Controlled generation of topological spin textures, such as merons and their bound state, the bimerons, is essential for advancing spintronic technologies and elucidating soliton physics in condensed matter. Using in situ Lorentz transmission electron microscopy coupled with femtosecond laser pulse, we demonstrate the creation of two distinct Bloch-type bimeron states in chiral magnet Co8Zn8Mn4 thin plates at room temperature. Magnetic imaging and micromagnetic simulations reveal that bimeron density varies with applied magnetic field strength, enabling dynamic topological control. We further establish that the topological classification of laser-generated bimerons is invariant with specimen thickness. Field-driven reversible transformations between elongated and circular bimeron morphologies are observed, governed by the competition of Zeeman energy and magnetic shape anisotropy. Micromagnetic simulations quantitatively reproduce these metastable states, validating a unified meron-skyrmion topological framework. This work establishes a single-pulse protocol for optical manipulation of topological spin textures.

Fe-based superconductors have attracted much attention. Among them, FeTe is unique in the series of FeSe 1- x Te x with absence of superconductivity. Interestingly, Fe 1+ y Te thin film shows superconductivity after oxygen annealing, and the mechanism is still elusive. This study investigates structural, superconducting, and magnetic properties of a series of Fe 1+ y Te thin films (FeTe:O x ) annealed under different oxygen partial pressures. Scanning transmission electron microscopy is used to examine the amount and distribution of excess Fe, the migration of excess Fe toward the film surface, and the structure and distribution of the iron oxide layer formed on the film surface. Exchange bias emerges at the interface between the ferromagnetic iron oxide and FeTe:O x , persisting in the superconducting state. Theoretical calculations suggest the occurrence of both interstitial oxygen and substitutional oxygen, and suppression of AFM order by the former, which can account for superconductivity. This work is helpful for understanding the interaction of oxygen with Fe 1+ y Te and mechanism of superconductivity for FeTe:O x thin films.

This study synthesized Bi2O3-ZnO-TiO2 composites via sol-hydrothermal method and incorporated them into conventional ceramic glazes, followed by sintering at 1250°C to prepare photocatalytic ceramic glazes. Using methylene blue (MB) as the target pollutant, adsorption and photocatalytic performance were evaluated under 450 nm blue light irradiation. Results showed that the composite with Bi:Zn:Ti molar ratio of 0.4:2:1 (PC-0.4) exhibited optimal photocatalytic activity, achieving 92.82% MB removal after 1 hour and 97.99% after 4 hours. When incorporated into glaze at 20 wt%, Glaze-0.4 achieved 63.1% MB degradation after 1 hours with stable performance across three cycling tests. Characterization confirmed that alkali metal corrosion and high-temperature induced decomposition of Bi4Ti3O12 into Bi2O3 and formation of Zn2TiO4 spinel phase. The composites were successfully embedded in the glaze matrix, broadening the light response range and providing a novel approach for fabricating high-temperature stable photocatalytic ceramic glazes.

The ultrafast transmission electron microscope (UTEM) provides a powerful platform for characterizing ultrafast laser-induced structural dynamics in functional materials. In this article, the ultrafast structural dynamics of silver nanowires (Ag NWs) were investigated using electron diffraction in UTEM. Both the diffraction intensity and Bragg peak shift from picosecond to microsecond scales were analyzed to track the full-cycle structural dynamics after laser excitation. The evolution of the diffraction intensity and the shift of Bragg peaks in various directions on the picosecond to nanosecond timescales have unveiled anisotropic atomic disorder and lattice expansion along the radial and axial directions. These anisotropic lattice responses are attributed to the unique one-dimensional structure of Ag NWs, which facilitates the subsequent energy transfer from the radial to the axial direction on the nanosecond timescale. The anisotropic lattice responses were corroborated by comparing them with the isotropic results obtained from a polycrystalline silver film. Additionally, we observed breathing and extension modes in the radial and axial directions, respectively. A two-step electron-phonon coupling process due to the trapping of hot electrons by surface oxidation states and recovery dynamics was also reported. Our findings elucidate the ultrafast lattice dynamics of Ag NWs across the picosecond to microsecond scale, thus laying the groundwork for their practical applications.

