Vol. 74, No. 20 (2025)
2025-10-20
VIEWS AND PERSPECTIVES
EDITOR'S SUGGESTION
2025, 74 (20): 200201.
doi: 10.7498/aps.74.20250864
Abstract +
The multilayer structure of extreme ultraviolet (EUV) masks limits the penetration depth of traditional inspection techniques at non-working wavelengths, thus hindering the effective examination of buried phase defects. Developing defect characterization techniques operating at the 13.5 nm wavelength is crucial for overcoming the quality bottleneck in EUV mask fabrication. Synchrotron radiation light source, with their stable EUV wavelength, cleanliness, and high power density, represents an ideal light source for EUV mask defect characterization research. In this work the current state of technology development for mask characterization at the world's four major synchrotron radiation facilities are systematically reviewed. Through comparative analysis, their working principles, technical advantages, and limitations are investigated in depth, and provide a forward-looking discussion on future trends. In response to the specific requirements for EUV mask defect detection and review, this paper discusses the requirements for the next-generation system platform, which integrates deep detection and review functions, develops novel compact light sources, and innovatively combines the advantages of various imaging techniques to improve the numerical aperture (NA) of imaging systems. This aims to achieve a theoretical resolution of over 20 nm, meeting the future demands of the EUV lithography industry for higher NA (>0.55) and shorter wavelengths (6.7 nm). Regarding the prospects of extending synchrotron radiation to industrial applications, a compact synchrotron radiation source, which can be developed on-site in semiconductor facilities, is introduced to accelerate the research and development cycle, while achieving the synergistic integration of imaging technologies. This paper focuses on the application of phase recovery principle of ptychography to Fourier synthesis illumination (FSI), achieving aberration correction in lens-based systems through synthetic aperture extension. In this paper, the working principles, performance benchmarks, technical challenges, and emerging development trends of existing synchrotron radiation-based EUV mask characterization techniques are investigated. It provides an important reference for designing next-generation EUV mask characterization system platforms.
SPECIAL TOPIC—Non-equilibrium transport and active control strategy in low-temperature plasmas
EDITOR'S SUGGESTION
2025, 74 (20): 205206.
doi: 10.7498/aps.74.20251183
Abstract +
Carbon quantum dots, as an emerging zero-dimensional carbon-based nanomaterial, have shown great potential applications in fields such as biomedicine, sensing detection, and LED lighting due to their excellent photoelectric properties, good biocompatibility, and ease of functionalization. Traditional synthesis methods like hydrothermal and microwave approaches often face challenges such as harsh reaction conditions, long reaction times, high energy consumption, and difficulties in controlling the optical properties of the products. The plasma electrochemistry method, which utilizes reactions between carbon source molecules and high-density electrons, ions, photons, and reactive radicals generated during the interaction of plasma with liquid, can efficiently drive the rapid synthesis and modification of carbon quantum dots. This method possesses the advantage of tunable multiple reaction parameters under mild conditions, providing a novel research method for synthesizing and modifying carbon quantum dots. This article first elucidates the growth mechanism of carbon quantum dots synthesized via plasma electrochemical methods and highlights the unique advantages of this approach in controlling product properties by regulating multidimensional parameters. Then, it reviews research progress of the regulation of the fluorescence quantum yield and wavelength of carbon quantum dots based on the adjustment of plasma reaction parameters. Finally, this article presents the application progress and prospects of plasma-prepared and plasma-modified carbon quantum dots in biomedicine, optoelectronic devices, pH sensing, and other fields.
EDITOR'S SUGGESTION
2025, 74 (20): 205201.
doi: 10.7498/aps.74.20250983
Abstract +
In neutral beam injection (NBI), which is a primary auxiliary heating method for tokamak plasmas, the negative hydrogen ion source (NHIS) functions as a critical front-end component governing neutral beam quality. The performance of NHIS remains a key challenge. This work presents a three-dimensional (3D) fluid model, which is developed for a double-driver NHIS to simulate and optimize surface-generated negative hydrogen ion density. A comparison of plasma parameters between the NHIS with Cs and without Cs shows that surface generation yields negative ion density one order of magnitude higher than volume generation. However, the presence of the magnetic filter field induces asymmetry in negative ion density within the extraction region. To improve this asymmetry, two approaches are proposed: 1) increasing the power of one of the drivers and 2) adding a spacer plate to the expansion region. After increasing the power of Driver I from 50 to 56 kW, the H– density asymmetry at the y = 25 cm intercept on the xy-plane (z = –22 cm) decreases from 0.04 to 0.01, and the value of H– density increases. Following the addition of a spacer plate, the H– density asymmetry further decreases to 0.004, but the value of H– density also shows a significant reduction. Finally, adding a magnetic shield to the back plate of the expansion region further optimizes H– density from 1.48×1017 m–3 to 2.50×1017 m–3, yielding a 69% increase downstream. This is because increased plasma transport into the expansion region enhances the dissociation rate of H2 molecules, thereby yielding more H atoms. The attenuation of the magnetic filter field in the driver region after adding a magnetic shield also enhances the symmetry of the H– density.
