Resolving the dynamic properties of entangled linear polymers in non-equilibrium coarse grain simulation with a priori scaling factors

The molecular weight of polymers can influence the material properties, but the molecular weight at the experiment level sometimes can be a huge burden for property prediction with full-atomic simulations. The traditional bottom-up coarse grain (CG) simulation can reduce the computation cost. However, the dynamic properties predicted by the CG simulation can deviate from the full-atomic simulation result. Usually, in CG simulations, the diffusion is faster and the viscosity and modulus are much lower. The fast dynamics in CG are usually solved by a posteriori scaling on time, temperature, or potential modifications, which usually have poor transferability to other non-fitted physical properties because of a lack of fundamental physics. In this work, a priori scaling factors were calculated by the loss of degrees of freedom and implemented in the iterative Boltzmann inversion. According to the simulation results on 3 different CG levels at different temperatures and loading rates, such a priori scaling factors can help in reproducing some dynamic properties of polycaprolactone in CG simulation more accurately, such as heat capacity, Young's modulus, and viscosity, while maintaining the accuracy in the structural distribution prediction. The transferability of entropy-enthalpy compensation and a dissipative particle dynamics thermostat is also presented for comparison. The proposed method reveals the huge potential for developing customized CG thermostats and offers a simple way to rebuild multiphysics CG models for polymers with good transferability.

Spectroscopic Identification of Charge Transfer of Thiolated Molecules on Gold Nanoparticles via Gold Nanoclusters

Investigation of charge transfer needs analytical tools that could reveal this phenomenon, and enables understanding of its effect at the molecular level. Here, we show how the combination of using gold nanoclusters (AuNCs) and different spectroscopic techniques could be employed to investigate the charge transfer of thiolated molecules on gold nanoparticles (AuNP@Mol). It was found that the charge transfer effect in the thiolated molecule could be affected by AuNCs, evidenced by the amplification of surface-enhanced Raman scattering (SERS) signal of the molecule and changes in fluorescence lifetime of AuNCs. Density functional theory (DFT) calculations further revealed that AuNCs could amplify the charge transfer process at the molecular level by pumping electrons to the surface of AuNPs. Finite element method (FEM) simulations also showed that the electromagnetic enhancement mechanism along with chemical enhancement determines the SERS improvement in the thiolated molecule. This study provides a mechanistic insight into the investigation of charge transfer at the molecular level between organic and inorganic compounds, which is of great importance in designing new nanocomposite systems. Additionally, this work demonstrates the potential of SERS as a powerful analytical tool that could be used in nanochemistry, material science, energy, and biomedical fields.

Robust Magnetoelectric Coupling in FeTiO3/Ga2O3 Non-van der Waals Heterostructures

Magnetoelectric coupling represents a significant breakthrough for next-generation electronics, offering the ability to achieve nonvolatile magnetic control via electrical means. In this comprehensive investigation, leveraging first-principles calculations, we unveil a robust magnetoelectric coupling within multiferroic heterostructures (HSs) by ingeniously integrating a non-van der Waals (non-vdW) magnetic FeTiO3 monolayer with the ferroelectric (FE) Ga2O3. Diverging from conventional van der Waals (vdW) multiferroic HSs, the magnetic states of the FeTiO3 monolayer can be efficiently toggled between ferromagnetic (FM) and antiferromagnetic (AFM) configurations by reversing the polarization of the Ga2O3 monolayer. This intriguing phenomenon arises from polarization-dependent substantial interlayer electron transfers and the interplay between superexchange and direct-exchange magnetic couplings of the iron atoms. The carrier-mediated interfacial interactions induce crucial shifts in Fermi level positions, decisively imparting distinct electronic characteristics near the Fermi level of composite systems. These novel findings offer exciting prospects for the future of magnetoelectric technology.

Magnetic skyrmions and their manipulations in a 2D multiferroic CuCrP2Te6 monolayer

Magnetic skyrmions and their effective manipulations are promising for the design of next-generation information storage and processing devices, due to their topologically protected chiral spin textures and low energy cost. They, therefore, have attracted significant interest from the communities of condensed matter physics and materials science. Herein, based on density functional theory (DFT) calculations and micromagnetic simulations, we report the spontaneous 2 nm-diameter magnetic skyrmions in the monolayer CuCrP2Te6 originating from the synergistic effect of broken inversion symmetry and strong Dzyaloshinskii-Moriya interactions (DMIs). The creation and annihilation of magnetic skyrmions can be achieved via the ferroelectric to anti-ferroelectric (FE-to-AFE) transition, due to the variation of the magnetic parameter D2/|KJ|. Moreover, we also found that the DMIs and Heisenberg isotropic exchange can be manipulated by bi-axial strain, to effectively enhance skyrmion stability. Our findings provide feasible approaches to manipulate the skyrmions, which can be used for the design of next-generation information storage devices.

Electrocatalytic Urea Synthesis via N2 Dimerization and Universal Descriptor

Electrocatalytic urea synthesis through N2 + CO2 coreduction and C-N coupling is a promising and sustainable alternative to harsh industrial processes. Despite considerable efforts, limited progress has been made due to the challenges of breaking inert N≡N bonds for C-N coupling, competing side reactions, and the absence of theoretical principles guiding catalyst design. In this study, we propose a mechanism for highly electrocatalytic urea synthesis using two adsorbed N2 molecules and CO as nitrogen and carbon sources, respectively. This mechanism circumvents the challenging step of N≡N bond breaking and selective CO2 to CO reduction, as the free CO molecule inserts into dimerized *N2 and binds concurrently with two N atoms, forming a specific urea precursor *NNCONN* with both thermodynamic and kinetic feasibility. Through the proposed mechanism, Ti2@C4N3 and V2@C4N3 are identified as highly active catalysts for electrocatalytic urea formation, exhibiting low onset potentials of -0.741 and -0.738 V, respectively. Importantly, taking transition metal atoms anchored on porous graphite-like carbonitride (TM2@C4N3) as prototypes, we introduce a simple descriptor, namely, effective d electron number (Φ), to quantitatively describe the structure-activity relationships for urea formation. This descriptor incorporates inherent atomic properties of the catalyst, such as the number of d electrons, the electronegativity of the metal atoms, and the generalized electronegativity of the substrate atoms, making it potentially applicable to other urea catalysts. Our work advances the comprehension of mechanisms and provides a universal guiding principle for catalyst design in urea electrochemical synthesis.

