Accepted
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Abstract +
In the near field of a subsonic jet, complex energy transport and transformation processes occur among kinetic, thermal, and acoustic energies, which play crucial roles in jet instability and noise radiation. Accurately characterizing the transport features of each energy component is essential for developing effective noise suppression technologies. Building upon Myers' [1991 J. Fluid Mech. 226 383] exact energy equation for total disturbances in arbitrary steady flow, the present study develops a modified energy equation based on hydro-acoustic mode decomposition to separate the contributions of vortical, entropic, and acoustic modes to the total disturbance energy. The methodology begins with the decomposition formulas for velocity, pressure, and density, following the hydro-acoustic mode decomposition method proposed by Han et al. [2023 Phys. Fluids 35 076107]. In Myers' energy equation framework, the disturbances of primitive variables (velocity, pressure, and density) are expressed as linear combinations of their vortical, entropic, and acoustic components. Through this formulation, vortical (entropic, acoustic) energy is defined as exclusively contributed by the corresponding mode's disturbances, while nonlinear energy is attributed to interactions among vortical, entropic, and acoustic components. This approach yields a modified energy equation capable of distinguishing the individual contributions of vortical, entropic, and acoustic modes to both total disturbance energy and energy flux, making it particularly suitable for analyzing energy transport characteristics in the near flow field. The developed equation is applied to analyze a Mach number 0.9 subsonic jet, revealing distinct spatial distributions and transport mechanisms of hydrodynamic and acoustic energies. The results demonstrate that vortical and entropic energies are predominantly concentrated in the near field, convecting downstream at approximately 0.8 times the jet velocity. In contrast, acoustic energy exhibits dual propagation characteristics: radiating outward to the far field through acoustic waves outside the potential core while propagating upstream via trapped waves within the potential core. The energy associated with multi-mode nonlinear interactions primarily concentrates in the jet wake, propagating without significant directivity. The total disturbance energy is predominantly contributed by vortical energy, while the acoustic energy accounting for only a minuscule fraction of the total disturbance energy, approximately on the order of 10-3 of the total. This refined analysis provides deeper insights into the complex energy dynamics in subsonic jets, offering valuable information for jet noise prediction and control strategies. The modified energy equation presents a robust framework for understanding and quantifying the intricate energy transport processes in jet flows.
Abstract +
Carbon monoxide cation (CO+) plays a dominant role in some astrophysical atmosphere environments, where theoretical studies of its opacity are essential for radiative transport modeling. In this work, based on experimentally observed vibrational energy levels of the X²Σ⁺, A²Π, and B²Σ⁺ electronic states of CO⁺, we refined and constructed potential energy curves using a Modified Morse (MMorse) potential function, then the vibrational energy levels and spectroscopic constants are extracted. In the meantime, the internally contracted multireference configuration interaction approach (MRCI) with Davison size-extensivity correction (+Q) is employed to calculate the potential energy curves and transition dipole moments. The refined MMorse potential exhibits excellent agreement with the computed potential energy curves, while the spectroscopic constants and vibrational levels show strong consistency with existing theoretical and experimental data. The opacities of the CO+ molecule is computed at different temperatures under the pressure of 100 atm. It is found that with the increase of temperature, the opacities for transitions at long wavelength range are enlarged because of the larger population on excited electronic states at the higher temperature.
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Abstract +
First-principles density functional theory was employed to systematically study the effects of pressure on the crystal structure, elastic properties, and electronic characteristics of Al4In2N6. The lattice constants of Al4In2N6 decrease with increasing pressure, exhibiting anisotropic compression with greater compressibility along the c-axis. In terms of mechanical properties, the bulk modulus increases with pressure, indicating enhanced compressive resistance. Notably, the Vickers hardness decreases with increasing pressure, suggesting that high pressure could induce plastic deformation in Al4In2N6. Calculations of elastic constants and phonon spectra confirm that Al4In2N6 retains mechanical and dynamical stability across the 0–30 GPa pressure range.
