Accepted
, , Received Date: 2025-08-31
Abstract +
Octafluorocyclobutane (C4F8)-based fluorocarbon plasmas have become a cornerstone of nanometre-scale etching and deposition in advanced semiconductor manufacturing, owing to their tunable fluorine-to-carbon (F/C) ratio, high density of reactive radicals, and superior material selectivity. In high-aspect-ratio pattern transfer, optical emission spectroscopy (OES) enables in-situ monitoring by correlating the density of morphology-determining radicals with their characteristic spectral signatures, thereby providing a viable pathway for the simultaneously optimizing pattern fidelity and process yield. A predictive plasma model that integrates kinetic simulation with spectroscopic analysis is therefore indispensable. In this study, a C4F8/O2/Ar plasma model tailored for on-line emission-spectroscopy analysis is established. First, the comprehensive reaction mechanism is refined through a systematic investigation of C4F8 dissociation pathways and the oxidation kinetics of fluorocarbon radicals. Subsequently, the radiative-collisional processes for the excited states of F, CF, CF2, CO, Ar and O are incorporated, establishing an explicit linkage between spectral features and radical densities. Under representative inductively coupled plasma (ICP) discharge conditions, the spatiotemporal evolution of the aforementioned active species is analyzed and validated against experimental data. Kinetic back-tracking is employed to elucidate the formation and loss mechanisms of fluorocarbon radicals and ions, and potential sources of modelling uncertainty are discussed. This model has promising potential for application in real-time OES monitoring during actual etching processes.
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Abstract +
Temporal- and angular-resolved photoionization experiments are essential for probing the geometric and electronic structural dynamics of atoms and molecules. Such studies require the measurement of full angular distributions of electrons and ions in free electron laser (FEL) experiments. Here, we present the first experimental results from the composite velocity imaging spectrometer (CpVMI) at the Shanghai Soft X-ray Free Electron Laser Facility (SXFEL). The study demonstrates its ability to capture energy and angular information for electrons and ions with high resolution and full solid-angle collection.
Krypton (Kr) atoms and carbon tetrachloride (CCl4) molecules are ionized using FEL pulses at 263.8 eV. Electron momentum images were recorded with an Andor Zyla 4.2 PLUS camera, while ion time-of-flight mass spectra and momentum distributions were acquired using a TPX3CAM. For Kr, the electron spectrum contains peaks from 3p, 3d, and 4p photoionization, as well as the Auger electrons from 3d and 3p levels. The measured anisotropy parameters (β) of these electrons show good agreement with previous theoretical Hartree-Fock calculations. Ion abundance in the time-of-flight mass spectra of Kr was consistent with the ratio derived from the intensities of the corresponding photoelectron peaks.
For CCl4, the electron spectrum contains Cl 2p photoelectrons, 2p Auger electrons, and valence-shell photoelectrons, with their angular distribution parameters also aligning with theoretical predictions. The TPX3CAM enabled direct measurement of the momenta of fragment ions without the need for inverse Abel transformation. By integrating the high-resolution flight time mass spectrometry and momentum imaging data obtained from TPX3CAM, we successfully visualized and analyzed the key photodissociation pathways of CCl4 molecules under the action of soft X-ray FEL. In particular, it distinguished between direct two-body dissociation and multi-step dissociation processes, and observed the unique angular distributions and kinetic energy release characteristics of different dissociation channels.
In conclusion, the experimental results clearly demonstrate that the CpVMI fully meets the technical requirements for FEL user experiments in terms of energy, angular distribution, and momentum measurement, offering a platform for FEL light-induced dynamics research. Future enhancements, including improved light focusing and the use of supersonic molecular beams, are expected to further advance the instrument's performance.
Krypton (Kr) atoms and carbon tetrachloride (CCl4) molecules are ionized using FEL pulses at 263.8 eV. Electron momentum images were recorded with an Andor Zyla 4.2 PLUS camera, while ion time-of-flight mass spectra and momentum distributions were acquired using a TPX3CAM. For Kr, the electron spectrum contains peaks from 3p, 3d, and 4p photoionization, as well as the Auger electrons from 3d and 3p levels. The measured anisotropy parameters (β) of these electrons show good agreement with previous theoretical Hartree-Fock calculations. Ion abundance in the time-of-flight mass spectra of Kr was consistent with the ratio derived from the intensities of the corresponding photoelectron peaks.
