Oxygen-rich Interface Research Articles

Effects of oxidant gas for atomic layer deposition on crystal structure and fatigue of ferroelectric HfxZr1−xO2 thin films

TiN/HfxZr1−xO2 (HZO)/TiN capacitors were prepared using two types of HZO films fabricated by atomic layer deposition using H2O or O2 plasma as an oxidant gas, and post-deposition annealing at 400 °C was performed before the TiN top-electrode fabrication. The ferroelectric orthorhombic phase was dominantly formed for the O2 plasma-based capacitor due to the strongly oxidizing source of O2 plasma, resulted in higher remanent polarization (2Pr = 20 µC/cm2) than that (13 µC/cm2) of the H2O-based capacitor. The fatigue properties for the O2 plasma-based capacitor were improved by 14 % after 106 cycles compared to the H2O-based capacitor. This could be attributed to an oxygen-rich interface reaction layer (IRL) including TiOx between the HZO film and TiN bottom-electrode for the O2 plasma-based capacitor. Based on these results, superior 2Pr and fatigue properties can be obtained using O2 plasma-based HZO films.

Evaluating the Impact of Physiologically Relevant Oxygen Tensions on Drug Metabolism in 3D Hepatocyte Cultures in Paper Scaffolds.

Oxygen is an essential regulator of cellular function and phenotype. Despite its importance, the incorporation of physiologically relevant oxygen tensions is often overlooked in experimental setups. Ambient oxygen tensions (pO2 ∼152 mmHg) are significantly higher than those in the alveolar-capillary barrier of the lung, which is the most oxygen-rich interface in the body (pO2 ∼104 mmHg). The discrepancy between standard culture practices and physiologically relevant oxygen tensions is more pronounced when considering the hepatocyte-lined sinusoids of the liver, whose pO2 values range from 65 mm Hg in the periportal region to 30 mm Hg in the perivenous region. Our previous work highlights the need to transition from standard culture conditions to more physiologically relevant microenvironments when predicting hepatocyte responses to drug candidates or potential toxins. This protocol details an experimental pipeline for quantifying differences in transcript levels, protein levels, and activity of the cytochrome P450 1A (CYP1A) enzyme family in hepatocytes maintained in a three-dimensional environment at ambient and physiologically relevant oxygen tensions. We quantify changes in transcript with qRT-PCR, protein expression with western blots, and activity with the ethoxyresorufin-O-deethylase (EROD) assay. This approach can be adapted to any drug-metabolizing enzyme. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Preparing tissue-like environments to evaluate HepG2 cells in paper-based cell culture platform at physiological oxygen levels Basic Protocol 2: Evaluating CYP1A activity of hepatocytes grown in the paper scaffolds using the EROD assay Basic Protocol 3: Evaluating CYP1A transcript levels of hepatocytes grown in the paper scaffolds using RT-qPCR Basic Protocol 4: Evaluating CYP1A protein levels of hepatocytes grown in the paper scaffolds using western blotting.

High-Performance Photoelectrochemical Enzymatic Bioanalysis Based on a 3D Porous CuxO@TiO2 Film with a Solid-Liquid-Air Triphase Interface.

The accurate detection of H2O2 is crucial in oxidase-based cathodic photoelectrochemical enzymatic bioanalysis but will be easily compromised in the conventional photoelectrode-electrolyte diphase system due to the fluctuation of oxygen levels and the similar reduction potential between oxygen and H2O2. Herein, a solid-liquid-air triphase bio-photocathode based on a superhydrophobic three-dimensional (3D) porous micro-nano-hierarchical structured CuxO@TiO2 film that was constructed by controlling the wettability of the electrode surface is reported. The triphase photoelectrochemical system ensures an oxygen-rich interface microenvironment with constant and sufficiently high oxygen concentration. Moreover, the 3D porous micro-nano-hierarchical structures possess abundant active catalytic sites and a multidimensional electron transport pathway. The synergistic effect of the improved oxygen supply and the photoelectrode architecture greatly stabilizes and enhances the kinetics of the enzymatic reaction and H2O2 cathodic reaction, resulting in a 60-fold broader linear detection range and a higher accuracy compared with the conventional solid-liquid diphase system.

