The 100 most-cited articles in Applied Physics Letters, 2024

Here we present a roadmap on Photonic metasurfaces. This document consists of a number of perspective articles on different applications, challenge areas or technologies underlying photonic metasurfaces. Each perspective will introduce the topic, present a state of the art as well as give an insight into the future direction of the subfield.

Moisture detection plays a crucial role in physiological monitoring and wearable electronics. Nevertheless, most of the humidity sensors were restricted by the power supply, hindering their applicability in internet of things and mobile healthcare. Herein, we reported a hierarchical piezoelectric composite film for active humidity detection and wearable biomonitoring. The as-electrospun piezoelectric transducing textile consists of samarium-modified lead magnesium niobate lead titanate piezoceramic fillers and polyvinylidene fluoride matrix, while the spin coated polyimide film serves as the humidity sensitive layer. By tuning the thickness ratio between transducing layer and the humidity sensing layer as well as the porosity of the electrode, an optimal moisture-sensing performance was accomplished with a high response of ∼500% and rapid response/recovery time of 23 s/31 s. Furthermore, a theoretical modeling of active humidity sensing mechanism was established by combining thermodynamic derivation and finite element calculation.

We present a high throughput computational search for altermagnetism in two-dimensional (2D) materials based on the Computational 2D Materials Database (C2DB). We start by showing that the symmetry requirements for altermagnetism in 2D are somewhat more strict compared to bulk materials and applying these yields a total of seven altermagnets in the C2DB. The collinear ground state in these monolayers is verified by spin spiral calculations using the generalized Bloch theorem. We focus on four d-wave altermagnetic materials belonging to the P21′/c′ magnetic space group—RuF4, VF4, AgF2, and OsF4. The first three of these are known experimentally as van der Waals bonded bulk materials and are likely to be exfoliable from their bulk parent compounds. We perform a detailed analysis of the electronic structure and non-relativistic spin splitting in k-space exemplified by RuF4. The magnon spectrum of RuF4 is calculated from the magnetic force theorem, and it is shown that the symmetries that enforce degenerate magnon bands in anti-ferromagnets are absent in altermagnets and give rise to…

Marine oil spills have become a major global environmental challenge, yet there remains a lack of effective and environmentally friendly strategies for the remediation of water contaminated with high-viscosity oil. In this study, we introduce a superhydrophobic oleophilic material with photothermal properties for efficient absorption of viscous oil. Femtosecond laser treatment methodology is applied to cork (FSLA-cork), which exhibits not only superior hydrophobic and oleophilic properties but also the exceptional ability to be rapidly heated from ambient conditions to 58 °C in 10 s under 1.8 solar irradiation. Under solar irradiance, the FSLA-cork adsorbent functions synergistically by capillary absorption and centrifugal pumping. At one-sun intensity, an oil absorption rate of 4.02 g cm−2 within 200 s was observed. The high adsorption rates of FSLA-cork combined with the high availability of the raw material and its eco-friendly fabrication methods indicate that such methods and materials can be utilized for large-scale clean up of aqueous environments contaminated with…

Modulating the thermal emission of a material in the infrared (IR) range can be essential for various practical applications such as smart textiles, camouflage, and anti-counterfeiting. Although many different materials or structures have been proposed, the complex manufacturing processes are still hindering their widespread use. Herein, a facile femtosecond laser processing technology and a drop-coating method are introduced to form a patternable low emissivity film. Laser-treated polyimide films resulted in superhydrophilic structured surfaces that are uniformly coated with silver-nanowires (AgNWs) in aqueous solutions for low emissivity surfaces. Furthermore, the emissivity of the samples is as low as ∼0.2 without deterioration over 800 bending-releasing cycles. The as-prepared films also display good thermal camouflage properties, namely, the films reduced the thermal radiation temperature of an object by 35.8 °C when the object temperature was ∼69.1 °C. Additionally, this IR camouflage effect of the AgNWs coated samples shows excellent stability even in harsh environments such…

The continuous growth in artificial intelligence and high-performance computing has necessitated the development of efficient optoelectronic artificial synapses crucial for neuromorphic computing (NC). Ga2O3 is an emerging wide-bandgap semiconductor with high deep ultraviolet absorption, tunable persistent photoconductivity, and excellent stability toward electric fields, making it a promising component for optoelectronic artificial synapses. Currently reported Ga2O3 optoelectronic artificial synapses often suffer from complex fabrication processes and potential room for improvement due to plasticity. To address the issue of low device plasticity and practical application scenarios, we present an amorphous Ga2O3 (α-GaOx) flexible optoelectronic artificial synapse. This synapse modulates light stimulus signals using electron/oxygen vacancies and optical stimulation and operates as a visual storage device for information processing. We investigate the improvement of the optoelectronic synapses' plasticity by controlling the number of oxygen vacancies via a plasma treatment method and…

Spontaneous and directional water droplet transportation based on patterned surface with super-wettability is crucial for the development of frontier science technology. However, water droplet transportation cannot meet both long distance and fast transportation simultaneously. Here, we overcame this limitation by proposing an asymmetric serial brachistochrone-shaped pattern (ASBP). Water droplet could be transported on the ASBP with a transportation distance of 72.52 mm and a transportation velocity of 158 mm/s after a series of single-factor experiments, orthogonal design optimization, and junction transition optimization. In addition, the water droplet could be transported on a curved ASBP, a super-long ASBP for multi-droplet scenarios, and an ASBP at an inclination angle. Moreover, acidic and alkaline aqueous solution droplet showed similar transportation distance and transportation velocity on the ASBP. Based on the aforementioned superb water transportation capacity, this ASBP can be applied in the fields of fog collection, solution mixing and reaction, and reagent detection.…

This paper proposes a hybrid microwave power receiving (MPR) metasurface array with efficient dual matching of surface impedance and phase gradient. The hybrid array comprises three components: a reflective phase gradient metasurface (R-PGM) array, a surface wave focusing array, and an energy harvesting port. The R-PGMs efficiently convert incident electromagnetic waves into surface waves. The surface wave focusing array then concentrates the energy onto the integrated harvesting port through dual matching of surface impedance and phase gradient. Connecting a rectifier circuit enables efficient microwave energy reception and RF-DC conversion, avoiding the need for multiple rectifiers or complex feeding networks in traditional MPR designs. Numerical analysis and experimental tests verify the superior performance of this hybrid array design in efficient microwave energy harvesting and RF-DC conversion, achieving 90.84% plane wave-to-surface wave conversion efficiency, 76.67% surface wave energy harvesting efficiency, and 49.28% overall RF-DC conversion efficiency. Across the wideband…

Neuromorphic computing provides alternative hardware architectures with high computational efficiencies and low energy consumption by simulating the working principles of the brain with artificial neurons and synapses as building blocks. This process helps overcome the insurmountable speed barrier and high power consumption from conventional von Neumann computer architectures. Among the emerging neuromorphic electronic devices, ferroelectric-based artificial synapses have attracted extensive interest for their good controllability, deterministic resistance switching, large output signal dynamic range, and excellent retention. This Perspective briefly reviews the recent progress of two- and three-terminal ferroelectric artificial synapses represented by ferroelectric tunnel junctions and ferroelectric field effect transistors, respectively. The structure and operational mechanism of the devices are described, and existing issues inhibiting high-performance synaptic devices and corresponding solutions are discussed, including the linearity and symmetry of synaptic weight updates,…

Frost formation is a normal phase transition phenomenon in cold climates, while it usually brings certain troubles to human lives and production. Therefore, it is of great significance to develop frost resistant materials and key technologies. Here, a salt-philic and superhydrophobic surface is designed on a PDMS substrate by femtosecond laser direct writing technology in combination with salt–ethanol–water mixtures droplet treatment. The laser-treated PDMS embedded salt (LTP-S) surface exhibits superhydrophobicity, which alone is a property that can resist the formation of frost and enables a self-cleaning effect. Meanwhile, the salt coating further enhances the frost resistance of the surface by reducing the freezing point temperature. The LTP-S surface is revealed to perform well in frosting-defrosting cycles, washing resistance, chemical corrosion resistance, heating resistance, and long-term air exposure tests as a highly efficient and stable anti-frosting surface. This work demonstrates a facile strategy to fabricate a salt-philic and superhydrophobic surface for efficient…

The safety and cycling stability of potassium-ion batteries are of paramount importance. This study investigates a class of phosphate electrolytes with different alkyl chains to understand the correlation between electrochemical properties and alkyl chains. Based on the traditional trimethyl phosphate, the impact of structural modifications on performance improvement was explored in a single-salt, single-solvent environment matched with 1 M bis(fluorosulfonyl)imide potassium salt (KFSI). The research findings indicate that appropriately altering the alkyl chain structure of the phosphate [1 M KFSI-tripropyl phosphate (TPP)] can enhance its electrochemical performance. Through characterization and calculations, it was revealed that TPP's weak solvation and steric hindrance properties favor the formation of a robust interphase on the electrode. Coupling with its excellent ion conductivity, the 1 M KFSI-TPP electrolyte enables good cycling stability of Kǁgraphite, KǁPrussian blue (PB), and PBǁgraphite full-cell configurations. This study provides essential guiding principles for…

Carbon materials exhibit diverse mechanical properties, from hard diamond to soft graphite. However, carbon materials with high ductility are rare, because of strong covalent bonds between carbon atoms. Here, we propose that the structures of triangular lattice have higher ductility than those of hexagonal or quadrangle lattice. A two-dimensional (2D) carbon network, named a carbon Kagome lattice (CKL), is used as an example to verify the point. The carbon structure has a Kagome lattice similar to the triangular lattice. Because empirical potentials cannot well simulate mechanical properties of carbon structures with triangular carbon rings, we work out a neuroevolution potential (NEP) based on a machine learning method. Structural evolution and phase transition under strain have been studied based on the NEP. The results indicate that the ductility of 2D CKL can approach 80%, and even at a high temperature, the ductility can reach 48%. The ductile values are the highest in all 2D crystal materials except the molecular materials. The high ductility is attributed to the phase…

Exceptional points are complex branching singularities of non-Hermitian bands that have lately attracted considerable interest, particularly in non-Hermitian photonics. In this article, we review some recent developments in non-Hermitian photonic platforms such as waveguides, photonic crystals, Fabry–Pérot resonators, and plasmonic systems and suggest how optical non-linearities and exceptional bound states can further inspire the development of non-Hermitian photonics in the near future.

