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CMOS programmable metachip for terahertz multifunctional sensing
A CMOS-based programmable terahertz (THz) metachip for multifunctional sensing is proposed and experimentally demonstrated in this work. Fabricated using a standard 55-nm CMOS process, the metachip is composed of periodically arranged meta-atoms with on-chip circuits, enabling multi-frequency amplitude modulation at 360, 413, and 493 GHz with a peak modulation index exceeding 20 dB. Proof-of-concept experiments are carried out for sensing object motion and fingerprint objects at distinct operational frequencies using the proposed metachip array. This work realizes multifunctional sensing, which will promote the development of multifunctional and highly integrated terahertz on-chip sensing systems.
Phosphine‐Catalyzed Unsymmetric [2 + 2] Annulation of Allenyl Phosphonates for Highly Substituted Cyclobutenes
ABSTRACT Allenes, as versatile intermediates with unique cumulative double bond systems, have been widely used in cycloaddition reactions for constructing various cyclic skeletons, yet the selective synthesis of cyclobutenes via double allenes [2 + 2] annulation still remains a long‐standing challenge. Herein, we report a phosphine‐catalyzed unsymmetric [2 + 2] annulation of allenyl phosphonates for the efficient construction of highly substituted cyclobutenes. The reaction exhibits broad substrate scope, delivering the target cyclobutenes in moderate to good yields with exceptional Z / E selectivities and diastereoselectivities. Mechanistic studies reveal that the reaction proceeds via phosphine‐induced zwitterion formation and deprotonation of allene. The Lewis acid enables precise control of diastereoselectivity, while silane effectively suppresses allene isomerization to conjugated dienes and prevents catalyst deactivation, thus ensuring reaction efficiency. Furthermore, the synthesized cyclobutene derivatives demonstrate good structural modifiability through diverse transformations. This work enriches the field of phosphine‐catalyzed allene chemistry, fills a gap in allene‐based [2 + 2] cyclization modes, expands the methodological toolbox for cyclobutene synthesis, and provides a versatile platform for accessing complex cyclobutene‐containing molecules.
Inhibition of graphitization on diamond surfaces via flash joule heating and construction of chemical bonds for tungsten metallization
Surface metallization is a critical process for diamonds in thermal management applications. However, bottlenecks such as graphitization, inhomogeneous interfacial phases, and high interfacial thermal resistance persist during metallization. This study presents a novel strategy for tungsten coating on diamond particle surfaces within an extremely short time using flash joule heating. In situ chemical bonding of a composite consisting of W, W2C, and WC was achieved on the diamond surface, yielding a uniform and conformal coating that suppressed diamond surface graphitization, retained 93.2% of the intrinsic thermal conductivity of diamond, and resulted in an equivalent thermal conductivity of 1864.69 W m−1 K−1. The chemically bonded metallization shell introduced an equivalent interfacial thermal resistance as low as 9.11 × 10−10 m2 K W−1. Photothermal conversion cycling tests demonstrated that the chemically bonded metallization on the diamond surface possesses excellent thermal fatigue resistance. Through photothermal conversion studies and the construction of a two-node thermal relaxation model, the analysis indicates that the W, W2C, and WC interfacial phases introduce a moderate interfacial thermal resistance, which effectively suppresses instantaneous and intense heat dissipation to the environment, thereby enabling controllable and stable heat release.
Asymmetric Deoxygenative Difunctionalization of 1,2‐Dicarbonyl Compounds Enabled by Phosphinite and Chiral Salen‐Molybdenum Catalyst Synergy
ABSTRACT The 2‐aryl benzofuran‐3‐ones serve as pivotal scaffolds in natural products and bioactive molecules, yet their synthesis and subsequent asymmetric functionalization are hindered by multi‐step protocols and the lability of their derivatives lacking electron‐rich substituents on the aromatic ring of benzofuran‐3‐one core. Herein, we report a phosphinite‐mediated, Mo‐catalyzed intermolecular asymmetric deoxygenative coupling reaction between 1,2‐dicarbonyl compounds and 3‐(methoxymethyl)indoles, thus providing a series of chiral 2‐aryl benzofuran‐3‐ones with a chiral quaternary carbon center with generally good yields and enantioselectivities. Mechanistic studies reveal that phosphinite and the Mo‐complex synergistically promote the in situ generation of key intermediates, while the formally tetravalent mononuclear Mo‐complex serves as the key species governing the enantioselectivity of the reaction. This work expands the application of chiral salen‐Mo catalysts in asymmetric catalysis, offering an efficient route to valuable chiral benzofuranone derivatives.
