Photoelectron emitters serve as critical components in ultrafast electron sources, photomultiplier tubes, and quantum technologies. While the planar photoelectron emitters based on a metal-insulator-semiconductor (MIS) structure offer advantages such as environmental robustness and high emission current densities without ultraviolet excitation or cesium functionalization, the fundamental physics governing photoelectron emission in fully stacked van der Waals heterostructures remains unexplored. Here, we have fabricated a MoS2/h-BN/graphene heterostructure photocathode and measured the photoelectron emission characteristics. The device exhibits external quantum efficiency (EQE) modulation of almost three orders of magnitude (900 times enhancement) within a minimal gate voltage range (9-16 V). Meanwhile, we developed a general photoelectron emission model for a MIS van der Waals heterostructure, based on a modified Fowler-Nordheim equation and first principles calculation. The calculation results indicated a strong correlation between the quantum efficiency of photoelectron emission and the applied electrical field strength, consistent with the experimental results. In addition, the photoelectron emission of the device is verified by pulsed photo-response measurement under light irradiation. Our work provides a more comprehensive understanding of the photoelectron emission characteristics and predicts the theoretical performance limitations of photocathodes.

With the trend toward high-power radio-frequency (RF) electronic devices, flexible thermally conductive composite films are regarded as a key engineering interfacial material to address the critical problem of signal transmission and heat dissipation. However, achieving simultaneous optimization of high thermal conductivity and low loss in the same material remains a significant challenge, particularly in films with high filler loading. Here, a bottom-up regulatory strategy is proposed to address this challenge. Through the synergistic optimization of interface modification design and spatial orientation arrangement of hexagonal boron nitride (BN), the fabricated composite film achieves an exceptional in-plane thermal conductivity of 78.50 W m⁻1 K⁻1, significantly surpassing that of the film with BN. This remarkable enhancement is primarily attributed to the altered surface properties of the aminated BN (BN-NH2). The introduction of amine groups enhances the compatibility with the polymer matrix through electrostatic interactions to facilitate more efficient interfacial thermal transport. Furthermore, the highly oriented spatial arrangement of BN in the film not only preserves the electromagnetic wave transparency (99.94

Graphene/hBN tunneling cathodes have been regarded as one of the most promising candidates for vacuum micro/nano electron sources. However, their emission efficiency is fundamentally limited by excessive hole tunneling current resulting from the low hole barrier height. A lateral tip emitter structure was used, which generates a non-uniform electric field within the insulator, forming an asymmetric tunneling barrier to suppress the hole current. Notably, measurements of two devices on the same heterostructure of graphene/hBN/graphene but with uniform and non-uniform fields demonstrate a 4-fold enhancement in emission efficiency under the non-uniform field case, verifying our tunneling barrier engineering strategy. Furthermore, using a multi-tip emitter structure, the highest reported emission efficiency of similar to 10 % in a graphene/hBN tunneling cathode was achieved, surpassing conventional planar structures by almost one order of magnitude. The results are important for not only a better understanding of the modulation of electron transport in field emission tunneling junctions but also for the realization of high-performance tunneling junction devices.

Metal-insulator-semiconductor (MIS) heterostructures have important applications in vacuum microelectronic devices. Among these, graphene-insulator-semiconductor (GIS) heterostructure field electron emitters are among the most widely utilized. Improving the electron emission performance is a major challenge for GIS heterostructure field emitters. A comprehensive theoretical model is needed to predict the electron emission process from such a structure. In this work, a theoretical calculation was carried out on the electron emission current from an GIS heterostructure structure based on a tunneling model that considers the density of states of the semiconductor, scattering of the insulation layer, and hot-hole-induced Auger emission process. Using graphene/h-BN/MoS2 as an example, we obtain the band structure of the MoS2 using first principle calculation, simulate the scattering in h-BN with the Monte Carlo method, and calculate the emission current density using the modified Fowler-Nordheim equation. The results indicate that h-BN thickness and Auger coefficient are key factor affecting emission current density and emission efficiency. To validate our model, a few-layer graphene/h-BN/MoS2 heterostructure device was prepared and the field emission results validate the calculation results. The theoretical model can be expanded to other GIS heterostructures and is useful for designing a high-performance electron source using a GIS tunneling junction.