The nitridation process can significantly improve the quality of the interfacial layer and suppress the unrecoverable electron trapping of the interfacial states during cycling, which is the main cause of endurance enhancement. In this work, through in-depth analysis of defect behavior during memory window (MW) degradation in ferroelectric field effect transistors (FeFETs), it is found that the degradation of FeFET devices with SiON interfacial layer starts within the HZO layer, while the degradation process of FeFET devices with SiO2 interlayer initially begins at the interlayer and then penetrates into the HZO layer. First, the MW degradation processes of nitridation/non-nitridation devices are measured and compared. Moreover, through the extended measure-stress-measure method, three types of defects are defined and the defect behaviors including trapping kinetics and energy locations during degradation are systematically investigated. The mechanism of nitrogen on the endurance enhancement is finally revealed. These results are valuable to better understand the reliability issues…

The extraordinary emergence of all-dielectric resonant meta-photonics underpinned by high refractive index and low optical loss materials promises a standout platform for unprecedented manipulation and subwavelength control of light. Recent significant breakthroughs in meta-photonics have to do with the exploration of the non-radiative eigenmodes that lie inside the light cone, called the bound states in the continuum (BICs), which have demonstrated considerable potential to achieve high quality (Q) factors but require ultra-small structure asymmetry, complicating fabrication and hindering precise control of Q factors. Here, we propose a scheme to excite quasi-BICs by breaking symmetry in the permittivity of the comprising meta-atoms where small permittivity perturbation renders the same effect in the conventional geometrically asymmetric design. Empowered by the insignificant permittivity perturbation introduced from chemical doping and carrier injection, arbitrarily small permittivity asymmetry, that is, infinitely high-Q factor, can be precisely and dynamically tailored. As an…

In this study, InGaSnO (IGTO)-based bilayer In2O3/IGTO and IGTO/In2O3 thin-film transistors (TFTs) were designed, and their carrier transport mechanisms and electrical performances were investigated. Herein, the ultrathin In2O3 layer provided a higher carrier concentration (Ne), thus accumulating free carriers and enhancing the carrier mobility. The thick amorphous IGTO layer controlled the device and carrier conductance, yielding a reasonable threshold voltage (Vth). Consequently, the optimized bilayer In2O3/IGTO TFTs exhibited high field-effect mobility (μFE) of 43.6 cm2 V−1s−1 and good control with Vth of 1.2 V compared to the single layer In2O3 and IGTO TFTs. Experimental analysis indicated a decrease in the oxygen vacancy (VO) formation energy owing to the interaction between interstitial Ini and Sn. Consequently, numerous unpaired electrons were generated from VO at the hetero-interfaces. In addition, an analysis of the energy band shift indicated that the heterojunction generated parasitic channels to control the Ne, and the In2O3/IGTO TFT exhibited a smaller Rc (0.34 KΩ μm),…

Polarization-sensitive ultraviolet (UV) photodetectors have attracted significant interest due to the broad applications in UV polarized imaging. However, the conventional UV photodetectors to realize polarization-sensitive properties require integrated filters and polarizers, which increase the system size and cost. In this work, self-powered polarization-sensitive UV photodetectors (PDs) with high efficiency and ultrafast response speed based on the MoS2/a-GaN heterojunction have been proposed and applied to UV polarized imaging. Benefiting from the type-I band alignment formed by MoS2/a-GaN, and the reduction of interfacial trapping effect, the PDs exhibit remarkable photovoltaic and polarization sensitivity under UV light at zero bias voltage, including a high responsivity of 15 mA/W, a specific detectivity of 4.7 × 1013 Jones, an ultrafast response speed of 4/8 ms, and a high polarization ratio of 1.5. Furthermore, the as-fabricated PDs demonstrate polarization-sensitive UV imaging. This work paves an approach for the development of high-performance polarization-sensitive UV…

Spin splitting plays a pivotal role in most modern spintronic effects. Conventionally, spin splitting accompanied by macroscopic magnetic moments has been typically discussed in the context of ferromagnets. Nevertheless, the amalgamation of spin splitting and antiferromagnets has led to a range of intriguing magnetoelectronic effects in the field of antiferromagnetic spintronics. Considering this perspective, this Letter focuses on exploring the emerging area of spin-split antiferromagnetic spintronics. It begins with a brief overview of the historical development of the anomalous Hall effect. Subsequently, recent studies on the spin-splitting-related anomalous Hall effects in antiferromagnets are elaborated upon. Finally, a summary is provided outlining the occurrence of spin splitting in different types of antiferromagnets, including noncollinear antiferromagnets and collinear altermagnets. Additionally, the associated magnetoelectronic effects are discussed.

High-quality III–V quantum structures, advanced epitaxial technologies, and characterization methods are essential to drive the development of infrared optoelectronic materials and devices. As an important component of type II superlattices, InAs/InxGa1−xAsySb1−y would play an important role in the field of high-performance infrared detectors due to their excellent luminescence efficiency and high crystal quality. However, their interfacial characteristics and the associated minority carrier lifetime are still difficult to identify. In this paper, an atomic imaging technique was used to identify the arrangement and distribution of elements of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice. Our results confirm the epitaxy mechanism that the quaternary alloy consists of two kinds of ternary alloy in one monolayer. Moreover, by separating the cation and anion columns in the elementally resolved atomic images of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice, we demonstrate that the interfacial atomic intermixing is less than one molecular layer thickness. Therefore, benefiting from excellent…

The recent demonstration of ferroelectricity in nitride materials has enabled a broad spectrum of applications across electronics, optoelectronics, photovoltaics, photonics, ferroelectrics, acoustoelectronics, and quantum devices and systems. Ensuring that nitride ferroelectrics meet the rigorous demands of modern microelectronics and photonics necessitates addressing significant challenges, such as large coercive fields, low endurance, poor stability, high leakage current, and high optical loss. In this perspective, we review the latest advancements, highlight the distinctive properties and notable achievements of nitride ferroelectrics, and delve into their origins, material synthesis, operational mechanisms and devices. Moreover, we highlight the principal obstacles faced by nitride ferroelectrics in practical applications. Finally, we discuss potential solutions, future research directions, and the prospects for further advancements in this rapidly evolving domain.

In this study, we have demonstrated a high-efficiency InGaN red (625 nm) light-emitting diode (LED) with an external quantum efficiency (EQE) of 10.5% at a current density of 10 A/cm2. To achieve this, we introduced GaN cap layers on InGaN quantum wells and AlGaN interlayers. The introduction of these layers resulted in a red shift of the wavelength. The AlGaN interlayer caused band bending, while the GaN cap layer modulated the electron wavefunction, thus helping to achieve the wavelength red shift of the InGaN red LED with high EQE. This technology is crucial for the realization of discrete or monolithic full-color micro-LED displays.

Altermagnets (AM) are a recently discovered third class of collinear magnets and have been attracting significant interest in the field of condensed matter physics. Here, based on first-principles calculations and theoretical analysis, we propose four two-dimensional (2D) magnetic materials—monolayers V2Te2O, V2STeO, V2SSeO, and V2S2O—as candidates for altermagnetic materials. We show that these materials are semiconductors with spin-splitting in their nonrelativistic band structures. Furthermore, in the band structure, there is a pair of Dirac-type valleys located at the time-reversal invariant momenta (TRIM) X and Y points. These two valleys are connected by crystal symmetry instead of time-reversal symmetry. We investigate the strain effect on the band structure and find that uniaxial strain can induce valley polarization, topological states in these monolayer materials. Moreover, piezomagnetism can be realized upon finite doping. Our result reveals interesting valley physics in monolayers V2Te2O, V2STeO, V2SSeO, and V2S2O, suggesting their great potential for valleytronics,…

This work reports high carrier mobilities and growth rates simultaneously in low unintentionally doped (UID) (1015 cm−3) metalorganic chemical vapor deposition (MOCVD)-grown thick β-Ga2O3 epitaxial drift layers, with thicknesses reaching up to 6.3 μm, using triethylgallium (TEGa) as a precursor. Record-high room temperature Hall mobilities of 187–190 cm2/V s were measured for background carrier density values of 2.4–3.5 × 1015 cm−3 grown at a rate of 2.2 μm/h. A controlled background carrier density scaling from 3.3 × 1016 to 2.4 × 1015 cm−3 is demonstrated, without the use of intentional dopant gases such as silane, by controlling the growth rate and O2/TEGa ratio. Films show smooth surface morphologies of 0.8–3.8 nm RMS roughness for film thicknesses of 1.24–6.3 μm. Vertical Ni Schottky barrier diodes (SBDs) fabricated on UID MOCVD material were compared with those fabricated on hydride vapor phase epitaxy material, revealing superior material and device characteristics. MOCVD SBDs on a 6.3 μm thick epitaxial layer show a uniform charge vs depth profile of ∼ 2.4 × 1015 cm−3, an…

Magnon, the quanta of spin waves, can serve as an efficient spin information carrier for memory and logic applications, with the advantages of the Joule-heating free induced low power-dissipation property and the phase-coherent induced quantum phenomena. In analogy to spintronics, magnonics focuses on the excitation, detection, and manipulation of magnons (spin waves). In recent years, with the development of nanotechnology, abundant magnonic phenomena emerge in the nanoscale, such as the spin Seebeck effect, magnon-mediated electric current drag effect, magnon valve effect, magnon junction effect, magnon resonant transimission, magnon transfer torque, spin wave propagation, subterahertz spin wave excitation, magnon Bose–Einstein condensation, and so on. Here, we review the recent progresses in magnonics from physics, materials to devices, shedding light on the future directions for magnonics.

Quantum key distribution, which ensures information-theoretically secret key generation, is currently advancing through photonic integration to achieve high performance, cost reduction, and compact size, thereby facilitating the large-scale deployment. Continuous-variable quantum key distribution is an attractive approach for photonic integrations due to its compatibility with off-the-shelf optical communication devices. However, its chip-based systems have encountered significant limitations primarily related to the shot-noise-limited receiver design, which demands low noise, wide bandwidth, high clearance, and well stability. Here, we report the implementation of a real local oscillator continuous-variable quantum key distribution system with an integrated silicon photonic receiver chip. Thanks to the well-designed chip-based homodyne detectors with a bandwidth up to 1.5 GHz and a clearance up to 7.42 dB, the transmission distance of the system has been extended to 28.6 km, achieving a secret key generation rate of Mbps level. This technological advancement enables the quantum key…

Self-powered deep ultraviolet (DUV) photodetectors (PDs) have attracted considerable attention in environmental, industrial, and military fields because of their power-independent and environmentally sensitive photodetection. However, DUV PDs based on traditional thin film structures are limited by the low intrinsic mobility of aluminum-gallium nitride (AlGaN) and the large barrier width of the heterogeneous structure, which makes it difficult to achieve efficient spontaneous separation, resulting in lower responsiveness and a slow response speed. Herein, a 2D/3D DUV PD based on the MXene, niobium carbide (Nb2CTx)/AlGaN van der Waals heterojunctions (vdWHs) has been proposed. The as-prepared DUV PDs revealed self-powered properties with a high responsivity of 101.85 mA W−1, as well as a fast response (rise/decay time of 21/22 ms) under 254 nm DUV illumination, thanks to the excellent electrical conductivity and tunable work function of the MXene. It also showed a large linear dynamic range of 70 dB under −2 V bias because of the strong DUV absorption of MXene/AlGaN vdWH, and the…

