Oxygen Incorporation Research Articles

Effect of Carbonate Source on the Dehydrofluorination Process in Polyvinylidene Fluoride/Alkali Metal Carbonate Composites.

In this paper, Raman and X-ray photoelectron spectroscopies were applied to analyze compositional and structural variations of the generated activated carbon (AC), as induced by changing carbonate source in three different types of systems, PVDF/M2CO3 (M = Li, Na, and K). According to the variations of I D/I G and sp2/sp3 ratios, a strong dependence of the AC structure on the type and content of the initial carbonate was found, determined by practical dehydrofluorination reactions associated with oxygen incorporation in AC and side reactions, because of the property variation induced by the difference in the cation of the carbonate sources. This procedure clarified the process of PVDF dehydrofluorination and the formation of activated carbon, which helps to optimize the material performance of the percolative composite for flexible energy storage applications.

Injectable Anhydrous Poly(ethylene glycol) Polymer Liquids Form Protein Depot for Extended Controlled Release Applications Via Rapid In Situ Gelation.

Water-free preparation of protein delivery systems has the potential to overcome the limitations of hydrogel depot systems such as off-target reactions, functional group hydrolysis, and limited loading capacity. However, a major roadblock in the development and use of these systems is administration as implantation is often required. In this study, we developed a biodegradable and water-free injectable protein delivery system via inverse electron demand Diels-Alder reaction between norbornene- and tetrazine-functionalized four-armed poly(ethylene glycol) macromonomers. 1:1 mixtures of these precursors gelled rapidly in situ, taking less than 11 s to reach their gelation point. Methyl substitution of tetrazine slowed the gelation time and increased the cross-linking density, whereas oxygen incorporation into norbornene changed the mechanical properties. Introduction of hydrolytically cleavable groups enabled biodegradability. Using phenyl carbamate and phenyl carbonate ester groups, we could tune the stability. Controlled release of the protein surrogate glucose oxidase was achieved over a period of 500 days. The novel preparation method presented here is a promising step toward the development of water-free injectable protein depots for controlled drug delivery.

Enhancing photocatalytic CO2 reduction reaction on amorphous Ni@NiO aerogel via oxygen incorporated tuning

Photochemical CO2 reduction to CO, acting as a mild and feasible method, holds huge prospects for atmospheric CO2 level diminution. Non-noble metal aerogel has been supposed to be an appealing material in the field of catalysis, yet suffering from low conductivity and poor activity. From the perspective of electronic structure modification, oxygen-incorporated Ni aerogel is prepared by a facile reduction-oxidation method. With the optimized electronic structure in Ni@NiO-2 aerogel by oxygen incorporation, brilliant photocatalytic activity with CO yield of 39.30 μmol/mg and CO selectivity of 94.4 % could be achieved, taking advantage of the electron-rich Ni and greatly increased conductivity as well as sufficient active sites exposure. This work sheds light on the design and development of high-performance non-noble metal-based systems for catalytic CO2 utilization.

Yttria-Doped Ceria Surface Modification Layer via Atomic Layer Deposition for Low-Temperature Solid Oxide Fuel Cells

Atomic layer deposition (ALD) is performed to obtain less than 1 nm thick yttria-doped ceria (YDC) layers as cathode functional layers to increase the surface oxygen incorporation rate for low-temperature solid oxide fuel cells (LT-SOFCs). Introducing a YDC surface modification layer (SML) has revealed that the optimized yttria concentration in YDC can catalyze surface oxygen exchange kinetics at the interface between the electrolyte and cathode. The YDC SML-containing fuel cell performs 1.5 times better than the pristine fuel cell; the result is an increased exchange current density at the modified surface. Moreover, a heavily doped YDC SML degrades the performance of LT-SOFCs, owing to the weakened oxygen surface kinetics due to the increased migration energy of the oxygen ions.

