Ultrahigh Néel Temperature Antiferromagnetism and Ultrafast Laser-Controlled Demagnetization in a Dirac Nodal Line MoB Monolayer.

Two-dimensional (2D) antiferromagnetic (AFM) materials boasting a high Néel temperature (), high carrier mobility, and fast spin response under an external field are in great demand for efficient spintronics. Herein, we theoretically present the MoB monolayer as an ideal 2D platform for AFM spintronics. The AFM MoB monolayer features a symmetry-protected, 4-fold degenerate Dirac nodal line (DNL) at the Fermi level.

Two-dimensional monolayer BiSnO: a novel wide-band-gap semiconductor with high stability and strong ultraviolet absorption.

The exploration of two-dimensional (2D) wide-band-gap semiconductors (WBGSs) holds significant scientific and technological importance in the field of condensed matter physics and is actively being pursued in optoelectronic research. In this study, we present the discovery of a novel WBGS, namely monolayer BiSnO, using first-principles calculations in conjunction with the quasi-particle GWapproximation. Our calculations confirm that monolayer BiSnOexhibits moderate cleavage energy, positive phonon modes, mechanical resilience, and high temperature resistance (up to 1000 K), which demonstrate its structural stability, flexibility, and potential for experimental realization.

Two-dimensional ferromagnetic semiconductors of monolayer BiXO (X = Ru, Os) with direct band gaps, high Curie temperatures, and large magnetic anisotropy.

Two-dimensional (2D) ferromagnetic semiconductors are highly promising candidates for spintronics, but are rarely reported with direct band gaps, high Curie temperatures (), and large magnetic anisotropy. Using first-principles calculations, we predict that two ferromagnetic monolayers, BiXO (X = Ru, Os), are such materials with a direct band gap of 2.64 and 1.

Two-dimensional carbon materials with an anisotropic Dirac cone: high stability and tunable Fermi velocity.

Among two-dimensional (2D) materials, Dirac-cone materials have attracted much attention due to their extraordinary electrical properties. In this work, we propose a new 2D carbon allotrope, 2D 2, which consists of 5-, 6-, 7- and 11-membered rings, and all carbon atoms are in one plane. Phonon dispersion curve calculations indicate that 2D 2 is kinetically stable under ambient conditions.

A perfect match between borophene and aluminium in the AlB heterostructure with covalent Al-B bonds, multiple Dirac points and a high Fermi velocity.

By performing a swarm-intelligent global structure search combined with first-principles calculations, a stable two-dimensional (2D) AlB heterostructure with directed, covalent Al-B bonds forms due to a nearly perfect lattice match between 2D borophene and the Al(111) surface. The AlB heterosheet with the 6 space group is composed of a planar Al(111) layer and a corrugated borophene layer, where the in-plane coordinates of Al covalently link with the corrugated B atoms. The resulting structure shows a similar interlayer interaction energy to that of the Al(111) surface layer to the bulk and high mechanical and thermal stability, possesses multiple Dirac points in the Brillouin zone with a remarkably high Fermi velocity of 1.

Half-Auxeticity and Anisotropic Transport in Pd Decorated Two-Dimensional Boron Sheets.

Upon strain, most materials shrink normal to the direction of applied strain. Similarly, if a material is compressed, it will expand in the direction orthogonal to the pressure. Few materials, those of negative Poisson ratio, show the opposite behavior.

Strain-controlled electronic and magnetic properties of tVS/hVS van der Waals heterostructures.

The structural, electronic and magnetic properties of the T-phase and H-phase of the VS monolayer and their heterobilayers are studied by means of first-principles calculations. We find that the two phases of the VS monolayer are both ferromagnetic (FM) semiconductors and that these two monolayers form a typical van der Waals (vdW) heterostructure with a weak interlayer interaction. By comparing the energy of different magnetic configurations, the FM state of the tVS/hVS heterostructure is found to be in the ground state under normal conditions or biaxial strains.

Polymorphism of low dimensional boron nanomaterials driven by electrostatic gating: a computational discovery.

The successful synthesis of two-dimensional (2D) boron sheets typically relies on the utilization of a silver surface, which acts as a gated substrate compensating for the electron-deficiency of boron. However, how the structures of one-dimensional (1D) boron are affected by the gating effect remains unclear. By means of an unbiased global minimum structure search and density functional theory (DFT) computations, we discovered the coexistence of 2D boron sheets and 1D ribbons triggered by electrostatic gating.

