Two-dimensional laser-induced periodic surface structures formed on crystalline silicon by GHz burst mode femtosecond laser pulses

Femtosecond laser pulses with GHz burst mode that consist of a series of trains of ultrashort laser pulses with a pulse interval of several hundred picoseconds offer distinct features in material processing that cannot be obtained by the conventional irradiation scheme of femtosecond laser pulses(single-pulse mode).However,most studies using the GHz burst mode femtosecond laser pulses focus on ablation of materials to achieve high-efficiency and high-quality material removal.In this study,we explore the ability of the GHz burst mode femtosecond laser processing to form laser-induced periodic surface structures(LIPSS)on silicon.It is well known that the direction of LIPSS formed by the single-pulse mode with linearly polarized laser pulses is typically perpendicular to the laser polarization direction.In contrast,we find that the GHz burst mode femtosecond laser(wavelength:1030 nm,intra-pulse duration:220 fs,intra-pulse interval time(intra-pulse repetition rate):205 ps(4.88 GHz),burst pulse repetition rate:200 kHz)creates unique two-dimensional(2D)LIPSS.We regard the formation mechanism of 2D LIPSS as the synergetic contribution of the electromagnetic mechanism and the hydrodynamic mechanism.Specifically,generation of hot spots with highly enhanced electric fields by the localized surface plasmon resonance of subsequent pulses in the bursts within the nanogrooves of one-dimensional LIPSS formed by the preceding pulses creates 2D LIPSS.Additionally,hydrodynamic instability including convection flow determines the final structure of 2D LIPSS.

Synthesis and Crystal Structure of a Novel Two-dimensional Layered Polymer [Zn(μ-O_2CCH=CHCO_2)(C_3H_4N_2)(H_2O)]_n

The title complex [Zn(-O2CCH=CHCO2)(C3H4N2)(H2O)]n was prepared by the reaction of zinc carbonate with maleic acid and imidazole in an aqueous-alcohol solution at 333 K, and its crystal structure has been solved by single-crystal X-ray diffraction. The complex crystallizes in the monoclinic system, space group Pc with a = 5.3858(7), b = 22.685(3), c = 7.6782(1) ? = 92.261(2)o, V = 937.4(2) 3, Z = 1, C14H16N4O10Zn2, Mr = 531.05, Dc = 1.882 g/cm3, = 2.623 mm1, F(000) = 532, the final R = 0.0372 and wR = 0.0930 for 1926 observed reflections with I>2s(I). The central zinc atom is five-coordinated in a distorted square pyramidal environment to three oxygen atoms of two different maleate ligands, a nitrogen atom of the imi- dazole ligand and an oxygen atom of water. In the complex two carboxylate groups of the maleate ligands have two coordination modes. One acts as a bidentate chelate ligand and the other a monoatomic monodentate ligand to bridge two zinc centers. As a result, 1-D infinite polymeric chains are formed, which are linked together by pairs of OH…O hydrogen bonds between the coordination water OH groups and carboxylate oxygen atoms to construct a 2-D layered polymer, and the layer structure is stabilized by p-p stacking of the imidozel ligands.

Magnetic and electronic properties of bulk and two-dimensional FeBi_(2)Te_(4):A first-principles study

Layered magnetic materials,such as MnBi_(2)Te_(4),have drawn much attention owing to their potential for realizing twodimensional(2D)magnetism and possible topological states.Recently,FeBi_(2)Te_(4),which is isostructural to MnBi_(2)Te_(4),has been synthesized in experiments,but its detailed magnetic ordering and band topology have not been clearly understood yet.Here,based on first-principles calculations,we investigate the magnetic and electronic properties of FeBi_(2)Te_(4)in bulk and 2D forms.We show that different from MnBi_(2)Te_(4),the magnetic ground states of bulk,single-layer,and bilayer FeBi_(2)Te_(4)all favor a 120°noncollinear antiferromagnetic ordering,and they are topologically trivial narrow-gap semiconductors.For the bilayer case,we find that a quantum anomalous Hall effect with a unit Chern number is realized in the ferromagnetic state,which may be achieved in experiment by an external magnetic field or by magnetic proximity coupling.Our work clarifies the physical properties of the new material system of FeBi_(2)Te_(4)and reveals it as a potential platform for studying magnetic frustration down to 2D limit as well as quantum anomalous Hall effect.

