Physics

There is a growing recognition of the importance of neutral density fields to the physics, and particularly facility related effects, of Hall-effect thrusters (HETs). This work presents the first high-resolution (mm scale) spatial maps of neutral density in the near-field plume of a HET using two-photon absorption laser-induced fluorescence (TALIF). We employ a 212.6 nm TALIF excitation scheme, based on a pulsed nanosecond dye laser, to map absolute krypton neutral densities in the plume of a SPT-70 HET. Absolute densities are determined via a ratio-based approach using cold-flow measurements. The diagnostic system incorporates active wavelength stabilization via a feedback-controlled dye laser with drift correction algorithms to maintain measurement accuracy through extended mapping campaigns. Neutral density maps are acquired under cold-flow conditions and four plasma-operating states (540 and 720 W at varying background pressures), highlighting the effects of power level and background pressure on the near-field neutral particle profile. These results provide important experimental benchmarks for validating computational models and advancing physical understanding of neutral behavior and electric propulsion facility effects.

To overcome the bottlenecks in achieving broadband absorption and thin-profile design for high-temperature absorber-load-bearing integrated fiber composites, this paper presents an in-depth study on H-shaped fiber array structures composed of carbon fibers and silicon carbide fibers. By integrating the minimal aperture method with equivalent medium theory, an accurate extraction model for the equivalent electromagnetic parameters of non-uniform structures was established, resolving the challenge of electromagnetic parameter inversion for traditional all-metal backplane structures. Using nonlinear fitting methods, the contributions of conduction loss and relaxation polarization loss to dielectric loss were quantitatively analyzed. Results indicate that in the X and Ku bands, relaxation polarization loss is dominant, accounting for 63.73% of the total loss. The carbon fiber skeleton primarily dissipates energy through eddy current effects and ohmic losses induced by high conductivity, while silicon carbide fibers contribute to relaxation polarization loss via interfacial dipole reorientation polarization. Furthermore, constructing a 2.5 mm uniform-thickness multilayer gradient stack structure effectively mitigates impedance mismatch and significantly broadens the absorption bandwidth. Notably, under 20° oblique incidence, absorption performance improved by 1.8 times, reaching −32.5 dB from −17.8 dB. The effective absorption bandwidth increased by 1.7 times, broadening from 4.66 to 7.83 GHz. With a fiber content of only 4.536%, this structure achieves high-efficiency broadband absorption within a 2.5 mm thickness.

Europium-doped wide-bandgap semiconductors are promising materials for red light-emitting devices. Here, we present a europium-doped Zn(Mg)O-based multi-quantum well (MQW) structure design consisting of undoped Zn1−xMgxO barrier layers and Eu-doped Zn1−yMgyO (x > y ≥ 0), quantum wells. A gradient in the Mg content between the layers provides the potential barrier necessary to confine Eu dopants. A reference structure consisting of 20 pairs of Zn0.9Mg0.1O/ZnO:Eu was grown on the c-ZnO substrate. The structural and luminescence properties of these MQWs grown using plasma-assisted molecular beam epitaxy technique are investigated. A systematic comparison of the luminescence intensity and decay dynamics of Zn1−xMgxO/Zn1−yMgyO:Eu MQWs with ZnMgO:Eu epilayers reveals the clear superiority of MQWs over epilayers. The photoluminescence of Eu ions in the MQWs is two orders of magnitude stronger than that of ZnMgO:Eu epilayers, when the Mg content in the Eu-doped QW layer and epilayer is comparable. This can be explained by the increased carrier density around the Eu ions, as a result of their localization in QWs. The results suggest that the Zn1−xMgxO/Zn1−yMgyO:Eu MQWs enhance Eu emission via exciton generation in both the barriers and QW layers, followed by carrier relaxation into the QWs and subsequent energy transfer to the Eu dopants.

