In Situ Lattice-Resolution Revelation of the Origins of Unexplored Anisotropic Sodiation Kinetics and Phase Transition in the Niobium Sulfide Anode.

Layered transition metal dichalcogenides (TMDs) have exhibited huge potential as anode materials for sodium-ion batteries. Most of them usually store sodium via an intercalation-conversion mechanism, but niobium sulfide (NbS2) may be an exception. Herein, through in situ transmission electron microscopy, we carefully investigated the insertion behaviors of Na ions in NbS2 and directly visualized anisotropic sodiation kinetics. Lattice-resolution imaging coupled with density functional theory calculations reveals the preferential diffusion of Na ions within layers of NbS2, accompanied by observable interlayer lattice expansion. Impressively, the Na-inserted layers can still withstand in situ mechanical testing. Further in situ observation vertical to the a/b plane of NbS2 tracked the illusive conversion reaction, which could result from interlayer gliding or wrinkling associated with stress accumulation. In situ electron diffraction measurements ruled out the possibility of such a conversion mechanism and identified a phase transition from pristine 3R-NbS2 to 2H-NaNbS2. Therefore, the NbS2 anode stores Na ions via only the intercalation mechanism, which conceptually differs from the well-known intercalation-conversion mechanism of typical TMDs. These findings not only decipher the whole sodiation process of the NbS2 anode but also provide valuable reference for unraveling the precise sodium storage mechanism in other TMDs.

High-Performance Solar-Blind Photodetector Based on (010)-Plane ß-Ga2O3 Thermally Oxidized from Nonpolar (110)-Plane GaN.

A high-performance planar structure metal-semiconductor-metal-type solar-blind photodetector (SBPD) was fabricated on the basis of (010)-plane ß-Ga2O3 thermally oxidized from nonpolar (110)-plane GaN. A full width at half maximum of 0.486° was achieved for the X-ray rocking curve associated with (020)-plane ß-Ga2O3, which is better than most reported results for the heteroepitaxially grown (-201)-plane ß-Ga2O3. As a result of the relatively high crystalline quality, a dark current as low as 6.30 × 10-12 A was achieved at 5 V, while the photocurrent reached 1.86 × 10-5 A under 254 nm illumination at 600 µW/cm2. As a result, the photo-to-dark current ratio, specific detectivity, responsivity, and external quantum efficiency were calculated to be 2.95 × 106, 2.39 × 1012 Jones, 3.72 A/W, and 1815%, respectively. Moreover, the SBPD showed excellent repeatability and stability in the time-dependent photoresponse characteristics with fast relaxation time constants for the rise and decay processes of only 0.238 and 0.062 s, respectively. This study provides a promising approach to fabricate the device-level (010)-plane ß-Ga2O3 film and a new way for the epitaxial growth of (010)-plane ß-Ga2O3 and (110)-plane GaN as mutual substrates.

Enhanced reduction of graphene oxide via laser-dispersion coupling: Towards large-scale, low-defect graphene for crease-free heat-dissipating membranes in advanced flexible electronics.

The advancement of flexible electronics demands improved components, necessitating heat dissipation membranes (HDMs) to exhibit high thermal conductivity while maintaining structural integrity and performance stability even after extensive deformation. Herein, we have devised a laser-modulated reduction technique for graphene oxide (GO), enabling the fabrication of high-quality, large-scale, low-defect graphene, which yields high-performance HDMs after orderly deposition. The work underscores the crucial role of the laser wavelength and dispersion liquid's coupling intensity in influencing the morphology and properties of graphene. Optimal coupling effect and energy conversion are realized when a laser of 1064 nm wavelength irradiates a triethylene glycol (TEG)/N,N-Dimethylformamide (DMF) dispersion. This unique synergy generates high transient energy, which facilitates the deprotonation process and ensures a swift, comprehensive GO reduction. In contrast to conventional water-based laser reduction methods, the accelerated reaction magnifies the size of the graphene sheets by mitigating the ablation effect. After membrane construction with an ordered structure, the corresponding membrane exhibits a high thermal conductivity of 1632 W m-1 K-1, requiring only ∼1/10 of the total preparation time required by other reported methods. Remarkably, the resulting HDM demonstrates superior resilience against creasing and folding, maintaining excellent smoothness and negligible reduction in thermal conductivity after violent rubbing. The combination of exceptional flexibility and thermal conductivity in HDMs paves the way for long-term practical use in the flexible electronics industry.

Simulating Synaptic Behaviors through Frequency Modulation in a Capacitor-Memristor Circuit.

Memristors, known for their adjustable and non-volatile resistance, offer a promising avenue for emulating synapses. However, achieving pulse frequency-dependent synaptic plasticity in memristors or memristive systems necessitates further exploration. In this study, we present a novel approach to modulate the conductance of a memristor in a capacitor-memristor circuit by finely tuning the frequency of input pulses. Our experimental results demonstrate that these phenomena align with the long-term depression (LTD) and long-term potentiation (LTP) observed in synapses, which are induced by the frequency of action potentials. Additionally, we successfully implement a Hebbian-like learning mechanism in a simple circuit that connects a pair of memristors to a capacitor, resulting in observed associative memory formation and forgetting processes. Our findings highlight the potential of capacitor-memristor circuits in faithfully replicating the frequency-dependent behavior of synapses, thereby offering a valuable contribution to the development of brain-inspired neural networks.

