Intrinsic Electronic Properties of BN-Encapsulated,van der Waals Contacted MoSe_(2)Field-Effect Transistors

Two-dimensional(2D)semiconductors have attracted considerable interest for their unique physical properties.Here,we report the intrinsic cryogenic electronic transport properties in few-layer MoSe_(2)field-effect transistors(FETs)that are fully encapsulated in ultraclean hexagonal boron nitride dielectrics and are simultaneously van der Waals contacted with gold electrodes.The FETs exhibit electronically favorable channel/dielectric interfaces with low densities of interfacial traps(<1010cm^(-2)),which lead to outstanding device characteristics at room temperature,including near-Boltzmann-limit subthreshold swings(65 mV/dec),high carrier mobilities(53–68 cm^(2)·V-1·s^(-1)),and negligible scanning hystereses(<15 mV).The dependence of various contact-related parameters with temperature and carrier density is also systematically characterized to understand the van der Waals contacts between gold and MoSe_(2).The results provide insightful information about the device physics in van der Waals contacted and encapsulated 2D FETs.

Overview of radar detection methods for low altitude targets in marine environments

In this paper,a comprehensive overview of radar detection methods for low-altitude targets in maritime environments is presented,focusing on the challenges posed by sea clutter and multipath scattering.The performance of the radar detection methods under sea clutter,multipath,and combined conditions is categorized and summarized,and future research directions are outlined to enhance radar detection performance for low-altitude targets in maritime environments.

Exploring device physics of perovskite solar cell via machine learning with limited samples

Perovskite solar cells(PsCs)have developed tremendously over the past decade.However,the key factors influencing the power conversion efficiency(PCE)of PSCs remain incompletely understood,due to the complexity and coupling of these structural and compositional parameters.In this research,we demon-strate an effective approach to optimize PSCs performance via machine learning(ML).To address chal-lenges posed by limited samples,we propose a feature mask(FM)method,which augments training samples through feature transformation rather than synthetic data.Using this approach,squeeze-and-excitation residual network(SEResNet)model achieves an accuracy with a root-mean-square-error(RMSE)of 0.833%and a Pearson's correlation coefficient(r)of 0.980.Furthermore,we employ the permu-tation importance(PI)algorithm to investigate key features for PCE.Subsequently,we predict PCE through high-throughput screenings,in which we study the relationship between PCE and chemical com-positions.After that,we conduct experiments to validate the consistency between predicted results by ML and experimental results.In this work,ML demonstrates the capability to predict device performance,extract key parameters from complex systems,and accelerate the transition from laboratory findings to commercialapplications.

Fabrication of YAG:Ce^(3+) and YAG:Ce^(3+),Sc^(3+) Phosphors by Spark Plasma Sintering Technique

In this study,a single-doped phosphors yttrium aluminum garnet(Y_(3)Al_(5)O_(12),YAG):Ce^(3+),single-doped YAG:Sc^(3+),and double-doped phosphors YAG:Ce^(3+),Sc^(3+) were prepared by spark plasma sintering(SPS)(lower than 1 200℃).The characteristics of synthesized phosphors were determined using scanning electron microscopy(SEM),X-ray diffraction(XRD),and fluorescence spectroscopy.During SPS,the lattice structure of YAG was maintained by the added Ce^(3+) and Sc^(3+).The emission wavelength of YAG:Ce^(3+) prepared from SPS(425-700 nm) was wider compared to that of YAG:Ce^(3+) prepared from high-temperature solid-state reaction(HSSR)(500-700 nm).The incorporation of low-dose Sc^(3+) in YAG:Ce^(3+) moved the emission peak towards the short wavelength.