Gas composition and substrate temperature play key roles in governing surface reaction pathways and the etching behavior of dielectric films. In this study, the temperature- and composition-dependent etching characteristics of silicon dioxide and silicon nitride films were investigated in cryogenic NF3/NO plasmas, with the aim of clarifying how NO modulates material-dependent surface reactions. A range of observations revealed systematic variations in NO-, F-, and NOF-related species as functions of substrate temperature and gas composition. When the substrate temperature was reduced below 0 °C, the dominant reaction pathway of NO shifted from gas-phase reactions to processes dominated by surface reactions. Surface chemical analysis using x-ray photoelectron spectroscopy revealed distinct material-dependent responses under cryogenic conditions. For SiO2, lowering the substrate temperature promoted fluorine transfer reactions at the surface, consistent with enhanced chemical etching. In contrast, SiN exhibited increased surface trapping of NO- and NOF-related species, which suppressed the overall etching reaction under otherwise identical plasma conditions. These results demonstrate that NO acts as a reaction moderator whose influence depends on both the material type and the processing conditions. By correlating plasma diagnostics with surface chemical analysis, this work provides insight into non-polymer-based selective etching mechanisms in cryogenic NF3/NO plasmas and contributes to the understanding of process control strategies for high-aspect-ratio dielectric structures.

Theoretical analysis of a prototypical two-qubit effective non-Hermitian system characterized by asymmetric Heisenberg XY interactions in the absence of external magnetic fields demonstrates that maximal bipartite entanglement and quantum phase transitions can be induced exclusively through non-Hermiticity. At thermal equilibrium as T→0, the system attains maximal entanglement C=1 for values of the non-Hermiticity parameter greater than a critical value γ>γc=J1−δ2, where J denotes the exchange interaction and δ represents the anisotropy of the system; conversely, for γ<γc, entanglement is nonmaximal and given by C=1−(γ/J)2. The entanglement undergoes a discontinuous transition to zero precisely at γ=γc. This phase transition originates from the closing of the energy gap at a non-Hermiticity-driven ground state degeneracy, which is fundamentally different from an exceptional point.

Acoustic metamaterials have been the focus of research in recent years. By designing the unit structure of materials at the sub-wavelength scale, materials have unprecedented special properties, such as the realization of acoustic beam collimation. However, in previous studies, these collimated acoustic beams either have strong sidelobes, or the structure of the metamaterials is complex and difficult to verify experimentally. In this paper, we propose a simple fence-structured unit that, after periodic arrangement, excites collective surface oscillations in a specific frequency band to achieve an acoustic beam collimation with almost no sidelobe, which is verified by numerical simulations and experiments. This structural unit provides an effective means for directional sound propagation in air.

The micro-spallation damage behavior of low-melting-point metals under double shock is a critical concern in advanced equipment design. However, there is currently a lack of detailed spatial distribution information on micro-spallation after the second shock. In this study, two experiments on tin under different loading paths were conducted using a double-shock apparatus with adjusted backing plates. In addition, the loading histories were accurately measured using photonic Doppler velocimetry and Asay window diagnostics. To overcome the limitation in conventional approaches for extracting spatial information from the Asay window, an innovative inversion method for the micro-spallation material impacting Asay windows in vacuum was proposed. A dedicated post-processing procedure was further implemented to reconstruct the corresponding spatial volume density distribution. Comparison of the reconstructed volume density distributions under different loading paths reveals a consistent increasing trend from the free surface toward the rear interface. However, the slopes of these trends differ, particularly in the region near the free surface. Further analysis indicated that the shorter time interval between the first and second shock and the stronger secondary loading affect the damage microstructure of the porous, cavitated regions, leading to a more extensive porous zone adjacent to the free surface. This study provides insights into the micro-spallation distribution under double-shock and serves as a foundation for further investigations.

Ion sputtering from loose powders remains poorly understood despite its relevance to planetary science and industry. We developed a multiscale Monte Carlo model to simulate sputtering from powders, using a higher-fidelity approach for the target geometry compared to voxel-based methods. Simulating Kr+ ions impacting Cu powders and flat slabs, we show that sputtering from loose powders differs markedly from that of flat slabs or rough surfaces. The main differences are: (1) for incident angles α > 0° relative to the bulk normal, the escaping sputtering yield is dominated by backward-directed ejecta for all ion energies; (2) for α ≤ 60°, the yield peaks toward the ion-beam origin, similar to the opposition effect seen in optical observations of airless bodies; (3) the angular distribution peak is half or less than that of a flat slab; (4) as ion energy increases, no evolution occurs from primary to secondary knock-on sputtering in the ejecta angular distribution. We attribute these behaviors to the powder's interconnected voids. Ions penetrate these voids and sputter underlying grains; the ejecta then preferentially escape toward the ion-beam origin, where shadowing is minimal. We derive two fitting functions: (1) relating the escaping sputtering yield of a powder to that of a flat surface, depending only on porosity, incident angle, mean local incidence angle, and the corresponding flat slab yield; (2) providing the double-differential angular distribution of the escaping ejecta for porosities ≥0.49. These provide a potentially universal fitting function of the absolute doubly differential escaping sputtering yield from loose powders.

