Browse Articles

Ligand engineering tailors hydrophobic microenvironments for efficient electrocatalytic oxidation of fatty alcohol

Investigation of Ti/Al/Ni/Au ohmic contacts for AlScN/GaN HEMTs

The high bandgap of AlScN makes it difficult to achieve ohmic contacts with a low specific contact resistance (ρc) to AlScN/GaN heterostructures. High ρc increases the on-resistance of the high-electron-mobility transistor fabricated from these heterostructures and reduces the achievable current densities. This work presents an ohmic recess process and Ti/Al/Ni/Au metallizations with a ρc of 8.83×10−5 Ω cm2 after annealing at 900 °C. Interestingly, time-of-flight secondary ion mass spectrometry reveals that out-diffusion of Sc from the barrier to the metal surface occurs at anneal temperatures above 700 °C. While this structural metamorphosis does not show a strong impact on ρc, it leads to an increase in the on-resistance and gate leakage currents, as well as to a decrease in the maximum drain current of HEMTs. At an anneal temperature of 600 °C, no thermal degradation was observed and ρc as low as 13.4×10−5 Ωcm2 are achieved.

Lorentz skew scattering and giant nonreciprocal magneto-transport

Spin–orbit torque-induced magnetization switching in electrochemically deposited CoPt oriented polycrystalline film

Current-induced spin–orbit torque (SOT) offers an efficient method of manipulating magnetization and is widely applied in emerging three-dimensional (3D) magnetic memory technologies. Electrochemical deposition presents a promising route for fabricating such 3D structures; yet, achieving high-quality magnetic films and spintronics phenomena remains challenging. Here, we demonstrate SOT in an electrochemically deposited 7.3 nm-thick CoPt thin film with strong perpendicular magnetic anisotropy, grown on a Pt seed layer, which serves as the spin source for this system. Accurate analysis of the SOT effective field using combined second-harmonic Hall measurements revealed the existence of SOT and its dependence on the magnetization angle. Furthermore, current-induced magnetization switching was achieved in a 2.8 nm-thick CoPt alloy film. This work unveils the potential of electrochemical deposition for next-generation 3D spintronics device applications.

Multi-electron nitrobenzothiadiazole sp-conjugated-alkynyl covalent organic frameworks for ammonium-ion batteries

Abstract Covalent organic frameworks containing periodic redox-active motifs and conjugation structures are booming as competitive negative electrodes for ammonium-ion batteries. Introducing substantial single-electron active motifs linked by dynamic imine bonds can increase their capacity; however, this design is constrained by suboptimal single-electron redox efficiency and insufficient linkage stability. Here we unlock a multiple two-electron-transfer nitrobenzothiadiazole covalent organic framework via integrating alkynyl benzenes and nitro-functionalized four-electron benzothiadiazoles. The high degree of π-electron sp -conjugation along alkynyl linkages and strong electron-drawing effect of nitrobenzothiadiazole motifs in nitrobenzothiadiazole covalent organic framework promise high NH 4 + accessibility of multi-two-electron nitro/thiazole sites (95.2% utilization) with a lower activation energy (25.93 vs . 35.99 kJ mol −1 of benzothiadiazole covalent organic framework).The fast octadeca-H-bonded NH 4 + coordination in nitrobenzothiadiazole units liberates a high specific capacity of 317 mAh g −1 for nitrobenzothiadiazole covalent organic framework negative electrode. The alkynyl-bridged π-conjugation network establishes structural anti-dissolution to enable a cycling durability of 70,000 cycles. Paired with high-voltage Prussian blue analogue positive electrode, the ammonium-ion full battery delivers a specific energy of 86.1 Wh kg −1 (based on total active material mass) and a lifespan of 25,000 cycles. This work extends the design landscape of high-performance covalent organic frameworks for advanced ammonium-ion batteries.

Numerical and experimental study of facility effects on a gridded ion engine’s plasma plume

Combined numerical and experimental investigations of facility effects on gridded ion engines and their plumes are necessary to improve the extrapolation of experimental data to in-space conditions. This work presents—for different operating points, background pressures, and thruster potentials—the comparison between the experimental characterization of the RIT10-EVO’s plasma plume and its simulations by means of an axisymmetric particle-in-cell code. The axial and radial profiles of the ion densities, energies, and axial currents in the thruster’s plume, as well as the electron temperature in the far plume computed by the code, fall within experimental error bars. The electron temperature closer to the thruster and the radial energies of backstreaming ions outside of the plasma beam are instead underestimated by, respectively, about 4 and 20 eV. Simulations that include an immersed probe in the modeled plume do not fully explain this mismatch, but showcase an important dependence of the plume’s potential on the probe’s biasing voltage, hinting to a possible deformation of the measured IV curve. A closer inspection of the effects of the facility background pressure reveals that both experiments and the numerical model observe an increase in plasma density, a drop in electron temperature, and a decrease in the backstreaming ion energy as the neutral density rises. Similarly, both simulations and experiments show an increase in the energy of backstreaming ions, and the formation of a negative net current flowing from the thruster to the facility walls, when the thruster potential with respect to ground is decreased.