Broadband and high-efficiency polarization rotation using a single-layer transmissive metastructure
A single-layer, free-standing metamaterial polarization rotator has been proposed, which achieves broadband and high-efficiency linear polarization rotation in transmission mode. The structure comprises a metal slab perforated with an array of subwavelength holes, each containing an embedded twisted U-shaped meander wire. By using the coupling between the perforated slab and the four adjacent excited modes of the meander wires, the incident linearly polarized wave is efficiently captured by the receiving arms and reradiated from the reradiating arms with a controllable polarization rotation angle. The proposed design offers a simple, efficient, and flexible approach to polarization manipulation, demonstrating potential value for applications in microwave and communication systems.
Enhancing the efficiency of ZnSeTe-based quantum-dot light-emitting diodes by manipulating charge dynamics
In conventional Cd-based quantum-dot light-emitting diodes (QLEDs), a reduced hole-injection barrier at the hole transport layer (HTL)–quantum-dot (QD) interface generally leads to enhanced device efficiency. However, this principle does not extend to the emerging class of environmentally friendly ZnSeTe blue QLEDs. In this work, we systematically examine the charge dynamics in ZnSeTe-based blue QLEDs, with particular focus on trap states, energy level alignment, and charge transport properties. Our findings reveal significant carrier accumulation at the ZnSeTe/ZnO interface, where emission quenching by ZnO substantially degrades device performance. To mitigate this issue, we introduce Mg-doped ZnO combined with an HTL featuring a shallow highest occupied molecular orbital level, thereby optimizing charge distribution across the device. Simulations corroborate that electrons and holes predominantly accumulate at the QD/HTL interface under this design. As a result, the efficiency of the ZnSeTe blue QLED is markedly improved, increasing from 2.1% to 6.3%. This study elucidates the critical influence of hole dynamics in ZnSeTe blue QLEDs and underscores the essential role of tailored charge management for high-performance QLED operation.
Comparative analysis of voltage losses in perovskite and GaAs solar cells at low temperatures
This study presents a comparative analysis of the open circuit voltage behavior of perovskite vs gallium arsenide (GaAs) solar cells at low temperatures relevant to space applications. While GaAs solar cells demonstrate high power conversion efficiencies and superior environmental stability, their widespread adoption is limited by high manufacturing costs. In contrast, perovskite solar cells have emerged as a promising alternative due to their high efficiency, excellent optoelectronic properties, and low fabrication costs. To evaluate and compare their optoelectronic characteristics and voltage losses at low temperatures, we have characterized both devices using temperature-dependent current–voltage (J–V) and photoluminescence-based radiative efficiency measurements in the range of 300–160 K. GaAs devices exhibited a linear increase in open-circuit voltage (Voc) with decreasing temperature, consistent with theory. In contrast, perovskite devices showed suppressed Voc enhancements and an S-shaped J–V response below 240 K. Using temperature-dependent external radiative efficiency measurements, we show that temperature-dependent entropic losses related to nonradiative recombination are higher in perovskite devices compared to GaAs at high temperatures, but the gap between the two shrinks substantially at lower temperatures. These findings provide valuable insight into temperature-dependent Voc in perovskite solar cells, particularly relevant for space deployment applications.
Bragg-grating engineering enables deterministic resonance control in an on-chip THz filter
On-chip filters are important for integrated terahertz (THz) communication and sensing systems. Deterministic control of resonance multiplicity in compact devices enables flexible spectral filtering. Here, we experimentally demonstrate an on-chip silicon THz filter based on a Bragg-grating-assisted Fabry–Pérot cavity, in which the resonance multiplicity is governed by the relation between the Bragg stopband and the cavity free spectral range (FSR). By engineering this stopband–FSR relation, single-, double-, and triple-resonance states are achieved within the 360–390 GHz band, with a packaged insertion loss of approximately 6 dB. The single-resonance device exhibits a through-port transmission minimum approaching −40 dB and a loaded quality factor of QL = 809.5. This work provides a compact strategy for deterministic spectral-state engineering in integrated THz filters.