Electronic structure calculations reveal that Al4In2N6 possesses a direct band gap, with non-overlapping conduction and valence bands at the Fermi level and higher carrier mobility in the conduction band compared to the valence band. The band gap increases nearly linearly with pressure, from 3.35 eV at 0 GPa to 4.24 eV at 30 GPa, demonstrating significant pressure-induced modulation of the electronic structure. Furthermore, differential charge density analysis reveals that increasing pressure strengthens Al-N and In-N bonds in Al4In2N6 through shortened interatomic distances and stronger atomic interactions, increasing its compression resistance.
In conclusion, this study not only enhances our understanding of the high-pressure properties of Al4In2N6 but also provides theoretical guidance for its application in UV optoelectronics. Pressure-driven modulation of its mechanical and electronic characteristics highlights its potential for efficient high-pressure optoelectronic devices and materials.
Electronic structure calculations reveal that Al4In2N6 possesses a direct band gap, with non-overlapping conduction and valence bands at the Fermi level and higher carrier mobility in the conduction band compared to the valence band. The band gap increases nearly linearly with pressure, from 3.35 eV at 0 GPa to 4.24 eV at 30 GPa, demonstrating significant pressure-induced modulation of the electronic structure. Furthermore, differential charge density analysis reveals that increasing pressure strengthens Al-N and In-N bonds in Al4In2N6 through shortened interatomic distances and stronger atomic interactions, increasing its compression resistance.
In conclusion, this study not only enhances our understanding of the high-pressure properties of Al4In2N6 but also provides theoretical guidance for its application in UV optoelectronics. Pressure-driven modulation of its mechanical and electronic characteristics highlights its potential for efficient high-pressure optoelectronic devices and materials.
, , Received Date: 2025-01-19
Abstract +
The Casimir effect has received extensive attention theoretically and experimentally in recent years. It arises from the macroscopic manifestation of quantum vacuum fluctuations, and this Casimir interaction force can be an effective means of driving and controlling components in micro-electro-mechanical system (MEMS) and nano-electromechanical system (NEMS). Due to the new possibilities provided by photonic topological insulator for designing and using photonic devices, in this work, the Casimir force between the multilayer structures of non-reciprocal photonic topological insulators with broken time-reversal symmetry is investigated, and the influences of the dielectric tensor of the photonic topological insulator, the spatial structural parameters of the multilayer system, and the rotational degree of freedom on the Casimir force are examined. It is found that there exists Casimir repulsive force in such a multilayer system, and the Casimir stable equilibrium and restoring force can be further realized and controlled. Continuous variation between anti-mirror-symmetric configuration and mirror-symmetric configuration is examined. Both the Casimir attraction and repulsion can be generally enhanced through structural optimization by increasing layer number and individual layer thickness. Furthermore, we focus on the detailed analysis of how the optical axis angle difference within the photonic topological insulator layers can be used to adjust the Casimir force. The overall relative rotation of the multilayer system may adjust the magnitude and the direction of the Casimir force, and some inflection points can be found from the influence curve of the optical axis angle difference between internal layers of the multilayer on the Casimir force, allowing the rotational degrees of freedom in the multilayer system to be used for fine-adjusting the Casimir interaction. This work introduces the enhanced degrees of freedom for probing and manipulating the interaction between small objects in micro/nano systems, thereby suppressing adverse Casimir forces and effectively using them.
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Abstract +
A novel target depth estimation method based on normal mode intensity match is proposed for shallow water environment using horizontal array to overcome the performance degradation observed in conventional approaches under seabed parameters mismatch condition. First, horizontal wavenumbers and normal mode intensities are estimated through wavenumber domain beamforming. Second, modal function of normal mode inversion is performed by solving the modal function characteristic equation through finite difference method. Third, the match degree between inverted and estimated normal mode intensities is evaluated to estimate target depth. Numerical simulation results demonstrate that the proposed method can achieve accurate target depth estimation in shallow water scenarios without knowledge of seabed parameters. Furthermore performance of the method is analyzed under varying conditions including different seabed parameters, array apertures and source frequencies. The results reveal three conclusions: (1) mismatch of seabed parameters has no impact on the method; (2) effective performance of all depth source estimation requires not less than 128 array elements, 50-150Hz frequency band range and the signal-to-noise radio in the element on a horizontal line array exceeds -10dB; (3) the method has robust performance against sound speed profile mismatch. Finally, the feasibility of the proposed method is validated through experimental data received by a horizontal towed 77-elements array during a shallow-water sea trial at the South China Sea.
