Real-space visualization of intrinsic magnetic fields of an antiferromagnet.

Characterizing magnetic structures down to atomic dimensions is central to the design and control of nanoscale magnetism in materials and devices. However, real-space visualization of magnetic fields at such dimensions has been extremely challenging. In recent years, atomic-resolution differential phase contrast scanning transmission electron microscopy (DPC STEM)1 has enabled direct imaging of electric field distribution even inside single atoms2. Here we show real-space visualization of magnetic field distribution inside antiferromagnetic haematite (α-Fe2O3) using atomic-resolution DPC STEM in a magnetic-field-free environment3. After removing the phase-shift component due to atomic electric fields and improving the signal-to-noise ratio by unit-cell averaging, real-space visualization of the intrinsic magnetic fields in α-Fe2O3 is realized. These results open a new possibility for real-space characterization of many magnetic structures.

Photocatalytic solar hydrogen production from water on a 100-m2 scale.

The unprecedented impact of human activity on Earth's climate and the ongoing increase in global energy demand have made the development of carbon-neutral energy sources ever more important. Hydrogen is an attractive and versatile energy carrier (and important and widely used chemical) obtainable from water through photocatalysis using sunlight, and through electrolysis driven by solar or wind energy1,2. The most efficient solar hydrogen production schemes, which couple solar cells to electrolysis systems, reach solar-to-hydrogen (STH) energy conversion efficiencies of 30% at a laboratory scale3. Photocatalytic water splitting reaches notably lower conversion efficiencies of only around 1%, but the system design is much simpler and cheaper and more amenable to scale-up1,2-provided the moist, stoichiometric hydrogen and oxygen product mixture can be handled safely in a field environment and the hydrogen recovered. Extending our earlier demonstration of a 1-m2 panel reactor system based on a modified, aluminium-doped strontium titanate particulate photocatalyst4, we here report safe operation of a 100-m2 array of panel reactors over several months with autonomous recovery of hydrogen from the moist gas product mixture using a commercial polyimide membrane5. The system, optimized for safety and durability, and remaining undamaged on intentional ignition of recovered hydrogen, reaches a maximum STH of 0.76%. While the hydrogen production is inefficient and energy negative overall, our findings demonstrate that safe, large-scale photocatalytic water splitting, and gas collection and separation are possible. To make the technology economically viable and practically useful, essential next steps are reactor and process optimization to substantially reduce costs and improve STH efficiency, photocatalyst stability and gas separation efficiency.

Photocatalytic water splitting with a quantum efficiency of almost unity.

Overall water splitting, evolving hydrogen and oxygen in a 2:1 stoichiometric ratio,  using particulate photocatalysts is a potential means of achieving scalable and economically viable solar hydrogen production. To obtain high solar energy conversion efficiency, the quantum efficiency of the photocatalytic reaction must be increased over a wide range of wavelengths and semiconductors with narrow bandgaps need to be designed. However, the quantum efficiency associated with overall water splitting using existing photocatalysts is typically lower than ten per cent1,2. Thus, whether a particulate photocatalyst can enable a quantum efficiency of 100 per cent for the greatly endergonic water-splitting reaction remains an open question. Here we demonstrate overall water splitting at an external quantum efficiency of up to 96 per cent at wavelengths between 350 and 360 nanometres, which is equivalent to an internal quantum efficiency of almost unity, using a modified aluminium-doped strontium titanate (SrTiO3:Al) photocatalyst3,4. By selectively photodepositing the cocatalysts Rh/Cr2O3 (ref. 5) and CoOOH (refs. 3,6) for the hydrogen and oxygen evolution reactions, respectively, on different crystal facets of the semiconductor particles using anisotropic charge transport, the hydrogen and oxygen evolution reactions could be promoted separately. This enabled multiple consecutive forward charge transfers without backward charge transfer, reaching the upper limit of quantum efficiency for overall water splitting. Our work demonstrates the feasibility of overall water splitting free from charge recombination losses and introduces an ideal cocatalyst/photocatalyst structure for efficient water splitting.

Atomistic Investigation of Grain Boundary Fracture in Alumina.

Grain boundary (GB) fracture is a major mechanism of material failure in polycrystalline ceramics. However, the intricate atomic arrangements of GBs have impeded our understanding of the atomistic mechanisms of these processes. In this study, we investigated the atomic-scale crack propagation behavior of an α-Al2O3 ∑13 grain boundary, using a combination of in situ transmission electron microscopy (TEM) and scanning TEM. The atomic-scale fracture path along the GB core was directly determined by the observation of the atomic structures of the fractured surfaces, which is consistent with density functional theory calculations. We found that the GB fracture can be attributed to the weaker local bonds and a smaller number of bonds along the fracture path. Our findings provide atomistic insights into the mechanisms of crack propagation along GBs, offering significant implications for GB engineering and the toughening of ceramics.