Controllable Electrocatalytic to Photocatalytic Conversion in Ferroelectric Heterostructures

Photocatalytic and electrocatalytic reactions to produce value-added chemicals offer promising solutions for addressing the energy crisis and environmental pollution. Photocatalysis is driven by light excitation and charge separation and relies on semiconducting catalysts, while electrocatalysis is driven by external electric current and is mostly based on metallic catalysts with high electrical conductivity. Due to the distinct reaction mechanism, the conversion between the two catalytic types has remained largely unexplored. Herein, by means of density functional theory (DFT) simulations, we demonstrated that the ferroelectric heterostructures Mo-BN@In2Se3 and WSe2@In2Se3 can exhibit semiconducting or metallic features depending on the polarization direction as a result of the built-in field and electron transfer. Using the nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) as examples, the metallic heterostructures act as excellent electrocatalysts for these reactions, while the semiconducting heterostructures serve as the corresponding photocatalysts with improved optical absorption, enhanced charge separation, and low Gibbs free energy change. The findings not only bridge physical phenomena of the electronic phase transition with chemical reactions but also offer a new and feasible approach to significantly improve the catalytic efficiency.

Ferroelectric Domain and Switching Dynamics in Curved In2Se3: First-Principles and Deep Learning Molecular Dynamics Simulations

Despite its prevalence in experiments, the influence of complex strain on material properties remains understudied due to the lack of effective simulation methods. Here, the effects of bending, rippling, and bubbling on the ferroelectric domains are investigated in an In2Se3 monolayer by density functional theory and deep learning molecular dynamics simulations. Since the ferroelectric switching barrier can be increased (decreased) by tensile (compressive) strain, automatic polarization reversal occurs in α-In2Se3 with a strain gradient when it is subjected to bending, rippling, or bubbling deformations to create localized ferroelectric domains with varying sizes. The switching dynamics depends on the magnitude of curvature and temperature, following an Arrhenius-style relationship. This study not only provides a promising solution for cross-scale studies using deep learning but also reveals the potential to manipulate local polarization in ferroelectric materials through strain engineering.

Bimetallic conjugated metal-organic frameworks as bifunctional electrocatalysts for overall water splitting

Stable, high-efficiency, and highly active electrocatalysts are critical for the conversion of renewable energy through overall water splitting. Our first-principles calculations identify two-dimensional conjugated metal-organic frameworks (2D c-MOFs) with dual metal sites as promising candidates for this process. Among them, PcCo-O₈-Rh stands out as the best catalyst, with Rh serving as the active site for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), resulting in a low η_HER/η_OER of -0.19/0.25 V. Our findings suggest that the HER/OER activity of PcTM-O₈-TM' can be optimized through tensile strain, as it is related to the absorption strength of intermediates and the d-band center (ε_d) of the TM atom. This study presents a new family of 2D c-MOFs as high-performance bifunctional electrocatalysts for overall water splitting, paving the way towards sustainable energy conversion.

Layer Hall Effect in Multiferroic Two-Dimensional Materials

The layer Hall effect (LHE) is of fundamental and practical importance in condensed-matter physics and material science; however, it was rarely observed and usually based on the paradigms of persistent electric field and sliding ferroelectricity. Here, a new mechanism of LHE is proposed by coupling layer physics with multiferroics using symmetry analysis and a low-energy k·p model. Due to time-reversal symmetry breaking and valley physics, the Bloch electrons on one valley will be subject to a large Berry curvature. This combined with inversion symmetry breaking gives rise to layer-polarized Berry curvature and can force the electrons to deflect in one direction of a given layer, thereby generating the LHE. We demonstrate that the resulting LHE is ferroelectrically controllable and reversible. Using first-principles calculations, this mechanism and predicted phenomena are verified in the multiferroic material of bilayer Co₂CF₂. Our finding opens a new direction for LHE and 2D materials research.

Magnetic Electrides: High-Throughput Material Screening, Intriguing Properties, and Applications

Electrides are a unique class of electron-rich materials where excess electrons are localized in interstitial lattice sites as anions, leading to a range of unique properties and applications. While hundreds of electrides have been discovered in recent years, magnetic electrides have received limited attention, with few investigations into their fundamental physics and practical applications. In this work, 51 magnetic electrides (12 antiferromagnetic, 13 ferromagnetic, and 26 interstitial-magnetic) were identified using high-throughput computational screening methods and the latest Materials Project database. Based on their compositions, these magnetic electrides can be classified as magnetic semiconductors, metals, or half-metals, each with unique topological states and excellent catalytic performance for N₂ fixation due to their low work functions and excess electrons. The novel properties of magnetic electrides suggest potential applications in spintronics, topological electronics, electron emission, and as high-performance catalysts. This work marks the beginning of a new era in the identification, investigation, and practical applications of magnetic electrides.