EDITOR'S SUGGESTION
Diagnosing global properties of dusty plasma based on machine learning from single particle dynamics
2025, 74 (20): 205202.
doi: 10.7498/aps.74.20251129
Abstract +
Currently, it is a great challenge to accurately diagnose global properties of dusty plasmas from limited data. Based on machine learning, a novel diagnostic method for various global properties in dusty plasma experiments is developed from single particle dynamics. It is found that for both two-dimensional (2D) dusty plasma simulations and experiments, the global properties such as the screening parameters κ and the coupling parameter Γ can be accurately determined purely from the position fluctuations of individual particles. Hundreds of independent Langevin dynamical simulations are performed with various specified κ and Γ values, resulting in a great number of individual particle position fluctuation data, which can be used for training, validating, and testing various convolutional neural network (CNN) models. To confirm the feasibility of this diagnostic method, three different CNN models are designed to determin the κ value. For the simulation data, all these CNN models perform excellently in determining the κ value, with the averaged determined κ value almost equal to the specified κ value. For the experiment data, the distribution of the determined κ values always exhibits one prominent peak, which is very consistent with the κ value obtained from the widely accepted phonon spectra fitting method. Furthermore, this diagnostic method is extended to simulatneously determining both the κ and Γ values, achieving satisfactory results by using 2D dusty plasma data from both simulations and experiments. The excellent performance of the CNN models developed here clearly indicates that through machine learning, the global properties of 2D dusty plasmas can be fully characterized purely from single particle dynamics.
EDITOR'S SUGGESTION
2025, 74 (20): 205203.
doi: 10.7498/aps.74.20251065
Abstract +
Complex plasmas are composed of ionized gases and mesoscopic particles, representing a typical non-equilibrium complex system. The particles are negatively charged due to the higher thermal velocity of the electrons and interact with each other via Yukawa interactions. Due to the easy recording of the individual particles' motion through video microscopy, the generic processes in liquids and solids can be studied at a kinetic level in complex plasmas. Under microgravity conditions, the particles are confined in the bulk plasma and form a three-dimensional cloud. In the PK-4 Laboratory on the International Space Station, melamine formaldehyde particles with diameters of 6.8 μm and 3.4 μm are consecutively injected into the plasma discharge. Due to the electrostatic force and ion drag force, usually, the particles cannot be mixed in the same region, thereby leading to a phase separation. During the particle injections, small particles penetrate into the big particle clouds and self-organize in different ways under different conditions. When the number density of the big particles is low, small particles form a channel in the center of the discharge tube due to the Yukawa repulsion, where the big particle cloud is weakly confined. When the number density of the big particles is moderate, lanes are formed during the penetration of the small particles, representing a typical nonequilibrium self-organization. When the number density of the big particles is high, dust acoustic waves are self-excited due to the two-stream instability. As the small and big particles interact with each other, the number density of particles in the wave crests sharply increases. However, the wave numbers and frequencies remain unchanged. This investigation offers insights into the different self-organizations during the particle injections in three-dimensional binary complex plasmas under microgravity conditions.
EDITOR'S SUGGESTION
2025, 74 (20): 205204.
doi: 10.7498/aps.74.20251096
Abstract +
Low-pressure radio-frequency inductively coupled discharges can produce uniformly distributed monodisperse particles and plasma, making them widely used in nanodevice fabrication. The manufacturing of nanodevices typically requires the generation of particles ranging from nanometer to submicron scales. These particles usually carry negative charges and can significantly influence the discharge characteristics of the plasma. This study investigates the effects of particle size and density on electron bounce resonance heating (BRH) and fundamental plasma properties in low-pressure inductively coupled plasmas (ICPs) by using a hybrid model. The hybrid model consists of kinetic equation, electromagnetic field equation, and global model equation. The simulation results show that as the dust radius or density increases, the BRH effect characterized by the formation of a plateau in the probability function of electron energy, is gradually suppressed and eventually disappears, accompanied by a decrease in electron temperature, an increase in electron density, and an increase in particle surface potential. The dust charge decreases with the increase of particle density, while exhibiting a nonmonotonic variation with particle radius. The results show that the loss of high-energy electrons caused by the dust particles may create a more favorable plasma environment for the growth of monodisperse nanoparticles with low defects. Such an improvement in particle quality is crucial for reducing trap densities and enhancing the electrical performance of nanoparticle-based electronic devices.
EDITOR'S SUGGESTION
2025, 74 (20): 209401.
doi: 10.7498/aps.74.20250788
Abstract +
In low-pressure plasmas, the collisions between particles are weak and insufficient damping from collisions, leading to the gradual development of various waves and instabilities. Thus, the effects of wave-particle interaction are non-negligible in the non-equilibrium transport processes in plasma under low pressure conditions. For example, the heating of ionospheric plasma by high-frequency electromagnetic waves plays an important role in achieving over-the-horizon communication. During the wave propagation through the ionosphere, the electromagnetic radiation changes the local electron temperature and density, and simultaneously, excites various wave modes and instabilities. This study focuses on the interactions between high-power electromagnetic waves emitted from the ground and ionospheric plasma. Based on the plasma fluid model and Zakharov method, a physical-mathematical model is established to describe the wave-wave and wave-particle interactions in the ionospheric plasmas under the excitation of the pump waves. The modeling results of the active heating of ionosphere show that when the ground-emitted waves propagate in the ionospheric plasma, the energy deposition of the electromagnetic waves at the reflection height will excite a strong localized electric field, leading to the parametric instabilities. When the frequency and wave vector matching conditions are satisfied, two different three-wave interactions will be excited, i.e. the parametric decay instability involving the pump wave, Langmuir wave and ion acoustic wave, as well as the parametric instability related to the pump wave, upper hybrid and lower hybrid waves. Within a certain range of pump frequency and power studied in this study, the decrease of the pump frequency will lead to the decrease of the reflection height of the ordinary waves, and simultaneously, the perturbation ratios of the electron temperature will also increase. A higher pump wave power will enhance the energy absorption of the ionospheric plasma by the pump wave, thereby increasing the electron temperature. The modeling results not only reveal the spatiotemporal evolutions of the ionospheric plasma characteristics under various pump parameters and the energy transport processes between waves and particles, but also theoretically explain the parametric instability, stimulated electromagnetic emission and other phenomena observed in experiments.