Nanoscale Localized Phonons at Al2O3 Grain Boundaries.

Nanoscale defects like grain boundaries (GBs) would introduce local phonon modes and affect the bulk materials' thermal, electrical, optical, and mechanical properties. It is highly desirable to correlate the phonon modes and atomic arrangements for individual defects to precisely understand the structure-property relation. Here we investigated the localized phonon modes of Al2O3 GBs by combination of the vibrational electron energy loss spectroscopy (EELS) in scanning transmission electron microscope and density functional perturbation theory (DFPT). The differences between GB and bulk obtained from the vibrational EELS show that the GB exhibited more active vibration at the energy range of <50 meV and >80 meV, and further DFPT results proved the wide distribution of bond lengths at GB are the main factor for the emergence of local phonon modes. This research provides insights into the phonon-defect relation and would be of importance in the design and application of polycrystalline materials.

IL24 Expression in Synovial Myofibroblasts: Implications for Female Osteoarthritis Pain through Propensity Score Matching Analysis.

(1) Introduction: Despite documented clinical and pain discrepancies between male and female osteoarthritis (OA) patients, the underlying mechanisms remain unclear. Synovial myofibroblasts, implicated in synovial fibrosis and OA-related pain, offer a potential explanation for these sex differences. Additionally, interleukin-24 (IL24), known for its role in autoimmune disorders and potential myofibroblast production, adds complexity to understanding sex-specific variations in OA. We investigate its role in OA and its contribution to observed sex differences. (2) Methods: To assess gender-specific variations, we analyzed myofibroblast marker expression and IL24 levels in synovial tissue samples from propensity-matched male and female OA patients (each n = 34). Gene expression was quantified using quantitative polymerase chain reaction (qPCR). The association between IL24 expression levels and pain severity, measured by a visual analog scale (VAS), was examined to understand the link between IL24 and OA pain. Synovial fibroblast subsets, including CD45-CD31-CD39- (fibroblast) and CD45-CD31-CD39+ (myofibroblast), were magnetically isolated from female patients (n = 5), and IL24 expression was compared between these subsets. (3) Results: Females exhibited significantly higher expression of myofibroblast markers (MYH11, ET1, ENTPD2) and IL24 compared to males. IL24 expression positively correlated with pain severity in females, while no correlation was observed in males. Further exploration revealed that the myofibroblast fraction highly expressed IL24 compared to the fibroblast fraction in both male and female samples. There was no difference in the myofibroblast fraction between males and females. (4) Conclusions: Our study highlights the gender-specific role of myofibroblasts and IL24 in OA pathogenesis. Elevated IL24 levels in females, correlating with pain severity, suggest its involvement in OA pain experiences. The potential therapeutic implications of IL24, demonstrated in autoimmune disorders, open avenues for targeted interventions. Notwithstanding the limitations of the study, our findings contribute to understanding OA's multifaceted nature and advocate for future research exploring mechanistic underpinnings and clinical applications of IL24 in synovial myofibroblasts. Additionally, future research directions should focus on elucidating the precise mechanisms by which IL24 contributes to OA pathology and exploring its potential as a therapeutic target for personalized medicine approaches.

Overall Water Splitting by a SrTaO2N-Based Photocatalyst Decorated with an Ir-Promoted Ru-Based Cocatalyst.

The development of narrow-bandgap photocatalysts for one-step-excitation overall water splitting (OWS) remains a critical challenge in the field of solar hydrogen production. SrTaO2N is a photocatalytic material having a band structure suitable for OWS under visible light (λ ≤ 600 nm). However, the presence of defects in the oxynitride and the lack of cocatalysts to promote simultaneous hydrogen and oxygen evolution make it challenging to realize OWS using this material. The present work demonstrates a SrTaO2N-based particulate photocatalyst for OWS. This photocatalyst, which was composed of single crystals, was obtained by nitriding SrCl2 and Ta2O5 together with NaOH, with the latter added to control the formation of defects. The subsequent loading of bimetallic RuIrOx nanoparticles accelerated charge separation and allowed the SrTaO2N photocatalyst to exhibit superior OWS activity. This research presenting the strategies of controlling the oxygen sources and promoting the cocatalyst function is expected to expand the range of potential OWS-active oxynitride photocatalysts and permit the design of efficient cocatalysts for photocatalytic OWS.

