Metal oxides derived from metal-organic frameworks (MOFs) have garnered significant attention for gas sensing owing to their superior properties and unique architectures. Doping is an effective strategy for enhancing gassensing capabilities. In this study, core-shell-structured Y-doped ZnO nanocages are synthesized via a twostep ZIF-8-templated calcination strategy. Material characterizations reveal that Zn and O are uniformly distributed and highly enriched within the core and shell layers, whereas the distribution of Y within the cavity establishes a highly conductive network throughout the nanocage. The 4Y-ZnO sensor demonstrate competitive room-temperature ammonia-sensing performance; it yields a high response of 602 toward 500 ppm NH3 with satisfactory selectivity and a detection limit of 0.64 ppm. Mechanistic investigations reveal that Y doping promotes oxygen-vacancy formation, thus enhancing the adsorption of the target gas to amplify gas-sensing reactions, whereas the inherited core-shell architecture provides a substantially enlarged surface area for efficient gas diffusion. Density functional theory (DFT) calculations confirm that Y doping effectively enhances charge transfer and modulates the surface electronic structure, thus promoteing selective NH3 adsorption and supporting the experimentally observed high sensitivity and selectivity. In this study, high-performance MOFderived gas sensors are designed through synergistic structural and compositional optimization.

The interplay between ferroelectricity and band topology offers a promising route for the nonvolatile control of quantum states in low-power electronic devices. In this work, we propose a two-dimensional van der Waals heterostructure composed of ferromagnetic CrSnTe3 and ferroelectric In2Se3, where ferroelectricity, magnetism, and nontrivial band topology coexist. First-principles calculations reveal that monolayer CrSnTe3 is a ferromagnetic semiconductor with an in-plane easy magnetization axis. However, in the CrSnTe3/In2Se3 heterostructure, the easy magnetization axis rotates to the out-of-plane direction, accompanied by strong coupling between the topological electronic structure and ferroelectric polarization. Reversal of the ferroelectric polarization in In2Se3 induces a reversible topological phase transition between a normal semiconductor and a quantum spin Hall insulator. This transition is driven by a band inversion between the valence band from the CrSnTe3 layer and the conduction band from the In2Se3 layer during polarization switching, accompanied by a reversal of band spin polarization. Additionally, calculated topological edge states, anomalous Hall conductivity and spin Hall conductivity further confirm the strong coupling between ferroelectricity and topology. These findings provide a feasible strategy for realizing electrically switchable, nonvolatile topological states, and open new avenues for ferroelectric-controlled topological electronics.

Interface engineering plays an important role in manipulating the nonlinear optical (NLO) properties of materials at the nanometer scales. Herein, we report on ultrastrong second harmonic generation (SHG) realized by interface-controlled strain engineering of organic 4-N,N-dimethylamino-4 '-N '-methyl-stilbazolium tosylate (DAST) nano-films. Combining the benefits of interface-controlled strain, substrate interference, intrinsic nonlinearity, and nanostructure effects with reduced constrains from phase-matching, these DAST nano-films emit ultrastrong SHG with a record second-order nonlinear susceptibility (chi(2)) of 23.02 nmV-1, one order of magnitude larger than that of the best two-dimensional NLO materials studied so far. Such giant SHG responses are wide-band tunable and long-term stable in air exposure, and the chi(2)and nonlinear optical anisotropy of DAST can be rationally modulated by changing the interfacial interactions and the resultant film strain. Particularly, a 36-fold enhancement of SHG is induced as the film strain is increased from +0.45 % to +2.14 %. The results of this work not only reveal the underlying opportunities and degrees of freedom in modulating the nonlinearities via strain-induced deformations in soft organic NLO materials, but also open up a new route to emission of ultrastrong SHG from organic DAST nano-films realized by interface engineering.

