Abstract Pulse-controlled atmospheric-pressure streamer discharges generate reactive oxygen and nitrogen species, and for many applications it is the O/N balance, not the amount of a single radical, that governs the outcome. Building on our previous study, which varied the voltage waveform at fixed gas composition, we examine how the N₂:O₂ ratio reshapes prompt O and N radical production. We performed 258 two-dimensional fluid simulations of a needle-to-plane streamer in dry N₂:O₂ = (100 − x):x mixtures (x = 20, 40, 60, 80%), independently varying the peak voltage (15–40 kV), rise time and pulse width with our previous fluid model. As the oxygen fraction rises, the deposited energy falls while the O-production efficiency increases; these partly offset, so at fixed peak voltage the O-atom yield declines only modestly (≈ 1.4-fold) whereas the N-atom yield falls sharply (≈ 3.6-fold) and the O/N selectivity rises roughly two-fold. A two-stage description, in which electron attachment first reduces the deposited energy and the yield is then proportional to that energy with a composition-dependent efficiency, organises these trends through the established oxygen-attachment mechanism, which suppresses the nitrogen channel mainly by N₂ dilution (≈ 90% of the logarithmic N-source decrease) with a smaller reduced-field contribution. A variance decomposition over all 258 cases attributes 96% of the variance in O-atom yield to Vmax and 80% of that in O/N selectivity to composition, so to a useful approximation the peak voltage sets the amount of O production and the composition the O/N selectivity. The two axes are not fully separable: the nitrogen yield is jointly controlled and the O/N ratio keeps a residual voltage dependence, but the simulations still provide a control map linking gas composition and voltage waveform to the radical output for this dry single-filament regime.
Abstract The O3 generation in the atmospheric air or O2 plasmas poses a significant hindrance to the design and development of atmospheric plasma devices for the preparation of plasma activated water (PAW), which are operated not in a sealed chamber. In this study, water is activated by N2-based instead of O2-based spark discharge over water to generate PAW at atmospheric pressure. Our analysis shows that the biological reactivity of N2 non-thermal plasma activated water (N2-PAW) is much higher than the one of O2 non-thermal plasma activated water (O2-PAW). The E. coli with their concentration of 1.8106 CFU/mL are completely inactivated in N2-PAW after the plasma treatment time of ≥40 s. The short-lived species such as OH, N, H, N2+, OH+, H2O+, and H- can be formed due to the collisions of N2 and H2O with electrons in the N2 spark discharge over water, and they are important intermediates for the subsequent gas-phase reactions and the dissolution of reactive nitrogen species. Fourier transform infrared spectrometer (FTIR) analysis shows that no O3 is detectable in the gas-phase N2 spark discharge over water. Our LC-MS measurements show that the functional groups in the side chains of amino acids such as -SS-, -SH, and aromatic rings are either oxidized, hydroxylated or nitrated in N2-PAW, which constitutes permanent chemical modifications of amino acids in proteins. The tertiary and quaternary structures of proteins in E. coli can be seriously destroyed in N2-PAW, where hydrophobic interactions, supplemented by auxiliary forces such as hydrogen bonds, salt bridges (ionic bonds), van der Waals forces, disulfide bonds, and ester bonds get unstable due to their interactions with aqueous RNS under weakly acidic conditions.
Abstract Topological semimetals (TSMs) have attracted significant attention for interconnect applications due to their unusually low electrical resistivity at reduced length scales. Despite this potential, TSM candidates for interconnect applications remain very scarce. Herein, we investigate the electrical resistivity of the TSM family MoP and XMoP (X = Hf, Zr, Ru) using a combination of density functional theory and semiclassical Boltzmann transport theory. At low temperatures, MoP-based TSMs exhibit chemically tunable and extremely low electrical resistivity and yield large residual resistivity ratios that rank among the highest reported for interconnect materials, exceeding those of state-of-the-art copper by more than two orders of magnitude. Being the most promising candidate, we demonstrate that MoP nanowires in the ultrathin regime exhibit a typical resistivity scaling attribute of TSMs. Analysis of scattering mechanisms indicates that acoustic phonons dominate the electron-phonon scattering. Despite higher scattering rates in ultrathin nanowires, bulk MoP exhibits lower resistivity due to its higher electronic group velocities. Our results identify the XMoP family as promising candidates for interconnect applications and clarify the microscopic origin of resistivity scaling in ultrathin TSM nanowires.
