Two-dimensional multiferroic RuClF/AgBiP2S6 van der Waals heterostructures with valley splitting properties and controllable magnetic anisotropy.

The investigation of new properties in two-dimensional (2D) multiferroic heterostructures is significant. In this work, the electronic properties and magnetic anisotropy energies (MAEs) of 2D multiferroic RuClF/AgBiP2S6 van der Waals (vdW) heterostructures are systematically studied by first principles calculations based on density functional theory (DFT). The Hubbard on-site Coulomb parameter (U) of Ru atoms is necessary to account for the strong correlation among the three-dimensional electrons of Ru. RuClF/AgBiP2S6 heterostructures in different polarizations (RuClF/AgBiP2S6-P↑ and RuClF/AgBiP2S6-P↓) are ferromagnetic semiconductors with stable structures. Valley polarizations are present in the band structures of RuClF/AgBiP2S6 heterostructures with spin-orbit coupling (SOC), the valley splitting energies of which are 279 meV and 263 meV, respectively. The MAEs of RuClF/AgBiP2S6 heterostructures indicate perpendicular magnetic anisotropy (PMA), which are primarily attributed to the differences in matrix elements within Ru (dyz, dz2) orbitals. In addition, valley splittings and MAEs of RuClF/AgBiP2S6 heterostructures are modified at different biaxial strains. Specifically, the highest valley splittings are 283 meV and 287 meV at ε = 2%, while they disappear at ε = -6%. The PMA of RuClF/AgBiP2S6-P↑ is gradually decreased at biaxial strains of -6% to 2%, and MAE is transformed into in-plane magnetic anisotropy (IMA) at ε = 4%. RuClF/AgBiP2S6-P↓ maintains PMA at different strains. The study of non-volatile electrical control of valley splitting phenomena in multiferroic RuClF/AgBiP2S6 heterostructures is crucial in the field of valleytronic devices, which has important theoretical significance.

Valley polarization and magnetic anisotropy of two-dimensional Ni2Cl3I3/MoSe2 heterostructures.

Two-dimensional (2D) Janus trihalides have attracted widespread attention due to their potential applications in spintronics. In this work, the valley polarization of MoSe2 at the K' and K points can be modulated by Ni2Cl3I3, a new 2D Janus trihalide. The Ni2Cl3I3/MoSe2 heterostructure has an in-plane magnetic anisotropy energy (IMA) and is characterized by three distinct electronic structures: metallic, semiconducting, and half-metallic. It is noted that the semiconducting state features a band gap of 0.07 eV. When spin-orbit coupling (SOC) is considered, valley polarization is exhibited in the Ni2Cl3I3/MoSe2 heterostructure, with the degree of valley polarization varying across different configurations and reaching a maximum value of 4.6 meV. The electronic properties, valley polarization and MAE of the system can be tuned by biaxial strains. The application of a biaxial strain ranging from -6% to +6% can enhance the valley polarization value from 0.9 meV to 12.9 meV. The directions of MAE of the Ni2Cl3I3/MoSe2 heterostructure can be changed at biaxial strains of -6%, +2%, +4% and +6%. The above calculation results show that the heterostructure system possesses rich electronic properties and tunability, with extensive potential applications in the fields of spintronic and valleytronic devices.

Magnetic phase transition regulated by an interface coupling effect in CrBr3/electride Ca2N van der Waals heterostructures.

Compared with ferromagnetic (FM) materials, antiferromagnetic (AFM) materials have the advantages of not generating stray fields, resisting magnetic field disturbances, and displaying ultrafast dynamics and are thus considered as ideal candidate materials for next-generation high-speed and high-density magnetic storage. In this study, a new AFM device was constructed based on density functional theory calculations through the formation of a CrBr3/Ca2N van der Waals heterostructure. The FM ground state in CrBr3 undergoes an AFM transition when combining with the electride Ca2N. In such a system, since the metal Ca atoms form the exposed layer in the electride, the heterostructure interface has a high binding energy and a large amount of charge transfer. However, for individual electron doping, the FM ground state in the CrBr3 monolayer is robust. Therefore, the main factor in magnetic phase transition is the interface orbital coupling caused by the strong binding energy. Furthermore, the interface coupling effect was revealed to be a competition between direct exchange and superexchange interactions. Additionally, different pathways of orbital hybridization cause a transition of the magnetic anisotropy from out-of-plane to in-plane. This work not only provides a feasible strategy for changing the ground state of magnetic materials on electride substrates but also brings about more possibilities for the construction and advancement of new AFM devices.