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Abstract +
Magnetic response from micro and macro scale is widely used for stress evaluation in Non-destructive testing and evaluation. The basic principle is that the magnetic domain pattern and magnetic domain dynamics is highly depend on the applied tensile stress. Understanding the evolution of magnetic domains under the action of multi-field coupling is critical for developing novel magnetic non-destructive testing technologies. In this work, the effect of stress on magnetic domain and magneto-acoustic emission signals in polycrystalline materials was investigated based on the magneto-optical Kerr imaging and magneto-acoustic emission detection system. From the macroscopic scale, the mapping relationship between the magneto-acoustic emission signal and stress is established. Microscopically, the influence of the stress and grain boundaries on the magnetic domain patterns were investigated. And the correlation between supplementary domains and stress are built. Finally, the interrelation between the domain wall dynamics and the magneto-acoustic emission signal is revealed from the nucleation of supplementary domains and their stress-dependent evolution.
The results indicated that the magnetoelastic effect reduces the density of supplementary domains and 90° domains, which weaken the magneto-acoustic emission signal. The stress-magneto-acoustic model and the influence of the stress on the magnetic domain in this work reveals mechanism of magneto-acoustic emissions technique for stress measurement. It also provides a theoretical foundation for advancing stress-magnetic-acoustic models and magnetic non-destructive testing technology.
The results indicated that the magnetoelastic effect reduces the density of supplementary domains and 90° domains, which weaken the magneto-acoustic emission signal. The stress-magneto-acoustic model and the influence of the stress on the magnetic domain in this work reveals mechanism of magneto-acoustic emissions technique for stress measurement. It also provides a theoretical foundation for advancing stress-magnetic-acoustic models and magnetic non-destructive testing technology.
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Abstract +
The channel plasma characteristics of an artificially triggered lightning in Guangdong, China, were analyzed using slit-free spectroscopy technology. Spectral diagnostics were performed to obtain the peak currents by about 30.9 kA (maximum) and 25.6 kA (minimum), which were subsequently simulated using the Modified Transmission Line model with Linear current decay (MTLL). To investigate the electric field distribution, the Finite-Difference Time-Domain (FDTD) method and Transmission Line (TL) model were employed. At a distance of 58 m, the TL-predicted radiation electric field deviates from experimental electric field when assuming a return stroke velocity of 1.3×108m/s, but becomes close alignment with the FDTD-simulation of vertical electric fields. Moreover, the analysis of magnetic fields at 58 m, 90 m, and 1.6 km were compared using FDTD simulations, Dipole approximations, and Charge Magnetic Field Limit (CMFL) estimations. The discrepancies between calculated and experimental values are appeared at 58 m and 90 m, probably due to the near-field interference and measurement limitation. However, they become small at 1.6 km.This work is helpful for the study of lightning electromagnetic field properties and spectral diagnosis.
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Abstract +
In the face of surging air transportation demands and increasingly intense flight conflict risks, effectively managing flight conflicts and accurately identifying key conflicting aircraft have become critically important. This paper presents a novel method for identifying critical nodes in flight conflict networks by integrating complex network theory with a weighted cycle ratio (WCR). By modeling aircraft as nodes and conflict relationships as edges, we construct a flight conflict network where the urgency of conflicts is reflected in edge weights. We extend the traditional cycle ratio (CR) concept to propose the WCR, which accounts for both the topological structure of the network and the urgency of conflicts. Furthermore, we combine the WCR with node strength (NS) to form an adjustable mixed indicator (MI), which adaptively balances the importance of nodes based on their involvement in cyclic conflict structures and their individual conflict intensity. Through extensive simulations, including node deletion experiments and network robustness analyses, we demonstrate that our method can precisely pinpoint critical nodes in flight conflict networks. The results indicate that regulating these critical nodes can significantly reduce network complexity and conflict risks. Importantly, our method's effectiveness grows with the complexity of the flight conflict network, making it especially suitable for scenarios with high aircraft densities and intricate conflict patterns. Overall, this study not only advances the theoretical understanding of complex network analysis in aviation but also offers a practical tool for enhancing air traffic control efficiency and safety, ultimately contributing to greener and more sustainable air transportation.
