Physics

ABSTRACT The rapid advancement of ionotronics has positioned ionic conductive materials as increasingly pivotal elements in the evolution of flexible wearable sensors. However, developing ionotronic fibers with sufficient mechanical robustness and ionic conductivity remains a formidable challenge. This issue primarily arises from the intrinsic predicament in formulating spinning dopes with concurrent high polymer content, high ion concentration, and desirable low spinning viscosity. Inspired by the liquid‐crystalline spinning of natural silk, herein, we fabricated cellulose ionotronic fibers (CIFs) from a nematic cellulose liquid‐crystalline dope. Leveraging the self‐alignment of cellulose chains, the nematic spinning dope exhibits suitable viscosity for stable extrusion even at high polymer concentrations. The resultant CIFs display remarkable mechanical strength (14.6 MPa), toughness (19.74 MJ·m −3 ), extensibility (308.9%), and excellent ionic conductivity (2.38 S·m −1 ). Furthermore, CIFs exhibit prominent stability and superior sensitivity in both triboelectric energy harvesting and humidity response, rendering them highly promising for human motion sensing and respiratory monitoring. In summary, this work offers critical perspectives into the construction of high‐performance and environmentally sustainable flexible ionotronic devices, laying a foundation for the sustainable manufacturing of flexible electronics.

ABSTRACT The co‐electrolysis of water into hydrogen (H 2 ) and hydrogen peroxide (H 2 O 2 ) offers a transformative dual‐energy molecule strategy that simultaneously generates a high‐value reductant and oxidant from a single feedstock. This coupled pathway not only enables closed‐loop energy storage and release but also eliminates the reliance on oxygen gas or anthraquinone processes for H 2 O 2 production. However, the cogeneration of H 2 and H 2 O 2 via hydrogen evolution reaction (HER) and two‐electron water oxidation reaction (2 e − ‐WOR) presents distinct challenges in terms of reaction selectivity, interfacial charge transfer, and system integration. This review provides a comprehensive mechanistic and technological roadmap across three critical dimensions: (i) advanced electrocatalyst design strategies to tune adsorption energetics and intermediate pathways, (ii) interfacial regulation via solvation environment and electric field modulation to promote H 2 /H 2 O 2 production, and (iii) reactor engineering innovations, including membrane‐based, bipolar, and flow‐assisted systems, to address mass transport, gas separation, and electrolyte compatibility. By integrating atomistic insights with system‐level design, this work offers a unifying framework to accelerate selective and scalable H 2 /H 2 O 2 coproduction, bridging fundamental electrochemistry with practical energy conversion technologies.

ABSTRACT Acoustic‐directed assembly (ADA) is a versatile strategy for structuring matter at multiple scales, offering contactless, noninvasive, and tunable control over a broad range of materials. This review surveys advances in acoustic manipulation of polymers, inorganic particles, metals, and living cells, focusing on how these building blocks are assembled and can be stabilized into permanent architectures. Previous reviews provide valuable insights into device design, manipulation mechanisms, and specific applications. Comparatively less emphasis has been placed on the role of materials and their transformation during and after acoustic manipulation. Here, we adopt a materials‐oriented perspective linking transient acoustic organization with the formation of stable and/or functional structures. We introduce a framework distinguishing assemblies of pre‐existing particles from those generated during acoustic manipulation and examine how this distinction shapes fixation strategies, structural fidelity, and applications. Case studies demonstrate directional conductivity in composites, formation of bio‐functional scaffolds with physiologically relevant architectures, and chemically organized structures. Integration with extrusion‐ and vat‐based printing is discussed, enabling tailored materials with embedded functionality. These advances position ADA as a platform for multifunctional materials in tissue engineering, flexible electronics, catalysis, and energy storage.

ABSTRACT N‐type conjugated polymers based on non‐fused‐ring electron‐deficient building blocks offer significant advantages, including simpler structures and lower production costs, compared with counterparts based on complex fused‐ring building blocks. Nonetheless, they have been scarcely investigated as electron transport layer (ETLs) in hybrid perovskite solar cells (HPSCs), probably limited by the small number of non‐fused‐ring electron‐deficient building blocks developed to date. Here, a thiophene‐based n‐type polymer (n‐PT3) composed of very simple non‐fused‐ring building blocks is employed as ETL in inverted Dion–Jacobson (DJ) HPSCs. Compared to the control polymer (P5O) with fused‐ring building blocks, n‐PT3 exhibits the merits of a planar conformation, electron‐rich backbones, and higher hydrophobicity, resulting in superior charge transport and defect passivation, as well as enhanced water resistance. Consequently, n‐PT3 as an ETL yields more efficient, reproducible, and stable devices that achieve a power conversion efficiency (PCE) of 14.86%, representing a remarkable 83% improvement compared to the control device. More importantly, devices using n‐PT3 as ETL retain 94.68% of their initial PCEs after aging in air for 1669 h, compared to 46.66% for the control device. These results demonstrate great potential of n‐type polymers with non‐fused‐ring electron‐deficient building blocks for efficient and stable DJHPSCs.

