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Recently, the AlB2-type compounds such as AlB2 and MgB2 have attracted immense interest due to the Dirac Nodal Line (DNL). This unique electronic structure is very important for the design and disc...

The structural, electronic, mechanical and optical properties of LaIn3 under pressure have been systemically investigated using the first-principles calculations based on density functional theory (DFT). Structural calculations show that the cubic LaIn3 is no structural phase transition in the pressure range of 0–30 GPa. From the calculated electronic band structures and density of states (DOS), it is found that the LaIn3 is metallic character and the bands which cross EF originate primarily from La-d states, with some contribution from In-p states. The electrical conductivity and metal properties are gradually decreasing with increasing pressure, and the electron transition becomes more difficult. The calculated elastic properties indicate that LaIn3 is mechanical stability and possess the superior mechanical properties in the considered pressure ranges. Moreover, a comparison of the two elastic constants C11 and C44 indicates that the LaIn3 is more resistant to the unidirectional compression than to the shear deformation, and the values of Poisson’s ratio ν and B/G demonstrate that LaIn3 is keep ductile behavior under pressure up to 30 GPa. In addition, the elastic anisotropy of LaIn3 under pressure is also examined. Finally, the optical properties and Debye temperature of the cubic LaIn3 under pressure are also predicted analytically.

Recently, the AlB2-type compounds (such as AlB2 and MgB2) which exhibit Dirac Nodal Line (DNLs) semimetal on their electronic band structure and Phononic Weyl Nodal Straight Lines (PTWNLs) on their...

With the synthesis of single-layer lead iodide (PbI2) in the laboratory in recent years, it has been widely used due to its stable structure and suitable bandgap (2.5 eV). We carried out first-prin...

Group-V elemental monolayers were recently predicted to exhibit exotic physical properties such as nontrivial topological properties, or a quantum anomalous Hall effect, which would make them very suitable for applications in next-generation electronic devices. The free-standing group-V monolayer materials usually have a buckled honeycomb form, in contrast with the flat graphene monolayer. Here, we report epitaxial growth of atomically thin flat honeycomb monolayer of group-V element antimony on a Ag(111) substrate. Combined study of experiments and theoretical calculations verify the formation of a uniform and single-crystalline antimonene monolayer without atomic wrinkles, as a new honeycomb analogue of graphene monolayer. Directional bonding between adjacent Sb atoms and weak antimonene-substrate interaction are confirmed. The realization and investigation of flat antimonene honeycombs extends the scope of two-dimensional atomically-thick structures and provides a promising way to tune topological properties for future technological applications.

LaMn3Ni2Mn2O12, a recently synthesized A- and B-site-ordered quadruple perovskite, was shown to display nontrivial orthogonal spin ordering at the B and B′ sites, which was the first example of orthogonal spin ordering in a quadruple perovskite to be reported in an experiment. To understand this novel spin order, we performed comprehensive first-principles calculations to investigate the magnetic properties and electronic structure of LaMn3Ni2Mn2O12. The B-site-ordered quadruple perovskite La2NiMnO6 and A-site-ordered quadruple perovskite LaMn3Al4O12 were also investigated. Our calculations showed that both LaMn3Al4O12 and LaMn3Ni2Mn2O12 had collinear G-type AFM orders in the A′-site-Mn3+ spins. For La2NiMnO6, the B-site Ni2+ and B′-site Mn4+ presented a collinear FM order. However, the Ni2+ and Mn4+ sites in LaMn3Ni2Mn2O12 showed a 90° canted spin alignment, leading to a noncollinear FM spin order, which was consistent with experimental observations. Our calculated magnetic interactions further demonstra...

The recent discovery of hidden spin polarization emerging in layered materials of specific nonmagnetic crystal is a fascinating phenomenon, though hardly explored yet. Here, we have studied hidden spin textures in layered nonmagnetic 1T-phase transition-metal dichalcogenides MX2 (M = Zr, Hf; X = S, Se, Te) by using first-principles calculations. Spin-layer locking effect, namely, energy-degenerate opposite spins spatially separated in the top and bottom layer respectively, has been identified. In particular, the hidden spin polarization of β-band can be easily probed, which is strongly affected by the strength of spin-orbit coupling. The hidden spin polarization of ξ-band locating at high symmetry M point (conduction band minimum) has a strong anisotropy. In the bilayer, the hidden spin polarization is preserved at the upmost Se layer, while being suppressed if the ZrSe2 layer is taken as the symmetry partner. Our results on hidden spin polarization in 1T-phase dichalcogenides, verifiable by spin-resolved and angle-resolved photoemission spectroscopy (ARPES), enrich our understanding of spin physics and provide important clues to search for specific spin polarization in two dimensional materials for spintronic and quantum information applications.

