Jing Zhang

Hollow Nanospheres

SMART RHESINs are novel iron oxide-filled hollow nanospheres coated with luminescent Eu(III) complex-containing silica nanoparticles. Unlike typical core/shell nanoparticles, SMART RHESINs retain unchanged effective Brownian and Néel relaxation even when fully immobilised in a viscous media. This unique behaviour makes SMART RHESINs potential quantitative magnetic particle imaging (MPI) probes for biological applications. More details can be found in article number 2301997 by Esther S. Rösch and co-workers.

Force-triggered self-destructive hydrogels are developed by using mechano-responsive DNA hairpins  that crosslink the gel network. The DNA is protected by folding under static conditions, but under force, cryptic sites are exposed, which allows Cas12a nuclease to destroy the phosphodiester DNA backbone. In this work, tunable force sensitivity is demonstrated to trigger self-destruction and cargo release from the hydrogel.

Abstract

Self-destructive polymers (SDPs) are defined as a class of smart polymers that autonomously degrade upon experiencing an external trigger, such as a chemical cue or optical excitation. Because SDPs release the materials trapped inside the network upon degradation, they have potential applications in drug delivery and analytical sensing. However, no known SDPs that respond to external mechanical forces have been reported, as it is fundamentally challenging to create mechano-sensitivity in general and especially so for force levels below those required for classical force-induced bond scission. To address this challenge, the development of force-triggered SDPs composed of DNA crosslinked hydrogels doped with nucleases is described here. Externally applied piconewton forces selectively expose enzymatic cleavage sites within the DNA crosslinks, resulting in rapid polymer self-degradation. The synthesis and the chemical and mechanical characterization of DNA crosslinked hydrogels, as well as the kinetics of force-triggered hydrolysis, are described. As a proof-of-concept, force-triggered and time-dependent rheological changes in the polymer as well as encapsulated nanoparticle release are demonstrated. Finally, that the kinetics of self-destruction are shown to be tuned as a function of nuclease concentration, incubation time, and thermodynamic stability of DNA crosslinkers.

Tubular microtubes of single-crystalline Si nanomembranes for photodetectors are prepared by a releasing and rolling process. The tubular geometry can trap light to improve the photoresponsivity of ultra-thin Si nanomembranes and demonstrate the advantage of wide-angle light coupling. Furthermore, the Si microtubes exhibit obvious polarization angle-dependent light absorption, enabling polarization-sensitive detection in the range of visible to near-infrared.

Abstract

Freestanding single-crystalline nanomembranes and their assembly have broad application potential in photodetectors for integrated chips. However, the release and self-assembly process of single-crystalline semiconductor nanomembranes still remains a great challenge in on-chip processing and functional integration, and photodetectors based on nanomembrane always suffer from limited absorption of nanoscale thickness. Here, a non-destructive releasing and rolling process is employed to prepare tubular photodetectors based on freestanding single-crystalline Si nanomembranes. Spontaneous release and self-assembly are achieved by residual strain introduced by lattice mismatch at the epitaxial interface of Si and Ge, and the intrinsic stress and strain distributions in self-rolled-up Si nanomembranes are analyzed experimentally and computationally. The advantages of light trapping and wide-angle optical coupling are realized by tubular geometry. This Si microtube device achieves reliable Ohmic contact and exhibits a photoresponsivity of over 330 mA W⁻¹, a response time of 370 µs, and a light incident detection angle range of over 120°. Furthermore, the microtubular structure shows a distinct polarization angle-dependent light absorption, with a dichroic ratio of 1.24 achieved at 940 nm. The proposed Si-based microtubes provide new possibilities for the construction of multifunctional chips for integrated circuit ecosystems in the More than Moore era.

A thermodynamically stable twin topotactic/nontopotactic Cu²⁺ accommodation mechanism is unprecedentedly established in an aqueous system. Nontopotactic conversion significantly improves the redox ability for superior ion storage, and the topotactic intercalated TiSe₂ structure anchors the reduced titanium monomers with high affinity and promotes efficient charge transfer. The proposed mechanism synergistically enhances the capacity and reversibility of advanced rechargeable aqueous battery.

