ABSTRACT Ferroelectric oxide heterostructures provide a versatile foundation for functional electronics, yet their performance is often hindered by the difficulty of manipulating domain states in ferroelectric films. Understanding the coupling between interfacial defects and polarization stability remains a central challenge for nanoscale ferroelectrics. This study investigates atomic‐scale mechanisms that influence the as‐grown polarization orientation in a BiFeO 3 /La 0.7 Sr 0.3 MnO 3 (BFO/LSMO) heterostructure. Utilizing piezoresponse force microscopy (PFM) and advanced aberration‐corrected STEM combined with energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and 4D‐STEM, we precisely mapped the polarization state and interfacial chemistry. A dual‐charge compensation mechanism is identified in which Sr cation diffusion into Bi vacancies is accompanied by the accumulation of oxygen vacancies at the interface. This synergistic mechanism promotes a strong built‐in field at the interface that electrostatically stabilizes the polar interface, leading to a large out‐of‐plane Fe displacement near the interface. Density functional theory (DFT) calculations further confirm that the Fe displacement increase is critically affected by the atomic plane positions of the oxygen vacancies relative to the diffused Sr atoms. The polarization remains robustly switchable under repeated cycling, demonstrating its viability for device operation. This work establishes atomic‐scale defect engineering as an effective strategy for stabilizing and manipulating domain states in ferroelectric thin films.

ABSTRACT The stabilization of ferroelectricity in non‐polar oxides remain a key challenge in the design of next‐generation functional materials, as existing approaches typically rely on chemical substitution, or metastable phases. Here, we report a universal and experimentally realizable route to emergent ferroelectricity based on interfacial symmetry frustration in oxide superlattices composed of dissimilar crystal symmetries. We design superlattice thin films heterostructures integrating cubic (CeO 2 , YSZ) and monoclinic (HfO 2 , ZrO 2 ) oxide layers showing spontaneous polarization that are non‐polar in their bulk phases. High‐resolution structural characterization confirms coherent heterointerfaces, while piezoresponse force microscopy and macroscopic electrical measurements establish switchable polarization. First‐principles calculations reveal that the crystalline symmetry mismatch across the interfaces breaks inversion symmetry and induces polar distortions through interface‐driven structural frustration, giving rise to emergent ferroelectricity without the need for chemical modification or metastable phase control. Our findings identify interfacial crystalline symmetry incompatibility as a general design principle for engineering ferroelectricity in superlattice heterostructures, opening new pathways for functional oxide electronics beyond conventional ferroelectric material systems.

Abstract High-entropy oxides (HEOs) originate from an innovative materials design strategy that stabilizes single-phase solid solutions despite the inclusion of multiple principal elements into a single cation sublattice. While prior efforts have largely focused on cation disorder, the impact of anion defects on the structure and properties of HEOs remains unexplored. Here, we examine the influence of oxygen non-stoichiometry on the nanostructure and magnetic properties of single-crystal high-entropy manganite (HE-Mn) films, (Gd0.2La0.2Nd0.2Sm0.2Sr0.2)MnO3. The films were deposited on single-crystal (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates under varying oxygen partial pressures p(O2). Phase-pure cube-on-cube epitaxy is maintained across all growth conditions. However, distinct nano-columnar Ruddlesden-Popper (RP) faults formed in oxygen deficient HE-Mn films. Unlike in conventional manganites, low-pressure-deposited films show no change in cation oxidation state, indicating the concurrent oxygen and manganese deficiency. This coupled cation-anion deficiency preserves the Mn3+/Mn4+ ratio and drives RP fault formation. Consequently, ferromagnetic ordering persists even in the low p(O2) HE-Mn films, demonstrating their resilience to oxygen non-stoichiometry. Additionally, an in-plane to out-of-plane magnetic anisotropy crossover was observed, likely arising from spatial variation in the c-axis lattice constant. These findings establish oxygen non-stoichiometry as an effective control parameter for defect nanostructuring and magnetic property tuning in HEO epitaxial films.