Orbital polarization change and magnetic enhancement in rutile MnO2-δ epitaxial films

Effectively manipulating the orbital configuration is an emerging method to design quantum functional materials with novel electronic ground states. Here, we report the realization of orbital polarization change in rutile MnO2-δ epitaxial thin films by reductive treatments such as CaH2 coating annealing and hydrogen atmosphere annealing. These treated samples show significant lattice expansion due to the generation of oxygen vacancies and incorporation of H, and the mixed valence states of Mn2+ and Mn3+ are formed with the decrease in the Mn valence state. The X-ray linear dichroism results show that the electron occupied state of Mn in the treated film samples changes from 3d3z2-r2 to 3dx2-y2, which means that the deprivation of oxygen atoms in the oxygen octahedron of MnO6 causes a change of orbital polarization. The resulting high spin state in the treated MnO2-δ films greatly enhances the magnetic properties of the films. This work not only demonstrates how the oxygen atoms in the edge-shared oxygen octahedron of rutile structures are replaced by reduction but also extends the study of orbital polarization and magnetic ground state control in oxide epitaxial films.

Fragmentation Mechanism in a Nitrogen Dielectric Barrier Discharge Plasma on Fluoropolymer Polymer Films.

Due to their chemical inertness and low friction coefficient, fluoropolymers are today widely employed in sectors of activity as diverse and distinct as the textile industry, architectural sector, and medicine. However, their low surface energy results in poor adhesion, for example, when used for a component in a composite device with multiple other materials. Among the techniques used to enhance their adhesion, atmospheric pressure discharges provide a fast and low-cost method with a reduced environmental impact. Although this approach has proven to be efficient, the different chemical and physical processes in the discharge remain not fully understood. In this study, fluoropolymer surfaces were modified using an atmospheric pressure dielectric barrier discharge in a nitrogen and organic precursor environment. To prevent any damage to fluoropolymer surfaces, the dissipated power in the discharges was tuned by applying a duty cycle. Evidence shows that plasma treatment allows for the incorporation of oxygen and nitrogen in the surface resulting in the formation of hydrophilic functionalities such as carbonyl groups both in ketone and amide form, amine, and hydroxyl groups after 180 s of treatment. Overall, the data reveal that the discharge duty cycle has more effect on the oxygen and carbon content in the coating than the precursor concentration. In addition, increasing the precursor concentration limits the molecular fragmentation and nitrogen incorporation into the coating. These experiments enable the building of a better fundamental understanding of the formation mechanism of such chemical moieties at the fluoropolymer surface.

Surface modification of carbon-fiber-reinforced plastic by using photo-activated chlorine dioxide radicals as pretreatment of electroless plating

Carbon fiber reinforced plastic (CFRP) plays an important role in industrial fields of automobiles, aerospace transportations and astronautics on account of its high stiffness and light weight. To further expand its utilizations, coating with metals can provide with metallic appearance while improving water-resistance, durability and electric conductivity. In general, the composites of CFRP are hydrophobic and have low affinities to metals. Therefore, it requires the surface pretreatments to increase the wettability and surface energy for stronger adhesive properties with metals via enhancing both mechanical and chemical bonding. In this study, photo-oxidized chlorine dioxide radicals were used to introduce oxygen–containing functional groups on CFRP surface. The hydrophilicity and adhesion strength to metals were successfully improved by the introduction of oxygen functional groups via eco-friendly photo-oxidation by photo-activated ClO2• radicals. The improvement of hydrophilicity was determined by water contact angle measurement, and the incorporation of oxygen was confirmed by infrared (IR) and X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy (SEM) observations revealed that the surface smoothness and structure of CFRP were maintained after pretreatment. Electroless plating of nickel and copper was then performed on both untreated and oxidized CFRP, demonstrating the enhanced adhesion properties of CFRP to both metals.