We report on metalorganic chemical vapor deposition (MOCVD) growth of controllably Si-doped 4.5 μm thick β-Ga2O3 films with electron concentrations in the 1015 cm−3 range and record-high room temperature Hall electron mobilities of up to 200 cm2/Vs, reaching the predicted theoretical maximum room temperature phonon scattering-limited mobility value for β-Ga2O3. Growth of the homoepitaxial films was performed on Fe-doped (010) β-Ga2O3 substrates at a growth rate of 1.9 μm/h using TEGa as the Gallium precursor. To probe the background electron concentration, an unintentionally doped film was grown with a Hall concentration of 3.43 × 1015 cm−3 and Hall mobility of 196 cm2/Vs. Growth of intentionally Si-doped films was accomplished by fixing all growth conditions and varying only the silane flow, with controllable Hall electron concentrations ranging from 4.38 × 1015 to 8.30 × 1015 cm−3 and exceptional Hall mobilities ranging from 194 to 200 cm2/Vs demonstrated. C-V measurements showed a flat charge profile with the ND+–NA− values correlating well with the Hall-measured electron…

Phase transitions in metastable α-, κ(ε)-, and γ-Ga2O3 films to thermodynamically stable β-Ga2O3 during annealing in air, N2, and vacuum have been systematically investigated via in situ high-temperature x-ray diffraction (HT-XRD) and scanning electron microscopy (SEM). These respective polymorphs exhibited thermal stability to ∼471–525 °C, ∼773–825 °C, and ∼490–575 °C before transforming into β-Ga2O3, across all tested ambient conditions. Particular crystallographic orientation relationships were observed before and after the phase transitions, i.e., (0001) α-Ga2O3 → (2¯01) β-Ga2O3, (001) κ(ε)-Ga2O3 → (310) and (2¯01) β-Ga2O3, and (100) γ-Ga2O3 → (100) β-Ga2O3. The phase transition of α-Ga2O3 to β-Ga2O3 resulted in catastrophic damage to the film and upheaval of the surface. The respective primary and possibly secondary causes of this damage are the +8.6% volume expansion and the dual displacive and reconstructive transformations that occur during this transition. The κ(ε)- and γ-Ga2O3 films converted to β-Ga2O3 via singular reconstructive transformations with small changes in…

High-entropy oxides (HEOs) with a multi-cation structure have attracted significant attention in the fields of electrochemistry owing to their high entropy stability and cocktail effect. However, there has been very limited research on the use of HEO in the field of sensing. In this work, we utilized FeCoNiCrMn high-entropy alloys as the precursor to synthesize (FeCoNiCrMn)3O4 HEO and investigated their crystal structure, microscopic morphology, elemental valence state information, and gas sensing performance. The sensor exhibited decent response to NO2 at room temperature (RT) without any modification or sensitization methods. To verify the gas sensing mechanism, we simulated the interaction between five metal elements in HEO and the NO2 molecules by density functional theory, which reveals a crucial synergistic effect from the multiple cations to enhance the adsorption and charge transfer of NO2 molecules. This work explores the application potential of (FeCoNiCrMn)3O4 in low-power gas sensors and enriches the material selection for RT sensors.

In this work, the single-event burnout (SEB) mechanism of p-GaN gate AlGaN/GaN HEMTs has been studied systematically. The irradiation experiment was carried out based on Ta ions with high linear energy transfer of 75.4 MeV/(mg/cm2), a standard criterion for commercial space applications. It is clearly observed that both the drain current and gate current increase during the irradiation. With the increasing drain bias, the device burns out eventually. Technology computer-aided design simulation was used to explore the possible burnout mechanism. The local high electric field peak induced by the electron and hole redistribution was proposed to explain the permanent damage. When heavy ions impact the device, electron–hole pairs are formed. With the aid of a horizontal electric field across the channel, electrons and holes move toward the drain and gate, respectively. The accumulation of electrons and holes around the drain edge and gate edge induces the local high electric field, which is even higher than the intrinsic breakdown electric field of GaN and AlGaN. The scanning electron…

To enhance the electron mobility in quantum-well high-electron-mobility transistors (QW HEMTs), we investigate the transport properties in AlN/GaN/AlN heterostructures on Al-polar single-crystal AlN substrates. Theoretical modeling combined with experiment shows that interface roughness scattering due to high electric field in the quantum well limits mobility. Increasing the width of the quantum well to its relaxed form reduces the internal electric field and scattering, resulting in a binary QW HEMT with a high two-dimensional electron gas (2DEG) density of 3.68×1013 cm–2, a mobility of 823 cm2/Vs, and a record-low room temperature (RT) sheet resistance of 206 Ω/□. Further reduction of the quantum well electric field yields a 2DEG density of 2.53×1013 cm–2 and RT mobility > 1000 cm2/V s. These findings will enable future developments in high-voltage and high-power microwave applications on the ultrawide bandgap AlN substrate platform.

Transparent conductive oxide (TCO) films are crucial in optoelectronic devices, such as photodetectors, due to their unique blend of transparency and electrical conductivity. ZnO is a top choice for TCOs owing to its excellent properties, non-toxicity, and cost-effectiveness. In this work, we explore the potential of carbon doping to enhance the electrical properties of ZnO films for transparent conductive applications. Our findings reveal that C-doped ZnO (ZnO:C) films retain the pristine high quality and surface morphology despite an increase in defects with higher C doping. Notably, C doping does not compromise the visible light transmittance of ZnO films, while inducing a gradual increase in optical bandgap, indicative of the typical Burstein–Moss effect. As carbon doping increases, the ZnO:C films exhibit improved carrier concentration, lower resistivity, and sustained high mobility, achieving optimal performance with an electron concentration of 3.73 × 1019 cm−3, resistivity of 3.69 × 10−3 Ω cm, and mobility of 46.08 cm2 V−1 s−1. Finally, we utilized ZnO:C films as a…

Potassium-ion batteries (PIBs) have emerged as promising candidates for cost-effective and sustainable energy-storage systems. Nevertheless, limited by the large K+ radius, PIBs have great difficulty in figuring out and designing suitable host materials. Herein, a suitable cathode material K3V2(PO4)2O2F (KVPOF) for PIBs has been carefully prepared. It exhibits a high specific capacity close to the theoretical value, 116.3 mAh/g at 20 mA/g within the voltage window of 2.0–4.5 V vs K+/K, corresponding to a de-/intercalation process of ∼2 mol K+ per formula unit. In addition, it presents an average operating voltage plateau of about 3.5 V, resulting in an energy density of about 410 Wh/kg. The crystal structure and phase transition are revealed by in situ x-ray diffraction, and the structure is found to be fully reversible during the de-/intercalation of K+. Furthermore, the potential of KVPOF cathode for applications at low temperatures was explored, and the full cell matched with graphite anode demonstrated fair electrochemical performance. The experimental results suggest the…

The high increase in interface density has become the main bottleneck for heat dissipation in gallium nitride/aluminum nitride (AlN)/silicon carbide (SiC) based nanodevices. In this paper, the interfacial thermal conductance (ITC) of AlN/SiC interface is investigated by non-equilibrium molecular dynamics simulation. It is found that introducing amorphous layers at AlN/SiC interface will result in an enhancement of its ITC by 2.32 times. Three different amorphous layers are investigated and can be achieved by fast thermal annealing. Among them, the amorphous SiC layers work best, and the amorphous AlN layers work worst. Further spectral analysis reveals that the enhancement of ITC comes from the strengthening of interfacial inelastic phonon processes, which boosts the transport of modes at a wide frequency range. What is more, as the thickness of amorphous layers increases, the enhancement of ITC weakens. This research provides a highly operational strategy to enhance ITC and enriches our understanding of inelastic phonon process at interface.

All-inorganic perovskite quantum dots (PeQDs) have aroused great research interest in white light-emitting diodes (WLED) due to their excellent optoelectronic properties, but the poor stability, caused by dynamically binding long-chain capping ligands, hinders their future practical applications. To address this issue, here, we exploit short-chain butyric acid (BA) to replace long-chain oleic acid (OA) as capping ligand of CsPbX3 PeQDs by a hot-injection method. The addition of BA not only makes the morphology of CsPbBr3 PeQDs uniform and improves the crystallinity but also effectively suppresses nonradiative recombination, achieving a near unit photoluminescence quantum yield of 96%. The BA capped CsPbBr3 PeQDs exhibit high stability up to 180 d stored in ambient environment and also significantly improved resistance against polar solvent, ultra-violet lamp irradiation, and heat, which is rationalized by the strong binding capacity and shortened distance of BA to the PeQDs through ab initio calculations. Furthermore, by combining green-emission CsPbBr3 and red-emission…

α -MnTe is an antiferromagnetic semiconductor with above room temperature TN = 310 K, which is promising for spintronic applications. Recently, it was reported to be an altermagnet, containing bands with momentum-dependent spin splitting; time-resolved experimental probes of MnTe are, therefore, important both for understanding novel magnetic properties and potential device applications. We investigate ultrafast spin dynamics in epitaxial MnTe(001)/InP(111) thin films using pump-probe magneto-optical measurements in the Kerr configuration. At room temperature, we observe an oscillation mode at 55 GHz that does not appear at zero magnetic field. Combining field and polarization dependence, we identify this mode as a magnon, likely originating from inverse stimulated Raman scattering. Magnetic field-dependent oscillations persist up to at least 335 K, which could reflect coupling to known short-range magnetic order in MnTe above TN. Additionally, we observe two optical phonons at 3.6 and 4.2 THz, which broaden and redshift with increasing temperature.