Mechanistic Insights into Enhanced Hydrogen Evolution of CrOx /Rh Nanoparticles for Photocatalytic Water Splitting.

The hydrogen evolution reaction (HER) of Rh nanoparticles (RhNP) coated with an ultrathin layer of Cr-oxides (CrOx ) was investigated as a model electrode for the Cr2 O3 /Rh-metal core-shell-type cocatalyst system for photocatalytic water splitting. The CrOx layer was electrodeposited over RhNP on a transparent conductive fluorine-doped tin oxide (FTO) substrate. The CrOx layer on RhNP facilitates the electron transfer process at the CrOx /RhNP interface, leading to the increased current density for the HER. Impedance spectroscopic analysis revealed that the CrOx layer transferred protons via the hopping mechanism to the RhNP surface for HER. In addition, CrOx restricted electron transfer from the FTO to the electrolyte and/or RhNP and suppressed the backward reaction by limiting oxygen migration. This study clarifies the crucial role of the ultrathin CrOx layer on nanoparticulate cocatalysts and provides a cocatalyst design strategy for realizing efficient photocatalytic water splitting.

Direct Observation of Atomistic Reaction Process between Pt Nanoparticles and TiO2 (110).

The catalytic activity and selectivity of heterogeneous catalysts are governed by atomic and electronic structures at the heterointerface between noble metal nanoparticles (NPs) and oxide substrates. In specific chemical reactions, it is well-known that the catalytic activity is strongly suppressed by annealing in a reducing atmosphere, so-called strong metal-support interaction (SMSI). However, it is still unclear the formation process and atomistic origin of the SMSI. By preparing well-defined platinum (Pt) NPs supported on atomically flat TiO2 (110) substrate, we directly show the formation of chemically ordered Pt-Ti intermetallic NPs and impregnation of NPs into TiO2 substrate at high temperatures by using atomic-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Furthermore, we observed negative charge transfer from the Pt-Ti intermetallic NPs to the TiO2 surface, which would strongly affect the catalytic activities.

Flux-Assisted Synthesis of Y2 Ti2 O5 S2 for Photocatalytic Hydrogen and Oxygen Evolution Reactions.

Photocatalytic water splitting is an ideal means of producing hydrogen in a sustainable manner, and developing highly efficient photocatalysts is a vital aspect of realizing this process. The photocatalyst Y2 Ti2 O5 S2 (YTOS) is capable of absorbing at wavelengths up to 650 nm and exhibits outstanding thermal and chemical durability compared with other oxysulfides. However, the photocatalytic performance of YTOS synthesized using the conventional solid-state reaction (SSR) process is limited owing to the large particle sizes and structural defects associated with this synthetic method. Herein, we report the synthesis of YTOS particles by a flux-assisted technique. The enhanced mass transfer efficiency in the flux significantly reduced the preparation time compared with the SSR method. In addition, the resulting YTOS showed improved photocatalytic H2 and O2 evolution activity when loaded with Rh and Co3 O4 co-catalysts, respectively. These improvements are attributed to the reduced particle size and enhanced crystallinity of the material as well as the slower decay of photogenerated carriers on a nanosecond to sub-microsecond time range. Further optimization of this flux-assisted method together with suitable surface modification is expected to produce high-quality YTOS crystals with superior photocatalytic activity.

Direct imaging of atomistic grain boundary migration.

Grain boundary (GB) migration plays an important role in modifying the microstructures and the related properties of polycrystalline materials, and is governed by the atomistic mechanism by which the atoms are displaced from one grain to another. Although such an atomistic mechanism has been intensively investigated, it is still experimentally unclear as to how the GB migration proceeds at the atomic scale. With the aid of high-energy electron-beam irradiation in atomic-resolution scanning transmission electron microscopy, we controllably triggered the GB migration in α-Al2O3 and directly visualized the atomistic GB migration as a stop motion movie. It was revealed that the GB migration proceeds by the cooperative shuffling of atoms on GB ledges along specific routes, passing through several different stable and metastable GB structures with low energies. We demonstrated that GB migration could be facilitated by the GB structural transformations between these low-energy structures.

Atomistic Origin of Li-Ion Conductivity Reduction at (Li3xLa2/3-x)TiO3 Grain Boundary.