Abstract

Titanium selenide (TiSe₂), a model transition metal chalcogenide material, typically relies on topotactic ion intercalation/deintercalation to achieve stable ion storage with minimal disruption of the transport pathways but has restricted capacity (<130 mAh g⁻¹). Developing novel energy storage mechanisms beyond conventional intercalation to break capacity limits in TiSe₂ cathodes is essential yet challenging. Herein, the ion storage properties of TiSe₂ are revisited and an unusual thermodynamically stable twin topotactic/nontopotactic Cu²⁺ accommodation mechanism for aqueous batteries is unraveled. In situ synchrotron X-ray diffraction and ex situ microscopy jointly demonstrated that topotactic intercalation sustained the ion transport framework, nontopotactic conversion involved localized multielectron reactions, and these two parallel reactions are miraculously intertwined in nanoscale space. Comprehensive experimental and theoretical results suggested that the twin-reaction mechanism significantly improved the electron transfer ability, and the reserved intercalated TiSe₂ structure anchored the reduced titanium monomers with high affinity and promoted efficient charge transfer to synergistically enhance the capacity and reversibility. Consequently, TiSe₂ nanoflake cathodes delivered a never-before-achieved capacity of 275.9 mAh g⁻¹ at 0.1 A g⁻¹, 93.5% capacity retention over 1000 cycles, and endow hybrid batteries (TiSe₂-Cu||Zn) with a stable energy supply of 181.34 Wh kg⁻¹ at 2339.81 W kg⁻¹, offering a promising model for aqueous ion storage.

Vascular grafts with circumferentially and axially oriented structures are fabricated to achieve the simulation of endothelial and medial layers of blood vessels. The spatio-anisotropic features of the different layers improve biofunctions of both endothelial and smooth muscle cells, inducing vessel regeneration similar to native blood vessels. The new fabrication strategy provides bioactive composite grafts with complex biomimetic features.

Abstract

Porous grafts facilitate constructive remodeling of blood vessels. Incorporating multiple biomimetic cues to porous grafts can promote vascular regeneration. However, the fabrication of such medical devices remains challenging. Here, beta-sheet rich silk nanofibers (BSN) are added to poly(vinyl alcohol) (PVA) solution and aggregated under a cylindric electric field to form circumferentially and axially oriented tubular structures, to simulate the endothelial and media layers of blood vessels. PVA in the aligned tubes is then crystallized through repeat freezing–thawing process to offer mechanical performances. Through tuning the ratio of BSN and PVA, the composite tubes with dual anisotropic microstructures exhibit better mechanical properties than pure PVA vascular grafts. Significantly improved cell adhesion, spreading, proliferation, and alignment are achieved. Both endothelial and smooth muscle cells show improved biological activity on the grafts due to the regulatory roles of the aligned structures. In vivo studies reveal the formation of endothelial layers within four weeks of implantation, ensuring long-term patency. The endothelial and smooth muscle double layers are regenerated after eight months postimplantation, forming hierarchical microstructures and compositions similar to native vessels. The porous composite grafts with multiple aligned structures guide vascular remodeling to regenerate blood vessels, demonstrating potential for clinical translation.

Energy transfer (ET) between quantum emitters is a key process for many scientific domains and technological applications, and can be influenced by strategic placement of appropriate materials in the vicinity. However, all explored conventional isotropic materials lacks directional control over this process. Here, we show that multilayered black phosphorus (bP), a novel anisotropic two-dimensional material, can simultaneously dramatically boost and directionally control ET rates in the near-field regime. We find that bP exhibits a critical thickness above which the ET rates increase by several orders of magnitude compared to vacuum. Moreover, we demonstrate that bP can manipulate the ET in specific in-plane directions due to its strong in-plane anisotropy. Our results build the framework and provide fundamental insights into the mechanisms of ET near anisotropic materials, and open up new possibilities for designing and optimizing ET-based devices, systems and applications.