Selective weakening of population-coupled synaptic activity in vivo in a mouse model of amyloid-beta pathology

Abstract Synaptic dysfunction in Alzheimer’s disease (AD) may drive synapse loss and cognitive impairment. Whether AD-related synaptic pathophysiology occurs globally, or in specific synapses, is unclear. We investigate in vivo AD-related synaptic dysfunction during early-stage amyloidosis in App NL-G-F mice. We find reduced presynaptic GABAergic proteins at c-Fos-positive excitatory neurons and increased calcium-mediated activity at excitatory and inhibitory neuronal assemblies. In vivo synaptic structure/function imaging finds reduced density and calcium-mediated activity of GABAergic axonal boutons. Rather than occurring globally, reduced synaptic activity is focused at GABAergic boutons strongly coupled to population activity in the amyloid microenvironment. The selective weakening of population-coupled synaptic activity also occurs in excitatory dendritic spines. Spatial transcriptomics finds parvalbumin-positive inhibitory neurons show differential gene expression associated with downregulated GABAergic synaptic transmission at early stages. We propose that early-stage AD-related synaptic pathophysiology is focused at population-coupled synapses, with molecular measures implicating abnormal synaptic processing as an early-stage feature in parvalbumin-positive interneurons.

Thermal hot-carrier breakdown in metasurface structures based on coplanar arrays of graphene microribbons connected with wide-gap bridges

We analyze the thermal and electrical characteristics of the metasurface composed of a coplanar interdigital array of the graphene microribbons (GMRs) connected by nanobridges (NBs). These nanobridges could be implemented using graphene nanoribbons (GNRs) or black-arsenic-phosphorus (b-AsP) nanostructures. When a bias voltage applied between neighboring GMRs, it induces electron and hole two-dimensional systems within the GMRs, leading to thermionic currents that flow through the connecting NB resulting in the self-heating effect. This self-heating effect increases the thermionic currents, creating an effective positive feedback loop between the carrier effective temperature and the injected currents, and the bias voltage. This mechanism may lead to thermal breakdown enabling threshold behavior of current–voltage characteristics and yielding an S-shaped response. The devices based on the GMR/GNR and GMR/AsP metasurface structures can serve as fast voltage-controlled current switches, sensors, thermal terahertz and infrared sources, and among other applications.

3D-printed mechanically reconfigurable all-dielectric metagrating for terahertz filters

We demonstrate a mechanically reconfigurable terahertz filter implemented by the 3D-printed all-dielectric metagrating, providing a versatile platform for adaptive photonic devices. The structure consists of parallel supporting bars connected by vertical grating elements, forming a lattice that can be mechanically reconfigured. By applying a controlled lateral displacement to the supporting bars, the grating elements are tilted, effectively reducing the grating period and inducing a systematic blue shift in the transmission dip frequency. By tilting the metagrating, we experimentally observed a 15% frequency modulation and a 95% transmission modulation. The numerical simulations show consistent results with the experimental results. In contrast to conventional approaches that rely on refractive index modulation, phase-change materials, or other active tuning mechanisms, this method achieves tunability purely through geometric reconfiguration. This strategy offers a simple, low-cost, and robust route to dynamic terahertz filtering, and it can be readily extended to other reconfigurable metamaterials and photonic devices requiring adaptive control of their optical response.

State-of-the-art research in conducting polymer thermoelectric composites: Design strategies, doping innovations, and emerging technologies

Conducting polymer-based thermoelectric composites have emerged as a promising candidate for flexible, lightweight, and cost-effective energy conversion systems, addressing the ever growing demand for sustainable energy solutions. Researchers have concentrated on optimizing thermoelectric properties by incorporating nanostructures, hybrid fillers, and doping methods, which enhance electrical conductivity alongside Seebeck coefficients while minimizing thermal conductivity. Further, novel processing techniques, including solution casting, melt blending, and surface functionalization, are employed to ensure uniform filler dispersion and enhance the mechanical flexibility of polymer-based composites, thereby paving their way in flexible and wearable thermoelectric devices. This review covers various aspects, such as different models describing charge transport, diverse array of nano-fillers, and the factors affecting thermoelectric properties of polymer nanocomposites, synthetic schemes, doping, and post-treatment strategies to maximize the power factor along with recent breakthroughs in diverse applications, namely, electrical, optoelectronics, electronics, sensing, and biomedical. Various research gaps, potential issues along with possible solutions, and future prospects have been elaborated at length and would assist the researchers for a better understanding and research direction.