Current-perpendicular-to-plane transport properties of 2D ferromagnetic material CrTe_(2)

Heterostructures of van der Waals(vdW)ferromagnetic materials have become a focal point in research of lowdimensional spintronic devices.The current direction in spin valves is commonly perpendicular to the plane(CPP).However,the transport properties of the CPP mode remain largely unexplored.In this work,current-in-plane(CIP)mode and CPP mode for CrTe_(2) thin films are carefully studied.The temperature-dependent longitudinal resistance transitions from metallic(CIP)to semiconductor behavior(CPP),with the electrical resistivity of CPP increased by five orders of magnitude.More importantly,the transport properties of the CPP can be categorized into a single-gap tunneling-through model with the activation energy(Ea)of1.34 meV/gap at 300–150 K,the variable range hopping model with a linear negative magnetoresistance at 150–20 K,and weak localization region with a nonlinear magnetic resistance below 20 K.This study explores the vertical transport in CrTe_(2) materials for the first time,contributing to understand its unique properties and to pave the way for its potential in spin valve devices.

Twisted Integration of Complex Oxide Magnetoelectric Heterostructures via Water‑Etching and Transfer Process

Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering.In recent years,lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations.Moreover,twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures.A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process,which could provide some insight in to the physical phenomena.In this work,the La_(0.67)Sr_(0.33)MnO_(3)(001)/0.7Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.3PbTiO_(3)(011)(LSMO/PMN-PT)heterostructures with 45.and 0.twist angles were assembled via water-etching and transfer process.The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO<110>.A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO[110]easy axis is observed for the 45°Sample by applying a 7.2 kV cm^(−1)electrical field,significantly different from a uniaxial anisotropy with LSMO[100]easy axis for the 0°Sample.The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45°twist angle causes different lattice distortion of LSMO,thereby enhancing both the fourfold and uniaxial anisotropy.This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures.

Effects of Mg-doping temperature on the structural and electrical properties of nonpolar a-plane p-type GaN films

Nonpolar(11–20) a-plane p-type GaN films were successfully grown on r-plane sapphire substrate with the metal–organic chemical vapor deposition(MOCVD) system. The effects of Mg-doping temperature on the structural and electrical properties of nonpolar p-type GaN films were investigated in detail. It is found that all the surface morphology, crystalline quality, strains, and electrical properties of nonpolar a-plane p-type GaN films are interconnected, and are closely related to the Mg-doping temperature. This means that a proper performance of nonpolar p-type GaN can be expected by optimizing the Mg-doping temperature. In fact, a hole concentration of 1.3×10^(18)cm^(-3), a high Mg activation efficiency of 6.5%,an activation energy of 114 me V for Mg acceptor, and a low anisotropy of 8.3% in crystalline quality were achieved with a growth temperature of 990℃. This approach to optimizing the Mg-doping temperature of the nonpolar a-plane p-type GaN film provides an effective way to fabricate high-efficiency optoelectronic devices in the future.

Efficient electrical control of magnetization switching and ferromagnetic resonance in flexible La_(0.7)Sr_(0.3)MnO_(3) films

Efficient electrical control of magnetic property is critical for the development of various spintronics. However, traditional magnetoelectric devices require adoption of piezoelectric component, resulting in complicated device architecture and complex conditioning circuit. More importantly, traditional strain-mediated magnetoelectric structures could not be developed in flexible form due to the existence of magnetostrictive component, which could be easily affected by mechanical deformation in flexible devices. Here we have systematically investigated pure current control of the magnetic properties of La_(0.7)Sr_(0.3)MnO_(3) thin films. Ferromagnetic to paramagnetic phase transition has been realized with a small current density of 5.2 × 10^(3) A/cm^(2), which is three orders smaller than the working current density of spintronics based on spin-orbit torque and spin-transfer torque. The effective tuning of magnetic property has been attributed to the current induced Joule heating effect. For La_(0.7)Sr_(0.3)MnO_(3) film grown on flexible Mica with a smaller thermal conductivity, dramatic change of ferromagnetic resonance field of 1340 Oe and nonvolatile magnetization switching have been achieved with an ultra-small current density of 7.4 × 10^(2) A/cm^(2). These results represent a crucial step towards effective electrical control of both static and dynamic magnetic properties in flexible magnetic thin films and open a new avenue for exploring electrical controlled flexible spintronics.