Abstract We investigate angular-momentum transfer efficiencies in hybrid Rb-Cs- 129 Xe vapor cells with different alkali compositions. Experiments were performed at a pump power of 40mW and a cell temperature of 110℃, where the Rb-Cs spin-exchange rate is comparable to the alkali electron-spin relaxation rate and complete spin-temperature equilibrium is not established. Using Rb-rich cells under Cs pumping and Cs-rich cells under Rb pumping, we measured the steady-state 129 Xe polarization and build-up time and determined the corresponding spin-exchange and photon efficiencies. Within each cell series, both efficiencies exhibit systematic composition-dependent trends arising from the combined effects of optical pumping, incomplete Rb-Cs polarization transfer, alkali relaxation, and alkali-Xe spin exchange. The Rb-Cs polarization-transfer factor converts the nominal alkali density ratio into an effective polarization-weighted ratio, which governs the relative contributions of the Rb-Xe and Cs-Xe spin-exchange channels. These results clarify angular-momentum transfer in hybrid Rb-Cs- 129 Xe systems and provide guidance for optimizing low-power hybrid spin-exchange optical pumping and alkali--noble-gas sensor platforms.
Abstract Hollow cathodes are indispensable electron sources in electric propulsion systems, and their operational stability and lifetime are strongly influenced by plume discharge instabilities and energetic-ion bombardment. Under ion-acoustic-wave-induced unstable operating conditions, enhanced plasma oscillations can lead to excessive emitter erosion, increased plume noise, distorted ion energy distributions, and severe sputtering of the keeper and orifice, thereby degrading thrust stability and limiting the service life of electric thrusters. Although extensive experimental and numerical studies have been conducted, the physical mechanisms linking ion acoustic turbulence, discharge instability, anomalous electron transport, and energetic-ion generation remain incompletely understood. This review systematically summarizes recent advances in experimental diagnostics and numerical simulations of hollow cathode plume instabilities under ion-acoustic oscillations. Experimental diagnostic techniques, including emissive probes, ion saturation probes, high-speed imaging, Thomson scattering, retarding potential analyzer, electrostatic energy analyzer, and laser-induced fluorescence, are critically reviewed with emphasis on their measurement principles, applicability, advantages, limitations, and complementary capabilities. Furthermore, fluid, particle-in-cell (PIC), hybrid-PIC, and kinetic models are comparatively analyzed in terms of physical assumptions, applicable plasma regimes, predictive accuracy, and agreement with experimental observations. Particular attention is devoted to the treatment of anomalous collisions and wave–particle interactions responsible for energetic-ion acceleration. Beyond summarizing previous studies, this review identifies common bottlenecks in experimental diagnostics and numerical simulations, analyzes the physical origins of discrepancies across numerical approaches, and discusses future research priorities, including synchronized non-invasive diagnostics, multiscale self-consistent simulations, and lifetime-oriented hollow cathode design. A unified framework linking ion acoustic turbulence, discharge instability, energetic-ion generation, and cathode erosion is established, guiding the development of next-generation long-life electric propulsion systems.
Abstract Nanosecond pulsed electric fields (nsPEFs) enable non-thermal and precise ablation, holding promising potential for fertility-sparing treatment of endometrial cancer. While biological impedance can be used as a physical marker to predict nsPEFs efficacy, the reliability of single-impedance monitoring needs improvement because pulse parameters influence the mapping between impedance and ablation effects. In this study, we systematically investigated the effects of key pulse parameters—including amplitude, pulse width (PW), inter- and intra-train pulse numbers (N1=20-120; N2=5-50), and their respective pulse repetition frequencies (f1=1-6 Hz and f2=0.2-1.2 kHz)—on biological impedance and ablation outcomes (ablation area and temperature) in Hec-1B cells. An optimized ablation prediction model integrating pulse parameter influence factors was then developed based on equivalent impedance variation to improve prediction accuracy. Experimental findings demonstrate that, for a given impedance change ratio (η ~8.6%), altering the pulse parameters (pulse width and amplitude) led to a nearly 1.5-fold variation in the ablation area (8.3 vs. 5.94 mm²). Validation in Ishikawa cells, a well-differentiated endometrial cancer cell line, confirmed the robust performance of the proposed model, which reduced the prediction error of ablation effects from 20.36% to 9.5%. Furthermore, validation in potato tissues showed that incorporating pulse parameters decreases the prediction error from 22.4% to 10.1%. This work offers theoretical and experimental support for the adaptive regulation of pulse parameters.