SPECIAL TOPIC—High-pressure modulation and in situ characterization of optoelectronic properties
EDITOR'S SUGGESTION
2025, 74 (20): 200701.
doi: 10.7498/aps.74.20251034
Abstract +
Two-dimensional (2D) materials, due to their outstanding photoelectric properties, have demonstrated significant potential in both fundamental scientific research and future technological applications, including optoelectronics, energy storage, and conversion devices, establishing them as a cutting-edge research field in condensed matter physics and materials science. The distinctive layered structure of 2D materials renders their physical properties highly sensitive to external stimuli. High-pressure technology, serving as an efficient, continuous, and clean tuning tool, enables precise structural control and optimization of the photoelectric properties of 2D materials by compressing atomic distances, strengthening interlayer coupling, and even inducing structural phase transitions. This article focuses on prototypical two-dimensional materials, including graphene, transition metal dichalcogenides (TMDs), and two-dimensional metal halide perovskites. Employing the diamond anvil cell combined with multimodal in situ high-pressure characterization techniques such as X-ray diffraction, Raman spectroscopy, photoluminescence, and electrical transport measurements, we systematically elucidate the effects of high pressure on the structural and photoelectric properties of these materials. The key findings indicate that high pressure can induce the graphene to transition from a semimetal state to a semiconducting state, even a superconducting state, triggering off structural phase transitions and semiconductor-to-metal transitions in TMDs such as MoS2 and WTe2, and leading to a pressure-dependent bandgap narrowing and significant enhancement of luminescence intensity in two-dimensional perovskites. This work highlights the utility of high-pressure techniques in revealing the intrinsic correlations between the microstructure and macroscopic properties of two-dimensional materials. Furthermore, it discusses the key challenges and opportunities in this emerging research area, providing insights into the development and practical application of novel functional materials.
EDITOR'S SUGGESTION
2025, 74 (20): 206201.
doi: 10.7498/aps.74.20250912
Abstract +
SPECIAL TOPIC—2D materials and future information devices
EDITOR'S SUGGESTION
2025, 74 (20): 207102.
doi: 10.7498/aps.74.20250890
Abstract +
INSTRMENTATION AND MEASURMENT
EDITOR'S SUGGESTION
2025, 74 (20): 200401.
doi: 10.7498/aps.74.20250852
Abstract +
Gravitational wave astronomy has rapidly developed into a powerful means of probing compact objects and understanding the evolution of the Universe. In order to improve sensitivity and expand the detection band, ground-based laser interferometers such as LIGO, Virgo, and KAGRA are constantly upgraded. This review summarizes their systematic development with an emphasis on noise sources and mitigation strategies. After outlining the principle of gravitational wave detection with laser interferometry, we analyze dominant noise sources, including quantum vacuum fluctuations, thermal noise, and seismic disturbances, and introduce techniques such as frequency-dependent squeezed light, advanced seismic isolation, multi-stage suspensions, and cryogenic mirrors. For LIGO, we highlight the transition from the Initial to Advanced configurations, which results in strain sensitivities of the order of $10^{-24}/\sqrt{\text{Hz}}$ and leads directly to the first detection, GW150914, and over one hundred subsequent events during O1 to O4. The unique superattenuator system of Virgo and its recent implementation of squeezed light, as well as the underground design of KAGRA and the use of cryogenic sapphire test masses, represent different approaches to suppressing low-frequency and thermal noise. In addition, we compare the technical routes adopted by different detectors and summarize the lessons learned from their upgrades, thereby providing valuable guidance for designing future detectors. Finally, we present next-generation projects, including LIGO Voyager, the Cosmic Explorer, and the Einstein Telescope, which aim to increase sensitivity by up to orders of magnitude and provide new research opportunities for developing gravitational-wave cosmology and fundamental physics. Overall, the development of detector technologies has been a key driving force for advances in gravitational wave astronomy, and the forthcoming facilities will change our ability to explore the universe.
REVIEW
EDITOR'S SUGGESTION
2025, 74 (20): 208101.
doi: 10.7498/aps.74.20250830
Abstract +
GENERAL
EDITOR'S SUGGESTION
2025, 74 (20): 200202.
doi: 10.7498/aps.74.20250982
Abstract +
Clouds exert a significant influence on infrared radiation, making cloud detection a crucial step in the application of infrared hyperspectral data. In particular, water vapor interference and the limited accuracy in high-cloud identification constitute two key challenges for ground-based infrared hyperspectral cloud detection. Traditional threshold-based cloud detection methods are difficult to adapt to different locations and dynamically changing atmospheric conditions,while machine learning methods can achieve cloud detection with higher accuracy, greater robustness, and improved automation. Building on the advantages of machine learning, observational data from the atmospheric sounder spectrometer by infrared spectral technology (ASSIST), collected at Lijiang (Yunnan), Motuo (Xizang Autonomous Region), and Ritu (Xizang Autonomous Region) in China, are used to analyze the spectral differences between sunny and cloudy conditions in this study. Based on these differences, a spectral feature enhancement-driven machine learning method for cloud detection is proposed. Finally, by incorporating synchronous observations from lidar, meteorological stations, and all-sky imagers, the proposed method is systematically evaluated under different relative humidity (RH) and cloud base height (CBH) conditions. The experimental results show that the consistency between the results obtained by the proposed method and lidar-based detection is as high as 97.61%. Under different RH conditions, the proposed method outperforms the method based on original spectral features. Notably, when ${\text{RH}} > 70{\text{%}} $, the accuracy of clear-sky spectral identification improves significantly: increasing from 86.01% to 91.89%. Similarly, under different CBH conditions, the proposed method also exhibits superior performance compared with the method in which original spectral features are used. In particular, the accuracy improvements are especially notable when identifying mid-level clouds with ${\text{3 km}} < {\text{CBH}} \leqslant 5{\text{ km}}$, as well as high-level clouds with ${\text{CBH}} > 5{\text{ km}}$. When ${\text{3 km}} < {\text{CBH}} \leqslant 5{\text{ km}}$, the accuracy increases from 95.45% to 98.64% and when ${\text{CBH}} > 5{\text{ km}}$, the accuracy improves from 87.5% to 91.67%. The proposed method significantly enhances the automation and accuracy of cloud detection, thereby providing higher-quality fundamental datasets for supporting subsequent applications such as radiative transfer simulation, remote sensing parameter retrieval, and data assimilation in numerical weather prediction (NWP) models.
