Browse Articles
Discover research articles across all indexed journals
Activating catalytically inert Janus diamane for efficient water splitting via 2D type-II C4HF/ <i>h</i> -BN heterostructures
We propose a two-dimensional (2D) type-II van der Waals heterostructure by vertically stacking Janus diamane C4HF with monolayer h-BN for efficient photocatalytic water splitting. While C4HF is catalytically inert due to fully saturated surfaces, h-BN suffers from an ultra-wide bandgap and low carrier mobility. The heterostructure leverages complementary functionality: h-BN provides chemisorption sites for reaction intermediates, while C4HF induces a pronounced red shift in optical absorption and enhances carrier mobility, achieving light-hole mobility up to 91.74 × 103 cm2 V−1 s−1. Type-II band alignment and an intrinsic out-of-plane built-in electric field drive spatial separation of photogenerated carriers, suppressing recombination. First-principles calculations predict spontaneous hydrogen evolution under illumination and near-spontaneous oxygen evolution, with corrected solar-to-hydrogen efficiency exceeding 20%. Through the quasihorizontal projectile motion model of the photogenerated carrier, we predict that the migration time of photogenerated carriers to the heterostructure surface is on the femtosecond scale, enabling them to participate rapidly in catalytic reactions. The heterostructure exhibits significant out-of-plane piezoelectricity, enabling strain-amplified carrier separation. These results establish C4HF/h-BN as a robust piezo-photocatalytic platform and provide a design paradigm for 2D carbon-based photocatalytic materials.
Detection of vortex beams with the orbital angular momentum by using plasmonic nanoparticles
Vortex beams with orbital angular momentum (OAM) have many advantages in optical communications, such as high-capacity communication, communication under extreme circumstances, high-security communication, and so on. So far, vortex beams have been measured by using the interference and diffraction properties of them or by converting them back to plane waves. In this paper, we suggest an alternative way to directly detect twisted lights by using optical responses of a gold nanosphere and a gold nanodisk, which have the simplest structures. We simulate and interpret plasmonic resonance modes excited by vortex beams carrying different spin angular momentums (SAMs) and OAMs in a gold nanodisk and a gold nanosphere. Unlike an on-center nanodisk, the excited plasmon modes in an on-center nanosphere do not exactly satisfy the selection rules when OAM increases. The plasmon modes excited by vortex beams are also very sensitive to the location of a nanoparticle in the light field. The information about the SAM and OAM can be obtained from the spectral information and radiation patterns of the plasmon modes excited in on-center nanoparticles and off-center nanoparticles. We can reversely find out the location of the nanoparticles in the vortex beam by measuring the optical spectrum and radiation patterns. Our finding provides a route to develop the optical communication using vortex beams in the future.
Photoacoustic viscoelasticity imaging of thin-cap fibroatheromas: Implications for detecting vulnerable plaques
Viscoelasticity is a key mechanical property for assessing the vulnerability of atherosclerotic plaques. In this Letter, we propose photoacoustic viscoelasticity imaging (PAVEI) to provide morphological information on necrotic-core fibroatheromas together with correlative viscoelastic contrast. Gelatin–collagen mixtures with different concentrations were used to simulate fibroatheromas with distinct viscoelastic properties and to validate the sensitivity of PAVEI. Pilot experiments were further performed on ex vivo murine artery specimens from an apolipoprotein E-knockout mouse. Thin-cap fibroatheromas exhibited significantly greater photoacoustic time delays than other atherosclerotic lesions. These results demonstrate that PAVEI can provide valuable viscoelastic information for detecting vulnerable plaques and evaluating the risk of plaque rupture.
Single-gate graphene thermopiles enabled by locally Al-modified graphene legs on PET substrates
We report a simplified graphene thermopile architecture fabricated on PET substrates. Conventional single-material graphene thermopiles typically require independent electrostatic control of the two thermoelectric legs, increasing both fabrication complexity and device footprint. Here, one graphene leg is locally modified by an Al overlayer, while the overall carrier density is tuned using a single global ionic-liquid gate. As a reference, graphene/Au thermopiles exhibit the expected linear scaling of thermovoltage with the number of thermocouples, but their output remains limited by the small thermopower of Au. In contrast, the Al-covered graphene leg generates a large, weakly gate-dependent negative thermovoltage contribution while preserving graphene-dominated transport, thereby enhancing the thermoelectric contrast with the uncovered graphene leg. Consequently, graphene/Al-covered graphene thermopiles exhibit a substantially higher output voltage, which increases approximately linearly with thermocouple number and surpasses that of the graphene/Au reference structure. These results establish local Al-induced electronic modification as a simple and scalable strategy for realizing graphene thermopiles without multiple local gates, providing a device platform compatible with flexible and transparent polymer substrates.
