The electronic and topological properties of the van der Waals heterostructure formed by graphene (Gr) and a ferromagnetic (FM) vanadium triiodide (VI3) monolayer (Gr/VI3) are investigated using first-principles calculations, within the framework of the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation, with particular emphasis on the effects of interlayer distance modulation. The results show that the system forms an Ohmic contact at the equilibrium interlayer distance of 3.33 & Aring;. By reducing the interlayer distance, the contact type transitions first to an n-type and then to a p-type Schottky contact, accompanied by an increase in the amount of charge transferred to graphene. When the interlayer distance is compressed to 2.42 & Aring;, a large nontrivial band gap of approximately 40.0 meV emerges, enabling the system to become a Chern insulator. This topological phase is confirmed by a nonzero Chern number and the presence of topological edge states. The study provides valuable insights into the realization of the quantum anomalous Hall effect in a topologically trivial Gr/ FM heterostructure through engineering interlayer distance, offering a promising strategy for the design of advanced topological materials and devices.

The spin-lattice interaction is pivotal in tailoring materials properties and is crucial for developing novel spintronic devices. In the current work, we aim to explore the effects of pressure and temperature on the magnetic properties of Cr2O3 to gain insights into its spin-lattice interaction. Through high-pressure neutron diffraction experiments, we observed an enhancement of the magnetic Bragg intensity with increasing pressure and it becomes more pronounced as the temperature increases. Results from first-principles calculations reveal a strengthening of the easy-axis magnetic anisotropy, doubling from 0 to 20 GPa. The exchange parameters, calculated based on this spin orientation, show an enhancement of the dominant magnetic interactions and an increase of magnetic ordering temperature when pressure increases. These findings suggest that the contributions from these two mechanisms are responsible for the observed increase in magnetic Bragg intensity.

The paper investigates the modulation of interface contact and electronic properties by external vertical strains and electric fields in graphene/WS2 van der Waals heterostructure (vdWH) using first-principles calculations. The results reveal that the graphene/WS2 vdWH exhibits an equilibrium interlayer spacing of 3.40 & Aring;. Both interlayer spacing adjustments and external electric fields can effectively induce charge transfer between graphene and WS2 monolayer, enabling tunability of the Schottky barrier height. Specifically, a positive electric field facilitates charge transfer from graphene to WS2, whereas a negative field drives charge transfer in the opposite direction, from WS2 to graphene. Notably, strain significantly influences the system's electrical transport properties, with optimal performance achieved at the equilibrium interlayer spacing of 3.40 & Aring;. These findings provide valuable insights for advancing graphene/WS2 vdWH-based electronic devices.

Based on the first-principles calculation, the electronic and optical properties of the graphene/MoS2 heterostructure at different twisting angles are studied. The interface contact type changes from N-Schottky contact to Ohmic contact with the interlayer twisting angle of 40.90 degrees, which is accompanied by the interfacial charge transfer from graphene to MoS2, and the increase of the contribution of Mo-d(xy), Mo-d(x2-y2) orbitals in the conduction band and S-p(z), Mo-s, Mo-p(z) and Mo-d(z2) orbitals in the valence band. Interestingly, the absorption coefficient, reflectivity and refractive index are improved in the infrared region when the twisting angle is 40.90 degrees. In the visible light range, the absorption coefficient increases, while the refractive index decreases, and the reflectivity at 2.8 eV increases. In the ultraviolet region, the absorption coefficient reaches 1.2 x 10(6) cm(-1) at 11.6 eV with a twisting angle of 30 degrees. The results provide an effective way to apply materials in the photoelectric field.

Modulation of the surface structure of high-entropy-alloy-based nitrides (HEANs) is considered essential for improving electrocatalytic H2 production. Compared with thermal nitridation, the plasma technique is a favorable alternative to directly fabricate HEANs, but the excessive surface heating effect during plasma treatment inevitably causes thermally stabilized nitride formation, resulting in deterioration of the highly active structure. To optimize the hydrogen evolution reaction (HER) behavior of HEANs, a facile cooling-mediated plasma strategy is proposed to precisely modulate the HEAN structure (cp-HEAN). The resultant cp-HEAN framework shows a preserved FCC (111) facet and yields an increased amorphous proportion, leading to enhanced HER behavior. In comparison, the normal plasma technique causes FCC lattice distortion with increased precipitation owing to the excessively high surface thermal field (np-HEAN). Operando plasma diagnostics and numerical simulation further confirmed the effect of surface heating on typical plasma parameters and the HEAN framework, indicating that this was the key factor responsible for the high performance of the nitride electrocatalyst.

