Switching Properties Research Articles

Highly reproducible and CMOS-compatible VO2-based oscillators for brain-inspired computing.

With remarkable electrical and optical switching properties induced at low power and near room temperature (68°C), vanadium dioxide (VO2) has sparked rising interest in unconventional computing among the phase-change materials research community. The scalability and the potential to compute beyond the von Neumann model make VO2 especially appealing for implementation in oscillating neural networks for artificial intelligence applications, to solve constraint satisfaction problems, and for pattern recognition. Its integration into large networks of oscillators on a Silicon platform still poses challenges associated with the stabilization in the correct oxidation state and the ability to fabricate a structure with predictable electrical behavior showing very low variability. In this work, the role played by the different annealing parameters applied by three methods (slow thermal annealing, flash annealing, and rapid thermal annealing), following the vanadium oxide atomic layer deposition, on the formation of VO2 grains is studied and an optimal substrate stack configuration that minimizes variability between devices is proposed. Material and electrical characterizations are performed on the different films and a step-by-step recipe to build reproducible VO2-based oscillators is presented, which is argued to be made possible thanks to the introduction of a hafnium oxide (HfO2) layer between the silicon substrate and the vanadium oxide layer. Up to seven nearly identical VO2-based devices are contacted simultaneously to create a network of oscillators, paving the way for large-scale implementation of VO2 oscillating neural networks.

Competing Charge Transfer and Screening Effects in Two-Dimensional Ferroelectric Capacitors.

Two-dimensional (2D) ferroelectrics promise ultrathin flexible nanoelectronics, typically utilizing a metal-ferroelectric-metal sandwich structure. Electrodes can either contribute free carriers to screen the depolarization field, enhancing nanoscale ferroelectricity, or induce charge doping, disrupting the long-range crystalline order. We explore electrodes' dual roles in 2D ferroelectric capacitors, supported by first-principles calculations covering a range of electrode work functions. Our results reveal volcano-type relationships between ferroelectric-electrode binding affinity and work function, which are further unified by a quadratic scaling between the binding energy and the transferred interfacial charge. At the monolayer limit, charge transfer dictates the ferroelectric stability and switching properties. This general characteristic is confirmed in various 2D ferroelectrics including α-In2Se3, CuInP2S6, and SnTe. As the ferroelectric layer's thickness increases, the capacitor stability evolves from a charge-transfer-dominated state to a screening-dominated state. The delicate interplay between these two effects has important implications for 2D ferroelectric capacitor applications.

Realizing Weak Light Detection in a 2D Dielectric Switching Hybrid Perovskite Incorporating Dimethylamine

Abstract2D organic–inorganic hybrid perovskites (OIHPs) are regarded as potential candidates for the advancement of multifunctional phase‐transition materials due to their ability to integrate flexible functionality and superior electronic features from both organic and inorganic components. However, the development of 2D OIHPs with dielectric switches and weak light detection capability that are crucial for high‐resolution sensing and imaging, remains challenge. Herein, a novel 2D OIHP BDADMAPb2Br7 (1, BDA = 1,4‐butanediamine and DMA = dimethylamine) is presented, featuring a 2D Dion–Jacobson (DJ) bilayered structure incorporated with secondary amine. Upon heating and cooling cycles, 1 demonstrates long‐term reversible dielectric switching properties at 328 K. Meanwhile, 1 also shows compelling semiconductor characteristics, including a low dark current of 2.87 × 10−11 A (10 V), a large switching ratio of 4 × 103, and a high detectivity of 1.3 × 1012 Jones. In addition, the photodetector based on 1 exhibits an excellent weak light detection ability of 340 nW cm−2 at 405 nm. Such a 2D OIHP demonstrates a novel platform for creating multifunctional materials and significantly promotes the development of integrated devices.

Dynamic Electrostatic Interfacial Engineering for Block Copolymer Microparticles with Reversible Structures.

