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A variety of organic electrochemical transistors have been recently developed; however, their self-healing performance has been largely ignored. In this study, we propose the use of a lithium-ion composite electrolyte membrane as a dielectric layer and the use of poly(3-hexylthiophene) (P3HT) as a channel layer to fabricate flexible self-supporting organic synaptic transistors. A variety of synaptic behaviors were emulated within the proposed organic synaptic transistors. By leveraging the self-healing features of polymer electrolytes, along with cross-linking reactions and low-resistance lithium-ion transmission, the device maintained its electrical performance. Testing involving different curvatures also revealed the device's potential for use in flexible electronics. Significantly, due to the device's self-healing ability, consistent dataset recognition rates were sustained. This work highlights its vast prospects in the field of flexible and wearable electronics. [ABSTRACT FROM AUTHOR]

We demonstrated a flexible artificial synapse device with a structure of Al/Cs3Bi2I9/ITO. It is found that the device displays a resistive switching behavior, effectively simulating the potentiation and depression processes observed in synapses under varying bending angles. Synaptic functions, such as excitatory postsynaptic current and paired-pulse facilitation, were performed. Furthermore, we conducted a systematic investigation into the impact of pulse amplitude, pulse width, and pulse number on the synaptic weight. Additionally, long-term plasticity was simulated by precisely controlling the time intervals between pre-synaptic and post-synaptic pulses. Remarkably, our prepared flexible artificial synapse exhibited exceptional flexibility and robustness, with no significant alteration in conductance even after undergoing 2000 bending cycles. This study establishes the feasibility of manufacturing lead-free halide perovskite-based artificial synapses for applications in flexible electronics. [ABSTRACT FROM AUTHOR]

Amorphous nanomembranes play a crucial role in flexible electronics due to their ability to create intricate 3D structures through strain engineering. To better understand the formation of these structures, accurately mapping the local elastic strain distribution is essential. In this study, we conducted position-sensitive nanobeam electron diffraction investigations on various rolled-up amorphous nanomembranes. By analyzing the diffraction rings obtained from different locations on the amorphous samples, we extracted anisotropic structure information in reciprocal space and determined the local strain distributions in real space. Our analysis revealed that particle-assisted dry-released samples exhibited higher strain values than pure amorphous samples. This suggests that nanoparticles introduce additional strain through dewetting effects, thereby facilitating the formation of self-rolling 3D structures. [ABSTRACT FROM AUTHOR]

With the development of flexible electronics, flexible tunable capacitors with high dielectric constant, high tunability, and low loss become important components in modern communication. A tunable Ba0.6Sr0.4TiO3 capacitor for radio frequency devices is prepared on a flexible substrate. The capacitor has a dielectric constant greater than 1000, capacitance tunability n exceeding 70%, and minimum loss tangent lower than 0.03 at 500 kHz. The Q factor can be above 103 at the GHz frequency range. These parameter values (especially the Q factor) have been comparable to the rigid substrate tunable capacitor. Meanwhile, the minimum radius of curvature of the flexible tunable capacitor can be 3 mm with stable electrical performances. The flexible tunable capacitor retains its mechanical and electrical stability after 24 000 high-frequency bending cycles, which provides potential uses in bendable, collapsible tunable capacitors at the radio frequency range. [ABSTRACT FROM AUTHOR]

The fundamental properties of two-dimensional α1-MA2Z4 (M = Mg, Ca, Sr; A = Al; Z = S, Se) monolayers have been systematically investigated based on the first principles calculations. Our results show that the α1-MA2Z4 monolayers have mixed ionic-covalent bonding character. The structural stability analyses reveal that all structures are dynamically stable and sustain stability below 800 K. All α1-MA2Z4 monolayers exhibit semiconducting property. The suitable bandgaps and the band edges alignment strides the redox potentials of water splitting, having potential as the candidates of the photocatalyst. All structures are predicted to possess isotropic electron-dominated mobility, which increases from 340.79 to 591.84 cm2 s−1 V−1 with the increase in atomic number of the alkaline-earth metal and chalcogen group. Further imposing the strain along the armchair direction, the electron mobility of α1-MA2Z4 can be enhanced to ∼103 cm2 V−1 s−1, especially the electron mobility of α1-MgA2S4 even increases to ∼2 × 103 cm2 V−1 s−1. The increased electron mobility indicates the reduced resistivity, which shows that the α1-MA2Z4 monolayers possess a remarked piezoresistive effect. The outstanding properties indicate that the α1-MA2Z4 is promising in photocatalysis and flexible electronics fields. [ABSTRACT FROM AUTHOR]

Achieving exceptional water-repellency and reliable reversible adhesion is crucial for the development of wearable flexible electronics. However, simultaneously achieving these properties presents a significant challenge, as water-repellency requires maximizing the presence of air while robust adhesion necessitates enhancing the solid fraction. In this study, we present a flexible and transparent conductive patch that addresses this challenge by offering simultaneous robust superhydrophobicity and strong adhesion in both dry and wet conditions. The device incorporates a unique combination of overhang micropillars, microgrids and a percolating network of carbon nanotubes. The proposed patch demonstrates outstanding water repellency with a contact angle exceeding 150°, while delivering impressive dry adhesion (>200 kPa) and wet adhesion (>150 kPa) performance. Furthermore, the device exhibits tunable electrical conductivity and optical transmittance. [ABSTRACT FROM AUTHOR]