For CCl4, the electron spectrum contains Cl 2p photoelectrons, 2p Auger electrons, and valence-shell photoelectrons, with their angular distribution parameters also aligning with theoretical predictions. The TPX3CAM enabled direct measurement of the momenta of fragment ions without the need for inverse Abel transformation. By integrating the high-resolution flight time mass spectrometry and momentum imaging data obtained from TPX3CAM, we successfully visualized and analyzed the key photodissociation pathways of CCl4 molecules under the action of soft X-ray FEL. In particular, it distinguished between direct two-body dissociation and multi-step dissociation processes, and observed the unique angular distributions and kinetic energy release characteristics of different dissociation channels.
In conclusion, the experimental results clearly demonstrate that the CpVMI fully meets the technical requirements for FEL user experiments in terms of energy, angular distribution, and momentum measurement, offering a platform for FEL light-induced dynamics research. Future enhancements, including improved light focusing and the use of supersonic molecular beams, are expected to further advance the instrument's performance.
, , Received Date: 2025-09-05
Abstract +
The micro-newton-level cusped field Hall thruster is an electric propulsion device that employs microwave-assisted ionization control. It serves as an actuator in drag-free control systems, ensuring control accuracy and stability by providing continuously adjustable thrust over a wide range. However, a mode transition occurring in the regulation process can lead to a sudden change in anode current, thereby degrading control precision and stability. Therefore, it is necessary to investigate the underlying patterns of mode transition. This study examines the variations in internal plasma parameters and discharge characteristics of the thruster before and after microwave mode transition, primarily through probe diagnostics. Experimental results indicate that prior to mode transition, the plasma luminous region is primarily concentrated within the electron cyclotron resonance (ECR) area, approximately 1—3 mm upstream of the anode. After the transition, the luminous region moves further upstream, and the plasma density near the anode exceeds the cutoff density, dropping sharply along the axial direction. The fundamental cause of the change in electron heating mechanism is the alteration in the propagation characteristics of fundamental waves due to this plasma density variation. When the plasma density rises to the cutoff density, the R-wave and O-wave, which drive ionization, are rapidly attenuated or reflected. At this point, the R-wave cannot reach the resonance layer, causing the dominant ECR ionization to become ineffective. The ionization mechanism shifts from being dominated by the R-wave and O-wave to being dominated primarily by the O-wave. Consequently, the electron heating mechanism shifts from volume heating to surface wave heating. This research will provide a basis for subsequently optimizing microwave transmission in the thruster and for reducing the threshold at which mode transition occurs.
, , Received Date: 2025-08-29
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The pantograph-catenary system (PCS) serves as the exclusive means of power supply for high-speed trains.As train speeds increase, traction power rises, and operations take place in complex and variable environments, pantograph arcing has become more frequent. This phenomenon is accompanied by changes in physical properties and increased hazards, which seriously threaten the safety of high-speed railways. This paper systematically reviews the recent researches on pantograph arc, and outlines physical characteristics, experimental techniques, and simulation methods. The study focuses on analyzing the effects and mechanisms of operating parameters and environmental conditions on pantograph arc, summarizes prevention strategies, and explores applications such as arc energy utilization. Existing research has sufficiently examined how operational parameters affect arc hazards, yet studies on arc physical properties and evolution mechanisms remain limited, particularly regarding special conditions such as icing. Current protection methods also require adaptation to complex environments to meet the growing demands for arc management. Two future research priorities are proposed: first, clarifying the physical properties of an arc under special environments and establishing the correlation among “environmental conditions, an arc’s physical properties, and its behavior” to enable accurate prediction; second, developing an efficient arc prevention system through the approach of “source suppression, interface protection, and process intervention”. This review aims to provide theoretical and practical guidance for realizing reliable current collection and effective arc control in high-speed railway PCS in China.