Two-dimensional transition metal dichalcogenides (TMDCs) have attracted worldwide attention due to their rich physical and chemical properties. How to regulate their electronic structures to meet different application requirements is a crucial issue. In this work, based on first-principle calculations, we demonstrate that surface fluorination can be a powerful method for tailoring the electronic and magnetic properties of TMDC monolayers. The fluorinated T-MX2F2 (X = S, Se, Te) monolayers cover semiconductors, half-metals, semimetals, and half-semimetals. In particular, monolayer T-CrS2F2 is a half-semimetal, and the spin-orbit coupling effect changes it to a quantum anomalous Hall insulator. Monolayer T-HfS2F2 is a non-magnetic semimetal, and monolayer T-CoS2F2 is a half-metal. These findings not only suggest that fluorination can dramatically alter the electronic properties of two-dimensional TMDCs but also provide a new research platform for developing nanoelectronic devices.

The Berry curvature dipole induced by symmetry breaking plays a pivotal role in electronic transport properties and nonlinear responses, such as the nonlinear Hall effect and circular photogalvanic effect. The study of the Berry curvature dipole is often explored in time-reversal symmetric systems, but it should not be limited to such materials. Here, we predicted that the ferroelectricity in monolayer CrNBr2 produces the Berry curvature dipole, leading to the nonlinear Hall effect and circular photogalvanic current. The linear anomalous Hall effect and circularly polarized optical absorption, governed by spin-orbit coupling, are independent of ferroelectric polarization and exhibit extremely small conductance. In contrast, multiferroic monolayer CrNBr2 achieves a large nonlinear Hall conductivity (similar to 1 e3/h & strns;eV-1 at 30 K) and circular photogalvanic current, despite its suppression at high temperatures from phonon scattering. The coupling between the ferroelectric polarization and the Berry curvature dipoles (intraband for nonlinear Hall conductance and interband for circular photogalvanic current) allows for nonvolatile switching of these effects, presenting substantial promise for nanoelectronic and optoelectronic devices.

The 2D architecture of MXenes offers a scaffold for high-density magnetic moments. Yet the microscopic magneto-structural coupling remains elusive. Here, combining first-principles calculations with crystal orbital Hamilton population (COHP) analysis, we conduct a qualitative trend study to unravel the lattice geometry modulation in B/C/N-substituted MXenes. We reveal that the increased population of antibonding states by nitrogen's excess electrons weakens the covalent network. This "lattice softening", a reduction in structural rigidity, facilitates spontaneous bond contractions driven by nitrogen's smaller intrinsic radius. To maximize the magnetic exchange energy gain, the lattice undergoes geometric relaxation. Via Harrison's relation, we qualitatively rationalize that this lattice contraction modulates the exchange interaction. A simplified d-7 scaling is employed strictly as a qualitative descriptor to illustrate the strong sensitivity of the magnetic coupling to distance variations. Our findings demonstrate that, under Goodenough-Kanamori constraints adapted for these systems, lattice geometry plays an important role in modulating magnetic exchange. This establishes MXenes as a platform for rational magneto-structural engineering in next-generation spintronics.

On-chip electrocatalytic microdevices (OCEMs) are versatile platforms for probing the intrinsic kinetics of individual nanomaterials. However, their applications in evaluating 2D van der Waals materials often suffer from substantial interfacial contact resistance at the electrode/catalyst junction and sluggish catalytic reaction kinetics at the catalyst/electrolyte interface. Herein, we develop an yttrium-doping strategy for monolayer MoS2 (Y-MoS2) that simultaneously optimizes charge injection across the solid-solid (electrode/catalyst) interface and hydrogen binding on the basal plane of MoS2. The Y doping downshifts the conduction band minimum of MoS2, lowering the Schottky barrier from 0.47 to 0.23 eV and enhancing electron injection across the electrode/catalyst interface. The matching spatial orbital symmetry of Y and Mo 4dxz/yz induces strong d-d electronic coupling, driving the formation of a favorable bridge hydrogen intermediate ( H bridge ∗ ) with an optimized binding energy of 0.36 eV for hydrogen evolution reaction (HER) at the catalyst/electrolyte interface. Benefiting from this synergistic optimization of band alignment and hydrogen binding, Y-MoS2 exhibits superior HER performance, delivering an overpotential of 187 mV at 10 mA cm-2, competitive with recent 2D MoS2-based electrocatalysts. This work establishes an optimized OCEM platform for decoupled mechanistic analysis and an orbital-level tuning strategy for efficient electrocatalyst design.

