Abstract We demonstrate a metastable fingerprint (mFP) state in a homeotropically aligned cholesteric liquid crystal (CLC) with negative dielectric anisotropy. The mFP forms upon gradual removal of a high-voltage, low-frequency electric field and persists for several hours at zero field. Factors influencing the stability of this state include the confinement ratio—the ratio of the cell thickness to the cholesteric pitch, ρ = d/p—the alignment layer rubbing strength, and material composition. Electro-optical characterization of the dichroic dye-doped CLC in a single-layer cell reveals four distinct optical states: a clear state, two tinted states, and a hazy state. Furthermore, CTAB-doping enables controlled erasure of the mFP and access to bubble domains, a distinct, weakly scattering, tinted state. In the optimized configuration (ρ ≈ 1, five-times rubbed alignment layer), driving at 80 mV s–1, the induced mFP persists for 400–500 min when the voltage is removed. These findings establish mFP textures as a promising route for developing bistable cholesteric optical devices such as liquid crystal windows.
Abstract Skin-interface pressure monitoring is essential for preventing pressure injuries caused by sustained mechanical loading between the human body and support surfaces. However, porous structure-based pressure sensors often exhibit high mechanical hysteresis and unstable response because of their intrinsic viscoelastic deformation and structural instability under repeated deformation, hindering reliable detection of sustained interface pressure. Herein, we report a fully flexible piezoresistive pressure sensor based on a carbon black (CB)/polydimethylsiloxane (PDMS)/ethyl cellulose (EC)-coated polyurethane (PU) sponge integrated with Ag nanowire (AgNW)-patterned textile electrodes. EC facilitated the formation of a continuous conductive coating on the PU sponge, while the pre-compression process during curing effectively reduced the mechanical hysteresis of the porous structure. The fabricated sensor exhibited a sensitivity of 0.019 kPa−1 in the low-pressure range of 0−19 kPa, a broad sensing range up to 185 kPa, and stable cyclic performance over 3000 compression cycles of 100 kPa. The sensor enabled real-time monitoring of interface pressure at pressure-vulnerable body sites during postural changes. In addition, a pilot study with six participants of different body weights demonstrated the ability of the sensor to detect site-dependent interface pressure and body weight-related pressure trends. These results suggest that the developed sensor has potential for continuous interface pressure monitoring in healthcare and rehabilitation applications.
Abstract Visible-light-responsive optoelectronic synapses are attracting increasing attention for neuromorphic vision systems because they integrate optical sensing and information processing within a single device. However, conventional oxide semiconductor phototransistors are generally limited by their wide bandgap, resulting in weak visible-light absorption and insufficient synaptic performance. Here, we demonstrate a thickness-optimized TeOx/IZO heterojunction optoelectronic synaptic phototransistor that achieves efficient visible-light sensing and neuromorphic functionality through enhanced photocarrier generation and defect-assisted carrier trapping. Systematic optimization of the TeOx layer reveals that a thickness of 5 nm provides the optimum balance between visible-light absorption, electrical switching characteristics, and carrier transport. The optimized device exhibits a low dark current of approximately 1 × 10−12 A, a high on/off current ratio of ∼108, and wavelength-dependent photoresponse enhancements of up to 2377.6% under green-light illumination compared with pristine IZO devices. Furthermore, the device successfully emulates essential synaptic functions, including excitatory postsynaptic current, short- and long-term memory, paired-pulse facilitation, and long-term potentiation/depression, while achieving a handwritten digit recognition accuracy of ∼88%. X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and photo-induced current transient spectroscopy reveal that the superior photosynaptic performance originates from an optimal balance among visible-light absorption, interfacial carrier transfer, and shallow-defect-assisted carrier trapping. These results establish the TeOx/IZO heterojunction as an effective platform for oxide-based visible-light neuromorphic vision systems.
