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Polarization selectivity in single-mode photonic molecule lasers
An efficient approach to achieve single-polarization selectivity in single-mode double microring lasers (photonic molecule lasers) is presented in this study. The fabricated microring lasers achieved polarization extinction ratios of 11.3 dB for TM polarization and −12.8 dB for TE polarization. The fabrication process was conducted by direct laser writing on SU-8 photoresist doped with Rhodamine B dye. In order to obtain an optimum single-mode operation with a specified polarization capability, the study employs Vernier effect double microring lasers and investigates the effects of geometric characteristics, surface scattering loss, and coupling efficiency on polarization performance. The finite-difference time-domain method was utilized to conduct simulations, and the results were verified experimentally. The proposed single-polarized microring lasers provide open possibilities for advanced integrated photonic systems with potential applications in quantum photonics, nonlinear optics, and optical sensors.
A multi-degree-of-freedom model-based method for Young's modulus determination of soft tissue by resonance spectroscopy
Elastic properties of soft tissues are important indicators for disease progression. Previous studies have utilized mechanical resonance spectroscopy to infer elastic properties of soft tissues by extracting their resonance frequencies. However, the method to accurately obtain the elastic modulus from the resonance frequencies remains inconclusive. In this study, we report a method based on a multi-degree-of-freedom (MDOF) model to determine the Young's modulus of soft tissue samples from the measured resonance spectroscopy. Resonance frequencies of agar tissue phantoms with different elastic properties were obtained, and Young's modulus was calculated using the MDOF-based method. The result was validated by mechanical compression tests and finite element method simulations. The results show that the multi-degree-of-freedom (MDOF)-based method is capable of determining Young's modulus of soft tissue samples with various elasticities and dimensions. This study provides an opportunity to accurately assess the elastic properties of small-sized soft tissue samples.
Polymer-integrated optical fiber Fabry–Pérot interferometer with Vernier effect for the detection of myoglobin
Acute myocardial infarction (AMI) is the most severe manifestation of coronary artery disease and one of the leading causes of morbidity and mortality worldwide. The concentration of myoglobin (Mb) in serum has been regarded as an essential indicator for the early diagnosis of AMI. Developing a rapid, sensitive, and accurate Mb detection method is very important for the early diagnosis of AMI. This study reports a fiber optic biosensor based on polymer and Vernier effect composite sensitization for real-time detection of serum Mb concentration. The sensor is made of a Fabry–Pérot interferometer cascade tapered microfiber filled with photothermal material polydimethylsiloxane. Two interference structures with similar but unequal free spectral range are combined, and the superposition spectrum produces periodic interference fringes, forming a fiber sensor with a Vernier effect. By detecting the photothermal signal generated by the absorption of light by Mb, marker-free, specific detection can be achieved. The sensing device attained a sensitivity of 5.235 nm/(mg/L) in the 0.0001–10 mg/L concentration range. The linearity reached 0.9978, with a limit of detection of 3.82 ng/ml, which meets the sensitivity requirements for detecting Mb concentration in serum, and the detection time was less than 40 s, which has potential in the early diagnosis of related diseases.
Preparation and simulation of high-frequency lead-free NBBT/epoxy 1–3 piezoelectric composites with high electromechanical coupling characteristics
In this article, we design and fabricate (1 − x)Na0.5Bi0.5TiO3-xBaTiO3 single-crystal/epoxy 1–3 piezoelectric composites (NBBT 1–3 composites) with high coefficients of electromechanical coupling and demonstrate their considerable potential for use in high-frequency ultrasonic devices. We conducted finite element simulations on samples of the NBBT 1–3 composite to optimize their dimensional parameters. We used the cut-and-fill method to prepare an array of the NBBT-based 1–3 composite with a spacing of 20 μm between elements. It exhibited an exceptionally high coefficient of electromechanical coupling kt of 80.8%, with measured resonant and antiresonant frequencies of 11.6 and 18.5 MHz, respectively. Lead-free NBBT 1–3 composites that can deliver excellent performance are highly promising for use in medical applications of high-frequency ultrasound, especially for the brain–computer interface and intravascular ultrasound imaging.