The rich nature of van der Waals interactions between artificially-stacked atomic layers has been demonstrated by various quantum states and resonant tunneling transport in low-dimensional materials. However, the role of topological fluctuations in quantum transport through artificially-stacked junctions of 2D superconducting materials, and the resulting energy dissipation, remain elusive. In this research, unique phase-slip centers are designed in artificially-stacked junction areas, where nonequilibrium quasiparticles are formed and relaxed with energy dissipation. The phase slips are observed as voltage steps (peaks or valleys) in transport measurements across a junction between two exfoliated NbSe2 flakes, and at a distance of 4 μm from the junction using local and nonlocal chemical potential probes. Accordingly, two types of energy dissipation modes are newly identified in the artificially-stacked NbSe2 when subjected to an in-plane magnetic field, which implies distinct vortex formation and current flow in the superconducting junction under magnetic fields.

The elongation of the luminescence kinetics of the ²E state of Mn⁴⁺ ions with increasing applied pressure in the Sr₄Al₁₄O₂₅ Mn⁴⁺ enables the development of a lifetime-based sensor with relative sensitivity as high as 35% GPa⁻¹.

Abstract

Enabling remote and temperature-independent pressure sensing based on luminescence kinetics holds significant potential for the development of a luminescence pressure sensor with a wide array of applications. To meet these requirements, in this work, a unique lifetime-based luminescence manometer is demonstrated for which an increase in pressure results in an elongation of lifetime of ²E state of Mn⁴⁺ due to a change in the probability of radiative depopulation of the ²E level of Mn⁴⁺ ions with an unprecedentedly high sensitivity of 35% GPa⁻¹. Furthermore, the pressure-induced modification in the covalency of the Mn⁴⁺─O²⁻ bond facilitates a manometer operating in spectral band shift and ratiometric modes with sensitivities of 26 cm⁻¹ GPa⁻¹ (1.2 nm GPa⁻¹) and 24.8% GPa⁻¹, respectively. This study firmly supports the belief that the distinct pressure-dependent kinetics governing the depopulation of Mn⁴⁺ ions at the ²E level, along with the resulting advantageous manometric performance, will pave the way for a new research trajectory in luminescence manometry.

Permanent magnetic particles embedded in a viscoelastic putty matrix result in a self-healing soft magnetic material with both high remanence and low coercivity, providing hard-magnetic performance without the need for inaccessible strong magnetic fields. Programmable and reconfigurable magnetization, frequency-dependent force output, and easy to shape and assemble, magnetic putty can be a versatile tool in research prototyping and inspire future explorations.

Abstract

Magnetically hard materials are widely used to build soft magnetic robots, providing large magnetic force/torque and macrodomain programmability. However, their high magnetic coercivity often presents practical challenges when attempting to reconfigure magnetization patterns, requiring a large magnetic field or heating. In this study, magnetic putty is introduced as a magnetically hard and soft material with large remanence and low coercivity. It is shown that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one-tenth of its coercivity. Additionally, magnetic putty is a malleable, autonomous self-healing material that can be recycled and repurposed. The authors anticipate magnetic putty could provide a versatile and accessible tool for various magnetic robotics applications for fast prototyping and explorations for research and educational purposes.

This study introduces multi-agent microrobot control using a laser and shape-memory alloy (SMA) structure. SMA microrobots can navigate complex paths and bypass obstacles through algorithm-based control and vision-based feedback. With high energy density, fast actuation speed, chemical resistance, and biocompatibility, multi-agent SMA microrobot control has potential applications in microchemical reactions and biomedical devices.

Abstract

Microrobots have a high demand for multi-agent control to enhance their effectiveness in performing various tasks. While light is a power source that can control many micro-structures, the range of controllable objects is limited to polymeric structures, simple particles, or bio-cells. This study presents a multi-agent microrobot control platform that utilizes a laser and artificial structures made of a shape-memory alloy (SMA). The SMA microrobots can travel at speeds of up to 150 µm s⁻¹ (2.5 BL s⁻¹) and demonstrate complex path navigation, algorithm-based control, and vision-based feedback control. By utilizing the minimum potential energy algorithm, the paths of microrobots are optimized to perform navigation tasks in the shortest routes, bypassing obstacles. Additionally, the vision system calibrates the paths before every laser scanning cycle. Finally, the SMA microrobot platform with algorithm-based path planning and real-time feedback allows multi-agent control, overcoming inconsistent locomotion caused by the uncertainty of complex microenvironments. As SMAs have a high energy density, fast actuation speed, good chemical resistance, and excellent biocompatibility, these SMA microrobots are expected to open up a wide range of potential applications for micro-robotics in various fields, such as micro-chemical reactions and biomedical devices.