A first-principles study on Ni-decorated MoS2 for efficient formaldehyde degradation over a wide temperature range.

The development of a high-efficiency, low-cost, and environmentally friendly catalyst for formaldehyde degradation is crucial for addressing the issue of indoor formaldehyde pollution. Given that modern individuals spend over 90% of their time indoors, effectively tackling indoor formaldehyde pollution holds significant importance. Therefore, this paper proposes an efficient catalyst for formaldehyde degradation: surface modification of MoS2 by single-atom Ni, which can convert formaldehyde into harmless H2O and CO2. The DFT method is employed to systematically investigate the oxidative degradation pathways of formaldehyde on the surface of Ni-doped MoS2. The research focuses on two common oxidative degradation pathways in both the L-H mechanism and E-R mechanism. Our findings demonstrate that these four reaction paths occur spontaneously within the temperature range of 300-800 K with a reaction equilibrium constant greater than 105. Moreover, even under extreme temperature conditions (100 K), the reaction rate remains favorable. Furthermore, our findings indicate that the minimum activation energy is merely 0.91 eV and H2O and CO2 only need to overcome an energy barrier of 0.71 eV for desorption from the catalyst surface. This substantiates its potential application both in indoor environments and under extreme temperature conditions. This theoretical research provides innovative ideas and strategies for effectively oxidizing formaldehyde.

Band inversion and switchable magnetic properties of two-dimensional RuClF/WSe2 van der Waals heterostructures.

Two-dimensional (2D) van der Waals (vdW) heterostructures have potential applications in new low-dimensional spintronic devices owing to their unique electronic properties and magnetic anisotropy energies (MAEs). The electronic structures and magnetic properties of RuClF/WSe2 heterostructure are calculated using first-principles calculations. The most stable RuClF/WSe2 heterostructure is selected for property analysis. RuClF/WSe2 heterostructure has half-metallicity. Considering spin-orbit coupling (SOC), band inversion is present in the RuClF/WSe2 heterostructure, which is also demonstrated by the weight of the energy contributions. The local density of states (LDOS) of the edge states can provide strong evidence that the RuClF/WSe2 heterostructure has topological properties. The MAE of RuClF/WSe2 heterostructure is in-plane magnetic anisotropy (IMA), which mainly originates from the contribution of matrix element difference in Ru (dxy, dx2-y2) orbitals. The electronic properties and MAE of RuClF/WSe2 heterostructure can be regulated by biaxial strains and electric fields. The band inversion phenomenon is enhanced at electric fields in the opposite direction, which is also modified at different biaxial strains. However, the band inversion phenomenon disappears at the biaxial strains of 6% and an electric field of 0.5 V Å-1. The MAE of RuClF/WSe2 heterostructure is transformed from IMA into perpendicular magnetic anisotropy (PMA) at certain compressive strains and positively directed electric fields. The above results indicate that the RuClF/WSe2 heterostructure has potential applications in spintronic devices.

Tunable electronic band structure and magnetic anisotropy in two-dimensional Dirac half-metal MnBr3 by external stimulus: strain, magnetization direction, and interlayer coupling.

Advancing technology and growing interdisciplinary fields create the need for new materials that simultaneously possess several significant physics qualities to meet human demands. Dirac half-metals with massless fermions hold great promise in spintronic devices and optoelectronic devices associated with nontrivial band topologies. In this work, we predict that a MnBr3 monolayer will be an intrinsic Dirac half-metal based on first-principles calculations. The lattice dynamics and thermodynamic stabilities were demonstrated by calculating the phonon spectra and performing molecular dynamics simulations. One property of a MnBr3 monolayer is that facile magnetization of its in-plane can be accomplished. A change in the magnetization direction significantly modifies the electronic band structure. When considering the spin-orbit coupling effect, the Dirac cone around the Fermi level in the spin-up channel opens a gap of 35 meV, which becomes a topological nontrivial insulator with a Chern number of -1. The Chern number sign and the chiral edge current can be tuned by changing the magnetization direction. The electronic band structure and magnetic anisotropy energy can be further modulated by applying biaxial and uniaxial strain, as well as introducing interlayer coupling in the bilayer. The unique performance of MnBr3 will broaden the utilization of two-dimensional magnetism in widespread application.