Abstract HfO2-based floating body (FB) ferroelectric field-effect transistors (FeFETs) have attracted growing interest owing to their applicability across a broad range of applications, including embedded nonvolatile memory, advanced logic device, and high-density storage memory. However, efficient erase (ERS) operation in these devices is fundamentally hindered by the absence of a direct hole supply to the isolated FB, and the mechanisms governing alternative hole generation pathways and their role in polarization reset remain poorly understood. In particular, insufficient hole generation and supply to the floating string channel during block-level ERS operations of three-dimensional ferroelectric NAND (3D FeNAND) impose significant constraints on both ERS voltage and ERS speed, underscoring the need for a deeper understanding of hole dynamics.In this work, the key enabler for ERS operation in FB FeFETs is systematically identified by clarifying the correlation between hole dynamics and polarization reset. In-depth electrical characterization of silicon-on-insulator FeFETs reveals that, in conventional ERS schemes employing a negative gate bias, polarization reset is driven by gate-to-source/drain band-to-band tunneling-induced hole generation, while subsequent hole accumulation in the FB leads to anomalous threshold voltage (Vth) transitions. To improve ERS efficiency, a switching-assist pulse scheme is proposed, which enhances both reset speed and reset degree at a reduced ERS voltage. These findings offer practical design guidelines for optimized ERS schemes in high-density 3D FeNAND.
Abstract Measuring absolute magnetic fields with high precision is valuable for numerous scientific and technological applications, including physics research, biomedical imaging, navigation systems, and materials characterization. Two-dimensional (2D) vdW materials, with their characteristic weak interlayer (van der Waals) bonding, are well suited for transfer onto a diverse range of substrates, making them amenable to a variety of sensing platforms. In this article, we explored the potential of CrCl3, a 2D vdW magnetic material, for application in a compact, laser-free absolute magnetometer. We found that the proposed CrCl3-based magnetometer provides electrical detection of the absolute magnetic field with nanotesla sensitivity, features a simple, compact design, and a small form factor, demonstrating a clear, attractive technology pathway. The sensor material is fabricated using Scotch tape-based room-temperature mechanical exfoliation processes, operates over a wide magnetic field and temperature range, and is robust at ambient conditions. The demonstrated magnetometer's sensitivity is ∼30 nT/√Hz at a 1 T applied magnetic field, and it can track magnetic field changes in real time at a rate exceeding 0.8 mT/s.
Abstract Triboelectric nanogenerators (TENGs) represent a revolutionary technology. As a crucial branch, rotary TENGs (R-TENGs) exhibit promising prospects in rotational energy harvesting owing to structural advantages. However, traditional 3D finite element method (FEM) simulations severe element deformation and time-consuming moving mesh issues, creating a bottleneck for rapid structural optimization. To address this, we propose a dimensionless solution method tailored for R-TENGs. By building upon the physical model of sliding-mode TENGs and integrating the inherent periodic dynamic characteristics of R-TENGs, an efficient dimensionless solution framework is successfully constructed and systematically validated against FEM simulations. The results demonstrate that the proposed method possesses excellent predictive capabilities for both transient responses and steady-state baseline shifts. Implemented via an in-house solver and validated against 3D FEM simulations, the framework achieves a steady-state coefficient of determination (R2) exceeding 0.98 and a normalized root mean square error (NRMSE) below 10%. Crucially, computational time is compressed by nearly three orders of magnitude, reducing simulation duration from over 5000 s in FEM to under 6 s. Although the continuous operational peak accuracy remains above 85% due to 3D fringing and charge leakage, the model maintains a total transferred charge deviation below 8% while accurately tracking dynamic trends. Compared to traditional finite element simulations, this dimensionless approach significantly simplifies numerical computation and enhances efficiency, providing a highly reliable and effective theoretical tool for the practical performance evaluation and structural optimization of rotary TENG systems.