Responsive nanoparticle surfactants (NPSs) can dynamically and reversibly modulate the interfacial interactions between incompatible components, which are essential in the interfacial catalysis, corrosion, and self-assembly of block copolymers (BCPs). However, NPSs with stimuli-responsive behavior often involve tedious chemical synthesis and surface modifications. Herein, we propose a strategy to in situ construct a kind of dynamic and reversible NPSs by the interfacial electrostatic interaction between the negatively charged nanoparticles (NPs) and the positively charged homopolymers. The NPSs assembled at the oil/water interface reduce the interfacial tension and direct the confined assembly of BCP. Meanwhile, the dynamic NPSs can be disassembled by increasing the pH value or introducing competitive electrostatic attractions, which can dynamically and reversibly change the interfacial properties as well as the alignment of polymer chains, enabling BCP microparticles with reversibly switchable lamellar and cylindrical structures. Furthermore, by the introduction of aggregation-induced emission luminogens as tails to the NPSs, the reversible transformation of BCP microparticles can be visualized by fluorescence emission, which is dependent on the nanostructures of microparticles. This work establishes a concept for dynamically manipulating interfacial interactions and reversibly switching BCP microparticles without time-consuming NPS synthesis, showing promising applications in the fabrication of smart materials with switchable structures and properties.

Strategies to Enhance the Electrochromic Properties of Conjugated Polymers Bearing Pyromellitic Diimide Acceptors.

A series of conjugated polymers bearing thiophene-based donors and pyromellitic diimide (PMDI) acceptor were prepared, and their electrochromic (EC) properties were studied via using fabricated thin-film EC devices. It was observed that structurally regular alternating polymers with fewer (1 and 2) thiophene donors do not exhibit any EC properties while increasing the number of donors eventually led to the emergence of orange-red-to-green colour switching. On this basis, two more random co-polymers containing higher donor-to-acceptor ratios were synthesized to further improve EC switching properties. The two polymers, which bear a PMDI-to-thiophene ratio of ca. 1 : 7 and 1 : 8, revealed orange red-to-blue colour switching and generally improved optical contrasts and switching speeds in both the visible and near infra-red (NIR) region. In addition, the subtle modulation of polymer colour and hue via variation of the number of thiophene donors was evident through colorimetric study. This work therefore demonstrates the potential and possibility of using the PMDI acceptor unit to construct EC-active conjugated polymers, and considerations for future tuning of colour and switching performances.

A superabsorbent and pH-responsive copolymer-hydrogel based on acemannan from Aloe vera (Aloe barbadensis M.): A smart material for drug delivery

Combining natural polysaccharides with synthetic materials improves their functional properties which are essential for designing sustained-release drug delivery systems. In this context, the Aloe vera leaf mucilage/hydrogel (ALH) was reacted with acrylic acid (AA) to synthesize a copolymerized hydrogel, i.e., ALH-grafted-Polyacrylic acid (ALH-g-PAA) through free radical copolymerization. Concentrations of the crosslinker N,N′-methylene-bis-acrylamide (MBA), and the initiator potassium persulfate (KPS) were optimized to study their effects on ALH-g-PAA swelling. The FTIR and solid-state NMR (CP/MAS 13C NMR) spectra witnessed the formation of ALH-g-PAA. Scanning electron microscopy (SEM) analysis revealed superporous nature of ALH-g-PAA. The gel fraction (%) of ALH-g-PAA was directly related to the concentrations of AA and MBA whereas the sol fraction was inversely related to the concentrations of AA and MBA. The porosity (%) of ALH-g-PAA directly depends on the concentration of AA and MBA. The ALH-g-PAA swelled admirably at pH 7.4 and insignificantly at pH 1.2. The ALH-g-PAA offered on/off switching properties at pH 7.4/1.2. The metoprolol tartrate was loaded on different formulations of ALH-g-PAA. The ALH-g-PAA showed pH, time, and swelling-dependent release of metoprolol tartrate (MT) for 24 h following the first-order kinetic and Korsmeyer-Peppas model. Haemocompatibility studies ascertained the non-thrombogenic and non-hemolytic behavior of ALH-g-PAA.

