The applicability of single-crystal lanthanum hexaboride emitters in hollow cathodes was investigated through comparative operational tests and surface analyses with polycrystalline emitters. The discharge voltage of the single-crystal emitter was slightly higher than that of the polycrystalline emitter, but the difference was not significant, while the electron temperature and electron density were nearly identical. This behavior is presumably due to the fact that the low-work function crystal planes were not effectively utilized in the single-crystal emitter. The single-crystal emitter exhibited superior resistance to contamination, preserving surface integrity even in high-temperature regions, while the polycrystalline emitter accumulated more carbon and oxygen contamination. However, although the sample number was limited to two, rapid increases in discharge current caused cracks due to thermal shock in both of the two single-crystal emitters tested. In one case, a complete brittle fracture was observed, as evidenced by hackle patterns, rib marks, and fatigue striations. In contrast, no cracking or fracture was observed in the polycrystalline emitter, likely because grain boundaries mitigated the thermal stress. These results highlight a critical trade-off: single-crystal emitters offer contamination resistance, but require careful thermal design to prevent fracture, whereas polycrystalline emitters provide structural robustness at the expense of contamination susceptibility. This study provides guidance for selecting lanthanum hexaboride crystal structures in hollow cathode applications.

Lead-free titanium halide perovskites with the formula Cs2TiClxBr6−x were integrated into an ethylene–vinyl acetate (EVA) matrix to form hybrid perovskite thin films with tunable optoelectronic properties. Importantly, this work goes beyond compositional tuning by demonstrating that the polymer–perovskite hybrid architecture actively governs interfacial charge transport and polarization phenomena. Structural and optical characterization confirmed the formation of vacancy-ordered double perovskites with visible-light absorption and photoluminescence features associated with defect-mediated electronic relaxation. The electrical and photoinduced responses of the composites were investigated using electrochemical impedance spectroscopy with symmetric fluorine-doped tin oxide (FTO)│EVA│FTO configurations. Upon illumination, the films exhibited a marked decrease in impedance, revealing the halide-dependent modulation of charge transport, interfacial polarization, and pseudocapacitive behavior. Mixed-halide compositions displayed improved electrical uniformity and reduced transport resistance compared to pristine EVA, indicating enhanced photoinduced charge dynamics. Hirshfeld surface analysis was employed as a structural descriptor to quantify halide surface exposure, thereby linking composition-dependent electronic localization to the observed photoelectrical response. As a functional demonstration of these charge dynamics, the hybrid films were also evaluated under photocatalytic conditions, where light-driven formate and hydrogen generation corroborated the effective charge separation inferred from impedance measurements.

In this work, the influences of the direct current blocking capacitor, stray capacitance, and stray resistance in the external circuit on the self-bias driven by tailored voltage waveform (TVW)-driven asymmetric capacitive discharges are investigated using a one-dimensional three-velocity particle-in-cell/Monte Carlo collision model coupled with an external circuit. Under a zero-initial-phase sinusoidal TVW drive with an amplitude ratio of 3:2:1, a dc self-bias voltage is generated and can be significantly modulated by the blocking capacitor, stray resistance, and stray capacitance. The approximate adjustment ranges of each external circuit parameter, as well as an optimized combination of circuit parameters under specific discharge conditions are presented. Based on bias control using a single external component, combined control of multiple external circuit parameters enables a wider tuning range of plasma density, ion flux, and ion energy at the boundary. In addition, the mechanisms responsible for the formation of positive and negative self-bias voltages at different pressures are discussed. These results may provide insight and a theoretical reference for the engineering design of bias control in electrical asymmetric capacitively coupled plasma systems.