Abstract The realization of silicon-carbide-based sensors usually requires lightly doped epitaxy as the functional region, which does not allow any induced defects from ion implantation. The constraint makes the formation of low-resistance ohmic contacts a challenge. This letter describes the approach of using a Ni/Ti/Ni trilayer metal stack and high-temperature annealing to form nickel-silicide compounds for a low specific contact resistivity of 6.18 mΩ·cm2 on 4H-SiC epitaxy layer with a doping concentration of 2.19 × 1015/cm3. The scheme also produces titanium carbide and titanium silicon carbide, serving as the carbon diffusion barrier to secure good nickel-silicide compound formation. The influences of annealing temperature and titanium thickness on ohmic contact quality are discussed.
Abstract Selector-only memory (SOM) has attracted attention as a promising memory technology because it enables programmable threshold-voltage state separation using a single ovonic threshold switch (OTS) device. In SOM devices, the electrode–chalcogenide interface strongly affects the threshold-voltage difference (ΔVth) and switching reliability, as repetitive switching induces interfacial reactions and elemental diffusion. In this study, the electrode-dependent SOM characteristics of Ge2Se3Te5 (GST) devices were investigated using W, TiN, and W with an ultrathin (∼6 nm) carbon interlayer (W/C) as top electrodes. The W/C device exhibited the largest ΔVth (∼1.0 V) and the widest read window margin (∼0.9 V), and maintained a ΔVth exceeding 0.7 V over repeated switching cycles, exhibiting the most stable characteristics. Conduction mechanism analysis based on the Poole–Frenkel emission model, Arrhenius analysis, and the thermally assisted hopping model revealed that the enhanced ΔVth originates from increased trap-state separation and trap-density difference between programmed states. Transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (TEM-EDS) and line-EDS analyses confirmed that the carbon interlayer effectively suppressed Te diffusion and interfacial phase formation at the W/GST interface during repetitive switching. These results demonstrate that ultrathin carbon interfacial engineering is an effective strategy for improving ΔVth and switching reliability in GST SOM devices.
Abstract Freestanding epitaxial ferroelectric membranes are essential for the advancement of flexible electronics and high-performance integrated devices. While water-soluble Sr3Al2O6 sacrificial layers are commonly used to produce such membranes, the requirement for SrTiO3 substrates limits their scalability and increases production costs. In this study, we report the synthesis of high-quality, epitaxial PbZr0.52Ti0.48O3 (PZT) freestanding sheets using a cost-effective and scalable r-plane Al2O3 (sapphire) substrate with a water-soluble CaO sacrificial layer. By incorporating a thin BaTiO3 buffer layer to prevent interfacial reactions, we successfully obtained crack-free, c-axis-oriented PZT membranes via a simple water-immersion process. The resulting PZT sheets exhibited a remarkably high remnant polarization of 58 μC/cm2, which is larger than that reported in PZT membranes grown on Sr3Al2O6/SrTiO3 and closely approaches the values of bulk PZT. Furthermore, the sheets maintained a low dielectric loss. Our findings demonstrate that the CaO/sapphire platform provides a scalable and efficient pathway for fabricating high-performance epitaxial ferroelectric membranes, facilitating their integration into next-generation flexible and large-area electronic systems.
Abstract We report a high-performance electron-controlled upconversion device (UCD) designed for photoplethysmography (PPG) monitoring and broadband near-infrared (NIR) imaging. By integrating a solution-processed inverted green quantum light-emitting diode (QLED) with an organic NIR photodetector, our UCD achieves a photon-to-photon efficiency (ηp-p) of 4.45%, a low turn-on voltage of 2.2 V, and a luminance on–off ratio exceeding ∼104 under NIR illumination. This innovative architecture employs a zinc oxide interconnecting layer and a transfer-printed hole-transport layer, promoting efficient charge injection while protecting the emission layer. The UCD successfully demonstrates balanced charge dynamics for non-contact arterial pulse monitoring and broadband NIR imaging from 808 to 980 nm. These findings highlight the significant potential of electron-controlled UCDs to advance integrated platforms for NIR imaging and health monitoring.