Abstract Polycrystalline vanadium nitride (VN) thin films with competitive superconducting transition temperature were achieved by a chemical solution deposition route. The VN thin films annealed at 850 °C, 900 °C and 950 °C show normal-state resistivity that decreases with decreasing measured temperature and undergo a superconducting transition with values between 6.9 and 8.4 K. Among the three VN thin films, the VN thin film annealed at 900 °C shows the highest superconducting transition temperature ( T C ), lowest transition width ( Δ T C ), lowest normal-state resistivity ( ρ n ), and highest residual resistivity ratio. X-ray photoelectron spectroscopy results reveal that the annealing temperature of 900 °C promotes the highest degree of nitridation, which correlates well with the observed improvement in superconductivity. This work demonstrates an easily realized solution-based process route for preparing polycrystalline superconducting VN thin films.
Abstract Hollow cathode discharge features a higher electron energy spectrum with a certain degree of tunability, making it more effective for exciting gas media, thus providing some advantages in producing metastable rare gas atoms. In this study, based on the spectral lines at 823.16 nm (6p[3/2] 2 → 6 s[3/2] 2 ) and 828.01 nm (6p[1/2] 0 → 6 s[3/2] 1 ), we investigate the kinetic processes involved in the generation of metastable Xe atoms in hollow cathode discharge. It has been speculated that the ‘electron-impact excitation + radiation’ process may dominate the production of metastable 6 s[3/2] 2 level Xe atoms, while the impact of the ‘ion-electron recombination’ process is extremely weak. Based on the temporal evolution of the spectral intensity at 823.16 nm, we obtained the total collisional decay rate constant k col for the 6p[3/2] 2 level as (2.10 ± 0.16)× 10 −11 cm 3 s −1 , and the total radiative decay rate k rad as (0.56 ± 0.02) ×10 7 s −1 , speculating that highly excited Xe atoms can replenish the number of particles in the 6p[3/2] 2 level through collision and radiation processes. The total decay rate of the intensity of the 828.01 nm spectral line exhibits an inflection point with increasing pressure, it is speculated that a fast process may be dominated by the near-resonance energy transfer pathway 5d[7/2] 4 → 6p[1/2] 0 → 5d[1/2] 1 , as well as a slow process governed by the collisions of ground state and highly excited Xe atoms, and electrons affecting the 6p[1/2] 0 level. In the pressure range of 100–300 Pa, these two processes exhibit opposing collisional decay dynamic parameters. In the pressure range of 300–700 Pa, the corresponding energy transfer process and collision process probably approach the equilibrium state.
Abstract Flexible electrochromic devices (ECDs) face significant challenges in simultaneously achieving high optoelectronic performance and robust mechanical flexibility. Herein, we propose a strategy employing dual aluminum-containing layers to synergistically enhance both the electrochemical functionality and mechanical durability of nickel oxide (NiO) thin films. First, Al 3+ doping into the NiO lattice (denoted as Al–NiO) substantially improves the electrochromic properties, yielding an optical modulation (Δ T ) of 40.2% at 550 nm. This represents a 44.1% enhancement relative to that of pure NiO (Δ T = 27.9%). The performance improvement is attributed to grain refinement, an increased Ni 3+ /Ni 2+ ratio, and a higher concentration of oxygen vacancies, which collectively promote charge transfer and ion diffusion kinetics. Second, the introduction of a 30 nm thick Al 2 O 3 buffer layer between the PET-ITO substrate and the Al–NiO film dramatically improves mechanical flexibility. The resulting Al 2 O 3 /Al–NiO heterostructure withstands over 2000 bending cycles (with a radius of 4 mm) without performance degradation, whereas the unbuffered film fails after only 200 cycles. The Al 2 O 3 layer serves dual functions: it acts as a chemical passivation barrier to suppress interfacial side reactions and as a physical stress-relief interlayer to effectively dissipate bending-induced strain. Furthermore, a complete flexible ECD fabricated with the Al 2 O 3 /Al–NiO anode and a WO 3 cathode demonstrates a high initial Δ T of 42.4% at 550 nm and exceptional cycling stability, maintaining 41.4% Δ T after 5000 cycles—a degradation of merely 2.3%. This work establishes a generic interface-bulk cooperative design strategy for developing durable, high-performance flexible optoelectronic devices.
