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Abstract In the early 2000s, low dimensional ferroelectric systems were predicted to have topologically nontrivial polar structures, such as vortices or skyrmions, depending on mechanical or electrical boundary conditions. A few variants of these structures have been experimentally observed in thin film model systems, where they are engineered by balancing electrostatic charge and elastic distortion energies. However, the measurement and classification of topological textures for general ferroelectric nanostructures have remained elusive, as it requires mapping the local polarization at the atomic scale in three dimensions. Here we unveil topological polar structures in ferroelectric BaTiO3 nanoparticles via atomic electron tomography, which enables us to reconstruct the full three-dimensional arrangement of cation atoms at an individual atom level. Our three-dimensional polarization maps reveal clear topological orderings, along with evidence of size-dependent topological transitions from a single vortex structure to multiple vortices, consistent with theoretical predictions. The discovery of the predicted topological polar ordering in nanoscale ferroelectrics, independent of epitaxial strain, widens the research perspective and offers potential for practical applications utilizing contact-free switchable toroidal moments.

Abstract Lattice defects such as oxygen vacancies, interstitials, and their complexes are present in crystalline oxide materials. In particular, anti‐Frenkel defects, which refer to charge‐neutral anion vacancy‐interstitial pairs, are strongly coupled with ferroelectric and dielectric properties as electric dipoles. However, in order to observe their macroscopic manifestation, delicate defect controls are required to the extent that electronic and ionic charges are almost completely suppressed. Here, the thermal cycle dependence of dielectric and piezoelectric properties is scrutinized in the strain‐driven morphotropic phase boundaries of multiferroic La‐substituted BiFeO3 thin films. Electrochemical impedance spectroscopy provides the Warburg feature that is considered evidence of the ionic origin. The observations are discussed based on anti‐Frenkel defects that are created or annihilated reversibly by thermal cycles through high‐temperature structural phase transition temperature or magnetic Néel temperature. The defect dipoles are spontaneously aligned by the flexoelectric effect in the phase boundaries inducing a metastable interfacial ferroelectric phase. The findings offer useful insight into defect dipoles.

Abstract Charge ordering (CO), characterized by a periodic modulation of electron density and lattice distortion, has been a fundamental topic in condensed matter physics, serving as a potential platform for inducing novel functional properties. The charge-ordered phase is known to occur in a doped system with high d-electron occupancy, rather than low occupancy. Here, we report the realization of the charge-ordered phase in electron-doped (100) SrTiO3 epitaxial thin films that have the lowest d-electron occupancy i.e., d 1-d 0. Theoretical calculation predicts the presence of a metastable CO state in the bulk state of electron-doped SrTiO3. Atomic scale analysis reveals that (100) surface distortion favors electron-lattice coupling for the charge-ordered state, and triggering the stabilization of the CO phase from a correlated metal state. This stabilization extends up to six unit cells from the top surface to the interior. Our approach offers an insight into the means of stabilizing a new phase of matter, extending CO phase to the lowest electron occupancy and encompassing a wide range of 3d transition metal oxides.

Abstract Nanotransfer printing (nTP) is one of the most promising nanopatterning methods given that it can be used to produce nano‐to‐micro patterns effectively with functionalities for electronic device applications. However, the nTP process is hindered by several critical obstacles, such as sub‐20 nm mold technology, reliable large‐area replication, and uniform transfer‐printing of functional materials. Here, for the first time, a dual nanopatterning process is demonstrated that creates periodic sub‐20 nm structures on the eight‐inch wafer by the transfer‐printing of patterned ultra‐thin (

Abstract Direct visualization of the atomic structure in scanning transmission electron microscopy has led to a comprehensive understanding of the structure-property relationship. However, a reliable characterization of the structural transition on a picometric scale is still challenging because of the limited spatial resolution and noise. Here, we demonstrate that the primary segmentation of atomic signals from background, succeeded by a denoising process, enables structural analysis in a sub-pixel accuracy. Poisson noise is eliminated using the block matching and three-dimensional filtering with Anscombe transformation, and remnant noise is removed via morphological filtering, which results in an increase of peak signal-to-noise ratio from 7 to 11 dB. Extracting the centroids of atomic columns segmented via K-means clustering, an unsupervised method for robust thresholding, achieves an average error of less than 0.7 pixel, which corresponds to 4.6 pm. This study will contribute to a profound understanding of the local structural dynamics in crystal structures.