Room temperature ferromagnetism and antiferromagnetism in two-dimensional iron arsenides.

The discovery of two-dimensional (2D) magnetic materials with high critical temperature and intrinsic magnetic properties has attracted significant research interest. By using swarm-intelligence structure search and first-principles calculations, we predict three 2D iron arsenide monolayers (denoted as FeAs-I, II and III) with good energetic and dynamical stabilities. We find that FeAs-I and II are ferromagnets, while FeAs-III is an antiferromagnet.

Rhombohedral Lanthanum Manganite: A New Class of Dirac Half-Metal with Promising Potential in Spintronics.

Dirac half-metals have drawn great scientific interests in spintronics because of their outstanding physical properties such as the large spin polarization and massless Dirac fermions. By using first-principles calculations, we investigate the perovskite-type lanthanum manganite (LaMnO) as a novel Dirac half-metal. Specifically, LaMnO displays multiple linear band crossings in the spin-up direction, while it has a large band gap (∼5 eV) in the spin-down orientation.

Free-radical gases on two-dimensional transition-metal disulfides (XS, X = Mo/W): robust half-metallicity for efficient nitrogen oxide sensors.

The detection of single gas molecules is a highly challenging work because it requires sensors with an ultra-high level of sensitivity. By using density functional theory, here we demonstrate that the adsorption of a paramagnetic unpaired free radical gas (NO) on a monolayer of XS (X = Mo, W) can trigger the transition from semiconductor to half metal. More precisely, the single-layer XS (X = Mo, W) with NO adsorbed on it would behave like a metal in one spin channel while acting as a semiconductor in the other spin orientation.

Two-dimensional GeP as a high capacity electrode material for Li-ion batteries.

Two-dimensional (2D) materials are promising for use in lithium (Li) electrodes due to their high surface ratio. By using density functional theory (DFT) calculations, we investigate the adsorption and diffusion of Li on a newly predicted 2D GeP material [Nano Lett., 2016, 17, 1833].

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride.

Spin-polarized materials with Dirac features have sparked great scientific interest due to their potential applications in spintronics. But such a type of structure is very rare and none has been fabricated. Here, we investigate the already experimentally synthesized manganese fluoride (MnF_{3}) as a novel spin-polarized Dirac material by using first-principles calculations.

Predicting a graphene-like WB nanosheet with a double Dirac cone, an ultra-high Fermi velocity and significant gap opening by spin-orbit coupling.

The zero-band gap nature of graphene prevents it from performing as a semi-conductor in modern electronics. Although various graphene modification strategies have been developed to address this limitation, the very small band gap of these materials and the suppressed charge carrier mobility of the devices developed still significantly hinder graphene's applications. In this work, a two dimensional (2D) WB monolayer, which exhibits a double Dirac cone, was conceived and assessed using density functional theory (DFT) methods, which would provide a sizable band gap while maintaining higher charge mobility with a Fermi velocity of 1.

Gas Protection of Two-Dimensional Nanomaterials from High-Energy Impacts.

Two-dimensional (2D) materials can be produced using ball milling with the help of liquid surfactants or solid exfoliation agents, as ball milling of bulk precursor materials usually produces nanosized particles because of high-energy impacts. Post-milling treatment is thus needed to purify the nanosheets. We show here that nanosheets of graphene, BN, and MoS can be produced by ball milling of their bulk crystals in the presence of ammonia or a hydrocarbon ethylene gas and the obtained nanosheets remain flat and maintain their single-crystalline structure with low defects density even after a long period of time; post-milling treatment is not needed.

Anomalous Enhancement of Mechanical Properties in the Ammonia Adsorbed Defective Graphene.

Pure graphene is known as the strongest material ever discovered. However, the unavoidable defect formation in the fabrication process renders the strength of defective graphene much lower (~14%) than that of its perfect counterpart. By means of density functional theory computations, we systematically explored the effect of gas molecules (H, N, NH, CO, CO and O) adsorption on the mechanical strength of perfect/defective graphene.

Substantial Band-Gap Tuning and a Strain-Controlled Semiconductor to Gapless/Band-Inverted Semimetal Transition in Rutile Lead/Stannic Dioxide.