2025, 74 (20): 200301.
doi: 10.7498/aps.74.20250715
Abstract +
Entanglement detection and classification of different kinds of entangled states in quantum many-body systems have always been a key topic in quantum information and quantum computation. In this work, we investigate the entanglement detection and classification of three special entangled states: 4-qubit GHZ state, 4-qubit $ {\mathrm{W}}\overline{{\mathrm{W}}} $ state, and 4-qubit SGT state, which cannot be distinguished by the general quantum Fisher information (QFI) under the usual local operations. By utilizing the experimentally mature and controllable one-axis twisting model, along with optimized rotations and adjustable interaction strength, we successfully classify the three states by QFI. Additionally, we also study the effects of four types of environmental noise on entanglement detection, namely, bit-flip channel, amplitude-damping channel, phase-damping channel, and depolarizing channel. The results show that under local operations, the changes of the QFI from the 4-qubit GHZ state with decoherence parameter p in four noise channels are significantly different from those of the $ {\mathrm{W}}\overline{{\mathrm{W}}} $ state and SGT state, and thus making them distinguished. However, the QFI about the $ {\mathrm{W}}\overline{{\mathrm{W}}} $ state and the QFI about the SGT state exhibit the same variations and cannot be classified. In the one-axis twisting model, the variation curves of the QFI of the three states under the four noise channels are different from each other, which can be clearly observed. It should be noted that in the bit-flip channel, the QFI curves of the $ {\mathrm{W}}\overline{{\mathrm{W}}} $ state and the SGT state overlaps in the middle region ($ p\approx0.5 $), which prevents their classification. Our work provides a new method for entanglement detection and classification in quantum many-body systems, which will contribute to future research in quantum science and technology.
2025, 74 (20): 200501.
doi: 10.7498/aps.74.20250954
Abstract +
The rich dynamical analysis and predefined-time synchronization of simple memristive chaotic systems are of great significance in fully understanding the mechanism of dynamics formation and expanding the potential applications of chaotic systems. A four-dimensional memristive chaotic system with only a single nonlinear term is proposed to reveal various dynamic behaviors under the change of parameters and initial conditions, and to realize effective synchronization control. Based on dissipativity analysis and Lyapunov exponent computation, and combined with bifurcation analysis and multi steady state exploration, it is shown that the system possesses an infinite number of unstable equilibrium points and exhibits homogeneous and heterogeneous multistability, including point attractors, periodic attractors, and chaotic attractors. Moreover, it is found that amplitude modulation of the output signals of the system can be precisely achieved by adjusting internal parameters of the memristor, thus providing a theoretical basis for achieving effective amplitude modulation of periodic and chaotic signals. A predefined-time sliding mode surface with linear and bidirectional power-law nonlinear decay terms is constructed to address synchronization. Sufficient conditions for predefined-time convergence of synchronization errors are derived using Lyapunov stability theory, and a double-stage sliding mode controller with an adjustable upper bound on synchronization time is designed. The resulting control law ensures an adjustable synchronization time bound and rapid error suppression under arbitrary disturbances. Numerical simulations further confirm the effectiveness and robustness of the proposed control scheme, indicating that even under external disturbances or significant variations in initial conditions, the error variables can still converge precisely within the predefined time.
2025, 74 (20): 200601.
doi: 10.7498/aps.74.20251032
Abstract +
The measurement of total energy on a target is a critical step in evaluating the performances of high-power laser systems. However, the laser spot on the target exhibits characteristics such as high power density, non-uniform spatial distribution and temporal distribution, and large spot size, which present a significant challenge to the accurate measurement of total energy. To meet the requirement for high-precision measurement of the total energy of a large spot, this work focuses on plate-based energy measurement technology. First, we investigate the physical processes of laser-heated plates and obtain analytical solutions, demonstrating that uniformly arranged temperature sensor arrays can shorten the relaxation period. Second, to overcome the limitations of traditional energy inversion algorithms, such as the need to preheat the absorber and potential non-uniform temperature effects, we propose correction methods. The non-preheated calorimetry method eliminates the requirement that the absorber temperature must be higher than the ambient temperature during the initial rating period. It iteratively optimizes the ambient temperature and heat loss coefficients based on corrected temperature invariance. Additionally, a non-uniform temperature correction algorithm is employed to minimize the errors caused by limited sensor sampling rates through reconstructing the temperature curve during the injection and adjustment periods. Finally, we develop a plate measurement device and conduct laser calibration tests, achieving a system repeatability of 2.7%, linearity of 0.3%, and a combined standard uncertainty of 4%. This study lays a theoretical foundation for flat-plate laser energy measurement technology, offering important insights into optimizing the apparatus design, improving usability, and achieving high-precision energy inversion.