Low-frequency multi-band sound absorption in triangular fractal acoustic metamaterials

Attaining broadband, low-frequency sound absorption within a sub-wavelength footprint remains an outstanding challenge. We introduce a triangular fractal acoustic metamaterial that couples perforated facesheets with coiled, cavity-backed channels. By means of thermo-viscous acoustic theory and finite-element simulations, we quantify how the fractal order, number of layers, channel width, channel thickness, and inlet area govern the absorption spectrum. Spatial maps of the sound pressure field and the resulting thermo-viscous loss reveal that the dominant loss mechanism is the synergistic interference of multiple slow-wave modes confined to the fractal network. Optimizing the fractal order alone shifts the fundamental absorption peak continuously from 63 to 80 Hz without any increase in overall thickness. Ultimately, the metamaterial prototype was manufactured by means of additive manufacturing (3D printing). Subsequent experimental characterization of its acoustic performance revealed that the as-fabricated architecture yields multiple distinct absorption peaks at frequencies below 500 Hz, while maintaining an overall thickness of merely λ/125.

Self-pulsed Tm:GdScO3 laser amplifier for near-diffraction-limited nanosecond pulse generation

Achieving high-peak-power, narrow pulse width 2 μm lasers with near-diffraction-limited beam quality is critical for precision micromachining, minimally invasive surgery, and sensitive gas sensing, as this wavelength coincides with a strong water absorption peak. Conventional master oscillator power amplifier (MOPA) systems exhibit inherent limitations in compactness and complexity due to their reliance on external active modulators and associated driving electronics. In this work, we demonstrate a simplified MOPA architecture centered on a self-pulsed thulium-doped oscillator. By leveraging intrinsic dynamic loss mechanisms, this oscillator directly generated high-quality nanosecond pulse trains without external modulators, thereby eliminating the primary source of system bulk, cost, and complexity. In experiments, the self-pulsed oscillator achieved a minimum pulse duration of 348.2 ns and a beam quality factor M2 < 1.1. After single-pass amplification using a 3 mm gain crystal, the pulse peak power reached 55.7 W while maintaining near-diffraction-limited beam quality. This work establishes a self-modulation-based pathway for high-performance miniaturized pulsed lasers, while guiding the development of monolithically integrated chip-scale sources.

Impact mitigation generated by localized softness on a 3D-printed topological lattice

Topological mechanics can exhibit localized softness through geometrically programmed unit cells, and a promising application of this property is impact mitigation. We experimentally demonstrate efficient impact mitigation achieved through localized softness in a topological lattice, where the lattices are fabricated via 3D printing of hinged structures, and their force responses under dynamic loading are measured. The introduced soft surface produces a plateau in the force–displacement response, thereby suppressing peak forces relative to the hard surface and enhancing energy absorption efficiency. These soft responses are consistent with the predicted zero-mode counts. Furthermore, the design relies solely on periodic structures rather than material and geometrical gradation, preserving modularity and simplifying fabrication. These results indicate that localized topological mechanics can effectively tune contact compliance and mitigate impact loads, offering an efficient strategy for impact attenuation.

Hydrodynamic tuning thermal conductivity and microstructure of wood-based nanocellulose through hydrochloric acid concentration

The continuous increase in power density of flexible electronic devices underscores the critical need for developing efficient thermal management solutions. Cellulose nanofibril (CNF) has emerged as an ideal base material owing to its advantageous properties, including biodegradability, high mechanical strength, and electrical insulation. However, conventional methods for enhancing thermal conductivity often adversely affect processability or increase interfacial thermal resistance, making the maximization of CNF's intrinsic thermal transport potential without additives a significant ongoing challenge. This study developed a novel approach combining microfluidic hydrodynamic focusing with hydrochloric acid-induced gelation, successfully fabricating CNF filaments with a highly aligned structure. The results demonstrate a non-monotonic dependence of thermal conductivity on HCl concentration, with an optimal value of 1.013 W m−1 K−1. Raman and micro-Fourier transform infrared spectroscopy analyses confirmed that this optimum performance stems from the synergistic enhancement of crystallinity and the hydrogen-bonding network. Notably, a radial crystallinity gradient structure, governed by H+ diffusion during non-equilibrium gelation, was identified. This heterogeneous structure simultaneously imparts high thermal conductivity, outstanding mechanical properties, and remarkable flexibility. By integrating chemical regulation with fluidic assembly techniques, this work elucidates the physical mechanism underlying the enhancement of intrinsic thermal transport in CNF, providing a new design strategy for developing high-performance flexible thermal management materials.