Tunable superconducting resonators via on-chip control of local magnetic field

Superconducting microwave resonators play a pivotal role in superconducting quantum circuits.The ability to finetune their resonant frequencies provides enhanced control and flexibility.Here,we introduce a frequency-tunable superconducting coplanar waveguide resonator.By applying electrical currents through specifically designed ground wires,we achieve the generation and control of a localized magnetic field on the central line of the resonator,enabling continuous tuning of its resonant frequency.We demonstrate a frequency tuning range of 54.85 MHz in a 6.21-GHz resonator.This integrated and tunable resonator holds great potential as a dynamically tunable filter and as a key component of communication buses and memory elements in superconducting quantum computing.

Effective approach for conformal subarray design based on maximum entropy of planar mappings

In this paper,an effective algorithm for optimizing the subarray of conformal arrays is proposed.The method first divides theconformal array into several first-level subarrays.It uses the X algorithm to solve the feasible solution of first-level subarray tiling and employs the particle swarm algorithm to optimize the conformal array subarray tiling scheme with the maximum entropy of the planar mapping as the fitness function.Subsequently,convex optimization is applied to optimize the subarray amplitude phase.Data results verify that the method can effectively find the optimal conformal array tiling scheme.

Critical behavior of quasi-two-dimensional ferromagnet Cr_(1.04)Te_(2)

The self-intercalation of Cr into pristine two-dimensional(2D) van der Waals ferromagnetic CrTe_(2),which forms chromium tellurides(Cr_(x)Te_(2)),has garnered interest due to their remarkable magnetic characteristics and the wide variety of chemical compositions available.Here,comprehensive basic characterization and magnetic studies are conducted on quasi-2D ferromagnetic Cr_(1.04)Te_(2) crystals.Measurements of the isothermal magnetization curves are conducted around the critical temperature to systematically investigate the critical behavior.Specifically,the critical exponents β=0.2399,γ=0.859,and δ=4.3498,as well as the Curie temperature T_(C)=249.56 K,are determined using various methods,including the modified Arrott plots,the Kouvel-Fisher method,the Widom scaling method,and the critical isotherm analysis.These results indicate that the tricritical mean-field model accurately represents the critical behavior of Cr_(1.04)Te_(2.A magnetic phase diagram with tricritical phenomenon is thus constructed.Further investigations confirm that the critical exponents obtained conform to the scalar equation near T_(C),indicating their self-consistency and reliability.Our work sheds light on the magnetic properties of quasi-2D Cr_(1.04)Te_(2),broadening the scope of the van der Waals crystals for developments of future spintronic devices operable at room temperature.

Electromagnetic scattering and imaging simulation of extremely large-scale sea-ship scene based on GPU parallel technology

Aiming to solve the bottleneck problem of electromagnetic scattering simulation in the scenes of extremely large-scale seas and ships,a high-frequency method by using graphics processing unit(GPU)parallel acceleration technique is proposed.For the implementation of different electromagnetic methods of physical optics(PO),shooting and bouncing ray(SBR),and physical theory of diffraction(PTD),a parallel computing scheme based on the CPU-GPU parallel computing scheme is realized to balance computing tasks.Finally,a multi-GPU framework is further proposed to solve the computational difficulty caused by the massive number of ray tubes in the ray tracing process.By using the established simulation platform,signals of ships at different seas are simulated and their images are achieved as well.It is shown that the higher sea states degrade the averaged peak signal-to-noise ratio(PSNR)of radar image.