2025, 74 (20): 200602.
doi: 10.7498/aps.74.20250915
Abstract +
Torsion information is important for rotating systems, industrial monitoring, transportation engineering, and medical equipment. Optical fiber torsion sensors have significant advantages, such as immune to electromagnetic interference, small size, and light weight. Sagnac loop interferometer (SI) torsion sensors have attracted much attention due to their compact structure, high sensitivity, excellent stability, and low cost. However, their nonlinear response limits the measurement range, while the wide full width at half maximum and low signal-to-noise ratio (SNR) reduce the resolution of torsion sensors. To solve these problems, a fiber ring laser torsion sensor (FRLTS) based on homemade polarization-maintaining photonic crystal fiber (PM-PCF) is proposed in this work. The torsion sensor introduces a PM-PCF based SI into the erbium-doped fiber ring cavity as a filter and torsion sensor device. The interference spectrum of SI is derived by the transmission matrix method and simulated, and then the sensing principle of the sensor is obtained. Subsequently, the experimental system is set up to study the lasing output characteristics and torsion response of the FRLTS. By taking advantage of the narrow linewidth and high signal-to-noise ratio (SNR) of fiber ring lasers, a high-resolution fiber torsion sensor is successfully obtained. The experimental results show that the maximum linear torsion measurement range of the sensor can be extended to 480° (from –260° to 220°), the maximum torsion sensitivity is 0.032 nm/(°), and the resolution is as high as 0.681°. Furthermore, in a temperature range from 20 ℃ to 95 ℃, the temperature-induced wavelength variation is only 4×10–3 nm/℃, corresponding to a torsion angle measurement error of 0.16(°)/℃. Compared with existing reports, its temperature stability is increased by 37.5 times, while the temperature-induced error in angle measurements is reduced by 9.375 times. The proposed FRLTS not only successfully achieves high-resolution and wide-range torsion sensing, but also effectively suppresses cross-sensitivity caused by temperature. Therefore, the torsion sensor has significant potential applications in fields such as aerospace and robotics where precise measurement of minute torsion angle is required in special environments.
2025, 74 (20): 200702.
doi: 10.7498/aps.74.20250824
Abstract +
Coherence, as a core element of cutting-edge X-ray research technology, has driven the vigorous development of many experiments such as coherent X-ray diffraction imaging and X-ray holography in the past two decades, as well as the construction of fourth-generation synchrotron radiation sources and hard X-ray free electron lasers. To measure the size of synchrotron radiation light source and coherence of beamline, an X-ray measurement system based on two-dimensional (2D) single grating interferometry is established in this work, and the measurement principles and propagation models used in the system are also investigated. Firstly, based on the VanCittert-Zernike theorem, the relationship between the visibility of the interference lattice and the spatial coherence of X-rays is established. Secondly, by combining the Talbot self imaging effect of a single grating, the X-ray spatial coherence length of the grating plane is measured, and the spatial distribution of the corresponding light source is obtained through further calculation. The relevant measurement experiments of this study are conducted at the BL09B bending magnet beamline of the Shanghai Synchrotron Radiation Facility (SSRF). A 2D checkerboard π phase-shift grating is used as the core device in the experiment. This setup can not only enable the acquisition of transverse coherence lengths in the vertical and horizontal directions but also further measure the transverse coherence lengths in the directions forming 45° and 135° angles with respect to the horizontal direction. The experimental process strictly follows the technical specifications outlined in this paper: measuring interferograms at different positions downstream of the phase grating along the beam propagation direction. For each interferogram, the corresponding visibility values are extracted by analyzing the harmonic peaks in its Fourier-transformed image. Ultimately, the transverse coherence length in each direction is derived based on the evolution law of visibility as a function of the grating-to-detector distance. The experimental results show that the coherence length of the emitted X-rays on SSRF testline is 4.2 μm(H)×13.8 μm(V) at 15 keV, and the size of the bending magnet source is 124 μm(H)×38 μm(V). The results obtained by this method can provide important references for measuring the electron source size and developing experimental methods with high requirements for uniform illumination.
NUCLEAR PHYSICS
EDITOR'S SUGGESTION
2025, 74 (20): 202101.
doi: 10.7498/aps.74.20250898
Abstract +
In this work, we investigate the properties of strange quark matter (SQM) and color-flavor-locked (CFL) quark matter under zero temperature or strong magnetic fields within MIT bag model. We find that the thermodynamical properties of CFL quark matter are strongly affected by pairing energy gap Δ and magnetic field. The sound velocity of CFL quark matter and the tidal deformability of CFL quark stars both increase with Δ increasing, while the central baryon density of the maximum star mass in CFL state decreases with Δ. Specifically, the equation of state (EOS) of the CFL quark matter becomes stiffer with the increase of Δ, and the pressure becomes anisotropic when considering the magnetic field in the CFL quark matter. Our results indicate that the mass-radius relations of the CFL quark matter within the MIT bag model can describe the recent observations of pulsars, and that the maximum mass of CFL quark star increases with the increase of Δ. Moreover, the research results indicate that the mass of CFL quark star depends on the magnetic field strength and its orientation distributions within the magnetars, and the polytropic index of CFL quark matter decreases with the increase of star mass.
ATOMIC AND MOLECULAR PHYSICS
EDITOR'S SUGGESTION
2025, 74 (20): 203101.
doi: 10.7498/aps.74.20250959
Abstract +
The challenge in transporting water molecules through one-dimensional, large, disjoint nanochannels arises from the breaking of the water bridge. Even under significant pressure differences, water molecules are difficult to transport through these large disjoint nanochannels. Restoring the broken water bridge is crucial for maintaining continuous water transport through disjoint nanochannels. Current repairing methods, including the application of uniform or terahertz electric fields, are passive solutions. Once the electric fields are removed, it will stop working, causing the bridge to break again. In this study, molecular dynamics simulations are employed to investigate water transport through disjoint nanochannels with large nanogaps mediated by the coverage of coaxial nanochannels. The results reveal that as the diameter of the covered nanochannel decreases, the peak interaction between water molecules and the nanochannel decreases, which facilitates the reformation of the water bridge within the nanogap region. The water transfer rate through the disjoint nanochannel exhibits a non-monotonic dependence on the covered nanochannel diameter: it increases rapidly initially, then decreases with further increase in diameter, eventually reaching a relatively stable flow rate. Increasing the diameter of the covered nanochannel enhances water occupancy within the disjoint nanochannel, while the velocity and order parameter of water molecules display an initial increase followed by a decrease with further increase in diameter. These results offer significant insights into understanding the influence of covered nanochannels on water transport through disjoint nanochannels andproviding novel approaches for repairing broken water bridges in disjoint nanochannel systems.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2025, 74 (20): 204101.
