Accepted
, , Received Date: 2025-06-08
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Investigating molecular fragmentation mechanisms and the kinetic energy distributions of fragments provides crucial insights into their roles in plasma physics, radiation-induced damage in biological tissues, and interstellar chemistry. In this study, we conducted collision experiments between 3 keV/u Ar8+ ions and CH3F molecules using a cold target recoil ion momentum spectrometer. We focused on the three-body fragmentation channel H+ + CH2+ + F+ resulting from C-F and C-H bond cleavage in CH3F3+ ions, and measured the three-dimensional momentum vectors of all fragment ions. The fragmentation mechanism involved was analyzed using ion-ion kinetic energy correlation spectra, Newton diagrams, Dalitz plots and other correlation spectra.
Our results reveal two distinct dissociation mechanisms for the H+ + CH2+ + F+ channel, i.e., concerted and sequential fragmentation, with the former one being dominant. In the sequential fragmentation process, H+ and the intermediate CH2F2+ are firstly formed, followed by further fragmentation of the intermediates into CH2+ and F+. No sequential pathways involving HF2+ or CH32+ intermediates were identified. Furthermore, we observed two types of concerted fragmentation processes with different dynamical characteristics, suggesting that hydrogen atoms in CH3F3+ may occupy different chemical environments. This phenomenon could originate from either molecular isomerization producing different structural geometries or the Jahn-Teller effect leading to inequivalent C-H bonds. This study reveals the three-body dissociation dynamics of CH3F3+ induced by highly charged ion collisions, highlighting the significant role of the Jahn-Teller effect or molecular isomerization in the ionic dissociation of polyatomic molecules.
Our results reveal two distinct dissociation mechanisms for the H+ + CH2+ + F+ channel, i.e., concerted and sequential fragmentation, with the former one being dominant. In the sequential fragmentation process, H+ and the intermediate CH2F2+ are firstly formed, followed by further fragmentation of the intermediates into CH2+ and F+. No sequential pathways involving HF2+ or CH32+ intermediates were identified. Furthermore, we observed two types of concerted fragmentation processes with different dynamical characteristics, suggesting that hydrogen atoms in CH3F3+ may occupy different chemical environments. This phenomenon could originate from either molecular isomerization producing different structural geometries or the Jahn-Teller effect leading to inequivalent C-H bonds. This study reveals the three-body dissociation dynamics of CH3F3+ induced by highly charged ion collisions, highlighting the significant role of the Jahn-Teller effect or molecular isomerization in the ionic dissociation of polyatomic molecules.
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Two-dimensional (2D) materials, owing 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 Xray 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. Key findings demonstrate that high pressure can induce the transition of graphene from a semimetal to a semiconductor or even a superconducting state, trigger structural phase transitions and semiconductor-to-metal transitions in TMDs such as MoS2 and WTe2, and result in pressuredependent bandgap narrowing and marked enhancements of luminescence intensity in two-dimensional perovskites. This work underscores the utility of high-pressure techniques in uncovering the intrinsic correlations between the microstructure and macroscopic properties of twodimensional materials. Furthermore, it discusses the key challenges and opportunities in this emerging research area, providing insights for the development and practical application of novel functional materials.
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Nonequilibrium heat transport and quantum thermodynamics in quantum light-matter interacting systems have recently attracted increasing attention. Consequently, quantum thermal devices, e.g., heat valve and head diode have been realized. Here, we investigate quantum heat flow in the nonequilibrium anisotropic Dicke model, where an ensemble of qubits collectively interacts with a photon field with anisotropic forms, each component individually interacting with bosonic thermal reservoirs. The quantum dressed master equation (DME) is included to properly study dissipative dynamics of the anisotropic Dicke model, which is able to handle strong qubit-photon coupling within the eigenbasis of the reduced anisotropic Dicke system. Our results demonstrate that anisotropic qubit-photon interactions are crucial for modulating steady-state heat flow, particularly at moderate and strong couplings. We also find that the analytical expressions of heat flows in the thermodynamic limit with limiting anisotropic factors can be used as the upper boundaries for the heat flows in the anisotropic Dicke model with finite qubit numbers. These heat flows exhibit cotunneling microscopic transport processes. Moreover, the large anisotropic factor and nonweak qubit-photon coupling are helpful in achieving the giant thermal rectification effect. We hope these results may deepen the understanding of nonequilibrium heat transport in the anisotropic quantum light-matter interacting systems.