We report a systematic evaluation of the effects of post-deposition annealing temperature and structural ordering on the anomalous Nernst effect (ANE) in Fe2CoSi (FCS) Heusler alloy thin films. The study reveals that amorphous/disordered FCS films exhibit a larger anomalous Nernst coefficient (SANE) compared to their crystalline counterparts, in stark contrast to conventional Co-based Heusler alloys, which typically show maximum SANE in highly ordered structures. Furthermore, as a strategy for enhancing transverse thermoelectric properties, we explore the (FCS)100−xPtx composite alloy films by systematically varying the Pt concentration and optimizing the composition. This method effectively enhances the transverse thermoelectric performance of the FCS-based alloys. Our findings offer valuable insights into the design and development of next-generation high-performance ANE materials.

Despite significant progress being made in research on the mechanism and control of vanadium dioxide (VO2) phase transition, localized metal-to-insulator transition (MIT) and monoclinic VO2 (M) nucleation evolution in rutile VO2 (R) thin films under the application of tip force remain unclear, particularly on how these processes depend on the film orientation and how the tip force selects M-phase variants. Here, based on phase-field simulations and theoretical analysis, the localized MIT and the domain nucleation evolution behavior in [001]R and [110]R oriented VO2 thin films under tip-force loading are revealed. Results show that under the conditions of identical film thickness and tip-force application, the [001]R-oriented thin films are more prone to inducing localized MIT and typically form a quatrefoil morphology of domain nuclei mixed with M1/M2 phase variants. In contrast, MIT nuclei in [110]R-oriented thin films have smaller sizes and typically form an olive-shaped along the [001]R axis. Moreover, the occasional formation of antiphase boundaries in the same M-phase variant during MIT is found to significantly affect the morphology of domain nuclei. Our results reflect a strong impact of the film orientation on the tip-force-induced MIT of VO2 thin films, which is essentially due to the distinct eigenstrain characteristics of M-phase variants in the [001]R and [110]R coordinate systems, which modulate the degeneracy of M-phase variants and their selection during MIT. The work provides new insights into the tip-force-induced MIT and nucleation dynamics in VO2 thin films, and it is instructive for engineering of the VO2 phase transition and domain structure.

We demonstrated the formation of a donor band even in Si quantum dots (Si-QDs) with fewer than ten donors. Hot P+-ions were implanted at 800 °C into Si-QDs fabricated by implanting hot Si+ ions into a SiO2 layer. After post-N2 annealing at 1000 °C, the P+-doped Si-QDs with a diameter of 2.5 nm were embedded into the SiO2 layer. The P+-ion dose (DP) varied from 1 × 1015 to 9 × 1015 cm−2. Energy-dispersive x-ray spectroscopy revealed that the implanted P atoms clustered in the Si-QDs, which led to the experimental verification of the co-clustering of hot Si+/P+-ion implantation. Thus, the DP dependence of the P-atom concentration (NP-EDX) in Si-QDs was accurately determined. Additionally, the P 1s spectrum obtained by hard x-ray photoelectron spectroscopy revealed that the P–Si bond of the P-doped Si-QDs, including substantial P atoms, directly verifies donor formation in the Si-QDs. The upper limit of activation rate RACTUP of the implanted P atoms in the Si-QDs was obtained by the P–Si bond ratio. Therefore, the upper limit of donor concentration in the Si-QDs (NDUP) was determined by NDUP =NP-EDX × RACTUP, resulting in 1.4 × 1020 ≤ NDUP ≤ 1.3 × 1021 cm−3. The upper limit of number of donors in the Si-QDs (nDUP) was overestimated to be between 1 and 12. Additionally, the photoluminescence revealed the bandgap EG narrowing (ΔEG), even in the Si-QDs with nDUP < 12 caused by donor band tailing. ΔEG was much lower than those of two- and three-dimensional Si.

