Control of light-matter interactions in two-dimensional materials with nanoparticle-on-mirror structures

Light–matter interactions in two-dimensional(2D)materials have been the focus of research since the discovery of graphene.The light–matter interaction length in 2D materials is,however,much shorter than that in bulk materials owing to the atomic nature of 2D materials.Plasmonic nanostructures are usually integrated with 2D materials to enhance the light–matter interactions,offering great opportunities for both fundamental research and technological applications.Nanoparticle-on-mirror(NPo M)structures with extremely confined optical fields are highly desired in this aspect.In addition,2D materials provide a good platform for the study of plasmonic fields with subnanometer resolution and quantum plasmonics down to the characteristic length scale of a single atom.A focused and up-to-date review article is highly desired for a timely summary of the progress in this rapidly growing field and to encourage more research efforts in this direction.In this review,we will first introduce the basic concepts of plasmonic modes in NPo M structures.Interactions between plasmons and quasi-particles in 2D materials,e.g.,excitons and phonons,from weak to strong coupling and potential applications will then be described in detail.Related phenomena in subnanometer metallic gaps separated by 2D materials,such as quantum tunneling,will also be touched.We will finally discuss phenomena and physical processes that have not been understood clearly and provide an outlook for future research.We believe that the hybrid systems of2D materials and NPo M structures will be a promising research field in the future.

Structured mirror array for two-dimensional collimation of a chromium beam in atom lithography

Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions.The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P40 of the chromium atom.The collimation ratio is 0.45 vertically（in x axis）,and it is 0.55 horizontally（in y axis）.The theoretical model is also simulated,and success of our structured mirror array is achieved.

Band gaps structure and semi-Dirac point of two-dimensional function photonic crystals

Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , are proposed and studied numerically. The band gaps structures of the photonic crystals for TE and TM waves are different from the two-dimensional conventional photonic crystals. Some absolute band gaps and semiDirac points are found. When the medium column radius and the function form of the dielectric constant are modulated, the numbers, width, and position of band gaps are changed, and the semi-Dirac point can either occur or disappear. Therefore,the special band gaps structures and semi-Dirac points can be achieved through the modulation on the two-dimensional function photonic crystals. The results will provide a new design method of optical devices based on the two-dimensional function photonic crystals.

TWO-DIMENSIONAL ALGEBRAIC SOLITARY WAVE AND ITS VERTICAL STRUCTURE IN STRATIFIED FLUID

The algebraic solitary wave and its associated eigenvalue problem in a deep stratified fluid with a free surface and a shallow upper layer were studied. And its vertical structure was examined. An exact solution for the derived 2D Benjamin-Ono equation was obtained, and physical explanation was given with the corresponding dispersion relation. As a special case, the vertical structure of the weakly nonlinear internal wave for the Holmboe density distribution was numerically investigated, and the propagating mechanism of the internal wave was studied by using the ray theory.

Effect of strain on structure and electronic properties of monolayer C_(4)N_(4)

The first-principles calculations are performed to examine structural,mechanical,and electronic properties at large strain for a monolayer C_(4)N_(4),which has been predicted as an anchoring promising material to attenuate shuttle effect in Li–S batteries stemming from its large absorption energy and low diffusion energy barrier.Our results show that the ideal strengths of C_(4)N_(4)under tension and pure shear deformation conditions reach 13.9 GPa and 12.5 GPa when the strains are 0.07 and 0.28,respectively.The folded five-membered rings and diverse bonding modes between carbon and nitrogen atoms enhance the ability to resist plastic deformation of C_(4)N_(4).The orderly bond-rearranging behaviors under the weak tensile loading path along the[100]direction cause the impressive semiconductor–metal transition and inverse semiconductor–metal transition.The present results enrich the knowledge of the structure and electronic properties of C_(4)N_(4)under deformations and shed light on exploring other two-dimensional materials under diverse loading conditions.

First‑principles study on electronic structure,optical and magnetic properties of rare earth elements X(X=Sc,Y,La,Ce,Eu)doped with two‑dimensional GaSe

The electronic structure,magnetic,and optical properties of two-dimensional(2D)GaSe doped with rare earth elements X(X=Sc,Y,La,Ce,Eu)were calculated using the first-principles plane wave method based on den-sity functional theory.The results show that intrinsic 2D GaSe is a p-type nonmagnetic semiconductor with an indi-rect bandgap of 2.6611 eV.The spin-up and spin-down channels of Sc-,Y-,and La-doped 2D GaSe are symmetric,they are non-magnetic semiconductors.The magnetic moments of Ce-and Eu-doped 2D GaSe are 0.908μ_(B)and 7.163μ_(B),which are magnetic semiconductors.Impurity energy levels appear in both spin-up and spin-down chan-nels of Eu-doped 2D GaSe,which enhances the probability of electron transition.Compared with intrinsic 2D GaSe,the static dielectric constant of the doped 2D GaSe increases,and the polarization ability is strengthened.The ab-sorption spectrum of the doped 2D GaSe shifts in the low-energy direction,and the red-shift phenomenon occurs,which extends the absorption spectral range.The optical reflection coefficient of the doped 2D GaSe is improved in the low energy region,and the improvement of Eu-doped 2D GaSe is the most obvious.