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In radiation environments, the radiation induced attenuation (RIA) of the active fiber will induce severe performance degradation to the fiber laser system. One effective way to solve this problem is to bleach the active fiber with pumps at certain wavelengths, namely photo-bleaching. Experiments have shown that, output power of irradiated Yb-doped fiber lasers experiences remarkable recovery with 976 nm pump. However, under 976 nm pump, signals at both 976 nm and 1070 nm co-exist inside of the Yb-doped fiber. And, it can hardly tell which wavelength is responsible for the photo-bleaching process. Here, a one-hundred level Yb-doped fiber laser is irradiated with gamma-ray radiation. During the radiation process, significant output decline from 129 W at 0 Gy to 81 W at 100 Gy is witnessed. Then, self-bleaching test is conducted with 976 nm pump. After 2 h of bleaching, the output power restored to 111 W, corresponding to a recovery ratio of about 37.0%. To verify the specific wavelength responsible for the performance recovery, photo-bleaching characteristics of Yb-doped fiber lasers are investigated under different pump wavelengths including 915 nm, 976 nm, 1070 nm and 1550 nm. Experiments show that, laser signal at 1 μm waveband is the primary cause for the bleaching of Yb-doped fibers, while, the pump at 915 nm, 976 nm and 1550 nm can hardly bleach the irradiated Yb-doped fiber. The RIA recovery curves of Yb-doped fibers under different 1070 nm bleaching powers are measured. And, related evolution parameters are obtained through curve fitting. With these parameters, the RIA evolution of the Yb-doped fiber and the corresponding output power evolution of the Yb-doped fiber laser during the radiation and bleaching process are simulated. Comparisons show that, the numerical results are consistent with the experiments qualitatively, demonstrating the reliability of the model. This work should be instructive for the performance prediction of fiber laser systems under radiation and bleaching environments.
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The photon blockade effects in a system consisting of an artificial giant atom coupled to three cavities are investigated. By solving the Schrödinger equation, we have obtained the steady-state probability amplitudes of the system and derived the analytical expressions for the equal-time second-order correlation function. Based on these analytical expressions, the optimal conditions for the photon blockade under different driving conditions are derived in detail. We first examine the energy spectrum and transition pathways for the single-photon and two-photon excitations under the case of weak driving the cavity mode, and then investigate the photon statistical properties . It is demonstrated that the optimal conventional photon blockade can be achieved by selecting appropriate driving detunings, characterized by the equaltime second-order correlation function of g(2) (0) ≈ 10-3.4. Remarkably, we observe that both cavities of the system exhibit photon blockade effects robust against the weak driving. It also can be found that the photon blockade phenomenon becomes more pronounced while maintaining its robustness to the weak driving with the increase of the coupling strength between the artificial giant atom and cavities. Furthermore, we consider the case of simultaneously driving both the artificial giant atom and cavity modes. The unique multi-point coupling characteristics of the artificial giant atom provide additional transition pathways for photons, allowing us to exploit the resulting quantum interference to further enhance photon blockade. When the system satisfies both the optimal parametric conditions for the conventional and unconventional blockade effects, one cavity exhibits exceptional photon blockade with g(2) (0) ≈ 10-6.5. This research significantly relaxes the stringent parameter requirements for the experimental realization of single-photon sources and provides a theoretical support for improving their quality, which is crucial for achieving high-performance single-photon source.
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The band gap, localization, and waveguide characteristics of phononic crystal structures offer extensive potential for applications in the transducer field, particularly for circular-hole phononic crystals, which are extensively utilized in performance optimization research for transducers owing to their straightforward structure and ease of fabrication. Nonetheless, studies have revealed that the bandgap width of circular-hole phononic crystal structures is directly proportional to their porosity. Typically, a higher porosity leads to enhanced energy localization of elastic waves. However, high porosity implies a narrower distance between circular holes, drastically compromising the mechanical strength of the structure. The introduction of columnar phononic crystal structures addresses the issues of high porosity and stringent dimensional accuracy demands of circular-hole phononic crystal structures, presenting novel avenues for enhancing the performance of piezoelectric ultrasonic transducers.