Oxygen‐Induced Phase Separation in Sputtered Cu–Sn–I–O Thin Films

Amorphous Cu–Sn–I is a promising p‐type transparent semiconductor. Therefore, herein, composition and structure of sputtered Cu–Sn–I thin films with varying thickness and Sn content are investigated by different electron microscopy techniques, energy‐dispersive X‐ray spectroscopy, and X‐ray absorption spectroscopy at the Cu, Sn, and I K‐edge. After exposure to air, the sputtered films are found to contain significant amounts of oxygen, leading to a complete phase separation of the resulting Cu–Sn–I–O films. Spatially‐resolved compositional analysis and high‐resolution transmission electron microscopy reveal that one phase consists of crystalline γ‐CuI while the other phase is composed of amorphous Cu–Sn–O, most likely a mixture of SnO2 and Cu2O/CuO. X‐ray absorption spectroscopy confirms that the local structural environment of the Sn and I atoms is similar to that in amorphous SnO2 and crystalline CuI, respectively. In contrast, the X‐ray absorption near edge structure and the extended X‐ray absorption fine structure of the Cu K‐edge both demonstrate that Cu atoms are not only bonded to I but also to O atoms. The incorporation of oxygen into the sputtered films thus completely alters the material and therefore clearly needs to be inhibited.

Upgrading polyethylene terephthalate plastic into commodity chemicals paired with hydrogen evolution over a partially oxidized CuIn5S8 nanosheet photocatalyst

A CuIn5S8 nanosheet photocatalyst with oxygen incorporation was developed, with the aim of converting PET plastic into commodity chemicals paired with water splitting into hydrogen.

Enhanced electrocatalytic activity with an incorporation of oxygen on the surface of di-nickel di-selenide for water splitting: A DFT-based computational design

Herein, we present a density functional theory study investigating the influence of oxygen on the surface of metal and metal chalcogenides (O–Ni2Se2) with respect to their trifunctional behavior. Our results show that the incorporation of oxygen into Ni2Se2 enhances the electrical conductivity of the electrochemical reactions. In particular, the involvement of the transition metal (Ni) and metal chalcogenide (Se) results in nearly zero Gibbs free energy of hydrogen adsorption for the HER and a lower overpotential for the OER/ORR activity in the presence of oxygen at different active sites of the catalyst. Furthermore, all atoms involved in this study (O–Ni2Se2) are strongly bonded together and constrained by the binding energy towards the intermediates. This binding energy originates from the electron-donating ability around the d-band center of the catalyst, as confirmed by the partial density of states around the Fermi level. This work is expected to create a new pathway for the development of cost-effective trifunctional catalysts.

Determination of temperature-dependent otolith oxygen stable isotope fractionation on chum salmon Oncorhynchus keta based on rearing experiment

Reconstruction of water temperatures experienced by marine fishes using otolith oxygen stable isotopes (δ18O) as natural thermometers has been proven to be a useful approach for estimating migration routes or movement patterns. This method is based on the mechanism that the equilibrium fractionation of δ18Ootolith against ambient water exhibits a species-specific thermal sensitivity during the process of otolith aragonitic CaCO3 precipitation. In this study, a laboratory-controlled rearing experiment was conducted to determine the temperature dependency of δ18O fractionation on the anadromous fish species, chum salmon (Oncorhynchus keta), of which the detailed migration routes have not been elucidated yet. To test that temperature was the only factor affecting δ18Ootolith fractionation, this study ensured a relatively stable rearing condition, evaluated the isotope composition of the rearing water, and analyzed carbon isotope (δ13Cotolith) to examine the potential effect of kinetic and metabolic isotopic fractionations. The δ18Ootolith fractionation equation on chum salmon was thereby determined within a temperature range of 9–20°C and was indistinguishable from the equation of synthetic aragonite; The δ13Cotolith was affected by both physiological processes and δ13CDIC; In lower temperatures settings, both oxygen and carbon isotopes depleted simultaneously. This study suggests that the chum salmon species-specific oxygen isotope fractionation equation could be used on reconstruction of temperature history and also throw insights into understanding the incorporation of oxygen and carbon sources during calcification process for otoliths.