Based on density functional theory (DFT), the interface contact and electronic properties of Ag/WS2 (SnS2) interfaces are studied under vertical strain and electric field, respectively. For Ag/WS2 interface, 12% compression strain or-0.40 V & ANGS;-1 electric field can induce the transition of interface charge from n-type Schottky contact to ohmic contact, which is due to the transfer of interface charge from Ag to WS2. Under the action of strain and electric field, the interface of Ag/SnS2 shows ohmic contact. Our research shows that, as the interface system of field effect transistor (FET), Ag/WS2 can show excellent performance, while Ag/SnS2 cannot because it does not have the characteristics of FET.

The adsorption characteristics of gas molecules HF and Cl-2 on monolayer WTe2 surface are studied by first-principles calculation method. The results show that monolayer WTe2 is more sensitive to gas molecule Cl-2. The adsorption performance of monolayer WTe2 to gas molecule HF cannot be improved by doping atoms. When the upward vertical electric field is applied, the sensitivity of monolayer WTe2 to gas molecule Cl-2 is improved, and when the downward vertical electric field is applied, the monolayer WTe2 shows an obvious desorption trend to gas molecule Cl-2. The vertical electric field cannot significantly enhance the interaction between gas molecule HF and Ag-doped monolayer WTe2. Our research confirms that monolayer WTe2 is more sensitive to gas molecule Cl-2 and can be improved or desorbed by the vertical electric field, while that of monolayer WTe2 for gas molecule HF cannot significantly change. Furthermore, the electrical transport characteristics of monolayer WTe2 and Cl-2-WTe2 system are studied to better explain the reason for the higher sensitivity to gas molecule Cl-2. The research results of this paper provide theoretical guidance for the experimental preparation of high sensitivity gas sensor based on two-dimensional transition metal dichalcogenide WTe2.

Hubble tension between the local measurement and global observation has been a key problem in cosmology. In this paper, we consider the quintessence scalar field, phantom field and quintom field as the dark energy to reconcile this problem. Different from most previous work, we start from the dimensionless equation of state ( w ) of dark energy, not a parameterization of potential. The combined analysis shows that observational data sets favor Hubble constant H 0 = 71.3 − 0.917 + 0.854 km s − 1 Mpc − 1 , which can reconcile Hubble tension within 1.20 σ . We also perform a Bayes factor analysis using the MCEvidence code, and confirm that the phantom scalar field is still the most effective. To investigate the reason of Hubble tension, we analyze the density parameter. The comparison shows that the scalar fields provide a slightly larger Ω b h 2 and smaller Ω c h 2 than the standard ΛCDM model. We finally analyze a possible reason of Hubble tension from the kinematic acceleration a ̈ . We find an interesting physical phenomenon. The acceleration a ̈ in these scalar fields are similar as the ΛCDM model at about redshift z > 0.5. However, they increase and deviate from each other at low redshift, especially in the near future. Only the a ̈ in phantom scalar field will decrease in the future.

Based on the first‐principles calculation, the effect of intercalated LiF on the contact characteristics of the interface between Au electrode and MoS2 layer is studied. It is found that adding LiF film can change the contact type between metal electrode Au and MoS2 layer from Schottky contact to ohmic contact, which is accompanied by interfacial charge transfer from LiF layer to MoS2 layer and the downward movement of d (dxy and dz2) orbital of Mo atom and p (px and py) orbital of S atom to Fermi level. And the interlayer spacing between LiF layer and Au electrode has a great impact on the interface contact characteristics. The electric field effect and stress effect of interface contact of Au, LiF and MoS2 (Au/LiF/MoS2)is more obvious than that of interface contact of Au and MoS2 (Au/MoS2). Au/LiF/MoS2 shows ohmic contact with the interlayer spacing between Au layer and LiF layer less than 3.05 Å and with the electric field less than 0.15 VÅ−1, respectively, while Au/MoS2 still shows N‐type Schottky contact. These findings are helpful to control the contact resistance and have guiding significance for high performance MoS2 field effect transistor and other electronic components.

Motivated by the rapid development of the next generation artificial intelligence, we propose a novel adaptive self-detection and self-classification algorithm using matrix eigenvector trajectory in the paper. This algorithm’s mathematical inferences are also described and proved theoretically. The proposed algorithm is used in a multi-class bearing faults classification problem to validate its effectiveness. Results show that in an online data processing scenario, it can automatically adapt to new data patterns so that self-detection and self-classification can be realized by monitoring the eigenvector evolution trajectory. By comparing with other machine learning algorithms, we have validated that the proposed algorithm does not require explicit training, its required data processing time dropped more than 78% and achieved the same classification accuracy on new testing data.