Integrating spin-dependent emission and dielectric switching in FeII catenated metal-organic frameworks

Mechanically interlocked molecules (MIMs) including famous catenanes show switchable physical properties and attract continuous research interest due to their potential application in molecular devices. The advantages of using spin crossover (SCO) materials here are enormous, allowing for control through diverse stimuli and highly specific functions, and enabling the transfer of the internal dynamics of MIMs from solution to solid state, leading to macroscopic applications. Herein, we report the efficient self-assembly of catenated metal-organic frameworks (termed catena-MOFs) induced by stacking interactions, through the combination of rationally selected flexible and conjugated naphthalene diimide-based bis-pyridyl ligand (BPND), [MI(CN)2]− (M = Ag or Au) and Fe2+ in a one-step strategy. The obtained bimetallic Hofmann-type SCO-MOFs [FeII(BPND){Ag(CN)2}2]·3CHCl3 (1Ag) and [FeII(BPND{Au(CN)2}2]·2CHCl3·2H2O (1Au) possess a unique three-dimensional (3D) catena-MOF constructed from the polycatenation of two-dimensional (2D) layers with hxl topology. Both complexes undergo thermal- and light-induced SCO. Significantly, abnormal increases in the maximum emission intensity and dielectric constant can be detected simultaneously with the switching of spin states. This research opens up SCO-actuated bistable MIMs that afford dual functionality of coupled fluorescence emission and dielectricity.

Resistive switching properties in polycrystalline LiNbO3 thin films

LiNbO3 (LNO) is currently intensively studied as an important ferroelectric material. In this work, polycrystalline LNO films were prepared through a sputtering technique, and their ferroelectricity-related resistive switching property was investigated using a device structure of PtSi/SiO2/LNO/Pt. The device exhibits a volatile resistance switching property at lower positive sweeping voltages and a stable bipolar nonvolatile switching property at higher sweeping voltages. The resistive switching mechanism of the device is discussed based on the domain wall conductivity characteristics of the polycrystalline LNO thin films. The PtSi/SiO2/LNO/Pt memristor device has potential applications in memory and artificial neural synapses.

Topological Quantum Switching Enabled Neuroelectronic Synaptic Modulators for Brain Computer Interface.

Aging and genetic-related disorders in the human brain lead to impairment of daily cognitive functions. Due to their neural synaptic complexity and the current limits of knowledge, reversing these disorders remains a substantial challenge for brain-computer interfaces (BCI). In this work, a solution is provided to potentially override aging and neurological disorder-related cognitive function loss in the human brain through the application of the authors' quantum synaptic device. To illustrate this point, a quantum topological insulator (QTI) Bi2Se2Te-based synaptic neuroelectronic device, where the electric field-induced tunable topological surface edge states and quantum switching properties make them a premier option for establishing artificial synaptic neuromodulation approaches, is designed and developed. Leveraging these unique quantum synaptic properties, the developed synaptic device provides the capability to neuromodulate distorted neural signals, leading to the reversal of age-related disorders via BCI. With the synaptic neuroelectronic characteristics of this device, excellent efficacy in treating cognitive neural dysfunctions through modulated neuromorphic stimuli is demonstrated. As a proof of concept, real-time neuromodulation of electroencephalogram (EEG) deduced distorted event-related potentials (ERP) is demonstrated by modulation of the synaptic device array.

Forming-less flexible memristor crossbar array for neuromorphic computing applications produced using low-temperature atomic layer deposition

The rapid development of wearable artificial intelligence devices based on memristor crossbar arrays has increased the demand for flexible electronics. However, fabricating crossbar arrays on flexible substrates faces inherent challenges, notably due to the complex fabrication process at low temperatures. Moreover, ensuring the stability and reliability of memristor device remains a crucial issue. To address these issues, this study introduced N-doped TaOx (N:TaOx) as a flexible memristor crossbar array fabricated via atomic layer deposition directly on a flexible substrate at an exceptionally low temperature (150 °C). The flexible PET/ITO/N:TaOx/TiN memristor device exhibited forming-less bipolar resistive switching properties with analog memory characteristics. This was accomplished by increasing the nitrogen doping concentration and effectively reducing oxygen-related defects in TaOx. The amorphous-phase flexible N:TaOx memristor demonstrated remarkable stability, enduring 500 switching cycles and retaining its state for 24 h during bending tests involving 104 bending cycles at 2.5 mm bending radius. Furthermore, a 6 × 6 flexible memristor crossbar array was fabricated successfully, with all 36 devices exhibiting well-defined memristor behavior and minimal variation attributed to the film's uniformity achieved through ALD process. Additionally, by programming the tunable conductance of each device in the array, characters of desired shapes can be formed and read. Regarding their synaptic behavior via long-term potentiation and depression, the proposed flexible memristor device showed an outstanding accuracy of 96.44 % in image recognition tasks under extreme bending conditions, employing the MNIST and Fashion-MNIST datasets. The N:TaOx memristor deposited at low temperatures thus exhibits significant potential for use in wearable neuromorphic hardware applications due to its high density, high performance, reliability, and precise image recognition.