Tungsten oxide (WO3−X) nanowire field emitters have important applications in vacuum microelectronic devices, such as cold cathode flat panel x-ray sources. In this study, large-area, high current density, and defect-rich monoclinic WO3−X nanowires were directly synthesized on a glass substrate by thermal oxidation. Field emission measurements from a 4.5 × 4.5 cm2 sample show that a turn-on field of 4.8 MV/m and a high current density of 15.2 mA/cm2 were achieved. Stable emission current with a fluctuation of 1.78% was obtained. Furthermore, a flat panel x-ray source with a reflective anode was fabricated using as-grown WO3−X nanowires as the cold cathode. A radiation dose rate of 1.83 mGy/s was obtained at an anode voltage of 60 kV and a current of 484.1 μA. X-ray imaging experiments were carried out and clear imaging results were obtained. This work is significant for promoting the application of WO3−X nanowires in large-area field emission devices.

Morphology reconstruction phenomenon of formamidinium lead triiodide (FAPbI3) under strong electrical field was revealed and the field electron emission was systematically studied. Field electron emission was enhanced after forming process of multiple increasing and decreasing the applied electric field under vacuum, with the maximum field emission current density (J) increasing from initial 57.6 mu A/cm2 to 12.1 mA/cm2, and the turn-on field (electric field at J = 1 mu A/cm2) decreasing from 26.7 V/mu m to 8.9 V/mu m. Stability tests of field emission current was also conducted for 1 h without significant degradation. The morphology tracking revealed that electric field assisted morphology reconstruction occurred during the forming process, leading to the formation of protrusion with high aspect ratio. Additionally, the enrichment phenomenon of I- ions on the surface after forming process were identified, indicating the ion migration appeared during the forming process. Regarding the above phenomenon, we proposed a model explaining the origin of the morphology reconstruction and ion migration which was attributed to the high electric field and heating effect induced by emission current. Based on the proposed model, the enhanced field emission current was well explained. Although higher surface work function caused by ion migration slightly hinders the electron emission, the strong field enhancement effect induced by reconstructed morphology ultimately determines the enhanced field electron emission. This study provides insights into the behavior of perovskites under strong electric fields and highlights the potential of FAPbI3 films for applications beyond traditional optoelectronic devices.

In this paper, the controlled synthesis of WO3-x nanostructures on glass substrates was achieved by using a catalyst-free thermal oxidation method. The effects of the oxidation atmosphere on the growth of these nanostructures were investigated. The morphology, structure, and composition of the as-grown nanostructures were characterized. WO3-x nanowires with high concentrations of oxygen vacancy defects were synthesized in the air atmosphere, while WO3-x nanosheets with good crystallinity were obtained in the oxygen atmosphere. A stress-driven growth mechanism was proposed to explain the observed phenomena. In addition, the field emission from WO3-x nanostructures was studied. WO3-x nanowires (exhibit) a higher emission current density and stability compared to that of WO3-x nanosheets, which can be attributed to defect-enhanced conductivity. Our results are important for understanding the growth mechanism of the WO3-x nanostructures and will prompt their applications in cold cathodes and other fields.

We demonstrate an on-chip vacuum nano-diode with a single-crystal CsPbBr3 cathode (thickness ~0.9 μm) and Si-tip anode (separation ~30 nm) for direct electron detection. At 15 V bias, it exhibits a dark current of 100 pA, current on/off ratio of 490 and electron efficiency of 33.1% under 10 keV electron-beam irradiation. Numerical simulations confirm full depletion of the cathode. The built-in field in the cathode facilitates rabid separation of electron-hole pairs generated by the injected electrons, while the generated electron supply for field emission. The vacuum diode shows promising potential for developing on-chip integrated diode array for ultrafast electron detection.