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Abstract +
Purpose
This study addresses the critical challenge of real-time beam monitoring in ultra-high dose rate X-ray FLASH (XFLASH) radiotherapy, where conventional ionization chambers suffer from severe electron-ion recombination losses under extreme dose rates (≥40 Gy/s). We propose a low-pressure ionization chamber (LPIC) as a novel beam monitor, aiming to achieve accurate dose measurement while maintaining beam penetration characteristics required for clinical applications.
Methods
The LPIC was designed with two independent chambers housing high-voltage, collecting, and guard electrodes. Key parameters included a 1 mm electrode gap and a reduced chamber pressure (~5 kPa) to mitigate recombination effects. Theoretical analysis based on the Boag model and numerical simulations (using the numerical-ks-calculator program) quantified recombination loss dependency on pressure (P), electrode spacing (d), and voltage (Uc). MCNP simulations evaluated X-ray transmission through chamber windows (Be, Al, Ti) with thicknesses up to 1000 μm. A prototype LPIC was fabricated and tested on a 10 MeV XFLASH accelerator (dose rate: 80 Gy/s) for plateau characteristics, dose repeatability, linearity, and dose-rate response, following national standards (GB/T15213-2016).
Key Physical Results
1.Recombination Loss Suppression: Theoretical analysis based on the Boag model revealed that the recombination ratio R scales with P3, d2, and Uc−1, validated by numerical simulations (R=0.2256P3; R=0.0534Uc−1; R=0.00548d2). At1.1 Gy/pulse, recombination losses were maintained below 1% by optimizing parameters: P<0.3 atm for d=0.1 mm or P<0.04 atm for d=1 mm.
2.Beam Transmission Optimization: MCNP simulations demonstrated that X-ray transmission exceeded 90% for beryllium (Be), aluminum (Al), and titanium (Ti) windows with thicknesses ≤1000 μm. While 0.1 mm Be achieved the highest transmission (>99%), 1 mm Al (transmission ~95%) was selected as the optimal window material due to its clinical acceptability (<5% dose loss), cost-effectiveness, and ease of fabrication.
3.LPIC Performance Validation: The prototype exhibited stable plateau characteristics (ΔI/I<0.069% at Uc>40V), exceptional dose repeatability (coefficient of variation <0.5% across 10–250 Gy/s), and linearity (R2>0.999 for dose and dose-rate measurements). These results confirm compliance with national standards (GB/T15213-2016) and suitability for real-time XFLASH monitoring.
Conclusion
The LPIC demonstrates robust suppression of recombination losses and reliable performance under XFLASH conditions. Its design—optimized via theoretical modeling and simulations—ensures high precision (meeting GB/T15213-2016 requirements) while preserving beam penetration. The use of 1 mm Al windows balances cost and functionality, making the LPIC a practical solution for clinical translation. Future studies will focus on multi-channel LPIC arrays for 2D beam profiling.
This study addresses the critical challenge of real-time beam monitoring in ultra-high dose rate X-ray FLASH (XFLASH) radiotherapy, where conventional ionization chambers suffer from severe electron-ion recombination losses under extreme dose rates (≥40 Gy/s). We propose a low-pressure ionization chamber (LPIC) as a novel beam monitor, aiming to achieve accurate dose measurement while maintaining beam penetration characteristics required for clinical applications.