A heterojunction photocatalyst composed of single-atom, atomically dispersed Ni sites on g-C3N4/TiO2 was developed for sacrificial-agent-free CO2-to-CO reduction under simulated solar irradiation. The optimized catalyst, containing 0.78 wt% Ni and 46 wt% g-C3N4, delivered 70% selectivity to CO over H2 and exhibited 16-fold enhancement in activity compared with bare g-C3N4/TiO2 and Ni-single-atom catalysts supported on either g-C3N4 or TiO2 alone. High-resolution transmission electron microscopy (HRTEM) revealed intimate interfacial coupling within the g-C3N4/TiO2 heterojunction, while atomically dispersed Ni species were predominantly anchored on g-C3N4 nanosheets coating the TiO2 surface. X-ray photoelectron spectroscopy revealed pronounced interfacial electronic redistribution following heterojunction formation and Ni incorporation, indicating strong electronic communication between the semiconductor components. Electrochemical impedance spectroscopy (EIS) and steady-state photoluminescence measurements showed significantly suppressed charge recombination, whereas transient absorption spectroscopy revealed that isolated Ni sites act as efficient electron traps, extracting photogenerated electrons and directing them toward catalytic reduction centers. Combined with the comparative photocatalytic performance of individual components, these findings identify the Ni-Nx moieties on g-C3N4 as active sites for CO2-to-CO conversion and support the S-scheme charge-transfer pathway, in which TiO2 preferentially consumes holes while highly reducing electrons accumulate on the g-C3N4-supported Ni single-atom sites to drive selective CO2 reduction in water.

Monochromated electron energy loss spectroscopy in advanced scanning transmission electron microscopes has become a powerful tool for probing local electronic and vibrational spectra in many materials. However, acquiring high-quality multi-dimensional hyperspectral image datasets remains challenging due to sample drift, low signal-to-noise ratio (SNR), and detector artifacts. These limitations often require shorter acquisition times to reduce their influence, which can in turn compromise the spatial and energy resolution of the final results. To overcome these challenges, we develop a new approach that aligns and integrates multi-frame, fast-scan datasets using optimized image-registration algorithms and selection criteria to achieve high-SNR, low-drift results. By mitigating time-dependent experimental instabilities, this approach effectively preserves the intrinsic energy and spatial resolution of the instrument in the final integrated dataset. Ultimately, this provides an efficient and versatile strategy for capturing high-fidelity multi-dimensional hyperspectral images without compromising the attainable resolution.

Nonlinear frequency conversion unlocks technologies ranging from telecommunications to quantum computation; however, weak nonlinearities and architectures that resist miniaturization currently limit devices. Here, we combine a bandstructure-engineered GaAs/AlGaAs heterostructure with a high quality factor dielectric metasurface to simultaneously tailor the intrinsic nonlinear susceptibility and optimize the electromagnetic field within the heterostructure. By engineering a resonant interband transition, we realize a large second-order nonlinear tensor element, 1.6 nm/V at 1.57 um wavelength. We then make it free-space-accessible and boost the effective nonlinearity to 14 nm/V using a metasurface patterned on the material. Our proof-of-concept experiment establishes that interband transition engineering and metasurfaces accessing otherwise unusable nonlinear tensor elements enable giant effective nonlinearities in the near-infrared to visible spectrum. This addresses material and device-level constraints in nonlinear photonics, providing a scalable route to compact, efficient devices.

The buried interface between charge transport layer and the overlying perovskite absorber is critical yet difficult to probe in perovskite solar cells. Because light enters through the transparent substrate and is predominantly absorbed near this region, photo-induced degradation processes are most likely initiated at hidden buried interface. Here, we reveal that instability at the buried SnO2/perovskite interface triggers structural and chemical decomposition of the perovskite layer. To address this issue, we introduce polymeric interlayers that simultaneously reinforce interfacial bonding and suppress tin-ion migration. Poly(1-ethenylpyrrolidine-2,5-dione) (PED) forms the most robust and chemically compatible interface, yielding enhanced phase purity, reduced defect density, and significantly mitigated tin diffusion. These findings identify the buried interface as the primary origin of perovskite degradation and highlight interfacial polymer design as an effective strategy for achieving intrinsically stable perovskite photovoltaics.

Freshwater scarcity demands desalination technologies that are both efficient and ecologically sustainable. Conventional solar evaporators, particularly those based on broadband-absorbing materials, block vital sunlight and generate excess heat, disrupting underwater photosynthesis and marine ecosystem health. Here, we present a hydrophobic, non-covalent pi-stacked organic framework (pi OF) designed to overcome this fundamental trade-off. pi OF exhibits narrow-bandwidth solar absorption, which minimizes parasitic heat loss and enables efficient photothermal conversion without complex structural engineering. Under one-sun irradiation in an atmospheric environment, the simple deployment of pi OF achieves the highest evaporation rates per unit energy among recently reported systems. Notably, its performance surpasses that of conventional planar (2D) evaporators as well as more sophisticated 3D evaporators that rely on complex structural designs to enhance evaporation efficiency. More critically, its spectral selectivity allows sufficient transmission of photosynthetically active radiation (PAR), while its inherent hydrophobicity confines heat to the air-water interface, maintaining near-ambient bulk water temperatures. These combined attributes enable high-rate localized evaporation while preserving and even enhancing the viability of marine flora in our tests. This work demonstrates that pi OF is not merely an efficient solar absorber, but an ecosystem-benign platform, offering a sustainable and scalable pathway for solar desalination that actively supports underwater photosynthetic life.

