Jing Zhang

This paper presents the wafer-scale synthesis of highly polycrystalline 2D molybdenum ditelluride (2H-MoTe₂), and its use as resistive switching layer in memristors. Most interestingly, the synthesized polycrystalline 2H-MoTe₂ film contains vertically aligned grain boundaries, providing confined diffusion paths for metal ions migration. This conductive filament confinement makes reliable resistive switching possible, applicable to artificial synaptic applications.

Abstract

2D materials have attracted attention in the field of neuromorphic computing applications, demonstrating the potential for their use in low-power synaptic devices at the atomic scale. However, synthetic 2D materials contain randomly distributed intrinsic defects and exhibit a stochasitc forming process, which results in variability of switching voltages, times, and stat resistances, as well as poor synaptic plasticity. Here, this work reports the wafer-scale synthesis of highly polycrystalline semiconducting 2H-phase molybdenum ditelluride (2H-MoTe₂) and its use for fabricating crossbar arrays of memristors. The 2H-MoTe₂ films contain small grains (≈30 nm) separated by vertically aligned grain boundaries (GBs). These aligned GBs provide confined diffusion paths for metal ions filtration (from the electrodes), resulting in reliable resistive switching (RS) due to conductive filament confinement. As a result, the polycrystalline 2H-MoTe₂ memristors shows improvement in the RS uniformity and stable multilevel resistance states, small cycle-to-cycle variation (<8.3%), high yield (>83.7%), and long retention times (>10⁴ s). Finally, 2H-MoTe₂ memristors show linear analog synaptic plasticity under more than 2500 repeatable pulses and a simulation-based learning accuracy of 96.05% for image classification, which is the first analog synapse behavior reported for 2D MoTe₂ based memristors.

Reliable and energy-efficient synaptic crossbar arrays based on layered NiPS₃ are reported. Concrete experimental evidence reveals the complex structure and phase evolution of NiPS₃ upon the electrochemical metallization process. Exploiting the highly linear and symmetric weight update characteristics, image recognition with a high accuracy of 96.4% is achieved in artificial neural network simulation.

Abstract

Designing reliable and energy-efficient memristors for artificial synaptic arrays in neuromorphic computing beyond von Neumann architecture remains a challenge. Here, memristors based on emerging layered nickel phosphorus trisulfide (NiPS₃) are reported that exhibit several favorable characteristics, including uniform bipolar nonvolatile switching with small operating voltage (<1 V), fast switching speed (< 20 ns), high On/Off ratio (>10²), and the ability to achieve programmable multilevel resistance states. Through direct experimental evidence using transmission electron microscopy and energy dispersive X-ray spectroscopy, it is revealed that the resistive switching mechanism in the Ti/NiPS₃/Au device is related to the formation and dissolution of Ti conductive filaments. Intriguingly, further investigation into the microstructural and chemical properties of NiPS₃ suggests that the penetration of Ti ions is accompanied by the drift of phosphorus-sulfur ions, leading to induced P/S vacancies that facilitate the formation of conductive filaments. Furthermore, it is demonstrated that the memristor, when operating in quasi-reset mode, effectively emulates long-term synaptic weight plasticity. By utilizing a crossbar array, multipattern memorization and multiply-and-accumulate (MAC) operations are successfully implemented. Moreover, owing to the highly linear and symmetric multiple conductance states, a high pattern recognition accuracy of ≈96.4% is demonstrated in artificial neural network simulation for neuromorphic systems.

The critical roles of local optoelectronic heterogeneities, especially at grain interiors (GIs) and grain boundaries (GBs) of polycrystalline photovoltaic materials, including polycrystalline silicon, inorganic compound materials, and emerging halide perovskites, can be identified by the advanced atomic force microscope (AFM)-based techniques, which bridge the local properties of materials to overall device performance and guide the optimization of the photovoltaic devices.

Abstract

Atomicforce microscopy (AFM)-based scanning probing techniques, including Kelvinprobe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM), have been widely applied to investigate thelocal electromagnetic, physical, or molecular characteristics of functional materials on a microscopic scale. The microscopic inhomogeneities of the electronic properties of polycrystalline photovoltaic materials can be examined by these advanced AFM techniques, which bridge the local properties of materials to overall device performance and guide the optimization of the photovoltaic devices. In this review, the critical roles of local optoelectronic heterogeneities, especially at grain interiors (GIs) and grain boundaries (GBs) of polycrystalline photovoltaic materials, including versatile polycrystalline silicon, inorganic compound materials, and emerging halide perovskites, studied by KPFM and C-AFM, are systematically identified. How the band alignment and electrical properties of GIs and GBs affect the carrier transport behavior are discussed from the respective of photovoltaic research. Further exploiting the potential of such AFM-based techniques upon a summary of their up-to-date applications in polycrystalline photovoltaic materials is beneficial to acomprehensive understanding of the design and manipulation principles of thenovel solar cells and facilitating the development of the next-generation photovoltaics and optoelectronics.