Methods
The LPIC was designed with two independent chambers housing high-voltage, collecting, and guard electrodes. Key parameters included a 1 mm electrode gap and a reduced chamber pressure (~5 kPa) to mitigate recombination effects. Theoretical analysis based on the Boag model and numerical simulations (using the numerical-ks-calculator program) quantified recombination loss dependency on pressure (P), electrode spacing (d), and voltage (Uc). MCNP simulations evaluated X-ray transmission through chamber windows (Be, Al, Ti) with thicknesses up to 1000 μm. A prototype LPIC was fabricated and tested on a 10 MeV XFLASH accelerator (dose rate: 80 Gy/s) for plateau characteristics, dose repeatability, linearity, and dose-rate response, following national standards (GB/T15213-2016).
Key Physical Results
1.Recombination Loss Suppression: Theoretical analysis based on the Boag model revealed that the recombination ratio R scales with P3, d2, and Uc−1, validated by numerical simulations (R=0.2256P3; R=0.0534Uc−1; R=0.00548d2). At1.1 Gy/pulse, recombination losses were maintained below 1% by optimizing parameters: P<0.3 atm for d=0.1 mm or P<0.04 atm for d=1 mm.
2.Beam Transmission Optimization: MCNP simulations demonstrated that X-ray transmission exceeded 90% for beryllium (Be), aluminum (Al), and titanium (Ti) windows with thicknesses ≤1000 μm. While 0.1 mm Be achieved the highest transmission (>99%), 1 mm Al (transmission ~95%) was selected as the optimal window material due to its clinical acceptability (<5% dose loss), cost-effectiveness, and ease of fabrication.
3.LPIC Performance Validation: The prototype exhibited stable plateau characteristics (ΔI/I<0.069% at Uc>40V), exceptional dose repeatability (coefficient of variation <0.5% across 10–250 Gy/s), and linearity (R2>0.999 for dose and dose-rate measurements). These results confirm compliance with national standards (GB/T15213-2016) and suitability for real-time XFLASH monitoring.
Conclusion
The LPIC demonstrates robust suppression of recombination losses and reliable performance under XFLASH conditions. Its design—optimized via theoretical modeling and simulations—ensures high precision (meeting GB/T15213-2016 requirements) while preserving beam penetration. The use of 1 mm Al windows balances cost and functionality, making the LPIC a practical solution for clinical translation. Future studies will focus on multi-channel LPIC arrays for 2D beam profiling.
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Abstract +
In recent years, dual-frequency capacitively coupled plasma discharge technology has significant advantages for material processing. In this paper, the one-dimensional PIC/MCC simulation method is used to discuss the influence of low-frequency frequency on the discharge characteristics of capacitively coupled argon/methane plasma driven by dual-frequency (20MHz/100MHz) dipole and by the introduction of an external magnetic field. The simulation results show that when the high-frequency frequency is an integer multiple of the low-frequency frequency, the superposition of high and low frequencies is significant, and the sheath oscillation is more obvious. With the increase of low-frequency frequency, the electron density, charge density, high-energy electron density and electron heating rate all increase. The electron density increases to 14% with the low-frequency frequency increase. The electron temperature near the sheath shows a downward trend with the increase of low-frequency frequency, dropping by approximately 12%. The electron energy probability distribution (EEPF) shows a double Maxwell distribution. When the low-frequency frequency increases, the layout numbers of both low-energy electrons and high-energy electrons increase. Meanwhile, the influence of the low-frequency frequency increase on the various ions density, and the Angle and energy distribution of CH4+ and CH3+ particles reaching the plates are discussed.
In the Ar/CH4 plasma driven by dual-frequency by adding external magnetic field, the controllability of ion energy can effectively optimize the structure and performance of carbon-containing films. By regulating discharge parameters to control the ions incident Angle on the substrate, carbon-containing atoms can be deposited in a specific direction, thereby achieving the directional growth of carbon-containing films. This is significant for the preparation of graphene films, carbon nanotube arrays, etc. Meanwhile, the regulation of the ion incident Angle is helpful to improve the binding force between the carbon film and the substrate. This study found that the average energy of the ions reached its peak when the Angle of the ions was around 0.32. This peak was most significant at a low-frequency frequency of 15 MHz. The results in this paper provides a theoretical reference for the preparation of carbon films.