An ultrahigh energy storage efficiency and recoverable density in Bi_(0.5)Na_(0.5)TiO_(3)with the modification of Sr_(0.85)La_(0.1)TiO_(3)via viscous polymer process

Currently,the development of dielectric ceramic capacitors is restricted by the contradiction between high efficiency and high recoverable density.Therefore,a novel strategy was designed to achieve a su-perior balance between them.Firstly,introducing Sr_(0.85)La_(0.1)TiO_(3)can enhance the content of the weak polar phase(P4bm)to become the main component,which can optimize the relaxor behaviour and improve efficiency.Then,the electric breakdown strength was effectively enhanced by grain refinement and viscous polymer processing.Finally,a high recoverable energy density of~5.3 J/cm^(3)and an excellent efficiency of~92.2%were attained in 0.9Bi_(0.5)Na_(0.5)TiO_(3)-0.1Na_(0.8)Sr_(0.1)NbO_(3)ceramic with the addition of 0.35Sr_(0.85)La_(0.1)TiO_(3)after viscous polymer processing.The piezoelectric force microscope had been applied to prove the high activity of the polar nanoregions and finite element analysis was adopted to explain the reasons for the enhancing electric breakdown strength.In addition,this ceramic exhibits good tem-perature and frequency stability,and a fast discharging rate of 0.11 ms,making it a potential candidate for the actual application.

Step-edge-guided nucleation and growth mode transition of α-Ga_(2)O_(3) heteroepitaxy on vicinal sapphire

Controlling the epitaxial growth mode of semiconductor layers is crucial for optimizing material properties and device performance.In this work,the growth mode ofα-Ga_(2)O_(3) heteroepitaxial layers was modulated by tuning miscut angles(θ)from 0°to 7°off the(1010)direction of sapphire(0002)substrate.On flat sapphire surfaces,the growth undergoes a typical three-dimensional(3D)growth mode due to the random nucleation on wide substrate terraces,as evidenced by the hillock morphology and high dislocation densities.As the miscut angle increases toθ=5°,the terrace width of sapphire substrate is comparable to the distance between neighboring nuclei,and consequently,the nucleation is guided by terrace edges,which energetically facilitates the growth mode transition into the desirable two-dimensional(2D)coherent growth.Consequently,the mean surface roughness decreases to only 0.62 nm,accompanied by a significant reduction in screw and edge dislocations to 0.16×10^(7) cm^(-2)and 3.58×10^(9) cm^(-2),respectively.However,the further increment of miscut angles toθ=7°shrink the terrace width less than nucleation distance,and the step-bunching growth mode is dominant.In this circumstance,the misfit strain is released in the initial growth stage,resulting in surface morphology degradation and increased dislocation densities.

Photoacoustic/ultrasound dual-modal imaging of human nails: A pilot study

Traditional diagnostic techniques including visual examination,ultrasound(US),and magnetic resonance imaging(MRI)have limitations of in-depth information for the detection of nail disorders,resolution,and practicality.This pilot study,for thefirst time,evaluates a dualmodality imaging system that combines photoacoustic tomography(PAT)with the US for the multiparametric quantitative assessment of human nail.The study involved a small cohort offive healthy volunteers who underwent PAT/US imaging for acquiring the nail unit data.The PAT/US dual-modality imaging successfully revealed thefine anatomical structures and microvascular distribution within the nail and nail bed.Moreover,this system utilized multispectral PAT to analyze functional tissue parameters,including oxygenated hemoglobin,deoxyhemoglobin,oxygen saturation,and collagen under tourniquet and cold stimulus tests to evaluate changes in the microcirculation of the nail bed.The quantitative analysis of multispectral PAT reconstructed images demonstrated heightened sensitivity in detecting alterations in blood oxygenation levels and collagen content within the nail bed,under simulated different physiological conditions.This pilot study highlights the potential of PAT/US dual-modality imaging as a real-time,noninvasive diagnostic modality for evaluating human nail health and for early detection of nail bed pathologies.