Niobium chloride (Nb3Cl8) is a layered two-dimensional semiconducting material with many exotic properties including a breathing kagome lattice, a topological flat band in its band structure, and a crystal structure that undergoes a structural and magnetic phase transition at temperatures below 90 K. Despite being a remarkable material with fascinating new physics, the understanding of its phonon properties is at its infancy. In this study, we investigate the phonon dynamics of Nb3Cl8 in bulk and few layer flakes using polarized Raman spectroscopy and density-functional theory (DFT) analysis to determine the material’s vibrational modes, as well as their symmetrical representations and atomic displacements. We experimentally resolved 12 phonon modes, five of which are A1g modes while the remaining seven are Eg modes, which is in strong agreement with our DFT calculation. Layer-dependent results suggest that the Raman peak positions are mostly insensitive to changes in layer thickness, while peak intensity and full width at half maximum are affected. Raman measurements as a function of excitation wavelength (473–785 nm) show a significant increase of the peak intensities when using a 473 nm excitation source, suggesting a near resonant condition. Temperature-dependent Raman experiments carried out above and below the transition temperature did not show any change in the symmetries of the phonon modes, suggesting that the structural phase transition is likely from the high temperature P\bar {\text{3}m}1 phase to the low-temperature R\bar {3m} phase. Magneto-Raman measurements carried out at 140 and 2 K between −2 and 2 T show that the Raman modes are not magnetically coupled. Overall, our study presented here significantly advances the fundamental understanding of layered Nb3Cl8 material which can be further exploited for future applications.

Biohybrid Microrobots

Biohybrid microbots integrate biological actuators and sensors into a synthetic chassis with the aim of providing the building blocks for next-generation micro-robotics. In article number 2214801, Roberto Di Leonardo and co-workers report that by using light-powered bacteria as propellers, 3D-printed microbots can be steered by unbalancing light over two parallel motor units. A central computer projects dynamical light patterns over multiple microbots to independently guide them through a series of spatially distributed checkpoints.

The cholesteric phase cellulose composite (CPCC) is created by integrating self-assembled hydroxypropyl cellulose with cholesteric liquid crystal structure, with crosslinked poly(N-isopropyl acrylamide) networks. The CPCC possesses transparency, thermochromic with different response degrees, and unique polarization properties. These features facilitate intricate yet accessible information encoding and decoding, paving the way for advanced anti-counterfeiting applications.

Abstract

The escalating need for enhanced cryptographic security necessitates the development of advanced materials designed for the secure storage and transmission of information. Drawing inspiration from the unique color-altering and polarizing capabilities of beetles, this work develops a transparent, thermochromic, and circularly polarized cholesteric phase cellulose composite (CPCC). This is achieved by integrating self-assembled hydroxypropyl cellulose with cholesteric liquid crystal (CLC) structure in tandem with a crosslinked poly(N-isopropyl acrylamide) (PNIPAM) network. The crosslinking density impacts the response degree of thermochromism, which can be regulated by modifying the UV exposure time during PNIPAM production. The CLC structure in CPCC uniquely results in reflected right circularly polarized light. When coupled with waveplates, this mechanism inverts the rotation direction of the reflected light, creating orthogonal structural colors of different brightness levels under left and right circularly polarized light. The excellent transparency of CPCC facilitates seamless integration with the environment, offering optimal camouflage. Sophisticated techniques, such as color coding and Morse coding, can further be incorporated within the CPCC to increase encryption security and the complexity of decryption. Collectively, the CPCC's transparency, thermochromism, and chirality present significant potential in the design and development of materials for high-security information encryption, contributing valuable insights to the field.

By successfully adopting the low temperature chemical vapor deposition carbon coating, the important cathode/electrolyte interface of iron difluoride (FeF₂) in lithium-ion batteries is significantly stabilized. The cycle life of FeF₂ in both concentrated and diluted ether-based electrolyte is remarkably improved, which can be attributed to the suppression of the serious electrolyte reduction during cycling.