Abstract Background Osteoarthritis (OA) is the most common type of degenerative arthritis and affects the entire joint, causing pain, joint inflammation, and cartilage damage. Various risk factors are implicated in causing OA, and in recent years, a lot of research and interest have been directed toward chronic low-grade inflammation in OA. Monocyte chemoattractant protein-1 (MCP-1; also called CCL2) acts through C–C chemokine receptor type 2 (CCR2) in monocytes and is a chemotactic factor of monocytes that plays an important role in the initiation of inflammation. The targeting of CCL2–CCR2 is being studied as part of various topics including the treatment of OA. Methods In this study, we evaluated the potential therapeutic effects the sCCR2 E3 gene may exert on OA. The effects of sCCR2 E3 were investigated in animal experiments consisting of intra-articular injection of sCCR2 E3 in a monosodium iodoacetate (MIA)-induced OA rat model. The effects after intra-articular injection of sCCR2 E3 (fusion protein encoding 20 amino acids of the E3 domain of the CCL2 receptor) in a monosodium iodoacetate-induced OA rat model were compared to those in rats treated with empty vector (mock treatment) and full-length sCCR2. Results Pain improved with expression of the sCCR2 gene. Improved bone resorption upon sCCR2 E3 gene activation was confirmed via bone analyses using micro-computed tomography. Histologic analyses showed that the sCCR2 E3 gene exerted protective effects against cartilage damage and anti-inflammatory effects on joints and the intestine. Conclusions These results show that sCCR2 E3 therapy is effective in reducing pain severity, inhibiting cartilage destruction, and suppressing intestinal damage and inflammation. Thus, sCCR2 E3 may be a potential therapy for OA.

Control of percolative dynamics of metal and insulator domains during electrically triggered insulator-metal transition underlies applications in energy-efficient switches. Jo et al. show that embedded metallic nanoparticles enhance the metastability and memory effects of metallic domains in VO2 switches.

Abstract Biopolymers are essential building blocks that constitute cells and tissues with well‐defined molecular structures and diverse biological functions. Their three‐dimensional (3D) complex architectures are used to analyze, control, and mimic various cells and their ensembles. However, the free‐form and high‐resolution structuring of various biopolymers remain challenging because their structural and rheological control depend critically on their polymeric types at the submicron scale. Here, direct 3D writing of intact biopolymers is demonstrated using a systemic combination of nanoscale confinement, evaporation, and solidification of a biopolymer‐containing solution. A femtoliter solution is confined in an ultra‐shallow liquid interface between a fine‐tuned nanopipette and a chosen substrate surface to achieve directional growth of biopolymer nanowires via solvent‐exclusive evaporation and concurrent solution supply. The evaporation‐dependent printing is biopolymer type‐independent, therefore, the 3D motor‐operated precise nanopipette positioning allows in situ printing of nucleic acids, polysaccharides, and proteins with submicron resolution. By controlling concentrations and molecular weights, several different biopolymers are reproducibly patterned with desired size and geometry, and their 3D architectures are biologically active in various solvents with no structural deformation. Notably, protein‐based nanowire patterns exhibit pin‐point localization of spatiotemporal biofunctions, including target recognition and catalytic peroxidation, indicating their application potential in organ‐on‐chips and micro‐tissue engineering.

Unrestricted integration of single-crystal oxide films on Si substrates allows for exploitation of emerging functionality of new materials in mature silicon devices. Here the authors integrate epitaxial oxide films with sharp metal-insulator transition on Si substrates by epitaxial lift-off of a freestanding nanomembrane.