In Situ Atomic-Scale Deciphering of Multiple Dynamic Phase Transformations and Reversible Sodium Storage in Ternary Metal Sulfide Anode.

Ternary metal sulfides (TMSs), endowed with the synergistic effect of their respective binary counterparts, hold great promise as anode candidates for boosting sodium storage performance. Their fundamental sodium storage mechanisms associated with dynamic structural evolution and reaction kinetics, however, have not been fully comprehended. To enhance the electrochemical performance of TMS anodes in sodium-ion batteries (SIBs), it is of critical importance to gain a better mechanistic understanding of their dynamic electrochemical processes during live (de)sodiation cycling. Herein, taking BiSbS3 anode as a representative paradigm, its real-time sodium storage mechanisms down to the atomic scale during the (de)sodiation cycling are systematically elucidated through in situ transmission electron microscopy. Previously unexplored multiple phase transformations involving intercalation, two-step conversion, and two-step alloying reactions are explicitly revealed during sodiation, in which newly formed Na2BiSbS4 and Na2BiSb are respectively identified as intermediate phases of the conversion and alloying reactions. Impressively, the final sodiation products of Na6BiSb and Na2S can recover to the original BiSbS3 phase upon desodiation, and afterward, a reversible phase transformation can be established between BiSbS3 and Na6BiSb, where the BiSb as an individual phase (rather than respective Bi and Sb phases) participates in reactions. These findings are further verified by operando X-ray diffraction, density functional theory calculations, and electrochemical tests. Our work provides valuable insights into the mechanistic understanding of sodium storage mechanisms in TMS anodes and important implications for their performance optimization toward high-performance SIBs.

Research Progress on Metal-Organic Frameworks by Advanced Transmission Electron Microscopy.

Metal-organic frameworks (MOFs), composed of metal nodes and inorganic linkers, are promising for a wide range of applications due to their unique periodic frameworks. Understanding structure-activity relationships can facilitate the development of new MOFs. Transmission electron microscopy (TEM) is a powerful technique to characterize the microstructures of MOFs at the atomic scale. In addition, it is possible to directly visualize the microstructural evolution of MOFs in real time under working conditions via in situ TEM setups. Although MOFs are sensitive to high-energy electron beams, much progress has been made due to the development of advanced TEM. In this review, we first introduce the main damage mechanisms for MOFs under electron-beam irradiation and two strategies to minimize these damages: low-dose TEM and cryo-TEM. Then we discuss three typical techniques to analyze the microstructure of MOFs, including three-dimensional electron diffraction, imaging using direct-detection electron-counting cameras, and iDPC-STEM. Groundbreaking milestones and research advances of MOFs structures obtained with these techniques are highlighted. In situ TEM studies are reviewed to provide insights into the dynamics of MOFs induced by various stimuli. Additionally, perspectives are analyzed for promising TEM techniques in the research of MOFs' structures.

Heterostructured Interface Enables Uniform Zinc Deposition for High-Performance Zinc-Ion Batteries.

Zinc metal has considerable potential as a high-energy anode material for aqueous batteries due to its high theoretical capacity and environmental friendliness. However, dendrite growth and parasitic reactions at the electrode/electrolyte interface remain two serious problems for the Zn metal anode. Here, the heterostructured interface of ZnO rod array and CuZn5 layer is fabricated on the Zn substrate (ZnCu@Zn) to address these two issues. The zincophilic CuZn5 layer with abundant nucleation sites ensures the initial uniform Zn nucleation process during cycling. Meanwhile, the ZnO rod array grown on the surface of the CuZn5 layer can guide the subsequent homogeneous Zn deposition via spatial confinement and electrostatic attraction effects, leading to the dendrite-free Zn electrodeposition process. Consequently, the derived ZnCu@Zn anode exhibits an ultra-long lifespan of up to 2500 h with symmetric cells at the current density and capacity of 0.5 mA cm-2 /0.5 mA h cm-2 . Besides, a remarkable cyclability (75% retention for 2500 cycles at 2 A g-1 ) is achieved in the ZnCu@Zn||MnO2 full cell with a capacity of 139.7 mA h g-1 . This heterostructured interface with specific functional layers provides a feasible strategy for the design of high-performance metal anodes.

In situ crafting of a 3D N-doped carbon/defect-rich V2O5-x·nH2O nanosheet composite for high performance fibrous flexible Zn-ion batteries.