Utilizing an Oxygen-Rich Interface by Hydroxyapatite to Regulate the Linear Diffusion for the Stable Solid-State Electrolytes.

Improving dissociation and diffusion of lithium ions is the key to solving the practical application of polymer-based solid-state electrolytes (SSE). Here, a low-cost three-dimensional hydroxyapatite (HAP) nanowire is used in polyethene oxide to obtain an enhanced lithium-ion electrolyte. The oxygen-rich interface of HAP provides an integrated dissociation-diffusion platform for lithium salts. The TFSI- anions tend to coordinate with calcium ions, which makes it easier for lithium ions to escape and stay in a free state. The lateral nucleus in the HAP polyethene electrolyte regulates the diffusion from spherical diffusion into linear planar diffusion, which is confirmed by chronoamperometry curves and in situ observation. The stability of the electrolyte at high voltages is improved by inhibiting the superoxide radicals of polyethene oxide chains, which is demonstrated by nuclear magnetic resonance and electron paramagnetic resonance spectroscopy methods. The initial specific charge capacity of the Li/SPE/LiFePO4 cell with HAP-modified polyethene oxide at 2 C is 148.8 mA h/g, and its initial Coulombic efficiency is 95.17%. After 100 cycles, the specific discharge capacity is 125.5 mA h/g with 99.91% retention per cycle. This oxygen-rich interface strategy would guide the discovery of novel materials for polymer-based SSE.

Oxygen-rich interface enables reversible stibium stripping/plating chemistry in aqueous alkaline batteries

Aqueous alkaline batteries see bright future in renewable energy storage and utilization, but their practical application is greatly challenged by the unsatisfactory performance of anode materials. Herein, we demonstrate a latent Sb stripping/plating chemistry by constructing an oxygen-rich interface on carbon substrate, thus providing a decent anode candidate. The functional interface effectively lowers the nucleation overpotential of Sb and strengthens the absorption capability of the charge carriers (SbO2− ions). These two advantageous properties inhibit the occurrence of side reactions and thus enable highly reversible Sb stripping/plating. Consequently, the Sb anode delivers theoretical-value-close specific capacity (627.1 mA h g−1), high depth of discharge (95.0%) and maintains 92.4% coulombic efficiency over 1000 cycles. A robust aqueous NiCo2O4//Sb device with high energy density and prominent durability is also demonstrated. This work provides a train of thoughts for the development of aqueous alkaline batteries based on Sb chemistry.

Electronic properties of graphene-ZnO interface: a density functional theory investigation

Electronic properties of graphene/ZnO interface have been theoretically investigated by applying first principles density functional theory calculations. This interface is demonstrated to have interesting electrical, optical and chemical properties and therefore, is employed in different applications. In our investigation the interface between graphene and different ZnO surfaces such as polar Zn-terminated and O-terminated surfaces as well as nonpolar surface are considered. Different interface properties such as equilibrium atomic structure, binding energy, charge transfer and band alignment are calculated for these interfaces. The calculated binding energies between graphene and different ZnO surfaces are within the range of van der Waals or physical adsorption. The results clearly reveal the essential role of oxygen density at the interface. The O- and Zn-terminated ZnO surfaces show the lowest and highest binding energies, respectively. The amount of charge transfer and the direction of interfacial dipole are also dominated by the number of oxygen atoms at the graphene/ZnO interface. Calculations for the interfacial band alignment reveal that a high/low density of oxygen atoms at the interface results in a Schottky/Ohmic contact. It is also shown that inducing oxygen vacancies at an oxygen rich interface leads to the lowering of the Schottky barrier.