Abstract Growing demands for comprehending complicated nano-scale phenomena in atomic resolution has attracted in-situ transmission electron microscopy (TEM) techniques for understanding their dynamics. However, simple to safe TEM sample preparation for in-situ observation has been limited. Here, we suggested the optical microscopy based micro-manipulating system for transferring TEM samples. By adopting our manipulator system, several types of samples from nano-wires to plate-like thin samples were transferred on micro-electro mechanical systems (MEMS) chip in a single step. Furthermore, the control of electrostatic force between the sample and the probe tip is found to be a key role in transferring process.

Metallic van der Waals magnets have considerable technological promise, due to their ability to be strongly coupled with electronic currents and integrated in two dimensional heterostructures. Here, Seo et al. demonstrate highly tunable itinerant antiferromagnetism in a van der Waals magnet.

Previous studies are limited to modulate oxygen octahedral rotation angles within the same pattern, and engineering the pattern remains a challenge. Here, the authors demonstrate a designed nonequilibrium oxygen octahedral rotation pattern leads to room-temperature ferroelectricity in CaTiO3.

Observation of a strain-gradient-induced piezoresponse at domain walls remains a challenge. Here, the authors find the piezoelectric response to be enhanced in the ferroelastic domain walls of centrosymmetric tungsten trioxide thin films due to a large strain gradient over a wide width of the wall.

The research to utilize chemical potential mismatch for materials synthesis has been limited across the oxide interface. Here, the authors show that directional ionic transport from the VO2 layers stabilizes the rutile TiO2 phase at extremely low temperatures, at which epitaxy is difficult, by effectively lowering the activation barrier for crystallization.

Two-dimensional (2D) materials are attracting increasing research interest owing to their distinct tunable physical properties. Moreover, the ubiquitous defects in 2D materials offer an opportunity to tailor their electronic properties. Recently, atomic-level structural modification methods for 2D materials have been developed, further triggering the need for the precise control of defects. Following the ground-breaking advancements in the atomic-scale characterization of defects in 2D materials, valuable information on defect-driven electronic properties has been published. It is therefore important to present a review work on the recent research developments on atomic-level defect control and characterization of 2D materials. This Perspective highlights the type and role of atomic defects in 2D materials, as well as some current technologies for engineering such defects. In addition, we emphasize on atomic-level characterization methods with a focus on aberration-corrected transmission electron microscopy and deep learning as a powerful method for characterizing defects in 2D materials. Based on the two characterization techniques, we present the experimental results of laser-induced structurally modified MoTe2 and transition metal decorated h-BN. We believe that this work will provide fundamental knowledge for engineering and characterizing defects in 2D materials for the design of application-specific electronic devices.

Mn-based layered oxides are promising cathode materials for next generation sodium ion batteries. To address two existing issues facing the system, here the authors show that a simple zinc doping can suppress both Jahn–Teller distortion and phase separation, enabling enhanced cycling performance.

Spin-orbit entangled pseudospins hold promise for a wide array of exotic magnetism ranging from a Heisenberg antiferromagnet to a Kitaev spin liquid depending on the lattice and bonding geometry, but many of the host materials suffer from lattice distortions and deviate from idealized models in part due to inherent strong pseudospin-lattice coupling. Here, we report on the synthesis of a magnetic superlattice comprising the single (n=1) and the double (n=2) layer members of the Ruddlesden-Popper series iridates Sr_{n+1}Ir_{n}O_{3n+1} alternating along the c axis, and provide a comprehensive study of its lattice and magnetic structures using scanning transmission electron microscopy, resonant elastic and inelastic x-ray scattering, third harmonic generation measurements, and Raman spectroscopy. The superlattice is free of the structural distortions reported for the parent phases and has a higher point group symmetry, while preserving the magnetic orders and pseudospin dynamics inherited from the parent phases, featuring two magnetic transitions with two symmetry-distinct orders. We infer weaker pseudospin-lattice coupling from the analysis of Raman spectra and attribute it to frustrated magnetic-elastic couplings. Thus, the superlattice expresses a near ideal network of effective spin-one-half moments on a square lattice.