In the Ar/CH4 plasma driven by dual-frequency by adding external magnetic field, the controllability of ion energy can effectively optimize the structure and performance of carbon-containing films. By regulating discharge parameters to control the ions incident Angle on the substrate, carbon-containing atoms can be deposited in a specific direction, thereby achieving the directional growth of carbon-containing films. This is significant for the preparation of graphene films, carbon nanotube arrays, etc. Meanwhile, the regulation of the ion incident Angle is helpful to improve the binding force between the carbon film and the substrate. This study found that the average energy of the ions reached its peak when the Angle of the ions was around 0.32. This peak was most significant at a low-frequency frequency of 15 MHz. The results in this paper provides a theoretical reference for the preparation of carbon films.
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Abstract +
Terahertz (THz) time-domain spectroscopy and imaging techniques at the nanoscale are imperative for materials research and devices detection, among others. However, conventional far-field THz time-domain spectroscopy faces inherent diffraction limits, restricting applications requiring femtosecond temporal resolution and nanoscale spatial precision for carrier dynamics analysis. We present a scattering-type scanning near-field optical microscopy that overcomes these constraints by combining ultrafast THz time-domain spectroscopy with AFM. The utilization of the near-field interaction between the needle's tip and the sample's surface has been demonstrated to facilitate the study of semiconductor materials and devices with static THz spectroscopy at a lateral spatial resolution of ~60 nm. This, in turn, enables the acquisition of static THz conductivity distributions of the semiconductor materials. Additionally, it facilitates the acquisition of transient conductivity distributions of semiconductor materials and laser THz emission ultrafast via photoexcited transient carrier kinetic processes. This aspect provides substantial support for the study of the performance of materials and devices in nanometer spatial resolution, ultrafast time resolution, and THz spectroscopic imaging.The experimental results show that the system has a signal-to-noise ratio as high as 56.34 dB in the static THz time-domain spectral mode, and can effectively extract the fifth-order harmonic signals covering the 0.2-2.2 THz frequency band with a spatial resolution of up to ~60 nm. Carrier excitation and complexation processes in topological insulators have been successfully observed by optical pump-THz probe with a time resolution better than 100 fs. Imaging of SRAM samples by the system reveals differences in THz scattering intensity due to non-uniformity in doping concentration, validating its potential for nanoscale defect detection.This study not only provides an innovative means for the study of nanoscale electrical characterization of semiconductor materials and devices, but also opens up new avenues for the application of THz technology in interdisciplinary subjects such as nanophotonics and spintronics. In the future, the temporal and spatial resolution and detection efficiency of the system are expected to be further improved by integrating the superlens technology, optimizing the probe design and introducing deep learning algorithms.
, , Received Date: 2025-01-26
Abstract +
The transition of Ga+ ions from 4s2 1S0 to 4s4p 3P0 has advantages such as a high quality factor and a small motional frequency shift, making it suitable as a reference for precision measurement experiments like optical clocks. Calculating the dynamic polarizability of 4s2 1S0-4s4p 3P0 transition for Ga+ ion is of great significance for exploring the potential applications of the Ga+ ion in the field of quantum precision measurement and for testing atomic and molecular structure theories. In this paper, the dynamic polarizability of the Ga+ ion 4s2 1S0 - 4s4p 3P0 transition is theoretically calculated using the relativistic configuration interaction plus many-body perturbation (CI+MBPT) method. The “tune-out” wavelengths for the 4s2 1S0 state and the 4s4p 3P0 state, as well as the “magic” wavelength of the 4s2 1S0 - 4s4p 3P0 transition, are also computed. It is observed that the resonant lines situated near a certain “turn-out” and “magic” wavelength can make dominant contributions to the polarizability, while the remaining resonant lines generally contribute the least. These “tune-out” and “magic” wavelengths provide theoretical guidance for precise measurements, which is important for studying the atomic structure of Ga+ ions. The accurate determination of the difference in static polarizability between the 4s2 1S0 and 4s4p 3P0 states is of significant importance. Additionally, based on the “polarizability scaling” method, this work also discusses how the theoretical calculation errors in static polarizability measurements vary with wavelength, which provides theoretical guidance for further determining the static polarizability of the 4s2 1S0 and 4s4p 3P0 states with high precision. This is crucial for minimizing the uncertainty of the blackbody radiation (BBR) frequency shift in Ga+ optical clock and suppressing the systematic uncertainty.