Ferroelectric Materials and Their Applications in Activation of Small Molecules

The demand for renewable and environmentally friendly energy sources has attracted extensive research on high-performance catalysts. Ferroelectrics, a class of materials with switchable polarization, are unique and promising catalyst candidates due to the significant effects of polarization on surface chemistry and physics. The band bending at the ferroelectric/semiconductor interface induced by the polarization flip promotes charge separation and transfer, thereby enhancing the photocatalytic performance. More importantly, the reactants can be selectively adsorbed on the surface of ferroelectric materials depending on the polarization direction, which can effectively lift the basic limitations as imposed by Sabatier's principle on catalytic activity. This Review summarizes the latest developments of ferroelectric materials and introduces ferroelectric-related catalytic applications. The possible research directions of 2D ferroelectric materials in chemical catalysis are discussed at the end. The Review is expected to inspire extensive research interests from physical, chemical, and materials science communities.

Layer-polarized anomalous Hall effects in valleytronic van der Waals bilayers

The layer-polarized anomalous Hall effect (LP-AHE), derived from the coupling between the Berry curvature and the layer degree of freedom, is of importance for both fundamental physics and device applications. Nonetheless, the current research paradigm is rooted in topological systems, rendering such a phenomenon rather scarce. Here, through model analysis, we propose an alternative, but general, mechanism for realizing the LP-AHE in valleytronic van der Waals bilayers by interlayer sliding. The interaction between out-of-plane ferroelectricity and A-type antiferromagnetism gives rise to the layer-locked Berry curvature and thus the long-sought LP-AHE in bilayer systems. The LP-AHE can be strongly coupled with sliding ferroelectricity, rendering it ferroelectrically controllable and reversible. The mechanism is demonstrated in a series of real valleytronic materials, including bilayer VSi₂P₄, VSi₂N₄, FeCl₂, RuBr₂ and VClBr. The new mechanism and phenomena provide a significant new direction to realize the LP-AHE and explore its application in electronics.

Multifold Fermions and Fermi Arcs Boosted Catalysis in Nanoporous Electride 12CaO·7Al2 O3

Topological materials have been recently regarded as ideal catalysts for heterogeneous reactions due to their surface metallic states and high carrier mobility. However, the underlying relationship between their catalytic performance and topological states is under debate. It has been discovered that the electride 12CaO·7Al₂ O₃ (C12A7:4e^- ) hosts multifold fermions and Fermi arcs on the (001) surface near the Fermi level due to the interstitial electrons. Through the comparison of catalytic performance under different doping and strain conditions, based on the hydrogen evolution process, it has been demonstrated that the excellent catalytic performance indeed originates from topological properties. A linear relationship between the length of Fermi arcs, and Gibbs free energy (ΔG_H* ) has been found, which not only provides the direct evidence to link the enhanced catalytic performance and surface Fermi arc states, but also fully clarifies the fundamental mechanism in topological catalysis.

Optoelectronic properties and applications of two-dimensional layered semiconductor van der Waals heterostructures: perspective from theory

Van der Waals heterostructures (vdWHs) which combine two different materials together have attracted extensive research attentions due to the promising applications in optoelectronic and electronic devices, the investigations from theoretical simulations can not only predict the novel properties and the interfacial coupling, but also provide essential guidance for experimental verification and fabrications. This review summarizes the recent theoretical studies on electronic and optical properties of two-dimensional semiconducting vdWHs. The characteristics of different band alignments are discussed, together with the optoelectronic modulations from external fields and the promising applications in solar cells, tunneling field-effect transistors and photodetectors. At the end of the review, the further perspective and possible research problems of the vdWHs are also presented.

Effect of nonaffine displacement on the mechanical performance of degraded PCL and its graphene composites: an atomistic investigation

Evaluating the mechanical properties of biodegradable implants can be challenging for in situ experiments and time-consuming for materials with a slow degradation rate, such as polycaprolactone (PCL). In this work, the effects of chain scission and water erosion on the mechanical properties of degraded PCL are investigated by molecular dynamics simulation. The decrease of the mechanical performance is correlated with the increase of the nonaffine displacement during the degradation. The nonaffine squared displacements (NSD) during the tensile deformation are calculated by subtracting the affine squared displacements from the mean squared displacements. After chain scission, short polymer chains increase the NSD of the system and weaken the modulus of the polymer matrix. The effect of the NSD is also observed in a water erosion model. When the bond break ratio is less than 5%, PCL still maintains a well-entangled network, which constrains the diffusion of the water molecules, resulting in a higher modulus of the erosion model than the chain scission model at a low degradation rate. The effect of NSD is also found in the PCL/graphene composites. For the degraded polymer chains, the diffusion of PCL is constrained by the graphene network, and such an effect increases during the degradation. As a result, the addition of graphene nanosheets slows down the decreasing trend of Young's modulus. Such findings can also explain the size effect of the graphene reinforcement on the mechanical properties of the polymer composites. This work provides atomistic insights into the mechanical property evolution during polymer degradation, revealing the possibility of tuning the mechanical performance by controlling the diffusion, which could be beneficial for the design and lifetime prediction of degradable implants.

MAX-phase Derived Tin Diselenide for 2D/2D Heterostructures with Ultralow Surface/Interface Transport Barriers toward Li-/Na-ions Storage

2D tin diselenide and its derived 2D heterostructures have delivered promising potentials in various applications ranging from electronics to energy storage devices. The major challenges associated with large-scale fabrication of SnSe₂ crystals, however, have hindered its engineering applications. Herein, a tin-extraction synthetic method is proposed for producing large-size SnSe₂ bulk crystals. In a typical synthesis, a Sn-containing MAX phase (V₂ SnC) and a Se source are heat-treated under a reducing atmosphere, by which Sn is extracted from the V₂ SnC phase as a rectified Sn source to form SnSe₂ crystals in the cold zone. After the following liquid exfoliation, the obtained 2D SnSe₂ nanosheets have a lateral size of a few centimeters and an atomic thickness. Furthermore, by coupling with 2D graphene to form 2D/2D SnSe₂ /graphene heterostructured electrodes, as validated by theoretical calculation and experimental studies, the superior Li-/Na-ion storage performance with ultralow surface/interface ion transport barriers are achieved for rechargeable Li-/Na-ion batteries. This innovative synthetic strategy opens a new avenue for the large-scale synthesis of selenides and offers more options into the practical application of emerging 2D/2D heterostructure for electrochemical energy storage.