Aqueous fibrous batteries with tiny volume, light weight and stretchability have furthered wearable smart textile systems like biocompatible electronics for a more efficient use of electricity. Challenges still faced by fibrous batteries include not only the deficient actual capacity but the cyclability on the cathode side. Herein, an in situ anodic oxidation strategy is reported to prepare 3D N-doped/defect-rich V2O5-x·nH2O nanosheets (DVOH@NC) as fibrous cathodes for aqueous zinc-ion batteries (AZIBs). Benefiting from the substantially abundant reaction sites, enhanced electrical conductivity, short electron/ion diffusion path and high mass loading, the newly designed DVOH@NC fibrous electrode delivers impressive capacity (711.9 mA h cm-3 at 0.3 A cm-3) and long-term durability (95.5% capacity retention after 3000 cycles), substantially outperforming previously reported fibrous vanadium-based cathodes. First-principles density functional theory (DFT) calculations further revealed that the oxygen vacancies can weaken the electrostatic interaction between Zn2+ and the host cathode accompanying the low Zn2+ diffusion energy barrier. To highlight the potential applications, a prototype wearable fiber-shaped AZIB (FAZIB) with remarkable flexibility and extraordinary weaving capability was demonstrated. More encouragingly, the resulting FAZIB could be charged with solar cells and power a pressure sensor. Thus, our work provides a promising strategy to rationally construct high-performance flexible vanadium-based cathodes for next-generation wearable AZIBs.

Wearable multimode sensor with a seamless integrated structure for recognition of different joint motion states with the assistance of a deep learning algorithm.

Accurate motion feature extraction and recognition provide critical information for many scientific problems. Herein, a new paradigm for a wearable seamless multimode sensor with the ability to decouple pressure and strain stimuli and recognize the different joint motion states is reported. This wearable sensor is integrated into a unique seamless structure consisting of two main parts (a resistive component and a capacitive component) to decouple the different stimuli by an independent resistance-capacitance sensing mechanism. The sensor exhibits both high strain sensitivity (GF = 7.62, 0-140% strain) under the resistance mechanism and high linear pressure sensitivity (S = 3.4 kPa-1, 0-14 kPa) under the capacitive mechanism. The sensor can differentiate the motion characteristics of the positions and states of different joints with precise recognition (97.13%) with the assistance of machine learning algorithms. The unique integrated seamless structure is achieved by developing a layer-by-layer casting process that is suitable for large-scale manufacturing. The proposed wearable seamless multimode sensor and the convenient process are expected to contribute significantly to developing essential components in various emerging research fields, including soft robotics, electronic skin, health care, and innovative sports systems applications.

Mechanical Failure Mechanism of Silicon-Based Composite Anodes under Overdischarging Conditions Based on Finite Element Analysis.

Overdischarge is a severe safety issue that can induce severe mechanical failure of electrode materials in lithium-ion batteries. A considerable volume change of silicon-based composite anodes undoubtedly further aggravates the mechanical failure. However, the mechanical failure mechanism of silicon-based composite anodes under overdischarging conditions still lacks in-depth understanding despite many efforts paid under normal charging conditions. Herein, we have modeled and tracked the mechanical failure evolution of silicon/carbon nanofibers, a typical silicon-based anode, under overdischarging conditions based on the finite element simulation, with derived optimization strategies of optimal Young's modulus and stable microstructure. The severe contact damage between silicon nanoparticles and carbon nanofibers, which causes larger shedding and breakage risks, has been found to contribute to mechanical failure. To improve the electrode stability, an optimal Young's modulus interval ranging from ∼75 to ∼150 GPa is found. Furthermore, increasing the embedding depth of silicon nanoparticles in carbon nanofibers has proven to be an effective strategy for improving electrochemical stability due to the faster lithium salt diffusion and more uniform current density distribution, which was further verified by the experimental capacity retention ratio of carbon-coated silicon and silicon/carbon nanofibers (84 vs 75% after 100 cycles). Our results provide meaningful insights into the mechanical failure of silicon-based composite anodes during overdischarging, giving reasonable guidance for electrode safety designs and performance optimization.

Variable segment roles: modulation of the packing modes, nanocrystal morphologies and optical emissions.

Three isomers were prepared by covalently grafting carbazole (Cz) onto spiro[fluorene-9,9'-xanthene] (SFX) at different positions. Due to the complicated and variable roles of molecular segments, an evolution of the corresponding molecular packing mode was realized, accompanied by the change of nanocrystal morphology and photoluminescence properties.

Can Radiation Dose Be Reduced and Image Quality Improved With 80-kV and Dual-Phase Scanning of the Lower Extremities With 64-Slice Computed Tomography Angiography?

OBJECTIVE: To prospectively compare the new computed tomographic angiography (CTA) protocol (NCP) using 80-kV and dual-phase scanning with the routine CTA protocol (RCP) using 120-kV and single-phase scanning in patients with peripheral arterial disease. METHODS: A total of 60 patients were randomized to undergo the NCP (30 patients) or RCP (30 patients) scan. We compared the arterial attenuation values, overriding of the contrast bolus, signal-to-noise ratio, and radiation dose between 2 groups. RESULTS: The occurrence rate of contrast bolus overriding was not statistically significant (P = 0.69). The average arterial attenuation value in the NCP group was significantly higher (P < 0.05) than that in the RCP group. The radiation dose in the RCP group was significantly higher (P < 0.001) than that in the NCP group. The mean signal-to-noise ratio in the NCP group was significantly lower (P < 0.001). CONCLUSIONS: Sixty-four-slice CTA with the NCP can significantly reduce the radiation dose and improve the arterial enhancement and calf arteries imaging.