Flexible Threshold Switching Based on CsCu2I3 with Low Threshold Voltage and High Air Stability.

Halide perovskites featuring remarkable optoelectronic properties hold great potential for threshold switching devices (TSDs) that are of primary importance to next-generation memristors and neuromorphic computers. However, such devices are still in their infancy due to the unsolved challenges of high threshold voltage, poor stability, and lead-containing features. Herein, a unipolar TSD based on an all-inorganic halide perovskite of CsCu2I3 is demonstrated, exhibiting the fascinating attributes of a low threshold voltage of 0.54 V, a high ON/OFF ratio of 104, robust air stability over 70 days, a steep switching slope of 6.2 mV·decade-1, and lead-free composition. Moreover, the threshold voltage can be further reduced to 0.23 V using UV illumination to reduce the barrier of iodide ion migration. The multilevel threshold switching behavior can be realized through the modulation of either the compliance current or the scan rate. The TSD with mechanical compliance and transparency is also demonstrated. This work enriches TSDs with expanded perovskite materials, boosting the related applications of this emerging class of device families.

Bimodal Tactile Sensor without Signal Fusion for User-Interactive Applications.

Tactile sensors with multimode sensing ability are cornerstones of artificial skin for applications in humanoid robotics and smart prosthetics. However, the intuitive and interference-free reading of multiple tactile signals without involving complex algorithms and calculations remains a challenge. Herein a pressure-temperature bimodal tactile sensor without any interference is demonstrated by combining the fundamentally different sensing mechanisms of optics and electronics, enabling the simultaneous and independent sensing of pressure and temperature with the elimination of signal separation algorithms and calculations. The bimodal sensor comprises a mechanoluminescent hybrid of ZnS-CaZnOS and a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thermoresistant material, endowing the unambiguous transduction of pressure and temperature into optical and electrical signals, respectively. This device exhibits the highest temperature sensitivity of -0.6% °C-1 in the range of 21-60 °C and visual sensing of the applied forces at a low limitation of 2 N. The interference-free and light-emitting characteristics of this device permit user-interactive applications in robotics for encrypted communication as well as temperature and pressure monitoring, along with wireless signal transmission. This work provides an unexplored solution to signal interference of multimodal tactile sensors, which can be extended to other multifunctional sensing devices.

The smart growth of self-assembled silver nanoloops.

Enclosed silver nanoloops have unique features in manipulating and controlling light. However, even the conception of their growth mechanism has not been established. The intermediate structure at the growth stage were revealed as the crucial issue for studying their smart growth mechanism of silver nanoloops and nanowires. Early growth stage showed that silver nanorods and nanoparticles were grown in their respective polyvinylpyrrolidone micelles. Then, the silver nanorods and nanoparticles were assembled in a rod-particle-rod pattern via micelle-micelle coupling, forming linear silver nanowires. These silver nanowires were attracted by Van der Waals forces forming the initial nanoloop. Notably, there was a silver nanoparticle between the ends of two adjacent nanowires. This silver nanoparticle acted like solder and played a crucial role in connecting the two adjacent nanowires; consequently, a silver nanoloop was formed. This finding also suggested that similar smart growth patterns might exist for other one-dimensional and looped nanomaterials.

Fabrication of a Hierarchical Ni(OH)2 @Ni3 S2 /Ni Foam Electrode from a Prussian Blue Analogue-Based Composite with Enhanced Electrochemical Capacitive and Electrocatalytic Properties.