The paper employs cylindrical and acoustic surface structures fabricated on the front and rear cover plates of piezoelectric ultrasonic transducers to manipulate the transmission behavior and pathway of sound waves, thereby achieving effective control over coupled vibrations within the transducer. This approach not only addresses the issue of uneven amplitude distribution on the radiation surface due to uneven vibration energy transmission but also markedly enhances the displacement amplitude of the transducer's radiation surface, ultimately boosting its operational efficiency. Simulation results elucidate the impact of the configuration of these cylindrical and acoustic surface structures on transducer performance. Experimental findings further validate that these structures can effectively elevate the performance of piezoelectric ultrasonic transducers. This research offers systematic design theoretical support for the engineering calculation and optimization of transducers.
The paper employs cylindrical and acoustic surface structures fabricated on the front and rear cover plates of piezoelectric ultrasonic transducers to manipulate the transmission behavior and pathway of sound waves, thereby achieving effective control over coupled vibrations within the transducer. This approach not only addresses the issue of uneven amplitude distribution on the radiation surface due to uneven vibration energy transmission but also markedly enhances the displacement amplitude of the transducer's radiation surface, ultimately boosting its operational efficiency. Simulation results elucidate the impact of the configuration of these cylindrical and acoustic surface structures on transducer performance. Experimental findings further validate that these structures can effectively elevate the performance of piezoelectric ultrasonic transducers. This research offers systematic design theoretical support for the engineering calculation and optimization of transducers.
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Purpose : The interaction of intense, ultrashort laser pulses with atoms gives rise to a rich tapestry of non-perturbative phenomena, encoded within the final-state photoelectron momentum distribution (PMD). A particularly enigmatic feature, often observed in the multiphoton ionization regime (Keldysh parameter $\gamma \gtrsim 1$), is a complex, fan-like interference pattern in the near-threshold, low-energy region of the PMD. The physical origin of this structure has been the subject of extensive debate, with proposed mechanisms ranging from multipath interference in the Coulomb field to complex sub-barrier dynamics. This work aims to provide a physical explanation for this phenomenon. We hypothesize and demonstrate that this fan-like structure is not a mere consequence of Coulomb focusing but serves as a direct and sensitive signature of non-adiabatic dynamics occurring as the electron tunnels through the laser-dressed atomic potential barrier. Our goal is to unambiguously isolate the key physical ingredients responsible for shaping this quantum interference.
Methodology : To achieve this, we employ a synergistic three-pronged approach that combines experiment, exact numerical simulation, and a sophisticated theoretical model.
1. Experiment : We performed velocity-map imaging measurements on argon atoms ionized by a 798 nm, 35 fs laser pulse at a peak intensity of $6.3 \times 10^{13}$ W/cm$^2$. This provides the experimental result, clearly revealing the low-energy fan-like interference pattern.
2. Quantum Benchmark : We solved the time-dependent Schrödinger equation (TDSE) within the single-active-electron (SAE) approximation, using a well-established model potential for argon that accurately reproduces its ionization potential and ground-state properties. After performing a focal-volume average to simulate experimental conditions, the TDSE results show excellent qualitative agreement with the measurements, establishing the TDSE as a reliable quantum benchmark for our investigation.
3. Semiclassical Model (CTMC-p) : The core of our analysis relies on a custom-developed semiclassical trajectory model based on the Feynman path-integral formulation. In this framework, ionization is a two-step process: (i) an electron tunnels through the potential barrier at an initial time $t_0$ and position $\mathbf{r}_0$, and (ii) it propagates classically in the combined laser and ionic fields according to Newton's equations. Crucially, each trajectory is endowed with a quantum phase accumulated along its path, $\Phi_k$, allowing for the coherent summation of all trajectories ending with the same final momentum, $M_j = \sum_k e^{i\Phi_k}$. Our model incorporates two critical physical effects beyond standard treatments:
Non-Adiabatic Tunneling : We introduce a non-zero initial longitudinal momentum, $v_{0\parallel} = -A(t_0)(\sqrt{1+\gamma_{\text{eff}}^2}-1)$, acquired by the electron at the tunnel exit. This term accounts for the non-instantaneous nature of the tunneling process, a key non-adiabatic effect.
Core Polarization : We include an induced dipole potential, $U_{\text{ID}} = -\alpha^I \mathbf{E}(t) \cdot \mathbf{r}/r^3$, to model the dynamic polarization of the Ar$^+$ ionic core, a multi-electron effect.
By selectively including or excluding these effects, we can unambiguously isolate their respective contributions to the final PMD.