The thermal management has been widely focused due to its broad applications. Generally, the deformation can largely tune the thermal transport. The main challenge of flexible electronics/materials is to maintain thermal conductance under large deformation. This work investigates the thermal conductance of a nano-designed Si metamaterial constructed with curved nanobeams by molecular dynamics simulation. Interestingly, it shows that the thermal conductance of the nano-designed Si metamaterial is insensitive under a large deformation (strain ∼ −41%). The new feature comes from the designed curved nanobeams, which exhibit a quasi-zero stiffness. Further calculations show that, when under large deformation, the average stress in nanobeam is ultra-small (<151 MPa), and its phonon density of states are little changed. This work provides valuable insight on the multifunction, such as both stable thermal and mechanical properties, of nano-designed metamaterials. [ABSTRACT FROM AUTHOR]

Flexible sensors are important for applications, such as wearable medical devices, soft robotics, and more, as they can easily conform to soft and irregularly shaped surfaces. This study presents elliptical planar Hall effect magnetic sensors fabricated on a polyamide tape with an equivalent magnetic noise (EMN) better than 200 pT/ Hz . The sensor is characterized in flat and bent states with a bent radius of 10 mm. An EMN of 200 and 400 pT/ Hz in flat and bent states, respectively, is achieved at a frequency of 100 Hz. The remarkable EMN combined with a simple, low-cost fabrication process makes these sensors a promising candidate for flexible electronics. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSC) have great potential for flexible and wearable electronics due to their significant energy supply. However, the brittleness of inorganic electron transport layers (ETL) and their large-area production make it difficult to use them in flexible inverted OSCs. Herein, an organic–inorganic hybrid cathode interlayer of incorporating poly(4-vinylphenol) (P4VP) into the ZnO precursor solution was developed. The addition of P4VP improves the conductibility of ETL and facilitates the favorable vertical component distribution of active layer on the ZnO:P4VP substrate. Thus, the blade-coated OSC based on ZnO:P4VP performs better than the ZnO-based OSC in terms of photovoltaic performance and thickness insensitivity. The P4VP acts as an adhesive in ZnO grain boundaries and eliminates cracks in the bent ETL, leading to a significantly improved mechanical flexibility. Consequently, the ZnO:P4VP-based large-area flexible OSC achieves a power conversion efficiency of 14.05% and retains 80% of its initial efficiency after 1000 bending cycles, which is much better than that based on pristine ZnO (12.26%, 44%). Furthermore, flexible inverted organic solar modules were fabricated and achieved a considerable efficiency of 12.01%. These findings provide a general approach for using inorganic materials in flexible and wearable electronics. [ABSTRACT FROM AUTHOR]

2D transition metal dichalcogenides such as MoS2 are promising candidates for optoelectronics because of atomically thin nature and strong light–matter interaction. However, the poor light absorption limited their photodetection performance. Surface plasma resonance (SPR) can improve light absorption, but the defects introduced during the metal deposition process limit their responsivity and response time. In this work, we transfer a plasmonic Au array onto MoS2 surface, in which van der Waals (vdWs) contact forms between defect-free Au array–MoS2 interface. The Au/MoS2 heterostructure photodetector performs 1.8 ms rising time, 186.6 A/W responsivity, and 1.41 × 1012 Jones detectivity. The damage free vdWs fabrication method also makes it possible to integrate the engineered SPR Au array with functional polymer for flexible electronics. Thus, a vdWs plasmonic Au array/MoS2/P(VDF-TrFE) photodetector with a 1.28 × 103 rectification ratio has been obtained. This approach not only optimizes the performance of the 2D optoelectronic devices but also expands the scope of its potential applications. [ABSTRACT FROM AUTHOR]

Biologically inspired by natural skin, polypropylene (PP) ferroelectret films with a human skin-like texture, featuring lightweight, light transmittance, small thickness, stretchability, as well as significant longitudinal and transverse piezoelectric activity, are prepared with a simple procedure, and their piezoelectric properties are characterized. The mechanical structure of the fabricated ferroelectret films is of a double-level cellular structure with distributed tight junctions and dipolar charges deposited on the opposite inner walls of cells. The preliminary results show that the area density, light transmittance, and thickness of the films are 3.5 g/m2, 80%, and 10–20 μm, respectively. A quasi-static piezoelectric d33 coefficient of a few thousand pC/N at 3.4 kPa and a dynamic piezoelectric d31 coefficient of −40 pC/N at a frequency of 80 Hz and a stress of 20 kPa are achieved. The improved piezoelectric performance seems mainly owing to the reduction of the elastic modulus for the double-level structure and the enhancement of charges in deep traps in very thin cell walls. The sound pressure level, generated by an ultrasonic emitter made of the PP ferroelectret film, is about 87 dB at 46 kHz as driven by a voltage of 20 V (peak to peak voltage). An ultra-thin tactile sensor based on the fabricated films can localize positions and detect the track and moving speed of applied force. These results indicate that the cost-efficient films may extend the applications of ferroelectrets in flexible electronics. [ABSTRACT FROM AUTHOR]