Abstract

Metal fluorides (MFs) are regarded as high-capacity conversion cathode materials for next-generation lithium-ion batteries with high energy density. However, these cathodes suffer from poor electronic conductivity, sluggish reaction kinetics, and deleterious cathode solid electrolyte interface (CEI) formation, which may cause rapid cell degradation upon cycling. Herein, a low temperature chemical vapor deposition (CVD) carbon coating technology is successfully achieved to coat MFs-FeF₂ with a thin amorphous carbon layer, which promotes the formation of a stable CEI with improved electronic and ionic transport property. Consequently, a discharge capacity higher than 450 mAh g⁻¹ of the CVD coated FeF₂ is achieved with a capacity retention at about 75% after 2500 cycles in a saturated electrolyte. Moreover, an unprecedented cycling performance with the discharge capacity of 350 mAh g⁻¹ after 500 cycles in a super diluted electrolyte is also achieved. Advanced cryo-electron microscopy reveals that the carbon coating significantly suppresses the undesirable CEI formation and promotes the formation of a thin CEI with excellent chemo-mechanical property. This work provides a feasible technology to stabilize the important interface on MFs and offers a new strategy to accelerate the commercial adoption of such cathodes.

A smart single-fluorophore polymer polyethyleneimine-grafted pyrene (PGP) incorporating four stimuli-triggers: amphiphilicity, supramolecular host–guest sites, pyrene fluorescence indicator, and reversible chelation sites, exhibits deformation and shape-dependent fluorescence in response to external stimuli. Besides, PGP driven by its reversible chelation capacity can be used as an advanced fluorescent ink with erasable and recoverable properties.

Abstract

A novel smart fluorescent polymer polyethyleneimine-grafted pyrene (PGP) is developed by incorporating four stimuli-triggers at molecular level. The triggers are amphiphilicity, supramolecular host–guest sites, pyrene fluorescence indicator, and reversible chelation sites. PGP exhibits smart deformation and shape-dependent fluorescence in response to external stimuli. It can deform into three typical shapes with a characteristic fluorescence color, namely, spherical core–shell micelles of cyan-green fluorescence, standard rectangular nanosheets of yellow fluorescence, and irregular branches of deep-blue fluorescence. A quasi-reversible deformation between the first two shapes can be dynamically manipulated. Moreover, driven by reversible coordination and the resulting intramolecular photoinduced electron transfer, PGP can be used as an aqueous fluorescence ink with erasable and recoverable properties. The fluorescent patterns printed by PGP ink on paper can be rapidly erased and recovered by simple spraying a sequence of Cu²⁺ and ethylene diamine tetraacetic acid aqueous solutions. This erase/recover transformation can be repeated multiple times on the same paper. The multiple stimulus responsiveness of PGP makes it have potential applications in nanorobots, sensing, information encryption, and anticounterfeiting.

2D transition metal dichalcogenides (2D TMDs) have attracted increasing attention as promising electrode materials for supercapacitors (SCs). In this review, basic knowledge and information of 2D TMD-based SCs are introduced, recent advances in strategies focusing on doping, structure, composition, phase, configuration, electrolyte to improve their supercapacitor performance are summarized and future perspectives are proposed.

Abstract

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Using initiated chemical vapor deposition (iCVD), organic and hybrid thin films can form directly on substrates of virtually any composition and geometry. Free-radical polymerization of adsorbed monomers is initiated by vapor phase radicals formed by thermal decomposition. The established fundamentals enable the rational optimization of iCVD polymers and copolymers for sensing, optoelectronics, electrochemical energy storage, and biotechnology.

Abstract

The initiated chemical vapor deposition (iCVD) technique is an all-dry method for designing organic and hybrid polymers. Unlike methods utilizing liquids or line-of-sight arrival, iCVD provides conformal surface modification over intricate geometries. Uniform, high-purity, and pinhole-free iCVD films can be grown with thicknesses ranging from >15 µm to <5 nm. The mild conditions permit damage-free growth directly onto flexible substrates, 2D materials, and liquids. Novel iCVD polymer morphologies include nanostructured surfaces, nanoporosity, and shaped particles. The well-established fundamentals of iCVD facilitate the systematic design and optimization of polymers and copolymers. The functional groups provide fine-tuning of surface energy, surface charge, and responsive behavior. Further reactions of the functional groups in the polymers can yield either surface modification, compositional gradients through the layer thickness, or complete chemical conversion of the bulk film. The iCVD polymers are integrated into multilayer device structures as desired for applications in sensing, electronics, optics, electrochemical energy storage, and biotechnology. For these devices, hybrids offer higher values of refractive index and dielectric constant. Multivinyl monomers typically produce ultrasmooth and pinhole-free and mechanically deformable layers and robust interfaces which are especially promising for electronic skins and wearable optoelectronics.