Results : Our central finding is that the non-adiabatic initial longitudinal momentum is the decisive factor for correctly describing the near-threshold interference. This is powerfully illustrated in Figure 6. The benchmark TDSE calculation [Fig. 6(a)] for a single intensity of $5 \times 10^{13}$ W/cm$^2$ ($\gamma \approx 1.6$) reveals a distinct 6-lobe interference pattern. A conventional semiclassical simulation based on the quasi-static tunneling approximation (i.e., setting $v_{0\parallel}=0$) qualitatively fails, predicting an incorrect 8-lobe structure [Fig. 6(c)]. However, upon including the non-zero initial longitudinal momentum ($v_{0\parallel} \neq 0$), our non-adiabatic semiclassical model quantitatively reproduces the correct 6-lobe structure in perfect agreement with the TDSE benchmark [Fig. 6(b)].
To understand the underlying physics, we performed a quantum-orbit decomposition. This analysis reveals that the overall fan-like structure arises from the interference of multiple trajectory types, including 'direct' (Category I), 'forward-scattered' (Category II), and 'glory-scattered' (Category III) orbits. While the full structure results from the collective interference of these paths, we have pinpointed the origin of the lobe-count correction. The initial longitudinal momentum contributes a phase term, $\Delta\Phi_{\text{initial}} \approx -\mathbf{v}_{0\parallel} \cdot \mathbf{r}_0$, to the total accumulated action. We found that the relative phase between the 'direct' and 'glory' trajectories is exquisitely sensitive to this term due to their vastly different paths and birth conditions. It is this specific and dramatic change in the I-III interference channel that ultimately corrects the topology of the entire pattern, reducing the lobe count from 8 to 6. In contrast, other interference pairs, such as the holographic pair II-III, are largely robust against this effect as their nearly identical birth conditions cause the initial phase term to cancel in their relative phase. In parallel, our simulations show that the ionic core polarization has a negligible effect on this low-energy structure but is essential for accurately describing higher-energy rescattering features by smoothing unphysical caustics caused by a pure Coulomb potential.
Conclusion : We have unequivocally demonstrated that the near-threshold fan-like interference pattern in the multiphoton regime is a direct manifestation of non-adiabatic dynamics during tunneling, specifically the acquisition of a longitudinal momentum component by the electron during its finite-time passage under the potential barrier. Our findings not only provide a clear, intuitive, and orbit-based physical picture for this complex quantum phenomenon but also highlight the predictive power of semiclassical methods when crucial non-adiabatic effects are properly incorporated. This understanding lays a foundation for future investigations, including the extension of this model to more complex molecular systems and its application in retrieving attosecond electron dynamics from holographic interference patterns.
Methodology : To achieve this, we employ a synergistic three-pronged approach that combines experiment, exact numerical simulation, and a sophisticated theoretical model.
1. Experiment : We performed velocity-map imaging measurements on argon atoms ionized by a 798 nm, 35 fs laser pulse at a peak intensity of $6.3 \times 10^{13}$ W/cm$^2$. This provides the experimental result, clearly revealing the low-energy fan-like interference pattern.
2. Quantum Benchmark : We solved the time-dependent Schrödinger equation (TDSE) within the single-active-electron (SAE) approximation, using a well-established model potential for argon that accurately reproduces its ionization potential and ground-state properties. After performing a focal-volume average to simulate experimental conditions, the TDSE results show excellent qualitative agreement with the measurements, establishing the TDSE as a reliable quantum benchmark for our investigation.
3. Semiclassical Model (CTMC-p) : The core of our analysis relies on a custom-developed semiclassical trajectory model based on the Feynman path-integral formulation. In this framework, ionization is a two-step process: (i) an electron tunnels through the potential barrier at an initial time $t_0$ and position $\mathbf{r}_0$, and (ii) it propagates classically in the combined laser and ionic fields according to Newton's equations. Crucially, each trajectory is endowed with a quantum phase accumulated along its path, $\Phi_k$, allowing for the coherent summation of all trajectories ending with the same final momentum, $M_j = \sum_k e^{i\Phi_k}$. Our model incorporates two critical physical effects beyond standard treatments:
Non-Adiabatic Tunneling : We introduce a non-zero initial longitudinal momentum, $v_{0\parallel} = -A(t_0)(\sqrt{1+\gamma_{\text{eff}}^2}-1)$, acquired by the electron at the tunnel exit. This term accounts for the non-instantaneous nature of the tunneling process, a key non-adiabatic effect.