Synergistic Ti doping and carbon-coating to modulate Na+ migration channels in Na2FeP2O7 cathode for fast sodium storage
Phosphate salt Na2FeP2O7 has emerged as a potential candidate material for sodium-ion batteries due to its high stability in the triclinic structure and low cost. However, its practical implementation is hindered by intrinsic limitations such as poor electronic conductivity and sluggish Na+ diffusion kinetics. In this study, Ti-doped Na2FeP2O7 composite coated with an in situ formed amorphous carbon layer (0.1Ti-NFO@C) was synthesized via a sol-gel method followed by high-temperature calcination. The introduced Fe/Ti–O bonding network and carbon coating synergistically enhance the electronic conductivity and Na+ transport kinetics, which significantly improve the rate performance and specific capacity. The resulting 0.1Ti-NFO@C delivers a reversible capacity of 109.67 mAh g−1 at 0.2C, and retains a capacity of 77.90 mAh g−1 even at a high current density of 10C. Furthermore, when assembled into a full cell with hard carbon, it exhibits an initial discharge capacity of 110.04 mAh g−1 at 0.5C and retains a capacity of 54.88 mAh g−1 after 200 cycles at 2.0C, with a Coulombic efficiency exceeding 99%. These structural modifications significantly enhance the material's performance, providing valuable insights toward the practical implementation of polyanion cathodes.
Periodically tunable continuous-wave intracavity diamond Raman laser via birefringent filter
We report a periodically tunable continuous-wave intracavity diamond Raman laser employing a rotating quartz birefringent filter (BRF). Experimental results reveal a counter-intuitive phenomenon where the insertion of a lossy BRF leads to higher Stokes output power compared to the free-running regime. This power enhancement is primarily attributed to the significant spectral narrowing of the fundamental field, which increases the effective Raman gain and overcompensates for the additional insertion losses. By utilizing BRFs with thicknesses of 0.5 and 1 mm, the system achieved stable tuning ranges of approximately 0.24 and 0.3 nm, respectively, with maximum Stokes output powers of 1.24 and 1.05 W. It should be noted that although the absolute wavelength span observed at extreme BRF rotation angles can extend to 2.06 and 1.77 nm, respectively, this is primarily due to intermittent outliers. Both the output wavelength and power exhibit a strict 180° periodicity relative to the BRF rotation angle.
Dislocations in (011)-oriented vertical Bridgman <b> <i>β</i> </b> -Ga2O3 substrates
Dislocations in (011)-oriented β-Ga2O3 substrates grown by the vertical Bridgman method was investigated using x-ray topography (XRT), combined with x-ray reticulography. Transmission XRT reveals dislocations lying on the (001) plane and extending along [010], forming arrays associated with domain boundaries. Dislocations on the (011) plane were also identified but differ from those responsible for line-shaped pits on (001) epilayers. Reflection XRT showed good agreement with transmission XRT and enables classification of dislocation types based on contrast features. Reticulography confirms domain boundaries with misorientation on the order of 10−5 rad, providing insight into defect formation relevant to epi-growth and device performance.
Gd2O3-induced electronic modulation of Cu for efficient oxygen reduction in aluminum–air batteries
A Gd2O3-modified copper-based composite catalyst (Gd2O3–Cu/C) was developed via solvothermal preassembly and high-temperature pyrolysis to overcome the sluggish oxygen reduction reaction (ORR) kinetics of aluminum–air batteries (AABs) and the limitations of Pt-based catalysts. The strong electronic interaction between Gd2O3 and Cu active sites efficiently regulates the electronic structure of the catalyst, reducing its work function and charge transfer resistance; this results in an increase in the valence band electron density, thus promoting a nearly four-electron ORR pathway and ultimately enhancing the overall ORR kinetics. The catalyst exhibited a half-wave potential of 0.82 V, a Tafel slope of 67 mV dec−1, a 90% current retention after 500 min, and outstanding methanol tolerance, demonstrating superior ORR kinetics and durability in alkaline electrolyte. When assembled into an AAB, the Gd2O3–Cu/C catalyst delivered an open-circuit potential of 1.521 V, a peak power density of 65.7 mW cm−2, and a specific capacity of 578.8 mAh g−1, outperforming the commercial Pt/C-based counterpart. Density functional theory calculations revealed that Gd-induced electronic modulation of Cu facilitates electron transfer from Gd2O3 to Cu, positively shifting the d-band center of Cu toward the Fermi level, optimizing the adsorption of ORR species, and thus enhancing the ORR performance. This work introduces a cost-effective and high-performance non-precious metal catalyst for ORR, with application in AABs for emergency power supplies.