Exploring topological textures in ferroelectrics facilitates the understanding and application of topological features in matter. Here the authors demonstrate the strain field induced evolution of topological vortices in nanoplatelets of rhombohedral phase BiFeO3 using the angle-resolved piezoresponse force microscopy.

Aimed at developing lead-free magnetoelectric (ME) composites with performances as good as lead (Pb)-based ones, this study employed (001) and (011) oriented 82BaTiO3-10BaZrO3-8CaTiO3 (BZT–BCT) piezoelectric single crystals, fabricated by the cost-effective solid-state single crystal growth (SSCG) method, in combination with inexpensive, magnetostrictive base metal Nickel (Ni). The off-resonance, direct ME coupling in the prepared Ni/BZT–BCT/Ni laminate composites was found to be strongly dependent on the crystallographic orientation of the BZT–BCT single crystals, as well as the applied magnetic field direction. Larger and anisotropic ME voltage coefficients were observed for the composite made using the (011) oriented BZT–BCT single crystal. The optimized ME coupling of 1 V/cm Oe was obtained from the Ni/(011) BZT–BCT single crystal/Ni composite, in the d32 mode of the single crystal, when a magnetic field was applied along its [100] direction. This performance is similar to that reported for the Ni/Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN–PZT) single crystal/Ni, but larger than that obtained from the Ni/Pb(Zr,Ti)O3 ceramic/Ni composites. The results of this work demonstrate that the use of lead-free piezoelectric single crystals with special orientations permits the selection of desired anisotropic properties, enabling the realization of customized ME effects in composites.

The PbTiO3/SrTiO3 superlattice thin films with a low volume fraction of PbTiO3 have not attracted much interest because they are thought to exhibit only a paraelectric state. In this study, we focus on a superlattice thin film with thin PbTiO3 (PTO) and thick SrTiO3 (STO) layers, wherein the hidden ferroelectricity in the thin PbTiO3 layer is revealed. Atomic scale imaging analysis and electron energy loss spectroscopy reveal the existence of a disordered ferroelectric polarization state without innate tetragonal distortion in the (6PTO/15STO)5 superlattice. The piezoelectric force microscopy analysis confirms that this disordered ferroelectricity can enhance piezoelectric response.

A hindrance to the practical use of sodium-ion batteries is the lack of adequate anode materials. By utilizing the co-intercalation reaction, graphite, which is the most common anode material of lithium-ion batteries, was used for storing sodium ion. However, its performance, such as reversible capacity and coulombic efficiency, remains unsatisfactory for practical needs. Therefore, to overcome these drawbacks, a new carbon material was synthesized so that co-intercalation could occur efficiently. This carbon material has the same morphology as carbon black; that is, it has a wide pathway due to a turbostratic structure, and a short pathway due to small primary particles that allows the co-intercalation reaction to occur efficiently. Additionally, due to the numerous voids present in the inner amorphous structure, the sodium storage capacity was greatly increased. Furthermore, owing to the coarse co-intercalation reaction due to the surface pore structure, the formation of solid-electrolyte interphase was greatly suppressed and the first cycle coulombic efficiency reached 80%. This study shows that the carbon material alone can be used to design good electrode materials for sodium-ion batteries without the use of next-generation materials.

The crystalline volume of nanocrystalline silicon (Si) films could be successfully controlled simply by changing the substrate scan speed at the high working pressure of 300 Torr. The Si crystalline volume fraction was increased from 30% to 57% by increasing the scan speed from 8 to 30 mm/s. When the Si film was prepared at a low scan speed (8 mm/s), Si crystals of size 5 nm grew homogeneously through the whole film. The higher scan speed was found to accelerate crystallization, and crystals of size up to 25 nm were deposited in the Si film deposited when the scan speed was 30 mm/s.