The proximity sensor plays a role in character recognition. Based on the edge electric field and the gas dielectric, the discriminable recognition toward conductor and insulator is realized only based on a single e-tattoo device. This work offers a new route to realize material category recognition, providing a user-friendly solution to help the visual impaired reintegrate into society.

Abstract

Easy and convenient reading for blinds is of great significance for lowering their learning, entertainment, and communication barrier, and improving their living quality. The general solution is to learn braille, far from satisfying the meet of the blinds’ daily learning and communication. Here, a new-type conductor/insulator-identifiable e-tattoo proximity sensor is developed by simply depositing the circular interdigitated electrodes on organic semiconductor. The discriminable recognition toward conductors and insulators is realized only based on a single e-tattoo device. The sensors not only enable recognition of the protruding characters like braille based on distance difference, but also enable recognition of the handwriting ink-brush and pencil graphite characters based on the unique advantage of the sensors in distinguishing conduct and insulator. These results open a new route to realize the material category recognition, provide a user-friendly way to help the visual impaired effectively reintegrate into society, and broaden the application field of proximity sensors.

GO-PVA/PVA polymer electret synaptic transistors with good stability and bending resistance are prepared by exploiting the slow polarization effect of dipoles. The devices can simulate various biological synaptic properties such as short-term plasticity, long-term plasticity, and pair-pulse facilitation. Furthermore, the recognition accuracy of images is simulated based on the constructed artificial neural network, which achieves 86.8% for the MNIST dataset.

Abstract

Polymer electret synaptic transistor is a promising three-terminal artificial synaptic device. In this work, the electrical characteristics of the composite insulator and transistor are enhanced by modulating the concentration of the 2D nanofiller graphene oxide (GO) and the stacked film structure based on a polyvinyl alcohol (PVA) matrix. The GO-PVA/PVA polymer electret synaptic transistors before and after dynamic/static bending exhibit typical synaptic characteristics, including short-term plasticity, long-term plasticity, pair-pulse facilitation, spike-timing-dependent plasticity, and “learning–forgetting–relearning” features. Importantly, the device exhibits good cycling stability, uniformity and linearity in the potentiation-depression cycling test, which is beneficial for improving the accuracy of neuromorphic computations. Also, it shows extremely low energy consumption (≈0.32 fJ). The recognition accuracy of images is simulated based on the constructed artificial neural network, which achieves 86.8% for the MNIST dataset. In addition, the devices maintain high recognition accuracy after dynamic/static bending, indicating that the devices are extremely bend-resistant. The GO-PVA/PVA polymer electret synaptic transistor is expected to be a potential candidate for neuromorphic computations and electronic skin.

The present study demonstrates the development of thefirst clananomaterials simultaneously exhibiting multiple efficient nonlinear optical (NLO) processes, nam second harmonic generation, third harmonic generation, and up-conversion photoluminescence. The synthesized nanoparticles are incorporated in 3D-printable polymers, fibers, and inks for anti-counterfeiting, fingerprint detection, biomedical applications, information processing, and thefirst dual-mode NLO optical coding based on parametric and nonparametric processes.

Abstract

Nonlinear optical materials are essential in areas such as nanophotonics, optical information processing, and biomedical imaging. However, nanomaterials employed for these diverse applications to date are efficient only for one type of nonlinear optical activity. Herein, the first multimodal nonlinear optically active class of nanomaterials based on lanthanide-doped lithium niobate nanoparticles, which simultaneously exhibit unprecedentedly efficient second and third harmonic generation, as well as up-conversion photoluminescence, is reported. These dielectric nanoparticles retain their high nonlinear optical conversion efficiency both as powder and as aqueous colloidal solution. The high stability also allows for the fabrication of optically active biocompatible micron-sized fibers and polymer-based 3D-printable objects, as well as for fingerprint detection. Finally, the first 8-bit coding platform purely based on multimodal nonlinear optical activity originating from different parametric and nonparametric processes is demonstrated, showcasing the technological potential of these materials for both anti-counterfeiting and advanced optical information processing.