Geometric structure and electronic properties of wurtzite GaN/HfO2 interface: A first-principles study

III-V interface with high-k oxide, especially HfO2, is crucial to the development of high mobility microelectronic devices. In this work, we systematically investigated the wurtzite GaN/cubic HfO2 interface based on the first-principles calculations with density functional theory in terms of the geometric structure and electronic properties. In order to mimic the high-k growth conditions, the interfacial oxygen contents in the slab interface models varied to study the interface stability and the relevant electronic structures. It is found that the oxygen rich interface, i.e., oxygen content of 83.3% (O5), shows the most stability in a large range of the oxygen chemical potential from 0 eV to −4.34 eV. Through the calculations of local density of states and Bader charge analysis, we noticed that increasing the interfacial oxygen content leads to the increase of the valence band offset (VBO) and the decrease of the conduction band offset (CBO), respectively. More importantly, interface O5 displays a promising VBO (0.86 eV) and CBO (1.34 eV), which meets the industrial requirements to confine the carrier in the III-V channel materials. Furthermore, no interfacial gap states are observed in interface O5, indicating that O5 is free of Fermi level pinning. This theoretical exploration suggests that varying oxygen content at the interface could result in the optimal interface for the applications of high mobility electronic devices.

The effect of interface oxygen content on magnetoelectric effect of epitaxial La0.7Sr0.3MnO3/BaTiO3 bilayer

The epitaxial La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) bilayer films are grown on (001) oriented LaAlO3 substrate by pulsed laser deposition technique. The oxygen-rich interface is obtained through in-situ annealing process in oxygen, and the oxygen-deficient interface is obtained without the annealing process. The results show that the ferromagnetic properties of the LSMO film and the magnetoelectric effect (ME) of the bilayer films strongly correlate to the oxygen content at the interface of LSMO/BTO. The saturated magnetization and the ME voltage coefficient of the oxygen-rich bilayer film are higher than that of oxygen-deficient one. It suggests a more effective ME coupling at the LSMO/BTO interface, which are generated through not only the interface strain but also the spin polarized carriers.

TiO2(100)/Al2O3(0001) interface: A first-principles study supported by experiment

We present the results of combined theoretical and experimental investigations of the TiO${}_{2}$/Al${}_{2}$O${}_{3}$ interface. High-quality rutile films are grown on sapphire substrates and characterized by XRD and pole figures analysis. The epitaxial relations established by experiment agree well with those reported in literature and are used as input for ab initio modeling. In order to cope with the problem of lattice mismatch, we introduce a stress balancing approach, which takes into account the elastic tensors of the bulk materials forming the interface. Applying this approach, optimized interface models are obtained and used to evaluate the work of separation of interfaces with various stoichiometries. It is shown that the work of separation of both, oxygen-rich (0.5 J/m${}^{2}$) and oxygen-poor (1.6 J/m${}^{2}$) interfaces, is significantly smaller than the one of the metal-oxygen-metal stacked interface close to stoichiometry (8.8--9.3 J/m${}^{2}$). The influence of atomic relaxation on the work of separation is discussed. Analysis of electronic structure and bonding reveals for the oxygen-rich interface, localized oxygen $2p$ states above and below the the valence-band region of the other types of interfaces. The oxygen-poor one turns out to be metallic, whereas the interfaces close to bulk stoichiometry remain insulating. It is shown that energetically favorable interfaces are formed when the two sides are most similar to each other in coordination and stacking.

Influence of Substrate Biasing on the Structural and Electrical Properties of Sputtered Zirconia Thin Films

AbstractZrOx thin films were deposited by sputtering a pure zirconia target under argon–oxygen atmosphere and soft conditions: low substrate temperature and applied power. An anode biasing was added for different time durations in order to modify the substrate/layer interface. Auger profiling showed a sub‐stochiometric character that increases with the ion bombardment. The latter treatment led to the formation of an oxygen rich interface. XPS analysis revealed that all the zirconium was bonded to oxygen. Moreover, using the energy loss from the O 1s photoelectron signal, the optical band gap was found to increase with the biasing time. Capacitance–voltage measurement showed a high dielectric constant for all the deposits and defect formation in the film bulk when the ion bombardment was added during the layer growth.