Dimensionality is a concept tied to crystalline order, electronic states, and physical properties. While the chemical basis of dimensionality in inorganic 3D and 2D solids is known, the evolution of the 25 structure and physical states of 2D layers into 1D chains remains poorly understood. Here, we leverage solid solutions in the InTeI—InSeI series representing the emergent III–VI–VII van der Waals class to demonstrate the seamless chalcogen-driven dimensional crossover of the 2D layered phase (InTeI) to the sought-after 1D chain analogue (InSeI) that manifests helicity. Computational and experimental structures, bond valencies, binding energies, and Bader charges establish that bond ionicity scale with Se content which 30 define the electronic states and drive the stabilization of 1D helical chains from the more Te-rich 2D phase. This interplay between ionicity and dimensionality reconciles the structural evolution in III–VI–VII crystals and can be invoked to rationally design new low-dimensional materials.

Spintronic terahertz emitters (STEs) generate broadband THz radiation via ultrafast spin–charge conversion in magnetic multilayers, offering spectral coverage beyond that of photoconductive antennas and nonlinear optical crystals. Here, we demonstrate STEs based on a PtxAu100−x alloy that achieve significantly higher THz output power than widely used Pt-based devices. Alloy composition and layer thickness tuning yield Pt75Au25 as the optimal alloy, providing a 30% increase in THz power in CoFeB/Pt75Au25 bilayer STEs compared to the optimized CoFeB/Pt reference STE. In W/CoFeB/Pt75Au25 trilayer STEs, we observe a 10% higher THz power than in the optimized W/CoFeB/Pt trilayer. The STE efficiency is reduced upon annealing for both Pt75Au25- and Pt-based STEs due to the formation of interfacial alloys. Our results establish Pt75Au25 as a promising platform for high-performance STEs, where its giant spin Hall effect significantly enhances efficiency over conventional Pt-based devices.

ABSTRACT Achieving high product selectivity in electrocatalytic carbon dioxide reduction (CO 2 RR) remains a critical challenge due to competition between multiple proton‐coupled electron‐transfer pathways on catalyst surfaces. Meanwhile, chirality‐induced spin selectivity (CISS), which enables spin‐polarized electron transport through chiral interfaces, has recently emerged as a promising strategy to modulate interfacial electrochemical reactions. Although the CISS effect has been shown to enhance selectivity and efficiency in the spin‐sensitive oxygen evolution reaction (OER), its role in regulating CO 2 RR pathways and in stabilizing intermediates remains largely unexplored. Here, chiral molecules (R‐ and S‐1,1′‐bi‐2‐naphthyl‐2,2′‐diyl hydrogen phosphate, BNP) were integrated with SnO 2 to construct chiral‐modified catalysts (R‐BNP/SnO 2 and S‐BNP/SnO 2 ). Compared with bare SnO 2 and racemic BNP‐modified SnO 2 (Rac‐BNP/SnO 2 ), the chiral catalysts exhibited a pronounced shift in product selectivity from CO toward formate production. Importantly, in‐situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) reveals that the chiral interface selectively stabilizes the O‐bound *OCHO intermediate associated with the formate pathway and modulates interfacial water structure and hydrogen‐bonding dynamics. These findings demonstrate that spin‐polarized interfacial electron transfer can regulate CO 2 RR pathway selectivity by modulating the stabilization of key intermediates. More broadly, this work establishes chiral spin‐selective interfaces as a new strategy for regulating competitive electrocatalytic reaction pathways.

The direct and selective oxidation of light alkanes into value-added liquid chemicals under mild conditions remains a long-standing challenge in catalysis. Here, we report a heterogeneous photocatalyst based on site-isolated decatungstate (DT) anions immobilized on SBA-15 via a silatrane linker (sil-DT). Under UV-light irradiation at room temperature and ambient pressure, the catalyst selectively oxidizes propane to acetone and exhibits an acetone production rate of 11.2 mmol gDT-1 h-1 , a total liquid product selectivity of 89.0%, and an acetone fraction of 69.0% within the liquid products. In contrast, bulk sodium DT (NaDT) shows negligible activity under identical conditions. Spectroscopic and computational studies reveal that the high catalytic performance arises from the uniform dispersion and site isolation of DT species, which retain the photo-physical properties of their homogeneous counterparts. This work demonstrates the critical role of molecular dispersion in enabling selective light-driven alkane oxidation and offers a sustainable route for propane valorization.