2D Higher-Metal Nitride Nanosheets for Solar Steam Generation

Higher-metal (HM) nitrides are a fascinating family of materials being increasingly researched due to their unique physical and chemical properties. However, few focus on investigating their application in a solar steam generation because the controllable and large-scale synthesis of these materials remains a significant challenge. Herein, it is reported that higher-metal molybdenum nitride nanosheets (HM-Mo₅ N₆ ) can be produced at the gram-scale using amine-functionalized MoS₂ as precursor. The first-principles calculation confirms amine-functionalized MoS₂ nanosheet effectively lengthens the bonds of MoS leading to a lower bond binding energy, promoting the formation of MoN bonds and production of HM-Mo₅ N₆ . Using this strategy, other HM nitride nanosheets, such as W₂ N₃ , Ta₃ N₅ , and Nb₄ N₅ , can also be synthesized. Specifically, under one simulated sunlight irradiation (1 kW m^-2 ), the HM-Mo₅ N₆ nanosheets are heated to 80 °C within only ≈24 s (0.4 min), which is around 78 s faster than the MoS₂ samples (102 s/1.7 min). More importantly, HM-Mo₅ N₆ nanosheets exhibit excellent solar evaporation rate (2.48 kg m^-2  h^-1 ) and efficiency (114.6%), which are 1.5 times higher than the solar devices of MoS₂ /MF.

Mechanical Behaviors in Janus Transition-Metal Dichalcogenides: A Molecular Dynamics Simulation

In this work, molecular dynamics simulations are performed to investigate the mechanical properties of Janus WSSe and MoSSe monolayers considering the effects of structural anisotropy, temperature, and tensile strain rates. The results demonstrate that Janus WSSe and MoSSe monolayers show strong mechanical anisotropy under tension along the armchair and zigzag directions, respectively. This anisotropy displays distinct temperature dependence. When the coupled effects of the temperature and anisotropy are considered for the tensions along the zigzag direction, there is a transition of ductile-to-brittle failure in the Janus WSSe monolayer at the critical temperature range of 80~90 K due to the competition between atomic thermal vibrations and structural bending/wrinkles. This phenomenon is further confirmed by both stress–strain curves and structural evolutions of the systems. Finally, a strain rate hardening mechanism is found when various strain rates are applied, and it demonstrates that the Janus monolayer could maintain stable mechanical properties under different loading conditions. Our investigations provide a helpful reference for subsequent theoretical and experimental studies on the mechanical properties of Janus monolayer structures and could shed some light on the design of promising nanoscale functional devices based on Janus transition-metal dichalcogenides.

Stacking-Dependent Interlayer Ferroelectric Coupling and Moiré Domains in a Twisted AgBiP2Se6 Bilayer

Rotation/twisting of bilayers could induce unprecedented new physics due to stacking-dependent electronic properties and interlayer coupling, such as the superconductivity in twisted bilayer graphene, which can find applications in electronics. However, deep understanding at the atomic/electronic levels is limited by the capability of accurate theoretical simulations. Here, from first-principles simulations, we found that the AgBiP₂Se₆ bilayer has stacking-dependent ferroelectric ground states due to interlayer polarization coupling. Interlayer ferroelectric coupling is preferred in an AA-stacked AgBiP₂Se₆ bilayer, but antiferroelectric coupling is preferred in AB- or AC-stacked configurations. The ferroelectric Moiré patterns are thus observed in a twisted AgBiP₂Se₆ bilayer with ferroelectric (antiferroelectric) interlayer couplings in the AA (AB/AC)-stacked areas. Our work for the first time unveils the effects of twisting/rotation on interlayer polarization coupling and provides a real example of ferroelectric Moiré patterns.

Mechano-ferroelectric coupling: stabilization enhancement and polarization switching in bent AgBiP2Se6 monolayers

Two-dimensional (2D) van der Waals (vdW) ferroelectrics are core candidates for the development of next-generation non-volatile storage devices, which rely highly on ferroelectric stability and feasible approaches to manipulate the ferroelectric polarization and domain. Here, based on density functional theory calculations, we demonstrate that the bending deformation can not only manipulate the polarization direction and domain size of AgBiP₂Se₆ monolayers but also significantly improve the ferroelectric stability. The ordered polarization in the bent AgBiP₂Se₆ monolayers can be well maintained at a temperature of 200 K in molecular dynamics simulations; by contrast, it is broken at only 100 K for their freestanding counterparts. These phenomena can be attributed to synergic effects from the asymmetric strain energy induced by a strain gradient and a reduced migration barrier of Ag ions from convex to concave surfaces. More interestingly, a ferroelectric bubble can be induced in the monolayer under biaxial compression strain. This mechano-ferroelectric coupling represents a new mechanism and feasible route towards stabilization and polarization flip in 2D ferroelectrics.