Unique microstructure and excellent mechanical properties of ADI

Amongst the cast iron family, ADI has a unique microstructure and an excellent, optimised combination of mechanical properties. The main microstructure of ADI is ausferrite, which is a mixture of extremely fine acicular ferrite and stable, high carbon austenite. There are two types of austenite in ADI: (1) the coarser and more equiaxed blocks of austenite between non-parallel acicular structures, which exist mainly in the last solidified area, and (2) the thin films of austenite between the individual ferrite platelets in the acicular structure. It is this unique microstructure, which gives ADI its excellent static and dynamic properties, and good low temperature impact toughness. The effect of microstructure on the mechanical properties is explained in more detail by examining the microstructure at the atomic scale. Considering the nanometer grain sizes, the unique microstructure, the excellent mechanical properties, good castability, (which enables near net shape components to be produced economically and in large volumes), and the fact that it can be 100% recycled, it is not overemphasized to call ADI a high-tech, nanometer and “green” material. ADI still has the potential to be further improved and its production and the number of applications for ADI will continue to grow, driven by the resultant cost savings over alternative materials.

Recent progress on the prediction of two-dimensional materials using CALYPSO

In recent years, structure design and predictions based on global optimization approach as implemented in CALYPSO software have gained great success in accelerating the discovery of novel two-dimensional(2D) materials. Here we highlight some most recent research progress on the prediction of novel 2D structures, involving elements, metal-free and metal-containing compounds using CALYPSO package. Particular emphasis will be given to those 2D materials that exhibit unique electronic and magnetic properties with great potentials for applications in novel electronics, optoelectronics,magnetronics, spintronics, and photovoltaics. Finally, we also comment on the challenges and perspectives for future discovery of multi-functional 2D materials.

Origin of diffraction fringes in two-dimensional photoelectron momentum distributions for single ionization of atoms in few-cycle intense laser pulses

We use the strong field approximation with a time window function controlling the release time of electrons to study the intra-cycle and inter-cycle interferences in few-cycle intense laser pulses impinging on He. The diffraction fringes, i.e., the vertical stripe-like structure, observed in the experimental two-dimensional photoelectron momentum distributions of Gopal et al. （2009 Phys. Rev. Lett. 103 053001） have been attributed to the interplay of the intra- and inter-cycle interferences. The pure numerical calculations by solving the time-dependent Schrrdinger equation are also performed and the results are compared with the experimental measurements directly. It has been found that the position of the stripe-like structure can be used to determine the duration of the laser pulses used in experiments.

Solvothermal Synthesis and Crystal Structure of a Layered Thioantimonate(Ⅲ) [C_4H_9NH_3]_2Sb_4S_7

An inorganic-organic hybrid thioantimonate（Ⅲ） [CH3（CH2）3NH3]2Sb4S7 1 with layered structure was synthesized by solvothermal method. 1 crystallizes in the triclinic system, space group P1 with a = 7.0124（11）, b = 11.919（2）, c =14.879（3）A, α = 108.791（3）, β= 102.441（3）, γ = 92.846（2）°, V= 1140.1（3）A3, Mr = 859.71, Z= 2, Do = 2.504 g/cm^3 ,μ = 5.324 mm^-1, F（000） = 804, S = 1.013, the Final R = 0.0297 and wR = 0.0618 for 3534 observed reflections with Ⅰ 〉 2 σ（Ⅰ）. 1 consists of [C4HgNH3]＋ cations and two-dimensional [Sb4ST]n^2n- anion which is composed of three SbS3 trigonal pyranaids and one SbS4 unit joined by sharing common comers. The anionic layers are stacked perpendicularly to the c axis of the unit cell forming two-dimensional channels between the layers. The [C4H9NH3]^＋ cations interdigitate in a bilayer and reside in the 2D channels leading to a sandwich-like arrangement of the anion and cations.

Guckenheimer structure of solution of Riemann problem with four pieces of constants in two space dimensions for scalar conservation laws

By using the generalized characteristic analysis method, the two-dimensional four-wave Riemann problem for scalar conservation laws, which is nonconvex along the y direction, was studied. Riemann solutions, which involve the Guckenheimer structure, were constructed.

