Diamond nitrogen-vacancy (NV) center quantum magnetic sensors show great potential for high-precision magnetic field measurement, but their complex, bulky discrete systems limit high-voltage electrical applications. This paper designs a compact "optical input-electrical output" sensing probe (3.12cm3) integrating optical excitation, fluorescence collection, and photoelectric conversion. With optimal magnetic sensitivity of 4.92nT/Hz1/2, average 6.5nT/Hz1/2, and low standard deviation (0.8nT/Hz1/2), it resolves insulation, anti-interference, and power consumption bottlenecks, enabling high-voltage equipment magnetic field monitoring.

In the realm of condensed matter physics, the properties of material are largely determined by the degrees of freedom associated with lattice, charge, orbital, and spin, as well as their intricate interplay. Unveiling the coupling mechanisms between these freedoms and effectively manipulating them necessitate a profound exploration into ultrafast dynamics, owing to the nanoseconds, femtoseconds, and even attoseconds timescales governing these fundamental interactions. Ultrafast transmission electron microscopy (UTEM) emerges as a powerful technique enabling the research of ultrafast dynamics with exceptional spatial-temporal resolution, showcasing diverse applications within nanoscale systems. Over the past decades, UTEM has witnessed significant advancements in instrument development, fostering its widespread utilization across various domains. This review firstly introduces the fundamental principles of UTEM and traces its historical evolution, intricately involving the integration of the pump-probe principle with transmission electron microscopy. Subsequently, the key performance characteristics of UTEM are succinctly summarized. Moreover, a detailed exposition is provided on the manifold applications of UTEM, encompassing structural dynamics, magnetic phenomena, and near-field optics, each delineated according to their respective time-resolved methodologies. Concluding the review, a forward-looking perspective on the UTEM technique is presented, envisioning its significance in the realm of ultra-fast dynamics research. UTEM

The ongoing downscaling of semiconductor devices necessitates gate dielectric materials that simultaneously possess a wide bandgap and ultrahigh dielectric constant to ensure efficient gate control. However, such materials remain scarce due to the inherent trade-off between bandgap widening and dielectric response enhancement in conventional insulators. Here, we demonstrate bismuth oxyfluoride (BiOF) as a promising dielectric candidate with a wide bandgap (Eg ≈ 4.5 eV) and a high out-of-plane dielectric constant (κ = 22.5). Moreover, we develop a scalable solid-state route for synthesizing phase-pure BiOF powder and achieve the chemical vapor deposition (CVD) growth of ultrathin BiOF nanosheets. The free-standing characteristic, temperature-stable dielectric properties, and inert van der Waals (vdW) surface of BiOF facilitate its seamless integration with two-dimensional (2D) materials to enhance device performance. Few-layer graphene double-encapsulated by BiOF demonstrates superior electron Hall mobility (μe,2K ≈ 134,000 cm2 V-1 s-1) and pronounced Shubnikov-de Haas (SdH) oscillations at 2 K. Our work not only expands the library of high-κ vdW materials but also overcomes the intrinsic trade-off between dielectric constant and bandgap.

Distinguishing surface recombination from subsurface transport is vital for optoelectronics but remains challenging in scanning ultrafast electron microscopy (SUEM) because of signal convolution. Here, we demonstrate that the detector bias (Vf) enables effective depth-selective probing to spatially disentangle these competing dynamics within the near-surface region. Experiments on p-type silicon reveal a striking voltage-tunable contrast inversion, marking a transition from surface-dominated to subsurface-dominated regimes. We attribute this to a mechanistic competition between surface potential restoration governing collection and subsurface band flattening modulating emission. Multiphysics simulations confirm this framework by linking depth-dependent charge distributions to contrast evolution. We thus achieve independent visualization of spatially entangled processes, specifically isolating surface trapping from subsurface diffusion and providing a physical basis for resolving vertical carrier stratification.