Abstract Although sulfur hexafluoride (SF 6 ) is widely used in high-voltage power equipment due to its excellent arc quenching performance, its extremely high global warming potential (GWP) has motivated the search for environmentally friendly alternatives. The design of such alternative gases requires the simultaneous optimization of arc quenching performance, environmental impact, and operational constraints such as liquefaction temperature, leading to a highly coupled and constrained multi-objective optimization problem. To address this challenge, a surrogate-assisted multi-objective optimization framework is proposed by integrating Deep Operator Networks (DeepONet) with decomposition-based, preference-conditioned reinforcement learning. Specifically, an Arc-DeepONet model is developed to efficiently predict arc temperature fields and extract thermal and pre-dielectric recovery characteristics, while a dielectric recovery DeepONet is constructed to evaluate post-arc dielectric recovery performance. Based on these surrogate models, a three-objective constrained optimization problem is formulated in the gas composition-pressure space under GWP and liquefaction temperature constraints. To enable flexible decision-making under different engineering requirements, preference vectors are introduced to encode trade-offs among objectives, and a shared scoring network is trained to directly recommend feasible solutions conditioned on given preferences. Taking the C 4 F 7 N–CO 2 mixture as a representative case, the proposed framework achieves an exact hit rate of 0.965 with a mean regret of 1.738 × 10 −4 over 200 unseen preference vectors under the GWP constraint. When both GWP and liquefaction temperature constraints are imposed, the exact hit rate further improves to 0.986, while the mean regret remains on the order of 10 −4 . In both cases, the Pareto precision remains 1.0. Furthermore, a balanced operating region is identified under dual constraints, corresponding to a C 4 F 7 N fraction of 10.5%–11.5% and an operating pressure of 0.65 MPa-0.71 MPa. Once trained, the proposed framework enables rapid generation of high-quality solutions for arbitrary preferences with significantly reduced computational cost. These results demonstrate that the method provides an efficient, reliable, and physically consistent approach for the design and screening of environmentally friendly SF 6 alternative gases.
Abstract Intravascular lithotripsy (IVL) has significantly improved stent delivery success rates and clinical outcomes in patients with severely calcified coronary artery disease. However, existing experimental methods cannot directly characterize the microsecond-scale stress evolution induced by shock wave propagation in multi-layered calcified coronary arteries. To address this, we developed a two-dimensional axisymmetric finite element model for multi-medium shock wave propagation, comprising the fluid domain, the three-layer anisotropic hyperelastic arterial wall, the linear elastic calcified plaque, and the hyperelastic semi-compliant balloon. Using this framework, shock waveforms with varying amplitudes and pulse profiles were applied to evaluate the effects of shock wave parameters on mechanical responses within the calcified plaque and vessel wall. Results reveal that shock wave propagation generates complex mechanical responses within calcified plaques, including compressive stress concentration, shear stress localization, tensile stress concentration, and wave-induced dynamic squeezing effects. The tensile stress response was influenced by the temporal characteristics of the shock waveform and transient stress wave propagation within the calcification. Parametric analysis indicates that a more rapidly varying compressive phase profile is associated with earlier and more localized stress concentration within calcification but may also increase mechanical loading on surrounding vascular tissues. The present model adopts an idealized axisymmetric geometry and a linear acoustic–structure interaction framework based on the small-perturbation assumption. Therefore, the results primarily provide mechanistic insights into transient stress evolution during IVL rather than quantitative prediction of plaque fracture. These findings provide mechanistic insights into IVL induced transient stress evolution and highlight the importance of shock waveform characteristics in regulating stress distributions within calcified plaques and surrounding vascular tissues.