Understanding the varied strain effects in AlGaN/GaN devices is crucial for realizing optimized flexible electronics systems and strain sensors. Here, we report on the effects of surface potential pinning, altered by the deposition of device-relevant SiNx passivation and Ni gate layers, on the strain-dependent carrier density, ns, of AlGaN/GaN two-dimensional electron gas structures. Flexible van der Pauw samples were made by separating AlGaN/GaN layers from the sapphire growth substrate using a two-dimensional boron nitride van der Waals release layer and transferring them to flexible substrates. For bare surface samples, we observed relatively large decreases in ns with tensile strain (Δns of −2 × 1011 cm−2 at 0.1% uniaxial strain), indicating an unpinned AlGaN surface potential. For the SiNx and Ni covered samples, the ns-strain trends were nearly flat, indicating a more pinned surface potential. Additionally, sub-bandgap 400 nm light is shown to effectively pin the surface potential as evidenced by flattening the ns-strain trend, the mechanism of which we explain in terms of the persistent photoconductivity effect. These observations could have important implications in tuning strain sensors and minimizing device variability in flexible electronics. [ABSTRACT FROM AUTHOR]

High-throughput printing-based fabrication has emerged as a key enabler of flexible electronics given its unique capability for low-cost integration of circuits based on printed thin film transistors (TFTs). Research in printing inorganic metal oxides has revealed the potential for fabricating oxide TFTs with an unmatched combination of high electron mobility and optical transparency. Here, we highlight recent developments in ink chemistry, printing physics, and material design for high-mobility metal oxide transistors. We consider ongoing challenges for this field that include lowering process temperatures, achieving high speed and high resolution printing, and balancing device performance with the need for high mechanical flexibility. Finally, we provide a roadmap for overcoming these challenges with emerging synthetic strategies for fabricating 2D oxides and complementary TFT circuits for flexible electronics. [ABSTRACT FROM AUTHOR]

Transparent conductive electrodes are essential in the application of flexible electronics. In this work, we successfully demonstrated a novel strategy for improving mechanical/electrical properties of indium tin oxide (ITO)-free flexible silver nanowire (Ag NW) thin films. To reduce the contact resistance of Ag NWs, an ethanol-mist was used to weld the cross junction of wires at room temperature. The nano-welded Ag NWs (W-Ag NWs) were then coated with an aluminum-doped ZnO (AZO) solution, which significantly reduce the roughness of the Ag NW thin film. Finally, an ultrathin SbOx thin film of 2 nm was deposited on the film surface using a water-free low-temperature atomic layer deposition technique to protect the W-Ag NW/AZO layer from water or oxygen degradation. The treated Ag NWs have a high transmittance of 87% and a low sheet resistance of about 15 Ω/sq, which is comparable with the ITO electrode's property. After 1000 cycles of bending testing, the W-Ag NW/AZO/SbOx film practically retains its initial conductivity. Furthermore, the samples were immersed in a solution with pH values ranging from 3 to 13 for 5 min. When compared to untreated Ag NWs or those coated with AlOx thin films, W-Ag NW/AZO/SbOx had superior electrical stability. The W-Ag NW/AZO/SbOxlayer was integrated as a gate electrode on low-power operating flexible Ti-ZnO thin film transistors (TFTs). The 5% Ti-ZnO TFT has a field-effect mobility of 19.7 cm2 V s−1, an Ion/Ioff ratio of 107, and a subthreshold swing of 147 mV decade−1. [ABSTRACT FROM AUTHOR]

The freestanding ferroelectric membranes with super-elasticity show promising applications in flexible electronic devices such as transducers, memories, etc. While there have been recent studies on the effect of mechanical bending on the domain structure evolutions and phase transitions in ferroelectric membranes, its influence on Young's modulus of these freestanding membranes is less explored, which is crucial for the design and application of flexible electronics. Here, a phase-field model is developed to simulate the tunability of Young's modulus of freestanding Ba1−xSrxTiO3 membranes under mechanical bending. It is demonstrated that the bended membrane shows a uniform Young's modulus compared with unbended membrane. By increasing the bending angle, Young's modulus tunability is enhanced, which can be attributed to the vortex-like domain structures induced by the mechanical bending. These vortex-like domains with large domain wall energy inhibit the subsequent domain switching under externally applied tensile strain and reduce the eigenstrain variation, which leads to a large Young's modulus. In addition, the formation of vortex domain structure is suppressed with increasing Sr2+ content in Ba1−xSrxTiO3 membranes at the same bending degree, resulting in a decrease in Young's modulus tunability. Our work reveals that the tunability of Young's modulus of freestanding ferroelectric membranes can be achieved by mechanical bending, which provides guidance for designing flexible electronic devices. [ABSTRACT FROM AUTHOR]

The development of the next generation of flexible electronics for biomedical applications requires the implementation of flexible active elements, potentially microcontrollers. The further step in this direction includes the development of devices for data processing directly on-chip, in particular, devices for neuromorphic computing. One of the key elements put forward within this paradigm is the memristor—the device emulating the plasticity of biological synapses. Due to the internal temporal dynamics of conductance, second-order memristors exhibit the most natural emulation of a biological synapse. Among different types of second-order memristors, ferroelectric memristors show the best cell-to-cell and cycle-to-cycle reproducibility. Here, we demonstrate a flexible ferroelectric second-order memristor on a mica substrate based on the 5-nm-thick polycrystalline Hf 0.5 Zr 0.5 O 2 film. The conductance (synaptic weight) modulation with R OFF / R ON ratio ∼ 20 is achieved via the gradual switching of the ferroelectric domains affecting the potential barrier in the structure. The devices demonstrate high reproducibility and various synaptic functionalities, including paired-pulse potentiation and paired-pulse depression. Functional properties persist both during static bending and after more than 100 bending cycles with a radius down to 1 cm. [ABSTRACT FROM AUTHOR]