Free-space electro-optic modulators are key to emerging photonic systems, yet their performance remains limited by trade-offs between modulation efficiency, bandwidth, and device aperture. Here we report a hybrid BaTiO3 (BTO)/TiO2 metasurface for large-aperture, efficient, gigahertz-speed free-space electro-optic modulation. Combining scalable BTO film growth by radio-frequency magnetron sputtering with mature TiO2 nanofabrication, we pattern the metasurface in TiO2 on an unetched BTO layer. The resulting devices support guided-mode resonances with quality factors exceeding 1300 and an optical confinement factor of 0.8, while the continuous BTO layer makes efficient use of the applied voltage, together maximizing the overlap between the optical and driving fields within the BTO. A device with a 0.3 mm x 0.3 mm metasurface achieves a transmittance modulation efficiency of 0.020 per volt and a -3 dB electro-optic bandwidth of 0.8 GHz, with an effective Pockels coefficient of 151 pm/V for the BTO. This establishes a scalable route to high-performance free-space electro-optic modulators for LiDAR, free-space optical communication, and reconfigurable optical computing.

The recent, rapid advances in nonlinear chipscale nanophotonics in the visible and near-infrared have been largely driven by manipulating the local dielectric environment proximate to decades-old workhorse bulk nonlinear optical materials, rather than increasing the inherent strength of their nonlinear response. While proposed decades ago, we demonstrate the first experimental realization of a new class of designer nonlinear materials that leverage the interband optical transition in asymmetric structures to provide strong second order susceptibility, $χ^{(2)}$. Using simple AlGaAs/GaAs coupled quantum wells operating in the near-infrared as a prototype, we observed strong second harmonic generation enhancement of 1550 nm to 775 nm over bulk controls. Extracted $χ^{(2)}$ values were as high as 2750 pm/V, which is $>$7x that of bulk GaAs. Furthermore, measured susceptibilities agreed well with quantum mechanical calculations of $χ^{(2)}$ using layer profiles extracted from electron microscopy. Growth interruptions were employed to improve interfacial abruptness in response to electron microscopy characterization, resulting in increased $χ^{(2)}$ toward the simulation predictions for ideal heterointerfaces. More complex layer designs showed predicted $χ^{(2)}$ up to 7 nm/V. Such materials are anticipated to find myriad applications, including entangled photon generation at telecommunications wavelengths for chipscale quantum information processing.

We demonstrate the growth of unintentionally doped p-type α-SnO (001) thin films by suboxide molecular-beam epitaxy at low growth temperatures of 330–360 °C without additional oxygen supply. By increasing the SnO flux, the hole concentration increases from 0.2 × 1018 to 1.3 × 1018 cm−3, while the hole mobility decreases from 8.5 to 3.9 cm2 V−1 s−1. The dependence of electrical properties on SnO flux is attributed to the associated changes in the chemical potential of SnO during growth, which likely influences the formation of tin vacancies and, therefore, the hole concentration. Similar trends were also observed under an added oxygen background pressure, although the effects were less pronounced. At a fixed SnO flux, the hole mobility increases with increasing growth temperature; however, higher deposition temperature inevitably leads to increased surface roughness. Temperature-dependent Hall measurements reveal a shallow apparent activation energy of 15.2–22.7 meV across the (0.1–8) × 1013 molecules cm−2 s−1 range of SnO fluxes investigated.

Local chemical ordering strongly influences the behavior of complex concentrated alloys, yet its characterization remains challenging due to the nanoscale dimensions and scattered spatial distribution of the ordered domains. Here, we study chemical ordering near grain boundaries, demonstrating that interfaces can act as microstructural anchor points that amplify chemical order and promote near-boundary compositional modulation. Atomistic simulations reveal the development of composition waves with ordering vectors normal to the boundary plane in two distinct material systems, CrCoNi and NbMoTaW. These waves manifest as periodic enrichment-depletion patterns that reflect the underlying chemical ordering tendencies of each system, with amplified contrast that can extend several nanometers into the grain interior before gradually decaying. By examining multiple grain boundary orientations and alloys, we show that both the interfacial segregation profile and the crystallographic terminating plane govern the extent and character of this amplification. This interplay between boundary-dictated directional ordering and the diffuse, untemplated chemical domain evolution within the grain advances our understanding of interface-mediated ordering phenomena and suggests new opportunities for experimentally detecting local chemical order in complex concentrated alloys.