doi: 10.7498/aps.74.20250838
Abstract +
2025, 74 (20): 204201.
doi: 10.7498/aps.74.20250804
Abstract +
2025, 74 (20): 204202.
doi: 10.7498/aps.74.20250886
Abstract +
Rare earth-activated phosphors have shown great potential applications in various fields, such as lighting, displays, anti-counterfeiting, and optical thermometry. This study aims to synthesize a series of Dy3+-doped Ca7NaY(PO4)6 phosphors through high-temperature solid-state reaction, focusing on developing multifunctional optical materials for lighting and temperature sensing. The phase purity and morphological characteristics of the obtained samples are confirmed by X-ray diffraction and scanning electron microscopy. Luminescence properties and energy transfer mechanisms are systematically investigated through photoluminescence spectroscopy and fluorescence decay analysis. Under 350-nm near-ultraviolet excitation, the emission intensity of Ca7NaY(PO4)6: Dy3+ increases with Dy3+ concentration rising until reaching an optimal value at x = 0.07, beyond which concentration quenching occurs. This quenching behavior is attributed to enhanced non-radiative energy transfer at higher Dy3+ concentrations, leading to a corresponding decrease in fluorescence lifetime. The optimized Ca7NaY(PO4)6: 0.07Dy3+ phosphor displays remarkable thermal stability, retaining 87.6% of its initial emission intensity at 150 ℃. The white light emitting diode(LED) device fabricated using the obtained phosphor and near-UV LED chip shows excellent performance with a correlated color temperature of 5680 K, CIE coordinates of (0.3275, 0.3883) in the white light region and a color rendering index of 85. Furthermore, temperature-dependent fluorescence intensity ratio analysis reveals excellent optical thermometric performance, achieving a maximum relative sensitivity (Sr) of 1.72 %/K. These results indicate that the Ca7NaY(PO4)6:Dy3+ phosphor exhibits significant potential applications in single-matrix phosphor-converted white LEDs and high-precision optical optical thermometry.
2025, 74 (20): 204701.
doi: 10.7498/aps.74.20250717
Abstract +
Bubble nucleation plays a pivotal role in microscale heat conduction, boiling heat transfer, and liquid-vapor phase change processes, because it not only governs heat transfer efficiency but also strongly regulates bubble dynamics. The nucleation processes are highly sensitive to the surface morphology and wettability of solid substrates. However, due to the inherent limitations of traditional experiments in terms of spatial resolution and observation times, revealing the microscopic mechanisms of bubble nucleation on a nanoscale remains a significant challenge—particularly under conditions involving complex surface structures and different wettability states. In this study, molecular dynamics simulations are employed to systematically investigate the mechanisms by which surface roughness and wettability influence bubble nucleation behavior on nanostructured surfaces on an atomic scale. Five copper substrates featuring sinusoidal protrusions are designed to represent different degrees of surface roughness. The sinusoidal profile, characterized by mathematical continuity and smoothness, not only facilitates the observation of bubble coalescence and contact angle evolution but also ensures comparability among models by maintaining identical protrusion height and overall width, thereby keeping the protrusion volume constant. This design allows for direct comparison of bubble growth rates and other physical quantities between different models. In addition, three different wettability conditions, namely hydrophobic, neutral, and hydrophilic, are achieved by modifying the interaction potential between oxygen and copper atoms. During the simulations, a constant heat flux is applied to the bottom copper substrate to trigger off spontaneous bubble nucleation, and local low-density regions are identified using density distribution analysis to track bubble nucleation sites; a piston-like pressure control mechanism is introduced through the top copper plate, and the displacement of this plate with time is used to quantify bubble growth rates under varying roughness and wettability. Additionally, the Kapitza resistance between solid and liquid phases is calculated to evaluate interfacial heat transfer efficiency. The results demonstrate that increasing surface roughness significantly promotes the formation of local low-density cavities, thereby accelerating the bubble nucleation and subsequent growth. As the surface wettability transitions from hydrophobic to hydrophilic, the solid–liquid interfacial thermal resistance decreases, leading to earlier bubble nucleation. Moreover, under hydrophilic conditions, the contact angle of the bubbles increases significantly, indicating enhanced detachment and growth behavior. Overall, the findings of this work advance the fundamental understanding of the microscopic mechanisms of bubble nucleation and provide theoretical guidance and technical references for designing high-efficiency heat transfer structures and tunable fluid–solid interfaces on a nanoscale.