Indium phosphide (InP), a promising III-V semiconductor material, demonstrates exceptional photocatalytic potential due to its moderate bandgap and high exciton mobility. Despite its advantages, enhancing the photo-catalytic efficiency of InP remains a challenge, primarily due to the rapid carrier recombination and insufficient charge transport. Here, we investigate the effects of silver nanoparticle (Ag NPs) decoration on InP's carrier dynamics using scanning ultrafast electron microscopy (SUEM), which enables the observation of charge separation, diffusion, and recombination at femtosecond and nanometer scales. The SUEM imaging results show that Ag NPs can substantially enhance light absorption and carrier excitation through localized surface plasmon resonance (LSPR) effects, significantly improving charge separation and reducing recombination. Crucially, the presence of Ag NPs significantly accelerates the charge diffusion, allowing carriers to persist longer and diffuse faster compared to InP. Furthermore, the introduction of Ag films, which form a Schottky barrier at the metal-semiconductor interface, was shown to improve charge separation but exhibited limited diffusion due to the absence of the LSPR effect and the existence of more interface states. This work provides new insights into how metal NP decoration modulates carrier dynamics in semiconductors, which are pivotal for advancing the design of photocatalytic materials and optoelectronic devices.

Ultrafast transmission electron microscopy (UTEM) has gained wide applications in the nanoscale dynamics with femtosecond, even attosecond, resolution. The instrument development is still in progress to satisfy the various applications. At Nankai University, we built an UTEM with a laser-driven Schottky field emitter based on a field emission TEM (Talos200i) of Thermo Fisher Scientific. This study comprehensively examines the performance of the UTEM, including the continuous mode and ultrafast photoemission mode. The investigation focuses on optimizing brightness, temporal resolution, energy dispersion, and stability in ultrafast photoemission mode, achieving a temporal resolution of ∼200 fs and an energy dispersion of 0.7 eV with excellent stability through careful adjustments of laser parameters and equipment settings. In scanning transmission electron microscopy mode, the beam size of the photoemission mode is ∼1.4 nm at specific settings with potential for further improvement. As application examples, we illustrate the results of photoinduced structural dynamics of gold film and MoS2 thin flake by ultrafast electron diffraction. We also report the polarization dependent optical interference pattern characterized by the photoinduced near field microscopy effect in a silicon thin film sample prepared by the focused ion beam method. These findings provide valuable insights for researchers aiming to leverage the UTEM’s capabilities for advanced electron microscopy applications and pave the way for future advancements in UTEM technology.

Carrier dynamics at Schottky junction interfaces are crucial for optimizing photoconversion efficiency in photovoltaic, optoelectronic, and photoelectrochemical devices. However, accurately detecting the embedded interfaces remains challenging, particularly with regard to the dynamics of carriers within the two-dimensional (2D) interfacial plane. Here, we use scanning ultrafast electron microscopy (SUEM) to directly image spatiotemporal photocarrier dynamics at the n-type gallium arsenide (n-GaAs)/aluminum (Al) Schottky interface with a nanoscale thickness. The recorded SUEM movies demonstrate that the electrons and holes are separated by the built-in electric field with holes subsequently trapped by interface states. These trapped holes exhibit a quasi-2D subdiffusion behavior along the junction interface via hopping through the interface states. Numerical simulations based on a developed subdiffusion dynamical model well repeat the observations. Our findings provide new insights into the carrier transport dynamics in Schottky junctions and unravel the pivotal role of the interface states.

The peculiar defect-related photon emission processes in 2D hexagonal boron nitride (hBN) have become a topic of intense research due to their potential applications in quantum information and sensing technologies. Here, it is reported on exotic single photons and enhanced deep-level emissions in 2D hBN strain crystal, which is fabricated by transferring multilayer hBN onto hexagonal close-packed silica spheres on a silica substrate. Effective activation of single photon emission is realized from the defect ensembles in the multilayer hBN at positions that are in contact with the apex of the SiO2 spheres. At these points, the local tensile strain-induced overall blue shift of the SPE ensembles is up to 12 nm. Furthermore, high spatial resolution cathodoluminescence measurements show remarkable strain-enhanced deep-level emissions in the multilayer hBN with the emission intensity distribution following the periodic hexagonal pattern of the strain crystal. The maximum deep-level emission enhancement is up to 350% with an energy redshift of 6 nm. These results provide a simple on-chip compatible method for activating and tuning the defect-related photon emissions in multilayer hBN, demonstrating the potential of hBN strain crystal as a building block for future on-chip quantum nanophotonic devices. The unique photon emissions from defects in 2D hexagonal boron nitride have garnered significant attention due to their potential in quantum information technologies. In this study, effective single photon emission, and intensified deep-level emissions within a strained 2D hBN crystal are successfully induced. Furthermore, the underlying physical mechanisms and the rules governing strain modulation are also well elucidated.image