Due to its unique features, laser-induced graphene (LIG) can be considered as disruptive technology for creating a few-layer graphene-based film that received much attention in the field of flexible electronics. Among all, energy storage, catalysis, sensing, and separation are the main applications that have been investigated in recent years with large improvements in the respective device performance. In particular, miniaturized supercapacitor—usually called a micro-supercapacitor (μSC)—is the most investigated field in which LIG can strongly provide outstanding results concerning the state of the art simplification of the fabrication procedure and intrinsically allowing the flexibility of the device. However, many open points still limit the possible full exploitation of this technology in the energy storage sector. This paper provides a concise overview of the LIG application in μSCs suggesting where the community should direct efforts to enhance the results together with associated challenges. [ABSTRACT FROM AUTHOR]

Investigating lateral electrical transport in p-type thin film chalcogenides is important to evaluate their potential for field-effect transistors (FETs) and phase-change memory applications. For instance, p-type FETs with materials sputtered at low temperature (≤ 250 °C) could play a role in flexible electronics or back-end-of-line silicon-compatible processes. Here, we explore lateral transport in chalcogenide films (Sb2Te3, Ge2Sb2Te5, and Ge4Sb6Te7) and multilayers, with Hall measurements (in ≤ 50 nm thin films) and with p-type transistors (in ≤ 5 nm ultrathin films). The highest Hall mobilities are measured for Sb2Te3/GeTe superlattices (∼18 cm2 V−1 s−1 at room temperature), over 2–3× higher than the other films. In ultrathin p-type FETs with Ge2Sb2Te5, we achieve field-effect mobility up to ∼5.5 cm2 V−1 s−1 with on/off current ratio of ∼104, the highest for Ge2Sb2Te5 transistors to date. We also explore process optimizations (e.g., the AlOx capping layer, type of developer for lithography) and uncover their tradeoffs toward the realization of p-type transistors with acceptable mobility and on/off current ratio. Our study provides essential insights into the optimization of electronic devices based on p-type chalcogenides. [ABSTRACT FROM AUTHOR]

Limited nonrenewable resources on earth motivate people to use natural polymer materials in the development of environment-friendly devices for flexible electronics. In this work, a biocompatible and biodegradable organic memristor based on regenerated cellulose is prepared by a facile and green route. Here, cellulose, the key functional layer material, is used as not only the resistive switching layer but also a substrate to construct a flexible self-supporting memristor. Both volatile and nonvolatile resistive switching can be achieved by controlling the compliance current in the SET process. Moreover, this cellulose-based memristor performs competitive environmental and temperature stability compared with other organic memristors. This research provides a facile strategy for constructing an environment-friendly memristor based on natural polymer-based materials. [ABSTRACT FROM AUTHOR]

The rapid development of flexible electronics, human–computer interaction, wireless technology, the Internet of Things, and internet health is promoting fast-past innovation in the field of wearable medical devices. Wearable devices are a category of personalized devices that include specialized sensors, which can make conformal contact with the human body or tissue to collect biochemical or electrophysiological signals. Hence, the development of high-precision flexible devices is attracting increasing interest as they can provide real-time medical data for monitoring the physiological state of patients and their diagnosis and treatment, as well as help individuals to pursue a healthier lifestyle. This Perspective reviews the developments and requirements of wearable flexible electronic devices in medical monitoring and then discusses the possible applications and challenges of using flexible sensor technology for point-of-care devices. Finally, an up-to-date discussion of the flexible sensor, its future prospects, and solutions it could provide in medical and diagnostic equipment are summarized. [ABSTRACT FROM AUTHOR]

Rationally engineered three-dimensional (3D) clusters of MoS2 nanowires vertically anchored over a nanostructured NiTiCu shape memory alloy are fabricated using magnetron sputtering for flexible thin film supercapacitive electrodes. The heterostructure MoS2/NiTiCu deposited directly over flexible stainless steel (SS) offers remarkable electrochemical performance along with excellent mechanical stability, arising synergistically from the large specific surface of MoS2 nanowires and a high mechanical strength of NiTiCu@SS. The electrochemical studies in sulfate electrolytes (Li2SO4 and Na2SO4) manifest dominant charge transport efficiency of Li+ into the easily accessible electroactive sites of MoS2. The electrode delivers a superior gravimetric capacitance (379.25 F/g at 0.78 A/g) in addition to outstanding cycling stability (95.9% over 5000 cycles), suggesting high Li+ conductivity, low equivalent series resistance, and good substrate adhesion. Furthermore, the Power law and Dunn's approach reveal that charge storage into the highly porous MoS2 networks occurs mainly through the pseudocapacitive mechanism in Li2SO4 and capacitive processes in Na2SO4. Practically flexing the working electrode over 1000 bending cycles degrades the capacitance by only 17.17%, achieving highly desirable mechanical stability. Significantly, a superior power density of 12.54 kW/kg, while simultaneously achieving a high energy density of 52.67 Wh/kg, presents the electrode's immense potential for high-performance supercapacitor devices in flexible electronics. [ABSTRACT FROM AUTHOR]