The insulator-to-metal transition (IMT) in strongly correlated materials, such as vanadium dioxide (VO2), offers a transformative platform for next-generation adaptive electronics and neuromorphic computing. However, harnessing this non-equilibrium phase transition for deterministic device operation is fundamentally hindered by the inability to disentangle electric-field effects from Joule heating, owing to a lack of operando techniques capable of resolving phase dynamics at nanoscale spatial and sub-nanosecond temporal scales. Here, using a newly developed electrical-pulse-pump ultrafast transmission electron microscope (E-UTEM), we directly visualize the multi-scale electro-thermo-mechanical dynamics of the IMT in suspended VO2 devices. Our results reveal that electric-field-induced Poole-Frenkel (PF) emission, localized by patterned oxygen vacancies, plays a decisive role in redistributing the internal electric field to trigger a deterministic Mott transition. The extreme non-linearity of this PF effect enables the formation of dynamically reconfigurable connectivity topologies that bypass conventional thermal limits. Furthermore, we observe that the coupling of thermal and elastic energies governs a discrete domain evolution, characterized by step-wise and period-doubling configurational resets, which is a hallmark of non-equilibrium phase dynamics in constrained geometries. By integrating experimental imaging with phase-field simulations, we establish a comprehensive framework for the electrically-driven IMT and predict sub-100-ps switching kinetics. These findings provide a fundamental basis for the rational design of ultrafast, low-energy functional devices through nanoscale defect and strain engineering in correlated systems.

Hopfions are three-dimensional (3D) topological solitons predicted to exist in diverse magnetic systems, yet their practical utility has been largely restricted to cryogenic environments. Here, we overcome this temperature constraint by demonstrating stable magnetic hopfions in the chiral magnet Co8Zn8Mn4 at and above room temperature. Using a transmission electron microscope equipped for in situ optical excitation, we generate magnetic hopfions with femtosecond laser pulses. Long-term observations further reveal Brownian-like motion at room temperature and thermally activated collapse upon approaching the high-temperature regime. Together with micromagnetic simulations and homotopy group analysis, our experimental observations uncover the hopfion formation mechanism through the fusion of bimeron pairs. These findings establish room-temperature magnetic hopfions and provide a framework for their further studies under technologically relevant conditions.

A comprehensive investigation of the superconducting response to disruptions is essential for elucidating the mechanisms underlying performance enhancement. Here, we systematically study the effects of Xe-ion irradiation in BaHfO3-doped EuBa2Cu3O7−δ films. Our results show that irradiation significantly modifies intrinsic superconducting parameters. Analysis of critical current density Jc and pinning energy reveals that the degradation of intrinsic properties is a primary factor driving performance decline, and we highlight that enhancing depairing current density Jd is more effective than defect engineering alone, particularly within the quantum critical region. Raman spectroscopy indicates that the degradation arises from disorder at the chain oxygen sites. These findings emphasize that a thorough understanding of both intrinsic superconducting properties and extrinsic pinning structures is critical for optimizing high-temperature superconductor performance.

Fe‐based superconductors have attracted much attention. Among them, FeTe is unique in the series of FeSe 1‐ x Te x with absence of superconductivity. Interestingly, Fe 1+ y Te thin film shows superconductivity after oxygen annealing, and the mechanism is still elusive. This study investigates structural, superconducting, and magnetic properties of a series of Fe 1+ y Te thin films (FeTe:O x ) annealed under different oxygen partial pressures. Scanning transmission electron microscopy is used to examine the amount and distribution of excess Fe, the migration of excess Fe toward the film surface, and the structure and distribution of the iron oxide layer formed on the film surface. Exchange bias emerges at the interface between the ferromagnetic iron oxide and FeTe:O x , persisting in the superconducting state. Theoretical calculations suggest the occurrence of both interstitial oxygen and substitutional oxygen, and suppression of AFM order by the former, which can account for superconductivity. This work is helpful for understanding the interaction of oxygen with Fe 1+ y Te and mechanism of superconductivity for FeTe:O x thin films.

In this study, ZrO2-ZnO-TiO2 composite materials were synthesized by sol-hydrothermal method at 1250 degrees C, and their photocatalytic degradation performance for methylene blue under 450 nm blue light irradiation was evaluated. Subsequently, the synthesized ZrO2-ZnO-TiO2 composite materials were mixed with ceramic glaze and fired at 1250 degrees C to obtain ZrO2-ZnO-TiO2-Glaze materials, and their photocatalytic degradation of methylene blue was also investigated. The ZrO2-ZnO-TiO2 materials and ZrO2-ZnO-TiO2-Glaze materials were characterized by XRD, UV-Vis, SEM, TEM, FT-IR and XPS. The results show that under the high-temperature firing condition of 1250 degrees C, when the molar ratio of nZr: nZn: nTi is 1:4:8, the ZrO2-ZnO-TiO2-Glaze material exhibits the highest photocatalytic efficiency for methylene blue. After being irradiated by 450 nm blue light for 7 h, the removal rate of methylene blue can reach 90.2 %.