This Letter demonstrates a high-performance 3.3 kV-class β-Ga2O3 vertical heterojunction diode (HJD) along with an investigation into its off-state leakage mechanism. The vertical β-Ga2O3 HJD with field plate assisted deep mesa (FPDM) termination was fabricated using a self-aligned technique to etch the deep mesa to a depth of 9 μm, thereby reducing electric field crowding at the anode edge. In addition, a thick dielectric is deposited to fill the trench, facilitating the utilization of a field plate to further reduce the electric field at the anode edge. TCAD (Technology Computer Aided Design) simulations show significant suppression of electric field crowding at the anode edge. The fabricated HJD exhibits a high current swing of ∼1010 over a temperature range from 25 °C to 175 °C. The specific on-resistance (Ron,sp) is extracted to be 3.9 mΩ cm2, and the breakdown voltage is 3.42 kV with the FPDM termination. These conduction and blocking characteristics lead to a high power figure of merit of 3 GW/cm2, which is one of the highest among multi-kilovolt β-Ga2O3 diodes. Furthermore,…

Beta gallium oxide (β-Ga2O3)-based semiconductor heterojunctions have recently demonstrated improved performance at high voltages and elevated temperatures and are, thus, promising for applications in power electronic devices and harsh environment sensors. However, the long-term reliability of these ultra-wideband gap (UWBG) semiconductor devices remains barely addressed and may be strongly influenced by chemical reactions at the p–n heterojunction interface. Here, we experimentally demonstrate operation and evaluate the reliability of Cr2O3:Mg/β-Ga2O3 p–n heterojunction diodes during extended operation at 600 °C, as well as after 30 repeated cycles between 25 and 550 °C. The calculated pO2-temperature phase stability diagram of the Ga-Cr-O material system predicts that Ga2O3 and Cr2O3 should remain thermodynamically stable in contact with each other over a wide range of oxygen pressures and operating temperatures. The fabricated Cr2O3:Mg/β-Ga2O3 p–n heterojunction diodes show room-temperature on/off ratios >104 at ±5 V and a breakdown voltage (VBr) of −390 V. The leakage current…

The widespread interest in high entropy alloy nanostructures stems from their potential utilization in a variety of technological and scientific fields. This study presents an innovative approach employing a one-step metal organic chemical vapor deposition to synthesize quinary high entropy alloy (CoNiFeCuV-C) core-shell nanoparticles designed for microwave absorption applications. Superior microwave absorption performance is attained through the optimization of conduction loss via thermal treatment, coupled with the interfacial polarization across the interfaces between CoNiFeCuV cores and C shell. The paraffin composite filled with an optimal 20% content of CoNiFeCuV-C core-shell nanoparticles demonstrates a minimal reflection loss (RLmin) of −51.8 dB at 13.76 GHz, achieving this performance with a thickness of 2.2 mm. Moreover, the absorbing bandwidth spans 7.44 GHz at a thickness of 2.4 mm. The outstanding accomplishments underscore the potential of utilizing CoNiFeCuV-C core-shell nanoparticles as a promising choice for lightweight, effective microwave absorber material.

A transparent pn junction comprising CuCrO2/Ba(Ti0.2Zr0.2Sn0.2Hf0.2Ce0.2)O3/WO3 was synthesized using a sol-gel-hydrothermal-annealing method. The CuCrO2/BaTiZrSnHfCe/WO3 achieves a transmittance of ∼83%–88%, with photovoltaic enhancement of ∼4.0 × 103-folds compared to the intrinsic device [photovoltaic conversion efficiency (PCE) of ∼1.22%], and it also demonstrates good stability over 5 months. This is mainly attributed to the BaTiZrSnHfCe HEO solid solution. In addition to an appropriate Fermi level/high QY, the BaTiZrSnHfCe HEO, with carrier inducing/injecting/driving by synergism of high entropy lattice distortion and charge compensation, can improve kinetic equilibrium for achieving PCE-transparency while increasing holes via Cu vacancies/interstitial oxygen. Moreover, inorganic CuCrO2, BaTiZrSnHfCe HEO, and WO3 maintain good structural stability, indicating promising applications for CuCrO2/BaTiZrSnHfCe/WO3 in optoelectronic devices.

The importance of higher-order anharmonic effects on thermal transport has recently been demonstrated in highly symmetrical 2D materials with large acoustic–phonon (A–O) gap. However, the phonon scattering and the thermal transport properties in low-symmetry structures remain ambiguous. In this work, we employed moment tensor potential and Boltzmann transport equation to investigate phonon thermal transport properties of 1T′-ReS2 and 2H-WS2. We show that the mechanism of four-phonon scattering in 1T′-ReS2 is quite different from that in 2H-WS2. In 1T′-ReS2, the four-phonon scattering can reduce the thermal conductivity by up to 40.29%, even in the absence of an acoustic-optical phonon bandgap. The strong four-phonon scattering in 1T′-ReS2 is attributed to A–O phonon scattering mediated by abundant flattening optical phonon modes. However, in 2H-WS2, the strong four-phonon scattering is attributed to the presence of a large A–O phonon bandgap. Our work suggests that considering the four-phonon scattering is essential for calculating the thermal conductivity of 2D materials, even in…

Rutile germanium dioxide (r-GeO2) has been identified as an ultrawide bandgap semiconductor recently, featuring a bandgap of 4.68 eV—comparable to Ga2O3—but offering bipolar dopability, higher electron mobility, higher thermal conductivity, and higher Baliga figure of merit (BFOM). These superior properties position GeO2 as a promising material for various semiconductor applications. However, the epitaxial growth of r-GeO2, particularly in its most advantageous rutile polymorph, is still at an early stage. This work explores the growth of r-GeO2 using metal-organic chemical vapor deposition (MOCVD) on an r-TiO2 (001) substrate, utilizing tetraethyl germane as the precursor. Our investigations reveal that higher growth temperatures significantly enhance crystalline quality, achieving a full width at half maximum of 0.181° at 925 °C, compared to 0.54° at 840 °C and amorphous structures at 725 °C. Additionally, we found that longer growth durations increase surface roughness due to the formation of faceted crystals. Meanwhile, adjusting the susceptor rotation speed from 300 to 170 RPM…

Photoelectric synaptic devices as a combination of electronic synapse and photodetector are considered as emerging bio-inspired device technologies. These devices have immense potential to conquer the bottleneck of von Neumann architecture based traditional computing systems. In this Letter, we propose an all-oxide based photoelectric neuro-synaptic resistive random access memory device with the structure of ITO/Ga2O3/ZnO/ITO/Glass, in which the conductance states are reversibly tuned by two different wavelengths (405/522 nm) of visible light spectrum. The strength of light pulse is altered to investigate the learning and forgetting phases of the photoelectric response of the device. A basic biomimetic function “learning-forgetting-rehearsal” behavior is imitated up to 20 cycles. Moreover, emulation of some typical synaptic functions such as associative learning and switching between short and long term plasticities indicate the wavelength awareness of the device. Based on the pure optically induced potentiation/depression characteristics, convolutional neural network simulation…

High-refractive-index nanostructures offer versatile opportunities for nonlinear optical effects, due to their ability to strongly confine field into a subwavelength scale. Herein, we propose a rhomboidal amorphous silicon metasurface to realize high-efficiency dual-band third-harmonic generation (THG), based on the supported dual quasi-bound states in the continuum (Q-BICs). Owing to the very large field confinement inside the metasurface empowered by Q-BICs, the THG efficiency up to 3.74 × 10−3 with the peak pump intensity of 30 MW/cm2 is observed. Meanwhile, thanks to the very high quality factor of Q-BICs, the ultra-narrow nonlinear process with the full width at half maximum less than 1 nm is also witnessed, suggesting the good monochromaticity. Interestingly, the dual-band THG is verified to be polarization-dependent and polarization-insensitive, respectively. The finite element method simulations exhibit that the polarization-dependent THG is attributed to the Q-BIC driven by the electric quadrupole characterized by a pair of anti-parallel electric dipoles along the x axis,…

The basic requirements for lithium-ion batteries in the field of electric vehicles are fast charging and high energy density. This will enhance the competitiveness of electric vehicles in the market while reducing greenhouse gas emissions and effectively preventing environmental pollution. However, the current lithium-ion batteries using graphite anodes cannot achieve the goal of fast charging without compromising electrochemical performance and safety issue. This article analyzes the mechanism of graphite materials for fast-charging lithium-ion batteries from the aspects of battery structure, charge transfer, and mass transport, aiming to fundamentally understand the failure mechanisms of batteries during fast charging. In addition, we review and discuss recent advances in strategies for optimizing fast-charging performance and summarize current improvement methods in graphite electrodes, electrolytes, battery structures, and charging algorithms. Moreover, the challenges and promising concepts for developing future fast-charging graphite anode are emphasized. This review is of…

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that…

Wurtzite ferroelectrics are an emerging material class that expands the functionality and application space of wide bandgap semiconductors. Promising physical properties of binary wurtzite semiconductors include a large, reorientable spontaneous polarization, direct band gaps that span from the infrared to ultraviolet, large thermal conductivities and acoustic wave velocities, high mobility electron and hole channels, and low optical losses. The ability to reverse the polarization in ternary wurtzite semiconductors at room temperature enables memory and analog type functionality and quasi-phase matching in optical devices and boosts the ecosystem of wurtzite semiconductors, provided the appropriate combination of properties can be achieved for any given application. In this article, advances in the design, synthesis, and characterization of wurtzite ferroelectric materials and devices are discussed. Highlights include: the direct and quantitative observation of polarization reversal of ∼135 μC/cm2 charge in Al1−xBxN via electron microscopy, Al1−xBxN ferroelectric domain patterns…

Bound state in the continuum (BIC), generally realized by structures with in-plane symmetry, has been under the spotlight in the control of the electromagnetic field. This Letter presents a terahertz metasurface that possesses broken in-plane symmetry for exciting BIC. The switch from a BIC to a quasi-BIC can be achieved through parameter modulation. According to multipolar decomposition, the BIC is constructed by the destructive interference of far-field radiation originating from the electric dipole and magnetic quadrupole. More importantly, considering that the metal material has finite conductivity, we analyze the relationship between radiation and non-radiation losses, based on the time domain coupled mode theory, which provides substantial theoretical support for the investigation of BIC phenomena. Furthermore, the proposed metasurface exciting quasi-BIC is highly sensitive to the changes in the dielectric environment, resulting in a high sensitivity of 135 GHz/RIU and a distinction between sucrose and glucose with the same solid content. As a result, our research provides a…

Diagnostic assays utilizing fluorescent reporters in the context of low abundance biomarkers for cancer and infectious disease can reach lower limits of detection through efficient collection of emitted photons into an optical sensor. In this work, we present the rational design, fabrication, and application of one-dimensional photonic crystal (PC) grating interfaces to accomplish a cost-effective prism-free, metal-free, and objective-free platform for augmentation of fluorescence emission collection efficiency. Guided mode resonance (GMR) of the PC is engineered to match the laser excitation (532 nm) and emission maximum (580 nm) of the radiating dipoles to arrive at optimized conditions. The photo-plasmonic hybrid nano-engineering using silver nanoparticles presented >110-fold steering fluorescence enhancement enabling placement of the sample between the excitation source and detector that are in a straight line. From the experimental and simulation inferences, we propose a radiating GMR model by scrutinizing the polarized emission properties of the hybrid substrate, in accordance…

In this work, we manifest that the epitaxial structure for p-GaN gate high-electron-mobility transistor is a versatile platform to develop electronics for operating in an extremely wide temperature range (X-WTR) from 2 to 675 K, with comprehensive X-WTR studies on device operation and circuit behaviors. The key enabler for the high-temperature operation is the wide bandgap that substantially suppresses the thermal excitation of the intrinsic carrier. However, for the low-temperature side, the two-dimensional electron and hole gas (2DEG and 2DHG) channels at the heterojunctions are formed by the temperature-insensitive polarization fields, which free the carriers from freezing out. The monolithically integrated GaN n-FET, p-FET, and the resultant complementary circuits are, therefore, shown to operate in X-WTR.