Ultrathin fully strained GaN channel high electron mobility transistors on AlN-on-sapphire templates engineered by ferroelectric ScAlN epilayers
In this work, we demonstrate fully strained GaN channel high electron mobility transistors (HEMTs) with superlattice barriers on AlN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Here, ferroelectric Sc0.18Al0.82N epilayers are introduced into the heterostructure to engineer the device performance. Instead of the conventionally thick AlN buffer, an ultrathin Sc0.18Al0.82N layer is positioned between the AlN template and the GaN channel to effectively suppress the leakage at the interface between the secondary epilayers and the AlN template, realizing fully strained epitaxial structures less than 60 nm. Besides, a Sc0.18Al0.82N layer serves as a part of the superlattice barrier with well-defined interfaces, which results in a stronger polarization effect and larger conduction band offset and thus a high carrier density of 3.12 × 1013 cm−2. The processed GaN HEMT engineered by Sc0.18Al0.82N epilayers exhibits direct-current transfer characteristics with an on/off current ratio of ∼106 and distinct counterclockwise ferroelectric hysteresis windows, with a widely tunable threshold voltage ranging from −6.3 to −2.7 V. The fabricated device with a 180-nm T-shaped gate and gate-drain space of 1.5 μm achieves a breakdown voltage of 80 V, a cutoff frequency of 32 GHz, and a maximum oscillation frequency of 70 GHz, respectively. This work provides a new approach for developing next-generation multifunctional transistors on an ultrawide bandgap AlN platform through synergistically integrating ferroelectric gate modulation with a superlattice barrier, offering a promising candidate for highly reliable microwave power electronics with tunable switching characteristics.
Device-area selection of memristive transport regimes in epitaxial Hf0.5Zr0.5O2-based ferroelectric devices
Ferroelectric memristive devices based on hafnia are promising systems for neuromorphic electronics, yet the interplay between polarization-modulated resistive changes and defect-mediated transport often leads to complex and debated switching mechanisms. Here, we investigate this competition in epitaxial Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 heterostructures with Pt top electrodes by combining structural, ferroelectric, and memristive characterization with a statistical analysis across a broad range of device areas spanning three orders of magnitude. We identify two distinct memristive regimes with opposite resistance–voltage chiralities. Small devices exhibit a low-resistance state that scales inversely with area, consistent with area-distributed electronic transport, while larger devices display an area-independent resistance indicative of localized conductive channels. A statistical nucleation model quantitatively captures this behavior and yields a crossover characteristic area of A*≈103μm2. This crossover also correlates with the onset of ferroelectric wake-up for the larger devices, linking conductive-channel nucleation and oxygen-vacancy redistribution within a unified physical picture. These results establish lateral device size as a key parameter controlling the dominant transport mechanism in epitaxial hafnia-based devices.
Improved light extraction and thermal management in thin-film GaAs LEDs using hemispherical ZnSe lenses
High-index optical elements enable improved photon outcoupling from high-refractive index III–V emitters, but their feasibility on electrically driven GaAs light-emitting diodes (LEDs) has been limited by the stringent requirement of near-optical contact between the element and the LED. Here, we demonstrate a practical and reversible integration of a ZnSe hemispherical lens with a thin-film GaAs LED using a spring-preloaded tip/tilt fixture that enables alignment and in situ optical contact monitoring. Integrating the ZnSe hemisphere consistently increases the emitted optical power and external quantum efficiency by a factor of 4.5–5.5 relative to emission into air, while a thin, moderately convex layer of oil used as a reference yields an intermediate enhancement. In addition to improved extraction, the hemisphere also strongly suppresses the current-induced spectral redshift, consistent with reduced self-heating; a bandgap-only estimate indicates that the air-emitting LED operates approximately 10 K hotter than the LED coupled to the hemisphere at 10 mA. Simulations describing the effect of the residual air gap thickness on the enhancement show a rapid degradation of the extraction benefits for gap thicknesses already starting from around 20 nm. These results show that a high-index external hemisphere can simultaneously enhance light extraction and improve thermal stabilization, addressing two coupled limitations in high efficiency GaAs LEDs and thermophotonic devices.
Heterocyclic aromatic amine-modified hole transport layer enables energy level regulation for enhanced performance of deep blue QLEDs
Quantum dots (QDs) exhibit great promise for next-generation displays, yet deep blue quantum dots light-emitting diodes [deep blue QLEDs, CIE (International Commission on illumination) y &lt; 0.06] lag behind red and green counterparts due to energy level mismatches and imbalanced carrier mobility. In this work, 2-aminopyridine was employed at the interface between the hole transport layer and the emitting layer to construct stepwise energy level regulation. The mechanism was elucidated through density functional theory calculations, photophysical characterization, and surface morphology analysis. The modifier deepens the HOMO level of the hole transport layer from −5.75 to −5.97 eV and increases hole mobility from 4.08 × 10−7 to 1.56 × 10−6 cm2 V−1 s−1. The device based on the modified hole transport layer achieved a record external quantum efficiency of 23.16% in deep blue QLED (CIE y = 0.027). Interface modification demonstrates an effective approach to high-efficiency deep blue QLEDs and supports the commercialization of QLEDs.