Ligand‐Enabled Stereoselective Coupling of Methylene C(sp <sup>3</sup> )─H Bonds With Alkenyl Bromide via Pd <sup>II</sup> /Pd <sup>0</sup> /Pd <sup>II</sup> Catalysis
ABSTRACT Utilizing C(sp 3 )─H bonds as coupling partners for the formation of C(sp 3 )─C(sp 2 ) bonds remains a significant challenge despite the progress in the past two decades. Notably, the previously reported coupling reactions of C(sp 3 )─H bonds with vinyl halides employing Pd II /Pd IV catalysis are highly limited in two ways: activated alkenyl halides and strong external directing groups were typically required. Here, we report stereoselective C(sp 3 )─C(sp 2 ) cross‐coupling of methylene C(sp 3 )─H bonds from aliphatic acids with alkenyl bromides via Pd II /Pd 0 /Pd II catalysis. A diverse array of readily available cyclic and acyclic aliphatic acids and various alkenyl bromides were coupled smoothly, affording a versatile method for forging C(sp 3 )─C(sp 2 ) bonds. Complex acids and the alkenyl bromide coupling partners derived from natural products and pharmaceuticals are compatible, rendering this method amenable to late‐stage modification. The stereoselectivity of this C(sp 3 )─C(sp 2 ) coupling reaction with respect to both the sp 3 carbon center and the double bond configuration is a valuable feature.
Anisotropic cation migration and strain driving compositional segregation in FACsPbI3
Formamidinium-cesium lead iodide (FACsPbI3) is among the most promising absorber materials for high-efficiency perovskite solar cells, and A-site cation mixing of FA and Cs represents a crucial strategy to enhance the long-term stability of devices. However, inhomogeneous spatial distribution of A-site cations can adversely impact photovoltaic performance. In this work, we employ density functional theory to investigate the influence of cation mixing on migration behavior and to elucidate the origin of compositional inhomogeneity. We find that the incorporation of Cs not only suppresses halide anion migration but also significantly inhibits the migration of both FA and Cs cations, with a particularly pronounced hindering effect on Cs migration under strain-free conditions. The spherical Cs ion exhibits anisotropic migration within the hybrid perovskite lattice, preferentially moving along the C-H axis of neighboring FA cation. In contrast, planar FA cations tend to migrate along pathways perpendicular to their own plane due to hydrogen-bond interactions, exhibiting behavior characteristic of a coupled rotational–translational motion. During the initial solidification stage of the hybrid perovskites, thermodynamically favorable Cs-aggregated domains readily form; subsequent lattice strain drives anisotropic migration of both Cs and FA, leading to spatially inhomogeneous cation distributions. These findings deepen the understanding of cation migration mechanisms in mixed-cation perovskites and reveal key factors responsible for compositional inhomogeneity, offering theoretical guidance for experimental strategies aimed at mitigating phase segregation in perovskites.
Equilibrium kink-like torsion deformation of a magnetoactive elastomer under a magnetic field
A novel effect involving the formation of a stable kink-like torsion deformation in a magnetoactive elastomer (MAE) beam subjected to a uniform magnetic field is theoretically predicted and experimentally confirmed. The phenomenon was demonstrated using an elastomer beam containing soft magnetic carbonyl iron microparticles within a silicone matrix. The torsion kink acts as a transition boundary between two undeformed homogeneous states of the beam. We show that the elastic moment is compensated by a magnetoelastic moment in the kink region, where the local magnetization of the beam is noncollinear to the applied magnetic field due to shape anisotropy. It is established that within the kink region, the MAE beam exists in a nonuniformly elastically deformed, low-symmetry magnetic state. Outside the kink, the beam's magnetization is collinear with the magnetic field, corresponding to an undeformed, high-symmetry homogeneous magnetic state.
Nonlinearly driven memory loss of incubation effects in fused silica excited by near single-cycle laser pulses
The nonlinear interaction of near-infrared ultrashort laser pulses with bulk fused silica at intensities below the catastrophic damage threshold is the birthplace of local electronic excitation events that may relax as point defects. The accumulation of defect centers creates additional sources of electronic excitation, gradually lowering the ionization threshold upon multi-pulse irradiation. However, the use of the near single-cycle sub-4 fs pulses erases in a surprising manner the contribution of defects to the damage threshold. This is the result of increasing the strong intensity clamping that limits energy density and therefore carrier collisional multiplication. Thus, the role of additional defect sources in the overall carrier population becomes secondary. In addition, the significant broadening of the near single-cycle pulse may enable impulsive depletion of defect levels, providing a possible additional pathway contributing to the suppression of nonlinear ionization memory.
