Physics

The pursuit of developing electrode materials that can seamlessly integrate both sensing and catalytic functions remains a key goal in the field of electrochemical materials research. This study introduces a hybrid electrochemical platform that utilizes copper nanoparticles on delaminated V2CTx MXene to explore the material's inherent electrochemical and catalytic characteristics. The two-dimensional V2CTx structure offers a substantial accessible surface area, excellent electrical conductivity, and surface terminations that can be chemically adjusted, while the electrodeposited Cu nanoparticles provide additional catalytic active sites and enhance charge transfer efficiency. The resulting V2C@Cu composite exhibits highly selective electrochemical detection of nitrate and nitrite ions in alkaline conditions, showing two linear concentration ranges (0.1-10 mM and 10-30 mM) with detection limits of 0.232 and 0.475 mM for nitrate and 0.08 and 0.45 mM for nitrite, respectively. Beyond its sensing capabilities, the material also demonstrates magneto-electrocatalytic activity for the hydrogen evolution reaction under low external magnetic fields (0-2000 G), where the overpotential decreases from 465.49 to 374.94 mV at 10 mA cm-2 and the Tafel slope improves from 126.78 to 93.25 mV dec-1. The composite electrode also shows remarkable electrochemical stability during repeated cycling and extended potentiostatic operation. Its practical applicability was further validated by successfully detecting nitrate and nitrite in environmental water samples with high recovery efficiencies. These results reveal the potential of V2C@Cu MXene as a versatile materials platform for combined electrochemical sensing and magneto-electrocatalytic applications.

Abstract Perovskite manganites have attracted considerable attention due to their strongly correlated structural, electronic, and magnetic properties arising from the interplay among 'charge', 'spin', and 'orbital' degrees of freedom of Mn '3d' electrons. In this work, La 0.8 Sr 0.2 MnO 3 (LSMO) manganites with systematically varied particle sizes were prepared via a sol-gel technique to investigate the influence of particle size on structural evolution and magnetic behavior. Xray diffraction data after Rietveld analysis substantiates the formation of a monophasic rhombohedral R-3c structure for samples sintered up to 1200 °C, whereas higher sintering temperatures (1350 °C and 1500 °C) lead to the emergence of a minor monoclinic P21 /c secondary phase (∼4-6%) coexisting with the dominant phase. Field emission scanning electron microscopy reveals a significant increase in grain size from ∼97 nm to ∼4.2 µm with enhanced sintering, accompanied by the development of terrace-like surface morphologies indicative of step-flow growth and enhanced crystallinity. These features are attributed to variations in surface chemical potential and critical nucleation processes. Magnetic measurements demonstrate the presence of a Griffiths phase (GP), whose strength progressively diminishes with increasing particle size and applied magnetic field, reflecting reduced magnetic inhomogeneity. The GP behavior is ascribed to quenched disorder and short-range ferromagnetic clustering within a paramagnetic matrix. Temperature-dependent magnetization measurements reveal a ferromagnetic-paramagnetic transition above room temperature. Additionally, the particle size dependence of spin-wave excitations and the 'spin-wave' stiffness constant highlights the role of exchange interactions in governing magnetic dynamics. Overall, the results establish a clear correlation between sintering-temperature-driven structural modifications and magnetic properties, underscoring the potential of LSMO manganites for room-temperature spintronic and magnonic applications.

We demonstrate a rapid, maskless fabrication method for superconducting terahertz Josephson plasma emitters (JPEs) based on direct ultraviolet laser micromachining of Bi2Sr2CaCu2O8+δ (Bi-2212) single crystals. Although machining debris is formed near the processed regions, uniform stacks of intrinsic Josephson junctions are preserved inside the crystal, enabling stable terahertz emission. Devices fabricated with Ag, Cu, and Cr electrodes all exhibited terahertz radiation, with Cu electrodes showing performance comparable with Ag while offering a low-cost alternative. Spectroscopic and polarization analyses indicate that the emitted radiation is elliptically polarized and dominated by the geometrical cavity resonance mode. Structural and electrical characterizations reveal that the machining width and depth are not limited by the optical spot size but are governed by the anisotropic thermal conductivity of Bi-2212, consistent with a thermally dominated laser ablation process. This direct laser micromachining approach provides a fast and versatile fabrication technique for JPEs and is broadly applicable to superconducting electronics and terahertz devices.