Two-dimensional (2D) alloys hold great promise to serve as important components of 2D transistors, since their properties allow continuous regulation by varying their compositions. However, previous studies are mainly limited to the metallic/semiconducting ones as contact/channel materials, but very few are related to the insulating dielectrics. Here, we use a facile one-step chemical vapor deposition (CVD) method to synthesize ultrathin Bi2SixGe1-xO5 dielectric alloys, whose composition is tunable over the full range of x just by changing the relative ratios of the GeO2/SiO2 precursors. Moreover, their dielectric properties are highly composition-tunable, showing a record-high dielectric constant of >40 among CVD-grown 2D insulators. The vertically grown nature of Bi2GeO5 and Bi2SixGe1-xO5 enables polymer-free transfer and subsequent clean van der Waals integration as the high-kappa encapsulation layer to enhance the mobility of 2D semiconductors. Besides, the MoS2 transistors using Bi2SixGe1-xO5 alloy as gate dielectrics exhibit a large I-on/I-off (>10(8)), ideal subthreshold swing of similar to 61 mV/decade, and a small gate hysteresis (similar to 5 mV). Our work not only gives very few examples on controlled CVD growth of insulating dielectric alloys but also expands the family of 2D single-crystalline high-kappa dielectrics.

Long persistent luminescence (LPL) materials widely employed in the fields of emergency lighting and anti‐counterfeiting are mostly used at room temperature. As temperatures rise, the performance of LPL materials deteriorates dramatically, which hinders their application in in vivo imaging, high‐temperature display, and information storage. Herein, a multifunctional material LiGa 5 O 8 :Tb 3+ (LGT) with green high‐temperature LPL (HT‐LPL) and blue cathodoluminescence (CL) is reported. Its LPL performance is anomalously enhanced with increasing temperature, and the duration time is more than 8 h at 423 K. With combined temperature‐dependent decay curves and thermoluminescence analyses, the unique quasi‐continuous defect levels are found in the band gap. The high‐concentration carriers in deep traps are frozen at room temperature and activated only at high temperatures, accompanied by changes in energy transfer pathways. The excellent HT‐LPL makes LGT a light‐emitting component of next‐generation smart wearable devices, as well as high‐temperature warning equipment in deep well exploration at a depth of 4500 m. The intense anti‐degradation blue CL makes it suitable for field emission displays, while the manipulable emission property makes it suitable for high‐level anti‐counterfeiting. This study fills a gap in HT‐LPL materials and opens up a new gateway for the efficient design of HT‐LPL and other multifunctional materials.

Regulating the electronic structures and carrier dynamics in 2D materials via elastic strain is a fascinating avenue for tailoring their optoelectronic properties at atomic scale. Here, the abnormal response of indirect excitons to non-uniform elastic strain in MoS2 flakes is reported. The non-uniform elastic strain in the MoS2 flakes is introduced by transferring them to pre-prepared convex cross structures on a SiO2/Si substrate, where the topography and strain distribution are determined by atomic force microscopy and Raman spectroscopy, respectively. It is observed that the emission energy of the indirect excitons shows an unexpected blue-shift followed by a red-shift with increasing the local tensile strain, which is in sharp contrast to the linear red-shift of the direct excitons. Density functional theory calculations reveal that the abnormal energy shift of the indirect excitons in the MoS2 flakes arises from the strain-induced competition between two indirect bandgap transitions and the spatial exciton funnel effect in the non-uniform strain field. This work provides new insights into the elastic strain effect on the indirect excitons in 2D semiconductors, which possesses potential applications in flexible optoelectronic devices.

Carrier dynamics detection in different dimensions (space, time, and energy) with high resolutions plays a pivotal role in the development of modern semiconductor devices, especially in low-dimensional, high-speed, and ultrasensitive devices. Here, a femtosecond electron-based versatile microscopy is reported that combines scanning ultrafast electron microscopy (SUEM) imaging and time-resolved cathodoluminescence (TRCL) detection, which allows for visualizing and decoupling different dynamic processes of carriers involved in surface and bulk in semiconductors with unprecedented spatiotemporal and energetic resolutions. The achieved spatial resolution is better than 10 nm, and the temporal resolutions for SUEM imaging and TRCL detection are ≈500 fs and ≈4.5 ps, respectively, representing state-of-the-art performance. To demonstrate its unique capability, the surface and bulk carrier dynamics involved in n-type gallium arsenide (GaAs) are directly tracked and distinguished. It is revealed, in real time and space, that hot carrier cooling, defect trapping, and interband-/defect-assisted radiative recombination in the energy domain result in ordinal super-diffusion, localization, and sub-diffusion of carriers at the surface, elucidating the crucial role of surface states on carrier dynamics. The study not only gives a comprehensive physical picture of carrier dynamics in GaAs, but also provides a powerful platform for exploring complex carrier dynamics in semiconductors for promoting their device performance.