Line-shape-based peak locking applied to the optical clock
In high-precision spectroscopy and quantum metrology, the stabilized system parameters at the peak of spectral lines are often required. Here, we propose a line shape-based peak locking (LSBPL) method that stabilizes system parameters at the maximum of arbitrary single-peak spectral lines. Unlike conventional proportional–integral–derivative (PID) control, which relies on a feedback function to convert an error signal into a control output, our approach exploits the intrinsic properties of the spectral line for peak locking. With application to the 171Yb+ ion optical clock using Rabi spectra, we demonstrated a comparable result to that of the PID method when the gain coefficient was set to g=0.3. The proposed LSBPL method also exhibits superior locking performance over the conventional PID method for asymmetric resonance profiles, maintaining stable closed-loop locking even when the PID method becomes ineffective. In addition, machine learning algorithms, especially random forest and support vector regression, are employed to fit single-peak spectral lines when an analytical expression is unavailable. This enables the peak-locking method to be universally applied even without requiring an explicit mathematical model, providing a flexible and generalizable tool for precision spectroscopy and quantum metrology.
Dual-barrier GeSn quantum-well lasers with operation up to 150 K
GeSn/SiGeSn quantum wells (QWs) have been investigated for the development of GeSn-based lasers. Barrier/well configurations including GeSn/GeSn and SiGeSn/GeSn were grown and characterized to evaluate carrier confinement and collection efficiency. In our previous work, a dual-barrier design (SiGeSn barrier/GeSn barrier/GeSn well) exhibited improved carrier collection efficiency for a GeSn single QW structure compared with a single-barrier configuration; however, no lasing had been reported from dual QW devices to date. Here, we report lasing from a GeSn dual-barrier single QW structure up to 140 K, with a threshold of 67 kW/cm2 at 77 K, representing a substantial threshold reduction. In addition, a 4-QW laser employing the same dual-barrier design demonstrates a clearly reduced threshold of 50 kW/cm2 at 77 K and a slightly increased maximum operating temperature of 150 K. The lower lasing threshold is attributed to decreased average carrier concentration in each well that improves the differential gain and the reduced Auger recombination rate.
Micro-array-enhanced structure–function analysis of effective thermal boundary resistance in GaN/SiN <i>x</i> /diamond heterostructures
The effective thermal boundary resistance (TBReff) of GaN/SiNx/diamond heterostructures is characterized using a micro-array-enhanced structure–function–transient dual interface method (SF–TDIM). To overcome the masking of the interfacial thermal resistance by the thick substrate in standard electrical measurements, surface-patterned etched micro-arrays are employed to reduce the effective heat-flow area and geometrically amplify the interfacial resistance contribution, while a high-precision temperature-sensing chip captures the thermal transient with negligible switching delay. For a structure with a 25-nm SiNx interlayer, SF–TDIM yields TBReff=35.2±6.4 m2K/GW (k=2), with consistent area-normalized results obtained from three array geometries. The result agrees, within the respective uncertainty intervals, with an independent transient thermoreflectance measurement on an unetched reference from the same fabrication batch. This work provides a practical electrical route with enhanced sensitivity for evaluating thermal transport across heterostructure interlayers.
Tailoring defects to boost Eu3 <b>+</b> emission in MgGeO3 phosphors
Owing to the centrosymmetric 4fn configuration of rare-earth ions, their electric-dipole 4f–4f transitions are parity-forbidden, resulting in low oscillator strengths and poor excitation efficiency. To overcome this limitation, in this work, we propose a synergistic defect-engineering strategy by introducing magnesium vacancies (VMg″) into MgGeO3:Eu3+ and systematically investigate their regulatory role in enhancing luminescence performance and the underlying microscopic mechanisms. Mg vacancies induce significant local lattice distortions around Eu3+ sites, breaking inversion symmetry and lifting the parity-forbidden nature of the electric-dipole 5D0→7F2 transition, thereby intrinsically enhancing the radiative transition probability and resulting in approximately threefold increases in both emission intensity and fluorescence lifetime. This work not only elucidates a general mechanism for synergistically tuning luminescence properties via cation-vacancy engineering but also substantially fills the research gap in Eu3+-doped Ge-based oxide systems, providing new insights for the rational design of high-efficiency and high-stability rare-earth luminescent materials.