Developing high-efficiency, cost-effective, and durable electrodes is significant for electrochemical capacitors and electrocatalysis. Herein, a 3D bifunctional electrode consisting of nickel hydroxide nanosheets@nickel sulfide nanocubes arrays on Ni foam (Ni(OH)2 @Ni3 S2 /NF) obtained from a Prussian blue analogue-based precursor is reported. The 3D higher-order porous structure and synergistic effect of different compositions endow the electrode with large specific surface area, facile ion/electron transport path, and improved conductivity. As a result, the Ni(OH)2 @Ni3 S2 /NF electrode exhibits a high specific capacity of 211 mA h g-1 at a current density of 1 A g-1 and 73 % capacity retention after 5000 cycles at 5 A g-1 . Moreover, the Ni(OH)2 @Ni3 S2 /NF electrode has superior electrocatalytic activity for the hydrogen evolution reaction with low overpotentials of 140 and 210 mV at current densities of 10 and 100 mA cm-2 , respectively. The synthetic strategy for the unique higher-order porous structure can be extended to fabricate other composite materials for energy storage and conversion.

Hierarchical FeCo2 S4 @FeNi2 S4 Core/Shell Nanostructures on Ni Foam for High-Performance Supercapacitors.

The design of electrode materials with rational core/shell structures is promising for improving the electrochemical properties of supercapacitors. Hence, hierarchical FeCo2 S4 @FeNi2 S4 core/shell nanostructures on Ni foam were fabricated by a simple hydrothermal method. Owing to their structure and synergistic effect, they deliver an excellent specific capacitance of 2393 F g-1 at 1 A g-1 and long cycle lifespan as positive electrode materials. An asymmetric supercapacitor device with FeCo2 S4 @FeNi2 S4 as positive electrode and graphene as negative electrode exhibited a specific capacitance of 133.2 F g-1 at 1 A g-1 and a high energy density of 47.37 W h kg-1 at a power density of 800 W kg-1 . Moreover, the device showed remarkable cycling stability with 87.0 % specific-capacitance retention after 5000 cycles at 2 A g-1 . These results demonstrate that the hierarchical FeCo2 S4 @FeNi2 S4 core/shell structures have great potential in the field of electrochemical energy storage.

Reset Voltage-Dependent Multilevel Resistive Switching Behavior in CsPb1- xBi xI3 Perovskite-Based Memory Device.

All-inorganic CsPb1- xBi xI3 perovskite film was successfully fabricated by incorporating Bi3+ in CsPbI3 to stabilize the cubic lattice. Furthermore, the perovskite film was applied to manufacture a simple Ag/CsPb1- xBi xI3/indium tin oxide (ITO) memory device with a bipolar resistive switching behavior. Nonvolatile, reliable, and reproducible switching properties are demonstrated through retention and endurance test under fully open-air conditions. The memory device also presents highly uniform and long-term stable characteristics. Importantly, by modulating the reset stop voltages, multilevel high-resistance states are observed for the first time in lead halide perovskite memory device. The resistive switching behavior is proposed to explain the formation and partial rupture of conductive multifilament that are dominated by the migration of iodine ions and their corresponding vacancies in perovskite film. This study suggests Ag/CsPb1- xBi xI3/ITO device potential application for multilevel data storage in a nonvolatile memory device.

Intense, stable and excitation wavelength-independent photoluminescence emission in the blue-violet region from phosphorene quantum dots.

Nanoscale phosphorene quantum dots (PQDs) with few-layer structures were fabricated by pulsed laser ablation of a bulk black phosphorus target in diethyl ether. An intense and stable photoluminescence (PL) emission of the PQDs in the blue-violet wavelength region is clearly observed for the first time, which is attributed to electronic transitions from the lowest unoccupied molecular orbital (LUMO) to the highest occupied molecular orbital (HOMO) and occupied molecular orbitals below the HOMO (H-1, H-2), respectively. Surprisingly, the PL emission peak positions of the PQDs are not red-shifted with progressively longer excitation wavelengths, which is in contrast to the cases of graphene and molybdenum disulphide quantum dots. This excitation wavelength-independence is derived from the saturated passivation on the periphery and surfaces of the PQDs by large numbers of electron-donating functional groups which cause the electron density on the PQDs to be dramatically increased and the band gap to be insensitive to the quantum size effect in the PQDs. This work suggests that PQDs with intense, stable and excitation wavelength-independent PL emission in the blue-violet region have a potential application as semiconductor-based blue-violet light irradiation sources.