In this paper, we present a spectral analysis of the strong prism of the chained polyomino network based on its normalized Laplacian matrix. First, by the decomposition theorem for normalized Laplacian characteristic polynomials in product graphs, we partition the normalized Laplacian matrix of the network into two symmetric matrices LA and LS, explicitly deriving their complete eigenvalue sets. Second, we explore the interconnection between the roots and polynomial terms of the characteristic polynomials of these two matrices. Third, the multiplicative degree-Kirchhoff index for chained networks was derived, which analyzes the properties of the network and is especially important to understand the electrical properties of the network. Finally, the complexity of chained networks was derived. These findings establish a solid foundation for understanding the structural complexity and connectivity of networks.

The tailored optical properties of (InxGa1−x)2O3 microcrystalline films were studied as a function of composition x via transmission, Urbach energy analysis, and spatial photoluminescence (PL) mapping of the self-trapped hole (STH) emission, with the objective of addressing material characteristics specific to this alloy system. Up to x = 0.46, the optical gap exhibited a redshift of 1 eV from the deep to the near-UV range, while the STH PL was redshifted by 0.5 eV in the visible range. For higher composition, x = 0.63, the transmission spectra indicated the co-existence of two optical gaps attributed to Ga-rich and In-rich domains, implying that this sample is phase-separated. However, the saturation behavior of the optical gap and that of the STH PL showed that incipient phase separation occurs at a lower composition: x ∼ 0.3. This is consistent with the compositional trend found for Urbach energy, implying that phase segregation in the alloys is a major defect even at its incipient stages. In addition, Urbach analysis of (InxGa1−x)2O3 was compared to that of MgxZn1−xO. Both systems were found to have similar compositional dependence: at lower range, Urbach energies exhibited a negligible increase, while at the higher range, a significant dependence on the composition was found. The main difference between the two alloy systems is in their Urbach energy: those for (InxGa1−x)2O3 were significantly larger than those for MgxZn1−xO. This stems from the strong hole coupling to phonons of (InxGa1−x)2O3, which provides a dynamic transition additional to that of the defect-type.

First-principles calculations were employed to investigate the effects of dilute vanadium (V) and sulfur (S) doping on the structural, phonon, thermal, electronic, and optical properties of VxMo1−xS2zSe2(1−z) alloys derived from two-layer hexagonal molybdenum diselenide (2H–MoSe2). The results indicate that all considered compositions preserve structural integrity with only slight lattice contraction and remain dynamically stable. Increasing sulfur concentration enhances lattice stiffness, Debye temperature, and overall thermal stability while simultaneously reducing lattice thermal conductivity. Electronic structure calculations reveal that the systems maintain an indirect semiconducting nature with tunable and moderately increased bandgaps as the sulfur doping concentrations increases, accompanied by an enhanced dielectric response. Thermodynamic analysis based on Helmholtz free energy suggests that alloys with moderate sulfur content exhibit greater thermodynamic stability, whereas higher sulfur substitution slightly decreases stability. Furthermore, the observed reduction in heat capacity and entropy at higher sulfur concentrations indicates stronger phonon scattering and suppressed lattice heat transport. Overall, V/S co-doping emerges as an effective strategy for tuning the multifunctional properties of two-layer 2H–MoSe2. Moderate sulfur concentrations are favorable for stable electronic and optoelectronic applications, while higher sulfur contents may be advantageous for thermal management technologies.

We present an ITER poloidal field (PF) coil scenario for reliable plasma breakdown using a two-dimensional ITER conductor model. Realistic engineering constraints, such as maximum voltage and current limits, are taken into account. To ensure reliable breakdown, magnetic constraints are imposed such that the toroidal electric field reaches ET = 0.3 V/m at breakdown while maintaining a high-quality field-null region with a poloidal stray field ∣B∣ < 3 mT. These constraints are implemented using a constrained quadratic programming method. The model provides an algorithm to determine PF coil power supply voltages that satisfy all constraints required for successful breakdown. The simulation code is developed using the ITER integrated modeling and analysis suite data structure to facilitate easy integration with future ITER integrated simulators.