Improving the hydrostability of zeolitic imidazolate framework coatings using a facile silk fibroin protein modification method

Zeolitic imidazolate frameworks (ZIFs) are an important subclass of metal-organic frameworks (MOFs) with zeolite-type topology, which can be fabricated under ambient synthesis conditions. However, the applications of ZIFs are commonly limited due to the weak hydrostability of their metal–ligand coordination bonds, particularly under humid and aqueous conditions. In this work, as an example, the hydrolysis behaviours of ZIF-L with a special focus on ZIF-L coatings were tested at aqueous conditions with a wide range of pHs to systematically study and fundamentally understand their structural stability and degradation mechanism. Pristine ZIF-L powder and ZIF-L coatings were severely damaged after only 24 h in aqueous media. Interestingly, the ZIF-L coatings showed two distinct hydrolyzation pathways regardless of pH conditions, exhibiting either a ring-shaped etching or unfolding behaviours. While the ZIF-L powders were hydrolyzed almost identically across all pH conditions. With this new understanding, a facile silk fibroin (SF) protein modification method was developed to enhance the hydrostability of ZIF-L coatings in aqueous media. The effect of protein concentration on surface coating was systemically studied. ZIF-L coating retained its surface morphology after soaking in water and demonstrated switchable super wetting properties and superior separation performance for oil/water mixture. As a result, the quick SF protein modification significantly enhanced the stability of ZIF-L coatings under various pHs, while retaining their switchable wetting property and excellent separation performance.

Atomic Layer Deposition Films for Resistive Random‐Access Memories

AbstractResistive random‐access memory (RRAM) stands out as a promising memory technology due to its ease of operation, high speed, affordability, exceptional stability, and potential to enable smaller memory devices with sizes under 10 nm. This has drawn significant attention, with atomic layer deposition (ALD) emerging as an ideal technology to tackle the challenges of nanoscale fabrication in the micro‐ and nanomanufacturing industry. ALD offers technological advantages such as functional multiple‐layer stacking, doping capabilities, and incorporating oxygen reservoirs or reactive layers. These factors contribute to achieving more intriguing, stable, and reliable nonvolatile resistance switching behaviors in RRAM. Specifically, ALD greatly benefits RRAM, that relies on the valence change mechanism, where high‐k transition metal oxides are commonly used as switching materials, and precise control over oxygen vacancies is achievable. This review provides a comprehensive overview of ALD films used in RRAM, delves into resistive switching properties and microscopic mechanisms in binary and ternary oxides and nitrides, and explores the impact of ALD‐prepared electrodes. Furthermore, the current status and future prospects of ALD‐based RRAM are highlighted, which is poised to catalyze further advancements in the fields of information storage and neural networks.

Layered Double Hydroxide-Based Photocatalysts for the Removal of Emerging Contaminants: Progress in Past Ten Years

Currently, public health is seriously threatened by the massive concentrations of emerging contaminants. Treating emerging contaminants in water using effective methods has become a major challenge worldwide. Photocatalytic technology, as an eco-friendly technology, has been recognized as an effective means of removing contaminants from water. Among the various photocatalysts, layered double hydroxides (LDHs), known as hydrotalcite-like materials, have been explored extensively in photocatalytic reactions due to their switchable properties and the large surface areas of their unique two-dimensional structures. In this article, recent advances in the photocatalytic degradation of emerging contaminants by LDH-based photocatalysts are reviewed. Firstly, the fundamental principles of the photocatalytic degradation of emerging contaminants using LDH-based materials are briefly introduced. Various LDHs applied in the photocatalytic degradation of emerging contaminants are broadly summarized into four types: pure-phase LDHs, interlayer-modified LDHs, LDH-based composites, and layered double oxides (LDOs). Moreover, the synthesis process and catalytic mechanism of LDH-based photocatalysts are also reviewed. An outlook on the problems and future development of LDH-based photocatalysts in water remediation is provided at the end.