We demonstrate a technique to quickly build and spatially map the frequency response of optoelectronic devices. The transfer function of a linear system is the Fourier transform of its impulse response. Such an impulse response is obtained from transient photocurrent measurements of devices such as photodetectors and solar cells. We introduce and apply Fourier transform impedance spectroscopy (FTIS) to a PbS colloidal quantum dot SiC heterojunction photodiode and validate the results using intensity-modulated photocurrent spectroscopy. Cutoff frequencies in the devices were as high as ∼10 kHz, showing their utility in advanced thin film and flexible electronics. The practical frequencies for FTIS lie in the mHz–kHz range, ideal for composite materials such as quantum dot films that are dominated by interfacial trap states. These can lead to characteristic lengths for charge collection ∼20–500 μm dominated by transmission line effects, rather than intrinsic diffusion and drift length scales, enabling extraction of interfacial capacitances and series/parallel resistances. [ABSTRACT FROM AUTHOR]

Flexible micro-supercapacitor (MSC) is an ideal energy storage device for flexible and small-scale electronics, specifically some human health sensors, because of its flexibility, long working life, high power density, and high charge and discharge rate. In this work, a smart power system of MSC is developed. First, utilizing ink-jet printing and electrochemical deposition, flexible MSC is fabricated on the biocompatible substrate of a modified silk protein film, making the power system suitable for implantable devices. Second, aiming at the common drawbacks of small energy density and large voltage variation of MSC, a wireless charging component and a wireless inductor–capacitor (LC) voltage sensor are integrated with the MSC unit. Using pulse charging mode, charging and voltage detection can be performed at the same time. The LC voltage sensor, using varactor diodes to realize voltage capacitance mapping, does not need extra ICs or consume any energy. Such a system has great application potential as the energy supply part of small devices implanted in the human body. [ABSTRACT FROM AUTHOR]

Ferroelectric organic field-effect transistor nonvolatile memories (Fe-OFET-NVMs) offer attractive features for future memory applications, such as flexible and wearable electronics. Polymer semiconductor-based top-gate Fe-OFET-NVMs possess natural advantages in the device structure and processing manufacturing, compared to small-molecule semiconductor-based bottom-gate Fe-OFET-NVMs. However, their performances, such as mobility and operating voltages, should be further improved to be comparable to those of the latter. In this Letter, we develop a route to achieve high-performance top-gate Fe-OFET-NVMs, by employing a polymer semiconductor channel and self-organized ferroelectric/dielectric gate insulators, which were processed by a solution spin-coating technique. The optimal Fe-OFET-NVM exhibits a high mobility of 1.96 cm2/V s on average, a reliable endurance over 400 cycles, a stable retention capability over 6 × 104 s, and a life more than one year. Furthermore, the operating voltage of the Fe-OFET-NVM is reduced to ±20 V by scaling down the thickness of the ferroelectric/dielectric gate insulator. The whole performances of our memories are comparable to or better than those of the previous Fe-OFET-NVMs. [ABSTRACT FROM AUTHOR]

This report presents a single-step deposition of crystalline and catalyst-free cobalt nitride (CoN) and zinc nitride (Zn3N2) electrodes on a flexible current collector for highly efficient flexible supercapacitors. These proposed electrodes take full advantage of mechanical strength, electrochemical stability, and tremendous electrical conductivity with excellent adhesion to a flexible current collector and show high capacitive performance with outstanding cyclic life. The asymmetric supercapacitor (ASC) was constructed using CoN as a negative electrode and Zn3N2 as a positive electrode, assembled with 1 M Na2SO4 aqueous electrolyte soaked Whatman filter paper as the separator. This ASC exhibits a wider voltage window (up to 2 V), good capacitance (75.4 Fg−1), and high specific energy (42 Wh kg−1) with good capacitance retention (93.6% for the flat cell and 80.1% for the 80° bend cell) over 5000 charging discharging cycles. Therefore, this design of ASC potentially expands the performance of high frequency and flexible electronics. [ABSTRACT FROM AUTHOR]

The first stages of plasticity in three-point bent Au nanowires are investigated by in situ three-point bending tests in combination with Laue micro-diffraction. To separate the elastic and plastic deformation, loading–unloading cycles were performed with increasing load in each consecutive cycle. The storage of the first four geometrically necessary dislocations of [ 01 1 ¯ ] (111) slip system is observed in the vicinity of both clamping points, which might be attributed to the local rotations induced by the rigid Si support. At later stages of the deformation, additional slip systems are activated either by the torsion of the nanowire or by unintentional indentation from the AFM tip. The cyclic loading–unloading approach combined with Laue microdiffraction thus allows to study the onset of plasticity in defect-scarce nanostructures deformed by bending, offering additional possibilities in studying the dislocation nucleation process in bent nano-objects, which are essential for future applications, e.g., in flexible electronics and nano-electromechanical systems. [ABSTRACT FROM AUTHOR]