Abstract Abnormal humidity in high-voltage substations poses a critical threat to the insulation safety of electrical equipment. Conventional humidity sensors rely on external power sources or batteries, which limits their feasibility for distributed deployment in complex electromagnetic environments. In this work, a self-powered wireless humidity monitoring system is developed by integrating a CeO2/Ag heterojunction composite sensor with a triboelectric nanogenerator (TENG) and a self-starting power management module, enabling ambient wind energy harvesting. The CeO2/Ag composite is synthesized via a hydrothermal method followed by in situ reduction. Characterization results reveal that Ag nanoparticles are uniformly distributed on the CeO2 surface. The sensor operates over a wide relative-humidity range of 0–97% RH and reaches a maximum response of 96.98% at 97% RH, with response and recovery times of 8.7 and 17.9 s, respectively. Density functional theory calculations demonstrate that the CeO2/Ag heterointerface significantly enhances water molecule adsorption and charge transfer through Schottky barrier modulation, with an adsorption energy of –1.447 eV. The TENG achieves a peak power of 732 μW, and the integrated system enables wireless data transmission every 75 s at a rotational speed of 200 rpm. This work offers a promising solution for self-powered, distributed humidity monitoring in substations and other complex industrial environments.
Abstract Flexible piezoresistive sensors hold promising application prospects in wearable health monitoring and human−machine interaction. However, existing devices struggle to achieve a favorable balance among high sensitivity, wide detection range, long cycle life, and low cost simultaneously. In this work, an N/A/CB/MWCNTs/MXene (PCMM) flexible piezoresistive sensor with a ternary conductive network was proposed based on a polyimide (N/A) sponge. The low-cost and high-resilience N/A sponge substrate was prepared via an isocyanate-assisted one-step in situ natural foaming method. A 0D−1D−2D hybrid three-dimensional conductive network was constructed on the substrate using carbon black (CB), multiwalled carbon nanotubes (MWCNTs), and two-dimensional MXene through a vacuum dip-coating process. At a MXene dosage of 30 mg, the composite material achieves a high electrical conductivity of 1.8 × 10−2 S/m with a residual strain of only 6.02%, demonstrating outstanding mechanical resilience. The as-prepared sensor delivers a high sensitivity of 4.393 kPa−1 within the pressure detection range of 0−5 kPa, shows a response time of less than 190 ms, and maintains stable electrical output over 3000 compression cycles. Compared with previously reported N/A-based flexible sensors, this work presents distinct advantages in the structural design of conductive networks and the synergistic optimization of sensitivity and durability. The fabricated sensor has been successfully applied to human motion monitoring, physiological signal detection, and voice recognition, showing great application potential in intelligent health monitoring and next-generation wearable electronics.
Abstract Growth induced defects in large area 2D materials have unique charge trapping dynamics. While the effective electron mobility on an average is almost the same in all devices (complete film (CF), merged flake (MF), and single flake (SF) MoS2 devices), the intrinsic carrier density and transport hysteresis vary largely in all the three fabricated devices (mainly with the just-merged flake MoS2 device). The overall trap site density of the monolayer changes nonmonotonically with the just-merged film having a higher trap site density than the complete film. Our results show an important interplay between various defect types in films and mobility, intrinsic carrier density, and hysteresis. Our model allows engineers to effectively predict device performance from material synthesis information.
Abstract The development of stretchable and deformable electronics demands semiconducting materials capable of maintaining efficient charge transport under large mechanical deformation; however, the structural features that favor high charge mobility, namely rigid conjugated backbones, high crystallinity, and strong intermolecular interactions, often make polymer thin films mechanically brittle. Hydrogen bonding has emerged as a powerful and versatile molecular design strategy for reconciling this trade-off in semiconducting polymers, owing to its directionality, tunable strength, and dynamic reversibility. This Spotlight highlights recent advances in the use of hydrogen bonding to design stretchable semiconducting polymers for organic field-effect transistors (OFETs), with emphasis on how supramolecular interactions influence polymer synthesis, thin-film organization, and device performance. This article discusses representative examples spanning side-chain functionalization, backbone engineering, and physical blending strategies to illustrate how hydrogen bonding can act as a multifunctional design tool, capable of simultaneously addressing mechanical resilience, thermal stability, and electronic performance. Additionally, a perspective is offered on integrating these molecular design principles with autonomous and AI-guided fabrication platforms, reflecting a broader paradigm shift in materials discovery and a path toward the rational, high-throughput design of stretchable and bio-integrated organic electronic technologies.