Abstract A unified optimization theory is developed for 3-D power vertical MOSFETs with a high-k insulating dielectric (HKMOS) on the condition of punch-through (PT), providing a generalized analytical model for circular and polygonal cell topologies. Starting from the circular topology, a 3-D analytical solution is derived using Green’s function-based superposition while accounting for interface charges (Nit). This circular topology solution is then extended to polygonal cell topologies through Schwarz-Christoffel (SC) conformal mapping, yielding a unified formulation of electric displacement distributions for different closed cell topologies. Within this theory, two representative configurations are investigated: cells with the silicon N-drift region located at the center (case I) and cells with the high-k dielectric located at the center (case II). It is shown that, for the same breakdown voltage (BV) class, case I achieves a 20% reduction in optimized specific ON-resistance (Ron,sp) than case II. The proposed theory establishes topology-dependent electrical characteristics and extends the optimization of 3-D HKMOS device structures and cell layouts to different cell topologies.

Abstract Low-cost and disposable neuromorphic devices are highly desirable for large-area sensing and edge intelligence applications. However, most reported synaptic transistors rely on single-gate configurations, which limit their ability to integrate multi-input signals and perform spatiotemporal processing. Here, we report paper-based multi-gate electric double-layer (EDL) synaptic thin-film transistors (MG Paper-TFTs) with an indium-zinc oxide (IZO) channel and a κ-carrageenan polyelectrolyte gate dielectric. The κ-carrageenan dielectric enables high EDL capacitance and conformal coverage on porous paper substrates, allowing stable low-voltage operation with good repeatability. By integrating a bottom gate and laterally coupled in-plane gates, the device realizes differentiated vertical and lateral modulation of the channel through ionic-electrostatic coupling within the shared dielectric layer. Representative synaptic behaviors are first established under bottom-gate stimulation, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), and short-term to long-term plasticity transition. Under multigate operation, the transfer characteristics can be systematically modulated by adjacent gate bias, indicating effective lateral coupling. This coupling further enables nonlinear multi-input integration and a training-dependent enhancement of postsynaptic response under paired stimuli, suggesting associative learning behavior. These results provide insight into multigate coupling in oxide EDL transistors and demonstrate a low-voltage strategy for realizing multi-input neuromorphic functions on paper substrates.

Carbon nanotubes were oxygen-functionalized using maleic anhydride under different cold plasma types, including radio frequency or bipolar pulsed discharges, with either capacitively coupled or dielectric barrier configurations, and with or without sample holder vibration. The samples were characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, N 2 adsorption test, and zeta potential measurements. The results show that using bipolar pulsed plasma in a capacitive coupled reactor without vibration are the parameters that promote the highest oxygen attachment to the CNT surface, which is 2.3 times the oxygen atomic content of untreated CNT. Other combinations also provided functionalization to varying degrees, along with samples’ drying and preservation of the nanoparticles’ structure. Batch sorption experiments evaluated the use of functionalized nanotubes in methylene blue removal from water. For the sample treated with the best set of plasma parameters, after 1 h the sorption capacity was about 33% higher compared to untreated nanotubes, and after 3 h, the removal efficiency reached 99%. Sorption isotherms also indicate that treated samples presented adsorption mechanisms more complex than untreated CNT, including multilayer and cooperative interactions.

Forgetting, an active optimization mechanism in the human brain, is governed by synaptic plasticity. This insight has motivated the development of artificial synapses for hardware-level emulation of forgetting. Among them, photonic synapses have drawn considerable attention owing to their ultrafast response and low crosstalk. However, short-term forgetting (STF) at ultrafast timescales remains unexplored in photonic synapses. Here, the STF at ultrafast timescales is demonstrated using a photonic synapse based on a vertical-cavity semiconductor optical amplifier (VCSOA). First, STF is realized by replicating bio-realistic paired-spike depression in a VCSOA under a paired optical spike injection, with dynamic control achieved by adjusting injection power and bias current. Subsequently, stimulating the VCSOA with multiple optical spikes produces multiple-spike depression, which can also simulate the STF at ultrafast timescales. To approximate a realistic STF scenario, a letter “T” pattern encoded by different spike numbers and time intervals is injected into the VCSOA-based photonic synapse, and a gradual forgetting trend similar to that of the human brain is clearly observed. Remarkably, all bio-inspired STF occur at nanosecond timescales, providing a tangible artificial synapse for photonic neuromorphic computing at nanosecond timescales.