Iron‐Catalyzed Asymmetric <i> NH <sub>2</sub> </i> ‐Amination of Sulfenamides
ABSTRACT The increasing prominence of stereogenic‐at‐sulfur motifs in drug discovery and catalysis has created a growing demand for versatile synthetic methods. We describe here an Fe( TIBS PDP)‐catalyzed enantioselective NH 2 ‐amination of sulfenamides to access chiral sulfinamidines. This method accommodates a broad range of sulfenamides, enabling direct access to diverse nitrogenated stereogenic‐at‐sulfur architectures. The synthetic utility is demonstrated by the efficient preparation of pharmaceutically relevant compounds, such as an aza‐analog of drug candidate LY181984 and a PP2A modulator. Moreover, this reaction represents the first example of asymmetric NH 2 transfer using the widely employed bioinspired Fe(PDP)‐type catalysts.
Enabling thin p-GaN Ohmic contacts through ultrathin magnesium deposition and brief thermal annealing
Gallium nitride (GaN) is a key semiconductor for optoelectronic and power electronic applications. However, achieving low-resistance Ohmic contacts to p-GaN remains challenging, particularly after plasma processing. Annealing of metallic magnesium (Mg) film on p-GaN has emerged as a promising approach, but severe surface roughening limits its applicability to thin (&lt;100 nm) p-GaN layers widely used in practical devices. Here, we demonstrate a capless ultrathin (&lt;10 nm) Mg deposition followed by a soft anneal (600 °C, 300 s) that forms a smooth, ultra-shallow, heavily acceptor-doped surface layer. The process maintains surface smoothness while achieving a low specific contact resistivity of (1–3) × 10−4 Ω cm2 at zero-bias with linear I–V characteristics, even on plasma-etched surfaces. Quasi-vertical p–i–n diodes fabricated using this approach exhibit low leakage currents and high breakdown voltages, indicating preserved junction integrity. This work provides a practical and scalable strategy for forming robust Ohmic contacts on thin p-GaN, with broad implications for GaN-based electronic and optoelectronic devices.
Frequency-tunable superconducting microwave resonators based on quantum paraelectricity
Frequency tuning enables both high-sensitivity and wide-bandwidth detection in the resonator. Potassium tantalate (KTO) is a quantum paraelectric with tunable permittivity and low microwave loss at cryogenic temperature, making it promising for tunable devices. Here, we demonstrate a superconducting microwave resonator on a KTO substrate. The resonant frequency can be tuned by ∼40 MHz using a 9 V bias at 20 mK, with no observable hysteresis. The absence of hysteresis is a key metric for practical devices, addressing one of the major obstacles in other paraelectric-based tunable resonators. More interestingly, we observed that the quality factor oscillates during voltage tuning, arising from the competition between phonon hardening and charge injection. Therefore, our work provides a practical tunable resonator platform and offers a potential approach to study energy-loss characteristics in quantum paraelectrics.
2.7-kV CuCrO2/Ga2O3 heterojunction diode with stepped-mesa termination and on-state electrical stress reliability
In this work, we report vertical CuCrO2/β-Ga2O3 p–n heterojunction diodes (HJDs) incorporating a stepped-mesa termination for enhanced blocking performance and robust on-state reliability. The optimized HJD achieves a breakdown voltage of 2.71 kV with a specific on-resistance of 5.84 mΩ cm2, corresponding to a power figure of merit of 1.3 GW/cm2. TCAD simulations reveal that the stepped-mesa structure effectively suppresses electric-field crowding at the termination edge, accounting for the improved blocking capability. The on-state stability is further evaluated using a measurement-stress-measurement protocol under both constant-voltage and constant-current stress conditions. The HJD exhibits an essentially unchanged turn-on voltage and a minor increase in dynamic on-resistance, with the stress-induced variation being largely reversible after stress removal. Temperature-dependent reverse-current analysis suggests that the high-field leakage is governed by the trap-assisted Poole–Frenkel emission, yielding a trap barrier height of ∼0.35 eV. By correlating the recoverable stress response with the leakage-mechanism analysis, the stress-induced electrical variation is mainly associated with reversible electron capture and emission in preexisting trap states. This work demonstrates that stepped-mesa-terminated CuCrO2/β-Ga2O3 HJDs provide a promising route toward reliable kilovolt-class ultra-wide-bandgap power rectifiers.