Gradient-based optimization of spintronic devices
The optimization of physical parameters serves various purposes in device development, including in system identification and efficiency. Spin-torque oscillators have been experimentally and theoretically applied to neuromorphic computing, but their physical parameters are usually optimized via grid search procedures. In this paper, we propose a scheme to optimize the dynamics parameters of macrospin-type spin-torque oscillators using the gradient descent method with automatic differentiation. First, we numerically create dynamic data for teaching and tune the parameters to reproduce the dynamics. This approach can be applied to determine the correspondence between spin-torque oscillator simulations and experiments. Next, we solve an image recognition task with high accuracy by connecting a coupled system of spin-torque oscillators to the input and output layers and training all of them through gradient descent. Combining this approach with experimentation makes it possible to design an experimental setup and physical system to solve a task with high precision using a spin-torque oscillator.
Strain-induced Kramers–Weyl phase in III–V zinc blende systems
We present theoretical observations on the topological nature of strained III–V semiconductors. By k·p perturbation, it can be shown that the strain-engineered conduction band hosts a Kramers–Weyl node at the Γ point. It is theoretically shown that a curated strain can create and then tune the sign of the topological charge. Furthermore, we outline experimental methods for both the realization and detection of strain-induced topological phase transitions.
A highly integrated three-axis vector diamond quantum magnetometer with a compact electrical package
Diamond nitrogen-vacancy (NV) center has been widely studied as a high-sensitivity solid-state quantum sensor with a wide range of applications, including magnetometry, thermometry manometry, and chemical sensing. However, its application in practical scenarios remains challenging due to difficulties of component manufacturing, miniaturization, and integration for NV control and readout. Here, we demonstrate an all-electric driving diamond sensor fabricated using standard microfabrication processes and micro-assembly, achieving integration of five key components—laser diode, diamond, microwave antenna, long pass filter, and photodiode in a hermetically sealed package case, with dimensions of 2.72 cm3. The integrated diamond magnetometer achieved a magnetic sensitivity of 2.25 nT · Hz−1/2. Additionally, the inherent crystallographic axes of the diamond are used to simultaneously detect vector magnetic field signals. The design and fabrication process allows for wafer-level assembly, enabling low-cost mass-production and easy integration with peripheral circuits.
High-frequency magnetic properties of modified Cu–Ni 18H ferrites with low magnetic loss up to 6 GHz for 5G communications
Rapidly developing fifth-generation (5G) communications urgently require a ferrite material with high permeability and low magnetic loss in frequency bands up to 6 GHz. However, none of the present magnetic materials are capable of meeting the requirements of 5G communications because their magnetic properties deteriorate drastically when approaching GHz frequencies. Herein, we report the high-frequency magnetic properties of the modified Ba5Cu2-xNixTi3Fe12O31 (Cu–Ni 18H) ferrites, achieving a relatively high permeability of 1.6 and a low magnetic loss of 0.05 at 6 GHz, which is much better than previous reports. Such excellent performance is attributed to the expanded mono-domain critical size and reduced damping of magnetic moment precession. Moreover, deploying Cu–Ni 18H ferrites as a substrate on a patch antenna working at 6 GHz can reduce the antenna dimensions to 35% of traditional commercial materials. The present work provides a proven and promising candidate material for 5G communications and expands the research landscape for the high-frequency magnetic properties of microwave ferrites.