Flexible Ba2Bi4Ti5O18 and BiFe0.93Mn0.07O3/Ba2Bi4Ti5O18 heterostructure thin-film capacitors were deposited onto LaNiO3 buffered fluorophlogopite mica substrates using a cost-effective all-solution chemical solution deposition method. The Ba2Bi4Ti5O18 film showed a high recoverable energy storage density (Ure) of 41.2 J/cm3 and efficiency (η) of 79.1%. The BiFe0.93Mn0.07O3/Ba2Bi4Ti5O18 film showed improved energy storage properties with an ultrahigh Ure of 52.6 J/cm3 and η of 75.9% due to its enhanced breakdown field strength and polarization. Meanwhile, both films showed good mechanical flexibility, excellent fatigue endurance up to 5 × 108 cycles, and excellent thermal stability over a wide temperature range from room temperature to 160 °C. These results indicate that the lead-free, flexible Ba2Bi4Ti5O18 and BiFe0.93Mn0.07O3/Ba2Bi4Ti5O18 heterostructure thin film capacitors show promise in the field of flexible electronics. [ABSTRACT FROM AUTHOR]

The scaling down of switching media encounters high leakage current in the traditional oxide material based memristors, resulting in high power consumption of chips. Two-dimensional (2D) materials promise an ultimate device scaling down to atomic layer thickness. Herein, black phosphorus (BP) and its self-assembly phosphorous oxide (BP) memristors are constructed, which leverages the high on/off ratio operation of oxides and low leakage current of 2D materials with high performance. The memristors exhibit reproducible and reliable switching characteristics with the on/off ratio >107 and data retention >104 s. Depending on the high reproducibility, basic "AND" and "OR" gates have been constructed on flexible substrates. Moreover, on the basis of the symmetry and linearity of conductance in the devices, the neural network simulation for supervised learning presents an online learning accuracy of 91.4%. This work opens an avenue for future flexible electronics. [ABSTRACT FROM AUTHOR]

This paper describes a simple and convenient approach to synthesize large amounts of ZnO nanosheets, which are suitable for producing a key component, i.e., colloidal nanoink, of printed ultraviolet photodetectors. ZnO nanosheets are produced by atomic layer deposition, where a three-dimensional polymer sponge with a large specific surface area is used as the template. Systematic studies including scanning electron microscopy, X-ray diffraction, and transmission electron microscopy reveal that the synthesized ZnO nanosheets have a good crystalline quality and mechanical flexibility. After dispersing ZnO nanosheets in a solvent to form a stable and colloidal nanoink, an ultraviolet photodetector is demonstrated through the printing method. Such a printed ultraviolet photodetector that utilizes ZnO nanosheets as the functional materials exhibits a high responsivity of ∼148 A/W and a response time of 19 s. Our present study may provide a practical method to produce large amounts of functional nanosheets for printing electronics, which paves the way for developing high-performance, low-cost, large-area printed, and flexible electronics. [ABSTRACT FROM AUTHOR]

Phosphorene, a single layer of black phosphorous (BLK-P), has significant potential for flexible and tunable electronics, but attempts to grow it epitaxially have been unsuccessful to date. Close-packed (111) surfaces of metals favor blue phosphorous (BL-P) over BLK-P due to the hexagonal symmetry of the former. Here, we investigate computationally the alternative offered by stepped substrates. Using the model of a Cu(311) surface, we find that surface steps can favor energetically BLK-P over BL-P. This can be rationalized in terms of surface density of states and orbital hybridization, which leads to a stronger surface bonding of BLK-P. This suggests that vicinal metal surfaces of metals can offer a viable path toward phosphorene synthesis. [ABSTRACT FROM AUTHOR]

Flexible electronics or hybrid electronics exhibit great potential for widespread applications in future wearable electronics. In this work, we fabricated flexible nanoscale MgO-barrier magnetic tunnel junctions (MTJs) using a transfer printing process. The magnetic transport measurements reveal that the fabricated devices possess excellent performance with a tunnel magnetoresistance ratio of ∼130% under different strained conditions. In addition, we also studied the spin-torque diode effect under different strained conditions and found that the resonant frequency and rectified voltage remain almost unchanged. These results demonstrate that the nanoscale MTJs have good strain endurance, which provides the feasibility to flexible spintronic storage and microwave applications. [ABSTRACT FROM AUTHOR]

Fiber-based devices with advanced functionalities are emerging as promising solutions for various applications in flexible electronics and bioengineering. Multimaterial thermal drawing, in particular, has attracted strong interest for its ability to generate fibers with complex architectures. Thus far, however, the understanding of its fluid dynamics has only been applied to single material preforms for which higher order effects, such as the radial dependency of the axial velocity, could be neglected. With complex multimaterial preforms, such effects must be taken into account, as they can affect the architecture and the functional properties of the resulting fiber device. Here, we propose a versatile model of the thermal drawing of fibers, which takes into account a radially varying axial velocity. Unlike the commonly used cross section averaged approach, our model is capable of predicting radial variations of functional properties caused by the deformation during drawing. This is demonstrated for two effects observed, namely, by unraveling the deformation of initially straight, transversal lines in the preform and the dependence on the draw ratio and radial position of the in-fiber electrical conductivity of polymer nanocomposites, an important class of materials for emerging fiber devices. This work sets a thus far missing theoretical and practical understanding of multimaterial fiber processing to better engineer advanced fibers and textiles for sensing, health care, robotics, or bioengineering applications. [ABSTRACT FROM AUTHOR]