Solid–liquid interface stability in the rapid solidification of a binary mixture

A concept of morphological instability of the solid–liquid interface introduced by W. W. Mullins and R. F. Sekerka [J. Appl. Phys. 35, 444 (1964)] is the basis for the evolution of phase interfaces and the formation of solid phase microstructures. We recently re-examined Mullins–Sekerka theory [D. V. Alexandrov and P. K. Galenko, J. Appl. Phys. 136, 055103 (2024); Alexandrov et al., J. Appl. Phys. 137, 125110 (2025)] and showed that the steady-state solutions and range of morphological instability essentially depend on the distance h between the cooling unit and solid–liquid interface. In addition, we showed that temperature perturbations appearing at the cooling unit and propagating through the solid–liquid interface into the liquid phase substantially increase the instability domain. Taking these aspects into account, we re-examine the morphological stability analysis of the planar solid–liquid interface in rapid nonequilibrium solidification of a binary melt. We derived a new dispersion relation that connects the amplification rate of perturbations and their wavenumber. A nonlinear system of equations defining the maximum amplification rate and the corresponding critical wavenumber of perturbations is found too. Numerical analysis of the dispersion relation shows the possibility of either (i) real and positive amplification rate or (ii) complex amplification rate with positive real part. Case (i) describes the morphological perturbations in the range of cellular/dendritic/eutectic microstructures, and case (ii) describes oscillatory perturbations in the range of band structures. Their mixing (morphological and oscillatory modes) corresponds to mixed-type microstructures. We analytically show that the solid–liquid interface is stable when the solidification velocity is larger than the diffusion speed.

YFeCo soft magnetic thin films with high ferromagnetic resonance frequency and low coercivity

High-frequency environments require higher demands on the ferromagnetic resonance frequency (fr) and loss performance of soft magnetic materials applied in electronics. However, it is difficult to simultaneously improve the fr, saturation magnetization (Ms), and loss performance of soft magnetic materials. Based on the FeCo with high Ms and the Y2Co17 with strong in-plane anisotropy, it is a rational route to prepare YFeCo thin films with different compositions, in order to optimize the high-frequency soft magnetic properties. In this study, we prepared YFeCo thin films with compositions of Y2Fe11Co6 and Y2Fe9Co8 via magnetron sputtering. It shows that the YFeCo thin films can exhibit the characteristics of the Y2Co17 phase in addition to the α-FeCo phase. Compared with the FeCo and Y2Co17 thin films, the YFeCo thin films significantly improve fr while maintaining a relatively high Ms. Specifically, the Ms of Y2Fe11Co6 is 15.9 kGs and its fr is 2.95 GHz, while the Ms of Y2Fe9Co8 is 15.4 kGs and its fr reaches even as high as 4.22 GHz. Contributing to the fine grains and uniform dense structure, the YFeCo thin films can maintain a low coercivity. Specifically, the coercivity of Y2Fe9Co8 is 34 Oe, while that of Y2Fe11Co6 is as low as 16 Oe. This study successfully prepared YFeCo thin films with low coercivity and high fr, which is conducive to the application of thin film materials in high-frequency devices.

Increase in Néel temperature in chromium oxide Cr2O3 subjected to severe shear stress

The effects of severe shear strain on the magneto-structure correlations of chromium oxide Cr2O3 were investigated. Shear stress was applied through high-pressure torsion (HPT) processing at a pressure of PHPT = 6 GPa. Through ac magnetization measurements, a maximum increase in the Néel temperature TN of Cr2O3 of approximately 30 K was observed in the HPT-processed sample for a revolution number of N = 1/2. This demonstrates the potential of HPT to expand the temperature stability range of antiferromagnetic order in Cr2O3. Analysis of the x-ray diffraction patterns of HPT-processed Cr2O3 revealed a special state of lattice expansion induced by shear strain within the unit cell. Direct exchange interactions originating from the overlapping of the Cr3+ ion orbitals and superexchange interactions involving the O2− ligands were examined using the variations in atomic distances and bonding angles. The increase in TN at a small N is attributed to enhanced antiferromagnetic interactions resulting from the decrease in the distance between the closest neighboring Cr3+ ions. By contrast, the reduction in TN observed at a higher N is explained by the modifications of the interchain interactions.