Polar Crystals Using Molecular Chirality: Pseudosymmetric Crystallization toward Polarization Switching Materials.

Polar compounds with switchable polarization properties are applicable in various devices such as ferroelectric memory and pyroelectric sensors. However, a strategy to prepare polar compounds has not been established. We report a rational synthesis of a polar CoGa crystal using chiral cth ligands (SS-cth and RR-cth, cth = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Both the original homo metal Co crystal and Ga crystal exhibit a centrosymmetric isostructure, where the dipole moment of metal complexes with the SS-cth ligand and those with the RR-cth ligand are canceled out. To obtain a polar compound, the Co valence tautomeric complex with SS-cth in the homo metal Co crystal is replaced with the Ga complex with SS-cth by mixing Co valence tautomeric complexes with RR-cth and Ga complexes with SS-cth. The CoGa crystal exhibits polarization switching between the pseudononpolar state at a low temperature and the polar state at a high temperature because only Co complexes exhibit changes in electric dipole moment due to metal-to-ligand charge transfer. Following the same strategy, the polarization-switchable CoZn complex was synthesized. The CoZn crystal exhibits polarization switching between the polar state at a low temperature and the pseudononpolar state at a high temperature, which is the opposite temperature dependence to that of the CoGa crystal. These results revealed that the polar crystal can be synthesized by design, using a chiral ligand. Moreover, our method allows for the control of temperature-dependent polarization changes, which contrasts with typical ferroelectric compounds, in which the polar ferroelectric phase typically occurs at low temperatures.

Textile-Based Adsorption Sensor via Mixed Solvent Dyeing with Aggregation-Induced Emission Dyes.

This study demonstrates a novel methodology for developing a textile-based adsorption sensor via mixed solvent dyeing with aggregation-induced emission (AIE) dyes on recycled fabrics. AIE dyes were incorporated into the fabrics using a mixed solvent dyeing method with a co-solvent mixture of H2O and organic solvents. This method imparted unique fluorescence properties to fabrics, altering fluorescence intensity or wavelength based on whether the AIE dye molecules were in an isolated or aggregated state on the fabrics. The precise control of the H2O fraction to organic solvent during dyeing was crucial for influencing fluorescence intensity and sensing characteristics. These dyed fabrics exhibited reactive thermochromic and vaporchromic properties, with changes in fluorescence intensity corresponding to variations in temperature and exposure to volatile organic solvents (VOCs). Their superior characteristics, including a repetitive fluorescence switching property and resistance to photo-bleaching, enhance their practicality across various applications. Consequently, the smart fabrics dyed with AIE dye not only find applications in clothing and fashion design but demonstrate versatility in various fields, extending to sensing temperature, humidity, and hazardous chemicals.

Versatile Titanium Carbide MXene Thin-Film Memristors with Adaptive Learning Behavior.

With the advent of the modern era, there is a huge demand for memristor-based neuromorphic computing hardware to overcome the von Neumann bottleneck in traditional computers. Here, we have prepared two-dimensional titanium carbide (Ti3C2Tx) MXene following the conventional HF etching technique in solution. After confirmation of Ti3C2Tx properties by Raman scattering and crystallinity measurements, high-quality thin-film deposition is realized using an immiscible liquid-liquid interfacial growth technique. Following this, the memristor is fabricated by sandwiching a Ti3C2Tx layer with a thickness of 70 nm between two electrodes. Subsequently, current-voltage (I-V) characteristics are measured, revealing a nonvolatile resistive switching property characterized by a swift switching speed of 30 ns and an impressive current On/Off ratio of approximately 103. Furthermore, it exhibits endurance through 500 cycles and retains the states for at least 1 × 104 s without observable degradation. Additionally, it maintains a current On/Off ratio of about 102 while consuming only femtojoules (fJ) of electrical energy per reading. Systematic I-V results and conductive AFM-based current mapping image analysis are converged to support the electroforming mediated filamentary conduction mechanism. Furthermore, our Ti3C2Tx memristor was found to be truly versatile as an all-in-one device for demonstrating edge computation, logic gate operation, and classical conditioning of learning by the brain in Psychology.