Abstract Hafnium zirconium oxide (HZO) is a promising ferroelectric gate-insulator material for ferroelectric field-effect transistors (FeFETs) owing to its excellent scalability and compatibility with complementary metal−oxide−semiconductor (CMOS) technology. However, stable ferroelectric phase formation generally requires annealing temperatures above 400 °C, imposing severe thermal constraints on oxide-semiconductor channels such as amorphous In−Ga−Zn−O (IGZO) and limiting back-end-of-line (BEOL) integration. Elevated thermal budgets promote oxygen-vacancy generation in IGZO, resulting in increased channel conductivity and degraded device reliability. In this work, a low-temperature stabilization strategy for HZO ferroelectric gate insulators is developed using a zirconium dioxide (ZrO2) seed layer combined with the hafnium dioxide (HfO2)/ZrO2 superlattice engineering. Structural and electrical analyses confirm that the optimized superlattice (SL6), consisting of individual 0.6-nm-thick HfO2 and ZrO2 sublayers, promotes low-temperature stabilization of the ferroelectric orthorhombic phase while maintaining robust polarization switching, low leakage current, and reliable endurance characteristics. When integrated with ultrathin IGZO channels in a double-gate (DG) architecture, the SL6 gate stack enables functional FeFET operation in devices subjected to two RTA steps at 350 °C for 30 s each, with no device-fabrication step exceeding 350 °C. The optimum transistor characteristics are obtained for devices subjected to two RTA steps at 380 °C for 30 s, which exhibit a minimum subthreshold swing (SS) of 61.8 mV dec−1, high current modulation, and stable retention characteristics. These results demonstrate the feasibility of low-temperature-stabilized HZO ferroelectric gate insulators for oxide-semiconductor devices and provide a practical pathway toward BEOL-compatible FeFET platforms for low-power and neuromorphic electronics.
Abstract We present a comprehensive first-principles investigation into the spin-resolved transport, mechanical, and piezoelectric properties of the two-dimensional (2D) RuO2(MgF)2 ferromagnetic system. The material demonstrates semiconducting behavior with an indirect band gap of 0.99 eV and pronounced spin-polarization along the zigzag (Γ-K) direction. An out-of-plane magnetic anisotropy energy of 0.879 meV/cell ensures magnetic stability and is a prerequisite for robust spintronic functionality. Notably, we uncover a large spin Seebeck coefficient of –1.59 mV/K (1.65 mV/K) under minimal hole (electron) doping, highlighting its potential for efficient spin transport applications. The lattice thermal conductivity was obtained via the optimized Slack model and is 0.81 W/m·K at 700 K. Beyond electronic performance, 2D RuO2(MgF)2 displays low in-plane rigidity and moderate strain tolerance, indicative of superior mechanical flexibility. Meanwhile, a large piezoelectric strain coefficient (d11= –1.65 pm/V) indicates strong electromechanical coupling, suitable for strain-responsive and flexible device applications. Consequently, these attributes, including robust spin-polarization, thermal spin-transport, mechanical adaptability, and enhanced piezoelectric performance, establish 2D RuO2(MgF)2 ferromagnet as a promising candidate for next-generation flexible and energy-efficient technologies in spintronics, spin-caloritronics, and piezotronics.
Abstract Recently, while investigating the crystal-plane- and crystal-orientation-dependent properties of materials, we discovered that a polar superstructure featuring a spontaneous electric field (Es) governs these very physical and chemical behaviors. In this Spotlight article, we discuss the enhanced properties of such polar superstructures and propose a universal model that elucid the underlying mechanisms in photocatalysis, the bulk photovoltaic effect, gas sensing, the piezoelectric effect, thermovoltaics, and chem-voltaics. Consequently, a broadly influential field of polar superstructure electronics and optoelectronics is established, where the underlying physics is based on the control of electrons and photogenerated electrons by the Es within polar superstructures. This theory not only reinterprets fundamental material properties but also unlocks atomic-scale routes for the rational design and fabrication of high-performance materials and devices. Polar superstructure materials are poised to become a major frontier in materials, chemistry, and physics.
