HgCdTe

The paper reports on a summary of the experimental data on the defect energy levels in HgCdTe, that have been collected in our experiments and from articles available over several decades. We have determined the location of the defect levels in HgCdTe for material composition from 0.17 to 0.6. It has been shown that that all specified trap levels are tied to the valence band and do not change (or change slightly) with temperature, and have the slopes with respect to the Cd molar content somewhat smaller than the HgCdTe energy gap.Two levels are formed by mercury vacancies – the first defect level is a shallow acceptor formed by neutral vacancy, the second deep level can be formed by singly negatively charged Hg vacancy. Contrary to earlier assumptions, it does not lie in the middle of the energy gap for the entire range of molar composition, but it is an acceptor-like for the wide-gap HgCdTe and a donor-like for the narrow gap, and may even be located in the conduction band forming a resonant state. Above this main defect level, two additional trap states can be found, most likely formed by oxygen atoms replacing Hg vacancies – positively charged and the neutral oxygen states.

Deciphering the chemical bonding of the trivalent oxygen atom in oxygen doped graphene.

Recently, planar and neutral tricoordinated oxygen embedded in graphene has been imaged experimentally (Nat. Commun., 2019, 10, 4570-4577). In this work, this unusual chemical species is studied utilizing a variety of state-of-the-art methods and combining periodic calculations with a fragmental approach. Several factors influencing the stability of trivalent oxygen are identified. A σ-donation and a π-backdonation mechanism between graphite and oxygen is established. π-Local aromaticity, with a delocalized 4c-2e bond involving the oxygen atom and the three nearest carbon atoms aids in the stabilization of this system. In addition, the framework in which the oxygen is embedded is crucial too to the stabilization, helping to delocalize the "extra" electron pair in the virtual orbitals. Based on the understanding gathered in this work, a set of organic molecules containing planar and neutral trivalent oxygen is theoretically proposed for the first time.

(Invited) Metal Oxide Nanoparticles for Stable Alkaline Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyser Cell

One of the key challenges to develop efficient water electrolysis system is to find effective and robust electrocatalysts for the oxygen evolution reaction (OER). Mixed transition metal oxides provide immense possibilities for such purpose.1 , 2 Abundant catalytically active sites could be generated via engineering the defects and oxygen vacancies within the transition metal oxides.3 The catalyst stability could also be improved by incorporating self-healing component into the catalysts .4 In this work, we adopt cobalt oxides as substrate materials to prepare mixed transition metal oxides. The catalysts are synthesized via a combined approach of hydrothermal and annealing processes. The final products are characterized thoroughly by a broad range of characterization techniques, including XRD, TEM, SEM, EDX, and XPS. The OER activities are initially evaluated in a three-electrode system. The results show that the as-prepared catalysts demonstrate high current density at a relatively low overpotential. Moreover, the catalysts exhibit excellent robustness for an 8-hours stability test in a three-electrode testing system. The stability and activity of the catalysts is further assessed in a lab-scale anion exchange membrane (AEM) electrolyser cell setup. Only a small degradation is observed for the best performing catalyst in 12 hours period. The details of the catalyst characterization and electrochemical measurements will be discussed. Acknowledgements This work was funded by European Union’s Horizon 2020 projects FlowPhotoChem (Grant agreement number 862453) and European Innovation Council Pathfinder ANEMEL (Grant agreement number 101071111). References Mohammed-ibrahim, J. & Moussab, H. Tuning the electronic structure of the earth-abundant electrocatalysts for oxygen evolution reaction (OER) to achieve efficient alkaline water splitting – A review. J. Energy Chem. 56, 299–342 (2021).Plevová, M., Hnát, J. & Bouzek, K. Electrocatalysts for the oxygen evolution reaction in alkaline and neutral media. A comparative review. J. Power Sources 507, (2021).Zhang, R. et al. Tracking the Role of Defect Types in Co3O4 Structural Evolution and Active Motifs during Oxygen Evolution Reaction. J. Am. Chem. Soc. (2023) doi:10.1021/JACS.2C10515.Silva, A. L. et al. Mn-doped Co3O4 for acid, neutral and alkaline electrocatalytic oxygen evolution reaction. RSC Adv. 12, 26846–26858 (2022).