A self-cleaning transparent pn junction in perovskite SrTiO3 QDs modified CuGaO2/Zn2SnO4 nanoarrays is prepared via the hydrothermal-solgel-surface plasma (SP) method. The CuGaO2/SrTiO3 QDs/Zn2SnO4 exhibits transmittance of ∼85%–90%, photovoltaic enhancement of ∼1.8 × 103-folds (photovoltaic conversion efficiency of ∼1.25%), stable output in 5 months, and good hydrophobicity (contact angle of ∼138.1°). The main reasons are mainly attributed to the SrTiO3 QDs and SP modification; besides the appropriate Fermi level and high quantum yield can improve the carrier kinetic equilibrium for balancing transparency-photovoltaic conversion efficiency, the SP modification can enhance the solar and carrier efficiency further, meanwhile achieving self-cleaning. Additionally, the CuGaO2 orderly nanoarrays can release stress, increase solar efficiency, and promote carrier transportation, in order to balance the structural stability, transparency, and photovoltaic efficiency.

In this work, we propose combining a low work function anode metal and junction barrier Schottky structure to simultaneously achieve low turn-on voltage (Von) and high breakdown voltage (BV), which alleviates the dilemma that high BV requires high Schottky barrier height (SBH) and high Von. Molybdenum (Mo) is used to serve as the anode metal to reduce the SBH and facilitate fast turn-on to achieve a low Von. To resolve the low SBH related low BV issue, a p-NiO/n-Ga2O3-based heterojunction structure is used to enhance β-Ga2O3 sidewall depletion during the reverse state to improve the BV. With such a design, a low Von = 0.64 V(@1A/cm2) and a high BV = 2.34 kV as well as a specific on-resistance (Ron,sp) of 5.3 mΩ cm2 are demonstrated on a 10 μm-drift layer with a doping concentration of 1.5 × 1016 cm−3. β-Ga2O3 JBS diodes with low Von = 0.64 V and a power figure of merit of 1.03 GW/cm2 show great potential for future high-voltage and high-efficiency power electronics.

Strong coupling between photons and excitons gives rise to Rabi splitting and hybridized states. These exhibit spectral anticrossing behavior and ultrafast energy exchange, demonstrating remarkable nanophotonic properties and offering exciting application possibilities. Herein, we propose a metasurface based on dimeric MoTe2 nanodisks for flexible control of the strong coupling between quasi-bound states in the continuum (QBIC) and excitons in the near-infrared region. It was found that introducing a gap perturbation transforms the BIC into a QBIC with a stable resonance wavelength, and the gap width can be used to customize its Q-factor. We confirmed that the upper limit of the Q-factor for achieving strong coupling is 500 in this QBIC metasurface system. It is noted that the wavelength of the QBIC mode and exciton peak are stable, so the coupling strength can be easily adjusted using the disturbance parameters. Moreover, significant Rabi splitting and typical anticrossing behavior were observed when the thickness and radius of the dimeric MoTe2 nanodisks were varied. The Rabi…

The development of dual-polarization irreversible radiators that can operate without external magnetic field is an arduous task. To avoid the need of strong magnetic field, a dual-polarization nonreciprocal thermal radiator with the introduction of Weyl semimetal is demonstrated. It consists of cross-shaped silicon nanopores, Weyl semimetal, and Ag reflective layer. The simulation results show that the proposed radiator offers both TE- and TM-polarized strong irreversible radiation with an incident angle of 1.6°. The TE-polarized absorptivity and TM-polarized emissivity are 98.8% and 97.6%, respectively. The dual-polarization nonreciprocity exceeds 80%. The physical principle is explained by the electric field energy distribution and impedance matching theory. The demonstrated scheme and radiator have potential application in dual-polarization multi-band irreversible radiation and thermal management.

Despite its importance, a sophisticated theoretical study of thermal conductivity in bulk h-BN has been lacking to date. In this study, we predict thermal conductivity in bulk h-BN crystals using first-principles predictions and the Boltzmann transport equation. We consider three-phonon (3ph) scattering, four-phonon (4ph) scattering, and phonon renormalization. Our predicted thermal conductivity is 363 and 4.88 W/(m K) for the in-plane and out-of-plane directions at room temperature, respectively. Further analysis reveals that 4ph scattering reduces thermal conductivity, while phonon renormalization weakens phonon anharmonicity and increases thermal conductivity. Eventually, the in-plane and out-of-plane thermal conductivities show intriguing ∼T−0.627 and ∼T−0.568 dependencies, respectively, far deviating from the traditional 1/T relation.

In this paper, top-gate thin-film transistors (TFTs) of two stacked double-channel layers derived from atomic layer deposition in combination with the plasma-enhanced chemical vapor deposition (PECVD) process were fabricated. The Hall measurement shows that the Hall mobility of the indium gallium oxide (IGO)/indium gallium zinc oxide (IGZO) active layer is 1.6 times more that of the amorphous In-rich IGZO/IGZO layer due to superior carrier percolation conduction paths from the polycrystalline IGO layer. Furthermore, x-ray photoelectron spectroscopy analysis indicates that the IGO/IGZO film has much less oxygen vacancy concentration, which is advantageous in improving not only mobility but also stability. The optimized IGO/IGZO TFT showed both high mobility (38.0 cm2 V−1 s−1) and high stability (ΔVTH = +0.14 V) of a positive bias stress under post-deposition annealing at 250 °C. This strategy provides a feasible process for realizing high-performance TFTs that is compatible with ALD-derived oxides and commercial PECVD techniques in the industry.

Neuromorphic computing can transcend the existing performance-limiting conventional computing architectures (i.e., von Neumann paradigm) by designing biologically inspired devices with intelligence capabilities. Optically stimulated synaptic devices have recently emerged as an alluring direction in neuromorphic computing due to their combined sensing, memory, and computing functions. This study introduces a new two-terminal optically stimulated synaptic device based on an amorphous Ga2O3/GaN heterostructure. This III-nitride-compatible device exhibits persistent photoconductivity at broad ultraviolet wavelengths, enabling it to mimic essential biological synapse functions, including pair-pulse facilitation, short-term plasticity (STP), long-term plasticity (LTP), and STP-to-LTP transition. Furthermore, memory and learning capabilities are achieved in this device, with an ultralow energy consumption of 0.05 pJ per synaptic event, comparable to the human brain. This work presents a CMOS-compatible nitride synapse, suggesting potential applications in low-power computing.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) semiconductors are considered to be promising candidates for extending Moore's law. 2D TMDs with tunable wrinkled nanostructures can effectively modulate their optoelectronic properties. However, the controlled synthesis of large-area TMDs wrinkled nanostructures remains a major challenge. In this work, 2D WSe2 wrinkled nanostructures were prepared on soda-lime glass substrate by ambient pressure chemical vapor deposition based on the thermal mismatch-induced strategy. WSe2 wrinkled nanostructures can be further precisely controlled by adjusting the growth temperature and substrate thickness. In addition, the growth mechanism of WSe2 wrinkled nanostructures was revealed according to systematic experimental characterization. Corresponding results indicate that the photoluminescence and surface potential of WSe2 were associated with wrinkled nanostructures. The controllable synthesis strategy of 2D WSe2 wrinkled nanostructures has been developed, which can provide important experimental and theoretical support for exploring…

The spatial anisotropic arrangement of magnetic particles is expected to increase the magnetic resonance frequency of magnetic particles and optimize the magnetic loss. Herein, helical carbon nanocoils were used as a chiral template to induce the spatial spiral distribution of Fe3O4 particles. Meanwhile, a linear control group was constructed with carbon nanofibers as a template. The three-dimensional spiral structure promotes the confined growth and uniform distribution of Fe3O4 particles. Due to the enhanced magnetic property, chiral samples exhibited superior impedance matching compared to linear samples. Experimental tests and theoretical simulation confirm that the spatial anisotropic distribution helps to increase magnetic loss and optimize impedance matching. This work illustrates the important role of chiral structure in improving the magnetic anisotropy of magnetic nanoparticles and provides an effective strategy for optimizing electromagnetic wave dissipation.

The manipulation of valley-dependent properties in two-dimensional (2D) materials is intriguing for developing valleytronics. Using first-principles calculations, we explore valley-dependent properties of Janus SVGeN2 monolayer and reveal large and tunable valley polarization by tensile strain. The SVGeN2 monolayer possesses excellent stability. Furthermore, strain-driven topological magneto-valley phase transitions are predicted for this monolayer, leading to the valley quantum anomalous Hall (VQAH) phenomenon. The VQAH state, which is featured by the coexistence of complete valley polarization and topological phase, is confirmed by sign reversal of Berry curvature and the nontrivial band topology. The calculated magnetic anisotropy energy indicates that the Janus SVGeN2 monolayer possesses a ferromagnetic ground state and in-plane magnetization. Our investigation provides some physical insights into the strain-driven topological phase transition and manipulation of valley-dependent properties to realize giant valley polarization in the Janus 2D magnet.

For the past few decades, structured light has been gaining popularity across various research fields. Its fascinating properties have been exploited for both previously unforeseen and established applications from new perspectives. Crucial to this is the several techniques that have been proposed for both their generation and characterization. On the one hand, the former has been boosted by the invention of computer-controlled devices, which combined with a few optical components allow flexible and complete control of the spatial and polarization degrees of freedom on light, thus enabling a plethora of proof-of-principle experiments for novel and old applications. On the other hand, characterizing light beams is important not only for gaining better insights into light's properties but also for potentially being used as metrics. In this perspective, we thus offer our take on a few key applied research fields where structured light is particularly promising, as well as some pivotal generation and characterization techniques. In addition, we share our vision of where we believe…

This Letter reports the stability of regrown and alloyed Ohmic contacts to AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) for high temperature applications up to 500 °C. Transfer length method (TLM) measurements from 25 to 500 °C in air show that the regrown contacts appear to be stable up to 500 °C during short term (approximately 1 h) testing, while alloyed contacts appear to decrease in contact resistance from 300 to 500 °C though increases in the error bounds due to increase sheet resistance make it difficult to conclude definitely. Additionally, longer term testing shows both technologies remain stable at least up to 48 h at 500 °C, after which the large increase in sheet resistance makes the measurement uncertainty too large to conclude definitively. Advanced microscopy images indicate both the regrown and alloyed contact regions remain structurally intact after prolonged high temperature exposure with no visible degradation in crystallinity or metal composition.