Enhancement of surface exchange and oxygen diffusion of Sr1.95Fe1.4Ni0.1Mo0.5O6–δ oxide determined by two independent isotope exchange methods

The mechanism of interaction between gaseous oxygen and the Sr1.95Fe1.4Ni0.1Mo0.5O6–δ promising material for cathodes of SOFC has been investigated by two isotopic methods: the pulse isotope exchange and the oxygen isotope exchange with the gas phase analysis, making it possible to obtain and compare the kinetic parameters under equilibrium conditions and the mixture gas carrier flow under the sample, which extends understanding of processes and makes experimental conditions of the second case closer to real operating conditions of electrode material. The time dependences of changes in 16O2, 16O18O and 18O2 over the sample allowed us to calculate the concentration of 18O labeled oxygen (α) at the temperatures ranging from 300 to 800 °C. The oxygen exchange rate (rH, atom/(cm2 × s)), the oxygen diffusion coefficient (D, cm2/s), the corresponding rates of elementary processes of dissociative adsorption (ra, atom/(cm2 × s)) and oxygen incorporation in the lattice (ri, atom/(cm2 × s)) are calculated. The results of two independent isotopic methods were analyzed and revealed a good agreement of the obtained data. The effect of modifying Sr2Fe1.5Mo0.5O6–δ by introducing deficiency in the Sr-sublattice and Ni-doping in the Fe-sublattice on the kinetic parameters is discussed.

Structural, vibrational, and electronic properties of γ-graphyne, γ-graphyne oxide, and boron nitride doped γ-graphyne: A DFT study

The interesting characteristics of graphyne structure inspired this research to study the effect of oxygen incorporation and boron nitride doping on γ-graphyne. The structural stability, vibrational, and electronic properties of γ-graphyne, γ-graphyne oxide, and boron nitride doped γ-graphyne have been studied via density functional theory. The negative formation energy verified the structural stability of all the structures. Both γ-graphyne oxide and boron nitride doped γ-graphyne showed a significantly deformed geometry compared to pure γ-graphyne. The energy gap of pure γ-graphyne was obtained to be 2.604 eV, which tuned to 3.059 eV and 3.51 eV through oxygen addition and boron nitride doping, respectively. Boron nitride doped γ-graphyne revealed better structural stability, whereas high reactivity was observed for pure γ-graphyne.

Effect of oxygen on the crystallinity and defect state of AlxGa1−xN epilayers

The effect of oxygen incorporation on the crystal quality and defect states in AlxGa1−xN epilayers (x = 0.4, 0.6, 0.8) grown by hydride vapor phase epitaxy with and without oxygen gas flow were studied. On the basis of the full width at half-maximum value of the (102) X-ray diffraction rocking curve, the crystal quality of AlxGa1−xN with oxygen was better than that of AlxGa1−xN without oxygen as the Al/Ga ratio increased. In Al0.6Ga0.4N epilayers with and without oxygen, two deep traps of H1ʹ and H2ʹ were measured by deep level transient spectroscopy. All traps were hole-like traps with activation energies of 1.28 eV (H1ʹ) and 0.61 eV (H2ʹ), which are the same as traps H1 and H2 measured in Al0.4Ga0.6N. Al0.8Ga0.2N with oxygen had only the D1 trap, as observed by thermally stimulated current, while the sample without oxygen has two traps of D1 (0.80 eV) and D2 (0.64 eV). The trap densities in AlxGa1−xN epilayers decreased with oxygen as the Al mole fraction increased in AlxGa1−xN. Therefore, the oxygen atoms can improve the crystal quality and suppress the defect states in AlxGa1−xN epilayers.

Deposition Mechanism and Properties of Plasma-Enhanced Atomic Layer Deposited Gallium Nitride Films with Different Substrate Temperatures

Gallium nitride (GaN) is a wide bandgap semiconductor with remarkable chemical and thermal stability, making it a competitive candidate for a variety of optoelectronic applications. In this study, GaN films are grown using a plasma-enhanced atomic layer deposition (PEALD) with trimethylgallium (TMG) and NH3 plasma. The effect of substrate temperature on growth mechanism and properties of the PEALD GaN films is systematically studied. The experimental results show that the self-limiting surface chemical reactions occur in the substrate temperature range of 250-350 °C. The substrate temperature strongly affects the crystalline structure, which is nearly amorphous at below 250 °C, with (100) as the major phase at below 400 °C, and (002) dominated at higher temperatures. The X-ray photoelectron spectroscopy spectra reveals the unintentional oxygen incorporation into the films in the forms of Ga2O3 and Ga-OH. The amount of Ga-O component decreases, whereas the Ga-Ga component rapidly increases at 400 and 450 °C, due to the decomposition of TMG. The substrate temperature of 350 °C with the highest amount of Ga-N bonds is, therefore, considered the optimum substrate temperature. This study is helpful for improving the quality of PEALD GaN films.