Nonvolatile magnetoelectric coupling in two-dimensional van der Waals sandwich heterostructure CuInP2S6/MnCl3/CuInP2S6.

Electrical control of magnetism is of great interest for low-energy-consumption spintronic applications. Due to the recent experimental breakthrough in two-dimensional materials, with the absence of hanging bonds on the surface and strong tolerance for lattice mismatch, heterogeneous integration of different two-dimensional materials provides a new opportunity for coupling between different physical properties. Here, we report the realization of nonvolatile magnetoelectric coupling in vdW sandwich heterostructure CuInP2S6/MnCl3/CuInP2S6. Using first-principles calculations, we reveal that when interfacing with ferroelectric CuInP2S6, the Dirac half-metallic state of monolayer MnCl3 will be destroyed. Moreover, depending on the electrically polarized direction of CuInP2S6, MnCl3 can be a half-metal or a ferromagnetic semiconductor. We unveil that the obtained ferromagnetic semiconductor in MnCl3 can be attributed to the different gain and loss of electrons on the two adjacent Mn atoms due to the sublattice symmetry broken by interlayer coupling. The effects of interfacial magnetoelectric coupling on magnetic anisotropy and ferromagnetic Curie temperature of MnCl3 are also investigated, and a multiferroic memory based on this model is designed. Our work not only provides a promising way to design nonvolatile electrical control of magnetism but also renders monolayer MnCl3 an appealing platform for developing low-dimensional memory devices.

Two dimensional Janus RuXY (X, Y = Br, Cl, F, I, X ≠ Y) monolayers: ferromagnetic semiconductors with spontaneous valley polarization and tunable magnetic anisotropy.

Two-dimensional (2D) ferromagnetic (FM) materials with valley polarization are highly desirable for use in valleytronic devices. The 2D Janus materials have fascinating physical properties due to their asymmetrical structures. In this work, the electronic structure and magnetic properties of Janus RuXY (X, Y = Br, Cl, F, I, X ≠ Y) monolayers are systematically studied using first-principles calculations. RuBrCl, RuBrF, and RuClF monolayers are all FM semiconductors. The valley polarization is present in the band structure and this is determined by the spin orbit coupling (SOC). The valley splitting energy of the RuClF monolayer is as large as 204 meV, with a perpendicular magnetic anisotropy (PMA) energy of 1.918 mJ m-2 and a Curie temperature of 316 K. Therefore, spontaneous valley polarization at room temperature will be seen in the RuClF monolayer. The Curie temperature of the RuBrF monolayer is higher than that of the RuClF, but the magnetic anisotropy energy (MAE) is in-plane magnetic anisotropy (IMA). The valley splitting energy of the RuBrCl monolayer is higher and the PMA energy is lower than that of the RuClF monolayer. The Curie temperature was only 197 K. The valley polarization was modulated in the RuXY monolayers at different biaxial strains, during which the semiconductor properties are still maintained. The PMA of the RuClF and RuBrCl monolayers is enhanced by the biaxial compressive strains, which are mainly attributed to the variation of the (dyz, d2z) orbital matrix elements of the Ru atoms. The MAE of the RuBrF monolayer is tuned from IMA into PMA at a biaxial strain of -6%. These results show an example of a 2D Janus ferrovalley material.

Bilayer hexagonal structure MnN2 nanosheets with room-temperature ferromagnetic half-metal behavior and a tunable electronic structure.