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With the increasing demand for materials capable of withstanding extreme service environments in fields such as advanced manufacturing, aerospace, and nuclear energy, the development of materials combining high strength, hardness, and thermal stability has become highly significant. Chromium monoboride(CrB), owing to its unique crystal structure and excellent mechanical properties, has attracted considerable attention; however, its deformation and failure mechanisms under complex stress states remain unclear. In this work, first-principles calculations are employed, combined with electronic structure analysis, to investigate the mechanical response and microstructural evolution of CrB under uniaxial tension, pure shear, and shear coupled with normal stress. The results reveal pronounced tensile anisotropy: the tensile strength is highest along the [100] direction (69.92 GPa) and lowest along the [010] direction (44.69 GPa). The minimum pure shear strength (35.68 GPa) occurs along the (010)[100] direction. Under pure shear and low normal stress, the Cr-Cr bimetallic layers undergo interlayer slip at the critical shear strain, leading to a sudden stress drop. In contrast, under high normal compressive stress coupled with shear, the interlayer spacing between Cr-Cr bimetallic layers is significantly reduced, which enhances interlayer bonding and suppresses interlayer slip. As a result, strain energy accumulates within the crystal lattice, eventually causing an abrupt structural collapse and catastrophic failure. Further analysis shows that the effect of normal stress on shear strength is non-monotonic: it increases with pressure at low stresses but softens under high pressures. The sensitivity to normal stress varies significantly with crystallographic orientation, and the anisotropy is further amplified as pressure increases. This study elucidates the instability mechanisms of CrB under multiaxial stress, providing theoretical guidance and design reference for its applications in extreme environments.
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Microwave-induced thermoacoustic imaging, as an emerging biomedical imaging technique, combines the high contrast of microwave imaging with the high spatial resolution of ultrasound imaging. As an important branch of this technology, microwave-induced thermoacoustic microscopy retains these advantages while providing the capability to visualize finer tissue characteristics. However, conventional raster scanning mechanisms introduce interference in microwave field distribution due to mechanical motion, necessitating multiple signal averages to maintain signal-to-noise ratio. Additionally, the idle time during motor movement leads to prolonged single-scan duration, limiting its practical applications. To address these limitations, this paper proposes a rapid imaging system based on one-dimensional galvanometer scanning. The system employs a hybrid galvanometer-translation stage architecture and an optimized scanning strategy to minimize microwave field interference, reduce the number of signal averages, and decrease idle time, ultimately achieving more than a tenfold improvement in imaging speed. A specially designed timing control algorithm ensures precise synchronization of microwave excitation, galvanometer motion, and ultrasound detection, while a reconstruction algorithm adapted to the optimized scanning method effectively corrects distortions generated during the scanning process. System performance was evaluated through phantom and ex vivo tissue experiments. Resolution tests demonstrated hundred-micrometer resolution along all three axes (332 μm × 324 μm × 79 μm), while contrast and depth imaging experiments confirmed its capability to clearly distinguish targets with different conductivities, achieving an effective detection depth of at least 10 mm in tissue. Early tumor mimicking experiments further demonstrated the system's ability to identify lesion boundaries, preliminarily revealing its potential for rapid tumor margin assessment. This approach maintains the imaging quality of microwave-induced thermoacoustic microscopy while enhancing imaging efficiency and system stability, laying a crucial foundation for advancing the technology from laboratory research to clinical applications.