Optoelectronic memristors (OMs) can emulate neurological functions within a bionic computing architecture, enabling energy-efficient in-memory computing. Identifying suitable techniques for integrating materials into integrated circuit platforms is imperative to advance the field. This review provides a comprehensive overview of the fundamental performance, mechanism, structures, applications, and integration roadmap of OMs aiming to establish a connection between materials and OM systems.

Abstract

Optoelectronic memristors (OMs) have emerged as a promising optoelectronic Neuromorphic computing paradigm, opening up new opportunities for neurosynaptic devices and optoelectronic systems. These OMs possess a range of desirable features including minimal crosstalk, high bandwidth, low power consumption, zero latency, and the ability to replicate crucial neurological functions such as vision and optical memory. By incorporating large-scale parallel synaptic structures, OMs are anticipated to greatly enhance high-performance and low-power in-memory computing, effectively overcoming the limitations of the von Neumann bottleneck. However, progress in this field necessitates a comprehensive understanding of suitable structures and techniques for integrating low-dimensional materials into optoelectronic integrated circuit platforms. This review aims to offer a comprehensive overview of the fundamental performance, mechanisms, design of structures, applications, and integration roadmap of optoelectronic synaptic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review seeks to provide insights into emerging technologies and future prospects that are expected to drive innovation and widespread adoption in the near future.

Ultrathin MXene thermoacoustic loudspeakers with the capability of shape configurations provide directivity-tunable and high sound generation under different mechanical deformations. MXene conductors with low heat-capacity-per-unit-area and parylene substrates with low thermal effusivity enable bidirectional and stable sound in concave/convex, on-needle, folded, and twisted configurations. High conformability can be affixed to diverse 3D surfaces, enabling focused and omnidirectional sound generation.

Abstract

Film-type shape-configurable speakers with tunable sound directivity are in high demand for wearable electronics. Flexible, thin thermoacoustic (TA) loudspeakers—which are free from bulky vibrating diaphragms—show promise in this regard. However, configuring thin TA loudspeakers into arbitrary shapes is challenging because of their low sound pressure level (SPL) under mechanical deformations and low conformability to other surfaces. By carefully controlling the heat capacity per unit area and thermal effusivity of an MXene conductor and substrates, respectively, it fabricates an ultrathin MXene-based TA loudspeaker exhibiting high SPL output (74.5 dB at 15 kHz) and stable sound performance for 14 days. Loudspeakers with the parylene substrate, whose thickness is less than the thermal penetration depth, generated bidirectional and deformation-independent sound in bent, twisted, cylindrical, and stretched-kirigami configurations. Furthermore, it constructs parabolic and spherical versions of ultrathin, large-area (20 cm × 20 cm) MXene-based TA loudspeakers, which display sound-focusing and 3D omnidirectional-sound-generating attributes, respectively.

Thermally and electrically conductive ink is designed with eutectic gallium indium (EGaIn) nanoparticle decorated silver (Ag) flake/polyvinyl butyral composite. The decorated nanoparticle provides a thermal transport junction and fills the gap between the Ag flakes, resulting in higher thermal conductivity. Besides, since the polymer binder provides the mechanical stability, this designed ink is promising for heat dissipation of soft electronics.

Abstract

Since heat generation in electronic devices causes thermal failure, heat dissipation is of critical importance. Furthermore, deformable devices are subjected to mechanical stress, therefore, mechanically stable thermal management material should be considered. Herein, a strategy for printable, thermally conductive, and mechanically stable composite ink for thermal management is introduced. Based on the galvanic replacement between eutectic gallium indium (EGaIn) nanoparticles and silver (Ag) flakes, decoration of the EGaIn nanoparticles on Ag flakes is resulted from the difference in standard reduction potential between Ag, Ga, and In. The resultant alloy formation(Ag–Ga or Ag–In) serves as the thermal transport junction between Ag flakes, leading to high thermal and electrical conductivity (≈140 W mK⁻¹ and ≈10⁶ S m⁻¹, respectively). In addition, owing to the polymer binder, the printed ink is mechanically stable on a substrate exhibiting stable thermal conductivity and sheet resistance under the cyclic bending test. Notably, the heat dissipation of the light-emitting diode (LED) showed better performance when applied with the developed composite ink compared to commercial Ag paste and thermal paste. The junction temperature of the LED is reduced effectively, resulting in a longer lifetime of the LED. The thermal management solution can be utilized in next-generation soft electronics.