To achieve the green and controllable preparation of high-efficiency oxygen evolution reaction (OER) catalysts, this study proposes a modification of microwave-synthesized nickel–iron layered double hydroxide (NiFe LDH) using N2 plasma treatment. The effects of plasma treatment power and duration on the material’s structure and catalytic performance were systematically investigated. The results indicate that under optimized conditions (100 W, 90 min), the prepared nitrogen-doped NiFe LDH exhibits an overpotential of only 258 mV at a current density of 10 mA cm−2 and a Tafel slope of 57.4 mV dec−1, significantly outperforming the untreated sample. Characterization results confirm that the plasma treatment successfully introduces nitrogen doping and constructs oxygen vacancy defects while maintaining the layered structure of the material, increasing the oxygen vacancy density by 86.8%, effectively increasing the number of active sites and optimizing the electronic structure. Electrochemical tests reveal a 55.8% reduction in charge transfer resistance and a 10.5% increase in the electrochemical active surface area after modification. Furthermore, after a 200 h stability test, the performance degradation was less than 5%. This study provides a new method for developing efficient and stable non-noble metal OER catalysts and elucidates the mechanism by which nitrogen doping and oxygen vacancies synergistically enhance catalytic performance.

Graphene/AlGaN/GaN heterostructures are proposed to investigate the drag and two-stream instability effects. In this study, graphene grown by chemical vapor deposition was transferred from copper onto the top of a “standard” AlGaN/GaN wafer, forming a heterostructure with two conducting layers separated by an AlGaN barrier layer. Contacts fabricated to the two-dimensional electron gas and graphene allowed us to study the drag current induced in graphene by passing the drive current through the two-dimensional electron gas. At low temperatures, the graphene drag current exhibited quantum oscillations as a function of the drive voltage. As temperature increases, quantum oscillations disappear, and the magnitude of the drag current increases. Graphene/AlGaN/GaN heterostructures are a promising platform for studying drag and two-stream instability effects, especially if the AlGaN barrier layer thickness can be reduced to a few nanometers.

The development of active and reconfigurable planar optical systems remains a central objective in modern photonics. Here, we propose and theoretically validate a computational inverse-design paradigm that integrates adjoint-based optimization with the linear Stark effect of moiré interlayer excitons embedded within a reflective Gires–Tournois Interferometer (GTI) architecture. By treating a user-defined target light field as the input, our framework automatically compiles it into a spatially resolved voltage map that programs the complex reflection coefficient of the moiré polariton microcavity on demand. The non-symmetric reflective GTI configuration overcomes the Ohmic losses inherent in transmissive designs, enabling full 2π phase modulation while maintaining a high spatially averaged reflectivity (>70%) and operating strictly within safe dielectric limits (Ez ≤ 0.8 V/nm). Leveraging this methodology, we demonstrate the fully automated, ab initio design of a high-numerical-aperture, aberration-managed varifocal reflective metalens with continuous focal-length tuning (up to Δf ≈ 344 μm) and a peak focusing efficiency of 77%. Systematic material screening identifies the twisted WSe2 homobilayer and the MoTe2/WSe2 heterostructure as optimal candidates. This work establishes a direct bridge between computational inverse design and programmable quantum materials, paving the way toward next-generation, chip-scale, field-programmable photonic systems for optical computing, adaptive imaging, and LiDAR applications.

We present a cost-effective quantitative phase imaging flow cytometry system that utilizes a low-coherence super luminescent diode (SLD) as the illumination source for off-axis digital holographic microscopy (DHM), enabling label-free imaging of biological cells in flow. While off-axis DHM systems for flow imaging typically rely on expensive coherent lasers, our system employs a low-coherence SLD to reduce both cost and coherence noise. Achieving a large field of view with low-coherence sources is inherently challenging due to limited coherence length; in this work, we address this by incorporating a diffraction grating in the reference beam, which enables large-area interference and supports parallel imaging of multiple cells for high-throughput analysis. The system maintains a short exposure time of 50 μs—critical for dynamic single-cell studies—while achieving a signal-to-noise ratio (SNR) of 48, enabled by the high optical power and low coherence of the SLD, which together reduce coherence noise and enhance SNR. Jurkat cells in flow were imaged using this integrated setup, and system characterization confirmed high spatial phase sensitivity and stable temporal stability. The integrated microfluidic flow control system, featuring a three-way valve, enabled sedimentation-free flow at lower flow rates. Quantitative morphological analysis confirmed that native cell shape was preserved during flow, demonstrating the system’s suitability for label-free imaging of single-cell morphology. This platform provides a scalable, high-performance solution for real-time cellular analysis and non-invasive imaging, with translational potential in biomedical and diagnostic applications.