Electronic modulation of two-dimensional bismuth-based nanosheets for electrocatalytic CO_(2) reduction to formate: A review

Electrocatalytic CO_(2) reduction reaction(eCO_(2) RR)has significant relevance to settle the global energy crisis and abnormal climate problem via mitigating the excess emission of waste CO_(2) and producing high-value-added chemicals.Currently,eCO_(2) RR to formic acid or formate is one of the most technologically and economically viable approaches to realize high-efficiency CO_(2) utilization,and the development of efficient electrocatalysts is very urgent to achieve efficient and stable catalytic performance.In this review,the recent advances for two-dimensional bismuth-based nanosheets(2D Bi-based NSs)electrocatalysts are concluded from both theoretical and experimental perspectives.Firstly,the preparation strategies of 2D Bi-based NSs in aspects to precisely control the thickness and uniformity are summarized.In addition,the electronic regulation strategies of 2D Bi-based NSs are highlighted to gain insight into the effects of the structure-property relationship on facilitating CO_(2) activation,improving product selectivity,and optimizing carrier transport dynamics.Finally,the considerable challenges and opportunities of 2D Bi-based NSs are discussed to lighten new directions for future research of eCO_(2) RR.

Thermal transport in semiconductor nanostructures, graphene,and related two-dimensional materials

We review experimental and theoretical results on thermal transport in semiconductor nanostructures（multilayer thin films, core/shell and segmented nanowires）, single-and few-layer graphene, hexagonal boron nitride, molybdenum disulfide, and black phosphorus. Different possibilities of phonon engineering for optimization of electrical and heat conductions are discussed. The role of the phonon energy spectra modification on the thermal conductivity in semiconductor nanostructures is revealed. The dependence of thermal conductivity in graphene and related two-dimensional（2 D） materials on temperature, flake size, defect concentration, edge roughness, and strain is analyzed.

Interfacial fracture analysis for a two-dimensional decagonal quasi-crystal coating layer structure

The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained based on the potential theory.An analogy method is proposed based on the relationship between the general solutions for 2D decagonal and one-dimensional(1D)hexagonal QCs.According to the analogy method,the fundamental solutions of concentrated point phonon displacement discontinuities are obtained on the interface.By using the superposition principle,the hypersingular boundary integral-differential equations in terms of displacement discontinuities are determined for a line interface crack.Further,Green’s functions are found for uniform displacement discontinuities on a line element.The oscillatory singularity near a crack tip is eliminated by adopting the Gaussian distribution to approximate the delta function.The stress intensity factors(SIFs)with ordinary singularity and the energy release rate(ERR)are derived.Finally,a boundary element method is put forward to investigate the effects of different factors on the fracture.

Highly stable two-dimensional graphene oxide:Electronic properties of its periodic structure and optical properties of its nanostructures

According to first principle simulations, we theoretically predict a type of stable single-layer graphene oxide（C_2O）.Using density functional theory（DFT）, C_2O is found to be a direct gap semiconductor. In addition, we obtain the absorption spectra of the periodic structure of C_2O, which show optical anisotropy. To study the optical properties of C_2O nanostructures, time-dependent density functional theory（TDDFT） is used. The C_2O nanostructure has a strong absorption near 7 eV when the incident light polarizes along the armchair-edge. Besides, we find that the optical properties can be controlled by the edge configuration and the size of the C_2O nanostructure. With the elongation strain increasing, the range of light absorption becomes wider and there is a red shift of absorption spectrum.

MXenes: Versatile 2D materials with tailored surface chemistry and diverse applications

MXenes,the most recent addition to the 2D material family,have attracted significant attention owing to their distinctive characteristics,including high surface area,conductivity,surface characteristics,mechanical strength,etc.This review begins by presenting MXenes,providing insights into their structural characteristics,synthesis methods,and surface functional groups.The review covers a thorough analysis of MXene surface properties,including surface chemistry and termination group impacts.The properties of MXenes are influenced by their synthesis,which can be fluorine-based or fluorinedependent.Fluorine-based synthesis techniques involve etching with fluorine-based reagents,mainly including HF or LiF/HCl,while fluorine-free methods include electrochemical etching,chemical vapor deposition(CVD),alkaline etching,Lewis acid-based etching,etc.These techniques result in the emergence of functional groups such as-F,-O,-OH,-Cl,etc.on the MXenes surface,depending on the synthesis method used.Properties of MXenes,such as electrical conductivity,electronic properties,catalytic activity,magnetic properties,mechanical strength,and chemical and thermal stability,are examined,and the role of functional groups in determining these properties is explored.The review delves into the diverse applications of MXenes,encompassing supercapacitors,battery materials,hydrogen storage,fuel cells,electromagnetic interference(EMI) shielding,pollutant removal,water purification,flexible electronics,sensors,additive manufacturing,catalysis,biomedical and healthcare fields,etc.Finally,this article outlines the challenges and opportunities in the current and future development of MXenes research,addressing various aspects such as synthesis scalability,etching challenges,and multifunctionality,and exploring novel applications.The review concludes with future prospects and conclusions envisioning the impact of MXenes on future technologies and innovation.