Time-resolved visualization of local structural dynamics driven by external fields is essential for understanding structure–property relationships in functional materials and devices. Conventional ultrafast methods primarily capture femtosecond-to-picosecond photoinduced dynamics, yet they lack real-space access to spatially inhomogeneous processes occurring at their intrinsic mesoscopic timescales that govern material and device performance—particularly electrically driven processes that closely mimic actual device operating conditions. Here, we report a multifunctional ultrafast transmission electron microscopy (UTEM) platform targeting reversible structural dynamics spanning nanoseconds to microseconds under stroboscopic multi-field excitation. Our system employs photoelectron pulses generated by nanosecond UV laser illumination as the probe, alongside optical and electric pulses as pump excitation. A unified electronic synchronization scheme based on a high-speed photodiode and a digital delay generator enables precise timing control among the optical pump, electrical pump, and photoelectron pulses across the nanosecond-to-microsecond range. Using vanadium dioxide (VO2) as a model system, we demonstrate a combined spatiotemporal resolution with measurable signals on the order of 10 nm–10 ns, allowing real-space mapping of spatially inhomogeneous dynamics. Electrical-pump experiments further reveal Joule-heating-induced non-uniform structural phase transitions and thermal-shock-excited megahertz-range mechanical oscillations. These results establish the developed multi-field UTEM platform as a practical tool for probing local structural dynamics in functional materials under optical and electrical excitation.

To address the limitations in temporal resolution of an ultrafast electron microscope (UEM) and the shortcomings of existing pulsed-electron characterization methods, we introduce a fast, energy-filter-free technique for measuring electron pulse duration that exploits the interaction between free electrons and the phase-matched near-field of a periodic grating. The interaction induces a measurable transverse broadening of the electron beam, which directly encodes the temporal profile of the electron pulse. Implementing this method on a Wehnelt-controlled UEM, we observe an asymmetric temporal distribution with a long trailing edge at high bias voltage. Finite-element simulations of electron trajectories replicate the experimental trends and identify the temporal aberration of the electrostatic lens as the primary cause of asymmetric broadening. This approach enables rapid, high-precision diagnostics of electron-pulse characteristics without requiring an energy-filter spectrometer, and the findings provide valuable insights into the factors that presently limit UEM temporal resolution.

Abstract Layered topological insulators such as Bi 2 Se 3 exhibit rich phonon dynamics, which are crucial for understanding their thermal transport mechanisms and electronic properties. In this work, we investigate the multiscale nonequilibrium lattice dynamics in Bi 2 Se 3 thin films using ultrafast transmission electron microscopy (UTEM). By exploiting the complementarity between real-space ultrafast electron microscopy (UEM) and ultrafast electron diffraction (UED), we show that the characteristic frequencies of the lattice dynamics are consistent in real and reciprocal space. This cross-validation supports the interpretation that the transient anti-phase oscillation of Friedel diffraction pairs originates from reciprocal-space geometric evolution induced by the breathing mode: under large-angle tilting, reciprocal rods with nonzero out-ofplane Miller indices undergo periodic stretching and displacement along the c * axis, thereby asymmetrically changing their intersections with the Ewald sphere. This process corresponds directly to the coherent motion of lattice bend contours observed in real space. The study further reveals that phonon propagation exhibits pronounced scale dependence. On the picosecond timescale, the dynamics are dominated by a longitudinal standing-wave breathing mode confined by the film thickness, with the oscillation frequency following an inverse dependence on film thickness. Under the [001] zone-axis condition, defect-mediated in-plane traveling waves propagating at the speed of sound are observed. Furthermore, on the nanosecond timescale, the suspended thin film exhibits mechanical resonance with a high quality factor, accompanied by a rich spectrum of higher-order harmonics. These findings provide direct visual evidence for the multilevel dynamical responses of coherent phonons under the same pump excitation, manifesting at different timescales and boundary conditions from the gigahertz (GHz) to megahertz (MHz) regime, highlighting the potential of Bi 2 Se 3 for high-frequency nanomechanical applications.