Nature Communications, Published online: 15 September 2023; doi:10.1038/s41467-023-40686-z

Designing bio-inspired multisensory neurons remains a challenge. Here, the authors develop an artificial visuotactile neuron based on the integration of a photosensitive monolayer MoS2 memtransistor and a triboelectric tactile sensor capable of super-additive response, inverse effectiveness effect, and temporal congruency.

Using direct magnetic imaging of CrSBr, a van der Waals material 2D antiferromagnet, it is demonstrated that the magnetic anisotropy and moment density are nearly preserved down to the monolayer. These images reveal the formation of Néel magnetic domain walls down to the monolayer. This material shows remarkable stability even for monolayer exposed to air.

Abstract

Recent advancements in 2D materials have revealed the potential of van der Waals magnets, and specifically of their magnetic anisotropy that allows applications down to the 2D limit. Among these materials, CrSBr has emerged as a promising candidate, because its intriguing magnetic and electronic properties have appeal for both fundamental and applied research in spintronics or magnonics. In this work, nano-SQUID-on-tip (SOT) microscopy is used to obtain direct magnetic imaging of CrSBr flakes with thicknesses ranging from monolayer (N = 1) to few-layer (N = 5). The ferromagnetic order is preserved down to the monolayer, while the antiferromagnetic coupling of the layers starts from the bilayer case. For odd layers, at zero applied magnetic field, the stray field resulting from the uncompensated layer is directly imaged. The progressive spin reorientation along the out-of-plane direction (hard axis) is also measured with a finite applied magnetic field, allowing evaluation of the anisotropy constant, which remains stable down to the monolayer and is close to the bulk value. Finally, by selecting the applied magnetic field protocol, the formation of Néel magnetic domain walls is observed down to the single-layer limit.

Eutectic gallium indium (EGaIn) is an attractive conductor for stretchable electronics but its high surface tension makes sub-micrometer patterning challenging. This limitation is overcome by electrodeposition, a “bottom-up” approach that benefits from the resolution of mature nanofabrication methods. A record-high integration of EGaIn lines of 300 nm half-pitch is achieved. Moreover, vertical integration is enabled, leading to omnidirectionally stretchable 3D electronics.

Abstract

The advancement of highly integrated stretchable electronics requires the development of scalable sub-micrometer conductor patterning. Eutectic gallium indium (EGaIn) is an attractive conductor for stretchable electronics, as its liquid metallic character grants it high electrical conductivity upon deformation. However, its high surface tension makes its patterning with sub-micrometer resolution challenging. In this work, this limitation is overcome by way of the electrodeposition of EGaIn. A non-aqueous acetonitrile-based electrolyte that exhibits high electrochemical stability and chemical orthogonality is used. The electrodeposited material leads to low-resistance lines that remain stable upon (repeated) stretching to a 100% strain. Because electrodeposition benefits from the resolution of mature nanofabrication methods used to pattern the base metal, the proposed “bottom-up” approach achieves a record-high density integration of EGaIn regular lines of 300 nm half-pitch on an elastomer substrate by plating on a gold seed layer prepatterned by nanoimprinting. Moreover, vertical integration is enabled by filling high-aspect-ratio vias. This capability is conceptualized by the fabrication of an omnidirectionally stretchable 3D electronic circuit, and demonstrates a soft-electronic analog of the stablished damascene process used to fabricate microchip interconnects. Overall, this work proposes a simple route to address the challenge of metallization in highly integrated (3D) stretchable electronics.

Advanced Materials, Volume 35, Issue 37, September 14, 2023.

Inspired by the microscopic dynamics in biological system, a dynamic memristor as an artificial dendrite and a Mott memristor as a spike-firing soma are integrated to construct a dendritic neuron for high-efficiency spatial-temporal information processing. Furthermore, a bio-plausible dendritic neural network is hardware implemented to demonstrate human-motion recognition, showing nearly 20% improvement in accuracy and 1000× higher powerefficiency than a graphics processing unit.