Core Polarization : We include an induced dipole potential, $U_{\text{ID}} = -\alpha^I \mathbf{E}(t) \cdot \mathbf{r}/r^3$, to model the dynamic polarization of the Ar$^+$ ionic core, a multi-electron effect.
By selectively including or excluding these effects, we can unambiguously isolate their respective contributions to the final PMD.
Results : Our central finding is that the non-adiabatic initial longitudinal momentum is the decisive factor for correctly describing the near-threshold interference. This is powerfully illustrated in Figure 6. The benchmark TDSE calculation [Fig. 6(a)] for a single intensity of $5 \times 10^{13}$ W/cm$^2$ ($\gamma \approx 1.6$) reveals a distinct 6-lobe interference pattern. A conventional semiclassical simulation based on the quasi-static tunneling approximation (i.e., setting $v_{0\parallel}=0$) qualitatively fails, predicting an incorrect 8-lobe structure [Fig. 6(c)]. However, upon including the non-zero initial longitudinal momentum ($v_{0\parallel} \neq 0$), our non-adiabatic semiclassical model quantitatively reproduces the correct 6-lobe structure in perfect agreement with the TDSE benchmark [Fig. 6(b)].
To understand the underlying physics, we performed a quantum-orbit decomposition. This analysis reveals that the overall fan-like structure arises from the interference of multiple trajectory types, including 'direct' (Category I), 'forward-scattered' (Category II), and 'glory-scattered' (Category III) orbits. While the full structure results from the collective interference of these paths, we have pinpointed the origin of the lobe-count correction. The initial longitudinal momentum contributes a phase term, $\Delta\Phi_{\text{initial}} \approx -\mathbf{v}_{0\parallel} \cdot \mathbf{r}_0$, to the total accumulated action. We found that the relative phase between the 'direct' and 'glory' trajectories is exquisitely sensitive to this term due to their vastly different paths and birth conditions. It is this specific and dramatic change in the I-III interference channel that ultimately corrects the topology of the entire pattern, reducing the lobe count from 8 to 6. In contrast, other interference pairs, such as the holographic pair II-III, are largely robust against this effect as their nearly identical birth conditions cause the initial phase term to cancel in their relative phase. In parallel, our simulations show that the ionic core polarization has a negligible effect on this low-energy structure but is essential for accurately describing higher-energy rescattering features by smoothing unphysical caustics caused by a pure Coulomb potential.
Conclusion : We have unequivocally demonstrated that the near-threshold fan-like interference pattern in the multiphoton regime is a direct manifestation of non-adiabatic dynamics during tunneling, specifically the acquisition of a longitudinal momentum component by the electron during its finite-time passage under the potential barrier. Our findings not only provide a clear, intuitive, and orbit-based physical picture for this complex quantum phenomenon but also highlight the predictive power of semiclassical methods when crucial non-adiabatic effects are properly incorporated. This understanding lays a foundation for future investigations, including the extension of this model to more complex molecular systems and its application in retrieving attosecond electron dynamics from holographic interference patterns.
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Aiming at the challenging problem of analyzing the strong nonlinear coupling effect between four-wave mixing and stimulated Raman scattering in single-mode optical fibers, this paper introduces a novel multi-scale physically constrained network, designated as MSPC-Net, which effectively integrates fundamental physical mechanisms with advanced neural network techniques. The proposed model incorporates the frequency domain residual derived from the nonlinear Schrödinger equation directly into the network optimization procedure as a differentiable physical constraint term. This strategic inclusion ensures that the learning process remains consistent with the underlying physical principles governing light propagation in optical fibers. Furthermore, the model architecture employs a multiscale dilated convolution module specifically designed to capture and fuse features across different granularities, including fine local spectral details, intermediaterange broadening effects, and long-range attenuation trends. This multi-scale approach enables the simultaneous and high-precision inversion of both separated spectral components and critical physical parameters.
Experimental evaluations were conducted using single-mode quartz fibers with lengths of 250 meters and 500 meters. The results demonstrate that the Stokes spectra reconstructed by MSPC-Net achieve remarkably low root mean square errors, measuring only 0.014 and 0.0173 for the two fiber lengths respectively. This performance represents a reduction of more than sixty-eight percent compared to conventional convolutional neural networks. Additionally, the average absolute errors for frequency offset prediction are as low as 0.03 nanometer and 0.04 nanometer, corresponding to an accuracy improvement of approximately ninety percent relative to existing state-of-the-art methods. Under noisy conditions with a signal-to-noise ratio of 6 decibels, the model maintains an exceptional detection accuracy of up to 95.3 percent for identifying FWM sub-peak information, while keeping the pseudo-peak rate below 4.7 percent.