Numerical modeling of blast-induced rock fragmentation in deep mining with 3D and 2D FEM method approaches

To optimize the excavation of rock using underground blasting techniques,a reliable and simplified approach for modeling rock fragmentation is desired.This paper presents a multistep experimentalnumerical methodology for simplifying the three-dimensional(3D)to two-dimensional(2D)quasiplane-strain problem and reducing computational costs by more than 100-fold.First,in situ tests were conducted involving single-hole and free-face blasting of a dolomite rock mass in a 1050-m-deep mine.The results were validated by laser scanning.The craters were then compared with four analytical models to calculate the radius of the crushing zone.Next,a full 3D model for single-hole blasting was prepared and validated by simulating the crack length and the radius of the crushing zone.Based on the stable crack propagation zones observed in the 3D model and experiments,a 2D model was prepared.The properties of the high explosive(HE)were slightly reduced to match the shape and number of radial cracks and crushing zone radius between the 3D and 2D models.The final methodology was used to reproduce various cut-hole blasting scenarios and observe the effects of residual cracks in the rock mass on further fragmentation.The presence of preexisting cracks was found to be crucial for fragmentation,particularly when the borehole was situated near a free rock face.Finally,an optimization study was performed to determine the possibility of losing rock continuity at different positions within the well in relation to the free rock face.

A color image encryption scheme based on a 2D coupled chaotic system and diagonal scrambling algorithm

A novel color image encryption scheme is developed to enhance the security of encryption without increasing the complexity. Firstly, the plain color image is decomposed into three grayscale plain images, which are converted into the frequency domain coefficient matrices(FDCM) with discrete cosine transform(DCT) operation. After that, a twodimensional(2D) coupled chaotic system is developed and used to generate one group of embedded matrices and another group of encryption matrices, respectively. The embedded matrices are integrated with the FDCM to fulfill the frequency domain encryption, and then the inverse DCT processing is implemented to recover the spatial domain signal. Eventually,under the function of the encryption matrices and the proposed diagonal scrambling algorithm, the final color ciphertext is obtained. The experimental results show that the proposed method can not only ensure efficient encryption but also satisfy various sizes of image encryption. Besides, it has better performance than other similar techniques in statistical feature analysis, such as key space, key sensitivity, anti-differential attack, information entropy, noise attack, etc.

Two-dimensional plane strain consolidation of unsaturated soils considering the depth-dependent stress

In practical engineering,the total vertical stress in the soil layer is not constant due to stress diffusion,and varies with time and depth.Therefore,the purpose of this paper is to investigate the effect of stress diffusion on the two-dimensional(2D)plane strain consolidation properties of unsaturated soils when the stress varies with time and depth.A series of semi-analytical solutions in terms of excess pore air and water pressures and settlement for 2D plane strain consolidation of unsaturated soils can be derived with the joint use of Laplace transform and Fourier sine series expansion.Then,the inverse Laplace transform of the semi-analytical solution is given in the time domain using a self-programmed code based on Crump’s method.The reliability of the obtained solutions is proved by the degeneration.Finally,the 2D plots of excess pore pressures and the curves of settlement varying with time,considering different physical parameters of unsaturated soil stratum and depth-dependent stress,are depicted and analyzed to study the 2D plane strain consolidation properties of unsaturated soils subjected to the depthdependent stress.