Abstract The study investigates the influence of an unexplored severe oxygen deficiency on the electrical transport properties of non-stoichiometric gallium oxide thin films, which are promising candidates for resistive switching in memristors. We employed pulsed-laser deposition to grow oxygen-deficient gallium oxide thin films on c-cut sapphire single-crystal substrates at 400 °C, with O/Ga ratios varying depending on the growth conditions. Increasing the laser fluence in vacuum (2 × 10–7 mbar) leads to a decrease in the O/Ga ratio from 1.3 to 0.8, resulting in anomalous low-temperature transport behavior. X-ray photoelectron spectroscopy revealed three chemical states for Ga, indicating oxygen deficiency, metallic Ga nanoclusters, and a gallium oxide matrix. The highly non-stoichiometric amorphous Ga2Ox thin films exhibit metastable behavior, consisting of metallic Ga nanoclusters embedded in a gallium oxide matrix, explained by a solid-state disproportionation reaction. The temperature-dependent electrical resistivity of the films between 4 and 300 K exhibited metallic and semiconducting behavior as a function of the O/Ga ratio, coupled in few cases with partial or complete superconducting transitions in the range from 5 to 6.3 K. These results contribute to the development of nanostructured materials with tailored electrical properties for advanced neuromorphic applications and quantum computing.
Abstract Crystal and oxygen-related defects are present at the buried interface between the tin oxide (SnO2) electron transport layer (ETL) and perovskite layer during the solution preparation in regular perovskite solar cells (PSCs), which poses a negative effect on their photovoltaic performance. Herein, sodium oleate (NaOA) is explored as a functional interlayer to modulate the interfacial defects in PSCs. The carboxylate group (COO-) of NaOA is coordinated with Sn4+ on the surface of the SnO2 film to generate the Sn–OOC– bond. As a result, an ordered interfacial dipole layer is formed to modulate the local electronic environment on the surface of the SnO2 layer, thereby improving the energy level alignment and modifying these oxygen-related defects. Finally, the PSCs incorporated with the NaOA interlayer exhibit an improved power conversion efficiency (PCE) of 18.31%, compared with 16.53% for pristine PSCs. This study offers an interfacial dipole engineering strategy using NaOA for high-performance PSCs.
Abstract Photomultiplication-type organic photodetectors (PM-OPDs) were fabricated by employing a blend of P3HT and the narrow-band gap small-molecule acceptor FM4. The blend ratio between P3HT and FM4 was optimized to 100:4 (wt/wt). Under –10 V bias, the PM-OPDs based on P3HT:FM4 (100:4, wt/wt) exhibit a spectral response range from 300 to 900 nm with EQE values of 1600% at 625 nm and 850% at 850 nm. This behavior is attributed to hole tunneling injection triggered by trapped electrons. To further improve the sensitivity of PM-OPDs, PEDOT:PSS is replaced by the self-assembled monolayer (SAM) Ph-4PACz as the interfacial layer. The dark current density (JD) of PM-OPDs drops from 2.11 × 10−6 to 4.84 × 10−7 A cm−2, while the light current density (JL) slightly increases by employing Ph-4PACz, resulting in an apparently improved signal-to-noise ratio from 560 to 2700. At –10 V bias, the optimized PM-OPDs deliver EQEs of 1800% (625 nm) and 950% (850 nm), along with specific detectivities (D*shot) of 1.36 × 1013 Jones at 625 nm and 6.31 × 1012 Jones at 850 nm. The optimized PM-OPD-based photoplethysmography PPG sensor enables reliable detection of blood oxygen saturation and heart rate, with measurement discrepancies remaining within 2% when benchmarked against a commercial smartwatch.
