Structures, Energetics, and Electronic Properties of Multifarious Stacking Patterns for High-Buckled and Low-Buckled Silicene on the MoS₂ Substrate

The interfaces between silicene and substrate materials play important roles in the electronic properties of the systems. High-buckled (HB) silicene synthesized on bulk MoS₂ surface has been reported [Adv. Mater. <b>2014</b>, 26, 2096−2101]. Using first-principles calculations, we studied the interfaces between silicene and the monolayer MoS₂ substrate. We found that silicene can adsorb on the MoS₂ substrate via van der Waals (vdW) interactions forming silicene/MoS₂ heterostructures with HB or low-buckled (LB) configuration. The lattice mismatch between LB silicene and the MoS₂ substrate leads to the formation of Moiré superstructures. The heterostructures of HB silicene on the MoS₂ substrate are metallic, while those of LB silicene on the MoS₂ substrate are semiconductors with small band gaps due to the interface effects. The band gap is dependent on the rotation angle and stacking pattern, whereas the formation energy is not. High carrier mobility of LB silicene is preserved in these heterostructures. More interestingly, the band gap can be further tuned by applying a vertical external electric field. These features are helpful for the fabrication of nanoscaled electronic devices using silicene

Theoretical Design of Highly Efficient CO₂/N₂ Separation Membranes Based on Electric Quadrupole Distinction

Membrane separation of CO₂/N₂ in fossil fuel gas is promising for the control of greenhouse gas emission, but challenging due to close kinetic diameters. Here, we propose a generalized model for the design of efficient CO₂/N₂ separation membranes by taking advantage of the large difference between the electric quadrupole moments of the two molecules. The interaction between the molecular electric quadrupole moment and the built-in electric field of the membrane leads to high CO₂/N₂ selectivity. We validate this model in five nitrogen-rich membranes, g-C₃N₄, g-C₃N₃, C₂N-<i>h</i>2D, g-C₁₂N₈, and p-BN, and demonstrate via molecular dynamics simulations that highly efficient CO₂/N₂ separation can be achieved in the theoretically predicted g-C₁₂N₈ membrane with a permeance of 2.8 × 10⁵ GPU. This work offers a guidance to improve the separation efficiency of molecules with distinct electric quadrupole moments

Giant Topological Nontrivial Band Gaps in Chloridized Gallium Bismuthide

Quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices but presently is achieved only at extremely low temperature. Searching for the large-gap QSH insulators with strong spin–orbit coupling (SOC) is the key to increase the operating temperature. We demonstrate theoretically that this can be solved in the chloridized gallium bismuthide (GaBiCl₂) monolayer, which has nontrivial gaps of 0.95 eV at the Γ point, and 0.65 eV for bulk, as well as gapless edge states in the nanoribbon structures. The nontrivial gaps due to the band inversion and SOC are robust against external strain. The realization of the GaBiCl₂ monolayer will be beneficial for achieving QSH effect and related applications at high temperatures

Novel Conductive Metal–Organic Framework for a High-Performance Lithium–Sulfur Battery Host: 2D Cu-Benzenehexathial (BHT)

Despite the high theoretical capacity of lithium–sulfur (Li–S) batteries, their commercialization is severely hindered by low cycle stability and low efficiency, stemming from the dissolution and diffusion of lithium polysulfides (LiPSs) in the electrolyte. In this study, we propose a novel two-dimensional conductive metal–organic framework, namely, Cu-benzenehexathial (BHT), as a promising sulfur host material for high-performance Li–S batteries. The conductivity of Cu-BHT eliminates the insulating nature of most S-based electrodes. The dissolution of LiPSs into the electrolyte is largely prevented by the strong interaction between Cu-BHT and LiPSs. In addition, orientated deposition of Li₂S on Cu-BHT facilitates the kinetics of the LiPS redox reaction. Therefore, the use of Cu-BHT for Li–S battery cathodes is expected to suppress the LiPS shuttle effect and to improve the overall performance, which is ideal for practical application of Li–S batteries

Chern Insulator and Chern Half-Metal States in the Two-Dimensional Spin-Gapless Semiconductor Mn₂C₆S₁₂

Two-dimensional metal–organic frameworks (2D-MOFs) with exotic electronic structures are drawing increasing attention. Here, using first-principles calculations, we demonstrate a spin-gapless MOF, namely, Mn₂C₆S₁₂, with the coexistence of a spin-polarized Dirac cone and parabolic degenerate points. The Curie temperature evaluated from Monte Carlo simulations implies Mn₂C₆S₁₂ possessing stable ferromagnetism at room temperature. Taking the spin–orbit coupling into account, the Dirac cone is gapped and the degenerate points are lifted, giving rise to multiple topologically nontrivial states with nonzero Chern number, which imply the possibility of Mn₂C₆S₁₂ to be a Chern insulator and a Chern half-metal. Our results offer versatile platforms for achieving spin filtering or a quantum anomalous Hall effect with promising application in spintronics devices