Abstract

Diverse microscopic ionic dynamics help mediate the ability of a biological neural network to handle complex tasks with low energy consumption. Thus, rich internal ionic dynamics in memristors based on transition metal oxide are expected to provide a unique and useful platform for implementing energy-efficient neuromorphic computing. To this end, a titanium oxide (TiO_x)-based interface-type dynamic memristor and an niobium oxide (NbO_x)-based Mott memristor are integrated as an artificial dendrite and spike-firing soma, respectively, to construct a dendritic neuron unit for realizing high-efficiency spatial-temporal information processing. Further, a dendritic neural network is hardware-implemented for spatial-temporal information processing to highlight the computational advantages achieved by incorporating dendritic functions in the network. Human motion recognition is demonstrated using the Nanyang Technological University-Red Green Blue (NTU-RGB) dataset as a benchmark spatial-temporal task; it shows a nearly 20% improvement in accuracy for the memristors-based hardware incorporating dendrites and a 1000× advantage in power efficiency compared to that of the graphics processing unit (GPU). The dendritic neuron developed in this study can be considered a critical building block for implementing more bio-plausible neural networks that can manage complex spatial-temporal tasks with high efficiency.

Nature Synthesis, Published online: 14 September 2023; doi:10.1038/s44160-023-00396-2

A chemical dedoping technique is introduced to mitigate excessive electron doping in molecular cation intercalated MoS2, producing a stable bulk monolayer material with monolayer-like optical properties but a much larger optical cross-section.

A memristor-based chip supporting efficient fully on-chip learning for edge intelligence applications was developed.

Nature, Published online: 14 September 2023; doi:10.1038/d41586-023-02900-2

The four-legged miniature machine is powered by tiny explosions.

Nature Electronics, Published online: 14 September 2023; doi:10.1038/s41928-023-01020-z

A neuromorphic biosensor that consists of a sensor input layer, an array of organic neuromorphic devices (forming a hardware neural network) and an output classification layer can be trained on the chip to classify a model disease and then retrained on the chip by switching the sensor input signals.

The nanoscale of SnS₂/BiVO₄ heterostructure is synthesized by chemical vapor deposition and hydrothermal method using a morphological design and energy band structure analysis. The Z-scheme SnS₂/BiVO₄ heterostructure photodetector demonstrates a high photoresponsivity (5.05 mA W⁻¹ at 0 V) and a fast response (≈6 ms). The heterostructure also shows a high hydrogen production rate (0.36 mmol cm⁻² h⁻¹ at 0.8 V).

Abstract

The construction of nanostructured Z-scheme heterostructure is a powerful strategy for realizing high-performance photoelectrochemical (PEC) devices such as self-powered photodetectors and water splitting. Considering the band structure and internal electric field direction, BiVO₄ is a promising candidate to construct SnS₂-based heterostructure. Herein, the direct Z-scheme heterostructure of vertically oriented SnS₂ nanosheet on BiVO₄ nanoflower is rationally fabricated for efficient self-powered PEC photodetectors. The Z-scheme heterostructure is identified by ultraviolet photoelectron spectroscopy, photoluminescence spectroscopy, PEC measurement, and water splitting. The SnS₂/BiVO₄ heterostructure shows a superior photodetection performance such as excellent photoresponsivity (10.43 mA W⁻¹), fast response time (6 ms), and long-term stability. Additionally, by virtue of efficient Z-scheme charge transfer and unique light-trapping nanostructure, the SnS₂/BiVO₄ heterostructure also displays a remarkable photocatalytic hydrogen production rate of 54.3 µmol cm⁻² h⁻¹ in Na₂SO₃ electrolyte. Furthermore, the synergistic effect between photo-activation and bias voltage further improves the PEC hydrogen production rate of 360 µmol cm⁻² h⁻¹ at 0.8 V, which is an order of magnitude above the BiVO₄. The results provide useful inspiration for designing direct Z-scheme heterostructures with special nanostructured morphology to signally promote the performance of PEC devices.