Moisture-driven persistent self-oscillating bimorph film is designed from two-dimensionally nano-capsulating liquid metal with MXene nanosheets. This film actuator oscillates persistently with an actuating speed of ≈260° s ⁻¹ under 20% cm⁻¹ humidity gradience and generates an alternating faradic current with an amplitude of at least 1360 µA m⁻² under 0.5 T magnetic field.

Abstract

Harvesting electricity from ubiquitous atmospheric moisture has drawn growing research attention. Despite great advances, moisture generators still suffer from performance decay during long-term service. Recently, self-oscillating actuators driven by humidity gradience have attracted great interests, which may give a clue to harvest energy persistently via electromagnetic induction. In order to combine high electric conductivity with self-oscillating actuators, bimorph composites of 2D conductive MXene with liquid metal (i.e., EGaIn) are designed. In presence of marine alginate, EGaIn droplets can be encapsulated by MXene nanosheets in their suspension. And simple liquid-casting can produce biomorph actuating films with top MXene-rich layer and bottom EGaIn-rich layer of self-sintered EGaIn droplets. When exposing to a humidity gradience (e.g., 20% cm⁻¹), this biomorph actuator can oscillate persistently with an actuating speed of ≈260° s⁻¹ and a frequency of ≈0.5 Hz, while without any human intervention. Under a magnetic field (e.g., intensity ≈0.5 T), this self-oscillating behavior can generate an alternating faradic current with an amplitude of at least 1360 µA m⁻². Thus, this study may not only provide an alternative pathway for producing self-oscillating and conductive actuators, but also offer a new strategy for persistent energy harvest from atmospheric moisture.

The thermal oxidation behavior and mechanism of GaSe are directly uncovered at multi-scale using microscopic techniques. Various surface structures are obtained depending on the oxidation temperature, leading to the achievement of surface regulation. Importantly, the photoluminescence of GaSe is effectively enhanced due to the oxidation surface construction, indicating the oxidation surface engineering has great potential in design/development of Van der Waals chalcogenides with tunable properties.

Abstract

The investigation of the oxidation behavior of van der Waals chalcogenides holds significant importance in terms of preventing and controlling oxidation, utilizing surface oxidation structures to regulate properties, and advancing applications. Here, taking GaSe as a candidate, its thermal oxidation and surface structure evolution are intensively studied. Through systematic microscopic analyses, oxidized structures at multi-scale (from atomic scale to millimeters) are resolved, and various assembly heterogeneous surfaces including Ga₂Se₃/Ga₂O₃ and Ga₂O₃ multilayers are uncovered at different oxidation temperatures. The temperature-dependent oxidation behavior and surface structure evolution of the GaSe are revealed, and the oxidation mechanisms in the entire temperature range are also disclosed. Finally, the photoluminescence regulation of the GaSe is initially explored via thermal oxidation, demonstrating great potential for surface oxidation engineering. This study is not only of great importance for the deep understanding and utilization of GaSe oxidation, but also beneficial for materials/device design and development of relative systems.

Nature Communications, Published online: 22 September 2023; doi:10.1038/s41467-023-41597-9

High-resolution single-photon imaging is challenging due to complex hardware and noise disturbances. Here, the authors realise simultaneous single-photon denoising and super-resolution enhancement by physics-informed deep learning, with a physical multi-source noise model, two single-photon image datasets, and a deep transformer network.

Core@shell Nanocrystals

In article number 2303621, Gabriele Saleh, Luca De Trizio, Liberato Manna, and co-workers report the synthesis of near-infrared-emitting InAs@ZnSe core@shell nanocrystals with high photoluminescence quantum yield (PLQY). The high PLQY stems from the in situ formation of an In–Zn–Se interlayer which plays a key role in dampening the strain between the InAs core and the ZnSe shell.

2D Ferroionic States

In article number 2302419, Yishu Zhang, Yang Xu, Bin Yu, and co-workers report the fabrication of a full 2D van der Waals heterostructure ferroelectric semimetal junction to unravel the conductive mechanism of CuInP₂S₆, and present a detailed phase diagram of the competing mechanisms and transition boundaries with temperature and an external electric field. Based on this understanding, an artificial synapse with automatic gain control is demonstrated.

Nature Nanotechnology, Published online: 21 September 2023; doi:10.1038/s41565-023-01500-5

Biosynthesis of magnetosomes is of interest for a range of applications. Here, factors needed for magnetosome biosynthesis are evaluated and new diverse bacteria are engineered to biofabricate magnetic nanoparticles, facilitating translation to biotechnology and nanomedicine.