Retainable large magnetoelectric coupling in BiFeO3@CoFe2O4 core-shell nanoparticle embedded P(VDF-TrFE) matrix
Flexible magnetoelectric composite devices have exceptional features and potential in peculiar scenes. However, maintaining the magnetoelectric response under extreme bending conditions remains a challenge. Polyvinylidene fluoride-based polymers, possessing favorable piezoelectric properties and high flexibility, provide a viable solution for magnetoelectric composites. This work constructed multiferroic core-shell nanoparticle-embedded flexible membranes and achieved a retainable high magnetoelectric (ME) coupling coefficient in the curved composite materials. A maximum ME coefficient of 74 mV cm−1 Oe−1 was obtained, far higher than the 0–3 ME nanocomposites reported thus far. The ME coefficient can be maintained above 40 mV cm−1 Oe−1 when the bending angle is less than 90° and expresses high sensitivity within the Hdc range of 100–2400 Oe. Based on crystal structure analysis and phase-field simulation, the synergy magnetoelectric effects accounting for the multiferroic core-shell nanoparticles, copolymer matrix, and magnetic cores contribute to the promoted ME coefficient in the flexible composites. This work provides a feasible pathway for next-generation flexible devices in the wearable and portable fields.
Realizing sub-6-nm-channel high-performance spin field-effect transistors in lateral Sc2CHO/Sc2CHF/Sc2CHO heterojunctions
In this work, nanoscale spin field-effect transistors (spin-FETs) based on lateral heterojunctions composed of two-dimensional (2D) ferromagnetic half-metallic Sc2CHO electrodes and nonmagnetic semiconductor Sc2CHF channel are theoretically designed. The channel lengths (Lc) for investigated nanoscale spin-FETs are shorter than 6 nm. The spin transport properties of these nanoscale spin-FETs are subsequently studied by using the nonequilibrium Green's function method in combination with density functional theory. Due to the strong electronic coupling at the interfaces between electrodes and channel, p-type Ohmic contacts are obtained for spin down. Calculations reveal that at very-low temperature, the spin injection efficiency can reach 100%, and the magnetoresistance ratio (MR) is generally larger than 109% for these nanoscale spin-FETs. Very-low subthreshold swing (SS) values below 60 mV/dec are found for spin-FETs with Lc≥ 4.05 nm, and the lowest SS value is 39 mV/dec for the spin-FET with Lc=5.75 nm. At room temperature, the values of MR exceed 106%, and the corresponding SS values are below 92 mV/dec with a minimum SS of 82 mV/dec, still demonstrating high performance for designed nanoscale spin-FETs. Our study provides valuable insights into the design of high-performance nanoscale spin-FET devices based on 2D MXenes.
Rapid preparation of high-performance Mg2Sn thermoelectric materials and their unique role in metal-air batteries
Magnesium-air batteries hold potential applications due to their high energy density and environmental friendliness. However, the formation of passivation films and the suboptimal standard electrode potential have been primary scientific challenges hindering the rapid advancement of magnesium-air batteries. This study develops Mg2Sn anode materials and conceptualizes a mechanism leveraging their superior thermoelectric properties to enhance the open-circuit voltage and inhibit the formation of passivation films. By employing a self-designed magnesium saturation temperature smelting method, high-performance n-type and p-type Mg2Sn thermoelectric materials are synthesized rapidly in the air. Notably, the n-type thermoelectric material exhibits a peak power factor of up to 4.83 mW m−1 K−2 and a thermoelectric figure of merit (ZT) exceeding 1. A unique Mg2Sn-air battery is engineered to utilize thermoelectric effects for modulating the built-in electric field. This design not only compensates for the open-circuit voltage but also harnesses the Seebeck electromotive force generated by Mg2Sn to suppress the formation of passivation films on the anode surface, giving the high thermoelectric performance Mg2Sn, which tends to deliquesce in air, a unique application prospect. It elucidates a pathway for utilizing thermoelectric effects to synergistically enhance the electrochemical performance of metal-air batteries.
High-yield growth of high-quality cubic BAs single crystals using the Bridgman method
The increasing complexity of semiconductor devices fabricated from wide-bandgap and ultra-wide-bandgap materials demand advanced thermal management solutions to mitigate heat buildup, a major cause of device failure. High thermal conductivity materials are thus becoming crucial for thermal management. Cubic boron arsenide (c-BAs) has emerged as a promising candidate. However, challenges remain in synthesizing high-quality crystals with low defect concentrations, high homogeneous thermal conductivity, and high yields using the conventional chemical vapor transport method. In this study, we report the synthesis of high-yield c-BAs single crystals using the Bridgman method. The crystals exhibit high uniformity, reduced defect densities, and lower carrier concentrations as confirmed through x-ray diffraction, Raman spectroscopy, temperature-dependent photoluminescence, and electrical transport measurements. Our work represents a significant step toward scalable production of high-quality c-BAs for industrial applications, offering a practical solution for improving thermal management in next-generation electronic devices.