Exploring advanced techniques capable of probing nanometric acoustic waves in nanostructures is critically important for the development of miniaturized acoustic devices.In this study,we probe the optically-excited acoustic waves in a single silicon nanowire(NW)using the time-resolved(tr-)high-order Laue-zone(HOLZ)lines under convergent-beam electron diffraction(CBED)conditions in an ultrafast transmission electron microscope(UTEM).We devise an experimental scheme to obtain tr-HOLZ lines under off-zone-axis CBED conditions.We also propose a geometric description of HOLZ line formation and use this alternative description to quantitatively evaluate the dynamics of optically-excited silicon NW.Using part of the deformation gradient tensor,our simulations of the dynamics of Si NW reproduce the experimental results.We further discuss the feasibility of a full retrieval of the deformation gradient tensor by using a set of HOLZ lines from three zone axes.Our findings illustrate a strategy for the quantitative access to dynamical acoustic waves optically excited in micro-and nano-structures using UTEM.

The microscopic crystalline structure of materials is widely recognized as having a profound impact on their functional properties and application potential. Alterations to the lattice often provide distinctive opportunities to finely tune specific properties, particularly in strongly correlated systems. A paradigmatic case is the iron‐based high‐temperature superconductors, where the microstructure plays an important role in modulating superconductivity. In this work, aberration‐corrected scanning transmission electron microscopy (STEM) is employed to investigate the microstructure and intrinsic chemical heterogeneity of Fe 1+y Te, Fe 1+y Te 0.8 Se 0.2 , and Fe 1+y Te 0.5 Se 0.5 . A previously unforeseen superstructure phase, characterized by a wave vector q = (0.4, 0, 0.5), arising from the ordered arrangement of interstitial iron atoms, is clearly visible in the parent compound Fe 1+y Te. Under these specific structural conditions, interstitial iron atoms interact with adjacent Fe atoms, forming iron polycomplexes that induce pronounced distortions in the FeTe 4 tetrahedra and may potentially foster the emergence of ferromagnetic clusters. The experimental findings further illustrate that appropriate Se substitution effectively suppresses interstitial iron concentration and ordering, with Fe 1+y Te 0.5 Se 0.5 notably exhibiting the lowest concentration. The observations also suggest that Se substitution occurs randomly and Te/Se‐induced nanoscale phase separation, driven by chemical heterogeneity is commonly observed within Fe 1+y Te 1−x Se x crystals.

The Chevrel phase (CP), characterized by its unique Mo6X8 (X = S, Se, Te) cluster structure, represents a class of promising materials demonstrating exceptional performance in various applications, including battery cathodes, electrocatalysts, and superconductors. However, the exploration of new CP derivatives remains challenging due to the inherent lattice destabilization caused by cation intercalation, particularly evident in selenide and telluride systems. This study reports the successful synthesis of thermodynamically metastable K1+δMo6Se8 (δ ∼ 0.37) and the superconducting properties therein. K1+δMo6Se8 crystallizes in the triclinic space group P1̅ (No. 2), where potassium cations occupy interstitial sites between the Mo6Se8 clusters. Comprehensive characterization through electrical resistivity, magnetization, and specific heat measurements reveals bulk superconductivity at Tc = 8.9 K. Notably, the upper critical field is estimated to be 26.4 T, violating the Pauli paramagnetic limit. Furthermore, low-temperature specific heat analysis indicates possible multigap superconducting behavior. Our findings not only expand the family of high-critical-field superconducting CPs but also demonstrate the potential to synthesize novel CP materials through solid-state reactions at lower temperatures.

The Chevrel phase (CP), characterized by its unique Mo6X8 (X = S, Se, Te) cluster structure, represents a class of promising materials demonstrating exceptional performance in various applications, including battery cathodes, electrocatalysts, and superconductors. However, the exploration of new CP derivatives remains challenging due to the inherent lattice destabilization caused by cation intercalation, particularly evident in selenide and telluride systems. This study reports the successful synthesis of thermodynamically metastable K1+delta Mo6Se8 (delta similar to 0.37) and the superconducting properties therein. K1+delta Mo6Se8 crystallizes in the triclinic space group P1 (No. 2), where potassium cations occupy interstitial sites between the Mo6Se8 clusters. Comprehensive characterization through electrical resistivity, magnetization, and specific heat measurements reveals bulk superconductivity at T c = 8.9 K. Notably, the upper critical field is estimated to be 26.4 T, violating the Pauli paramagnetic limit. Furthermore, low-temperature specific heat analysis indicates possible multigap superconducting behavior. Our findings not only expand the family of high-critical-field superconducting CPs but also demonstrate the potential to synthesize novel CP materials through solid-state reactions at lower temperatures.