Rational Design of Black Phosphorus-Based Direct Z‑Scheme Photocatalysts for Overall Water Splitting: The Role of Defects

Black phosphorus (BP) has received increasing interest as a promising photocatalyst for water splitting. Nevertheless, exploring the underlying hydrogen evolution reaction (HER) mechanism and improving the water oxidizing ability remains an urgent task. Here, using first-principles calculations, we uncover the role of point defects in improving the HER activity of BP photocatalysts. We demonstrate that the defective phosphorene can be effectively activated by the photoinduced electrons under solar light, exhibiting high HER catalytic activity in a broad pH range (0–10). Besides, we propose that the direct Z-scheme in the defective BP/SnSe2 heterobilayer is quite feasible for photocatalytic overall water splitting. This mechanism could be further verified based on the excited state dynamics method. The role of point defects in the photocatalytic mechanism provides useful insights for the development of BP photocatalysts

Theoretical Discovery of a Superconducting Two-Dimensional Metal–Organic Framework

Superconductivity is a fascinating quantum phenomenon characterized by zero electrical resistance and the Meissner effect. To date, several distinct families of superconductors (SCs) have been discovered. These include three-dimensional (3D) bulk SCs in both inorganic and organic materials as well as two-dimensional (2D) thin film SCs but only in <i>inorganic</i> materials. Here we predict superconductivity in 2D and 3D <i>organic</i> metal–organic frameworks by using first-principles calculations. We show that the highly conductive and recently synthesized Cu-benzenehexathial (BHT) is a Bardeen–Cooper–Schrieffer SC. Remarkably, the monolayer Cu-BHT has a critical temperature (<i>T</i>_c) of 4.43 K, while <i>T</i>_c of bulk Cu-BHT is 1.58 K. Different from the enhanced <i>T</i>_c in 2D inorganic SCs which is induced by interfacial effects, the <i>T</i>_c enhancement in this 2D organic SC is revealed to be the out-of-plane soft-mode vibrations, analogous to surface mode enhancement originally proposed by Ginzburg. Our findings not only shed new light on better understanding 2D superconductivity but also open a new direction to search for SCs by interface engineering with organic materials

Two-Dimensional Metal–Organic Half-metallic Antiferromagnet: CoFePz

Half-metals are always accompanied by ferromagnetism with undesired stray magnetic field which may be harmful in highly integrated circuits. By contrast, half-metallic antiferromagnets (HMAFMs) can achieve fully spin-polarized current without stray magnetic field, enabling spintronic filed sensing and magnetic memories. Using first-principles calculations, we demonstrated that the tantalizing HMAFM can be realized in a two-dimensional (2D) metal–organic framework (MOF) containing Co ions and octa-amino-substituted iron-porphyrazines (CoFePz). The strong p–d exchange interaction between ions and ligands leads to an antiferromagnetic ground state with metallic features in one spin direction and semiconducting features in the opposite spin direction. Monte Carlo simulations based on the Ising model on an edge-centered square lattice indicate that the Néel temperature of the CoFePz (247 K) is much higher than the temperature of liquid nitrogen. Considering the huge number of MOFs, it is expected that the present findings can shed light on a new way to develop organic HMAFMs

Kane Fermion in a Two-Dimensional π‑Conjugated Bis(iminothiolato)nickel Monolayer

Massless Kane fermions revealed in zinc-blende semiconductors have recently gained interest in the broad study of relativistic materials. In particular, two-dimensional (2D) Kane fermions were expected to be hybrids of pseudospin-1 and -1/2 Dirac fermions. Based on first-principles calculations, we demonstrated that 2D Kane fermions can be realized in a recently synthesized metal–organic framework, namely, bis­(iminothiolato)nickel monolayer. A slight compression takes the system from a semimetal to a semiconductor. At the critical strain of ∼1%, the upper and lower conical bands linearize and touch at a single point intersecting a flat band, showing the same dispersion as the pseudospin-1 Dirac–Weyl systems. We adopted a tight-binding Hamiltonian of a line-centered honeycomb lattice to reveal the origins and topology of the electronic band structure. The coexistence of Kane-type and Dirac-type spectra in the bis­(iminothiolato)nickel monolayer is expected to benefit the study of multi quasiparticle effects

Additional file 1 of The transcription factor GCN4 contributes to maintaining intracellular amino acid contents under nitrogen-limiting conditions in the mushroom Ganoderma lucidum

Supplementary Material