Intrinsically Elastic Semiconductors through Aldehyde-Amine Polycondensation and Its Application on Stretchable Transistor.

With the increasing demand for elastic electronics, as a crucial component, elastic semiconductors have been widely studied. However, there are some issues for the current preparation of elastic semiconductors, such as harsh reaction conditions, low atomic economic utilization, and complicated product separation and purification. Aldehyde-amine polycondensation is an important chemical reaction with the advantages of mild reaction conditions, high atomic-economic efficiency, and easy separation and purification. Herein, intrinsically elastic semiconductors are developed via aldehyde-amine polycondensation, including a semiconducting segment and an elastic segment. The resulting polymer containing 42.62 wt % soft segments exhibits excellent stretchability and mechanical reversibility, especially with a lower modulus. Interestingly, the carrier mobility displays up to 0.04 cm2·V-1·s-1, in the range of the fully conjugated reference polymer (0.1 cm2·V-1·s-1). In brief, this strategy provides important guiding principles for the development of intrinsically elastic polymer semiconductors.

Robust Ferrimagnetism and Ferroelectricity in 2D ɛ-Fe2O3 Semiconductor with Ultrahigh Ordering Temperature.

2D single-phase multiferroic materials with the coexistence of electric and spin polarization offer a tantalizing potential for high-density multilevel data storage. One of the current limitations for application is the scarcity of the materials, especially those combine ferromagnetism and ferroelectricity at high temperatures. Here, robust ferrimagnetism and ferroelectricity in 2D ɛ-Fe2O3 samples with both single-crystalline and polycrystalline form are demonstrated. Interestingly, the polycrystalline nanosheets also exhibit easily switchable ferroelectric polarizations comparable to that of single crystals. The existence of grain boundary does not hinder the switching and retention of ferroelectric polarization. Furthermore, the ɛ-Fe2O3 nanosheets show ferrimagnetic and ferroelectric Curie temperatures up to 800 K, which reaches record highs in 2D single-phase multiferroic materials. This work provides important progress in the exploration of 2D high-temperature single-phase multiferroics for potentially compact high-temperature information nanodevices.

Quasi-1D Conductive Network Composites for Ultra-Sensitive Strain Sensing.

Highly performance flexible strain sensor is a crucial component for wearable devices, human-machine interfaces, and e-skins. However, the sensitivity of the strain sensor is highly limited by the strain range for large destruction of the conductive network. Here the quasi-1D conductive network (QCN) is proposed for the design of an ultra-sensitive strain sensor. The orientation of the conductive particles can effectively reduce the number of redundant percolative pathways in the conductive composites. The maximum sensitivity will reach the upper limit when the whole composite remains only "one" percolation pathway. Besides, the QCN structure can also confine the tunnel electron spread through the rigid inclusions which significantly enlarges the strain-resistance effect along the tensile direction. The strain sensor exhibits state-of-art performance including large gauge factor (862227), fast response time (24 ms), good durability (cycled 1000 times), and multi-mechanical sensing ability (compression, bending, shearing, air flow vibration, etc.). Finally, the QCN sensor can be exploited to realize the human-machine interface (HMI) application of acoustic signal recognition (instrument calibration) and spectrum restoration (voice parsing).

Advances in Flexible Magnetosensitive Materials and Devices for Wearable Electronics.

Emerging fields, such as wearable electronics, digital healthcare, the Internet of Things, and humanoid robots, highlight the need for flexible devices capable of recording signals on curved surfaces and soft objects. In particular, flexible magnetosensitive devices garner significant attention owing to their ability to combine the advantages of flexible electronics and magnetoelectronic devices, such as reshaping capability, conformability, contactless sensing, and navigation capability. Several key challenges must be addressed to develop well-functional flexible magnetic devices. These include determining how to make magnetic materials flexible and even elastic, understanding how the physical properties of magnetic films change under external strain and stress, and designing and constructing flexible magnetosensitive devices. In recent years, significant progress is made in addressing these challenges. This study aims to provide a timely and comprehensive overview of the most recent developments in flexible magnetosensitive devices. This includes discussions on the fabrications and mechanical regulations of flexible magnetic materials, the principles and performances of flexible magnetic sensors, and their applications for wearable electronics. In addition, future development trends and challenges in this field are discussed.

A more biofriendly piezoelectric material.

A ferroelectric molecular crystal displays characteristics required for implantation.

Elastic Relaxor Ferroelectric by Thiol-ene Click Reaction.