Integrated in-memory sensor and computing of artificial vision system based on reversible bonding transition-induced nitrogen-doped carbon quantum dots (N-CQDs)

Carbon quantum dots (CQDs) have been used in memristors due to their attractive optical and electronic properties, which are considered candidates for brain-inspired computing devices. In this work, the performance of CQDs-based memristors is improved by utilizing nitrogen-doping. In contrast, nitrogen-doped CQDs (N-CQDs)-based optoelectronic memristors can be driven with smaller programming voltages (−0.6 to 0.7 V) and exhibit lower powers (78 nW/0.29 µW). The physical mechanism can be attributed to the reversible transition between C–N and C=N with lower binding energy induced by the electric field and the generation of photogenerated carriers by ultraviolet light irradiation, which adjusts the conductivity of the initial N-CQDs to implement resistance switching. Importantly, the convolutional image processing based on various cross kernels is efficiently demonstrated by stable multi-level storage properties. An N-CQDs-based optoelectronic reservoir computing implements impressively high accuracy in both no noise and various noise modes when recognizing the Modified National Institute of Standards and Technology (MNIST) dataset. It illustrates that N-CQDs-based memristors provide a novel strategy for developing artificial vision system with integrated in-memory sensor and computing.

Anisotropic Band Evolution of Bulk Black Phosphorus Induced by Uniaxial Tensile Strain

We investigate the anisotropic band structure and its evolution under tensile strains along different crystallographic directions in bulk black phosphorus(BP)using angle-resolved photoemission spectroscopy and density functional theory.The results show that there are band crossings in the Z-L(armchair)direction.

The Combined Effect of Spin-Transfer Torque and Voltage-Controlled Strain Gradient on Magnetic Domain-Wall Dynamics:Toward Tunable Spintronic Neuron

Magnetic domain wall(DW), as one of the promising information carriers in spintronic devices, have been widely investigated owing to its nonlinear dynamics and tunable properties. Here, we theoretically and numerically demonstrate the DW dynamics driven by the synergistic interaction between current-induced spin-transfer torque(STT) and voltage-controlled strain gradient(VCSG) in multiferroic heterostructures. Through electromechanical and micromagnetic simulations, we show that a desirable strain gradient can be created and it further modulates the equilibrium position and velocity of the current-driven DW motion. Meanwhile, an analytical Thiele's model is developed to describe the steady motion of DW and the analytical results are quite consistent with the simulation data. Finally, we find that this combination effect can be leveraged to design DW-based biological neurons where the synergistic interaction between STT and VCSG-driven DW motion as integrating and leaking motivates mimicking leaky-integrate-and-fire(LIF) and self-reset function. Importantly, the firing response of the LIF neuron can be efficiently modulated, facilitating the exploration of tunable activation function generators, which can further help improve the computational capability of the neuromorphic system.

Shape-influenced non-reciprocal transport of magnetic skyrmions in nanoscale channel

Skyrmions, with their vortex-like structures and inherent topological protection, play a pivotal role in developing innovative low-power memory and logic devices. The efficient generation and control of skyrmions in geometrically confined systems are crucial for the development of skyrmion-based spintronic devices. In this study, we focus on investigating the non-reciprocal transport behavior of skyrmions and their interactions with boundaries of various shapes. The shape of the notch structure in the nanotrack significantly affects the dynamic behavior of magnetic skyrmions. Through micromagnetic simulation, the non-reciprocal transport properties of skyrmions in nanowires with different notch structures are investigated in this work.

Physical mechanism of secondary-electron emission in Si wafers

CMOS-compatible RF/microwave devices,such as filters and amplifiers,have been widely used in wireless communication systems.However,secondary-electron emission phenomena often occur in RF/microwave devices based on silicon(Si)wafers,especially in the high-frequency range.In this paper,we have studied the major factors that influence the secondary-electron yield(SEY)in commercial Si wafers with different doping concentrations.We show that the SEY is suppressed as the doping concentration increases,corresponding to a relatively short effective escape depthλ.Meanwhile,the reduced narrow band gap is beneficial in suppressing the SEY,in which the absence of a shallow energy band below the conduction band will easily capture electrons,as revealed by first-principles calculations.Thus,the new physical mechanism combined with the effective escape depth and band gap can provide useful guidance for the design of integrated RF/microwave devices based on Si wafers.