,
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Hydrogenation or protonation provides a feasible pathway for exploring exotic physical functionality and phenomena within correlated oxide system through introducing an ion degree of freedom. This breakthrough provides great potential for enhancing the application of multidisciplinary equipment in the fields of artificial intelligence, related electronics and energy conversions. Unlike traditional substitutional chemical doping, hydrogenation enables the controllable and reversible control over the charge-lattice-spin-orbital coupling and magnetoelectric states in correlated system, without being constrained by the solid-solution limits. Our findings identify proton evolution as a powerful tuning knob to cooperatively regulate the magnetoelectric transport properties in correlated oxide heterojunction, specifically in metastable VO2(B)/La0.7Sr0.3MnO3(LSMO) systems grown via laser molecular beam epitaxy (LMBE). Upon hydrogenation, correlated VO2(B)/LSMO heterojuction undergoes a reversible magnetoelectric phase transition from a ferromagnetic half-metallic state to a weakly ferromagnetic insulating state. This transition is accompanied by a pronounced out-of-plane lattice expansion due to the incorporation of protons and the formation of O—H bonds, as confirmed by X-ray diffraction (XRD). Proton evolution extensively suppresses both the electrical conductivity and ferromagnetic order in the pristine VO2(B)/LSMO system. Remarkably, these properties recover through dehydrogenation via annealing in an oxygen-rich atmosphere, underscoring the high reversibility of hydrogen-induced magnetoelectric transitions. Spectroscopic analyses, including X-ray photoelectron spectroscopy (XPS) and synchrotron-based soft X-ray absorption spectroscopy (sXAS), provide further insights into the physical origin underlying the hydrogen-mediated magnetoelectric transitions. Hydrogen-related band filling in the d-orbital of correlated oxides accounts for the electron localization in VO2(B)/LSMO heterostructure through hydrogenation, while the suppression of the Mn3+-Mn4+ double exchange leads to the magnetic transitions. This work not only expands the hydrogen-related phase diagram for related oxide system but also establishes a versatile pathway for designing exotic magnetoelectric functionalities via ionic evolution, which has great potential for developing protonic devices.
, , Received Date: 2025-11-17
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,
Abstract +
Exploited in radiation environments, including space, nuclear reactors and large accelerators, fibers would experience significant parameter change induced by the interaction with radiation, including radiation induced attenuation, radiation induced refractive index change, radiation induced lifetime change and radiation induced luminescence, which would then result in severe performance degradation of the fiber laser system. Here, the response characteristics of Yb-doped fiber lasers to gamma-ray radiation are investigated through both experiments and simulations. The performance variation of various fiber components after gamma radiation, including passive fiber, pump combiner, fiber Bragg grating and active fiber, is studied and compared with an accumulated total dose up to 1000 Gy. And, experiments show that, in a fiber laser system, the active fiber is the most sensitive part to gamma radiation, while various passive fiber components show negligible response. Then, impacts of cavity configuration parameters, such as pump scheme and active fiber length, on the response of fiber lasers are explored through series of radiation experiments. It’s shown that, compared to forward pump, backward pump scheme helpful to improve the radiation-resistant capability of fiber lasers. And, lasers with relatively shorter active fiber show smaller power drop when operated in radiation situations. Besides, corresponding simulations are carried out with the previously developed multi-physics thermal model considering hundred-watt level Yb-doped fiber lasers, demonstrating consistent results with the experiments. This research should be instructive for the design optimization of fiber laser systems operated in radiation environments.
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Abstract +
109Ag located on the path of the slow neutron capture process, and 79% of 109Ag is generated via the rapid neutron capture process.Meanwhile, the mass fraction of 109Ag in Ag-In-Cd control rods is 38.56%. Therefore, the neutron capture cross-section of 109Ag is crucial for both nuclear energy and nuclear astrophysics applications.In this work, a neutron capture cross-section measurement was performed using a 109Ag isotope target at the Back-n white neutron facility of the CSNS. Neutron capture cross-section in the 1-500 eV energy region were obtained by combining the time-of-flight method and the pulse-height weighting technique. The 109Ag resonance energy, neutron resonance width, and gamma resonance width parameters were extracted using the SAMMY code, which is based on R-matrix theory. The neutron resonance parameters extracted from this study at 139.4 eV are in agreement with the values in the JENDL-4.0 evaluation, while those at 169.9 eV and 328.1 eV agree with the JEFF-4.0 evaluation. Additionally, the result at 259.3 eV is consistent with the CENDL-3.2 evaluation.The datasets presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.j00213.00197 (Please use the private access link https://www.scidb.cn/s/RNfUnq to access the dataset during the peer review process)