As ferroelectrics hold significance and application prospects in wearable devices, the elastification of ferroelectrics becomes more and more important. Nevertheless, achieving elastic ferroelectrics requires stringent synthesis conditions, while the elastification of relaxor ferroelectric materials remains unexplored, presenting an untapped potential for utilization in energy storage and actuation for wearable electronics. The thiol-ene click reaction offers a mild and rapid reaction platform to prepare functional polymers. Therefore, we employed this approach to obtain an elastic relaxor ferroelectric by crosslinking an intramolecular carbon-carbon double bonds (CF=CH) polymer matrix with multiple thiol groups via a thiol-ene click reaction. The resulting elastic relaxor ferroelectric demonstrates pronounced relaxor-type ferroelectric behaviour. This material exhibits low modulus, excellent resilience, and fatigue resistance, maintaining a stable ferroelectric response even under strains up to 70 %. This study introduces a straightforward and efficient approach for the construction of elastic relaxor ferroelectrics, thereby expanding the application possibilities in wearable electronics.

Neuromorphic Nanoionics for Human-Machine Interaction: From Materials to Applications.

Human-machine interaction (HMI) technology has undergone significant advancements in recent years, enabling seamless communication between humans and machines. Its expansion has extended into various emerging domains, including human healthcare, machine perception, and biointerfaces, thereby magnifying the demand for advanced intelligent technologies. Neuromorphic computing, a paradigm rooted in nanoionic devices that emulate the operations and architecture of the human brain, has emerged as a powerful tool for highly efficient information processing. This paper delivers a comprehensive review of recent developments in nanoionic device-based neuromorphic computing technologies and their pivotal role in shaping the next-generation of HMI. Through a detailed examination of fundamental mechanisms and behaviors, the paper explores the ability of nanoionic memristors and ion-gated transistors to emulate the intricate functions of neurons and synapses. Crucial performance metrics, such as reliability, energy efficiency, flexibility, and biocompatibility, are rigorously evaluated. Potential applications, challenges, and opportunities of using the neuromorphic computing technologies in emerging HMI technologies, are discussed and outlooked, shedding light on the fusion of humans with machines.

High-Curie-Temperature Elastic Polymer Ferroelectric by Carbene Cross-Linking.

With the emergence of wearable electronics, ferroelectrics are poised to serve as key components for numerous potential applications. Currently, intrinsically elastic ferroelectrics featuring a network structure through a precise "slight cross-linking" approach have been realized. The resulting elastic ferroelectrics demonstrate a combination of stable ferroelectric properties and remarkable resilience under various strains. However, challenges arose as the cross-linking temperature was too high when integrating ferroelectrics with other functional materials, and the Curie temperature of this elastic ferroelectric was comparatively low. Addressing these challenges, we strategically chose a poly(vinylidene fluoride)-based copolymer with high vinylidene fluoride content to obtain a high Curie temperature while synthesizing a cross-linker with carbene intermediate for high reactivity to reduce the cross-linking temperature. At a relatively low temperature, we successfully fabricated elastic ferroelectrics through carbene cross-linking. The resulting elastic polymer ferroelectrics exhibit a higher Curie temperature and show a stable ferroelectric response under strains up to 50%. These materials hold significant potential for integration into wearable electronics.

Controlled Growth of Submillimeter-Scale Cr5Te8 Nanosheets and the Domain Wall Nucleation Governed Magnetization Reversal Process.

Two-dimensional (2D) ferromagnets have attracted widespread attention for promising applications in compact spintronic devices. However, the controlled synthesis of high-quality, large-sized, and ultrathin 2D magnets via facile, economical method remains challenging. Herein, we develop a hydrogen-tailored chemical vapor deposition approach to fabricating 2D Cr5Te8 ferromagnetic nanosheets. Interestingly, the time period of introducing hydrogen was found to be crucial for controlling the lateral size, and a Cr5Te8 single-crystalline nanosheet of lateral size up to ∼360 µm with single-unit-cell thickness has been obtained. These samples exhibit a leading role of domain wall nucleation in governing the magnetization reversal process, providing important references for optimizing the performances of associated devices. The nanosheets also show notable magnetotransport response, including nonmonotonous magnetic-field-dependent magnetoresistance and sizable anomalous Hall resistivity, demonstrating Cr5Te8 as a promising material for constructing high-performance magnetoelectronic devices. This study presents a breakthrough of large-sized CVD-grown 2D magnetic materials, which is indispensable for constructing 2D spintronic devices.

Size Dependent Phase Transformation of Liquid Gallium.

As the most popular liquid metal (LM), gallium (Ga) and its alloys are emerging as functional materials due to their unique combination of fluidic and metallic properties near room temperature. As an important branch of utilizing LMs, micro- and submicron-particles of Ga-based LM are widely employed in wearable electronics, catalysis, energy, and biomedicine. Meanwhile, the phase transition is crucial not only for the applications based on this reversible transformation process, but also for the solidification temperature at which fluid properties are lost. While Ga has several solid phases and exhibits unusual size-dependent phase behavior. This complex process makes the phase transition and undercooling of Ga uncontrollable, which considerably affects the application performance. In this work, extensive (nano-)calorimetry experiments are performed to investigate the polymorph selection mechanism during liquid Ga crystallization. It is surprisingly found that the crystallization temperature and crystallization pathway to either α -Ga or ß -Ga can be effectively engineered by thermal treatment and droplet size. The polymorph selection process is suggested to be highly relevant to the capability of forming covalent bonds in the equilibrium supercooled liquid. The observation of two different crystallization pathways depending on the annealing temperature may indicate that there exist two different liquid phases in Ga.

