The cognition of spatiotemporal tactile stimuli, including fine spatial stimuli and static/dynamic temporal stimuli, is paramount for intelligent robots to feel their surroundings and complete manipulation tasks. However, current tactile sensors have restrictions on simultaneously demonstrating high sensitivity and performing selective responses to static/dynamic stimuli, making it a challenge to effectively cognize spatiotemporal tactile stimuli. Here, we report a high-sensitive and self-selective humanoid mechanoreceptor (HMR) that can precisely respond to spatiotemporal tactile stimuli. The HMR with PDMS/chitosan@CNTs (PDMS: polydimethylsiloxane; CNT: carbon nanotube) graded microstructures and polyurethane hierarchical porous spacer exhibits high sensitivity of 3790.8 kPa⁻¹. The HMR demonstrates self-selective responses to static and dynamic stimuli with mono signal through the hybrid of piezoresistive and triboelectric mechanisms. Consequently, it can respond to spatiotemporal tactile stimuli and generate distinguishable and multi-type characteristic signals. With the assistance of the convolutional neural network, multiple target objects can be easily identified with a high accuracy of 99.1%. This work shows great potential in object precise identification and dexterous manipulation, which is the basis of intelligent robots and natural human-machine interactions.

Two-dimensional (2D) semiconductors, especially transition metal dichalcogenides (TMDCs), have been proven to be excellent channel materials for the next-generation integrated circuit (IC). However, the contact problem between 2D TMDCs and metal electrodes has always been one of the main factors restricting their development. In this review, we summarized recent work on 2D TMDCs contact from the perspective of compatible integration with silicon processes and practical application requirements, including the contact performance evaluation indicators, special challenges encountered in 2D TMDCs, and recent optimization methods. Specifically, we sorted out and highlighted the performance indicators of 2D TMDCs contacts, including contact resistance (R_C), contact scaling, contact stability, and contact electrical/thermal conductivity. Special challenges of 2D TMDCs and metal contact, such as severe Fermi level pinning, large R_C, and difficult doping, are systematically discussed. Furthermore, typical methods for optimizing 2D TMDCs R_C, edge contact strategies for scaling contact lengths, and solutions for improving contact stability are reviewed. Based on the current research and problems, the development direction of 2D TMDCs contacts that meet the silicon-based compatible process and application performance requirements is proposed.

Monolayer two-dimensional (2D) semiconductors are emerging as top candidates for the channels of the future chip industry due to their atomically thin body and superior immunity to short channel effect. However, the low saturation current caused by the high contact resistance (R_c) in monolayer MoS₂ field-effect transistors (FETs) limits ultimate electrical performance at scaled contact lengths, which seriously hinders application of monolayer MoS₂ transistors. Here we present a scalable strategy with a clean end-bond contact scheme that leads to size-independent electrodes and ultralow contact resistance of 2.5 kΩ·μm to achieve record high performances of saturation current density of 730 μA·μm^-1 at 300 K and 960 μA·μm^-1 at 6 K. Our end-bond contact strategy in monolayer MoS₂ FETs enables the great potential for atomically thin integrated circuitry.

van der Waals (vdW) heterostructures based on two-dimensional (2D) materials holding design-by-demand features offer astonishing opportunities to construct novel electronics and optoelectronics devices due to the vdW force interaction between their stacked components. At the atomically thin confinement, vdW heterostructure not only exhibits unprecedented properties as an entire counterpart, but also provides unique platforms to manipulate the vdW interfacial behaviors. Therefore, developing characterization techniques to comprehensively understand the coupling effect on structure-property-performance relationship of vdW heterostructures is crucial for fundamental science and practical applications. Here, we focus on the most widely studied 2D semiconductor transition metal dichalcogenides (TMDCs) and systematically review significant advances in characterizing the material and interfacial coupling effect of the related vdW heterostructures. Specially, we will discuss microscopy techniques for unveiling the structure-property relationship of vdW heterostructures and optical spectroscopy measurements for analyzing vdW interfacial coupling effect. Finally, we address some promising strategies to optimize characterization technologies for resolving vdW heterostructures, including coupling multiple characterization technologies, improving temporal and spatial resolution, developing fast, efficient, and non-destructive techniques and introducing artificial intelligence.

The dangling bond free nature of two-dimensional (2D) material surface/interface makes van der Waals (vdW) heterostructure attractive for novel electronic and optoelectronic applications. But in practice, edge is unavoidable and could cause band bending at 2D material edge analog to surface/interface band bending in conventional three-dimensional (3D) materials. Here, we report a first principle simulation on edge band bending of free standing MoS₂/WS₂ vdW heterojunction. Due to the imbalance charges at edge, S terminated edge causes upward band bending while Mo/W terminated induces downward bending in undoped case. The edge band bending is comparable to band gap and could obviously harm electronic and optoelectronic properties. We also investigate the edge band bending of electrostatic doped heterojunction. N doping raises the edge band whereas p doping causes a decline of edge band. Heavy n doping even reverses the downward edge band bending at Mo/W terminated edge. In contrast, heavy p doping doesn’t invert the upward bending to downward. Comparing with former experiments, the expected band gap narrowing introduced by interlayer potential gradient at edge is not observed in our free-standing structures and suggests substrate’s important role in this imbalance charge induced phenomenon.