2025, 74 (20): 204702.
doi: 10.7498/aps.74.20250783
Abstract +
In this study, a clustering method is used to extract the coherent structures associated with intense streamwise velocity fluctuations and temperature fluctuations in high-speed turbulent channel flow. Based on their spatial locations, these structures are categorized into wall-attached type and wall-detached type. A subset of the wall-attached structures exhibits self-similarity in scale, consistent with Townsend (1976)’s attached eddy hypothesis, and these structures are further classified as squat structure, self-similar structure, and tall structure. Conditional averaging results indicate that the streamwise Reynolds normal stress and the intensity of temperature fluctuations follow a logarithmic law in the logarithmic layer, a phenomenon that aligns with the attached eddy hypothesis; meanwhile, the strong Reynolds analogy relationship between velocity and temperature fluctuations remains valid within these attached structures. Analysis based on the RD (Renard-Deck) identity decomposition reveals that tall structures related to low streamwise momentum mainly control the generation of wall friction and heat flux, while tall structures related to high-temperature events play a main role in the of wall-normal heat flux transfer.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
EDITOR'S SUGGESTION
2025, 74 (20): 205205.
doi: 10.7498/aps.74.20250841
Abstract +
To meet the application requirements for continuous variable thrust capability and high-resolution characteristics for ion thrusters in drag-free flight missions of gravity gradient measurement satellites and precise orbit maintenance missions of near-Earth high-resolution observation satellites, the technical research on a high-resolution wide-range variable thrust ion thruster and its application verification are conducted. Leveraging the weak coupling and relative independence between the two critical physical processes of plasma discharge and ion beam extraction in Kaufman-type ion thrusters, a wide-range variable thrust ion thruster technical scheme with a divergent magnetic field configuration is proposed. The key technical investigations include wide-range discharge stability in the discharge chamber, a concave spherical ion optical system configuration design balancing wide-temperature-range ignition and high-density extraction requirements, and hollow cathode current emission continuity design. The discharge chamber structure based on a divergent magnetic field configuration can rapidly adjust plasma density under varying discharge intensities through optimal coordination of anode gas supply, magnetic induction intensity, and anode current, while resolving critical technical challenges in low-power discharge stability and high-power operational reliability. Adopting a concave spherical ion optical system, the technical challenge in matching grid thermal deformation spacing with the reliable extraction of high-density ion beams is addressed. The concave spherical configuration can realize full-power ion beam extraction within approximately 10 s in low-temperature environments. Meanwhile, the hollow cathode based on a lanthanum hexaboride (LaB6) emitter, through redundant design of emitter thickness and adaptive design of the cathode orifice aspect ratio, not only extends the emitter evaporation loss lifespan but also achieves stable operation within an emission current range of 0.5–3.4 A. Based on this, the design optimization and ground-based performance evaluation of a 10-cm-aperture high-resolution wide-range continuously variable thrust ion thruster are completed (In fact, such an ion thruster already achieved on-orbit flight in 2023.). Satellite on-orbit test results indicate that the 10-cm-aperture thruster achieves thrust regulation of 1.39–20.05 mN within a power range of 98.3–585.3 W, with specific impulse maintained at 547–3056 s, consistent with ground test results. The thrust response rate reaches approximately 3 mN/s, and thrust resolution exceeds 15 μN, outperforming ground test metrics. Compared with traditional chemical propulsion systems used for satellite orbit control, this thruster improves orbit maintenance accuracy by two orders of magnitude, effectively ensuring the implementation of satellite’s on-orbit engineering missions.
COVER ARTICLE
COVER ARTICLE
2025, 74 (20): 206301.
doi: 10.7498/aps.74.20250960
Abstract +
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
EDITOR'S SUGGESTION
2025, 74 (20): 206801.
doi: 10.7498/aps.74.20251021
Abstract +
SnTe-type topological crystalline insulators (TCIs) possess multiple Dirac-like topological surface states under the mirror-symmetry protection. Superconducting SnTe-type TCIs are predicted to form multiple Majorana zero modes (MZMs) in a single magnetic vortex. For the spatially isolated MZMs, there is only one MZM in a single vortex at surface. However, experimental demonstration of coupling the two isolated MZMs by changing wire length or intervortex distance is very challenging. For the multiple MZMs, two or more MZMs can coexist together in a single vortex. Thus, the novel property is expected to significantly reduce the difficulty in producing hybridization between MZMs. Recently, the experimental evidence for multiple MZMs has been observed in a single vortex of the superconducting SnTe/Pb heterostructure. However, SnTe is a heavily p-type semiconductor which is very difficult to induce the p-type to n-type transition via doping or alloying. The study on the Fermi-level tuning of SnTe-type TCIs is important for detecting and manipulating multiple MZMs. In this work, we report the influence of defects, such as film edge, grain boundary and dislocation, on the electronic property of Sn1–xPbxTe/Pb. The Sn1–xPbxTe films are prepared on the Pb (111) films grown on the Si (111) substrate by the molecular beam epitaxial technology. The structural and electronic properties of the Sn1–xPbxTe films are detected in situ by using low-temperature scanning tunneling microscopy and spectroscopy. The differential conductance tunneling spectra show that the minima of dI/dV spectra taken in the areas near the film edge, the grain boundary and the dislocation of Sn1–xPbxTe grown on Pb can be significantly changed to the energy very close to the Fermi level or even about –0.2 eV below the Fermi level, whereas the minima of dI/dV spectra taken in the areas far away from the defects are always at about 0.2 eV above the Fermi level. It indicates that these quasi one-dimensional defects, rather than Pb alloying, play an important role in modifying electronic property of the Sn1–xPbxTe/Pb heterostructure. Moreover, the Pb alloying will suppress the formation of zero-energy peak in the vortex. These results are expected to develop the new methods that do not require doping or alloying for the Fermi-level tuning of the SnTe-type topological superconducting devices.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2025, 74 (20): 207101.