Based to the first-principles calculations, we study the electronic properties of graphene/MoS2 heterostructure by modulating the vertical strains and applying external electric field. Graphene/MoS2 heterostructure is a van der Waals heterostructure (vdWH) with the interlayer spacing is 3.2 angstrom for the equilibrium state, and the contact property of the interface is n-type Schottky contact. The Schottky barrier height (SBH) changes with vertical strains which induces a change of charge transfer between graphene and MoS2 layer. In addition, with strain or without strain, the applied positive electric field can effectively promote the charge transfer from graphene to MoS2, while the negative electric field has the opposite effect. These findings support for the design of field effect transistors based on graphene vdWHs.

The electronic properties and interfacial contact of the graphene-based heterostructure graphene/CrSiTe3 (Gr/CrSiTe3) are modulated by tuning the interfacial distance, along with application of an external electric field. Our first-principles calculations show that the gap is enlarged to 27.6 meV in Gr/CrSiTe3 when the interfacial distance is reduced to a distance of 2.75 Å. Gr/CrSiTe3 changes from an n-type to a p-type Schottky contact with a decrease in interfacial space. The most significant effect of applying a positive electric field is the presence of a p-type Schottky contact along with an increase of interfacial charge transfer to graphene, while an electric field in the opposite direction enhances the n-type Schottky contact effectively with a decrease of interfacial charge transfer to graphene. The Schottky contact transforms into an Ohmic contact when a positive electric field of 0.41 eV Å-1 is applied to this interface. The work proposes an approach to manipulate the interfacial properties, which can be very useful for future experimental studies and graphene-based interfaces.

This paper investigates the synergistic effect of hydrogen and strain on the electronic properties of the p-Cr2O3/n-Fe2O3 interface structure in passive films using density functional theory and non-equilibrium Green's function calculations. It is reported that hydrogen doping at the interface can enhance the electronic transport in the interface region by reducing interfacial electric field strength and weaken the interfacial bonding strength. Tensile strain could reduce interfacial electric field strength and promote the interface structure to combine with hydrogen. Moreover, a high synergistic effect of hydrogen and tensile strain enhances electronic transport even more and thus reduces corrosion resistance. These results have a guiding significance in understanding the mechanisms of stress corrosion and hydrogen embrittlement in passive films on stainless steel.

From first-principles calculations, the magnetism and electronic structures of bilayer bismuth (stannum) films at the monolayer CrI3 (CrBr3) interface are studied. The Curie temperature (TC) of CrX3 (X = Br, I) can be enhanced by coupling bilayer bismuth (Bi) with van der Waals (vdW) heterostructures. The n-doping of CrX3, induced by interlayer charge-transfer from the Bi film, leads to the enhancement of TC. The quantum spin Hall phases of bilayer bismuth and stannum films are destroyed by the magnetic substrate. Although the interface system of the bilayer stannum (Sn) film on a CrBr3 monolayer shows a band gap (57 meV), the inexistence of edge states with valence and conduction bands connected across the insulating gap is a manifestation of the trivial state without the feature of quantized anomalous Hall effect in the interface. The percentage reduction of the corresponding work function is 22.6%, 12.7%, 25.4% and 16.5% for Bi/CrI3, Sn/CrI3, Bi/CrBr3 and Sn/CrBr3 interface systems, respectively. Our findings demonstrate that the Bi(Sn)-CrI3(CrBr3) interface system with vdW engineering is an efficient way to tune magnetism and electronic structures, which is of importance for future applications in spintronics and nanoelectronics devices.

2D heterostructures are promising gas sensor materials due to their surface/interface effects and hybrid properties. In this research, Cu2O/Fe2O3 heterostructure ordered arrays were synthesized using an in situ electrodeposition method for H2S detection at low temperatures. These arrays possess a periodic long range ordered structure with horizontal multi-heterointerfaces, leading to superior gas sensitivity for synergistic effects at the heterointerfaces. The sensor based on the Cu2O/Fe2O3 heterostructure ordered arrays exhibits a dramatic improvement in H2S detection at low temperatures (even as low as -15 °C). The response is particularly significant at room and human body temperatures since the conductivity of the arrays can change by up to three orders of magnitude in a 10 ppm H2S atmosphere. These good performances are also attributed to the formation of metallic Cu2S conducting channels. Our results imply that the Cu2O/Fe2O3 heterostructure ordered arrays are promising candidates for high-performance H2S gas sensors that function at low temperatures as well as breath analysis systems for disease diagnosis.