This review presents various methodologies for the production of solution-processed 2D nanomaterial dispersions with an emphasis on their synthetic strategies. The techniques involved in the fabrication of 2D vdW thin films are discussed for scalable electronic and optoelectronic applications. The potential of scalable 2D vdW thin films in driving advancements in both electronics and optoelectronics is discussed in detail.

Abstract

In the rapidly evolving field of thin-film electronics, the emergence of large-area flexible and wearable devices has been a significant milestone. Although organic semiconductor thin films, which can be manufactured through solution processing, have been identified, their utility is often undermined by their poor stability and low carrier mobility under ambient conditions. However, inorganic nanomaterials can be solution-processed and demonstrate outstanding intrinsic properties and structural stability. In particular, a series of two-dimensional (2D) nanosheet/nanoparticle materials have been shown to form stable colloids in their respective solvents. However, the integration of these 2D nanomaterials into continuous large-area thin with precise control of layer thickness and lattice orientation still remains a significant challenge. This review paper undertakes a detailed analysis of van der Waals thin films, derived from 2D materials, in the advancement of thin-film electronics and optoelectronic devices. The superior intrinsic properties and structural stability of inorganic nanomaterials are highlighted, which can be solution-processed and underscor the importance of solution-based processing, establishing it as a cornerstone strategy for scalable electronic and optoelectronic applications. A comprehensive exploration of the challenges and opportunities associated with the utilization of 2D materials for the next generation of thin-film electronics and optoelectronic devices is presented.

Nature, Published online: 20 September 2023; doi:10.1038/s41586-023-06353-5

To demonstrate the power of multistability, a specific class of groovy metasheets is introduced as a new shape-morphing platform that allows repeated switching from the flat state to multiple, precisely selected and stable three-dimensional shapes.

A novel tactile sensor, which integrates biomimetic slow-adapting mechanoreceptors in a soft medium, enables self-decoupled sensing of local pressure and strain at the contact surface. In robotic manipulation, the sensor can achieve the self-adaptive perception of material softness and enhance tactile perception by establishing two relevant deformation attributes (material softness and compliance) for an object.

Abstract

The perception of object's deformability in unstructured interactions relies on both kinesthetic and cutaneous cues to adapt the uncertainties of an object. However, the existing tactile sensors cannot provide adequate cutaneous cues to self-adaptively estimate the material softness, especially in non-standard contact scenarios where the interacting object deviates from the assumption of an elastic half-infinite body. This paper proposes an innovative design of a tactile sensor that integrates the capabilities of two slow-adapting mechanoreceptors within a soft medium, allowing self-decoupled sensing of local pressure and strain at specific locations within the contact interface. By leveraging these localized cutaneous cues, the sensor can accurately and self-adaptively measure the material softness of an object, accommodating variations in thicknesses and applied forces. Furthermore, when combined with a kinesthetic cue from the robot, the sensor can enhance tactile expression by the synergy of two relevant deformation attributes, including material softness and compliance. It is demonstrated that the biomimetic fusion of tactile information can fully comprehend the deformability of an object, hence facilitating robotic decision-making and dexterous manipulation.

An overview of the recent advances in implantable optoelectronics for neural activity monitoring and modulation is provided. Combining optical and electrical modes in a unitary neural network interface has gained momentum in recent years, and controlling the spatial coverage of illumination, designing light-activated modulators, and developing wireless light delivery and data transmission are crucial for maximizing the use of optical neuromodulation.

Abstract

Optogenetic modulation of brain neural activity that combines optical and electrical modes in a unitary neural system has recently gained robust momentum. Controlling illumination spatial coverage, designing light-activated modulators, and developing wireless light delivery and data transmission are crucial for maximizing the use of optical neuromodulation. To this end, biocompatible electrodes with enhanced optoelectrical performance, device integration for multiplexed addressing, wireless transmission, and multimodal operation in soft systems have been developed. This review provides an outlook for uniformly illuminating large brain areas while spatiotemporally imaging the neural responses upon optoelectrical stimulation with little artifacts. Representative concepts and important breakthroughs, such as head-mounted illumination, multiple implanted optical fibers, and micro-light-delivery devices, are discussed. Examples of techniques that incorporate electrophysiological monitoring and optoelectrical stimulation are presented. Challenges and perspectives are posed for further research efforts toward high-density optoelectrical neural interface modulation, with the potential for nonpharmacological neurological disease treatments and wireless optoelectrical stimulation.

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.

Abstract

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.