A high-<i>T</i> <i>c</i> superconducting diode with large current carrying capacity
Superconducting diodes enable lossless current flow in one direction and could serve in a variety of applications similar to their semiconductor counterparts, such as current rectification, temperature sensing, and logic circuits. However, no superconducting diodes reported in the literature have a forward current carrying capacity exceeding 1 A, and hence are not suitable for use in superconducting power applications. Here, we present a high-Tc superconducting diode that leverages permanent magnets to induce an asymmetry in the critical current of a superconducting coated conductor upon current reversal. The magnets are arranged to replicate the self-field of the conductor at Ic, causing constructive or destructive interference with the transport current's self-field depending on the current direction. This interference generates asymmetric internal magnetic field distributions, leading to the directional suppression of the critical current density and a diode effect. We demonstrate ΔIc values &gt; 150 A and a half-wave transformer rectifier using a single high-Tc flux diode submerged in liquid nitrogen, which rectifies 30 A into a 220 μH superconducting magnet.
Magnonic Fabry–Pérot resonators as programmable phase shifters
We explore the use of magnonic Fabry–Pérot resonators as programmable phase shifters for spin-wave computing. The resonator, composed of an yttrium iron garnet film coupled with a CoFeB nanostripe, operates through dynamic dipolar coupling, leading to wavelength downconversion and the formation of a magnonic cavity. Using super-Nyquist sampling magneto-optical Kerr effect microscopy and micromagnetic simulations, we demonstrate that these resonators can induce a π phase shift in the transmitted spin wave. The phase shift is highly sensitive to the magnetization alignment within the resonator, allowing for on-demand control via magnetic switching. This feature, combined with low-loss transmission, positions the magnonic Fabry–Pérot resonator as a promising component for reconfigurable magnonic circuits and spin-wave computing devices.
Temperature-dependent random telegraph signal in Co/CoO/Co point contact devices
Nanoscale Co/CoO/Co point contact devices are promising for spintronics, magnetic sensors, single-electron transistors, and memory devices. We fabricated Co/CoO/Co point contact devices and studied their random telegraph signal (RTS) characteristics at various temperatures. In the time domain, the current fluctuates asymmetrically with respect to zero bias, with RTS behavior emerging above a certain voltage threshold. In the frequency domain, the RTS power spectral density exhibits Lorentzian lines. As temperature increases from 50 to 300 K, two RTS behaviors are observed: at ≤100 K, the high current state dominates; at ≥200 K, the low current state prevails, with RTS absent at 150 K. Single exponential fitting shows that RTS state lifetimes decrease with temperature. The charge capture and release model explains the RTS origins and temperature-dependent behavior from an energy band perspective. This study provides insights into charge dynamics, single-electron transport, and the noise mechanisms affecting the reliability of nanoscale devices.
Strong coupling of excitons in a two-dimensional atomic crystal with quasi-bound state in the continuum supported by a single nanoparticle
Bound states in the continuum (BICs) supported by high-index dielectric nanoparticles have garnered significant attention due to their ability to achieve subwavelength confinement with high-quality factors, offering great potential for both fundamental studies of light–matter interactions and the development of compact photonic devices. However, the strong coupling of BICs with quantum emitters in single-particle systems has not been reported. In this paper, we propose a dielectric nanodisk integrated with a monolayer of transition metal dichalcogenides. A supercavity mode known as Friedrich–Wintgen BIC is launched in the nanodisk to enable strong coupling of BIC with WS2 excitons. We demonstrate that the reduction in coupling strength as the quasi-BIC quality factor increases is due to a decrease in the number of excitons participating in the coupling. Additionally, the coupling strength can be manipulated by adjusting the shape and aspect ratio of the nanoresonators, enabling a transition from strong to weak coupling regimes. Near-field analysis shows that the manipulation of the BIC–exciton interaction arises from the overlap of the BIC mode's near-field with the excitons. Our findings offer a promising strategy for manipulating light–matter interactions and enhance the potential applications of BIC resonances in photonics.