Benefiting from the strong guidance provided by embedded physical constraints and its lightweight structural design, the proposed model exhibits only a 9.8 percent increase in root mean square error even under challenging noise conditions with a signal-to-noise ratio of 15 decibels. Moreover, MSPC-Net demonstrates satisfactory real-time processing capabilities, making it suitable for deployment on embedded devices. This practical efficiency positions the model as a promising solution for optimizing high-power optical communication systems and advancing distributed optical fiber sensing applications. By successfully combining rigorous physical laws with multi-scale feature extraction, this research provides an effective approach to resolving the analytical difficulties associated with complex nonlinear effects in long-distance optical fibers, while significantly enhancing both the theoretical consistency and noise robustness of the prediction outcomes.
Experimental evaluations were conducted using single-mode quartz fibers with lengths of 250 meters and 500 meters. The results demonstrate that the Stokes spectra reconstructed by MSPC-Net achieve remarkably low root mean square errors, measuring only 0.014 and 0.0173 for the two fiber lengths respectively. This performance represents a reduction of more than sixty-eight percent compared to conventional convolutional neural networks. Additionally, the average absolute errors for frequency offset prediction are as low as 0.03 nanometer and 0.04 nanometer, corresponding to an accuracy improvement of approximately ninety percent relative to existing state-of-the-art methods. Under noisy conditions with a signal-to-noise ratio of 6 decibels, the model maintains an exceptional detection accuracy of up to 95.3 percent for identifying FWM sub-peak information, while keeping the pseudo-peak rate below 4.7 percent.
Benefiting from the strong guidance provided by embedded physical constraints and its lightweight structural design, the proposed model exhibits only a 9.8 percent increase in root mean square error even under challenging noise conditions with a signal-to-noise ratio of 15 decibels. Moreover, MSPC-Net demonstrates satisfactory real-time processing capabilities, making it suitable for deployment on embedded devices. This practical efficiency positions the model as a promising solution for optimizing high-power optical communication systems and advancing distributed optical fiber sensing applications. By successfully combining rigorous physical laws with multi-scale feature extraction, this research provides an effective approach to resolving the analytical difficulties associated with complex nonlinear effects in long-distance optical fibers, while significantly enhancing both the theoretical consistency and noise robustness of the prediction outcomes.
, , Received Date: 2025-06-03
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Based on density functional theory (DFT), the formation energies of intrinsic vacancy defects (VC, VSi, and VSi+C) and oxygen-related defects (OC, OSi, OCVSi, and OSiVC) in 3C-SiC are systematically investigated. The results indicate that all defects considered, except for OC, possess neutral or negative charge states, thereby making them suitable for detection by positron annihilation spectroscopy (PAS). Furthermore, the electron and positron density distributions and positron annihilation lifetimes for the perfect 3C-SiC supercell and various defective configurations are computed. It is found that the OSi and OSiVC complexes act as effective positron trapping centers, leading to the formation of positron trapped states and a notable increase in annihilation lifetimes at the corresponding defect sites. In addition, coincidence Doppler broadening (CDB) spectra, along with the S and W parameters, are calculated for both intrinsic and oxygen-doped point defects (OC, OSi, OCVSi, and OSiVC). The analysis reveals that electron screening effects dominate the annihilation characteristics of the OSi defect, whereas positron localization induced by the vacancy is the predominant contributor in the case of OSiVC. This distinction results in clearly different momentum distributions of these two oxygen-related defects for different charge states. Overall, the PAS is demonstrated to be a powerful technique for distinguishing intrinsic vacancy-type defects and oxygen-doped composites in 3C-SiC. Combining the analysis of electron and positron density distributions, the electron localization and positron trapping behavior in defect systems with different charge states can be comprehensively understood. These first-principles results provide a solid theoretical foundation for identifying and characterizing the defects in oxygen-doped 3C-SiC by using positron annihilation spectroscopy.