Oxygen influence on ceramics wettability by liquid metals: Ag/α-Al 2O 3—Experiments and modelling

A renewed interest in the effects of oxygen on the wetting of solid oxides has recently risen in connection to the development of the technique of “air brazing” which makes use of the strong effect of oxygen to increase the wettability of oxides by means of processes running in air or in atmospheres with high oxygen content. Adsorption of oxygen not only at the liquid–vapour surface but also at the solid–liquid interface has been postulated by many previous researches, mainly on the basis of thermodynamic considerations. Along the same line, new results of the wetting behaviour in the system Ag/α-Al 2O 3 as a function of oxygen partial pressure are presented, with the simultaneous measurement of the liquid surface tension. These results are compared with the existing ones, and discussed on the basis of thermodynamic principles. The resulting work of adhesion is compared with the “work of separation” computed by the density functional theory (DFT) approach. DFT calculations are also employed, at variance with previous models, to investigate the structures that are formed at the interface upon addition of oxygen in different sites energetics, atomic and electronic properties of this oxygen-rich interface are discussed together with the connection with experiments.

Fermi Pinning in Metal-Oxide-Semiconductor Structures Results from Low Oxygen Content at the Metal-Oxide Interface

The selection of a proper metal for replacement of polycrystalline silicon as the metal gate in future generation transistors has been hampered by pinning of the metal Fermi level at the metal/dielectric interface. Using monoclinic hafnia and zirconia as the gate dielectric we compare two different metal gate/gate dielectric interface structures where the oxygen affinity of the metal gate is either low or high under normal processing conditions. We show that for the metal gate with high oxygen affinity (molybdenum) the metal Fermi pinning is weaker than for the metal gate with low oxygen affinity (platinum). Through first principles calculations this behavior is explained as the result of an oxygen-rich interface for the former and a reduced interface for the latter. Based on these observations we propose a general model for Fermi pinning at the metal/metal oxide interface as mainly caused by low levels of interfacial oxygen. Such red uced interfaces may result from processing conditions as well as by the metal gate low affinity for oxygen.

Segregation trends of the metal alloys Mo–Re and Mo–Pt on HfO2: A first-principles study

Using first-principles calculations, we compared the segregation trends at the surface of metal alloys with those at an interface with HfO2. The choice of this oxide was motivated by its significance as a potential replacement for SiO2 in advanced transistors. We considered Mo–Re and Mo–Pt alloys as typical examples of disordered and ordered alloys, respectively. The segregation to the surface/interface was analyzed in terms of metal and oxygen adsorption energies. It is shown that chemical bonding at the metal/oxide interface strongly influences segregation both in Mo–Re and Mo–Pt alloys. In particular, bonding with oxygen atoms at the oxide/Mo–Re alloy interface depletes the Re content of the interfacial layer. In the case of Mo–Pt on HfO2 an oxygen-rich interface promotes the formation of one monolayer (but not two monolayers) of Mo separating PtMox from HfO2, while a stoichiometric interface favors an abrupt PtMox∕HfO2 interface. This study also shows that the presence of Mo in the alloy stabilizes Pt which can potentially decrease the tendency of Pt to diffuse into the oxide matrix. The individual constituents of these intermetallic compounds exhibit high vacuum work functions, and therefore these alloys are also likely to have sufficiently high work functions to be considered as promising candidates for p-type gate electrodes in future generations of transistors.

Permeation behavior of deuterium implanted in electro- and sputter-deposited copper coatings on aluminum alloy substrates

Permeation behavior of deuterium in copper coatings (∼6 μm thickness) deposited on Al-6061 substrates by the electro- and the sputter-deposition methods is compared. The electroplated coating contained copper and aluminum phases, and exhibited microcracks that were distributed uniformly all over the surface. The sputtered coating contained Cu 9Al 4 and CuAl 2 phases in addition to copper and aluminum, and was fairly dense. Both the coatings contained oxygen at the free surface and at the coating–substrate interface. Deuterium was implanted in both the coatings under identical conditions and the deuterium profiles were subsequently measured using secondary ion mass spectrometry (SIMS). In case of the electroplated coating, the implanted deuterium diffused into the sample without any interference and reached the oxygen-rich interface where it was trapped by the aluminum oxide. On the contrary, in case of the sputtered coating, the diffusing deuterium was trapped continuously before reaching the oxygen-rich coating–substrate interface. The results are discussed.