Lithium lanthanum titanate (LLTO) is one of the excellent candidates for an electrolyte in the all-solid-state Li-ion battery, owing to the high Li-ion conductivity in the bulk. However, the Li-ion conductivity at the grain boundary (GB) is largely reduced, and it is therefore important to reveal the origin of Li-ion conductivity reduction at the GB. Here, by using atomic-resolution scanning transmission electron microscopy combined with atomic force microscopy, we investigate the charge states, Li-ion conductivities, atomic and electronic structures at the LLTO Σ5 and Σ13 GBs. Although the Σ5 GB has no significant influence on Li-ion conductivity, the Σ13 GB shows the evident reduction of Li-ion conductivity. We further elucidate that the Σ13 GB is positively charged by the formation of oxygen vacancies at the GB. Such a positive charge would form the Li-ion depletion layers adjacent to the GB, which causes the significant reduction of Li-ion conductivity.

Enhanced Overall Water Splitting by a Zirconium-Doped TaON-Based Photocatalyst.

Solar-powered one-step-excitation overall water splitting (OWS) using semiconducting materials is a simple means of achieving scalable and sustainable hydrogen production. While tantalum oxynitride (TaON) is one of the few photocatalysts capable of promoting OWS via single-step visible-light excitation, the efficiency of this process remains extremely poor. The present work employed 15 nm amorphous Ta2 O5 ⋅3.3 H2 O nanoparticles as a new precursor together with Zr doping and an optimized nitridation duration to synthesize a TaON-based photocatalyst with reduced particle sizes and low defect densities. Upon loading with Ru/Cr2 O3 /IrO2 cocatalysts, this material exhibited stoichiometric water splitting into hydrogen and oxygen, with an order of magnitude improvement in efficiency. Our findings demonstrate the importance of inventing/selecting the appropriate synthetic precursor and of defect control for fabricating active OWS photocatalysts.

Experimental Observation of Long-Range Magnetic Order in Icosahedral Quasicrystals.

Quasicrystals (QCs), first discovered in 1984, generally do not exhibit long-range magnetic order. Here, we report on long-range magnetic order in the real icosahedral quasicrystals (i QCs) Au-Ga-Gd and Au-Ga-Tb. The Au65Ga20Gd15 i QC exhibits a ferromagnetic transition at TC = 23 K, manifested as a sharp anomaly in both magnetic susceptibility and specific heat measurements, along with an appearance of magnetic Bragg peak below TC. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviors observed for the other magnetic quasicrystals found to date. Moreover, when Gd is replaced by Tb, i.e., for the Au65Ga20Tb15 i QC, a ferromagnetic behavior is still retained with TC = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15 i QC becomes broadened upon Tb substitution, neutron diffraction experiments clearly show marked development of magnetic Bragg peaks just below TC, indicating long-range magnetic order for the Au65Ga20Tb15 i QC also. Our findings can contribute to the further investigation of exotic magnetic orders formed on real quasiperiodic lattices with unprecedented highest global symmetry, i.e., icosahedral symmetry.

Surface Modifications of (ZnSe)0.5(CuGa2.5Se4.25)0.5 to Promote Photocatalytic Z-Scheme Overall Water Splitting.

Charge separation is crucial for an efficient artificial photosynthetic process, especially for narrow-bandgap metal sulfides/selenides. The present study demonstrates the application of a p-n junction to particulate metal selenides to enhance photocatalytic Z-scheme overall water splitting (OWS). The constructed p-n junction of CdS-(ZnSe)0.5(CuGa2.5Se4.25)0.5 significantly boosted charge separation. A thin TiO2 coating layer also was introduced to inhibit photocorrosion of CdS and suppress the backward reaction of water formation from hydrogen and oxygen. By employing Pt-loaded TiO2/CdS-(ZnSe)0.5(CuGa2.5Se4.25)0.5 as a hydrogen evolution photocatalyst (HEP), we assembled a Z-scheme OWS system, together with BiVO4:Mo and Au as an oxygen evolution photocatalyst and electron mediator, respectively. An apparent quantum yield of 1.5% at 420 nm was achieved, which is by far the highest among reported particulate photocatalytic Z-scheme OWS systems with metal sulfides/selenides as HEPs. The present work demonstrates that a well-tailored p-n junction structure is effective for promoting charge separation in photocatalysis and opens new pathways for the development of efficient artificial photosynthesis systems involving narrow bandgap photocatalysts.

Simultaneously Tuning the Defects and Surface Properties of Ta3N5 Nanoparticles by Mg-Zr Codoping for Significantly Accelerated Photocatalytic H2 Evolution.