A Discolorable Flexible Synaptic Transistor for Wearable Health Monitoring.

Multifunctional intelligent wearable electronics, providing integrated physiological signal analysis, storage, and display for real-time and on-site health status diagnosis, have great potential to revolutionize health monitoring technologies. Advanced wearable systems combine isolated digital processor, memory, and display modules for function integration; however, they suffer from compatibility and reliability issues. Here, we introduce a flexible multifunctional electrolyte-gated transistor (EGT) that integrates synaptic learning, memory, and autonomous discoloration functionalities for intelligent wearable application. This device exhibits synergistic light absorption coefficient changes during voltage-gated ion doping that modulate the electrical conductance changes for synaptic function implementation. By adaptively changing color, the EGT can differentiate voltage pulse inputs with different frequency, amplitude, and duration parameters, exhibiting excellent reversibility and reliability. We developed a smart wearable monitoring system that incorporates EGT devices and sensors for respiratory and electrocardiogram signal analysis, providing health warnings through real-time and on-site discoloration. This study represents a significant step toward smart wearable technologies for health management, offering health evaluation through intelligent displays.

Wearable Magnetic Field Sensor with Low Detection Limit and Wide Operation Range for Electronic Skin Applications.

Flexible electronic devices extended abilities of humans to perceive their environment conveniently and comfortably. Among them, flexible magnetic field sensors are crucial to detect changes in the external magnetic field. State-of-the-art flexible magnetoelectronics do not exhibit low detection limit and large working range simultaneously, which limits their application potential. Herein, a flexible magnetic field sensor possessing a low detection limit of 22 nT and wide sensing range from 22 nT up to 400 mT is reported. With the detection range of seven orders of magnitude in magnetic field sensor constitutes at least one order of magnitude improvement over current flexible magnetic field sensor technologies. The sensor is designed as a cantilever beam structure accommodating a flexible permanent magnetic composite and an amorphous magnetic wire enabling sensitivity to low magnetic fields. To detect high fields, the anisotropy of the giant magnetoimpedance effect of amorphous magnetic wires to the magnetic field direction is explored. Benefiting from mechanical flexibility of sensor and its broad detection range, its application potential for smart wearables targeting geomagnetic navigation, touchless interactivity, rehabilitation appliances, and safety interfaces providing warnings of exposure to high magnetic fields are explored.

Structural Design and DLP 3D Printing Preparation of High Strain Stable Flexible Pressure Sensors.

Flexible pressure sensors are crucial force-sensitive devices in wearable electronics, robotics, and other fields due to their stretchability, high sensitivity, and easy integration. However, a limitation of existing pressure sensors is their reduced sensing accuracy when subjected to stretching. This study addresses this issue by adopting finite element simulation optimization, using digital light processing (DLP) 3D printing technology to design and fabricate the force-sensitive structure of flexible pressure sensors. This is the first systematic study of how force-sensitive structures enhance tensile strain stability of flexible resistive pressure sensors. 18 types of force-sensitive structures have been investigated by finite element design, simultaneously, the modulus of the force-sensitive structure is also a critical consideration as it exerts a significant influence on the overall tensile stability of the sensor. Based on simulation results, a well-designed and highly stretch-stable flexible resistive pressure sensor has been fabricated which exhibits a resistance change rate of 0.76% and pressure sensitivity change rate of 0.22% when subjected to strains ranging from no tensile strain to 20% tensile strain, demonstrating extremely low stretching response characteristics. This study presents innovative solutions for designing and fabricating flexible resistive pressure sensors that maintain stable sensing performance even under stretch conditions.

Controlled Growth and Size-Dependent Magnetic Domain States of 2D γ-Fe2O3.

Nonlayered two-dimensional (2D) magnets have attracted special attention, as many of them possess magnetic order above room temperature and enhanced chemical stability compared to most existing vdW magnets, which offers remarkable opportunities for developing compact spintronic devices. However, the growth of these materials is quite challenging due to the inherent three-dimensionally bonded nature, which hampers the study of their magnetism. Here, we demonstrate the controllable growth of air-stable pure γ-Fe2O3 nanoflakes by a confined-vdW epitaxial approach. The lateral size of the nanoflakes could be adjusted from hundreds of nanometers to tens of micrometers by precisely controlling the annealing time. Interestingly, a lateral-size-dependent magnetic domain configuration was observed. As the sizes continuously increase, the magnetic domain evolves from single domain to vortex and finally to multidomain. This work provides guidance for the controllable synthesis of 2D inverse spinel-type crystals and expands the range of magnetic vortex materials into magnetic semiconductors.