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GeSn alloy, as a novel silicon-based optoelectronic material, demonstrates significant application potential in the field of infrared photonics due to its tunable bandgap properties and compatibility with silicon-based CMOS processes. Although the experimental performance of GeSn lasers under low-temperature conditions has been preliminarily validated, the optimization and practical application of this device still face challenges such as insufficient understanding of material properties. This paper addresses issues such as the unclear carrier dynamics mechanisms in GeSn alloy applications in infrared photonics. A theoretical model incorporating band parameters, non-equilibrium carrier transport, and radiative recombination have been proposed to systematically investigate the mechanism by which thermal excitation and phonon-assisted processes influence the direct-band spontaneous emission in GeSn alloys under variable temperature conditions. Results indicate that the carrier transfer process between the ΓCBM and LCBM energy bands of GeSn alloys exhibits significant composition dependence: for low-Sn-content GeSn alloys with Sn content below 10%, temperature-induced LCBM→ΓCBM electron transfer dominates, leading to an increase in direct band emission efficiency with rising temperature; whereas in high-Sn-content GeSn alloys with Sn content between 10% and 20%, the ΓCBM→LCBM electron escape process is more pronounced, resulting in a decrease in direct band emission efficiency with rising temperature. A modified Arrhenius modeling of the carrier dynamics competition further indicates that thermal excitation and phonon scattering synergistically regulate electron transfer between ΓCBM and LCBM. Analysis based on the modified Arrhenius model further demonstrates that both thermal excitation and phonon-assisted processes promote the injection and escape of electrons in the ΓCBM valley, serving as key factors in modulating the radiative recombination efficiency at the direct bandgap of GeSn alloys. The red shift of the peak position in the spontaneous emission spectrum of GeSn alloys primarily originates from the bandgap contraction effect; simultaneously, phonon-assisted processes reduce the dispersion of carrier energy distributions, leading to a pronounced narrowing effect in the direct band emission spectrum. Quantitative findings further elucidate the mechanism by which thermal excitation and phonon-assisted processes influence direct bandgap luminescence in GeSn alloys, offering theoretical guidance for performance regulation in infrared optoelectronic devices.
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Abstract +
Inductively coupled plasma (ICP) generators involve complex interactions between electromagnetic, thermal, and chemical processes, making direct diagnostics difficult. To clarify these coupling mechanisms, a two-dimensional axisymmetric model of an argon ICP torch operating at kilopascal pressure was developed using COMSOL Multiphysics under both local thermodynamic equilibrium (LTE) and nonequilibrium (NLTE) assumptions. A two-dimensional axisymmetric magnetohydrodynamic (MHD) model was established, incorporating electromagnetic induction, convective–radiative heat transfer, and a seven-reaction argon plasma chemistry mechanism. The LTE model assumes a uniform temperature for all species, while the NLTE model independently solves for the electron temperature (Te) and gas temperature (Tg), thereby accounting for incomplete energy exchange between electrons and heavy particles.At a discharge power of 1000 W and working pressure of 10 kPa, the LTE model predicts a peak temperature of approximately 8200 K, concentrated around the induction coils. In contrast, the NLTE model yields a maximum gas temperature of about 5990 K, with the hot zone shifted downstream. The NLTE model reveals a clear two-temperature structure: Te peaks near the coil wall (~0.93 eV) while Tg reaches its maximum downstream, indicating a pronounced thermal non equilibrium state where electrons are preferentially heated by the induced field. The calculated skin depth (~11.3 mm) coincides with the region of strongest electromagnetic energy deposition.Species analysis shows that the plasma core is dominated by ground-state argon (Ar) (>99%), while excited argon (Ar*) and argon ions (Ar+) increase notably near the coil region, confirming that excitation and ionization processes are localized within the skin layer. Furthermore, comparison between 5 kPa and 10 kPa cases demonstrates that as pressure decreases, the difference between Te and Tg widens, reflecting enhanced thermal non-equilibrium due to reduced collisional coupling.Overall, the results highlight that LTE and NLTE assumptions lead to markedly different predictions of temperature and energy coupling at kilopascal pressures. The NLTE model captures delayed energy transfer and spatial temperature decoupling more realistically, providing new insights into the electromagnetic– thermal–flow interactions of ICP discharges and offering a modeling reference for ICPbased high-enthalpy plasma wind tunnel design and related aerospace applications.