Fabricating aligned arrays of hexagonal transition metal dichalcogenide nanoribbons is essential for high-density integrated devices but remains challenging due to the intrinsic lattice symmetry, which typically favors multi-directional orientations. Here, we report a step-guided anisotropic etching strategy that exploits the reconstructed steps of annealed c-sapphire substrates to overcome this symmetry constraint, yielding unidirectional MoS2 nanoribbon arrays. This process achieves precise orientation control while preserving the high crystallinity of the parent film. Crucially, angle-resolved spectroscopic investigations reveal a striking decoupling between the linear and nonlinear optical responses in these one-dimensional nanostructures. While polarized Raman spectroscopy confirms a strain-free lattice with isotropic phonon response, second harmonic generation measurements uncover an anisotropy governed by the one-dimensional confinement and strong depolarization field effects. Our findings not only establish a top-down pathway for orientation-controlled nanomanufacturing but also highlight the potential of geometric engineering in tailoring nonlinear light-matter interactions, enabling polarization-sensitive functionalities.

To overcome the intrinsic physical constraints of strict near-field coupling in conventional plasmonic sensors, this work proposes a metal-insulator-metal (MIM) waveguide configuration. By integrating a periodic array of silver nanoblocks within a sensing region positioned over 2 mu m from the bus waveguide, the sensor achieves effective remote refractive index sensing at the micrometer scale. Finite-difference time-domain (FDTD) simulations demonstrate that the localized surface plasmon resonance (LSPR) peaks can be deterministically tuned by adjusting the dimensions of the composite periodic cavity. This versatility allows for precise adaptation to specific detection windows, such as [1.0, 1.2] or [1.2, 1.4]. After optimizing the structure of the resonator, although the sensing region is far away from the bus waveguide, it can still obtain a sensitivity of 1105 nm RIU-1 while maintaining a low signal loss. Through the numerical verification of glucose solutions with different concentrations, the device achieved a mass concentration sensitivity of 0.131 nm & centerdot;l g-1. This result shows that the structure has good application potential in the field of high-performance remote biomedical sensing.

Abstract Topological semimetals hold great promise for nonlinear optics (NLO). It is challenging to probe tilted Dirac fermion-driven intrinsic second harmonic generation (SHG) and topological band structure modulation of second-order nonlinearity in spatial inversion and time-reversal-symmetric nonmagnetic Dirac semimetals. Here, we identify NiTe2, featuring a type-II Dirac cone, as an ideal platform for investigating SHG in centrosymmetric crystals. Through comprehensive NLO measurements, we demonstrate that the highly efficient SHG emission in NiTe2 arises predominantly from bulk electric-quadrupole contribution. Under interband optical transition conditions, we quantify a giant effective nonlinear susceptibility |χEQ(3)q| ≈ 7.07 pm/V at 475 nm, which is an order of magnitude higher than that of commonly used NLO crystals. Furthermore, the striking spectral consistency between SHG and four-wave mixing (FWM) unambiguously identifies the shared interband excitation and radiation channels as the unified driving mechanism. Collectively, these findings pave the way for harnessing centrosymmetric topological semimetals in next-generation nonlinear optoelectronic devices.

The realization of multiferroic altermagnets featuring giant intrinsic spin splitting holds great promise for next-generation spintronics. In this work, based on the recently proposed concept of spin-antiferroelectricity (spin-AFE), we construct a class of two-dimensional (2D) multiferroic altermagnets, termed 2D spin-antiferroelectric altermagnets (2D spin-AFEAMs), enabling electrical control of spin polarization via a gate field. Furthermore, we propose a general design strategy for constructing 2D spin-AFEAMs with large intrinsic spin splitting. Guided by this strategy, we predict monolayer (CoCl)2Te and its family materials as potential candidates of 2D spin-AFEAM. We uncover a highly tunable transport regime in monolayer (CoCl)2Te, where the spin current can be switched via the in-plane electric field angle when hole-doped and via the gate field polarity when electron-doped. Our work enriches the family of 2D multiferroics and provides a blueprint for realizing high-performance, electrically switchable altermagnetic spintronic devices.