We present a GeSe/SnSe van der Waals heterojunction fabricated using the wet transfer technique. GeSe and SnSe were synthesized via a low-temperature and atmospheric-pressure chemical vapor deposition method. The GeSe/SnSe heterostructure photodetector demonstrates remarkable rectification characteristics, boasting a rectification ratio of 102, along with an exceptionally low dark current, indicating minimal power consumption. Furthermore, it exhibits a broad optical response, spanning from the visible spectrum (450 nm) to the near-infrared (1064 nm). Under 808 nm laser illumination and reverse bias, the device achieves a responsivity of 19.82 A/W, a detectivity of 4.74 × 109 Jones, and an external quantum efficiency of 3048.32%. Notably, the GeSe/SnSe heterojunction photodetector also exhibits self-powered characteristics, with a responsivity of 0.11 mA/W and a detectivity of 5.44 × 106 Jones at zero bias voltage, accompanied by a fast response time of 23/61 ms (rise/fall). These findings underscore the effectiveness of the GeSe/SnSe heterojunction as a strategy for near-infrared…

NiO/Ga2O3 heterojunction diodes have attracted attention for high-power applications, but their high temperature performance and reliability remain underexplored. Here, we report the time evolution of the electrical properties in the widely studied p-NiO/n-Ga2O3 heterojunction diodes and formation of NiGa2O4 interfacial layers at high temperatures. Results of our thermal cycling experiment show an initial leakage current increase which stabilizes after sustained thermal load, due to reactions at the NiO–Ga2O3 interface. High-resolution TEM microstructure analysis of the devices after thermal cycling indicates that the NiO–Ga2O3 interface forms a ternary compound at high temperatures, and thermodynamic calculations suggest the formation of the spinel NiGa2O4 layer between NiO and Ga2O3. First-principles defect calculations find that NiGa2O4 shows low p-type intrinsic doping and hence can serve to limit electric field crowding at the interface. Vertical NiO/Ga2O3 diodes with intentionally grown ∼5 nm thin spinel-type NiGa2O4 interfacial layers show an excellent device ON/OFF ratio of…

The optical and chromatic characteristics of InGaN-based micro-light-emitting diodes (micro-LEDs) grown on silicon substrates with blue, green, and red emissions have been investigated. The red micro-LEDs exhibited a large full-width at half maximum and a strong blueshift upon increasing current density. The 20 μm blue, green, and red micro-LEDs achieve a maximum external quantum efficiency of 8.2% at 2.65 A/cm2, 5.1% at 5 A/cm2, and 0.62% at 0.1 A/cm2, respectively, which is superior to their 8 μm counterparts. The dependences of a color gamut on the temperature and current density of InGaN-based tri-color micro-LEDs can provide guidance for improving the performance of full-color micro-LED displays.

The electrical control of magnetic anisotropy in spintronic devices holds significant promise for various applications but remains challenging. Here, based on first-principles calculations, we demonstrate nonvolatile electrical control of magnetic anisotropy by constructing a van der Waals multiferroic structure comprising a ferromagnetic LaBr2 monolayer (ML) and a ferroelectric In2Se3 ML. By utilizing the electric polarization of the In2Se3 ML, the LaBr2 ML, which exhibits properties of a two-dimensional XY ferromagnet, can transition into an Ising ferromagnet, resulting in a switch in the easy magnetization axis (EMA) from in-plane to out-of-plane directions. Additionally, the LaBr2 ML undergoes a phase transition from a semiconductor to a metallic state, offering potential for logic devices. These remarkable changes in EMA and electronic properties stem from polarization field-induced band bending at the interface and interfacial charge transfer. Our findings not only pave the way for achieving nonvolatile electrical control of magnetic anisotropy in a ferromagnetic LaBr2 ML on a…

In this study, we propose a wind-direction adaptive piezoelectric energy harvester employing a small wing passive control configuration (WDEH-SW) for bidirectional wind energy harvesting. Our design significantly enhances bidirectional wind energy harvesting capabilities, addressing the limitations of traditional wind energy harvesters by modifying the aerodynamic characteristics of the bluff body via small wing rotations. Additionally, we introduce a criterion for determining the impact of wind direction changes on energy harvesting efficiency. Experimental comparisons with conventional galloping-based and vortex-induced vibration-based piezoelectric wind energy harvesters demonstrate the superior performance of the proposed structure. The experiment results indicate that the proposed structure effectively adapts to changes in wind direction, thereby preventing significant decrease or failure in energy harvesting efficiency. Compared to the conventional unidirectional galloping-based wind energy harvester, the proposed structure exhibits a 34.6% increase in 1.63 μW in power output,…

This study investigates the broad-energy-spectrum reactor-neutron irradiation effects on the electrical characteristics of Ni/β-Ga2O3 Schottky barrier diodes (SBDs), where the irradiated neutron fluence was up to 1 × 1016 cm−2. On the one hand, the high neutron fluence of 1016 cm−2 resulted in a reduction in forward current density by two orders of magnitude and an extremely high on-resistance property due to the radiation-generated considerable series resistance in the SBD. On the other hand, the irradiation brought little influence on the Ni/β-Ga2O3 Schottky contact, since the extracted ideality factor and barrier height from temperature-dependent current–voltage (I–V–T) characteristics showed no significant changes after the radiation. Moreover, the capacitance–voltage (C–V) characterization revealed that the net carrier density in the β-Ga2O3 material was only reduced by 25% at the neutron fluence of 1015 cm−2 but a significant reduction by 2–3 orders at 1016 cm−2. Within the neutron fluence range of 2 × 1014 cm−2 up to 1016 cm−2, the carrier removal rates trended to be…

All-dielectric perfect absorbers powered by quasi-bound states in the continuum (-BIC) are of great importance for developing high-performance optoelectronic devices because they provide high Q-factor absorption. However, these structures usually require the addition of metal back reflectors or degenerate critical coupling to achieve high absorption, which often introduces problems such as Joule heat output and sensitivity to geometrical parameters. In this work, we present an all-dielectric high Q-factor metasurface perfect absorber (MPA) with a cell structure consisting of split Si elliptical disks. By adjusting the tilt angle of the gap, the metasurface can excite a single quasi-BIC resonance in a highly reflective background, corresponding to the electric quadrupole (EQ) mode. Due to the asymmetric coupling of the EQ mode, the proposed metasurface easily breaks the 50% absorption limit. At the wavelength of 894.645 nm, the metasurface achieves a perfect absorption of more than 99% and has a Q-factor of up to 1955. In addition, the structure shows excellent tolerance to…

Phase change materials (PCMs) present opportunities for efficient thermal management due to their high latent heat of melting. However, a fundamental challenge for PCM cooling is the presence of a growing liquid layer of relatively low thermal conductivity melted PCM that limits heat transfer. Dynamic phase change material (dynPCM) uses an applied pressure to pump away the melt layer and achieve a thin liquid layer, ensuring high heat transfer for extended periods. This paper investigates heat transfer during dynPCM cooling when the heated surface has extended features made from high thermal conductivity copper (Cu). Using experiments and finite element simulations, we investigate the heat transfer performance of dynPCM paraffin wax on finned Cu surfaces. A total of 102 transient temperature measurements characterize the performance of dynPCM with extended surfaces and compare the performance with other cooling methods including hybrid PCM and air cooling. The study examines the effects of fin geometry, applied power (20–65 W), and pressure (0.97–12.5 kPa). For dynPCM on a finned…

We experimentally demonstrate waveguide and microring resonator (MRR) polarizers by integrating 2D graphene oxide (GO) films onto silicon (Si) photonic devices. The 2D GO films with highly anisotropic light absorption characteristic are on-chip integrated with precise control over their thicknesses and sizes. Detailed measurements are performed for the fabricated devices with different GO film thicknesses, coating lengths, and Si waveguide widths. The results show that a maximum polarization-dependent loss of ∼17 dB is achieved for the hybrid waveguides, and the hybrid MRRs achieved a maximum polarization extinction ratio of ∼10 dB. We also characterize the wavelength- and power-dependent response for these polarizers. The former demonstrates a broad operation bandwidth of over ∼100 nm, and the latter verifies performance improvement enabled by photothermal changes in GO films. By fitting the experimental results with theoretical simulations, we find that the anisotropy in the loss of GO films dominates the polarization selectivity of these devices. These results highlight the…

The advancement of acoustic metamaterials enables the highly efficient absorption of low-frequency noise with a subwavelength structure thickness, but the complexity of these structures often hinders their large-scale practical applications. Here, we propose a straightforward and compact acoustic metamaterial structure composed of Helmholtz resonators with side slits (HRSS) for low-frequency noise absorption. The introduction of side slits not only simplifies the overall structure but also allows for easy adjustment of acoustic characteristics. By adjusting the depth of the resonator within the slit across 25 distinct units, an absorption coefficient above 0.8 is realized from 470 to 930 Hz. This work demonstrates the extensive low-frequency sound absorption capability of HRSS, providing valuable insights into the design of future practical acoustic materials.

The synergistic impact of reverse bias stress and 3 MeV proton irradiation on the β-Ga2O3 p–n diode has been studied from the perspective of the defect in this work. The forward current density (JF) is significantly decreased with the increase in proton irradiation fluence. According to the deep-level transient spectroscopy results, the increase in the acceptor-like trap with an energy level of EC-0.75 eV within the β-Ga2O3 drift layer, which is most likely to be Ga vacancy-related defects, can be the key origin of the device degradation. The increase in these acceptor-like traps results in the carrier concentration reduction, which in turn leads to a decrease in JF. Furthermore, compared with the case of proton irradiation with no bias, the introduction of −100 V electrical stress induced a nearly double decrease in JF. Based on the capacitance–voltage (C–V) measurement, with the support of the electric field, the carrier removal rate increased from 335 to 600 cm−1. Similar to the above-mentioned phenomenon, the trap concentration also increased significantly. We propose a…

Heterogeneous integration of β-Ga2O3 on highly thermal conductive SiC substrate by the ion-cutting technique is an effective solution to break the heat-dissipation bottleneck of β-Ga2O3 power electronics. In order to acquire high-quality β-Ga2O3 materials on SiC substrates, it is essential to understand the influence of the ion-cutting process on the current transport in β-Ga2O3 devices and to further optimize the electrical characteristics of the exfoliated β-Ga2O3 materials. In this work, the high quality of β-Ga2O3/SiC structure was constructed by the ion-cutting process, in which an amorphous layer of only 1.2 nm was formed between β-Ga2O3 and SiC. The current transport characteristics of Au/Pt/Ni/β-Ga2O3 Schottky barrier diodes (SBDs) on SiC were systematically investigated. β-Ga2O3 SBDs with a high rectification ratio of 108 were realized on a heterogeneous β-Ga2O3 on-SiC (GaOSiC) substrate. The net carrier concentration of the β-Ga2O3 thin film for GaOSiC substrate was down to about 8% leading to a significantly higher resistivity, compared to the β-Ga2O3 donor wafer, which…