High-thermal-conductivity polycrystalline diamond grown on GaN via a cyclic-methane-modulation-assisted strategy
The self-heating effect severely limits the performance and reliability of GaN high-electron-mobility transistors (HEMTs). Direct deposition of thin-film polycrystalline diamond (PCD) on GaN is regarded as a promising strategy as it allows the heat spreader to be placed as close as possible to the hotspots. However, rapid grain coalescence during the initial growth stage usually leads to the formation of high-density graphitic carbon phases, which significantly degrades the thermal conductivity (k) of the as-grown diamond films. Here, we report a cyclic-methane-modulation-assisted (CMMA) two-step growth strategy with periodically cycled methane concentration that balances the growth rate and grain quality while suppressing the incorporation of graphite. This approach achieves a remarkably high k of 632 ± 76 W/m K for 2.4-μm-thick PCD on GaN, accompanied by a low thermal boundary resistance of 8.5 ± 0.5 m2 K/GW even with a 5 nm-thick SiNx interlayer. Finite-element simulation predicts a 70 °C reduction in peak temperature for the HEMTs integrated with CMMA-grown diamond, which highlights its substantial potential for effective thermal dissipation in high-power electronic applications.
Probe–suspended membrane resonance model for obtaining out-of-plane shear modulus and prestress in graphene
The out-of-plane shear modulus of two-dimensional (2D) materials is critical for understanding their strain-modulated electronic, optical, and tribological behavior. However, existing experimental methods are limited and often yield inconsistent results due to substrate interference. Here, we introduce a contact-resonance-based methodology utilizing a probe–suspended membrane system to simultaneously measure both the out-of-plane shear modulus and in-plane prestress of 2D material membranes. The membrane's load–deflection response is modeled via a novel cubic equation fitted from numerical simulations. The probe–membrane dynamic system is modeled as a tilted cantilever with normal and lateral springs at its tip, yielding a frequency equation that links resonance frequency to membrane stiffness. Experimental measurements on suspended multilayer graphene under varying loads yield an out-of-plane shear modulus of 4.16 ± 0.30 GPa, consistent with theoretical predictions. The in-plane prestress is observed to decrease with membrane thickness. Pressure-blister tests corroborate that van der Waals attraction from the hole sidewalls is a primary origin of this prestress. This work establishes a precise, nondestructive method for characterizing 2D material mechanical properties with minimal substrate influence, offering fundamental insights for the design and performance evaluation of 2D material-based nanodevices and flexible systems.
Ferroelectric nitrogen-polar ScAlN heterostructures on 4H-SiC enabled by thin AlN buffer layers
The expansive functional landscape of ferroelectric nitrides has sharpened interest in host platforms that can preserve excellent structural quality while extending operation to high-temperature, harsh-environment regimes. 4H-SiC is especially compelling owing to its thermal robustness, high thermal conductivity, and close lattice correspondence with AlN. Here, we report robust ferroelectric ScAlN-on-4H-SiC heterostructures enabled by thin, exceptionally high-quality AlN templating, grown via plasma-assisted molecular beam epitaxy. A 40 nm nitrogen-polar AlN buffer layer on carbon-terminated 4H-SiC yields highly ordered and dense films, providing an abrupt, structurally coherent, true wurtzite interface for ScAlN heteroepitaxy. Across a broad Sc composition range, a single dominant epitaxial orientation and monocrystalline wurtzite character are maintained without detectable secondary phases. Electrical measurements reveal room-temperature ferroelectricity in as-grown films with coercive fields and remanent polarizations comparable to ScAlN films grown directly on conductive substrates. Taken altogether, these findings establish AlN templating on 4H-SiC as a practical route to structurally controllable and reproducible all-epitaxial ferroelectric nitride heterostructures for extreme-environment electronic, acoustic, and memory applications.
Heat superdiffusion in carbon nanotubes
Like many one-dimensional systems, carbon nanotubes are known to exhibit a divergent thermal conductivity as the length of the nanotube is increased, but the precise form of this divergence has so far been disputed, some even arguing for a final convergent conductivity. In this work, the solution given by mode-coupling theory, which precisely describes the heat divergence as a power law for sufficiently large lengths, is clearly revealed in molecular dynamics simulations where the tubes' ends are kept at different temperatures. The precise localization of such an asymptotic power law explains why it has not been found before and helps resolve a long-standing puzzle in nanoscale heat transport. It is estimated to show up in carbon nanotubes of macroscopic lengths, currently achievable experimentally.