, , Received Date: 2025-09-09
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, , Received Date: 2025-08-29
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With the technological advantages of high thrust, high specific impulse, long life, variable specific impulse, and high efficiency, the variable specific impulse magnetoplasma rocket engine has become the essential advanced propulsion system for the deep space exploration and manned space flight in the future. In the variable specific impulse magnetoplasma rocket engine, the ion cyclotron resonance heating stage is linked with the helicon plasma source. The operation status of the helicon plasma source has a direct influence on the ion heating process in the ion cyclotron resonance heating stage. It is of great significance for the testing and the optimization of the engine performance to reveal the influence of the ionization process on the ion heating process. In this paper, a multi-fluid model in which the ion cyclotron resonance heating stage is linked with the helicon plasma source is developed. The numerical simulations with different input currents of helicon plasma source and different pressures are performed to analyze the effect of the operation status in the helicon plasma source on the ion energy density in the ion cyclotron resonance heating stage. The results show that the discharge mode of the helicon plasma source gradually changes with the increase of the input current and that the plasma density jump appears while the ion temperature remains basically unchanged. With the plasma density jump and nearly identical ion temperature the ion energy density jump also appears in the simulation domain. Similar to the results of the simulation under different input currents of the helicon plasma source, the plasma density and the ion energy density also jump when the pressure increases. However, the ion temperature decreases due to the discrepancy between the input frequency and the resonance frequency. With the numerical model and the input conditions of this study, the ionization process in the helicon plasma source is decoupled with the ion heating process in the ion cyclotron resonance heating stage. The energy gain of a single ion in the ion cyclotron resonance heating stage does not change with the operation status of the helicon plasma source, thereby accounting for the ability of the engine to work in multi mode.
, , Received Date: 2025-07-29
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Rotating spokes, as one of the low-frequency, long-wavelength instabilities, are commonly observed in the ${\boldsymbol{E}} \times {\boldsymbol{B}}$ plasma discharge devices, such as the magnetrons and Hall thrusters. In Hall thrusters, the rotating spokes, which are located in the discharge channel and rotate in the azimuthal direction, feature the bright luminous regions. The space potential will be distorted by the instability of rotating spokes, thereby increasing the possibility for electrons to reach the anode and enhancing their drift along the equipotential lines. However, the excitation mechanism of the rotating spoke and its influencing factors remain ambiguous. In order to address this problem, we conduct numerical simulations and linear stability analysis to investigate the effects of the magnetic field gradient on the driving mechanism and mode characteristics of the rotating spoke instability. In this work, a particle-fluid two-dimensional hybrid model in the axial-azimuthal plane is employed to numerically study the effect of axial magnetic field gradient in the discharge channel on the rotating spoke. The numerical simulation results are analyzed using a dispersion relation derived from fluid theory, which combines the effects of plasma density and the magnetic field gradient. The output profiles of ion density, potential, and electric field from the numerical simulation serve as input parameters for the dispersion relation used in the linear stability analysis. The simulation results show that the frequency and propagation velocity of the $m = 1$ rotating spoke slightly increase as the magnetic field gradient in the discharge channel decreases. However, changing the magnetic field gradient in the discharge channel does not affect the propagation direction nor intrinsic characteristics of the rotating spoke. More specifically, when the value of ${\alpha _1}$increases from 1.1 to 1.7, which means a decrease of the magnetic field gradient in the discharge channel, the mode frequency rises from 6.2 kHz to 7.5 kHz, remaining within the frequency range of the rotating spoke instability. At the same time, the phase velocity also increases form 1013 m/s to 1225 m/s, which is consistent with the propagation velocity of the rotating spoke instability, and the rotating spoke instability still propagates along the ${\boldsymbol{E}} \times {\boldsymbol{B}}$ direction. Dispersion relation analysis indicates that the rotating spoke arises from an azimuthal drift instability which is located near downstream region of the thruster exit, and it is excited by the plasma density and magnetic field gradient effects. The axial position of the azimuthal drift instability, responsible for the rotating spoke formation, is slightly modulated by density profile variations caused by the change of magnetic field in the discharge channel. However, it remains near the downstream region of the thruster exit. The results indicate that the rotating spoke does not originate from ionization instabilities, and changing the magnetic field distribution in the discharge channel does not affect its propagation direction nor mode number. The research results provide theoretical support for explaining the excitation mechanism and key influencing factors of rotating spoke.
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