We demonstrate a flexible radiofrequency filter based on graphene assembly films with a high conductivity up to 106 S/m and a thickness of 10 μm. The flexible high-conductivity graphene film (HCGF) used in the filter has a fifth-order low-pass Chebyshev frequency response, and it operates at 3.6 GHz with a 0.82 dB in-band maximum insertion loss and 26.21 dB insertion loss at 5 GHz. Such performance observed in the HCGF-based flexible filters is comparable to that of commercial copper-based filters in passband and roll-off. The HCGF exhibits good mechanical flexibility even after 200 cycles of bending. Nearly no mechanical failure or performance degradation occurs during 20 cycles of 0°–50° bending for the flexible HCGF filter. Our results suggest that the flexible HCGF filter has good repetitive bending stability. This makes this type of filter suitable for future applications in flexible wireless communication. [ABSTRACT FROM AUTHOR]

Nickel silicides are widely used as contact materials for electronic devices based on silicon (Si). However, they have been predominantly fabricated by annealing separate Ni and Si phases which leads to phase and structural complexity. In this letter, direct epitaxial growth of a single-phase nickel disilicide (NiSi2) thin film by sputter deposition of NiSi2 is achieved on low-cost and flexible Hastelloy tapes which offers a promising route to fabricate low-cost, flexible electronic devices. Biaxially textured titanium nitride (TiN) is applied as the seeding layer and the diffusion barrier under NiSi2. An epitaxial relationship of (001)⟨100⟩NiSi2 ǁ (001)⟨110⟩TiN is observed with an extra-large lattice mismatch (∼10.3%) between NiSi2 and TiN. Both the bonding similarity and the passivation effect by hydrogen promote the epitaxial growth of NiSi2 on TiN. The flat and smooth NiSi2 thin film consists of grains with a size of 50–100 nm. An epitaxially grown Si film on NiSi2 further demonstrates the potential of manufacturing high-performance Si flexible electronics with NiSi2/TiN/Hastelloy as the direct contact through this approach. [ABSTRACT FROM AUTHOR]

Recently, a novel two-dimensional (2D) metal-free organic material, the C4N3H monolayer, has been proposed and predicted to be a 2D Dirac material with high Fermi velocities. Herein, we investigated its mechanical properties and tensile strain effects on its electronic properties based on first-principles calculations. We demonstrated that this material is quite soft with small stiffness constants and can sustain large strains. Compared to many other 2D materials, this material presents a remarkable elastic anisotropy and a large Poisson's ratio, which are very important for strain engineering. We also found that the Dirac cone of this material is very robust against the tensile strains and the Fermi velocity is high. The small stiffness constant, large Poisson's ratio, robust Dirac cone, and high Fermi velocity make the C4N3H monolayer a promising material in high-speed flexible electronic devices. [ABSTRACT FROM AUTHOR]

Gold nanoparticle (AuNP)-polymer composites have emerged as promising candidates for flexible electronics due to their super-high stretchability and metal-like conductivity. Their percolation threshold is, however, much higher than that of 1D carbon nanotubes or silver nanowires. A practical and appealing solution is to assemble AuNPs into 1D quasi-nanowires via the van der Waals interaction. In this letter, electron tunneling is incorporated into the theory of traditional composites to explore the percolation of these nanocomposites. The geometries of AuNP-chains are found to play a key role in determining the effect of electron tunneling and thus the overall percolation behavior. Small and/or short AuNP-chains yield the substantial tunneling effect, leading to the rapid growth in conductivity across a transition zone where the conductivity mechanism transfers from electron tunneling to contact conductance. This unique feature agrees with experimental observation but cannot be characterized directly by existing theories. [ABSTRACT FROM AUTHOR]

The integration of a high-performance metamaterial (MM) onto mechanically flexible and deformable substrates offers significant promise in flexible electronics. Here, we propose two types of stretchable infrared (IR) MMs to design a tunable perfect absorber with a ring-shape (PA-RS) and a cross-shape (PA-CS) on a PDMS/Au/PDMS substrate, respectively. By stretching devices along different directions, PA-RS and PA-CS exhibit ultra-narrowband, polarization-dependent/independent, and switchable characterizations in the IR wavelength range. The tuning ranges are 2.37 μm and 2.36 μm for PA-RS and PA-CS with the deformation quantity of 2.50 μm along two-dimensional directions, respectively, without extra power supply. In this deformation range, most of the incident light is perfectly absorbed for PA-RS design operated at a wavelength of 4.31 μm and PA-CS design operated at a wavelength of 4.24 μm. The corresponding Q-factors of two devices are 98 and 118 for PA-RS and PA-CS, respectively. Such results are very suitable for high-performance refractive index sensor applications. Furthermore, two devices exhibit the functionalities of s-polarization switches and s-/p-polarization switches. To further investigate the characterizations of devices deformed by a tensile force, PA-CS could be actively tuned by bending devices at a certain angle. In the future, these proposed stretchable IR MMs could potentially possess high portability, applicability, and cost-effectiveness for wearable electronic devices in a variety of sensor fields. [ABSTRACT FROM AUTHOR]