Exploring efficient and stable long-persistent luminescence (LPL) materials is of great value for promoting their advanced applications. Here, the metal halide CsCdCl3:Mn2+ crystals with tunable afterglow properties and good stability were grown by a facile solution method. Upon ultraviolet excitation, CsCdCl3:Mn2+ crystals exhibited a bright orange emission at 590 nm from the d–d transition of Mn2+ ions. Mn2+ doping concentrations matter for the LPL performance. By optimizing the doping amount of Mn2+, an enhanced afterglow duration up to 12 000 s was achieved, compared with undoped sample, originating from a trap redistribution. The deep traps in CsCdCl3:0.1Mn2+ crystal that provide little contribution to the LPL at room temperature shifted to shallow levels, thus synergistically enhancing the afterglow intensity and duration. Based on the variable afterglow durations by tuning Mn2+ doping concentrations, a multi-dimensional information storage encryption model was designed. This work gives deep understanding in doping effect on the afterglow and provides examples for the…

The presently available commercial photodetectors have a broadband photoresponse and require different external optical filters to block the undesired light outside the detection spectrum window, e.g., near-infrared (NIR) detection. The use of an NIR bandpass has technical limitations in curved or flexible large-area photodetectors, as an NIR bandpass depends critically on the difference in the interference of the optical path in the filter. This work reports the effort to develop a high-performance filter-free organic photodetector (OPD) with a double bulk heterojunction (BHJ) structure. The visible-blind NIR photodetection is realized by eliminating the photocurrent generated in the front visible light-absorbing BHJ optical depletion layer, due to the suppression of electron transport by incorporating a copper thiocyanate-based electron-blocking layer in the OPD. Only excitons generated in the rear NIR-absorbing BHJ contribute to photocurrent in the OPD, thereby achieving visible-blind NIR photodetection. The double BHJ OPD has a high responsivity of 0.38 A/W at 1050 nm and a…

Si-doped β-phase (010) Ga2O3 epi-films with fast growth rates were comprehensively investigated using trimethylgallium (TMGa) as the Ga precursor via metalorganic chemical vapor deposition (MOCVD). Two main challenges facing the MOCVD growth of thick (010) β-Ga2O3 films with fast growth rates include high impurity carbon (C) incorporation and rough surface morphologies due to the formation of imbedded 3D pyramid-shaped structures. In this work, two different categories of oxygen source (high-purity O2 > 99.9999% and O2* with 10 ppm of [H2O]) were used for β-Ga2O3 MOCVD growth. Our study revealed that the size and density of the 3D defects in the β-Ga2O3 epi-films were significantly reduced when the O2* was used. In addition, the use of off-axis (010) Ga2O3 substrates with 2° off-cut angle leads to further reduction of defect formation in β-Ga2O3 with fast growth rates. To suppress C incorporation in MOCVD β-Ga2O3 grown with high TMGa flow rates, our findings indicate that high O2 (or O2*) flow rates are essential. Superior room temperature electron mobilities as high as 110–190…

Lead sulfide (PbS) is widely recognized as a promising n-type thermoelectric material for use in the middle-temperature range. Although it already exhibits favorable electronic and thermal properties, its thermoelectric performance could be further enhanced by addressing the disparity between the light and heavy bands in the conduction band, thereby optimizing electrical transport, and by modifying the strength of its chemical bonds to reduce lattice thermal conductivity. In this study, we demonstrate that introducing just small amounts of antimony (Sb) into PbS generates a unique combination of interstitial and substitutional doping that leads to a significant improvement in both directions. Substitutional doping enhances the degeneracy between the light and heavy bands, increasing carrier mobility. At the same time, interstitial doping introduces a new resonance state near the Fermi level, providing an additional channel for electron transport while boosting carrier concentration. These synergistic effects lead to a marked increase in the power factor of PbS, achieving an average…

The development of manufacturable and scalable integrated nonlinear photonic materials is driving key technologies in diverse areas, such as high-speed communications, signal processing, sensing, and quantum information. Here, we demonstrate a nonlinear platform—InGaP-on-insulator—optimized for visible-to-telecommunication wavelength χ(2) nonlinear optical processes. In this work, we detail our 100 mm wafer-scale InGaP-on-insulator fabrication process realized via wafer bonding, optical lithography, and dry-etching techniques. The resulting wafers yield 1000 s of components in each fabrication cycle, with initial designs that include chip-to-fiber couplers, 12.5-cm-long nested spiral waveguides, and arrays of microring resonators with free-spectral ranges spanning 400–900 GHz. We demonstrate intrinsic resonator quality factors as high as 324 000 (440 000) for single-resonance (split-resonance) modes near 1550 nm corresponding to 1.56 dB/cm (1.22 dB/cm) propagation loss. We analyze the loss vs waveguide width and resonator radius to establish the operating regime for optimal 775–1550…

Liquid droplets on superheated surfaces produce the Leidenfrost effect. This phenomenon might lead to droplet manipulation and control strategies in microfluidics and thermal management. However, Leidenfrost droplets move randomly and irregularly on superheated surfaces and the manufacturing of special surfaces to control Leidenfrost droplet movement poses great challenges. Here, we propose a simple and environment-friendly method to create heterogeneously wetting surface structures to control the spin motion of droplets on superheated brass using femtosecond laser patterning. The water contact angle of the superhydrophobic area on the surface was ∼160°, and the superhydrophilic area showed ∼7°. A z-shaped pattern was fabricated, which segmented the vapor film and influenced gas flow, and it resulted in the spinning of oval-shaped droplets analogous to a spinning egg. We used simulation to explain this phenomenon and also expanded the application of this droplet control in accelerating dissolution of solids and mechanical driving. This study provides the basis for a creative control…

Nonreciprocity has become a research hotspot in the field of thermal radiation. Nonetheless, the majority of current nonreciprocal thermal radiation is confined to TM polarization. This paper introduces a two-dimensional nanograting structure exhibiting strong dual-polarization nonreciprocal thermal radiation. The grating is composed of a GaAs-based periodic nanoarray, a magneto-optic medium layer (InAs), and a metallic reflective layer (Al). The impact of nonreciprocity under different polarizations was investigated using rigorous coupled-wave analysis. Additionally, the magnetic field energy distribution was studied, and an explanation for the observed phenomenon of the device's nonreciprocal thermal radiation was given for both TE and TM polarizations. The present study is expected to contribute insights for the study of nonreciprocal thermal radiation.

Wide and ultrawide bandgap semiconductors, such as GaN, play a crucial role in high-power applications, yet their performance is often constrained by thermal management challenges. In this work, we introduce a high-quality interface between GaN and AlN, prepared through wafer-scale bonding and verified via high-resolution transmission electron microscopy and transport experiments. We experimentally measured the thermal boundary conductance of the GaN–AlN interface, achieving up to 320 MW/m2K at room temperature using an ultrafast optical technique and sensitivity examinations. Non-equilibrium atomistic Green's functions and density functional theory simulations were conducted to model the interface phonon modes and their contributions to thermal transport, demonstrating good agreement with the experimental results from 80 to 300 K. Additionally, we observed a size-dependent effect on the thermal boundary conductance related to the GaN film thickness from 180 to 450 nm, which we attributed to quasi-ballistic thermal transport through molecular dynamics simulations. Our study has…

In this work, chirality in spin-active electronic states is explained clearly to address confusion about chiral effects recently discovered in materials science. We stress that the electronic toroidal monopole G0 can serve as a measure of chirality. By using the symmetry classification in terms of four distinct types of multipole bases, we extend the concept of chirality from materials to physical fields and material-field composites. Additionally, we illustrate specific examples from physics and chemistry that demonstrate the process of acquiring chirality through the combination of seemingly achiral degrees of freedom, which we term the emergence of chirality. Interference between multiple chiralities exhibiting phenomena specific to handedness is also discussed.

Recent advancements in nonreciprocal thermal emitters challenge the conventional Kirchhoff's law, which states that emissivity and absorptivity should be equal for a given direction, frequency, and polarization. These emitters can break Kirchhoff's law and enable unprecedented thermal photon control capabilities. However, current studies mainly focus on increasing the magnitude of the contrast between emissivity and absorptivity, with little attention paid to how the sign or bandwidth of the contrast may be controlled. In this work, we show such control ability can be achieved by coupling resonances that can provide opposite contrasts between emissivity and absorptivity.

Ultrawide bandgap heterojunction p–n diodes with polarization-induced AlGaN p-type layers are demonstrated using plasma-assisted molecular beam epitaxy on bulk AlN substrates. Current–voltage characteristics show a turn-on voltage of Vbi≈5.5 V, a minimum room temperature ideality factor of η≈1.63, and more than 12 orders of current modulation at room temperature. A stable current operation of the ultrawide bandgap semiconductor diode is measured up to a temperature of 300 °C. The one-sided n+–p heterojunction diode design enables a direct measurement of the spatial distribution of polarization-induced mobile hole density in the graded AlGaN layer from the capacitance–voltage profile. The measured average mobile hole density is p∼5.7×1017 cm−3, in close agreement with what is theoretically expected from distributed polarization doping. Light emission peaked at 260 nm (4.78 eV) observed in electroluminescence corresponds to interband radiative recombination in the n+ AlGaN layer. A much weaker deep-level emission band observed at 3.4 eV is attributed to cation-vacancy and silicon…

A grating coupler on 700-nm-thick Z-cut lithium-niobate-on-insulator platform with high coupling efficiency, large bandwidth, and high fabrication tolerance is designed and optimized by inverse design method. The optimized grating coupler is fabricated with a single set of e-beam lithography and etching process, and it is experimentally characterized to possess peak coupling efficiency of −3.8 dB at 1574.93 nm, 1 dB bandwidth of 71.7 nm, and 3 dB bandwidth of over 120 nm, respectively.