Two-dimensional (2D) layered materials have atomically thin thickness and outstanding physical properties, attracting intensive research in the past year. As one of these materials, a 2D magnet is an ideal platform for fundamental physics research and magnetic device development. Recently, a non-MoS2-type geometry was found to be more favorable in 2D transition-metal dinitrides. In this work, driven by this new configuration, we perform a comprehensive first-principles study on the bilayer hexagonal structure of 2D manganese dinitrides. Our results show that 2D MnN2 is a ferromagnetic half-metal at its ground state with 100% spin-polarization ratio at the Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamics simulation show that the 2D MnN2 crystal has a high thermodynamic stability and its 2D lattice can be retained at room-temperature. Monte Carlo simulations based on the Heisenberg model predict a Curie temperature of over 563 K and its electronic properties can be regulated by biaxial strain. The half-metallic states are mainly contributed by Mn d orbitals, and the magnetic exchange of the system mainly comes from the Mn-N-Mn super-exchange. The p-d orbital hybridization will provide a small antiparallel magnetic moment of N atoms, and the p-orbital dangling bond can be eliminated by oxidation to enhance the total magnetic moment of the system. The study of magnetic anisotropy energy indicates that the easy magnetization axis is in-plane and hybridization between Mn dyz and dz2 orbitals gives the largest magnetic anisotropy contribution. In view of these results, we consider that novel 2D MnN2 is one of the most promising two-dimensional materials for nano-spintronic applications.

Nonvolatile electrical control of valley splitting by ferroelectric polarization switching in a two-dimensional AgBiP2S6/CrBr3 multiferroic heterostructure.

The generation and controllability of valley splitting are the major challenge in effectively utilizing valley degrees of freedom in valleytronics. Using first-principles calculations, we propose a novel multiferroic system, a AgBiP2S6/CrBr3 van der Waals heterostructure, with ferromagnetism, ferroelectricity and ferrovalley behaviors. The ferroelectric monolayer AgBiP2S6 originally has two degenerate valleys with a large spin splitting (∼423.1 meV) at the conduction band minimum of K/K' points, due to inversion symmetry breaking combined with strong spin orbit coupling. Magnetic proximity coupling with the ferromagnetic layer CrBr3 breaks the time-reversal symmetry, damaging the degeneracy of K/K' valleys and causing valley splitting (∼30.5 meV). The transition energy barrier between two ferroelectric states with opposite polarization direction of the heterostructure is sufficient to prevent the spontaneous transition at room temperature, and the large intermediate barrier suggests that the ferroelectric state should be observed experimentally under ambient conditions. Nonvolatile electrical control of the valley degrees of freedom is achieved by switching the polarization direction of the ferroelectric layer in the heterostructure. The modulation of valley splitting can also be achieved by applying an external electric field and biaxial strain, as well as changing the magnetization direction. The research of nonvolatile electrical control of valley splitting in the two-dimensional AgBiP2S6/CrBr3 multiferroic heterostructure is crucial for designing all-in-one valleytronic devices, and has important theoretical significance and practical value.

Centimetre-scale single crystal α-MoO3: oxygen assisted self-standing growth and low-energy consumption synaptic devices.

High-density storage and neuromorphic devices based on 2D materials are hindered by large-scale growth. Moreover, the lack of a mature mechanism makes it difficult to obtain high-quality single crystals in large-scale 2D materials. In this work, we prepared a centimeter-scale single crystal α-MoO3via an oxygen assisted substrate-free self-standing growth method and mechanism and constructed high-performance synaptic devices based on the centimeter-scale α-MoO3. The oxygen assisted growth mechanism of α-MoO3 was developed from the periodic bond chain theory. The large-scale α-MoO3 is up to 2 cm and exhibits high homogeneity and single crystalline characteristic. Furthermore, with an optimized oxygen partial pressure (18%), the centimeter-scale α-MoO3 makes the as-prepared memristor achieve continuous conductance modulation. Moreover, the trap-controlled electron conducting mechanism of the memristor was demonstrated through I-V curve fitting analysis at various temperatures, in which the high resistance state section demonstrates space-charge-limited conduction (SCLC) mode. Moreover, the as-prepared α-MoO3 memristors exhibit low-energy consumption and well emulate the essential synaptic behaviors including excitatory/inhibitory postsynaptic current, paired-pulse facilitation and long-term plasticity.

Two-channel electrochemical immunosensor based on one-step-synthesized AuPt-boron-doped graphene electrode for CA153 detection.