Green's functions of two-dimensional piezoelectric quasicrystal in half-space and bimaterials

In this paper,we obtain Green’s functions of two-dimensional(2D)piezoelectric quasicrystal(PQC)in half-space and bimaterials.Based on the elastic theory of QCs,the Stroh formalism is used to derive the general solutions of displacements and stresses.Then,we obtain the analytical solutions of half-space and bimaterial Green’s functions.Besides,the interfacial Green’s function for bimaterials is also obtained in the analytical form.Before numerical studies,a comparative study is carried out to validate the present solutions.Typical numerical examples are performed to investigate the effects of multi-physics loadings such as the line force,the line dislocation,the line charge,and the phason line force.As a result,the coupling effect among the phonon field,the phason field,and the electric field is prominent,and the butterfly-shaped contours are characteristic in 2D PQCs.In addition,the changes of material parameters cause variations in physical quantities to a certain degree.

Waveguide-integrated optical modulators with two-dimensional materials

Waveguide-integrated optical modulators are indispensable for on-chip optical interconnects and optical computing.To cope with the ever-increasing amount of data being generated and consumed,ultrafast waveguide-integrated optical modulators with low energy consumption are highly demanded.In recent years,two-dimensional(2D)materials have attracted a lot of attention and have provided tremendous opportunities for the development of high-performance waveguide-integrated optical modulators because of their extraordinary optoelectronic properties and versatile compatibility.This paper reviews the state-of-the-art waveguide-integrated optical modulators with 2D materials,providing researchers with the developing trends in the field and allowing them to identify existing challenges and promising potential solutions.First,the concept and fundamental mechanisms of optical modulation with 2D materials are summarized.Second,a review of waveguide-integrated optical modulators employing electro-optic,all-optic,and thermo-optic effects is provided.Finally,the challenges and perspectives of waveguide-integrated modulators with 2D materials are discussed.

Numerical study on THz radiation of two-dimensional plasmon resonance of GaN HEMT array

The Ga N high electron mobility transistor(HEMT)has been considered as a potential terahertz(THz)radiation source,yet the low radiation power level restricts their applications.The HEMT array is thought to improve the coupling efficiency between two-dimensional(2D)plasmons and THz radiation.In this work,we investigate the plasma oscillation,electromagnetic radiation,and the integration characteristics of Ga N HEMT targeting at a high THz radiation power source.The quantitative radiation power and directivity are obtained for integrated Ga N HEMT array with different array periods and element numbers.With the same initial plasma oscillation phase among the HEMT units,the radiation power of the two-element HEMT array can achieve 4 times as the single HEMT radiation power when the array period is shorter than 1/8electromagnetic wavelength.In addition,the radiation power of the HEMT array varies almost linearly with the element number,the smaller array period can lead to the greater radiation power.It shows that increasing the array period could narrow the main radiated lobe width while weaken the radiation power.Increasing the element number can improve both the radiation directivity and power.We also synchronize the plasma wave phases in the HEMT array by adopting an external Gaussian plane wave with central frequency the same as the plasmon resonant frequency,which solves the problem of the radiation power reduction caused by the asynchronous plasma oscillation phases among the elements.The study of the radiation power amplification of the one-dimensional(1D)Ga N HEMT array provides useful guidance for the research of compact high-power solid-state terahertz sources.

Two-Dimensional Riemann Problems:Transonic Shock Waves and Free Boundary Problems

We are concerned with global solutions of multidimensional(M-D)Riemann problems for nonlinear hyperbolic systems of conservation laws,focusing on their global configurations and structures.We present some recent developments in the rigorous analysis of two-dimensional(2-D)Riemann problems involving transonic shock waves through several prototypes of hyperbolic systems of conservation laws and discuss some further M-D Riemann problems and related problems for nonlinear partial differential equations.In particular,we present four different 2-D Riemann problems through these prototypes of hyperbolic systems and show how these Riemann problems can be reformulated/solved as free boundary problems with transonic shock waves as free boundaries for the corresponding nonlinear conservation laws of mixed elliptic-hyperbolic type and related nonlinear partial differential equations.

Recent Progress in the Fabrication, Properties, and Devices of Heterostructures Based on 2D Materials

With a large number of researches being conducted on two?dimen?sional(2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of combining distinct functional 2D materials into heterostructures naturally emerged that pro?vides unprecedented platforms for exploring new physics that are not accessible in a single 2D material or 3D heterostructures. Along with the rapid development of controllable, scalable, and programmed synthesis techniques of high?quality 2D heterostructures, various heterostructure devices with extraordinary performance have been designed and fabricated, including tunneling transistors, photodetectors, and spintronic devices. In this review, we present a summary of the latest progresses in fabrications, properties, and applications of di erent types of 2D heterostruc?tures, followed by the discussions on present challenges and perspectives of further investigations.