Electromechanical and ferroelectric hysteresis in dense and porous PZT-type piezoceramics

In the present study, particular aspects of the large-signal switching properties and electromechanical hysteresis of the lead zirconate titanate (PZT)-type porous piezoceramics were studied in comparison with the dense piezoceramics of the same composition. Large-signal ferroelectric polarization and strain hysteresis loops were recorded at the bipolar electric fields in the range of 0 ÷ 5 kV/mm and in the frequency range of 0.01 ÷ 5 Hz. Measurements and analysis were performed by means of the electromechanical measurement system (STEPHV) and electromechanical response characterization program (STEP), combining large-signal modeling of the mechanical and electrical behavior of ferroelectric materials.

Active strong coupling of exciton and nanocavity based on GSST-WSe2 hybrid nanostructures

The strong coupling between optical resonance microcavity and matter excitations provides a practical path for controlling light-matter interactions. However, conventional microcavity, whose functions are fixed at the fabrication stage, dramatically limits the modulation of light-matter interactions. Here, we investigate the active strong coupling of resonance mode and exciton in GSST-WSe2 hybrid nanostructures. It is demonstrated that significant spectral splitting is observed in single nanostructures, tetramers, and metasurfaces. We further confirm the strong coupling by calculating the enhanced fluorescence spectra. The coupling effect between the excited resonance and exciton is dramatically modulated during the change of GSST from amorphous to crystalline, thus realizing the strong coupling switching. This switching property has been fully demonstrated in several systems mentioned earlier. Our work is significant in guiding the study of actively tunable strong light-matter interactions at the nanoscale.

The effect of substrate-induced defects on structural and resistive switching properties in Gd0.2Ca0.8MnO3 thin films

Gd0.2Ca0.8MnO3 thin films were deposited on various substrate materials and their structural and resistive switching (RS) properties were investigated. The deposition resulted in epitaxial and polycrystalline films, with the latter also exhibiting distorted film surfaces. Both epitaxial and a part of polycrystalline films used as RS devices showed consistent RS performance in which an order of magnitude, or higher, switching ratios were achieved between high and low resistance states. The devices showed strong endurance during repeated switching cycles. However, under retention characterization, the resistance states did not remain distinguishable in devices constructed on polycrystalline films, while other devices maintained separable resistance states. The RS results are discussed in relation to the structural characteristics of the films, and this work helps us understand the RS mechanisms that still remain elusive in manganite-based devices.

Modulating resistive switching in Ni0.5Zn0.5Fe2O4 memristors: The role of manganese doping concentrations

Memristors, recognized as key devices for mitigating the von Neumann bottleneck, show great potential in non-volatile memory technology. Their performance is fundamentally linked to the chemical composition and structural characteristics of their intermediate dielectric layer. Owing to the inherent advantages of metal oxides, such as their simplistic chemical makeup and superior thermal stability, memristors featuring a Metal-Insulator-Metal (MIM) sandwich structure with metal oxides as the intermediate layer have received extensive focus. In this study, a Pt/Ni0.5Zn0.5MnxFe2-xO4(NZMFO)/Pt composite film was prepared, and its resistance switching behavior was modulated by altering the doping concentration of Mnn+ in NZMFO. The experimental results indicate that altering the Mnn+ doping concentration does significantly impact the content of oxygen vacancies. As the concentration of Mnn+ increases from 0.10 to 0.20 at.%, the content of oxygen vacancies correspondingly rises from 46.58 % to 76.42 %. Concurrently, variations in Mnn+ doping concentration significantly alter the resistance switching properties of the Pt/NZMFO/Pt composite films. This includes elevating the set/reset voltage, diminishing the resistance ratio, and enhancing the durability with the augmentation of Mnn+ concentration. By meticulously adjusting the Mnn+ doping concentration, we can achieve a memristor characterized by superior performance across all metrics. Considering all performance aspects, this study determined that the Pt/NZMFO/Pt thin film memristor with x = 0.15 exhibits adequate endurance (100 cycles), high data retention, and stable set/reset voltage. This work underscores the critical role of Mnn+ doping concentration in optimizing the electrochemical properties of NZFO memristors, illustrating a strategic pathway to engineer memristive devices with enhanced performance for future non-volatile memory applications.