Abstract This study employs a λ /4 coaxial resonant cavity to generate a pulsed-modulated microwave plasma jet and compares discharge behaviors in N 2 , N 2 H 2 and Ar systems. Time-resolved optical emission spectroscopy is combined with incident and reflected microwave power measurements and phase diagrams to diagnose the ignition and decay processes. The results show that a stable localized enhanced electric field forms at the needle tip, enabling reliable discharge. Power signals and phase diagrams indicate stable microwave-plasma coupling, while the power-balance analysis at 60% duty cycle shows only minor differences in absorbed power and coupling efficiency among the three gas systems. Time-resolved spectroscopy reveals distinct temporal evolution among the three gases. At 25 kHz and 80% duty cycle, the N 2 and N 2 /H 2 emissions reach their observed maxima within the first 0.2 μ s acquisition interval and relax toward quasi-steady levels within 2.6 and 2.2 μ s, respectively. Their detectable afterglow durations are both 0.4 μ s. The Ar emission reaches its first transient maximum after 1.2 μ s and remains detectable for 3.2 μ s after microwave termination. A simplified CR framework relates these characteristic intervals to the competition between effective excitation and loss processes. The slightly shorter N 2 /H 2 relaxation is consistent with an additional H 2 -induced collisional-loss contribution, whereas the prolonged Ar afterglow supports the involvement of long-lived metastable species and residual stepwise excitation. The results indicate that gas-dependent kinetic processes contribute substantially to the observed emission dynamics under matched pulse-modulation and incident-power settings.
Abstract Protein-based molecular devices are gaining prominence for their potential to integrate biomimetic functionality into conventional electronic architectures. However, realizing these technologies requires a quantitative understanding of charge transport across biomolecule-modified electrode junctions. In this study, we investigate bias-driven electron tunneling and barrier modulation in amyloid beta-42 (A β -42) modified highly oriented pyrolytic graphite junctions using scanning tunneling microscopy-based spectroscopy. Comparative current–voltage ( I − V ) and differential conductance (d I /d V ) measurements reveal a pronounced modification of the tunneling barrier upon molecular adsorption, giving rise to distinct molecular conductance onsets. Temperature-dependent transport analysis within a double-barrier tunnel junction framework rules out thermally activated conduction and demonstrates electric-field-assisted tunneling, yielding an effective zero-field barrier of approximately 88 meV. Fowler–Nordheim analysis confirms a field-induced transition from direct to field-assisted tunneling across the composite junction. Furthermore, low-temperature inelastic electron tunneling spectroscopy identifies specific inelastic channels associated with the molecular vibrational modes of A β -42, confirming direct electronic coupling to the peptide backbone and aromatic residues. These results demonstrate that physisorbed A β -42 on graphite surface introduces dipole-mediated, field-dependent modulation of the effective tunneling barrier. This study establishes tunneling spectroscopy as an effective approach for probing localized barrier modifications in peptide-modified graphite junctions, providing insights relevant to protein-based bioelectronics.
Abstract RF generators are core components of magnetic hyperthermia (MH) systems, yet output quality is rarely characterized beyond nominal frequency and amplitude. Harmonic distortion can introduce parasitic components that complicate reproducibility and accurate field characterization; MH-specific spectral quality indices remain limited. This study proposes two indices for RF generator output quality assessment in MH: the harmonic residual index ( HRI ) and a simulation-derived harmonic specific absorption rate (SAR) contribution index ( Λ ¯ SAR ). A sinusoidal RF generator (50–200 kHz, 115 W) was evaluated with three coil configurations at 10%–100% power. Spatial magnetic-field measurements were acquired using a passive search coil, and HRI was computed pointwise to generate harmonic distortion maps. THD was computed from the same spectra for benchmarking. Spatial mean HRI ( HRI ― ) and THD ( THD ― ) were modelled using weighted power-law fitting. Inductive heating experiments (120–166.5 mg ml −1 MNP) evaluated the reliability of experimental calorimetry, motivating a shift toward simulation-based dosimetry. Finite element method (FEM) simulations of a simplified neck model driven by measured harmonics estimated relative harmonic SAR contributions and Λ ¯ SAR . HRI ― ranged from 0.17 ± 0.04 to 16.41 ± 3.48 (RMSE = 0.301–1.523) and increased monotonically with power level across all coils, while THD showed smaller variations and less spatially structured behaviour. Experimental heating trials yielded marginal temperature elevations (⩽2.5 °C) with quantization errors, demonstrating that standard calorimetry is metrologically insufficient for SAR derivation at clinical field intensities. Conversely Λ ¯ SAR ranged from 2.23E + 4 to 2.70E + 6, indicating low harmonic contributions relative to the fundamental under the tested conditions. HRI enables spatially resolved quantification of RF generator spectral impurities in MH systems and provides greater spatial sensitivity than THD under the tested conditions. Combined with FEM screening of harmonic SAR contributions, the framework supports reproducible, standardized characterization of RF generator output quality for MH instrumentation quality assurance.