The Mo electrode thickness in AlScN-based bulk acoustic wave (BAW) resonators is constrained to sub-100 nm to satisfy high-frequency operational requirements, leading to degraded electrical conductivity and increased electrical losses. In this work, the electrical properties of the Mo electrode were enhanced through rapid thermal annealing (RTA). The Mo films showed a 102.5% enhancement in electrical conductivity, attributed to improved crystalline quality and suppressed surface scattering. Furthermore, thermal annealing reduced the residual stress in the film and promoted in-plane atomic rearrangement, thereby enhancing the effective electromechanical coupling coefficient (keff2) and reducing acoustic losses in the resonators. As a result, the figure of merit of the device increased by approximately 46.5%, reaching 152 after the annealing process. Moreover, the influence of electrode conductivity on resonator performance was analyzed using finite-element analysis. This work presented a promising strategy—the RTA process—for enhancing the electrical properties of the Mo electrode and improving the performance of BAW filters at high operating frequencies.

Artificially structured oxide superlattices provide a fertile ground for engineering electronic states. In this work, we report the synthesis of high-quality La0.7Sr0.3MnO3/LaCoO3 superlattices, which exhibit insulating ferromagnetism with a Curie temperature (TC) elevated to 230 K. Unlike conventional La0.7Sr0.3MnO3/SrTiO3 counterparts, the magnetic ordering in this system is driven by a distinct interfacial mechanism. By systematically varying the layer thickness, we observe a clear correlation between the ferromagnetic coupling and the interface density. Spectroscopic evidence from x-ray absorption identifies a valence shift toward the Co2+ state, indicative of Mn-to-Co charge transfer. This electronic reconstruction activates a strong superexchange pathway between Mn4+ and Co2+, consistent with Goodenough–Kanamori–Anderson rules. Furthermore, element-specific magnetic circular dichroism reveals robust magnetic moments on both sublattices, persisting well above 200 K. Our findings demonstrate that interfacial charge redistribution in superlattices is a viable route to overcome the low-TC limitations of ferromagnetic insulators.

In this study, we present a GaN-on-Si pseudo-vertical p–n diode fabricated using selective area growth (SAG). The device achieved a high current density of 1.5 kA cm−2 and a low specific on-resistance (Ron,sp) of 3.3 mΩ cm2. A very high on/off current ratio (Ion/Ioff) of 1012 was also recorded. Notably, for the first-time using SAG, uniform avalanche breakdown behavior of 850 V was demonstrated through temperature-dependent reverse bias measurements, corresponding to a Baliga figure of merit of 0.2 GW cm−2. These results emphasize the advantages of localized epitaxy in achieving high-quality p–n junctions on Si substrates, paving the way for scalable, high-performance GaN power devices monolithically integrated with Si technology. To evaluate the influence of geometric parameters on epitaxial quality and device performance, the mesa spacing was systematically varied while keeping the diameter fixed. Optimal results were obtained with 5–15 μm spacing, offering the best trade-off between forward conduction efficiency and reverse blocking robustness. This comprehensive investigation underscores the importance of geometric optimization and localized epitaxy in advancing high-performance GaN-on-Si p–n diodes for next-generation power applications.

Ceramic films possess inherently high stiffness; however, their brittleness and limited hardness constrain their use in practical applications. In this study, we demonstrate a strategy to concurrently enhance the mechanical and tribological performance of BaTiO3 (BTO) films by incorporating Au nanostructures at controlled molar ratios (BTO:Au = 5:1, 5:3, 5:5 refer to B5A1, B5A3, B5A5). Nanoindentation tests reveal substantial increases in nanohardness and toughness for the B5A1 and B5A3 films. Complementary tribological testing shows notable reductions in both friction coefficient and wear rate, with the B5A1 film exhibiting the most pronounced improvement, which is attributed to the favorable dispersion state of the Au phase. This work highlights an effective pathway for engineering hard yet damage-tolerant ceramic films through metal incorporation and microstructural tailoring.