, , Received Date: 2025-05-16
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Clouds exert a significant influence on infrared radiation, making cloud detection a crucial step in the application of infrared hyperspectral data. Ground-based infrared hyperspectrometers are capable of measuring downward atmospheric thermal radiation with high temporal resolution; however, their spectral radiance measurements are strongly affected by atmospheric conditions. In particular, water vapor interference and the limited accuracy in high-cloud identification constitute two key challenges for ground-based infrared hyperspectral cloud detection. Conventional threshold-based cloud detection methods struggle to adapt to varying locations and dynamically changing atmospheric conditions, whereas machine learning approaches 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 (Tibet), and Ritu (Tibet) were used to analyze the spectral differences between clear-sky and cloudy conditions in this study. Based on these differences, we propose a spectral feature enhancement-driven machine learning method for cloud detection. Finally, by incorporating synchronous observations from lidar, meteorological stations, and all-sky imagers, the proposed method is systematically evaluated under varying relative humidity (RH) and cloud base height (CBH) conditions. Experimental results show that the proposed method achieves a high consistency of up to 97.61% with lidar-based detection results. Under different RH conditions, the proposed method outperforms the approach based on original spectral features. Notably, when RH＞70%, 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 demonstrates superior performance compared to the approach using original spectral features. In particular, the accuracy improvements are especially notable when identifying mid-level clouds with 3 km＜CBH≤5 km, as well as high-level clouds with CBH＞5 km. When 3 km＜CBH≤5 km, the accuracy increases from 95.45% to 98.64% and when CBH＞5 km, the accuracy improves from 87.5% to 91.67%. The proposed method significantly enhances the automation and accuracy of cloud detection in ground-based infrared hyperspectral radiance data, thereby providing higher-quality fundamental datasets to support subsequent applications such as radiative transfer simulation, remote sensing parameter retrieval, and data assimilation in numerical weather prediction (NWP) models.
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Low-pressure radio-frequency inductively coupled discharges can produce uniformly distributed monodisperse particles and plasma densities, 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 carrying negative charges, 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 ICPs using a hybrid model. The hybrid model consists of kinetic equation, electromagnetic field equation, global model equation. Simulation results show that with increasing dust radius or density, the BRH effect—characterized by the formation of a plateau in the electron energy probability function—is gradually suppressed and eventually vanishes, accompanied by a decrease in electron temperature, an increase in electron density, and an increase in particle surface potential. The dust charge decreases with increasing particle density, while exhibiting a nonmonotonic variation with particle radius. The results indicate that the loss of high-energy electrons induced by the presence of dust particles may create a more favorable plasma environment for the growth of low-defect, monodisperse nanoparticles. Such improvement in particle quality is crucial for reducing trap densities and enhancing the electrical performance of nanoparticle-based electronic devices.
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The multilayer structure of EUV masks limits the penetration depth of traditional inspection techniques at non-working wavelengths, hindering the effective review 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 sources, with their stable EUV wavelength, cleanliness, and high power density, represent an ideal light source for EUV mask defect characterization research. This paper systematically reviews the current state of technology development for mask characterization at the world's four major synchrotron radiation facilities. Through comparative analysis, it delves into their working principles, technical advantages, and limitations, and provides a forward-looking discussion on future trends. For the specific requirements for EUV mask defect inspection and review, the paper discusses the need for next-generation system platforms to deeply integrate inspection and review functionalities, develop novel compact light sources, and innovatively combine the strengths of various imaging techniques to enhance the numerical aperture (NA) of imaging systems. This aims to achieve a theoretical resolution surpassing 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 for extending synchrotron radiation to industrial applications, it introduces compact synchrotron sources that enable on-site deployment within semiconductor facilities to accelerate R&D cycles, alongside the synergistic integration of imaging technologies. The paper highlights applying the phase retrieval principle of Ptychography to Fourier Synthesis Illumination (FSI), enabling aberration correction in lens-based systems through synthetic aperture extension. This paper examines the working principles, performance benchmarks, technical challenges, and emerging development trends of existing synchrotron radiation-based EUV mask characterization techniques. It provides a significant reference for designing next-generation EUV mask characterization system platforms.
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The study employs a clustering method 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 and wall-detached types. A subset of the wall-attached structures exhibits self-similarity in scale, consistent with Townsend's attached eddy hypothesis, and are further classified into squat, self-similar, and tall structures. 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 identity decomposition reveals that tall structures associated with low streamwise momentum predominantly govern the generation of wall friction and heat flux, whereas tall structures linked to high-temperature events play a primary role in the transport of wall-normal heat flux.
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