X-ray detectors based on halide perovskite have attracted considerable attention due to their unique properties. However, the issues of ambient stability and high dark current still remain challenges to be solved. Using a vacuum microelectronic device-based detector is a possible solution. In this work, we synthesized MAPbBr3 single crystals via the inverse temperature crystallization (ITC) method and investigated its X-ray response characteristics from field emission current. The significant enhancement in field emission current upon X-ray exposure was observed. Furthermore, we systematically analyzed the correlation between detection sensitivity and applied electric field, and the mechanism for the detection was explored.

Improving the emission current of zinc oxide (ZnO) nanowire field emitters is critical for their applications in vacuum microelectronic devices, such as flat-panel X-ray sources. This study demonstrates that enhanced field-emission characteristics through conformal titanium nitride (TiN) coating by atomic layer deposition (ALD) is achieved. Ultrathin TiN films (2-3 nm thickness) were precisely deposited on ZnO nanowires using ALD technology. Comparative analysis showed the TiN-coated nanowires demonstrated a 195 % enhancement in maximum current density (3.83 mA/cm(2) compared with 1.3 mA/cm(2) for uncoated ZnO nanowires) along with a 16 % increase in turn-on field (6.5 MV/m compared with 5.5 MV/m for uncoated ZnO nanowires at 10 mu A/cm(2)). The TiN-coated ZnO nanowires maintained >95 % current stability during 1000-s continuous operation @3.15 mA/cm(2). The TiN coating was found to increase nanowire conductivity using in situ nanoprobe characterization. Field emission simulations were carried out incorporating the field-induced hot-electron emission mechanism for uncoated ZnO nanowires and the Murphy-Good formula for TiN-coated counterparts. The obtained results are consistent with the experimental results, which indicated that higher electrical conductivity and thermal conductivity of TiN account for the enhanced emission current. These results establish ALD-deposited TiN film as an effective surface engineering strategy for developing field-emitter arrays (FEAs) with enhanced electron emission capabilities.

Zinc oxide (ZnO) nanowire field emitters have significant applications in vacuum microelectronic devices. In this work, field emission properties of titanium nitride (TiN)-coated ZnO nanowires were investigated in situ using nanoprobe technique. The TiN layer was deposited on the ZnO nanowires by direct-current magnetron sputtering. Statistical analysis of the results from in situ field emission measurement on individual nanowire shows that the turn-on voltage (corresponding to emission current of 0.1 nA) was higher after TiN coating when measured at a fixed anode-to-cathode distance. The maximum current was further measured, and higher maximum emission current was obtained from the TiN-coated ZnO nanowires. The higher turn-on field was explained by the smaller penetration length in the ZnO nanowire after coating, and the increased maximum current was attributed to the increased electrical and thermal conductance after TiN coating.

The exploration of adaptive robotic systems capable of performing complex tasks in unstructured environments, such as underwater salvage operations, presents a significant challenge. Traditional rigid grippers often struggle with adaptability, whereas bioinspired soft grippers offer enhanced flexibility and adaptability to varied object shapes. In this study, we present a novel bioinspired soft robotic gripper integrated with a shape memory alloy (SMA) actuated suction cup, inspired by the versatile grasping strategies of octopus arms and suckers. Our design leverages a tendon-driven composite arm, enabling precise bending and adaptive grasping, combined with SMA technology to create a compact, efficient suction mechanism. We develop comprehensive kinematic and static models to predict the interaction between arm bending deflection and suction force, thereby optimizing the gripper's performance. Experimental validation demonstrates the efficacy of our integrated design, highlighting its potential for advanced manipulation tasks in challenging environments. This work provides a new perspective on the integration of bioinspired design principles with smart materials, paving the way for future innovations in adaptive robotic systems.

Suction cups has been widely utilized to grasp objects, but they typically encounter challenges with sealing failure and non-adjustable adhesion force. In this study, a bioinspired suction cup integrated with an shape memory alloy actuated module was proposed to solve these problems. The actuating performance under different input current was firstly investigated to ensure the effectiveness of the module. Then, inspired by the surface structures of the tree frog's toe pad, the synthetic bioinspired suction cups with hexagonal microstructures at the rims were designed. The regular cup with soft and smooth rim was also fabricated for comparison study. Furthermore, the adhesion performance and surface adaptability of different two cups were studied in both dry and water conditions on substrates with various roughness levels. The results indicated that the proposed active bioinspired suction cup exhibited higher pull-off strength and better sealing on less rough substrates. The proposed bioinspired suction cup possessed the advantages of compactness and lightweight, thus demonstrating potential for integration into arrayed suction grippers.