A conventional vortex-induced vibration (VIV)-based energy harvester is typically restricted to capturing wind energy from a very limited range of wind directions, making it inefficient in varying wind conditions. This Letter proposes a tri-section beam configuration for VIV-based piezoelectric energy harvester to enable harnessing wind energy from varying incident angle with different vibration modes being triggered. The finite element analysis investigates the tri-section beam harvester's mode shapes and natural frequencies. A wind tunnel experiment is conducted for a comparative study of the energy output performance of the harvesters with straight and tri-section beams. The findings show that the proposed harvester with the tri-section beam can efficiently capture wind energy from a much wider range of incident angles, as opposed to the specific limited directions of its counterpart with the straight beam. The proposed harvester can also widen the lock-in speed range with a higher bending mode being triggered and achieve the optimal output power of 1.388 mW when the proposed…

Electromagnetically induced transparency (EIT), nonlinearity, and optical chirality hold significant applications in many areas such as optical switches, slow-light devices, chiral harmonic conversion, and optical storage. In this work, we theoretically propose an asymmetric all-dielectric metasurface supporting toroidal dipole-quasi-bound states in the continuum (TD-q-BICs). High quality (Q) EIT, strong third harmonic generation (THG), and giant nonlinear chirality are achieved via the extremely enhanced electric field energy localized in the Si plate by the TD-q-BIC. A huge transition from high Q EIT with transmission of ∼0.99 to strong chirality with circular dichroism (CD) of ∼0.9 is realized by tuning the angle and polarization state of incident light. Strong THG with efficiency of 4.5 × 10−3 under linear polarization light is due to the highly localized electric field supported by the TD-q-BIC and perfect nonlinear CD chirality with theoretically value of ∼1 originates from the large discrepancy in electric field distributions under different circularly polarized light. Our…

Resonant nanostructures have emerged as versatile photonic platforms for boosting optical nonlinear responses on a subwavelength scale for their ability to confine intense electromagnetic fields while relaxing the phase-matching requirements. Recent significant advances in this field are associated with the utilization of non-radiative eigenmodes above the light cone, termed bound states in the continuum (BICs), which provide a unique mechanism for light trapping to realize excitation of ultrahigh quality (Q) factor resonances. Nevertheless, the current studies on BICs predominantly focus on symmetry-protected BICs (SP-BICs), whose excitation requires symmetry breaking, and Q factors are limited by fabrication imperfections. Here, we demonstrate a simple and feasible scheme for creating degenerate pairs of mirror-coupled super-BICs by harnessing magnetic dipole resonances coupled to their mirror images in adjacent metal films. Unlike trivial SP-BICs, mirror-coupled BICs showcases the huge enhancement of Q factors and are resilient against fabrication imperfections. By combining…

High-entropy alloy (HEA) superconductors have attracted significant attention due to their exceptional low-temperature mechanical and superconducting properties. We report the synthesis and thorough characterization of an equiatomic HEA superconductor with the composition Sc0.20V0.20Ti0.20Hf0.20Nb0.20, crystallizing in a body-centered cubic crystal structure (Im3m¯). Our investigation, using magnetization, transport, and heat capacity measurements, reveals the presence of weakly coupled, fully gapped superconductivity with a transition temperature of 4.17(3) K and the upper critical field exceeding the Pauli paramagnetic limit. The metallic nature, combined with a high upper critical field, positions it as a promising candidate for applications in superconducting devices.

The advancements in chiroptics have propelled applications beyond traditional optics, expanding its reach into domains such as heat and fluid mechanics. The current research predominantly focused on utilizing plasmonic materials in the photothermal and photofluidic systems. However, these systems face limitations in circular dichroism due to inherent Ohmic loss associated with plasmonic materials. Herein, we introduce the concept of topological polarization singularity in an all-dielectric structure, which supports chiral bound states in the continuum. The introduction of topological polarization singularity gives the structure an impressive chiral light absorption response. The BICs resonant mode achieves a 147-fold field enhancement, significantly improving the photothermal conversion efficiency of dielectric material. Moreover, the g factors of photothermal and optical fluids reach 1.9, approaching the theoretical limit value. Consequently, an exceptionally high degree of circular dichroism is realized in multiple systems including light absorption, photothermal, and photofluidic…

This study investigates the structural, electronic, mechanical, and optical properties of the perovskites Mg3AsX3 (X = F, Cl, Br, I) using DFT and SCAPS-1D. The tolerance factor study shows that these materials are thermodynamically stable. Furthermore, the perovskites Mg3AsF3, Mg3AsCl3, Mg3AsBr3, and Mg3AsI3 exhibit direct bandgaps of 3.48, 2.06, 1.26, and 0.265 eV, respectively, confirming their semiconducting nature. The Mg3AsBr3 stands out for its ductility and excellent optical properties, such as a high dielectric constant and good conductivity, making it ideal for solar cells. Under optimal conditions, the FTO/WS2/Mg3AsBr3/Au structure demonstrated a PCE of 31.70%, with a VOC of 1.08 V, JSC of 36.03 mA/cm2, and a fill factor (FF) of 81.64%. These computational findings suggest that Mg3AsBr3-based perovskites are promising candidates for developing highly efficient, lead-free, durable, and cost-effective solar cells, offering valuable insights for their practical application in renewable energy technologies.

Two-dimensional (2D) materials exhibiting both second-harmonic generation (SHG) and ferroelectric properties are promising candidates for high-performance optoelectronic devices. However, the relationship between SHG response and ferroelectric polarization and bandgap in such materials has not been revealed clearly. Therefore, by using first-principles calculations based on many-body theory, we comprehensively study the structural, electronic, linear and nonlinear (SHG) properties of ferroelectric NbOCl2 monolayer under strain regulation to clarify the influence of ferroelectric polarization (Ps) and bandgap on the SHG coefficient. Our results show a ferroelectric to nonpolar phase transition under compressive strain larger than 5% along the polar direction. Moreover, under strain, the electronic bandgap, optical gap Eo, and SHG coefficient can be modified to a large extent and show different variation tendencies before and after phase transition. Importantly, a volcano relationship between SHG coefficient and a combined parameter (β1 = Ps*Eo) is established. Our findings…

In this paper, the ferroelectric properties of TiN/Ti/Si:HfO2/TiN stacks are shown to be modulated by the Ti oxygen scavenging layer, leading to improved remanent polarization and wake-up at low switching fields. Hard x-ray photoelectron spectroscopy is used to measure the oxygen vacancy (VO) concentration in Si-doped HfO2 based capacitors. This VO engineered ferroelectric stack is then assessed at the wafer scale within 16 kbit 1T-1C FeRAM arrays integrated into 130 nm CMOS. The introduction of a Ti oxygen scavenging layer at the top interface of Si:HfO2-based BEOL-integrated metal/ferroelectric/metal capacitors enhances their ferroelectric (FE) behavior (+100% remanent polarization 2.Pr), confirming the positive role of modest concentrations of VO in orthorhombic phase crystallization at low thermal budgets. It is statistically demonstrated at 16 kbit array level that VO-rich FE Si:HfO2 facilitates 2.5 V FeRAM array operation with improved memory window. The field cycling dependence of the memory window is correlated with the VO concentration, and an endurance of 108 cycles is…

The wurtzite structure is one of the most frequently found crystal structures in modern semiconductors and its inherent spontaneous polarization is a defining materials property. Despite this significance, confusion has been rampant in the literature with respect to the orientation of the spontaneous polarization inside the unit cell of the wurtzite structure, especially for the technologically very relevant III-N compounds (AlN, GaN, and InN). In particular, the spontaneous polarization has been reported to either point up or down for the same unit cell orientation, depending on the literature source—with important implications for, e.g., the carrier type and density expected at interfaces of heterostructures involving materials with the wurtzite structure. This perspective aims to resolve this ambiguity by reviewing available reports on the direction of the energetically preferred polarization direction in the presence of external electric fields as well as atomically resolved scanning transmission electron microscopy images. While we use ferroelectric wurtzite Al1−xScxN as a key…

Power Schottky barrier diodes (SBDs) face an inherent trade-off between forward conduction loss and reverse blocking capability. This limitation becomes more severe for ultra-wide bandgap (UWBG) SBDs due to the large junction field. A high Schottky barrier is usually required to suppress the reverse leakage current at the price of an increased forward voltage drop (VF). This work demonstrates a Ga2O3 junction barrier Schottky (JBS) diode that employs the embedded p-type NiO grids to move the peak electric field away from the Schottky junction, thereby allowing for the use of an ultra-low barrier TiN Schottky contact. This JBS diode concurrently realizes a low VF of 0.91 V (at forward current of 100 A/cm2) and a high breakdown voltage over 1 kV, with the VF being the lowest in all the reported vertical UWBG power diodes. Based on the device characteristics measured up to 200 °C, we further analyze the power loss of this JBS diode across a wide range of operational duty cycles and temperatures, which is found to outperform the TiN/Ga2O3 SBDs or NiO/Ga2O3 PN diodes. These findings…

The dielectric constants (Dk) and dissipation factors (Df) of 11 types of polyimides (PIs) were systematically measured between 25 and 330 GHz using Fabry–Pérot resonators. Herein, the relationships between their frequency dependence and chemical structure are discussed. As the frequency increased, all the PIs exhibited a continuous decrease in Dk and a consistent increase in Df. Notably, no distinct peaks were observed over the entire frequency range. The decrease in Dk with frequency gradually approached the square of the refractive index (n2) in the near-infrared region. Additionally, based on the correlation between the dielectric dispersion and dielectric polarization (Pt), Dk showed a stronger correlation with the electronic polarization (Pe) at higher frequencies than with the dipolar orientational polarization (Pd). Moreover, in fluorine-containing PIs, Dk declined faster with increasing frequency as the fluorine content (F%) increased. Meanwhile, the increase in Df showed a negative correlation with the weight fraction of polar groups (polar%), and the PIs containing –CF3…

The transparent conducting oxide SnO2 is a wide bandgap semiconductor that is easily n-type doped and widely used in various electronic and optoelectronic applications. Experimental reports of the electron mobility of this material vary widely depending on the growth conditions and doping concentrations. In this work, we calculate the electron mobility of SnO2 from first principles to examine the temperature and doping concentration dependence and to elucidate the scattering mechanisms that limit transport. We include both electron–phonon scattering and electron-ionized impurity scattering to accurately model scattering in a doped semiconductor. We find a strongly anisotropic mobility that favors transport in the direction parallel to the c-axis. At room temperature and intrinsic carrier concentrations, the low-energy polar-optical phonon modes dominate scattering, while ionized-impurity scattering dominates above 1018 cm−3.

In the development of any type of magnetic field sensor based on magnetic films, special consideration must be given to the magnetic layer component. The presented work investigates the use of scalable flux closing magnetostrictive multilayers for inverse magnetoelectric sensors. In such a type of magnetic field sensor, highly sensitive AC and DC field detection relies on strong excitation of the incorporated magnetic layers by piezoelectrically driven cantilever oscillation at mechanical resonances. The provoked periodic flux change is influenced by the magnetic field to be measured and is picked up by a coil, which generates the measured output. The multilayered inverse magnetoelectric sensor is investigated with regard to linearity, noise behavior, and detection limit of DC and AC signals. A significant advancement for inverse magnetoelectric thin film sensors is demonstrated in this study. Using exchange bias stabilized magnetic multilayers with flux closure structures, detection limits are improved by an order of magnitude to less than 8 pT/Hz1/2 at 10 Hz and 18 pT/Hz1/2 at DC.

In this work, we report on the high-performance p-GaN/InGaN/AlN multi-heterostructure p-channel metal–semiconductor field effect transistors (MESFETs) with energy-band modulated quantum well-like InGaN channel and low work function metal tungsten (W) as the gate material. A negative threshold voltage (VTH) of −0.35 V is achieved by precisely controlling the self-aligned etching depth at the active region. Benefiting from the enhanced hole confinement, the ION/IOFF ratio and subthreshold swing of the fabricated-channel MESFET are extracted to be 1.2 × 107 and 66 mV/dec, respectively, at room temperature. The idealized Schottky interface with TMAH and post-gate-annealing treatment shows an ultra-low voltage hysteresis of 0.08 V extracted at subthreshold area in the dual-sweep transfer curves.