The performance of the free layer in a magnetic tunnel junction (MTJ) is critical for optimizing magnetic random access memory devices. In this study, we systematically investigate a quad-interface free-layer structure, MgO/B-FM/W/T-FM/MgO/B-FM/W/T-FM/MgO, focusing on the modulation of key magnetic properties, including saturation magnetization (Ms), magnetic dead layer thickness (tdl), perpendicular magnetic anisotropy (PMA), and interfacial anisotropy energy constant (Ki), by varying the thicknesses of the ferromagnetic (FM) and tungsten (W) layers, the annealing process, FM composition, and interfacial symmetry. Our results demonstrate that the insertion of the W layer is pivotal in achieving the transition from IPM (in-plane magnetization) to PMA. Moreover, the W layer thickness strongly influences interfacial atomic interdiffusion; as the W thickness increases, Ms decreases. The annealing process effectively suppresses dead layer growth, further enhancing magnetic performance. Comparative analysis of FeB and CoFeB systems reveals that FeB exhibits superior PMA, Ki, and Ms, owing to its more favorable 3d orbital half-filling and better lattice matching with MgO. An extremely large PMA value of 1.5 erg/cm2 has been achieved by the quad-interface free-layer structure. Finally, investigations varying the thickness ratio between the top (T-FM) and bottom (B-FM) layers highlight significant interfacial asymmetry, showing that interfacial loss in the T-FM layer is lower than in the B-FM layer. Overall, this study provides crucial experimental evidence and theoretical insight for structural engineering and comprehensive performance optimization of multi-interface MTJs.

Epitaxial growth of orthorhombic SnSe on cubic substrates is challenging due to lattice symmetry mismatch and anisotropic bonding. Here, we demonstrate that epitaxial films with sharp interfaces can be achieved for layered SnSe grown directly on both on-axis and 4° miscut GaAs(001) substrates. The substrate miscut strongly influences the growth morphology, evolving from spirals on on-axis GaAs to a terraced structure on miscut GaAs. X-ray diffraction reveals that on-axis GaAs supports SnSe with two in-plane orientation variants, whereas the miscut substrate stabilizes a single orientation and introduces a small out-of-plane tilt. Accordingly, in-plane optical anisotropy is enhanced in the single-variant film compared to the double variant, as determined by cross-polar reflectance. High-resolution TEM shows that the SnSe/GaAs interface is atomically abrupt and incoherent, characteristic of quasi-van der Waals epitaxy. We find a pronounced tendency for the zigzag edges of SnSe to align parallel to step edges on both substrates, and we show that step skipping nucleation and layer growth on the miscut substrate lead to the additional tilt. These results establish direct SnSe/GaAs heteroepitaxy as a route to integrate anisotropic layered semiconductors with cubic platforms and show that miscut substrates provide additional control over in-plane anisotropy.

Metasurfaces have emerged as powerful platforms for controlling electromagnetic waves through field confinement and resonance engineering. This work investigates the interplay between magnetic field-driven quasi-Bound State in the Continuum (quasi-BIC) resonance and lattice mode coupling in a complementary metasurface comprising coupled bar resonators. By introducing opposite tilts in the bar resonators, we observe the emergence of sharp resonance resulting from anti-symmetric current distributions, forming a quasi-BIC mode with strong field confinement. It is observed that the strategic change in periodicity significantly enhances the quality factor of the resonance, reaching maximum when the quasi-BIC mode couples to the fundamental lattice mode. We performed terahertz time domain spectroscopy of the fabricated samples and observed that the results are consistent with simulations, further confirming a strong interaction between the modes. These findings opens up an avenue for designing high-Q low loss metasurfaces with potential applications in sensing, filtering, and terahertz photonic devices.

The evolution of reacting metal ejecta continues to be a topic of interest at the forefront of metals in reactive and extreme environments. Ejecta are small particles formed when the surface of a metal undergoes Richtmyer–Meshkov instability from a strong shock. Experiments have shown that in the case where ejecta are in ambient conditions that induce a reaction, the ejecta behave irregularly. The ejecta temperature rises and then plateaus, and the acceleration profile shows unexpected jumps. These variations are assumed to be related to the exothermic heat release and particle mass loss caused by the reaction. To explain this phenomenon, efforts to model this in simulations have increased. While current models can capture many of these physical processes, they currently assign a constant reaction shell thickness with little physical reasoning. This work remedies this problem by assigning a dynamic physically informed shell thickness to the reacting particles, using solid analysis. The shell thickness of the particles impacts the rate of change of reacted mass in the system, as well as the rate at which the particles react. The model is based on a simple stress–strain relationship and gives a dynamic assignment for when the reacting particle should begin to fracture. We compare our model to the previous computational and simulation data to analyze the effects of different model parameters.