CuI as a Hole-Selective Contact for GaAs Solar Cells

Carrier-selective contacts have emerged as a promising architecture for solar cell fabrication. In this report, the first hole-selective III-V semiconductor solar cell is demonstrated using copper iodide (CuI) on i-GaAs. Surface passivation quality of GaAs is found to be essential for open-circuit voltage (VOC), with good correlation between photoluminescence properties of the GaAs layer and the VOC. Passivation with <10 nm thick In0.49Ga0.51P layers is shown to provide an over 300 mV improvement. Oxygen-rich CuI is formed by natural oxidation in the atmosphere, and the increased oxygen content of ∼10% is validated by energy-dispersive X-ray measurements. The oxygen incorporation is shown to improve hole selectivity and thus solar conversion efficiency. Ultraviolet photoelectron spectroscopy indicates a high work function of ∼6 eV for the oxygen-rich CuI. With optimized GaAs surface passivation and oxygen-rich CuI, a VOC of nearly 1 V and a solar conversion efficiency of 13.4% are achieved. The solar cell structure includes only undoped GaAs, a surface passivation layer, and non-epitaxial CuI contact and is therefore very promising to various low-cost crystal growth methods. The results have a significant impact on III-V solar cell fabrication and costs as it (i) enables fully carrier-selective architectures, (ii) reduces cell fabrication complexity, and (iii) is suitable for layers grown by low-cost crystal growth techniques.

Facile Pathways to Synthesize Perovskite Strontium Cobalt Oxides

AbstractTopotactic phase transition obtains extensive research attention due to its associated rich physics as well as a promising potential application. Particularly, the oxygen incorporation into brownmillerite oxides leads to the structural transition into perovskite oxides with distinct magnetic and electronic properties. Using brownmillerite SrCoO2.5 (BM‐SCO), two novel pathways are revealed to achieve the topotactic phase transition into its corresponding perovskite SrCoO3 (P‐SCO). It is demonstrated that by using aqueous alkali as the electrolyte during gating, the negative biased voltage triggers a rapid transition into P‐SCO, which is attributed to the presence of strong oxidizing hydroxyl radicals. While surprisingly, it is observed that the acid solution with rich protons can also trigger an unexpected phase transition from BM‐SCO into P‐SCO in a much faster manner. With density functional theory calculations, this transition is elucidated as a proton‐assist ionic disproportionation, in which the Co ions are simultaneously oxidized and reduced, while the latter one is dissolved within the solution. These case studies not only achieve a deep understanding of the structural phase transition in BM‐SCO but also shed new light on the topotactic phase transition of complex oxides.

Carbon and silicon background impurity control in undoped GaN layers grown with trimethylgallium and triethylgallium via metalorganic chemical vapor deposition

The unintentional impurity incorporation in GaN epitaxial layers impacts the electrical conductivity and optical properties of the films grown by metalorganic chemical vapor deposition (MOCVD). It is critical to control impurity-related states for device structure development. The aim of this work is to contribute to the understanding of the reasons for the presence of certain background impurities. In this paper, the unintentional impurity incorporation of carbon, hydrogen, oxygen, and silicon in undoped (u-) GaN films grown by low-pressure MOCVD were studied. Background impurity concentrations were evaluated by secondary ion mass spectroscopy (SIMS) to optimize growth parameters including V/III ratio, growth temperature (Tg), growth pressure (Pg), and gallium (Ga) precursors of trimethylgallium (TMG) or triethylgallium (TEG). Unintentional [C] and [Si] incorporations are found to be highly dependent on the growth parameters. For the same growth conditions, u-GaN films grown with a TEG precursor exhibited a lower background concentration of C compared to that of GaN grown with TMG. However, the lowest background [C] achieved was grown with TMG using optimized conditions and exhibited [C] < 4 × 1015 cm−3 which was at the detection limit of the SIMS measurement. These results were measured for a u-GaN layer grown with TMG at 200 Torr, 1030 °C, and a V/III of 3700. The lowest background [Si] of 4 × 1015 cm−3 was achieved by growing with TMG at 200 Torr, 1000 °C, and V/III of 650.