Herein, a novel dual-channel electrochemical immunosensor was fabricated via vertical growth of AuPt-decorated boron-doped graphene (AuPt-BG) nanosheets as a signal amplification platform to detect cancer antigen 153 (CA153). Highly open, porous AuPt-BG films were synthesized using one-step electron-assisted hot-filament chemical vapor deposition. The Au-Pt alloy nanoparticles were dispersed on BG nanosheets to improve their biocompatibility, and antibodies (Ab) were directly bonded to the AuPt-BG electrode. The architectures enlarged the loading of CA153Ab and efficiently catalyzed the Fe(CN)63-/4- reaction, ultimately amplifying the signals. This novel strategy allows the simultaneous detection of CA153 in the oxidation and reduction channels, improving the reliability of the detection results. The AuPt-BG-based immunosensor exhibited a lower detection limit (0.0012 mU mL-1, S/N = 3) and wider linear range (0.1-4 × 104 mU mL-1) along with improved reproducibility, selectivity, and stability for the assay of CA153. Owing to the high process controllability of AuPt-BG films, a large-area electrode for in-vitro analyses and a flexible microelectrode for in-vivo analyses were prepared, which confirmed that the AuPt-BG-based sensor is an ideal CA153 detection platform for clinical diagnosis and practical applications.

Two-dimensional Cs3Sb2I9/C2N van der Waals type-II heterostructure: a promising photocatalyst for high efficiency water splitting.

The development of high-efficiency photocatalysts for photocatalytic hydrolysis using solar energy and water resources is of great significance for alleviating the current energy shortage. Finding rational photocatalysts remains a major challenge and great efforts have already been made. Here we propose a novel two-dimensional perovskite-based vdW heterostructure (Cs3Sb2I9/C2N) and systematically investigate its stability, electronic and optical properties and the effects of applied biaxial strain based on the first-principles approach to investigate its ability as a photocatalyst for water splitting. In order to ensure the significance of the calculation results in guiding experiments, a hybrid functional was used for all the calculations on the electronic structure. The results show that the Cs3Sb2I9/C2N heterostructure has satisfactory dynamic and thermal stability, and exhibits the characteristics of type-II band alignment in the equilibrium configuration. Charge density difference, Bader charge analysis and work function further prove that the photogenerated electrons flow from Cs3Sb2I9 to the C2N monolayer by the influence of the interface dipole, which promotes the separation and transfer of photogenerated charge carriers and inhibits the recombination of the photogenerated charge carriers. Furthermore, the Cs3Sb2I9/C2N heterostructure has a suitable redox potential for photocatalytic water splitting and exhibits enhanced light absorption in the visible light region. In addition, the electronic and optical properties of the Cs3Sb2I9/C2N heterostructure can be tuned by strain, and the Cs3Sb2I9/C2N heterostructure always possesses photocatalytic ability after applying -2% to 6% biaxial strain. These results suggest that the Cs3Sb2I9/C2N heterostructure will be a promising candidate for water splitting photocatalysts.

Two dimensional Zr2CO2/H-FeCl2van der Waals heterostructures with tunable band gap, potential difference and magnetic anisotropy.

Two dimensional (2D) van der Waals (vdW) heterostructures have potential applications in novel low dimensional spintronic devices due to their unique electronic and magnetic properties. Here, the electronic and magnetic properties of 2D Zr2CO2/H-FeCl2heterostructures are calculated by first principles calculations. The 2D Zr2CO2/H-FeCl2heterostructures are magnetic semiconductor. The electronic structure and magnetic anisotropy of Zr2CO2/H-FeCl2heterostructure can be regulated by the biaxial strain and external electric field. The band gap and potential difference of Zr2CO2/H-FeCl2heterostructure can be affected by in-plane biaxial strain. At a compressive strain of -8%, the Zr2CO2/H-FeCl2heterostructure becomes metallic. All of the Zr2CO2/H-FeCl2heterostructures are magnetic with in-plane magnetic anisotropy (IMA). The Zr2CO2/H-FeCl2heterostructure is a semiconductor at the electric field from -0.5 V Å-1to +0.5 V Å-1. Furthermore, Zr2CO2/H-FeCl2heterostructure shows IMA at the negative electric field, while it shows perpendicular magnetic anisotropy at the positive electric field. These results show that Zr2CO2/H-FeCl2heterostructure has potential applications in multifunctionalnanoelectronic devices.

Promoted photocarrier separation by dipole engineering in two-dimensional perovskite/C2N van der Waals heterostructures.