Continuous-wave terahertz photomixing in a silicon-compatible Ge-on-Si nano-air-channel photodiode
We demonstrate a silicon-compatible Ge-on-Si nano-air-channel photodiode for continuous-wave terahertz photomixing at 1550 nm. While nano-air-channel devices offer a promising route to ultrafast carrier transport, their implementation in a telecom-band, silicon-compatible photomixer has remained largely unexplored. The device is fabricated by a two-step buffered oxide-etch release process that forms a 50 nm air channel between the Ge surface and suspended Au/Ti electrodes. Under 1550 nm illumination, it exhibits an estimated internal quantum efficiency of 473% at 10 V, indicating that this is due primarily to localized high-field-assisted processes in the near-surface Ge region. Bias-dependent analysis reveals a transport transition near 2.5 V from leakage-dominated collection to nano-air-channel-assisted extraction, and dual-laser excitation produces continuous-wave heterodyne signals from 170 to 260 GHz. These results establish Ge-on-Si nano-air-channel photodiodes as a compact platform for silicon-compatible terahertz photomixers and photonic-electronic interfaces.
A Radial‐Linear π‐Conjugated Polymer by Integrating Poly(Para‐phenylene Vinylene) and Cycloparaphenylene for Enhanced Optoelectronic and Electrochemical Performance
ABSTRACT Herein, we present a new class of hybrid conjugated polymer that integrates [8]cycloparaphenylene ([8]CPP) directly into poly(para‐phenylene vinylene) (PPV) frameworks, creating a π‐extended poly(cyclo(para‐phenylene vinylene)) ( [8]CPPV ). Comprehensive characterization confirmed its well‐defined alternating structure. Photophysical analyses revealed curvature‐driven electronic coupling between the radial CPP and linear PPV π‐systems, resulting in broadened absorption, red‐shifted emission, and high fluorescence quantum yield. Furthermore, [8]CPPV demonstrates excellent performance as a lithium‐ion battery anode, combining high initial capacity with stable cycling enabled by mixed pseudocapacitive and diffusion‐controlled Li + storage mechanisms. These results establish [8]CPPV as a versatile all‐carbon polymeric framework that bridges molecular nanohoops and extended π‐networks, offering a tunable platform for optoelectronic and energy storage applications.
Demonstration of ferroelectric GaN transistors with area-ratio-controlled AlScN-based MFMIS gate stack
In this study, we demonstrate an AlScN/GaN ferroelectric high-electron-mobility transistor (FE-HEMT) employing an area-ratio (AR)-controlled metal–ferroelectric–metal–insulator–semiconductor (MFMIS) gate stack. Configured with an AR of 8:1, the device exhibits a steep subthreshold slope of 26.8 mV/dec and a wide DC memory window of 5.7 V. The FE-HEMT structure facilitates AR tuning to regulate voltage partitioning, effectively preventing dielectric breakdown while enabling extensive polarization switching. Furthermore, a large pulse-induced VTH modulation of 22.9 V is achieved. The device also demonstrates robust endurance up to 3 × 107 cycles with a maintained ΔVTH of ∼7 V, highlighting the potential of the AR-controlled MFMIS FE-HEMT for GaN-based energy-efficient reconfigurable devices.
Thermal expansion coefficients and unit cell parameters for r-GeO2 heteroepitaxy on r-TiO2/Ti1− <i>x</i> Ge <i>x</i> O2
The disclosure of the full potential of rutile germanium dioxide (r-GeO2) as a new generation material for power electronics requires the development of its heteroepitaxy. In this context, the isostructural r-TiO2 is one of the most investigated substrates, often requiring buffer layers to accommodate lattice mismatch. In this work, we investigate, via in situ variable temperature powder x-ray diffraction, the thermal expansion behavior of r-TiO2, r-GeO2, and the limit solid solution r-Ti0.88Ge0.12O2. The collected data allowed an extraction, under identical experimental conditions, of lattice parameters and thermal expansion coefficients. Based on these results, in-plane lattice mismatch was evaluated as a function of temperature, considering all the commercially available r-TiO2 single crystal cuts [i.e., (001), (110), (111), (100), and (101)] and extrapolating data up to reasonable r-GeO2 deposition temperatures. The r-Ti1−xGexO2 solid solution is shown to effectively reduce both the mismatch and its thermal evolution, highlighting its potential as an effective strain-engineering buffer layer. These findings depict a comprehensive framework for the optimization of r-GeO2 heteroepitaxy.