The simultaneous control of the defect species and surface properties of semiconducting materials is a crucial aspect of improving photocatalytic performance, yet it remains challenging. Here, we synthesized Mg-Zr-codoped single-crystalline Ta3N5 (Ta3N5:Mg+Zr) nanoparticles by a brief NH3 nitridation process, exhibiting photocatalytic water reduction activity 45 times greater than that of pristine Ta3N5 under visible light. A coherent picture of the relations between the defect species (comprising reduced Ta, nitrogen vacancies and oxygen impurities), surface properties (associated with dispersion of the Pt cocatalyst), charge carrier dynamics, and photocatalytic activities was drawn. The tuning of defects and simultaneous optimization of surface properties resulting from the codoping evidently resulted in the generation of high concentrations of long-lived electrons in this material as well as the efficient migration of these electrons to evenly distributed surface Pt sites. These effects greatly enhanced the photocatalytic activity. This work highlights the importance and feasibility of improving multiple properties of a catalytic material via a one-step strategy.

Nanometre imaging of Fe3GeTe2 ferromagnetic domain walls.

Fe3GeTe2 is a layered crystal which has recently been shown to maintain its itinerant ferromagnetic properties even when atomically thin. Here, differential phase contrast scanning transmission electron microscopy is used to investigate the domain structure in a Fe3GeTe2 cross-sectional lamella at temperatures ranging from 95 to 250 K and at nanometre spatial resolution. Below the experimentally determined Curie temperature (T C) of 191 K, stripe domains magnetised along 〈0001〉, bounded with 180◦ Bloch type domain walls, are observed, transitioning to mixed Bloch-Néel type where the cross-sectional thickness is reduced below 50 nm. When warming towards T C, these domains undergo slight restructuring towards uniform size, before abruptly fading at T C. Localised loss of ferromagnetic order is seen over time, hypothesised to be a frustration of ferromagnetic order from ambient oxidation and basal cracking, which could enable selective modification of the magnetic properties for device applications.

Direct Measurement of Electronic Band Structures at Oxide Grain Boundaries.

Grain boundaries (GBs) modulate the macroscopic properties in polycrystalline materials because they have different atomic and electronic structures from the bulk. Despite the progress on the understanding of GB atomic structures, knowledge of the localized electronic band structures is still lacking. Here, we experimentally characterized the atomic structures and the band gaps of four typical GBs in α-Al2O3 by scanning transmission electron microscopy and valence electron energy-loss spectroscopy (EELS). It was found that the band gaps of the GBs are narrowed by 0.5-2.1 eV compared with that of 8.8 eV in the bulk. By combing core-loss EELS with first-principles calculations, we elucidated that the band gap reductions directly correlate with the decrease of the coordination numbers of Al and O ions at the GBs. These results provide in-depth understanding between the local atomic and electronic band structures for GBs and demonstrate a novel electronic-structure analysis for crystalline defects.

Oxysulfide photocatalyst for visible-light-driven overall water splitting.

Oxysulfide semiconductors have narrow bandgaps suitable for water splitting under visible-light irradiation, because the electronegative sulfide ions negatively shift the valence band edges of the corresponding oxides1,2. However, the instability of sulfide ions during the water oxidation is a critical obstacle to simultaneous evolution of hydrogen and oxygen3. Here, we demonstrate the activation and stabilization of Y2Ti2O5S2, with a bandgap of 1.9 eV, as a photocatalyst for overall water splitting. On loading of IrO2 and Rh/Cr2O3 as oxygen and hydrogen evolution co-catalysts, respectively, and fine-tuning of the reaction conditions, simultaneous production of stoichiometric amounts of hydrogen and oxygen was achieved on Y2Ti2O5S2 during a 20 h reaction. The discovery of the overall water splitting capabilities of Y2Ti2O5S2 extends the range of promising materials for solar hydrogen production.

Atomic Scale Origin of Enhanced Ionic Conductivity at Crystal Defects.

In oxide materials, the presence of dislocations often strongly affects the properties of thin film and multilayer devices. Although it was reported that ionic conduction can be enhanced by introducing dislocations in ionic conductors, the underlying mechanism of such enhancement remains unclear. Here we analyzed the ionic conduction enhancement in an yttria-stabilized zirconia (YSZ) single edge dislocation from a structural point of view, using atomic resolution scanning transmission electron microscopy (STEM). First, the atomic structure and chemistry of a dislocation in YSZ were characterized by STEM and energy dispersive X-ray spectroscopy (EDS). A relative ionic conduction variation map around the dislocation was then estimated based on the well-established strain-conductivity and chemistry-conductivity relationships in YSZ. We propose that a faster ionic conductivity path can be formed around the dislocation core due to the coupling of the tensile strain field and dopant segregation, which could account for enhanced ionic conductivity along dislocations.