Dynamic surface reconstruction critically governs the performance and durability of oxide-based electrocatalysts for the oxygen evolution reaction (OER), yet controlling this process under operating conditions remains challenging. Here, we demonstrate that lattice strain regulates the extent of surface reconstruction in perovskite oxides by modulating the redox behavior of lattice nickel (Ni). Using epitaxial LaNiO₃ (LNO) thin films as a model system, we show that strain-induced changes in Ni-oxygen(O) bond length systematically tune the reducibility of Ni³⁺, thereby controlling the degree of surface reconstruction. Tensile strain enhances Ni reducibility, promotes Ni (oxy)hydroxide formation, and results in a nearly order-of-magnitude increase in reconstruction compared to compressive strain. Under OER conditions in iron (Fe)-containing alkaline electrolytes, tensile-strained LNO exhibits a 5.7-fold enhancement in activity due to synergistic interactions between Fe species and the reconstructed Ni-based surface. By extending this concept to powder-type catalysts through isovalent doping, we demonstrate that modulation of the Ni-O bond length through Scandium (Sc) doping induces comparable surface reconstruction behavior and catalyst activity, thereby confirming the scalability of this approach. These results identify metal-oxygen bond length as a general design parameter for tuning dynamic surface reconstruction and catalytic activity in perovskite oxide electrocatalysts.

The persistent burden of respiratory viruses requires rapid, simple, and robust screening and environmental surveillance technologies that enable widespread and frequent testing. Importantly, these technologies should be based on infectivity-relevant signals, as RNA detection alone has limited correlation with transmission risk. Here, we present a membrane fusion-mediated platform that autonomously detects viruses by recapitulating the native viral entry mechanism. Fusogenic vesicles selectively fuse with fusion-competent viral particles, triggering encapsulated CRISPR-Cas13a components to generate fluorescent signals upon recognition of the released viral RNA. Through an autonomous workflow and accelerated signal generation within a confined vesicle, our platform achieves one-step detection of viruses within 2 min. The assay robustly detects three major respiratory viruses, with analytical sensitivities down to 5 TCID₅₀/mL for RSV and 50 TCID₅₀/mL for SARS-CoV-2 and IAV. Clinical validation with 100 nasopharyngeal samples achieved 91.7% sensitivity. Remarkably, the sprayable format enables large-area surveillance of surface contamination-like luminol revealing hidden bloodstains, it makes invisible viral threats visible. This approach establishes an intuitive real-time detection platform, extending beyond clinical specimens to encompass environmental threats.

Seawater electrolysis for green hydrogen is severely limited by the competing chloride oxidation reaction (ClOR) and the sluggish kinetics of oxygen evolution reaction (OER). This study introduces a lattice renormalization strategy to direct the reconstruction of Co-Mo-O catalysts in alkaline electrolyte, effectively shifting the OER pathway from the traditional adsorbate evolution mechanism (AEM) to the more efficient lattice oxygen mechanism (LOM). Selective Mo leaching induces the construction of a CoOOH/Co(OH)₂ with a stable Co³⁺-O-Co²⁺ electron-withdrawing chain, which significantly enhances Co-O covalency and activates lattice oxygen. The optimized catalyst, r-CoO_xH_y@NF, achieves low overpotentials of 330 and 380 mV at 500 and 1000 mA cm^- ² in simulated alkaline seawater, respectively. When configured into a membrane electrode assembly (MEA) electrolyzer, the system attains a low cell voltage of 1.66 V at 1.0 A cm^- ² for 480 h. In situ characterization and theoretical analysis reveal a "lattice oxygen-hydrogen-bonding network" synergy, where dynamically evolving hydrogen-bonding network at the interface not only facilitates rapid proton transfer but also electronically modulates the lattice oxygen orbitals via polarization effects, with stabilizing the LOM pathway and conferring superior chloride resistance. This work underscores the pivotal role of metal-ligand covalency and interfacial microenvironment in steering reconstruction pathways for industrial seawater splitting.