High efficient arsenic removal by In-layer sulphur of layered double hydroxide

High-risk arsenic contamination found in aqueous system is reported across the world and causing severe environmental issues. In this study, the Mg-Al Layered Double Hydroxide (LDH) modified by sulphur species (LDH-S) was found exhibiting high effectivity and selectivity in As(V) removal owing to the strong interaction between embedded HS^- and AsO₄^3-. The LDH-S with Mg to Al ratio 2-1 give the best performance with As(V) adsorption capacity 40.8 mg/g, which is 715% higher than that of pristine LDH (2-1). The adsorbent exhibits a high tolerance to concentrated competitive anions. In the continuous flow test, the adsorbent can reduce the As(V) concentration from 20 ppm to below-ppb-level indicating the potential in industry application. The adsorption mechanism is experimentally investigated and examined by Density Function Theory (DFT) calculation. The result illustrates that, differ from the traditional ion exchange mechanism of LDH, the enhanced removal capacity and selectivity of LDH-S for As(V) is attributed to the strong affinity between H atom from HS- ion (in the interlayer region of LDH) and the O atom from AsO₄^3-.

2D ferroelectric devices: working principles and research progress

Two-dimensional (2D) ferroelectric materials are promising for use in high-performance nanoelectronic devices due to the non-volatility, high storage density, low energy cost and short response time originating from their bistable and switchable polarization states. In this mini review, we first discuss the mechanism and operation principles of ferroelectric devices to facilitate understanding of these novel nanoelectronics and then summarize the latest research progress of electronic devices based on 2D ferroelectrics. Finally, the perspectives for future research and development directions in various fields are provided. We expect this will provide an overview regarding the application of 2D ferroelectrics in electronic appliances.

Controllable CO2 electrocatalytic reduction via ferroelectric switching on single atom anchored In2Se3 monolayer

Efficient and selective CO₂ electroreduction into chemical fuels promises to alleviate environmental pollution and energy crisis, but it relies on catalysts with controllable product selectivity and reaction path. Here, by means of first-principles calculations, we identify six ferroelectric catalysts comprising transition-metal atoms anchored on In₂Se₃ monolayer, whose catalytic performance can be controlled by ferroelectric switching based on adjusted d-band center and occupation of supported metal atoms. The polarization dependent activation allows effective control of the limiting potential of CO₂ reduction on TM@In₂Se₃ (TM = Ni, Pd, Rh, Nb, and Re) as well as the reaction paths and final products on Nb@In₂Se₃ and Re@In₂Se₃. Interestingly, the ferroelectric switching can even reactivate the stuck catalytic CO₂ reduction on Zr@In₂Se₃. The fairly low limiting potential and the unique ferroelectric controllable CO₂ catalytic performance on atomically dispersed transition-metals on In₂Se₃ clearly distinguish them from traditional single atom catalysts, and open an avenue toward improving catalytic activity and selectivity for efficient and controllable electrochemical CO₂ reduction reaction.

Exceptional Deformability of Wurtzite Zinc Oxide Nanowires with Growth Axial Stacking Faults

To ensure reliability and facilitate the strain engineering of zinc oxide (ZnO) nanowires (NWs), it is significant to understand their flexibility thoroughly. In this study, single-crystalline ZnO NWs with rich axial pyramidal I (π₁) and prismatic stacking faults (SFs) are synthesized by a metal oxidation method. Bending properties of the as-synthesized ZnO NWs are investigated at the atomic scale using an in situ high-resolution transmission electron microscopy (HRTEM) technique. It is revealed that the SF-rich structures can foster multiple inelastic deformation mechanisms near room temperature, including active axial SFs' migration, deformation twinning and detwinning process in the NWs with growth π₁ SFs, and prevalent nucleation and slip of perfect dislocations with a continuous increased bending strain, leading to tremendous bending strains up to 20% of the NWs. Our results record ultralarge bending deformations and provide insights into the deformation mechanisms of single-crystalline ZnO NWs with rich axial SFs.

Strain-tuned magnetism and half-metal to metal transition in defective BCN monolayer

Recently, two-dimensional (2D) BCN, an in-plane heterostructure formed by graphene and hexagonal boron nitride, has been successfully synthesized experimentally and exhibits diverse electronic properties. Unfortunately, it has been slow on the application of 2D BCN for spintronics due to the lack of the magnetic ordering. Here, using density functional theory calculations, we explored the effect of vacancy defect and biaxial strain on the electronic and magnetic properties of BCN monolayer. It is demonstrated that BCN monolayer can be converted from nonmagnetic semiconductor to magnetic half-metal/metal by introducing C or B vacancies. The half-metal/metal behavior can be remained under the different vacancy concentrations in defective BCN monolayer. In addition, BCN monolayer with C and B vacancies can be converted between half-metal and metal by applying biaxial strain. Moreover, the magnetic properties of defective BCN monolayer can also be efficiently modulated under the biaxial strain by regulating the spin polarization of the C/N/B 2porbitals. Our findings not only provide an effective way to achieve half-metal/metal transition, but also can induce and manipulate the magnetism of BCN monolayer, which may be utilized for the development of 2D BCN spintronic nanodevices.

Catalysis based on ferroelectrics: controllable chemical reaction with boosted efficiency

Catalysts, which can accelerate chemical reactions, show promising potential to alleviate environmental pollution and the energy crisis. However, their wide application is severely limited by their low efficiency and poor selectivity due to the recombination of photogenerated electron-hole pairs, the back-reaction of interactants. Accordingly, ferroelectrics have emerged as promising catalysts to address these issues with the advantages of promoted light adsorption, boosted catalytic efficiency as a result of their intrinsic polarization, suppressed electron-hole pair recombination, and superior selectivity via the ferroelectric switch. This review summarizes the recent research progress of catalytic studies based on ferroelectric materials and highlights the controllability of catalytic activity by the ferroelectric switch. More importantly, we also comprehensively highlight the underlying working mechanism of ferroelectric-controlled catalysis to facilitate a deep understanding of this novel chemical reaction and guide future experiments. Finally, the perspectives of catalysis based on ferroelectrics and possible research opportunities are discussed. This review is expected to inspire wide research interests and push ferroelectric catalysis to practical applications.