Thermal Kinetic Inductance Detectors (TKIDs) inherently combine the phonon-limited noise performance of traditional bolometers with the array scalability and responsivity of superconducting kinetic inductance detectors. Using a superconducting resonator as the thermally sensitive element provides high responsivity and a tunable dynamic range, with phonon noise set by the cryogenic operating temperature of the free-standing membrane. In this work, MgB2-based TKIDs are demonstrated operating from below 1 K up to 20 K with characterized noise-equivalent power using integrated on-membrane heaters. A comprehensive characterization of electrical, thermal, and noise properties is presented. The internal quality factor of the prototype devices is measured to be Qi>2×104 at 4.2 K, with a bolometer time constant of τ<0.7 ms below 5.6 K. The intrinsic detector noise is NEPmeasured<10−14 W/Hz for T<8 K, demonstrating phonon noise-limited performance from 4 to 8 K.

We studied the effective magnetic field Heff arising from the spin–orbit torque (SOT) and/or orbital torque (OT) by measuring shifts of out-of-plane hysteresis loops under various in-plane currents Is and in-plane magnetic fields Hxs along I in perpendicularly magnetized Pd/Co2MnGa (CMG) and Pd/Co2MnSi (CMS). The Heff for Pd/CMS is explained well by the SOT originating from the spin Hall effect (SHE) in Pd, whereas that for Pd/CMG points in the opposite direction under a given polarity of I and Hx. Neither the self-induced SOT in CMG nor the SOT originating from the interfaces is responsible for the Heff reversing in Pd/CMG. The magnitude of the effective spin/orbital Hall angle, derived from the Heff, increases with the thickness of both the CMG and Pd layers in Pd/CMG, which is consistent with the predicted behavior of the OT originating from the orbital Hall effect in Pd. Considering these results and the fact that CMG has stronger spin–orbit interaction than CMS, the OT, which is larger than and opposite to the SOT originating from the SHE in Pd, is a plausible candidate for reversing the Heff in Pd/CMG.

We investigate the influence of heterostructure engineering on the generation, propagation, and decoherence of coherent acoustic phonons (CAPs) in GaN-based materials using ultrafast pump–probe transient differential transmission spectroscopy. Measurements are performed on an AlGaN/AlN/GaN high electron mobility transistor (HEMT) heterostructure, the same structure after selective removal of the AlGaN/AlN layers, and a bare Mg-doped GaN epilayer with embedded InGaN/GaN superlattice layers. Femtosecond excitation launches longitudinal acoustic phonons whose coherent oscillations are tracked in the time and frequency domains using wavelength-resolved probing. The intact AlGaN/AlN/GaN heterostructure exhibits long-lived, narrowband CAP oscillations with a dominant frequency near 40 GHz, whereas etched GaN shows pronounced decoherence, spectral broadening, and mode mixing due to enhanced phonon–phonon and interfacial scattering. The quality factor of the coherent phonons in the heterostructure is approximately three times higher than that of the etched sample, highlighting the role of top layers in preserving phonon coherence and facilitating heat transport. In contrast, Mg-doped GaN epilayer displays strong waveform distortion and rapid dephasing, consistent with phonon scattering from superlattice interfaces. Time–frequency analysis reveals probe wavelength-dependent detection of phonon modes via Brillouin scattering, with shorter probe wavelengths accessing higher-frequency components. These results demonstrate that phonon coherence in GaN can be engineered through heterostructure design and doping control, with direct implications for thermal management and reliability of high-power GaN HEMTs.

Ferroelectric materials have colossal optical nonlinearities, but their integration into quantum photonic chips is made challenging by the additional loss mechanisms that they introduce. Here, we present a perturbative theory that expresses non-absorptive (elastic) photon scattering-induced loss as a functional of a general spectral density for spatial fluctuations of electric permittivity. We apply the theory to calculations of attenuation coefficients α in slab waveguides in order to compare two distinct loss mechanisms: Interface roughness and ferroelectric domain disorder. Our theory can account for realistic roughness without special symmetry considerations, and it demonstrates how to use electron microscopy images of ferroelectric domains to obtain explicit numerical predictions for α. Loss is maximum when the mean domain length is comparable to the wavelength of light (Mie regime), indicating that, for telecom wavelengths, sub-micron domains (Rayleigh regime) or single domain waveguides provide equivalent strategies for reducing loss.

The three-dimensional (3D) stress distribution in a bulk GaN substrate with laser-induced indentations for laser slicing was characterized using stimulated Raman scattering (SRS) microscopy. Local shifts in the Raman peak corresponding to the E2H mode were detected around the indentations, indicating the induction of local stress. The spatial distribution of internal stress was successfully visualized, revealing a clear in-plane anisotropy with compressive and tensile stresses along the a- and m-axes, respectively, as well as its extension in the depth direction. SRS microscopy enables the 3D visualization of residual stress in bulk GaN substrates, facilitating the optimization of fabrication processes.