Hydrothermal Synthesis and Structure Characterization of Diamine-templated Two-dimenisional Cerium Sulfate,[C_6N_2H_(14)][Ce(SO_4)_2(H_2O)_2]·0·5SO_4·2·5H_2O

Open-framework materials are of great interest from both the theoretical and practical points of view due to their catalytic, absorbent, and ion-exchange properties. In the past decade, the study of structurally and chemically diverse open framework solids has been flourishing. A large variety of silicates, phosphates and carboxylates with open-framework structures have been synthesized with organic amines as templates. It has also been demonstrated that other oxysalts such as selenate, arsenate and germanate are used to build up open architectures. As far as the sulfate is concerned,

Photonic Band Modulation in a Two-Dimensional Photonic Crystal with a One-Dimensional Periodic Dielectric Background

A two-dimensional photonic crystal with a one-dimensional periodic dielectric background is proposed. The photonic band modulation effects due to the periodic background are investigated based on the plane wave expansion method. We find that periodic modulation of the dielectric background greatly alters photonic band structures, especially for the E-polarization modes. The number, width and position of the photonic band gaps （PBGs） sensitively depend on the structure parameters （the layer thicknesses and dielectric constants） of the one-dimensional periodic background,

High-throughput computational material screening of the cycloalkane-based two-dimensional Dion–Jacobson halide perovskites for optoelectronics

Two-dimensional(2D) layered perovskites have emerged as potential alternates to traditional three-dimensional(3D)analogs to solve the stability issue of perovskite solar cells. In recent years, many efforts have been spent on manipulating the interlayer organic spacing cation to improve the photovoltaic properties of Dion–Jacobson(DJ) perovskites. In this work, a serious of cycloalkane(CA) molecules were selected as the organic spacing cation in 2D DJ perovskites, which can widely manipulate the optoelectronic properties of the DJ perovskites. The underlying relationship between the CA interlayer molecules and the crystal structures, thermodynamic stabilities, and electronic properties of 58 DJ perovskites has been investigated by using automatic high-throughput workflow cooperated with density-functional(DFT) calculations.We found that these CA-based DJ perovskites are all thermodynamic stable. The sizes of the cycloalkane molecules can influence the degree of inorganic framework distortion and further tune the bandgaps with a wide range of 0.9–2.1 eV.These findings indicate the cycloalkane molecules are suitable as spacing cation in 2D DJ perovskites and provide a useful guidance in designing novel 2D DJ perovskites for optoelectronic applications.

Crystal Structure and Property Research on Compounds Co(Ⅱ) and Zn(Ⅱ) with 3-Methylbenzoic Acid

Two compounds with 3-methylbenzoic acid（HL） [Co（L）2（4,4＇-bipy）]n 1 and [Zn2（L）4（4,4＇-bipy）]n 2（L = 3-methylbenzoic acid） have been hydrothermally synthesized directly and characterized by single-crystal X-ray diffraction analysis,elemental analyses,IR spectra and ultraviolet-visible diffuse reflection integral spectra（UV-Vis DRIS）.The two compounds are both one-dimensional infinite chains.The structural difference is that 1 is a double-chain structure and 2 is only a single chain one.At the same time,the carboxylate groups adopt different modes in the two compounds,relatively.Additionally,in order to explore the structural characteristic,two-dimen-sional IR spectra are investigated for 1 and 2.Photo-luminescent property of 2 is also researched in detail.

High-temperature ferromagnetism and strongπ-conjugation feature in two-dimensional manganese tetranitride

Two-dimensional(2D)magnetic materials have attracted tremendous research interest because of the promising application in the next-generation microelectronic devices.Here,by the first-principles calculations,we propose a twodimensional ferromagnetic material with high Curie temperature,manganese tetranitride MnN4monolayer,which is a square-planar lattice made up of only one layer of atoms.The structure is demonstrated to be stable by the phonon spectra and the molecular dynamic simulations,and the stability is ascribed to theπ–d conjugation betweenπorbital of N=N bond and d orbital of Mn.More interestingly,the MnN_(4)monolayer displays robust 2D ferromagnetism,which originates from the strong exchange couplings between Mn atoms due to theπ–d conjugation.The high critical temperature of 247 K is determined by solving the Heisenberg model using the Monte Carlo method.

Nodeless superconductivity in a quasi-two-dimensional superconductor AuTe2Se(4/3)

We performed ultra-low temperature thermal conductivity measurements on the single crystal of a new gold-based quasi-two-dimensional superconductor Au Te2Se（4/3）, which has a superconducting transition temperature Tc = 2.70 K. A negligible residual linear term κ0/T in zero magnetic field is observed, which suggests fully gapped superconducting state.Furthermore, the field dependence of κ0/T is similar to that of the multi-band s-wave superconductor Ba Fe1.9 Ni0.1 As2 at low field. These results reveal multiple nodeless superconducting gaps in this interesting quasi-two-dimensional superconductor with Berezinsky–Kosterlitz–Thouless topological transition.

Synthesis, Structure and Decarboxylative Behavior of a Nitro-coordinated Potassium Compound

A novel nitro-coordinated potassium compound [K(Htdc)(H_2O)]_n(tdc = 3-nitro-thiophene-2,5-dicarboxylate), has been synthesized and characterized. The complex with a two-dimensional(2D) layer structure contains an infinite K-O ladder-shaped chain, which is connected through carboxyl and unusual nitro-coordination of Htdc– anion. Then the 2D layers are further extended by intermolecular hydrogen-bonding to form a three-dimensional(3D) supramoleculalr network. Variable temperature powder X-ray diffractions, thermogravimetric analysis and nuclear magnetic resonance studies exhibit that the compound has a thermal-induced decarboxylative behavior.