High-Temperature 2D Optical Relaxation Visualizes Enhanced Oxygen Exchange Kinetics at Metal-Mixed Conducting Oxide Interfaces.

Solid-state heterointerfaces are of interest for emergent local behavior that is distinct from either bulk parent compound. One technologically relevant example is the case of mixed ionic/electronic conductor (MIEC)-metal interfaces, which play an important role in electrochemistry. Metal-MIEC composite electrodes can demonstrate improved catalytic activity vs single-phase MIECs, improving fuel cell efficiency. Similarly, MIEC surface reaction kinetics are often evaluated using techniques that place metal current collectors in contact with the surface under evaluation, potentially altering the response vs the native surface. Techniques enabling direct and local in situ observation of the behavior at and around such heterointerfaces are needed. Here, we develop a spatially resolved optical transmission relaxation (2D-OTR) method providing continuous evaluation of local, high-temperature, controlled atmosphere defect kinetics across a ∼1 cm2 sample area simultaneously in a contact-free manner. We apply it to observe the spatial variance of oxygen incorporation and evolution rates at ∼525-620 °C, in response to step changes in oxygen partial pressure, on MIEC SrTi0.65Fe0.35O3-x films as a function of distance from porous Pt and Au layers. Using this model geometry, we find significant enhancements in kinetics adjacent to the metals that decay over a few millimeter distance. To extract kinetic parameters, we fit the short-term optical data (initial portion of relaxations) with an exponential decay function appropriate for surface-exchange-limited kinetics, yielding apparent surface exchange coefficients (kchem) with spatial resolution, decreasing with distance from the metal. To understand the kinetic processes governing the complete (long-term) optical relaxations, we performed COMSOL simulations, which demonstrated that a combination of laterally varying kchem and in-plane diffusion controls the observed kinetics over the full time range. Further support for spatially varying kchem comes from demonstrations of changing surface and bulk chemistry vs distance from the metal-MIEC interface, by X-ray photoelectron and optical absorption spectroscopies, respectively. Although microporous Pt and Au are not excellent electrodes in isolation, both metals exert a synergistic effect on the oxygen surface exchange rate in the presence of the mixed conducting film.

Surface Exchange Reaction of Mixed Conductive La0.65Ca0.35FeO3−δ during Oxygen Evolution and Incorporation as Traced by Operando X-ray Photoelectron Spectroscopy

High oxygen permeability of mixed conductive La0.65Ca0.35FeO3-δ (LCF) is applicable to pure oxygen gas generators and cathodes for solid oxide fuel cells, etc.; however, lower surface exchange reactions at temperatures below 800 °C reduce permeability. To understand the microscopic surface reaction mechanism, operando soft X-ray photoelectron spectroscopy of an LCF film surface was conducted during the evolution and incorporation of oxygen. LCF film was prepared on yttria-stabilized zirconia and a current was applied throughout the film at ∼600 °C. From operando X-ray photoelectron spectra, surface oxide species involved in the surface exchange reaction obviously appeared on the film during the evolution of oxygen from the surface. The number of surface oxide species abruptly decreased during incorporation of oxygen. By applying the current from a negative to positive value, the numbers of surface oxide species and ligand holes near Fe3+ ions on the surface both significantly increased. The results infer that ligand holes in the Fe 3d-O 2p hybrid orbitals correspond to active reaction sites at which surface oxide species change to oxygen molecules. Increasing the number of active reaction sites is key to improving oxygen evolution of mixed conductive oxides.