By first-principle calculations, we have systematically studied the effect of strain/pressure on the electronic structure of rutile lead/stannic dioxide (PbO/SnO). We find that pressure/strain has a significant impact on the electronic structure of PbO/SnO. Not only can the band gap be substantially tuned by pressure/strain, but also a transition between a semiconductor and a gapless/band-inverted semimetal can be manipulated.

Two-Dimensional Boron Hydride Sheets: High Stability, Massless Dirac Fermions, and Excellent Mechanical Properties.

Two-dimensional (2D) boron sheets have been successfully synthesized in recent experiments, however, some important issues remain, including the dynamical instability, high energy, and the active surface of the sheets. In an attempt to stabilize 2D boron layers, we have used density functional theory and global minimum search with the particle-swarm optimization method to predict four stable 2D boron hydride layers, namely the C2/m, Pbcm, Cmmm, and Pmmn sheets. The vibrational normal mode calculations reveal all these structures are dynamically stable, indicating potential for successful experimental synthesis.

Tubular Shape Fullerenes Inside Single Wall Boron Nitride Nanotubes: A Theoretical Simulation.

The orientations of fullerene molecules filled in nanotubes have important influence on the electronic properties of the formed peapods and their transformations such as polymerization under certain conditions. Here we present a investigation on the preferable orientations of tubular C70, C80 and C90 fullerenes confined inside single-walled boron nitride nanotubes (SWBNNTs) by calculating the van der Waals energy between the encapsulated molecule and the hosting nanotube. The minimum entering radius and the energetically favorable radius for encapsulating C70, C80 and C90 have been determined by the reaction energy calculation.

Graphene-like Two-Dimensional Ionic Boron with Double Dirac Cones at Ambient Condition.

Recently, partially ionic boron (γ-B28) has been predicted and observed in pure boron, in bulk phase and controlled by pressure [ Nature 2009 , 457 , 863 ]. By using ab initio evolutionary structure search, we report the prediction of ionic boron at a reduced dimension and ambient pressure, namely, the two-dimensional (2D) ionic boron. This 2D boron structure consists of graphene-like plane and B2 atom pairs with the P6/mmm space group and six atoms in the unit cell and has lower energy than the previously reported α-sheet structure and its analogues.

Calculations of helium separation via uniform pores of stanene-based membranes.

The development of low energy cost membranes to separate He from noble gas mixtures is highly desired. In this work, we studied He purification using recently experimentally realized, two-dimensional stanene (2D Sn) and decorated 2D Sn (SnH and SnF) honeycomb lattices by density functional theory calculations. To increase the permeability of noble gases through pristine 2D Sn at room temperature (298 K), two practical strategies (i.

Predicting Single-Layer Technetium Dichalcogenides (TcX₂, X = S, Se) with Promising Applications in Photovoltaics and Photocatalysis.

One of the least known compounds among transition metal dichalcogenides (TMDCs) is the layered triclinic technetium dichalcogenides (TcX2, X = S, Se). In this work, we systematically study the structural, mechanical, electronic, and optical properties of TcS2 and TcSe2 monolayers based on density functional theory (DFT). We find that TcS2 and TcSe2 can be easily exfoliated in a monolayer form because their formation and cleavage energy are analogous to those of other experimentally realized TMDCs monolayer.

Single Layer Bismuth Iodide: Computational Exploration of Structural, Electrical, Mechanical and Optical Properties.

Layered graphitic materials exhibit new intriguing electronic structure and the search for new types of two-dimensional (2D) monolayer is of importance for the fabrication of next generation miniature electronic and optoelectronic devices. By means of density functional theory (DFT) computations, we investigated in detail the structural, electronic, mechanical and optical properties of the single-layer bismuth iodide (BiI3) nanosheet. Monolayer BiI3 is dynamically stable as confirmed by the computed phonon spectrum.

Predicting a new phase (T'') of two-dimensional transition metal di-chalcogenides and strain-controlled topological phase transition.

Single layered transition metal dichalcogenides have attracted tremendous research interest due to their structural phase diversities. By using a global optimization approach, we have discovered a new phase of transition metal dichalcogenides (labelled as T''), which is confirmed to be energetically, dynamically and kinetically stable by our first-principles calculations. The new T'' MoS2 phase exhibits an intrinsic quantum spin Hall (QSH) effect with a nontrivial gap as large as 0.