Abstract When AC and DC power transmission and transformation projects pass through areas prone to sandstorms, the external insulation characteristics of transmission lines undergo complex changes, which may affect the reliable operation of the power system. Research into the air gap discharge process under wind-blown sand conditions is of significant guiding importance for the design of external insulation for power lines in disaster-prone areas. To this end, a wind-blown sand environment simulation test device was constructed to investigate the streamer-leader discharge process in a 1.8 m rod-plate gap under positive switching impulse voltage. The test results indicate that, in a wind-only condition without sand, high-speed airflow inhibits the development of the leader, the discharge voltage is slightly higher than in a calm and clean condition, the onset of the leader and the moment of gap breakdown are significantly delayed, the development rate slows down, the duration of the dark period increases and the mean streamer region angles decrease by 11.8%. In a wind-blown sand condition, the distortion effect of charged sand particles on the gap electric field accelerates the discharge process, the discharge voltage decreases by up to 36.1 kV, the continuity of leader development is enhanced, the development rate increases, the dark period is shortened, the time to gap breakdown is significantly reduced, and the mean streamer region angles decrease by up to 19.3% compared with a calm and clean condition, the standard deviation fell from 5.16° to 3.80°, and the dispersion was markedly reduced. The findings of this study contribute to the refinement of the theory of long gap discharges in wind-blown sand conditions.
Abstract Hybrid nanocomposites of conducting emeraldine polyaniline (EP) and tungsten oxide (WO3) nanoparticles synthesized via in-situ oxidative polymerization were investigated for their electrical conduction behavior. The UV-Vis spectroscopy reveals optical transition energies of ~1.4 – 1.5 eV for the undoped EP and EP-WO3 composites, along with the characteristic π → π* and polaronic transitions confirming conductive emeraldine salt polyaniline. Fourier transform infrared (FTIR) and Raman spectroscopy analysis confirms the characteristic vibrational and stretching modes, thereby confirming the incorporation of WO3 phase into the conducting polyaniline matrix. X-ray photoelectron spectroscopy (XPS) analysis of W 4f, O 1s and N 1s core-level spectrum of composite confirms the presence of interfacial bonding that are different from that of the individual constituent phases of the composites. Current - Voltage (I-V) measurements conducted under constant current source exhibited a linear (ohmic) conduction behavior at relatively lower currents, while at relatively higher currents, the hybrid nanocomposites demonstrated a phase fraction-dependent nonlinear switching, including both S-type and N-type NDR characteristics. The observed resistivity switching behavior and the NDR phenomena is associated with the interfacial tunneling mediated charge transport and electroforming process occurring at the EP-WO₃ interfaces. The formation of electrically active interfaces is further supported by impedance spectroscopy measurements, where the estimated relaxation time (~ 26 µs) and the semi-circular trend in the Nyquist plot confirms the formation of interfacial potential barriers between EP and WO3. This modulates the electrical switching characteristics and facilitates the transition between S-type to N-type NDR behavior as a function of temperature, applied currents and phase fractions of the composite. These findings highlight the potential of EP-WO3 hybrid nanocomposites for controlled switching devices and advanced electronic applications that demands tuneable NDR characteristics.
Abstract Laser ablation propulsion utilizes the momentum generated by an expanding plume produced by a focused laser beam to impart thrust on an object. This method offers a propellant-agnostic system with applications ranging from orbital debris removal to asteroid deflection for planetary defense. This study examines the effect of axial magnetic fields in a diverging nozzle configuration on thrust performance and efficiency. A hanging pendulum thrust stand is used to perform direct impulse measurements of aluminum targets ablated with a nanosecond pulsed laser under peak magnetic fields of up to 0.4400 Tesla. Triple Langmuir probe measurements temporally resolve electron temperature and density. ICCD imaging captures plasma evolution, and a Faraday probe characterizes plume divergence. Confocal microscopy of ablation craters provides mass removal estimates. Aluminum targets demonstrated thrust enhancements of up to 16.9% and specific impulse improvements of up to 18.7% under magnetic confinement. However, increasing field strengths enhanced plasma shielding and suppressed mass removal, resulting in decreased thrust. The results reveal two competing mechanisms: plume focusing, which reduces divergence losses at lower field strengths, and plasma shielding, which suppresses ablation at higher field strengths. These findings indicate an optimum field strength exists where focusing benefits are maximized before shielding penalties are significant.