Enhanced Ion Sieving of Graphene Oxide Membranes via Surface Amine Functionalization

Membranes based on two-dimensional (2D) nanomaterials have shown great potential to alleviate the worldwide freshwater crisis due to their outstanding performance of freshwater extraction from saline water via ion rejection. However, it is still very challenging to achieve high selectivity and high permeance of water desalination through precise d-spacing control of 2D nanomaterial membranes within subnanometer. Here, we developed functionalized graphene oxide membranes (FGOMs) with nitrogen groups such as amine groups and polarized nitrogen atoms to enhance metal ion sieving by one-step controlled plasma processing. The nitrogen functionalities can produce strong electrostatic interactions with metal ions and result in a mono/divalent cation selectivity of FGOMs up to 90 and 28.3 in single and binary solution, which is over 10-fold than that of graphene oxide membranes (GOMs). First-principles calculation confirms that the ionic selectivity of FGOMs is induced by the difference of binding energies between metal ions and polarized nitrogen atoms. Besides, the ultrathin FGOMs with a thickness of 50 nm can possess a high water flux of up to 120 mol m^-2 h^-1 without sacrificing rejection rates of nearly 99.0% on NaCl solution, showing an ultrahigh water/salt selectivity of around 4.31 × 10³. Such facile and efficient plasma processing not only endows the GOMs with a promising future sustainable water purification, including ion separation and water desalination, but also provides a new strategy to functionalize 2D nanomaterial membranes for specific purposes.

Enhanced Hardness in Transition-Metal Monocarbides via Optimal Occupancy of Bonding Orbitals

An efficient strategy that can guide the synthesis of materials with superior mechanical properties is important for advanced material/device design. Here, we report a feasible way to enhance hardness in transition-metal monocarbides (TMCs) by optimally filling the bonding orbitals of valence electrons. We demonstrate that the intrinsic hardness of the NaCl- and WC-type TMCs maximizes at valence electron concentrations of about 9 and 10.25 electrons per cell, respectively; any deviation from such optimal values will reduce the hardness. Using the spark plasma sintering technique, a number of W_1-xRe_xC (x = 0-0.5) have been successfully synthesized, and powder X-ray diffractions show that they adopt the hexagonal WC-type structure. Subsequent nanoindentation and Vickers hardness measurements corroborate that the newly developed W_1-xRe_xC samples (x = 0.1-0.3) are much harder than their parent phase (i.e., WC), marking them as the hardest TMCs for practical applications. Furthermore, the hardness enhancement can be well rationalized by the balanced occupancy of bonding and antibonding states. Our findings not only elucidate the unique hardening mechanism in a large class of TMCs but also offer a guide for the design of other hard and superhard compounds such as borides and nitrides.

Hydroxyl-Boosted Nitrogen Reduction Reaction: The Essential Role of Surface Hydrogen in Functionalized MXenes

MXenes, an emerging family of two-dimensional (2D) metal carbides and nitrides, have been demonstrated to be effective nitrogen reduction reaction (NRR) catalysts. So far, most of the theoretical studies toward NRR are based on bare MXenes; however, the structural stabilities are questionable. In this work, we studied the NRR process on several synthesized MXenes (Ti₂C, V₂C, Cr₂C, Zr₂C, Nb₂C, Mo₂C, Hf₂C, and Ta₂C) with hydroxyl (OH) termination since the structures are preferred under NRR operating conditions as per Pourbaix stability diagrams. It is found that OH plays an essential role in tuning the NRR chemistry, as a new surface-hydroxylation mechanism. Different from the widely accepted NRR mechanism where only protons are involved in the reaction, hydrogen (H) atoms from surface hydroxyl could be captured by the intermediate and participate into the NRR, while the remaining H vacancy can subsequently be self-repaired by the protons under the applied potential. The cooperative effect of surface hydroxylation can effectively boost the NRR, while Mo₂C(OH)₂ stands out with the most favorable limiting potential of -0.62 V and highest selectivity. Moreover, new scaling relationships based on the H vacancy energy are established, elucidating the possibility for structure-activity tuning. This study not only elaborates the essential role of surface OH functionalization in evaluating NRR performance but also affords new insights into advance sustainable NH₃ production.

Robust Magnetoelectric Effect in the Decorated Graphene/In2Se3 Heterostructure

The magnetoelectric effect is a fundamental physical phenomenon that synergizes electric and magnetic degrees of freedom to generate distinct material responses like electrically tuned magnetism, which serves as a key foundation of the emerging field of spintronics. Here, we show by first-principles studies that ferroelectric (FE) polarization of an In₂Se₃ monolayer can modulate the magnetism of an adjacent transition-metal (TM)-decorated graphene layer via a ferroelectrically induced electronic transition. The TM nonbonding d-orbital shifts downward and hybridizes with carbon-p states near the Fermi level, suppressing the magnetic moment, under one FE polarization, but on reversed FE polarization this TM d-orbital moves upward, restoring the original magnetic moment. This finding of robust magnetoelectric effect in the TM-decorated graphene/In₂Se₃ heterostructure offers powerful insights and a promising avenue for experimental exploration of ferroelectrically controlled magnetism in two-dimensional (2D) materials.

Negative Poisson Ratio in Two-Dimensional Tungsten Nitride: Synergistic Effect from Electronic and Structural Properties

Low-dimensional materials with high stabilities and outstanding mechanical properties are essential for next generation microelectromechanical systems (MEMS). The successful synthesis of two-dimensional (2D) tungsten nitride makes it a promising candidate for the MEMS application. Here, we have confirmed the existence of experimentally synthesized W₂N₃ and predicted three additional new 2D monolayer tungsten nitrides: WN₂, WN₄, and W₃N based on extensively structural searches by CALYPSO method and first-principle calculations. The calculations indicate that the nitrogen-rich WN₄ monolayer possesses large in-plane negative Poisson ratios attributed to the 4-fold-coordinated WN₄ ν_x = -0.103 and ν_y = -0.113, which are tetrahedron combined with the strong coupling between the 2p orbitals of N and 5d orbitals of W. Our findings not only enrich the family of 2D transition metal nitrides with excellent mechanical properties but also open avenues for design and synthesis of other novel 2D layered materials.