Due to the aggravation of environmental pollution and the energy crisis, it is urgent to develop and design environment-friendly and efficient photocatalysts for water splitting. van der Waals heterostructures composed of different two-dimensional materials offer an easily accessible way to combine properties of individual materials for applications. Herein, a novel Cs3Bi2I9/C2N heterostructure is proposed through first-principles calculations. The structural, electronic, and optical properties, as well as the charge transfer mechanism at the interface of Cs3Bi2I9/C2N are systematically investigated. Due to the difference between the work functions of Cs3Bi2I9 and C2N monolayers, when they are constructed into heterostructures, redistribution of charge occurs in the whole structure, and some of the charge transfer occurs at the interface due to the formation of an internal electric field. The band structure of Cs3Bi2I9/C2N has type-II band alignment, and the band edge position as well as the band-gap value of the heterostructure are suitable for visible light water splitting. The in-plane biaxial strain, interfacial spacing, and external electric field can effectively modulate the electronic structure and photocatalytic performance of the heterostructure. Under certain conditions, the heterostructure can be changed from type-II to type-I band alignment, accompanied by the transition from an indirect band-gap semiconductor to a direct band-gap semiconductor. Moreover, the intrinsic anion defect (I vacancy) at different positions, as donor defects, can introduce defect levels near the conduction band edge, which affects the transition of photogenerated carriers in these systems. Our findings provide a theoretical design for strategies to improve the performance of two-dimensional perovskites/C2N in photocatalytic and optoelectronic applications.

Conduction band-edge valley splitting in two-dimensional ferroelectric AgBiP2S6 by magnetic doping: towards electron valley-polarized transport.

Two-dimensional valleytronic systems, using the valley index of carriers to perform logic operations, serves as the basis of the next-generation information technologies. For efficient use of the valley degree of freedom, the major challenge currently is to lift the valley degeneracy to achieve valley splitting. In this work, using first-principles calculations, we propose that valley splitting can be readily achieved in a ferroelectric AgBiP2S6 monolayer by TM doping (TM = V, Cr, Mn, Fe, Co, and Ni), which is highly feasible in experiments. In sharp contrast to most previous reports of valley-related features in the valence band-edge, the pristine AgBiP2S6 monolayer has a direct band-gap located at K/K' points of the Brillouin zone and harbors strong coupled spin and valley physics around the conduction band-edge, due to inversion symmetry breaking combined with strong spin-orbit coupling. By TM-doping, the local magnetic moment can be introduced into the system, which can destroy the valley degeneration of the conduction band-edge and induce valley splitting. Especially in a V-doped system, accompanied with a large valley splitting (26.8 meV), there is a serious n-type doping in AgBiP2S6. The efficient electron-doping moves the Fermi level just located between the conduction band minimum of the K/K' valleys, which is suitable for valley-polarized transport. Moreover, the valley-polarized index can be flipped by applying a small magnetic field to rotate the magnetocrystalline direction. The magnitude of valley splitting relies on the strength of orbital hybridization between the TM-d and Bi-p states and can be tuned continually by applying biaxial strain. Under an in-plane electric field, such valley degeneracy breaking would give rise to the long-sought anomalous valley Hall effect, which is crucial to design a valleytronic device.

Valley splitting and magnetic anisotropy in two-dimensional VI3/MSe2 (M = W, Mo) heterostructures.

As a new van der Waals ferromagnetic material, VI3 can be used to lift the valley degeneracy of transition metal dichalcogenides at the K' and K points. Here, the electronic structure and magnetic anisotropy of the VI3/MSe2 (M = W, Mo) heterostructures are studied. The VI3/WSe2 heterostructure is semiconducting with a band gap of 0.26 eV, while the VI3/MoSe2 heterostructure is metallic. Considering the spin-orbit-coupling, a maximum valley splitting of 3.1 meV appears in the VI3/WSe2 heterostructure. The biaxial strain can tune the valley splitting and magnetic anisotropy of VI3/MSe2 heterostructures. In the VI3/WSe2 heterostructure, which has the most stable stacking, valley splitting can be increased from 1.8 meV at 4% compressive strain to 3.1 meV at 4% tensile strain. At a biaxial strain of -2% to 4%, the VI3/WSe2 heterostructure maintains a small perpendicular magnetic anisotropy, while the VI3/MoSe2 heterostructure shows in-plane magnetic anisotropy under different strains. The significantly tunable electronic structure and magnetic anisotropy under biaxial strain suggest that the VI3/MSe2 heterostructures have potential applications in spintronic devices.