Enhanced Stress Stability in Flexible Co/Pt Multilayers with Strong Perpendicular Magnetic Anisotropy.

Due to the magnetoelastic coupling, the magnetic properties of many flexible magnetic films (such as Fe, Co, and Ni) are sensitive to mechanical stress, which deteriorates the performance of flexible magnetoelectronic devices. We show that by stacking Co and Pt alternatively to form multilayers with strong perpendicular magnetic anisotropy (PMA), both magnetic hysteresis and magnetic domain measurements reveal robust PMA against external stress. As the PMA weakens at increased Co thickness, the magnetic anisotropy is vulnerable to external stress. These results were understood based on a micromagnetic model, which suggests that the strength of magnetoelastic anisotropy with respect to initial effective magnetic anisotropy affects the stress-stability of the film. Although the stress coefficient of magnetoelastic anisotropy is enhanced at reduced Co thickness, the concomitant increase of initial effective magnetic anisotropy guarantees a robust PMA against external stress. Our results provide a route to constructing flexible magnetoelectronic devices with enhanced stress stability.

Intrinsically elastic polymer ferroelectric by precise slight cross-linking.

Ferroelectrics are an integral component of the modern world and are of importance in electrics, electronics, and biomedicine. However, their usage in emerging wearable electronics is limited by inelastic deformation. We developed intrinsically elastic ferroelectrics by combining ferroelectric response and elastic resilience into one material by slight cross-linking of plastic ferroelectric polymers. The precise slight cross-linking can realize the complex balance between crystallinity and resilience. Thus, we obtained an elastic ferroelectric with a stable ferroelectric response under mechanical deformation up to 70% strain. This elastic ferroelectric exerts potentials in applications related to wearable electronics, such as elastic ferroelectric sensors, information storage, and energy transduction.

Ti3C2Tx MXene-Based Multifunctional Tactile Sensors for Precisely Detecting and Distinguishing Temperature and Pressure Stimuli.

Although skin-like sensors that can simultaneously detect various physical stimuli are of fair importance in cutting-edge human-machine interaction, robotic, and healthcare applications, they still face challenges in facile, scalable, and cost-effective production using conventional active materials. The emerging two-dimensional transition metal carbide, Ti3C2Tx MXene, integrated with favorable thermoelectric properties, metallic-like conductivity, and a hydrophilic surface, is promising for solving these problems. Herein, skin-like multifunctional sensors are designed to precisely detect and distinguish temperature and pressure stimuli without cross-talk by decorating elastic and porous substrates with MXene sheets. Because the combination of the thermoelectric and conductive MXene with the thermally insulating, elastic, and porous substrate integrates efficient Seebeck and piezoresistive effects, the resultant sensor exhibits not only an ultralow detection limit (0.05 K), high signal-to-noise ratio, and excellent cycling stability for temperature detection but also high sensitivity, fast response time, and outstanding durability for pressure detection. Based on the impressive dual-mode sensing properties and independent temperature and pressure detections, a multimode input terminal and an electronic skin are created, exhibiting great potential in robotic and human-machine interaction applications. This work provides a scalable fabrication of multifunctional tactile sensors for precisely detecting and distinguishing temperature and pressure stimuli.

Highly Stable Liquid Metal Conductors with Superior Electrical Stability and Tough Interface Bonding for Stretchable Electronics.

Ga-based liquid metal stretchable conductors have recently gained interest in flexible electronic devices such as electrodes, antennas, and sensors. It is essential to maintain electrical stability under strain or cyclic strain for reliable data acquisition and exhibit tough interfacial bonding between liquid metal and polymers to prevent performance loss and device failure. Herein, a highly stable conductor with superior electrical stability and tough interface bonding is introduced by casting curable polymers and a peeling-activated process from liquid metal particles. Based on the compensating effect of liquid metal, similar to the recharge relationship of water between rivers and lakes in nature, the conductor is not only strain-insensitive (ΔR/R0 < 10% for 100% strain) but also immune to cyclic deformation (ΔR/R0 < 7% with 5000 stretching cycles at 50% strain). Embedding liquid metal within the elastomer to create stretchable conductors effectively improves interfacial adhesion properties (the fluid-solid interfacial adhesion force increases from 0.48 to 0.62 mN/mm2). The constructed tough interface could even withstand sonication treatment. Finally, by combining strategies in material design and fabrication, an integrated array composed of vertical interconnect access and robust electrodes is fabricated, which simultaneously holds tough interfacial bonding with the upper and lower layers.