Electronic and effective mass modulation in 2D BCN by strain engineering

2D BCN material consisting of graphene and hexagonal boron nitride (h-BN) has received extensive attention due to its abundant electronic properties and promising applications. The actual applications of 2D BCN require that there be precise control over its electronic properties. Using density functional theory calculations, we systematically investigate the electronic structure and effective mass of 2D BCN under biaxial strain. It is demonstrated that the band gap of zigzag BCNs decreases monotonously as the tensile strain increases. Moreover, the system exhibits a similar trend, regardless of the C/h-BN ratio. In sharp contrast, the band gap of armchair BCNs depends on the C/h-BN ratio. Specifically, the band gap of C₂(BN)₄ decreases significantly, while the band gap of C₃(BN)₃ and C₄(BN)₂ initially remains almost unchanged and then increases with increasing biaxial strain in armchair BCNs. In addition, it is found that the effective masses of the electron and hole of BCNs can be effectively modulated by the biaxial strain. Our results suggest a new route to control the electronic properties of 2D BCN and may also facilitate the realization of electronic devices based on 2D BCN material.

Tuning Magnetism of Metal Porphyrazine Molecules by a Ferroelectric In2Se3 Monolayer

Electric field tuning of magnetism is highly desirable for nanoelectronics, but volatility in electron spin manipulation presents a major challenge that needs urgent resolution. Here, we show by first-principles calculations that magnetism of metal porphyrazine (MPz) molecules can be effectively tuned by switching ferroelectric polarization of an adjacent In₂Se₃ monolayer. The magnetic moments of TiPz and VPz (MnPz, FePz, and CoPz) decrease (increase) at one polarization but remain unchanged at reversed polarization. This intriguing phenomenon stems from distinct metal d-orbital occupation caused by electron transfer and energy-level shift associated with the polarization switch of the In₂Se₃ monolayer. Moreover, the ferroelectric switch also tunes the underlying electronic properties, producing a metallic, half-metallic, or semiconducting state depending on polarization. These findings of robust ferroelectric tuning of magnetism and related electronic properties in MPz-adsorbed In₂Se₃ hold great promise for innovative design and implementation in advanced magnetic memory storage, sensor, and spintronic devices.

Multiferroic decorated Fe2O3 monolayer predicted from first principles

Two-dimensional (2D) multiferroics exhibit cross-control capacity between magnetic and electric responses in a reduced spatial domain, making them well suited for next-generation nanoscale devices; however, progress has been slow in developing materials with required characteristic properties. Here we identify by first-principles calculations robust 2D multiferroic behaviors in decorated Fe2O3 monolayers, showcasing Li@Fe2O3 as a prototypical case, where ferroelectricity and ferromagnetism stem from the same origin, namely Fe d-orbital splitting induced by the Jahn-Teller distortion and associated crystal field changes. These findings establish strong material phenomena and elucidate the underlying physics mechanism in a family of truly 2D multiferroics that are highly promising for advanced device applications.

Intercalation-Induced Disintegrated Layer-By-Layer Growth of Ultrathin Ternary Mo(Te1-xSx)2 Plates

Nanometer-thick transition-metal dichalcogenides (TMDs) have attracted increasing research interest because of their exotic physical properties, but their high-yield and large-scale synthesis remains a challenge for their practical device applications. In this study, we realize the high-yield synthesis of nanometer-thick single-crystalline Mo(Te_1-xS_x)₂ plates by a facile chemical vapor deposition method. Adding S powders in the precursors can result in the products varying from well-faceted MoTe₂ hexagonal plates to irregular Mo(Te_1-xS_x)₂ plates with randomly stacked nanometer-thick layer steps. Moreover, their lateral dimension increases from several μm for binary MoTe₂ to several tens of μm for ternary Mo(Te_1-xS_x)₂. More interestingly, such irregular Mo(Te_1-xS_x)₂ plates can form few layers by ultrasonic exfoliation. Our detailed electron microscopy analyses show that three kinds of S forms influence the ternary growth. In particular, elemental S₈ intercalations play an important role in the growth and exfoliation of ultrathin Mo(Te_1-xS_x)₂ plates. This study enriches the fundamental understanding of zero-valent intercalation in TMDs and provides a new insight into secure high-yield nanometer-thick TMDs, which is critical for practical applications.

Janus WSSe Monolayer: An Excellent Photocatalyst for Overall Water Splitting

Stable photocatalysts with excellent optical adsorption and low reaction barrier are the key for the water splitting. Here, we find that a two-dimensional Janus WSSe monolayer possesses the compelling photocatalytic properties from density functional theory simulations, which can be well modulated with strain deformation. Comprehensive investigations indicate that the Janus material not only exhibits strong optical absorbance in the visible spectrum, suitable band edge potentials, high carrier separation, and transfer efficiency but also has adequate driving forces of photoexcited carrier for water redox reaction and good resistance against photoinduced corrosion. Janus WSSe is therefore predicted to be a promising photocatalyst for water splitting. Moreover, we also find that tensile strains could further improve the photocatalytic performance for water splitting by effectively increasing the energy conversion efficiency and reducing the exciton binding energy. Our results not only predict a photocatalyst, which can utilize the visible light for overall water splitting, but also propose an effective path to extend the absorption spectra and raise the photocatalytic efficiency.