, , Received Date: 2025-01-05
Abstract +
, , Received Date: 2025-01-10
Abstract +
Secondary hardening ultra-high-strength steel is widely utilized in aerospace and other advanced engineering, with the nanoscale M2C precipitates serving as the primary strengthening factor. Mo plays a crucial role in the forming of Mo2C secondary hardening phase, which can form composite M2C precipitates with elements such as Cr, V, and W, thereby modifying the composition and properties of Mo2C. To investigate the effects of V and W doping on Mo2C, first-principles calculations are used to analyze the formation enthalpy, electronic structure, and mechanical properties of the doped systems. The CASTEP module is utilized in this study, with the Perdew-Burke-Ernzerhof (PBE) functional adopted in the generalized gradient approximation (GGA) framework. The results indicate that V doping reduces the lattice parameters and the formation enthalpy, thereby enhancing structural stability. In contrast, W doping increases the lattice parameters and lowers the formation enthalpy but leads the structural stability to decrease. In terms of mechanical properties, V doping reduces toughness while increasing hardness, whereas W doping improves the strength-toughness balance by mitigating the rate of hardness reduction. Covalent bonds are formed within the system, with V and W doping changing their characteristics: compared with the C—Mo bond, the C—V bond exhibits weaker covalency, while the C—W bond displays stronger covalency. Additionally, V doping enhances the stability of Mo—C bonds, whereas W doping reduces their stability. Charge population analysis reveals that metal atoms (Mo, V, and W) act as electron donors, while carbon atoms act as electron acceptors.
, , Received Date: 2024-12-21
Abstract +
In recent years, bound states in the continuum (BICs) have become a hot research topic because of their strong ability to facilitate light-matter interactions, and they are also an ideal platform for realizing optical resonances with ultra-high quality factors (Q). Nowadays, BICs have been found to exist in various photonic microstructures and nanostructures such as waveguides, gratings, and metasurfaces, among which metasurfaces have attracted much attention due to their ease of adjustment and considerable robustness. Traditional precious metal-based metasurfaces inevitably have low Q-factors due to the inherent defect of high ohmic losses. In contrast, due to lower ohmic losses, all-dielectric metasurfaces can be an excellent alternative to metallic metasurface structures. In this work, an all-dielectric metasurface is designed, with a silicon disc as the unit cell, and symmetric protected BIC (SP-BIC) is observed on the metasurface. When introducing eccentric holes to break the symmetry in the structural plane (QBIC), the SP-BIC can be transformed into a quasi-BIC, with radiation dominated by magnetic dipoles and has a high-quality Q-factor. For QBICs formed on the metasurface, the resonance wavelength is usually greatly dependent on the refractive index of the surroundings due to the strong localization of the electric field within the cell. As the refractive index of the background changes, the positions of the resonance peaks change accordingly, and identification sensing of some biological components is achieved by this principle. This metasurface-based bio-refractive index sensor is less invasive in free space and is expected to overcome the drawbacks of traditional electrochemical-based biosensing technologies, which have cumbersome detection steps and high time and material costs. In terms of sensing parameters, due to the quadratic inverse relationship between the quality factor and asymmetric parameters, by adjusting the asymmetric parameters, the quality factor will also change, thereby enhancing and adjusting the sensing performance. After adjusting, the refractive index sensing sensitivity and figure of merit of this metasurface reach 162.55 nm/RIU and 1711.05 RIU–1, respectively, which are higher than those achieved in many other existing studies. This high Q-factor all-dielectric metasurface design provides a new avenue for achieving high-sensitivity and high-precision bio-detection.
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