Lewis Acid Driving Asymmetric Interfacial Electron Distribution to Stabilize Active Species for Efficient Neutral Water Oxidation.

Neutral oxygen evolution reaction (OER) with unique reactive environments exhibits extremely slow reaction kinetics, posing significant challenges in the design of catalysts. Herein, a built-in electric field between the tungstate (Ni-FeWO4 ) with adjustable work function and Lewis acid WO3 is elaborately constructed to regulate asymmetric interfacial electron distribution, which promotes electron accumulation of Fe sites in the tungstate. This decelerates the rapid dissolution of Fe under the OER potentials, thereby retaining the active hydroxyl oxide with the optimized OER reaction pathway. Meanwhile, Lewis acid WO3 enhances hydroxyl adsorption near the electrode surface to improve mass transfer. As expected, the optimized Ni-FeWO4 @WO3 /NF self-supporting electrode achieves a low overpotential of 235 mV at 10 mA cm-2 in neutral media and maintains stable operation for 200 h. Furthermore, the membrane electrode assembly constructed by such self-supporting electrode exhibits robust stability for 250 h during neutral seawater electrolysis. This work deepens the understanding of the reconstruction of OER catalysts in neutral environments and paves the way for development of the energy conversion technologies.

Science Opportunities for IMAP-Lo Observations of Interstellar Neutral Helium, Neon, and Oxygen during a Maximum of Solar Activity

Direct-sampling observations of interstellar neutral (ISN) species and their secondary populations give information about the physical state of the local interstellar medium and processes occurring in the outer heliosheath. Such observations are performed from Earth’s orbit by the IBEX-Lo experiment on board the Interstellar Boundary Explorer (IBEX) mission. IBEX ISN viewing is restricted to directions close to perpendicular to the Earth–Sun line, which limits the observations of interstellar species to several months during the year. A greatly improved data set will be possible for the upcoming Interstellar Mapping and Acceleration Probe (IMAP) mission due to a novel concept of putting the IMAP ISN detector, IMAP-Lo, on a pivot platform that varies the angle of observation relative to the Sun–Earth line and the detector boresight. Here, we suggest a 2 yr scenario for varying the viewing angle in such a way that all the necessary atom components can be observed sufficiently well to achieve the science goals of the nominal IMAP mission. This scenario facilitates, among others, removal of the correlation of the inflow parameters of interstellar gas, unambiguous analysis of the primary and secondary populations of interstellar helium (He), neon (Ne), and oxygen (O), and determination of the ionization rates of He and Ne free of possible calibration bias. The scheme is operationally simple, provides good counting statistics, and synergizes observations of interstellar species and heliospheric energetic neutral atoms.

Promoting oxygen reduction kinetics of single Fe sites for robust neutral Zn-air batteries via engineering synergistic Fe nanocluster as proton-feeding center

Constructing highly efficient and cost-effective catalysts for neutral oxygen reduction reaction (ORR) remains extremely challenging due to the sluggish reaction kinetics resulting from the low ionic conductivity and limited OH− concentration in the neutral electrolytes. Herein, we intentionally integrate the atomic Fe-N4 sites and Fe nanoclusters on N-doped multimodally porous carbon (FeSA+NC@NMPC) to achieve coherent optimization of rapid oxygen-containing intermediate conversions and fast water dissociation to provide abundant protons for boosting neutral ORR performance. As expected, the FeSA+NC@NMPC exhibits an excellent half-wave potential of 0.76 V in 0.1 M phosphate buffer solutions, outperforming that of commercial Pt/C (0.73 V). Theoretical calculations reveal the synergistic effect between atomic Fe-N4 sites and Fe nanoclusters, in which the former possess stable O2 adsorption and rapid intermediate conversion, while the latter facilitates fast water dissociation to supply protons for accelerating the proton-coupled electron transfer process. Moreover, the FeSA+NC@NMPC-based neutral zinc-air batteries afford a high open-circuit potential of 1.42 V and outstanding cycling stability at 5 mA cm−2 for 100 h. This work utilizes the advantages of both single sites and clusters of Fe to provide an in-depth understanding of the neutral ORR mechanism and advances the development of related energy storage and conversion technologies.