Planar-gate nanowire field emitters have potential applications in vacuum microelectronic devices. However, analyzing their electrical characteristics often uses finite element analysis which consumes enormous calculation resources and the device physics is not straightforward. In this article, we developed an analytical model for the current-voltage (I-V) characteristics of standard planar-gate nanowire field emitters. The expression for the electric field at the vertex of the nanowire is obtained by using the line charge model (LCM) and considering the superposition of anode and gate voltages. The formula for current is derived using the Fowler-Nordheim (F-N) equation. In addition, the model has been generalized for planar-gate field emitters with randomly distributed nanowires based on probabilistic statistical methods. The analytical solution has been validated through COMSOL Multiphysics simulation and experimental results. We also expanded this model to top planar-gate nanowire field emitters. Our study provides a quick and precise method to obtain the device characteristics of planar-gate nanowire field emitters and save calculation resources.

The planar metal-insulator-semiconductor (MIS) emitter using van der Waals heterostructure of two-dimensional (2D) materials have potential applications in vacuum microelectronic and optoelectronic devices. In this work, the MoS2/h-BN/FLG heterostructure was prepared by all-dry transfer technique. The photoelectron emission characteristics of the device were studied under white laser irradiation. Maximum responsivity of 7.1x10(-5) A/W for anode current was recorded under the gate voltage of 7 V. The time-resolved photoresponse of device exhibits long rise and fall time. The mechanisms for observed phenomena were discussed.

ZnO nanowire is a promising candidate for large-area gated field emitter arrays. How to improve its temporal response is one of the key problems to be solved for applications. In this work, a device model for a gated ZnO nanowire field emitter with consideration of charging and self-heating effect has been established to investigate its temporal response. It is found that while the charging effect is responsible for the delay at the beginning of the pulse, the self-heating effect which induces delay due to the thermal conduction process can shorten the charging time because of its lowering of nanowire resistance. The response time can be minimized when these two effects are balanced at an optimal field which is below the critical field for thermal runaway. We further investigate the optimal response time of a nanowire with the same resistance but a different length, radius, and electrical properties. The results imply that a lower heat capacity and higher critical temperature for thermal runaway are in favor of a shorter response time, which must be taken into account in the reduction in nanowire resistance for improving response speed. All the above should be useful for the device design of a fast-response gated ZnO nanowire field emitter array.

Climbing robots have gained significance in hazardous and steep terrains, yet adapting to complex environments remains a challenge. Inspired by nature's climbers, this paper introduces a climbing dynamics model that integrates foot-end contact forces, crucial for safe and efficient wall climbing. Drawing insights from animal locomotion and biomechanics, we present a comprehensive dynamic model for quadruped robots. Our model, built upon multibody dynamics and a dynamic contact model based on spiny claw mechanisms, accurately simulates robot forces and motion during climbing, even predicting failure scenarios. Experimental validation further establishes model accuracy. This study advances climbing robot research by addressing attachment interaction dynamics and provides valuable insights for optimizing robot structural design and gait strategies.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler–Nordheim (FN) and Seppen–Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Geckos are renowned for their exceptional climbing abilities, enabled by their specialized feet with hairy toes that attach to surfaces using van der Waals forces. Inspired by these capabilities, various gecko-like robots have been developed for high-risk applications, such as search and rescue. While most research has focused on adhesion mechanisms, the gecko’s tail also plays a critical role in maintaining balance and stability. In this study, we systematically explore the impact of tail dynamics on the climbing performance of gecko-inspired robots through both simulation and experimental analysis. We developed a dynamic climbing simulation system that models the robot’s specialized attachment devices and predicts contact failures. Additionally, an adjustable-angle force measurement platform was constructed to validate the simulation results. Our findings reveal the significant influence of the tail on the robot’s balance, stability, and maneuverability, providing insights for further optimizing climbing robot performance.