Abstract Chromatic dispersion fundamentally limits metasurface performance by coupling beam steering to frequency, thereby constraining bandwidth and undermining practical deployment. Here, we break this limitation by introducing a fundamentally different design paradigm for metasurfaces that decouples wavefront control from frequency. Our approach is enabled by a physics-grounded parallel equivalent circuit model that directly governs dispersion at the meta-atom level, transforming achromatic metasurface synthesis from an empirical, geometry-driven process into a deterministic and scalable design problem. Using this framework, we generate a large-scale meta-atom library exceeding 100,000 candidates with systematically engineered dispersion responses. This large and diverse library allows the direct selection of meta-atoms with near-unity reflection amplitude and independently tailored phase slopes, enabling precise control of both phase and its frequency derivative. As a result, we realize metasurfaces that preserve prescribed beam deflection angles (0° and 25°) across a wide bandwidth with negligible angular dispersion. A fabricated prototype experimentally demonstrates achromatic reflection from 8.0 to 16.0 GHz, representing a broad bandwidth for dispersion-free beamforming metasurfaces. The measured results closely match full-wave simulations and theoretical predictions, validating the robustness and accuracy of the proposed framework. By establishing dispersion as a directly engineerable degree of freedom, this work redefines the design methodology of metasurfaces and unlocks a universal route toward broadband, multifunctional wavefront control, with far-reaching implications for next-generation satellite and mobile communication systems.
Abstract Amorphous carbon layer (ACL) neck formation is a contour change frequently observed during high-aspect-ratio (HAR) SiO2 etching, yet its dependence on plasma chemistry and operating parameters remains insufficiently understood. This study investigates ACL neck formation using C3F6O- and C3F6-based fluorocarbon plasmas in a low-pressure inductively coupled plasma system. Geometric parameters were introduced to quantify both lateral contraction (ΔCD) and the vertical position of the minimum necking (Yneck) in patterned structures. Increasing the C3F6O fraction enlarges the reference ACL mask entrance dimension and shifts the neck toward the entrance, accompanied by a decrease in the fluorocarbon-to-fluorine emission ratio and variations in ACL mask loss, indicating a shift in surface reaction equilibrium associated with oxygen-containing chemistry. In contrast, oxygen-free C3F6 plasmas exhibit smaller ΔCD and negligible neck evolution across the same fraction range. Under fixed gas fraction, increasing source power reduces the minimum aperture (CDneck) and shifts Yneck downward while the reference critical dimension measured 200 nm below the ACL top surface (CD200nm) increases gradually. Plasma diagnostics show increased electron temperature and ion saturation current density with nearly constant ion acceleration energy, suggesting coupled changes in reactive flux and ion-assisted surface reactions along the feature depth. These results distinguish composition-dependent and depth-dependent plasma-surface interaction mechanisms governing ACL neck evolution during HAR SiO2 etching.
Abstract Magnetized coaxial plasma guns (MCPGs) provide controllable high-energy-density plasma flows, but how an externally applied bias magnetic field modifies the internal current path evolution and thereby tailors the output plasma characteristics remains insufficiently understood. In this study, spatially resolved magnetic probes, photodetectors, a ballistic pendulum, and a radial calorimeter array are employed to investigate the current path evolution, plasma dynamics, and output characteristics of a MCPG. The measurements show that the bias field modifies both current path evolution and plasma dynamics. Increasing the bias flux shifts the dominant current conduction region, while the axial motion of the plasma across the radial component of the bias field induces an azimuthal current J_θ within the plasma. The interaction of J_θ with the radial bias field produces an axial retarding force that impedes plasma motion. Meanwhile, the interaction of J_θ with the self-generated axial magnetic field produces a pinch-opposing force, thereby mitigating the pinch effect. As the bias flux increases from 0 to 2.0 mWb, the axial velocity decreases from 67 to 44 km/s, the axial momentum from 37 to 15 mN·s, the effective ejected mass from 0.55 to 0.34 mg, and the on-axis absorbed energy density from 118 to 17 kJ/m². An order-of-magnitude estimate for axial retarding force yields a momentum loss consistent with the measured reduction. A moderate bias flux also improves the radial uniformity of energy deposition: within a region 64 mm in diameter, the nonuniformity decreases from 0.14 at 0 mWb to 0.02 at 1.5 mWb. These results establish an experimental connection between the current path evolution, the plasma dynamics, and the output characteristics of MCPGs, and provide guidance for tailoring plasma parameters in material processing applications.