Nature Communications, Published online: 09 September 2023; doi:10.1038/s41467-023-40784-y

Magnetization reversal in magnetic topological insulators drives quantum phase transitions between quantum anomalous Hall, axion insulator, and normal insulator states. Using novel analysis protocol, the authors investigate critical behaviours of these transitions and establish their electronic origin.

High-quality 2D ferroelectric perovskite films with mixed spacer cations (BA⁺ and BDA²⁺) are prepared for self-powered photodetectors (PDs). The self-powered ultraviolet (UV) PDs exhibit excellent photoelectric properties, together with excellent reproducibility and stability. After applying pressures to the PD, the maximum responsivities can be modulated by the piezo–phototronic effect with an effective enhancement ratio of 480%.

Abstract

Self-powered photodetectors (PDs) have the advantages of no external power requirement, wireless operation, and long life. Spontaneous ferroelectric polarizations can significantly increase built-in electric field intensity, showing great potential in self-powered photodetection. Moreover, ferroelectrics possess pyroelectric and piezoelectric properties, beneficial for enhancing self-powered PDs. 2D metal halide perovskites (MHPs), which have ferroelectric properties, are suitable for fabricating high-performance self-powered PDs. However, the research on 2D metal halide perovskites ferroelectrics focuses on growing bulk crystals. Herein, 2D ferroelectric perovskite films with mixed spacer cations for self-powered PDs are demonstrated by mixing Ruddlesden–Popper (RP)-type and Dion–Jacobson (DJ)-type perovskite. The (BDA_0.7(BA₂)_0.3)(EA)₂Pb₃Br₁₀ film possesses, overall, the best film qualities with the best crystalline quality, lowest trap density, good phase purity, and obvious ferroelectricity. Based on the ferro–pyro–phototronic effect, the PD at 360 nm exhibits excellent photoelectric properties, with an ultrahigh peak responsivity greater than 93 A W⁻¹ and a detectivity of 2.5 × 10¹⁵ Jones, together with excellent reproducibility and stability. The maximum responsivities can be modulated by piezo–phototronic effect with an effective enhancement ratio of 480%. This work will open up a new route of designing MHP ferroelectric films for high-performance PDs and offers the opportunity to utilize it for various optoelectronics applications.

Molecular beam epitaxy is used to realize the wafer-scale growth of uniform 1T-CrTe₂ films and establish the van der Waals integration of Bi₂Te₃/CrTe₂ heterostructures. Endorsed by the intrinsic perpendicular magnetic anisotropy and strong spin-orbit coupling, the Bi₂Te₃/CrTe₂-based crossbar array is fabricated to achieve reliable spin-orbit torque-driven magnetization switching, hence laying out a solid framework for energy-efficient spintronic applications.

Abstract

To harness the intriguing properties of 2D van der Waals (vdW) ferromagnets (FMs) for versatile applications, the key challenge lies in the reliable material synthesis for scalable device production. Here, the epitaxial growth of single-crystalline 1T-CrTe₂ thin films on 2-inch sapphire substrates are demonstrated. Benefiting from the uniform surface energy of the dangling bond-free Al₂O₃(0001) surface, the layer-by-layer vdW growth mode is observed right from the initial growth stage, which warrants precise control of the sample thickness beyond three monolayer and homogeneous surface morphology across the entire wafer. Moreover, the presence of the Coulomb interaction at the CrTe₂/Al₂O₃ interface plays an important role in tailoring the anomalous Hall response, and the structural optimization of the CrTe₂-based spin-orbit torque device leads to a substantial switching power reduction by 54%. The results may lay out a general framework for the design of energy-efficient spintronics based on configurable vdW FMs.

A broadband phototransistor is designed by combining the excellent electrical transportation features of oxide semiconductors with the superior optoelectronic response of InP quantum dots (QDs). The phototransistor array manifests a realistic environmental self-adaptation process on perceiving simple letters. Handwriting pattern recognition accuracy reaches 93% due to the satisfactory weight update linearity, demonstrating its faultless competence for image processing capabilities.