Maintaining the microstructure of energetic materials under specific margins is critical to ensure safety and performance. We investigate microstructural evolution of pentaerythritol tetranitrate thin films during thermal aging using phase-field simulations that integrate physical vapor deposition, grain coarsening, porosity evolution, and anisotropic mechanical response. We generate thin films with initial microstructures via physical vapor deposition simulations, followed by aging at two different temperatures. Our results demonstrate three primary stress-driven mechanisms: (1) void elongation along grain boundaries; (2) grain coarsening; and (3) preferential growth of grains with (110) orientations. Additionally, we find that porosity acts as a drag on grain boundary migration, with higher porosity levels reducing grain coarsening rates. These findings reveal the critical role of stresses and elastic anisotropy in controlling long-term microstructural stability of energetic thin films.

Terahertz metamaterials provide an effective platform for manipulating terahertz waves and have attracted significant interest for sensing applications. However, realizing compact devices that simultaneously achieve high sensitivity and high spatial resolution remains challenging. To address this issue, we investigate the thickness-dependent resonance behavior of nanoscale terahertz metamaterial sensors excited by a near-field point terahertz source. This source is locally generated via optical rectification in a nonlinear optical crystal under femtosecond laser irradiation at the subwavelength scale. Owing to the highly localized excitation, strong resonance is achieved even in an ultrathin, 20-nm-thick 3 × 3 metamaterial array with a subdiffraction-limited footprint of 0.54 × 0.54 λTHz2. We specifically examine the skin-depth (δ) effect by varying metal thickness below the skin depth and analyzing the resulting electric-field distributions and surface current patterns, which govern the coupling modes among the meta-atoms, the fundamental building blocks of the metamaterial. Numerical simulations show that transmission resonance emerges at a metal thickness of approximately 5 nm (0.045 δ), predicting the existence of an ultrathin critical thickness, while a thickness of 20 nm (0.18 δ) represents a practical boundary for achieving sufficiently strong resonance both in the simulation and experiment. Using a 20-nm-thick 3 × 3 meta-atom array, we further demonstrate trace-level biosensing by discriminating between single-stranded and double-stranded DNA, producing resonance frequency shifts of 30 and 40 GHz, respectively, in transmission measurements. These results identify metal thickness as a key physical parameter governing near-field-induced resonance and highlight the potential of ultrathin, ultracompact terahertz metamaterials for highly sensitive sensing applications.

Aluminum (Al), a key material in many high-energy density systems, is known to undergo phase transition (PT) from face-centered cubic (fcc) to hexagonal close-packed (hcp) and body-centered cubic (bcc) structures under static compression. Recently, through extensive non-equilibrium molecular dynamics simulations, we showed that shock-induced fcc to hcp and fcc to bcc structural PT in single-crystal (sc) Al occurs at pressures nearly an order of magnitude lower than those required for static compression. With the aim of capturing these transient phases experimentally, we undertake a detailed investigation of solid–solid PT in sc-Al subjected to isentropic compression with varying ramp times, reminiscent of impact by different thickness graded density impactors or functionally graded materials. The bcc phase fraction is found to increase with increasing ramp pressure, reaching an optimal value at 160 GPa. Furthermore, the pressure for persistence of bcc crystalline phase, PbccMax, can be extended beyond 600 GPa under ramp compression through suitable tailoring of piston velocity profile and target thickness, representing a substantial enhancement compared to 110 GPa limit observed for single-shock compression. A systematic investigation of the influence of different peak piston velocities and its rise time on bcc phase fraction and disorder atoms is presented. Finally, phase distributions arising from simulations using five different interatomic potentials are compared for selected piston velocities.