Strain robust spin gapless semiconductors/half-metals in transition metal embedded MoSe2monolayer

The realization of spin gapless semiconductor (SGS) and half-metal (HM) behavior in two-dimensional (2D) transition metal (TM) dichalcogenides is highly desirable for their applications in spintronic devices. Here, using density functional theory calculations, we demonstrate that Fe, Co, Ni substitutional impurities can not only induce magnetism in MoSe2monolayer, but also convert the semiconducting MoSe2to SGS/HM system. We also study the effects of mechanical strain on the electronic and magnetic properties of the doped monolayer. We show that for all TM impurities we considered, the system exhibits the robust SGS/HM behavior regardless of biaxial strain values. Moreover, it is found that the magnetic properties of TM-MoSe2can effectively be tuned under biaxial strain by controlling the spin polarization of the 3dorbitals of Fe, Co, Ni atoms. Our findings offer a new route to designing the SGS/HM properties and modulating magnetic characteristics of the TM-MoSe2system and may also facilitate the implementation of SGS/HM behavior and realization of spintronic devices based on other 2D materials.

Controlled growth of large-scale uniform 1T' MoTe2 crystals with tunable thickness and their photodetector applications

The monoclinic-phase 1T' MoTe₂ crystal exhibits inversion symmetry as an anisotropic semi-metal, dictating its interesting quantum transport phenomenon and other novel physical properties. However, large-scale controllable growth of uniform MoTe₂ crystals still remains a great challenge, hindering its further fundamental research and applications for novel devices. Herein, we report a modified growth method for synthesizing few-layer 1T' MoTe₂ crystals with large-scale uniformity with the assistance of molecular sieves. The theoretical simulations demonstrated that due to the temperature-dependent formation energies of different edges, the edge of (010) orientation shows a higher thermodynamic stability than that of (100) orientation, and results in the anisotropic growth behavior of 1T' MoTe₂ crystals while the temperature changes. The photoresponse of tri-layer 1T' MoTe₂-based devices shows a broad-spectrum response from 532 nm to 1550 nm. The photo-response time of 1T' MoTe₂ crystals demonstrates that it supposes to be the synergistic mechanism of photo-conductive and photo-radiation effects. Our findings not only provide a method for the controllable growth of anisotropic two-dimensional materials at a wafer scale, but also explore a broad-spectrum photodetector with the MoTe₂-based device.

Mechanical properties of CNT-reinforced Ni3Al composites: the role of chirality, temperature, and volume fraction

[Formula: see text] is an extremely significant reinforcing phase in nickel-based single crystal superalloys. As an alternative strengthening method to improve its mechanical properties, carbon nanotube (CNT)-reinforced [Formula: see text] composites have recently been synthesized in experiments. Here, in order to explore the corresponding influence factors and the underlying mechanism, tensile and compressive mechanical properties of CNT-[Formula: see text] composites are systematically investigated by using molecular dynamics simulations. It is shown that the dispersion of a minor fraction of a CNT into [Formula: see text] matrix leads to a sufficient enhancement in the stiffness of CNT-[Formula: see text] composites compared with the pure [Formula: see text]. It is demonstrated that CNT reinforcement takes effect in the elastic stage under compression while it works continuously during tension. Compared with armchair CNTs, zigzag CNTs are predicted to provide more strength for raising the elastic modulus while armchair CNTs can provide superior elongation. Particularly, CNTs are found to hinder the generation of slip bands under tensile loading owing to the robust interfacial interactions. Furthermore, quantitative analysis reveals that the impact of volume fraction of CNT is much more significant than the size effect. The role of chirality, temperature and volume fraction of CNT obtained in the present work could provide beneficial references for subsequent theoretical and experimental investigations, and shed some light on the design of CNT-reinforced composites in nanoscale engineering.

Two-Dimensional Ferroics and Multiferroics: Platforms for New Physics and Applications

Two-dimensional (2D) ferroics, including ferromagnets, ferroelectrics, ferroelastics, and multiferroics, recently have been theoretically proposed or experimentally revealed. The research has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics, revealing ferroics in the 2D limit. In the present Perspective, we comprehensively review the recent research progress and also the proposed applications of 2D ferromagnetic, ferroelectric, and ferroelastic materials from theoretical and experimental viewpoints. We then introduce the coupling between ferroic orders and highlight the latest research on 2D multiferroic materials. The promising research directions and outlooks are discussed at the end of the Perspective. It is expected that the comprehensive overview of 2D ferroic materials can provide guidelines for researchers in the area and inspire further explorations of new physics and ferroic devices.

Enhanced sensitivity of MoSe2 monolayer for gas adsorption induced by electric field

According to recent studies, gas sensors based on MoSe₂ have better detection performance than graphene-based sensors, especially for N-based gas molecules, but the reason for that is not fully understood at the microscopic level. Here, we investigate the adsorption of CO, CO₂, NH₃, NO and NO₂ gas molecules on MoSe₂ monolayer by the density functional theory calculations. Our results reveal that indeed MoSe₂ monolayer is more sensitive to adsorption of N-containing gas molecules than C-containing, which can be attributed to the distinct charge transfer between the gas molecules and MoSe₂. The conductance was further calculated using the nonequilibrium Green's function (NEGF) formalism. The reduced conductance was found for NH₃ and NO₂ adsorbed MoSe₂, consistent with the high sensitivity of MoSe₂ for NH₃ and NO₂ molecules in the recent experiments. In addition, the adsorption sensitivity can significantly be improved by an external electric field, which implies the controllable gas detection by MoSe₂. The magnetic moments of adsorbed NO and NO₂ molecules can also be effectively modulated by the field-sensitive charge transfer. Our results not only give microscopic explanations to the recent experiments, but also suggest using MoSe₂ as a promising material for controlled gas sensing.