The performance of luminescent dosimetric materials is governed by the complex interplay between lattice distortions and nonequilibrium charge carriers. Alkali metals doped LiMgPO4 has been reported experimentally to exhibit enhanced radiation dosimetry performance, yet the microscopic mechanisms underlying this improvement remain poorly understood. Here, using nonadiabatic molecular dynamics simulations, we uncover a carrier decoupling mechanism driven by dopant induced lattice distortions operating on different length scales. Excited electrons rapidly localize into stable small polarons on an ultrafast timescale, stabilized by strong local distortions surrounding the dopant sites. In contrast, holes form mobile polarons whose transport is facilitated by long-range lattice distortions that reorganize the valence band states and promote intersite hopping. This pronounced asymmetry between electron localization and hole mobility suppresses carrier recombination and prolongs nonequilibrium carrier lifetimes. These findings reveal how hierarchical lattice distortions regulate carrier relaxation pathways and provide a microscopic framework for understanding the enhanced luminescent response in alkali metals doped LiMgPO4. More broadly, the results suggest that tuning local and extended lattice distortions offers an effective strategy for engineering carrier trapping and recombination in phosphate-based luminescent dosimetric materials.

Metallic altermagnets offer advantages for exploring physical phenomena associated with low-energy quasiparticle excitations and for applications in spintronics. The emergence of spin-density-wave (SDW) order in a recently synthesized metallic altermagnet KV2Se2O was reported, but the underlying mechanism remains unexplored. The charge and magnetic disproportionation in perovskites are often attributed to the electron correlation effects. In this work, we carry out first-principles calculations and find that the SDW phase emerges when the Hubbard U exceeds a critical value (U = 2 eV), suggesting a possible correlation-driven mechanism. This scenario is unchanged with K vacancies or alkali-metal substitutions. Our findings highlight the potential of metallic altermagnets for realizing emergent quantum phenomena.

Rational design and construction of a high-activity bifunctional nonprecious metal catalyst for overall water splitting is vital for hydrogen fuel production. In this work, a novel FeP/NiCoP nanowire array (FCNP nanowires) with porosity loaded onto carbon cloth is designed and prepared via a simple two-step route. The precise regulation of coordination number (CN) adjusts the electron configuration and micromorphology of the composite catalyst, which can optimize the adsorption/desorption of hydrogen/hydroxyl in an alkaline electrolyte, thus improving catalytic activity. As expected, the FCNP nanowire requires only 87.9 and 247.3 mV overpotentials at a current density of 10 mA cm-2 for a hydrogen evolution reaction (HER) and at a current density of 100 mA cm-2 for an oxygen evolution reaction (OER) in an alkaline electrolyte, respectively, outperforming most related catalysts reported. The corresponding low Tafel slopes of 54.4 mV dec-1 and 25.8 mV dec-1 and low charge transfer resistance (Rct) suggest its quick reaction kinetics. Moreover, the assembled electrolyzer applying the FCNP nanowire as both the cathode and anode only needs 1.63 V to deliver a current density of 20 mA cm-2. This work provides a new insight for constructing high-activity catalysts with a clear correlation between the coordination environment and intrinsic catalytic activity.

Due to the role of the valley as an information carriers, two-dimensional valleytronics materials have broad prospects in information storage in the future. However, materials with intrinsic valley polarization are rare. In our work, using first-principles calculations, we propose a valleytronics material monolayer (ML) AgMoP2S6 with a ferromagnetic(FM) ground state. The ferromagnetic exchange interaction breaks the time-reversal symmetry, which results in a spontaneous valley polarization of 78 meV at the K/-K points on the valence band under the action of strong SOC. The valley polarization can be tuned by biaxial strain and Hubbard U, and when the tensile strain exceeds 4 % and U exceeds 2 eV, valley polarization also appears in the conduction band. Under the action of an in-plane electric field, the breaking of valley degeneracy makes the appearance of anomalous valley Hall effect (AVHE) effect a possibility. ML AgMoP2S6 is an ideal valleytronics material.