Since the invention of the triboelectric nanogenerator (TENG) in 2012, it has become one of the most vital innovations in energy harvesting technologies. The TENG has seen enormous progress to date, particularly in applications for energy harvesting and self-powered sensing. It starts with the simple working principles of the triboelectric effect and electrostatic induction, but can scavenge almost any kind of ambient mechanical energy in our daily life into electricity. Extraordinary output performance optimization of the TENG has been achieved, with high area power density and energy conversion efficiency. Moreover, TENGs can also be utilized as self-powered active sensors to monitor many environmental parameters. This review describes the recent progress in mainstream energy harvesting and self-powered sensing research based on TENG technology. The birth and development of the TENG are introduced, following which structural designs and performance optimizations for output performance enhancement of the TENG are discussed. The major applications of the TENG as a sustainable power source or a self-powered sensor are presented. The TENG, with rationally designed structures, can convert irregular and mostly low-frequency mechanical energies from the environment, such as human motion, mechanical vibration, moving automobiles, wind, raindrops, and ocean waves. In addition, the development of self-powered active sensors for a variety of environmental simulations based on the TENG is presented. The TENG plays a great role in promoting the development of emerging Internet of Things, which can make everyday objects connect more smartly and energy-efficiently in the coming years. Finally, the future directions and perspectives of the TENG are outlined. The TENG is not only a sustainable micro-power source for small devices, but also serves as a potential macro-scale generator of power from water waves in the future.

Magnetic metals (Fe, Co, Ni) and alloys thereof are easily synthesized as nanoparticles, but obtaining highly dispersed graphene-based magnetic nanomaterials remains challenging. Here, three CoNi/graphene nanocomposites (CoNi/GN) are successfully assembled for the first time via a one-pot strategy without templating by manipulating the reaction time and solvents used for the same precursors. Moreover, the reduction of graphene oxide utilizing this method is more effective than that by conventional methods and the alloy particles are firmly embedded on the GN substrate. Compared to n- and p-CoNi/GN nanocomposites, o-CoNi/GN nanocomposites show the best electromagnetic wave absorption properties with the maximum reflection loss of-31.0 dB at 4.9 GHz for a thickness of 4 mm; the effective absorption bandwidth (< 10.0 dB) is 7.3 GHz (9.5–16.8 GHz) for a thickness of 2 mm. The structures and electromagnetic wave absorption mechanisms of the three composites were also investigated. This research provides a new platform for the development of magnetic alloy nanoparticles in the field of microwave-absorbing devices.

Methylammonium lead halide perovskites have been reported to be promising candidates for high-performance photodetectors. However, self-powered broadband ultraviolet-visible-near infrared (UV-Vis-NIR) photodetection with high responsivity is difficult to achieve in these materials. Here, we demonstrate, for the first time, a novel trilayer hybrid photodetector made by combining an n-type Si wafer, TiO₂ interlayer and perovskite film. By precisely controlling the thickness of the TiO₂ layer, enhanced separation and reduced recombination of carriers at the Si–perovskite interface are obtained. As a result, perovskite film, when combined with a low-bandgap Si, extends the wavelength range of photo response to 1, 150 nm, along with improved on/off ratio, responsivity, and specific detectivity, when compared to pristine perovskite. Results obtained in this work are comparable or even better than those reported for perovskite-based UV-Vis-NIR photodetectors. In particular, the hybrid photodetectors can operate in a self-powered mode. The mechanism of enhancement has been explored and it is found that the increased separation and reduced recombination of photogenerated carriers at the junction interface leads to the improved performance.

The mixed-dimensional van der Waals (vdW) heterostructure is a promising building block for strained electronics and optoelectronics because it avoids the bond fracture and atomic reconstruction under strain. We propose a novel mixed-dimensional vdW heterostructure between two-dimensional graphene and a one-dimensional ZnO nanowire for high-performance photosensing. By utilizing the piezoelectric properties of ZnO, strain modulation was accomplished in the mixed-dimensional vdW heterostructure to optimize the device per­formance. By combining the ultrahigh electrons transfer speed in graphene and the extremely long life time of holes in ZnO, an outstanding responsivity of 1.87 × 10⁵ A/W was achieved. Under a tensile strain of only 0.44% on the ZnO nanowire, the responsivity was enhanced by 26%. A competitive model was proposed, in which the performance enhancement is due to the efficient promotion of the injection of photogenerated electrons from the ZnO into the graphene caused by the strain-induced positive piezopotential. Our study provides a strain-engineering strategy for controlling the behavior of the photocarriers in the mixed-dimensional vdW heterostructure, which can be also applied to other similar systems in the future.

A cobaltosic-oxide-nanosheets/reduced-graphene-oxide composite (CoNSs@RGO) was successfully prepared as a light-weight broadband electromagnetic wave absorber. The effects of the sample thickness and amount of composite added to paraffin samples on the absorption properties were thoroughly investigated. Due to the nanosheet-like structure of Co₃O₄, the surface-to-volume ratio of the wave absorption material was very high, resulting in a large enhancement in the absorption properties. The maximum refection loss of the CoNSs@RGO composite was–45.15 dB for a thickness of 3.6 mm, and the best absorption bandwidth with a reflection loss below–10 dB was 7.14 GHz with a thickness of 2.9 mm. In addition, the peaks of microwave absorption shifted towards the low frequency region with increasing thickness of the absorbing coatings. The mechanism of electromagnetic wave absorption was attributed to impedance matching of CoNSs@RGO as well as the dielectric relaxation and polarization of RGO. Compared to previously reported absorbing materials, CoNSs@RGO showed better performance as a lightweight and highly efficient absorbing material for application in the high frequency band.