The reduction of radiation damage represents a long-term objective for electron microscopists, particularly those engaged in the study of biological and organic matter. Recently, electron pulses in ultrafast transmission electron microscopy have been demonstrated to serve as a damage mitigation technique for radiation-sensitive materials. Nevertheless, the underlying mechanism of the mitigation effects remains unclear. In this study, we investigate the radiation damage of graphene induced by pulsed electrons using molecular dynamics simulations within the framework of binary elastic collisions. For electron irradiation at 200 keV, it was found that the pulsed electron beam corresponds to a larger threshold angle (1.4 rad) than that for a random beam (1.0 rad). This is because two electrons can be prevented from briefly interacting with the same or a neighboring atom by the use of well-controlled electron pulses. While such a mitigation of radiation damage is only apparent near the threshold angle, and there are likely other reduction mechanisms, our results provide insight into the mitigated radiation damage of electron pulses.

Manipulation of the stacking order between layers in two-dimensional layered van der Waals materials provides a fascinating platform for exploring exotic phenomena. Femtosecond laser offers the capability to instantaneously modulate the lattice structure and even stacking order of layered materials, and vice versa, changes in stacking order may affect ultrafast structural dynamics. Here, we use ultrafast electron microscopy (UEM) to investigate the laser-excited lattice dynamics in T' and Td phases of octahedral MoTe2. Two crystal plane-dependent acoustic phonon modes in the room temperature T' phase are identified by ultrafast selected-area electron diffraction (SAED) in reciprocal space and confirmed by ultrafast real-space imaging, which are attributed to the breathing mode and shear mode, respectively. Temperature-dependent ultrafast SAED results directly indicate that the acoustic shear mode switches to the optical shear mode when the stacking order is changed by crossing the phase transition temperature. Based on simple model derivations, shear acoustic waves in principle can be excited by the thermal elastic effect in low-symmetric 2D layered materials. However, incorporating numerical calculations and model analysis, we speculate that the laser-induced inverse piezoelectric effect plays a key role in the large-amplitude shear phonons observed in T'-MoTe2. Our research demonstrates examples of stacking sequence identification using coherent phonons revealed by UEM, as well as the regulation of coherent shear phonons and topology switching via stacking order.

The microscopic crystalline structure of materials is widely recognized as having a profound impact on their functional properties and application potential. Alterations to the lattice often provide distinctive opportunities to finely tune specific properties, particularly in strongly correlated systems. A paradigmatic case is the iron-based high-temperature superconductors, where the microstructure plays an important role in modulating superconductivity. In this work, aberration-corrected scanning transmission electron microscopy (STEM) is employed to investigate the microstructure and intrinsic chemical heterogeneity of Fe1+yTe, Fe1+yTe0.8Se0.2, and Fe1+yTe0.5Se0.5. A previously unforeseen superstructure phase, characterized by a wave vector q = (0.4, 0, 0.5), arising from the ordered arrangement of interstitial iron atoms, is clearly visible in the parent compound Fe1+yTe. Under these specific structural conditions, interstitial iron atoms interact with adjacent Fe atoms, forming iron polycomplexes that induce pronounced distortions in the FeTe4 tetrahedra and may potentially foster the emergence of ferromagnetic clusters. The experimental findings further illustrate that appropriate Se substitution effectively suppresses interstitial iron concentration and ordering, with Fe1+yTe0.5Se0.5 notably exhibiting the lowest concentration. The observations also suggest that Se substitution occurs randomly and Te/Se-induced nanoscale phase separation, driven by chemical heterogeneity is commonly observed within Fe1+yTe1-xSex crystals.

Efficient coupling between light and bulk plasmons (BPs) remains a central challenge because of their inherent mode mismatch, limited penetration depth, and pronounced resonant energy mismatch between visible-range photons and BPs. In this work, we demonstrate that ultrafast free electrons can coherently mediate an interaction between electromagnetic fields and BPs at the nanoscale. An electron pulse emitted from the photocathode of ultrafast transmission electron microscope, functions as a quantum intermediary that is capable of simultaneously interacting with the laser field by multiphoton processes and BPs by perturbative scattering. Electron energy-loss spectroscopy can capture this indirect interaction, the final electron energy distribution encodes both quantum pathways arising from distinct combinations of multiphoton absorption and emission and BP scattering events. Interference among these pathways gives rise to characteristic spectral modulations, directly revealing the exchange of energy and information between photons and BPs via the electron delivery. Our results show that femtosecond-driven, ultrafast electrons provide a viable route to modulate and even control bulk plasmon excitations in a volume, thereby extending beyond the conventional nanoplasmonics schemes on manipulating surface plasmons by light. This indirect light-BP interaction paves the promising way for exploring fundamental light-matter interaction at ultrafast and nanometer scales.