Liquid metal synthesis facilitates precise atomic-scale material engineering. An instant-in-air method is presented that introduces oxygen vacancies into 2D bismuth oxide nanosheets, disrupting its centrosymmetry and enabling energy transducing and memory functions. These nanosheets exhibit intriguing piezoelectric, ferroelectric, mechanical, friction, and magnetic properties. These atomically thin, mechanically flexible, memory-capable, power-generating crystals are pivotal for technological progress in devices.

Abstract

Atomically thin, mechanically flexible, memory-functional, and power-generating crystals play a crucial role in the technological advancement of portable devices. However, the adoption of these crystals in such technologies is sometimes impeded by expensive and laborious synthesis methods, as well as the need for large-scale, mechanically stable, and air-stable materials. Here, an instant-in-air liquid metal printing process utilizing liquid bismuth (Bi) is presented, forming naturally occurring, air-stable, atomically thin, mechanically flexible nanogenerators and ferroelectric oxides. Despite the centrosymmetric nature of the monoclinic P21/c system of achieved α-Bi₂O_3-δ the high kinetics of liquid metal synthesis leads to the formation of vacancies that disrupt the symmetry which is confirmed by density functional theory (DFT) calculations. The polarization switching is measured and utilized for ferroelectric nanopatterning. The exceptional attributes of these atomically thin multifunctional stable oxides, including piezoelectricity, mechanical flexibility, and polarizability, present significant opportunities for developing nano-components that can be seamlessly integrated into a wide range of devices.

Confinement effects in molecular beam epitaxy-grown (111)-oriented antimony-telluride (Sb₂Te₃) thin films are investigated for thicknesses ranging from 1.3 to 55.8 nm. Pronounced and persistent structural, vibrational, and optical changes upon varying film thickness are found. The observed trends are discussed in terms of a recently proposed bonding mechanism that renders the material a suitable candidate for phase-change and thermoelectric applications.

Abstract

Scaling effects in Sesqui-chalcogenides are of major interest to understand and optimize their performance in heavily scaled applications, including topological insulators and phase-change devices. A combined experimental and theoretical study is presented for molecular beam epitaxy-grown films of antimony-telluride  (Sb₂Te₃). Structural,vibrational, optical, and bonding properties upon varying confinement are studied for thicknesses ranging from 1.3 to 56 nm. In ultrathin films, the low-frequency coherent phonons of A_1g ¹ symmetry are softened compared to the bulk (64.5 cm⁻¹ at 1.3 nm compared to 68 cm⁻¹ at 55.8 nm). A concomitant increase of the high-frequency A_1g ² Raman mode is seen. X-ray diffraction analyses unravel an accompanying out of plane stretch by 5%, mainly stemming from an increase in the Te-Te gap. This conclusion is supported by density functional theory slab models, which reveal a significant dependency of chemical bonding on film thickness. Changes in atomic arrangement, vibrational frequencies, and bonding extend over a thickness range much larger than observed for other material classes. The finding of these unexpectedly pronounced thickness-dependent effects in quasi-2D material Sb₂Te₃ allows tuning of the film properties with thickness. The results are discussed in the context of a novel bond-type, characterized by a competition between electron localization and delocalization.

This work reviews the recent progress of conductive hydrogels for bioelectronic devices from the aspect of classifications and typical applications. Furthermore, the current challenges and the corresponding strategies for the future development are in-depth discussed, aiming to promote the practical application of conductive hydrogels in the fields of biomedicine and clinical medicine.

Abstract

Conductive hydrogels (CHs) for flexible bioelectronic devices have raised great attention due to their tunable mechanical performances, adhesion, anti-swelling, and biocompatibility. This review summarizes the current development of conductive hydrogel-based flexible bioelectronic devices in the aspect of classifications and applications. Firstly, the conductive hydrogels are classified into two kinds according to the types of conductivity: ionic conductive hydrogels and electronic conductive hydrogels (hydrogel based on pure conductive materials, introducing conductive micro/nano-materials). Secondly, the applications of conductive hydrogels for bioelectronic device, like wearable devices (strain sensor, body fluid detector, serviced in extreme environment), tissue engineering (skin, heart, nerve, muscle), and other applications (bionic robot, cancer treatment), are highly illustrated. Finally, a depth outlook is given, which aims to promote the development of this field in the future.

Herein, an effective binary metal precursor co-reaction chemical vapor deposition method to synthesize the self-intercalated V₃S₅ nanosheets is revealed. A phase transition in V₃S₅ crystal appears at 20 K. Importantly, the electron–electron interaction was confirmed in the V₃S₅ nanosheets. This work realizes a new strategy to synthesize 2D intercalated V _x S _y single crystals for fundamental studies and spintronic applications.