Abstract

The exploration of bionic neuromorphic chips, capable of processing sensory data in a human-like manner, is both a trend and a challenge. There is a strong demand for phototransistors that offer broadband in-sensor adaptability. This study introduces a bioinspired vision sensor based on InP quantum dots (QDs)/InSnZnO hybrid phototransistors. This novel design combines the excellent electrical transportation features of oxide semiconductors with the superior optoelectronic response of InP QDs. The resulting hybrid devices exhibit exceptional gate controllability and a robust visible-light response. These characteristics enable the emulation of multiple functions of the human visual system and the accommodation of varying light intensity environments. Furthermore, the phototransistor array successfully replicates the scotopic and photopic adaptation recognition behaviors of the human retina. Notably, the device demonstrates faultless competency in image processing, achieving an impressive 93% accuracy for digit recognition. These findings contribute to the advancement of bionic neuromorphic chips and offer promising opportunities for future developments in the bioinspired visual system.

This comprehensive article provides an in-depth review of recent advancements in 2D semiconductor-based optoelectronics for artificial vision. The scope includes 2D semiconductor-based photodetectors, optoelectronic memory, artificial synapses, and innovative applications inspired by retinal cells and vision systems. Furthermore, the review addresses critical technical challenges, outlines strategic approaches for development, and explores potential applications in detail.

Abstract

Artificial retina technologies aim to restore visual function by mimicking the natural processes of the eye. These biomimetic devices can convert light into electrical signals that the brain can interpret as visual information, bypassing damaged or non-functional cells of the eye. To be effective, these devices should possess high sensitivity to light, high spatial resolution, biocompatibility, power efficiency, and so on. Recently, 2D semiconductor materials have appeared as a promising candidate for artificial retinal devices, thanks to their excellent optoelectronic properties, ultrathin body, flexible nature, and biocompatibility. Here the recent developments in the field of 2D semiconductors-based optoelectronics for visual function recovery are reviewed and their potential applications are discussed. The photodetector, optoelectronic memory, and artificial synapse mechanisms and devices utilized in artificial systems that are based on 2D semiconductor materials are summarized. Additionally, a range of application scenarios for devices that are inspired by retinal cells and vision systems is explored. Finally, it is concluded with an overview of the critical technical challenges and strategies that must be addressed for the successful development of artificial retina technologies. It also highlights the potential for new applications in other fields, such as robotics and artificial intelligence.

Nature Communications, Published online: 08 September 2023; doi:10.1038/s41467-023-41047-6

Here, the authors report the emergence of dark-excitons in transition-metal-dichalcogenide heterostructures that strongly rely on the stacking sequence, i.e., momentum-dark K-Q excitons located exclusively at the top layer of the heterostructure.

A novel optical design concept is proposed for a dual-microcavity structure that controls high-order modes with the same cavity length of electroluminescent (EL) devices for each red, green, and blue (RGB) subpixel. The structure can overcome the challenges of EL devices, such as different electrical characteristics and complex patterning for each subpixel due to different cavity lengths of RGB wavelengths.

Abstract

Microcavity structures are used in inorganic-, organic-, quantum-dot-, and perovskite-based electroluminescent (EL) devices to advance next-generation displays. However, there are difficulties in controlling electrical characteristics and patterning processes for producing different thicknesses for each red, green, and blue (RGB) subpixel, and the issues are more challenging in the high-resolution display for future realistic media. Here, a novel design method is presented for a dual-microcavity structure that controls high-order modes of a second cavity stacked on top of EL devices with the same cavity length for each subpixel to produce multiple peaks at RGB resonant wavelengths. The dual-microcavity effect demonstrated by top-emitting organic light-emitting diodes (OLEDs) can be conveniently fabricated via in situ deposition. By modulating the high-order modes, the spectral characteristics of each RGB dual-microcavity top-emitting OLED (DMTOLED) are manipulated while its electrical properties are maintained. Green DMTOLED exhibits a maximum luminance of 2.075  ×  10⁵ cd m⁻², allowing applications not only for commercialized displays but also for outdoor augmented reality and automotive displays. Furthermore, dual-microcavity structures with narrow spectral bandwidths can be applied to next-generation EL devices for more realistic media. The method is expected to be applied industrially, promoting the advancement of EL devices for next-generation displays.