Preparation of Two-dimensional Ti_2CT_x by Molten Fluorinated Salt Method

We prepared a two-dimensional transition metal carbide Ti_2CT_x by treatment of Ti_2 AlC in molten fluoride salt. Two fluorinated salt systems were used to etch Al from Ti_2 AlC powder precursor under the argon atmosphere, and then the resulting MXene was delaminated with TBAOH to produce few-layered nanosheets of Ti_2CT_x. The reaction was undergone at different temperatures to study the effect of temperature.The results show that the optimal reaction temperature is 600 ℃ in LiF-NaF-KF system, and 850 ℃ in NaFKF system. The molten salt treated products are delaminated and quasi-2 D MXene sheets can be obtained. The thickness of the MXene sheets prepared from the binary molten salt system is smaller than that of the ternary molten salt system.

Synthesis, Bioactivity, and Crystal Structure Analysis of 2-(3-Oxobenzo[d]isothiazol-2(3H)-yl)ethyl Benzoates

Fifteen novel 2-（3-oxobenzo[d]isothiazol-2（3H）-yl）ethyl benzoates were synthesi- zed by the condensation of 2-（2-hydroxyethyl）benzo[d]isothiazol-3（2H）-one with substituted benzoic acids in dichloromethane. All the compounds were characterized by elemental analysis, IR, ESI-MS and 1H NMR. The crystal structures for 2-（2-hydroxyethyl）benzo[d]isothiazol-3（2H）-one （2） and 2-（3-oxobenzo[d]isothiazol-2（3H）-yl）ethyl 2-methoxybenzoate （30） have been determined by X-ray crystal structure analysis. Compound 2 （C9H9NO2S） crystallizes in the monoclinic system, space group Pn with a = 10.552（3）, b = 7.849（2）, c = 10.765（4） A, β = 103.128（4）°, V= 868.3（5） A3, Mr = 195.24, Dc = 1.493 Mg.m-3, μ = 0.33 mm-1, F（000） = 408, Z = 4, R= 0.0314 and wR= 0.0628. Compound 30 （C17H15NO4S） crystallizes in the triclinic system, space group P1 with a = 8.028（2）, b = 9.300（2）, c = 10.430（3）A, V= 752.1（3）A3, Mr = 329.36, D,= 1.454 Mg.m-3, p = 0.24 mm-1, F（000） = 344, Z = 2, R = 0.0377 and wR = 0.0904. The preliminary biological test indicated that the title compounds show better growth inhibitory activity against the gram-positive bacteria than the gram-negative bacteria.

Synthesis,Bioactivity and Crystal Structure Analysis of Novel Benzo[d]isothiazol-3(2H)-ones

Two compounds,3-oxo-N-o-tolylbenzo[d]isothiazole-2（3H）-carboxamide （1） and N-（2-methoxyphenyl）-3-oxobenzo[d]isothiazole-2（3H）-carboxamide （2）,were synthesized from the initial compound benzo[d]isothiazol-3（2H）-one （BIT） and characterized by 1 H NMR,IR and elemental analysis,respectively.The single crystals of compounds 1 and 2 were obtained and determined by X-ray diffraction analysis.The preliminary results of biological activity experiment show that some of the title compounds exhibited a favorable antimicrobial activity.

Synthesis, Crystal Structure, Magnetic Property and DFT Study of a Novel 2D Polymer [Cu(pdc)(bpy)]·H_2O

A new copper complex [Cu（pdc）（bpy）]·H2 O（1, H2 pdc = 3,5-pyridinedicarboxylic acid, bpy = 2,2-bipyridine） has been solvothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, UV-vis spectroscopy and magnetic measure- ments. Complex 1 crystallizes in monoclinic system, space group P21 /c, a = 10.893（2）, b = 7.3641（15）, c = 1.9921（4）, β = 92.16（3）, V = 1596.9（6）3, Dc = 1.676 g/cm3, Mr = 402.84, Z = 4, F（000） = 820, μ = 1.404 mm-1, the final R = 0.0237 and wR = 0.0693. The Cu（II） ion is five-coordinated by two O atoms from two pdc ligands, one N atom from another pdc ligand and two N atoms from the bpy ligand. The pdc anion, which acts as a tridentate ligand, links three Cu ions, forming（3,3）-connected two-dimensional（2D） sheets. We also studied the electronic structure and orbital energies of complex 1 by DFT methods, and the results are consistent with UV-vis spectrum.