doi: 10.7498/aps.74.20250801
Abstract +
Under high temperature and pressure conditions, silicon-based devices experience leakage and deformation due to the self-heating effect, making them unable to operate stably for a long time. Silicon carbide (SiC), as a representative third-generation semiconductor material, is an ideal option for high-temperature, high-frequency, and high-power electronic devices. However, the high-temperature performance limitations of 4H-SiC devices stem from the stability of ohmic contact electrodes and metal interconnections. The output of the lead electrodes is unstable at present, and oxygen intrusion at high temperatures can easily cause output failures. Previous studies indicate that the SiC/Ti/TaSi2/Pt multilayer structure holds significant potential for ohmic contacts. Building upon this ohmic contact foundation, this study proposes a batch sputtering-annealing process to prepare high-temperature-resistant lead electrodes. This involves altering the sequence of annealing and sputtering: first sputtering Ti/TaSi2 onto the SiC substrate and annealing to form the ohmic contact, followed by depositing a Pt protective layer to construct a novel SiC/Ti/TaSi2/Pt electrode structure. Comparative analysis of the two experimental groups is conducted using scanning electron microscope (SEM), auger electron spectroscopy (AES), X-ray diffraction (XRD), thin-film stress measurement, and semiconductor analyzers. The batch-sputtered and annealed electrode structure can enhance density and reduce residual stress, with an initial specific contact resistivity of 6.35×10–5 Ω·cm2. High-temperature aging tests at 600 ℃ demonstrates superior electrical stability for electrodes formed by sputtering Pt onto Ti/TaSi2 after ohmic contact formation. These electrodes maintain ohmic characteristics even after 20-hour air aging, whereas traditional co-sputtered ohmic contacts transition to Schottky contacts. Pt effectively suppresses atomic diffusion and oxidation reactions, resulting in a smooth electrode microstructure without curling. The batch sputtering-annealing process not only greatly enhances the overall performance of SiC ohmic contacts but also provides crucial guidance for realizing the structural design and performance improvement of ohmic contacts by using other metal combinations. This approach holds significant reference value for the high-temperature packaging of third-generation semiconductor power devices and the development of electronic systems operating in harsh environments.
2025, 74 (20): 207501.
doi: 10.7498/aps.74.20250734
Abstract +
Multiferroic tunnel junctions (MFTJs), characterized by a ferroelectric barrier encapsulated between two ferromagnetic electrodes, represent a highly promising platform for next-generation nonvolatile memory applications. The recent discovery of intrinsic ferromagnetism and ferroelectricity in van der Waals (vdW) materials further provides a compelling material foundation for constructing multifunctional MFTJs based on vdW heterostructures. In this paper, aiming at high-performance and multifunctional van der Waals multiferroic tunnel junctions (vdW-MFTJs) devices, we investigate the spin-dependent transport properties of vdW-MFTJs with a bilayer VTe2 sliding ferroelectric barrier and Fe3GaTe2/Fe3GeTe2 magnetic electrodes by using first-principles calculations based on density functional theory (DFT). Our results reveal that multiple non-volatile resistance states can be achieved by controlling the polarization direction of the ferroelectric barrier and the magnetization configuration of the ferromagnetic electrodes in the Fe3GaTe2/bilayer VTe2/Fe3GeTe2 MFTJs. Specifically, when the double-layer ferroelectric material VTe2 undergoes relative interlayer slippage, the polarization of the ferroelectric barrier switches from a left-oriented state (P←) to a right-oriented state (P→). Consequently, the tunneling magnetoresistance (TMR) ratio at the Fermi level increases from 7.27×105% to 1.01×106%. Moreover, switching the magnetization configuration of the ferromagnetic electrodes from parallel alignment (M↑↑) to antiparallel alignment (M↑↓) leads to an almost twofold increase in the tunneling electroresistance (TER) ratio. Furthermore, nearly 100% spin filtering efficiency is observed in all four non-volatile resistance states of the MFTJs. These findings demonstrate that the engineered Fe3GaTe2/bilayer VTe2/Fe3GeTe2 MFTJs hold promising potential applications in multi-state non-volatile memory and spin filters, providing a versatile platform for developing multifunctional electronic devices.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2025, 74 (20): 208801.
doi: 10.7498/aps.74.20250798
Abstract +
The high exciton binding energy of organic semiconductor materials limits charge separation efficiency. Investigating the excited state characteristics and modulation mechanisms of polymer donor and non-fullerene acceptor molecules is crucial for optimizing material design and enhancing the performance of organic photovoltaic devices. Therefore, this study investigates the excited state characteristics in polymer and non-fullerene organic materials. The tight-binding quantum mechanical method is used to systematically compare the excited state characteristics (including lattice geometry, band structure, and binding energy) between polymer donor and non-fullerene acceptor molecules, with particular emphasis on the role of electron-phonon coupling in modulating these excited state characteristics. The results indicate that non-fullerene acceptor molecules exhibit smaller lattice distortion, narrower bandgap, and lower binding energy than polymer donor molecules. It is precisely due to the different excited state characteristics of the polymer donor and non-fullerene acceptor molecules that the exciton binding energy in the organic photovoltaic system they constitute can be effectively reduced, while also providing a favorable energy-level shift for exciton dissociation. This significantly enhances the efficiency of charge transfer and separation. Furthermore, the decrease of electron-lattice coupling strength can further reduce these parameters in both polymer donor and non-fullerene acceptor molecules. By enhancing the electron-donating capability of central groups or the electron-withdrawing capacity of end groups in non-fullerene acceptor molecules, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels can be shifted upward or downward. The upshifted HOMO and LUMO energy levels are accompanied by an increase in molecular polarizability and a decrease in reorganization energy, while the downshifted HOMO and LUMO energy levels lead to an enhanced molecular dipole moment and improved electron affinity. This optimized energy-level structure further reduces the binding energy and achieves efficient charge separation. These findings demonstrate that the efficient charge transfer and separation in polymer/non-fullerene organic photovoltaic systems originate from their distinct molecular excited state characteristics. This basic understanding enables the rational design of high-performance organic optoelectronic materials and the development of novel organic photovoltaic devices by strategically adjusting the electron-phonon coupling strength and push-pull electronic structures of non-fullerene acceptors.