Tailoring transverse magneto-optical Kerr effect enhancement in Mie-resonant nanowire-based metasurfaces
Tailoring of the transverse magneto-optical Kerr effect (TMOKE) in hybrid metasurfaces comprising rectangular silicon nanowires coupled with a nickel substrate is demonstrated. The excitation of Mie modes of different orders in nanowires causes TMOKE enhancement. The in-plane magnetic dipole mode leads to the largest TMOKE enhancement compared to other Mie modes. Changing the width of silicon nanowires entails a modification of that mode, thereby ensuring tailoring of the TMOKE within the range of 2.2%–3.8%. This tunability is associated with the modification of the near-field localized at the Si/Ni interface and the far-field response of the excited magnetic dipole mode. Adjusting these two quantities allows one to achieve the highest values of the TMOKE caused by individual Mie modes in silicon nanowires.
Effects of the RF bias power of ICP etching on the electrical properties of n-type Ohmic contact on high-Al-fraction AlGaN
The effects of the radio frequency (RF) bias power of inductively coupled plasma etching on the electrical properties of n-type Ohmic contact have been investigated. By reducing the RF bias power, a high-quality n-type Ohmic contact has been achieved on n-Al0.70Ga0.30N, with a specific contact resistivity of 1.2 × 10−4 Ω cm2. It is confirmed that low-power etching introduces fewer acceptor-state defects on the etched surface, which not only reduces the compensation for electrons but also reduces the degree of oxidation on the etched surface, providing favorable conditions for improving the electrical properties of metal–semiconductor contacts.
Modulation of nonlinearity and asymmetry in a spin–orbit torque driven artificial synapse
Unconventional computing schemes inspired by biological neural networks are being explored with ever growing interest to eventually replace traditional von Neumann architecture-based computation. Realization of such schemes necessitates the development of device analogs to biological neurons and synapses. Particularly, in spin-based artificial synapses, the spin–orbit torque (SOT) can be utilized for changing between multiple resistance states of the synapse. In this work, we demonstrate synaptic behavior, namely long-term potentiation and long-term depression in a ferrimagnet (GdFe) via SOT generated using a heavy metal (Pt). The dependence of the synapse-like output on the input parameters is extensively investigated. Synaptic arrays based on experimental results are simulated and used to perform the classification of a handwritten digit dataset. Correlating the classification accuracy with the experimentally observed synaptic behavior, the performance of the synapse is found to depend on the critical switching currents. Understanding the correlation between the input parameters and synaptic performance could accelerate the development of artificial spintronic synapses possessing high operation speed, nonvolatility and plasticity, thereby enabling efficient compute in-memory systems in the near future.
Large positive VFB shift achieved by a band alignment modulated with insertion of Ga2O3 dipole layer
In this Letter, a Ga2O3 dipole layer deposited at the SiO2/HfO2 interface by in situ atomic layer deposition (ALD) has been demonstrated to be a great positive dipole. Through the in situ ALD of 10–30 cycles Ga2O3 dipole layer, a 1.09–1.59 V flatband voltage positive modulation range is obtained with a small 0.05–0.36 nm equivalent oxide thickness penalty, respectively. The modification of the band alignment is verified by x-ray photoelectron spectroscopy measurement on the gate stacks before and after Ga2O3 dipole layer insertion. The valence band offset between SiO2/HfO2 has been suppressed by the insertion of Ga2O3, proving a p-type dipole nature of Ga2O3 dipole layer. The first interface of SiO2/Ga2O3 more dominantly decides the p-type nature, and the second Ga2O3/HfO2 suppresses it. This work indicates that ALD of Ga2O3 is a promising positive dipole candidate for multiple threshold voltage technology in advanced process nodes.