Mixed-dimensional heterostructures have drawn significant attention due to their intriguing physical properties and potential applications in electronic and optoelectronic nanodevices. However, limited by the lattice matching, the preparation of heterostructures is experimentally difficult and the underlying growth mechanism has not been well established. Here, we report a three-step seeding epitaxial growth strategy for synthesizing mixed-dimensional heterostructures of one-dimensional microwire (MW) and two-dimensional atomic thin film. Our growth strategy has successfully realized direct epitaxial growth of WSe2 film on WOx MW and significantly improves the quality of the epitaxial WSe2 monolayer, which is evidenced by the remarkably enhanced photoluminescence (PL). More intriguingly, the as-synthesized WOx MWs exhibit a strong nonlinear optical response due to the enhancement effect of the core (WOx)-shell (WSe2) nanocavity. Our work provides a feasible route for direct growth of WOx-based mixed-dimensional heterostructures, which possess potential applications in high-performance optoelectronic devices.

The peculiar defect-related photon emission processes in 2D hexagonal boron nitride (hBN) have become a topic of intense research due to their potential applications in quantum information and sensing technologies. Recent efforts have focused on activating and modulating the defect energy levels in hBN by methods that can be integrated on a chip, and understanding the underlying physical mechanism. Here, we report on exotic single photon and enhanced deep-level emissions in 2D hBN strain superlattice, which is fabricated by transferring multilayer hBN onto hexagonal close-packed silica spheres on silica substrate. We realize effective activation of the single photon emissions (SPEs) in the multilayer hBN at the positions that are in contact with the apex of the SiO2 spheres. At these points, the local tensile strain induced blue-shift of the SPE is found to be up to 12 nm. Furthermore, high spatial resolution cathodoluminescence measurments show remarkable strain-enhanced deep-level (DL) emissions in the multilayer hBN with the emission intensity distribution following the periodic hexagonal pattern of the strain superlattice. The maximum DL emission enhancement is up to 350 energy redshift of 6 nm. Our results provide a simple on-chip compatible method for activating and tuning the defect-related photon emissions in multilayer hBN, demonstrating the potential of hBN strain superlattice as a building block for future on-chip quantum nanophotonic devices.

Elastic strain has been an important method to regulate the electronic structures and physical properties of nanoscale semiconductors due to the promising potentials in improving the performance of their optoelectronic devices. Here, we report the investigation of bending strain effects on the optical and optoelectric properties of individual gallium nitride (GaN) nanowires (NWs). By charactering the near-band emission spectrum of individual GaN NWs at different bending strains with low temperature cathodoluminescence (CL), we reveal that the near-band emission splits into two peaks, where the low energy peak displays a linear redshift with increasing the bending strain while the high energy one shows a slight blueshift. Further localized ultraviolet (UV) photoresponse measurements illustrate that the photoresponse of the GaN NWs shows a linear increase with the bending train, and the maximum enhancement is more than two orders of magnitude. The experimental observations are well interpreted by theoretical calculations on the strain modulation on the electronic band structure of GaN combined with analysis of carrier dynamics and optical waveguide effect in the bending strain field. Our results not only shed light on the bending strain effects on the optical and optoelectric properties of semiconductors, but also hold potential to help the future design of high performance nano-optoelectric devices.

Elastic strain engineering is an important way to reversibly tune the properties of micro/nanoscale semiconductors for promising applications in the emerging advanced nanotechnologies, such as the strain enhanced high-mobility transistors, nanogenerators, etc. However, direct observation and control of energetic carrier dynamics with precise strain gradient fields remains a challenge. Here, observation of temperature-dependent exciton funnel dynamics is reported in a precisely controlled strain gradient field by time-resolved photoluminescence. An efficient exciton hopping process is revealed at picosecond time scale as the donor-bound excitons in ZnO microwires funnel along the strain gradient, which strongly depends on the temperature. Combined experiments and simulations unravel that, in addition to the exciton funnel by the strain gradient, both the excitation efficiency and emission lifetime of the excitons increase gradually from the compressive side to the tensile side due to the role of local strain regulation. The results give a clear physical picture of the energetic carrier dynamics in the strain gradient field in semiconductors, which provides a promising paradigm for the design of high-performance optoelectronic devices.