Biaxial strain, electric field and interlayer distance-tailored electronic structure and magnetic properties of two-dimensional g-C3N4/Li-adsorbed Cr2Ge2Te6 van der Waals heterostructures.

Recently, it has been proven that the biaxial strain (ε), electric field (E) and interlayer distance (d) can effectively modulate the electronic structure and magnetic properties of two-dimensional (2D) van der Waals (vdW) heterostructures, which have potential applications in spintronic devices. Here, the electronic structure and magnetic properties of 2D g-C3N4/Li-adsorbed Cr2Ge2Te6 vdW heterostructures are investigated using first-principles calculations. Their lattice structures are seriously affected by adsorption combination. With external stimulation, the band gap of the heterostructures changes. The heterostructures are metallic at ε = -6% and -4%, and others are n-type semiconductors, where the band gap is 23 meV at ε = 6%. In addition, the magnetic moments of g-C3N4 in the adsorption systems are in the range from 0.029 to 0.226 µB. The vdW heterostructures show in-plane magnetic anisotropy (IMA) at ε = -6%, -2% and 6% and perpendicular magnetic anisotropy (PMA) at ε = -4%, 0, 2% and 4%. On applying an electric field and changing the interlayer distance, the vdW heterostructures show PMA. These results are significant to the low-dimensional spintronic devices.

Heterostructure Engineering of Core-Shelled Sb@Sb2 O3 Encapsulated in 3D N-Doped Carbon Hollow-Spheres for Superior Sodium/Potassium Storage.

In this work, the core-shelled Sb@Sb2 O3 heterostructure encapsulated in 3D N-doped carbon hollow-spheres is fabricated by spray-drying combined with heat treatment. The novel core-shelled heterostructures of Sb@Sb2 O3 possess a mass of heterointerfaces, which formed spontaneously at the core-shell contact via annealing oxidation and can promote the rapid Na+ /K+ transfer. The density functional theory calculations revealed the mechanism and significance of Na/K-storage for the core-shelled Sb@Sb2 O3 heterostructure, which validated that the coupling between the high-conductivity of Sb and the stability of Sb2 O3 can relieve the shortcomings of the individual building blocks, thereby enhancing the Na/K-storage capacity. Furthermore, the core-shell structure embedded in the 3D carbon framework with robust structure can further increase the electrode mechanical strength and thus buffer the severe volume changes upon cycling. As a result, such composite architecture exhibited a high specific capacity of ≈573 mA h g-1 for sodium-ion battery (SIB) anode and ≈474 mA h g-1 for potassium-ion battery (PIB) anode at 100 mA g-1 , and superior rate performance (302 mA h g-1 at 30 A g-1 for SIB anode, while 239 mA h g-1 at 5 A g-1 for PIB anode).

Electric polarization related Dirac half-metallicity in Mn-trihalide Janus monolayers.

A two-dimensional Dirac half-metal system, in which the 100% spin polarization and massless Dirac fermions can coexist, will show more advantages on the efficient spin injection and high spin mobility in spintronic devices. Moreover, it is attractive to achieve out-of-plane electric polarization in addition to the Dirac half-metal behavior, because this will open a new horizon in the field of multifunctional devices. In this work, a systematic study is made of Janus monolayers of Mn2X3Y3 (X, Y = Cl, Br and I, X ≠ Y) with asymmetric out-of-plane structural configurations, based on first-principles calculations. We demonstrate that monolayer Mn2X3Y3 freestanding films will remain stable experimentally by using the stability analysis. All the Janus monolayers show a ferromagnetic ground state and maintain their original DHM behavior. However, due to the large electric polarization, the hybridization intensities of Mn and the halogen atoms on both sides of Mn2Cl3I3 are very different, resulting in an obvious distortion of the spin-polarized Dirac cone. The distorted Dirac cone is repaired by the compression, indicating that strain can improve the orbital distortion induced by the electric polarization. All Mn2X3Y3 monolayer have in-plane magnetization anisotropy, which is mainly contributed by heavy halogen elements (Br and I), and the polarized substitution and biaxial strain will not change the easy magnetization orientation of the system. Thus, the electrically polarized Dirac half-metal system has potential for application in multifunctional spintronic devices.