Abstract

2D intercalated vanadium chalcogenides have attracted intensive interest based on their physical properties and potential applications. However, controllable synthesis of the intercalated vanadium chalcogenides via chemical vapor deposition is still a big challenge. Here, a binary metal precursor co-reaction growth mechanism to manipulate the evaporation rate of vanadium precursors is reported, thus the intercalated 2D V_{1+ X} S₂ – V₃S₅ single crystal can be controllably synthesized. The quality of 2D V₃S₅ nanosheets is identified by Raman spectroscopy and high-resolution scanning transmission electron microscopy. Interestingly, a phase transition in 2D metallic V₃S₅ nanosheets is observed at 20 K. Meanwhile, the resistance upturn and unsaturated negative magnetoresistance induced by electron–electron interaction is confirmed. This work proposes a new strategy to synthesize the 2D intercalated V _x S _y single crystals with different compositions for studying their excellent properties and potential applications.

Synthesized 2D (PA)₂PbBr₄ perovskite microplatelets enable the development of high-performance detectors with exceptional sensitivity to UV light, a broad linear dynamic range, and outstanding stability, while also demonstrating excellent applicability for UV weak-light imaging.

Abstract

Weak-light imaging holds immense significance in various imaging applications. Recently, there has been significant research focused on 2D perovskites for photodetectors (PDs), owing to their superior photoelectric properties. However, the utilization of 2D perovskites for high-performance weak-light detection remains limited, and there is a notable absence of demonstration in weak-light ultraviolet (UV) imaging. Herein, a high-sensitive UV detectors with an ultra-low detection limit for weak-light imaging are demonstrated, utilizing 2D perovskite (PA)₂PbBr₄ (PPB) single crystals (SCs). Leveraging the exceptional quality of SCs, the PPB-based PD exhibits outstanding operational performances, including a low dark current of 0.735 pA, high on/off ratio of 4150 under 263.3 mW cm⁻² illimitation,  and extensive linear dynamic range of 153.61 dB, which is currently the highest reported value among 2D perovskite SC detectors. Notably, PPB PDs demonstrate a remarkable response under 5.49 nW cm⁻² illumination, enabling it to exhibit outstanding photo-response with an excellent detectivity of 2.3 × 10¹³ Jones and responsivity of 2.22 A W⁻¹. Importantly, high-resolution images are successfully obtained under weak-light illumination. These findings underscore the immense potential of 2D perovskite for UV weak-light imaging.

To develop high performance phosphor, Ln³⁺(Ln = Dy, Ho, Er, Tm, Nd, and Pr) are co-doped into Sr₂Si₅N₈:Eu²⁺ to form Sr₂Si₅N₈:Eu²⁺,xLn³⁺ (Ln _x -258, 0 ≤ x ≤ 0.05). The Dy_0.01-258 sample has a high external quantum efficiency of 78.6%, and the luminescence intensity at 200 °C can be maintained at 94.7% of room temperature. This phosphor also exhibits excellent cathodoluminescence performance.

Abstract

To solve the problem of thermal stability of the red-emitting phosphor Sr₂Si₅N₈:Eu²⁺ with great valuable luminescence performance, trivalent rare earth ions Ln³⁺ (Ln = Dy, Ho, Er, Tm, Nd, and Pr) are co-doped into Sr₂Si₅N₈: Eu²⁺ lattice to form thermally robust phosphors Sr₂Si₅N₈:Eu²⁺,xLn³⁺(Ln _x -258, 0 ≤ x ≤ 0.05). The successful incorporation of rare earth ions in the crystal structure and the regulation of luminescent properties are proven by a variety of material characterization techniques and analysis. Although the co-doping of the selected rare earth ions reduces the luminescence intensity of the phosphor, the Dy_0.01-258 sample still has a high external quantum efficiency (EQE) of 78.6%. More importantly, the co-doping of Dy³⁺ with x = 0.01 significantly improves the luminescent thermal stability of phosphors at high temperature and the luminescence intensity of Dy_0.01-258 samples at 200 °C can be maintained at 94.7% of room temperature. The thermoluminescence spectrum shows that the defects brought about by co-doping of Dy³⁺ with x = 0.01 introduce trap energy levels, which can compensate for the Eu²⁺ luminescence at high temperature. At the same time, the cathodoluminescence mapping and spectra show that the phosphor has a high saturation current under high-energy electron bombardment, which indicates that this nitride phosphor also has the potential to be used in field emission display (FEDs). Based on its extraordinary EQE and thermal stability data, this nitride phosphor is the first-rate among the red phosphors for pc-wLEDs, and has excellent application prospects in FEDs.