Stabilizing ferroelectric domain configurations is critical to driving the exploration of the fundamental physics and governing principles of domain formation in ferroelectrics. Charged domain walls have attracted interest in nanoelectronics due to their high conductivity but are usually not utilized due to their conventional instability. In this study, we investigate charged domains impacted by reduced dimensionality and surface boundary conditions in BiFeO3 nanoneedles. The BiFeO3 nanoneedle’s domain structure was examined in three dimensions using a low-order tilt projection series collected by scanning transmission electron microscopy. We find that surfaces of varying surface curvature can facilitate the formation of charge-compensating surface terminations and can play a role in the stabilization of charged domains in BiFeO3. Additionally, phase-field simulations support the formation of charged domains in the bulk of BiFeO3 nanoneedles by charge domains forming to reduce the total energy at the needle interior through domain wall reconstruction. Our results pave a novel pathway to stabilize inherently unstable charged domains in ferroelectric oxides and provide insights into geometric boundary condition engineering of thin films and nanostructures. The authors propose a top down strategy of modifying the surface boundary conditions in a BiFeO3 nanoneedle sample through ion milling. Surface curvature gradients and terminations induce charge compensation and ferroeleastic effects that facilitate charged domain wall stabilization.

Colloidal two-dimensional semiconductors are promising for scalable optoelectronics, but their development has been fundamentally limited by defect-induced nonradiative recombination that suppresses exciton emission. In particular, sulfur vacancies in solution-processed MoS2 introduce charge doping and trap states that favor trion formation, preventing bright neutral exciton photoluminescence. Here we show that simple oxidative chemistry activates bright neutral exciton emission in colloidal MoS2 monolayers. Ultraviolet (UV) irradiation under ambient conditions enhances photoluminescence by over 2 orders of magnitude, accompanied by a pronounced blueshift and a similar to 100-fold increase in exciton lifetime (0.07 to 6.14 ns), indicating a transition from trion-dominated to neutral exciton recombination. We identify UV-driven oxygen reduction as the key process that passivates sulfur vacancies and induces electron dedoping effect, thereby suppressing nonradiative decay pathways. This mechanism is general: a range of oxidants, including H2O2, (NH4)2S2O8, (NH4)2Ce(NO3)6, and NaIO4, rapidly activate emission, in some cases without UV irradiation. These findings establish a chemically tunable strategy for controlling excitonic emission in solution-dispersed MoS2, enabling scalable optoelectronic and photonic applications.

The exotic geometry of the kagome lattice drives emergent quantum states and advances energy technologies; however, the anomalous Nernst effect (ANE)-based magnetic systems are fundamentally limited by low thermopowers (<6μ V K-1) and stray-field interference. Here we propose goniopolarity (axis-dependent carrier polarity) to achieve high zero-field transverse thermoelectric responses in kagome systems. By exploiting flat-band- and van Hove singularity-driven electronic states, we uncover exceptionally large goniopolar thermoelectric responses in LuCo6Ge6, including a transverse thermopower of 18.4 μV K-1 and a transverse Peltier conductivity of 105 A m-1 K-1 at room temperature and zero field. The synergy of flat bands with high electrical conductivity yields values an order of magnitude greater than those achieved in conventional ANE-based systems. Our findings establish goniopolar kagome metals as promising candidates for thermoelectrics.

Defects trap photocarriers and hinder solar water splitting. The nanoscale photocarrier transport, trapping, and recombination mechanisms are usually inferred from ensemble-averaged measurements and remain elusive. Because an individual high-performing nanoparticle photocatalyst may outperform the ensemble average, design rules that would otherwise enhance catalytic efficiency remain unclear. Here, we introduce photomodulated electron energy-loss spectroscopy (EELS) in an optically coupled scanning transmission electron microscope (STEM) to map photocarrier localization. Using rhodium-doped strontium titanate (SrTiO3:Rh) solar water-splitting nanoparticles, we directly image the carrier densities concentrated at oxygen-vacancy surface trap states. This is achieved by separating photothermal heating from photocarrier populations through experimental and computational analyses of low-loss spectra. Photomodulated STEM-EELS enables angstrom-scale imaging of defect-induced photocarrier traps and their impact on photocatalytic efficiency.