Due to their high thermal conductivity, stability, light weight, and low cost, graphite products are widely used as thermally conductive materials in current electronic devices and are promising materials for future flexible electronics. However, the intrinsic high rough surface of graphite severely impedes the fabrication of thermal transistors based on graphite products. On the other hand, most of the flexible thermal transistors reported to date are based on polymer substrates, whose thermal conductivities are extremely low for thermal sensing. To address these issues herein, a flexible commercial graphite paper with high thermal conductivity was used as both the substrate and the back gate of thermal transistors. Fluorinated polyimide was also synthesized as a high performance dielectric material and was skillfully blade-coated on a flexible graphite paper to reduce the surface roughness. As a result, the as-fabricated flexible device exhibits extremely low hysteresis, wide operating temperature range (20–100 °C), high stability, and temperature sensing performance. Moreover, the as-fabricated pentacene device reached the mobility of 0.146 cm2 V−1 s−1, which is highly competitive among the reported flexible organic thermal transistors. Such thermal transistors are promising for integration in current electronic devices and promote the diversity of the flexible transistor substrates. [ABSTRACT FROM AUTHOR]

A spiral interconnect array is a commonly used architecture for stretchable electronics, which accommodates large deformations during stretching. Here, we show the effect of different geometrical morphologies on the deformation behavior of the spiral island network. We use numerical modeling to calculate the stresses and strains in the spiral interconnects under the prescribed displacement of 1000 μ. Our result shows that spiral arm elongation depends on the angular position of that particular spiral in the array. We also introduce the concept of a unit-cell, which fairly replicates the deformation mechanism for full complex hexagon, diamond, and square shaped arrays. The spiral interconnects which are axially connected between displaced and fixed islands attain higher stretchability and thus experience the maximum deformations. We perform tensile testing of 3D printed replica and find that experimental observations corroborate with theoretical study. [ABSTRACT FROM AUTHOR]

Flexible electronics, which is of great importance as fundamental sensor and communication technologies for many internet-of-things applications, has established a huge market encroaching into the trillion-dollar market of solid state electronics. For the capability of being processed by printing or spraying, colloidal quantum dots (CQDs) play an increasingly important role in flexible electronics. Although the electrical properties of CQD thin-films are expected to be stable on flexible substrates, their electrical performance could be tuned for applications in flexible touch sensors. Here, we report CQD touch sensors employing polydimethylsiloxane (PDMS) triboelectric films. The electrical response of touching activity is enhanced by incorporating CQD field-effect transistors into the device architecture. Thanks to the use of the CQD thin film as a current amplifier, the field-effect CQD touch sensor shows a fast response to various touching materials, even being bent to a large curvature. It also shows a much higher output current density compared to a PDMS triboelectric touch sensor. [ABSTRACT FROM AUTHOR]

Wearable flexible electronics often require sustainable power sources that are also mechanically flexible to survive the extreme bending that accompanies their general use. In general, thinner microelectronic devices are under less strain when bent. This paper describes strategies to realize ultra-thin GaAs photovoltaics through the interlayer adhesiveless transfer-printing of vertical-type devices onto metal surfaces. The vertical-type GaAs photovoltaic devices recycle reflected photons by means of bottom electrodes. Systematic studies with four different types of solar microcells indicate that the vertical-type solar microcells, at only a quarter of the thickness of similarly designed lateral-type cells, generate a level of electric power similar to that of thicker cells. The experimental results along with the theoretical analysis conducted here show that the ultra-thin vertical-type solar microcells are durable under extreme bending and thus suitable for use in the manufacturing of wearable flexible electronics. [ABSTRACT FROM AUTHOR]

Flexible electronics have a great potential to impact consumer electronics and with that our daily life. Currently, no direct growth of epitaxial functional oxides on commercially available flexible substrates is possible. In this study, in order to address this challenge, muscovite, a common layered oxide, is used as a flexible substrate that is chemically similar to typical functional oxides. We fabricated epitaxial MoO2 films on muscovite via pulsed laser deposition technique. A combination of X-ray diffraction and transmission electron microscopy confirms van der Waals epitaxy of the heterostructures. The electrical transport properties of MoO2 films are similar to those of the bulk. Flexible or free-standing MoO2 thin film can be obtained and serve as a template to integrate additional functional oxide layers. Our study demonstrates a remarkable concept to create flexible electronics based on functional oxides. [ABSTRACT FROM AUTHOR]

Recent interest in flexible electronics and wearable devices has created a demand for fast and highly repeatable printing processes suitable for device manufacturing. Robust printing technology is critical for the integration of sensors and other devices on flexible substrates such as paper and textile. An atmospheric pressure plasma-based printing process has been developed to deposit different types of nanomaterials on flexible substrates. Multiwalled carbon nanotubes were deposited on paper to demonstrate site-selective deposition as well as direct printing without any type of patterning. Plasma-printed nanotubes were compared with non-plasma-printed samples under similar gas flow and other experimental conditions and found to be denser with higher conductivity. The utility of the nanotubes on the paper substrate as a biosensor and chemical sensor was demonstrated by the detection of dopamine, a neurotransmitter, and ammonia, respectively. [ABSTRACT FROM AUTHOR]