Altermagnets (AMs) are an emergent class of magnetic materials that combine properties of ferromagnets and antiferromagnets, exhibiting spin-polarized Fermi surfaces and zero net magnetic moment due to combined time-reversal and crystal symmetry. Here, we construct a Kondo-lattice model on a two-dimensional (2D) square Lieb lattice to investigate the topological properties of AMs. We identify a type-II quantum spin Hall state characterized by spin-polarized counterpropagating edge states. Breaking the C4zT symmetry, which connects magnetic sublattices, induces a transition to a quantum anomalous Hall state. We further establish a straininduced mechanism to control these topological phase transitions and present the corresponding phase diagram. Finally, we demonstrate the predicted transitions in monolayer CrO, a realistic altermagnetic candidate, using first-principles calculations. Our findings highlight the potential of 2D AMs as a versatile platform for topological spintronics, enabling strain-tunable helical and chiral edge states within a single system.

High-harmonic generation (HHG) in two-dimensional materials offers a compelling route toward compact extreme ultraviolet sources and probing electron dynamics on the attosecond scale. However, achieving precise control over the emission and disentangling the complex interplay between intraband and interband quantum pathways remains a central challenge. Here, we demonstrate through first-principles simulations that HHG in monolayer WS2 can be subjected to precise, complementary control by combining all-optical two-color laser fields with mechanical strain engineering. This dual-mode strategy provides distinct, orthogonal control over harmonic yield, polarization, and spectral features. We reveal that sculpting the two-color field's relative phase provides a sub-femtosecond switch for the quantum coherence of electron-hole pairs, thereby optimizing harmonic emission. Crucially, we uncover that tensile strain modulates the total harmonic yield and specifically amplifies the perpendicular harmonic component by nearly a factor of two. This enhancement arises through a dual mechanism-while strain-modified band dispersion enhances the intraband current, a significant reshaping of the Berry curvature substantially increases the anomalous velocity contribution to the interband response. This quantum geometric effect manifests as a robust, monotonic dependence of the harmonic yield on strain and a significant amplification of the perpendicularly polarized harmonics, providing a clear experimental signature for probing quantum geometric effects. Our findings establish a versatile framework for optimizing solid-state HHG and introduce a powerful all-optical method to map strain and quantum geometric properties of materials, positioning monolayer WS2 as a model system for exploring attosecond physics at the nexus of bulk and atomic scales.

Monolayer 1T-TiTe2 hosts a unique charge density wave (CDW) instability absent in its bulk form, yet the active control of this state for electronic applications remains a challenge. Here, using first-principles calculations, we demonstrate that biaxial strain acts as a deterministic switch to drive a metal-semiconductor transition and robustly stabilize the CDW order. We reveal that tensile strain significantly deepens the phonon softening at the M point, enhancing the Peierls instability and opening a discrete CDW band gap. Conversely, compressive strain effectively suppresses the structural distortion, completely quenching the CDW order to restore the metallic normal phase. Notably, our thermodynamic modeling predicts that tensile strain significantly enhances the thermal stability of the CDW phase. While mean-field estimations suggest high stability, we discuss how strain robustly counters thermal fluctuations. These findings elucidate the strain-dependent phase diagram of TiTe2, establishing it as a promising candidate for robust, tunable phase-change electronic devices.

Controllable modulation of Rashba spin-orbit coupling (RSOC) in two-dimensional (2D) quantum systems remains a key challenge in advancing next-generation spintronic devices. Taking MoSi2N4 as a prototype, this study designs a series of 2D semiconductors with significantly enhanced RSOC by strategically incorporating heavy elements and applying structural engineering techniques. Results demonstrate that substituting C and Bi at the A and Z sites in the MoSi2N4 framework efficiently activates substantial RSOC. Further structural modifications to the MXAZ2 system yield even stronger RSOC strength (alpha R), with values such as 2.09 eV & Aring; in HfTeCAsBi. Detailed characteristic analysis indicates that there is a strong correlation between the work function difference (Delta Phi), the dipole moment (mu) and alpha R. External field modulation show that biaxial strain, uniaxial strain, and out-of-plane electric fields can dynamically adjust alpha R through lattice distortion and interfacial charge redistribution. Additionally, the short channel length of HfSeCAsBi-based spin field-effect transistors (s-FETs) provides significant advantages for high-density device integration. This work can offer valuable theoretical insights for band engineering in high-performance spintronic applications.

MA 2 Z 4 -based 2D materials enable tunable Rashba spin–orbit coupling. Intrinsic RSOC can be achieved via structural engineering and elemental substitution, while its strength is further adjustable through strain and electric fields.