Estimation of the charge injection of low-density polyethylene in a double-layer structure: From mathematical fitting to simulation

Polymer materials have excellent electrical insulation properties and play a crucial role in high-voltage direct current equipment. Unlike the electric field–current relationship at the low-density polyethylene (LDPE)/Al interface with a single-layer LDPE sample, which approximates the Schottky relationship, this study employed a double-layer sample structure to establish unipolar conditions, thereby eliminating the influence of extraction current, displacement current, and electric field distortion present under bipolar conditions. The electric field–current relationship at different temperatures was derived. The relationship between the injection current and the electric field mathematically fit the Poole–Frenkel effect, rather than the Schottky effect, and the charge injection barrier, the trap depth, and carrier mobility were calculated. To validate the obtained parameters, this paper proposes an improved bipolar charge transport model and conducts simulations of space charge, current, and electric field. The simulation results with the Poole–Frenkel injection parameters fit the dynamics of space charge and current under different voltages and temperatures well. The temporal evolution of the electric field and the injection current under various conditions, along with their correlation, demonstrates remarkable agreement with the experimental results. In contrast, simulation results based on the approximate Schottky parameters obtained under bipolar conditions did not match the experimental outcomes. It indicates that the Poole–Frenkel effect is more accurate for describing the charge injection process, especially in the analysis of space charge and current dynamic characters.

Temperature dependences of dielectric function and critical points of SnSe

The temperature-dependent dielectric functions of orthorhombic single-crystal SnSe were determined along the a-, b-, and c-axes over the full temperature range from 27 to 350 K using spectroscopic ellipsometry. Intrinsic dielectric functions for each orientation were extracted by multilayer optical modeling to remove the contribution of the surface roughness layer. The obtained spectra exhibit notable temperature-induced shifts and broadening of interband transition features. Second-derivative analysis using the standard analytic expression was performed. This analysis enabled the identification of more than ten critical point (CP) transitions for each crystallographic direction. The temperature dependence of the CP energies was systematically analyzed, providing a quantitative comparison of their anisotropic behavior along the three principal axes. These findings provide a complete, temperature-resolved set of dielectric functions and transition energies for SnSe, offering a quantitative reference for optical modeling and device-oriented applications.

Transport–magnetism correlations in (1 −  <i>x</i> ) La0.67Ca0.33MnO3:( <i>x</i> ) Ag2O perovskite manganite-composites

In this paper, we report a comprehensive study on the correlation between electrical resistivity (ρ) and magnetization (M) in La0.67Ca0.33MnO3 (LCMO) polycrystalline-composite with Ag2O, synthesized by a conventional solid-state reaction method. The introduction of Ag2O modifies the intergranular regions without altering the intrinsic perovskite lattice and leads to distinct effects in different temperature regimes. At low temperatures, grain-boundary contributions dominate the total magnetoresistance through spin-polarized tunneling, which is significantly suppressed in the Ag2O composites due to the formation of additional conductive pathways between grains. At higher temperatures, improved intergranular connectivity shifts the metal–insulator transition temperature (TM-I) closer to the Curie temperature (TC), resulting in a clear correlation between transport and magnetism, with charge transport below TC governed by a polaron hopping mechanism. The sharpening of TM-I in the Ag2O composites leads to a substantial enhancement in magnetoresistance, reaching ∼68.6% at 270 K (x=0.15) under a magnetic field of 20 kOe, which is about 60% higher than pristine LCMO, along with a temperature coefficient of resistance of ∼21%, corresponding to a threefold improvement. Importantly, the strong ρ–M correlation enables a transport-based estimation of the isothermal magnetic entropy change (−ΔSM) from resistivity measurements performed across TM-I/TC, showing good agreement with values obtained using Maxwell relations. A maximum −ΔSM of 5.15 J kg−1 K−1 is obtained near 271 K, while the temperature-averaged entropy change (TEC) over a broad temperature span is estimated to be 5 J kg−1 K−1 [TEC(3)] and 4.6 J kg−1 K−1 [TEC(10)] for a field change of 20 kOe. These results highlight the correlation between transport, magnetism, and magnetocaloric response in manganite perovskites when grain-boundary effects are effectively controlled.