It is challenging to realize the quantum anomalous Hall effect (QAHE) at high operating temperatures using the two-dimensional (2D) Dirac surface states of three-dimensional (3D) topological insulators (TIs). Given the small non-trivial gap induced by adsorbing ferromagnetic (FM) CrI3 monolayer (ML) on the surface of Bi2Se3 films, we here propose another TI and FM semiconductor interfaced system to enhance the gap by inserting CrI3 ML between the first top (bottom) quintuple layers (QL) and sub-top (sub-bottom) QL of Bi2Se3 films symmetrically. The 2D non-trivial phase emerges in the Bi2Se3 films with five or more QLs and the gap is enlarged to 30 meV in 1QL-Bi2Se3/CrI3/4QL-Bi2Se3/CrI3/1QL-Bi2Se3, which can be understood by the enhanced magnetic proximity effect. The topological non-triviality is confirmed by the nonzero Chern number and the existence of chiral edge state. Our finding will provide useful guidance to optimize the Bi2Se3–CrI3 interface system for realizing QAHE at relatively high operating temperatures.

MnSb2Te4 has the same crystal structure as MnBi2Te4. Whether it is an intrinsic antiferromagnetic TI, quantum anomalous Hall insulator or axion insulator like MnBi2Te4 [CHIN. PHYS. LETT. 36, (2019) 076801] has not been reported yet. The electronic structure and magnetism of MnSb2Te4 have been studied using first-principles calculations. The results show that the MnSb2Te4 is an antiferromagnetic semiconductor with a trivial energy gap (~ 0.132 eV). The band gap decreases to 0.057 eV under the tensile strain (1.03a0, 1.03c0). The feature of Weyl semimetal could be presented in MnSb2Te4 with ferromagnetic phase under strain 3%. Thin films (011) are metals with antiferromagnetic order and also metals with ferromagnetic order. Thin film (111) with alternate of thick (1 septuple layer–7 septuple layers) is an intrinsic magnetic semiconductor with a trivial energy gap (0.002–0.344 eV) rather than an intrinsic quantum anomalous Hall insulator or axion insulator.

Exploring a quantum topological phase, such as the quantum spin Hall (QSH) effect and quantum anomalous Hall (QAH) effect in two-dimensional metal-organic frameworks (MOFs), has been attracting significant attention. In this study, we propose to realize a topological phase transition via NO2 adsorption in a recently synthesized two-dimensional Ni-hexaaminobenzene [Ni3(HAB)2]. First-principles calculations show a QSH state of the pristine Ni3(HAB)2 nanosheet. However, when NO2 molecules are adsorbed on the Ni3(HAB)2 surface, the system changes to a ferromagnetic state and the time-reversal symmetry is broken. We find that the NO2-adsorbed Ni3(HAB)2 exhibits an intrinsic QAH state with the Fermi level exactly located within a topologically nontrivial bandgap. The calculated gapless edge states and quantized Hall conductance further confirm the QSH-to-QAH phase transition. Our finding offers an alternative approach of tuning the topological phase transition in a real MOF material.

The prevention of hydrogen penetration into steels can effectively protect steels from hydrogen damage. In this study, we investigated the effect of a monolayer MoS2 coating on hydrogen prevention using first-principles calculations. We found that monolayer MoS2 can effectively inhibit the dissociative adsorption of hydrogen molecules on an Fe(111) surface by forming a S–H bond. MoS2 coating acts as an energy barrier, interrupting hydrogen penetration. Furthermore, compared with the H-adsorbed Fe(111) film, the work function of the MoS2-coated film significantly increases under both equilibrium and strained conditions, indicating that the strained Fe(111) film with the MoS2 coating also becomes more corrosion resistant. The results reveal that MoS2 film is an effective coating to prevent hydrogen damage in steels.

By means of first-principles calculations based on the density-functional theory, we investigate the vacancy trappings prevent hydrogen damage in two dimension alpha-Cr2O3/alpha-Fe2O3 (0 0 0 1) interface structure. Our calculations show that H atoms prefer to occupy the unoccupied O atoms octahedral interstitial site (O-site) in the center of the interface structure without vacancy defect, weakening the cleavage strength of Fe and O atoms and decreasing the work function and stability of interface structure. To prevent hydrogen damage in this interface structure, we model three Fe, Cr and O vacancy defects in this interface structure, respectively. Fe and Cr vacancy defects with lower H binding energy and higher work function, are better hydrogen trappings compared to O vacancy. These results confirm the Fe and Cr vacancy defects are effective hydrogen trappings to prevent hydrogen damage for passive film of steel, which has significant practical implications.