For the research of Transition Metal Dichalcogenides (TMDCs), the predecessors have already involved a lot. However, the research of the two-dimensional square-octagon MoS2 (so-MoS2) with elastic and thermal properties are not enough. Here, we have investigated the electronic, phonon, elastic and thermal properties of the primitive monolayer so-MoS2 by first-principles calculations and theoretical analysis. Firstly, The Dirac point exists on its band structure and mainly contributed by d orbits of Mo atoms, it will open the energy gap and enter the insulating phase when the spin–orbit coupling is added. Secondly, the phonon spectrum indicates that so-MoS2 is dynamically stable. The Raman, infrared active modes were also studied. Thirdly, we investigated the elastic constants of monolayer so-MoS2 by the nonlinear least-squares fitted the relation between energy density and strain. We find monolayer so-MoS2 has better flexibility than other two-dimensional materials, such as, monolayer MoS2. Moreover, we investigated the elastic properties of twisted and strained so-MoS2 and it is found that twisting and straining have little effect on the elasticity of monolayer so-MoS2 and they are all elastic isotropic. Finally, the thermodynamic properties of the Gruneisen parameter, thermal expansion coefficient, CV, entropy and lattice thermal conductivity of monolayer so-MoS2 were also studied. We used two methods of grun and phonopy-qha to analyze Gruneisen parameter and Thermal expansion coefficient, and find phonopy-qha method is better and more common. The study from hexagonal honeycomb lattice monolayer MoS2 to square lattice monolayer so-MoS2, which broadens the promising topological material systems.

Single-layer transition-metal dichalcogenides (TMDs) such as MoS2 and MoSe2 exhibit unique electronic band structures ideal for hosting many exotic spin-orbital orderings. It has been widely accepted that Rashba spin splitting (RSS) is linearly proportional to the external field in heterostructure interfaces or to the potential gradient in polar materials. Surprisingly, an extraordinary nonlinear dependence of RSS is found in semiconducting TMD monolayers under a gate field. In contrast to small and constant RSS in polar materials, the potential gradient in non-polar TMDs gradually increases with the gate bias, resulting in nonlinear RSS with a Rashba coefficient an order-of-magnitude larger than the linear one. Most strikingly, under a large gate field MoSe2 demonstrates the largest anisotropic spin splitting among all known semiconductors to our knowledge. Based on the k·p model via symmetry analysis, we identify that the third-order contributions are responsible for the large nonlinear Rashba splitting. The gate tunable spin splitting found in semiconducting pristine TMD monolayers promises future spintronics applications in that spin polarized electrons can be generated by external gating in an experimentally accessible way.

Two-dimensional boron sheets (borophenes) have been successfully synthesized in experiments and are expected to exhibit intriguing transport properties such as the emergence of superconductivity and Dirac Fermions. However, quantitative understanding of intrinsic electrical transport of borophene has not been achieved. Here, we report a comprehensive first-principles study on electron-phonon driven intrinsic electrical resistivity (\r{ho}) of emerging borophene structures. We find that the resistivity is highly dependent on the atomic structures and electron density of borophene. Low-temperature resistivity of borophene \r{ho} exhibits a universal scaling behavior, which increases rapidly with temperature T (\r{ho}~T^4), while \r{ho} increases linearly for a large temperature window T > 100 K. It is observed that this universal behavior of intrinsic resistivity is well described by Bloch-Gr\"unesisen model. Different from graphene and conventional three-dimensional metals, the intrinsic resistivity of borophenes can be easily tuned by adjusting carrier densities while the Bloch-Gr\"unesisen temperature is nearly fixed at ~100 K. Our work suggests monolayer boron can serve as an intriguing platform for realizing high-tunable two-dimensional electronic devices.

The superconducting property of platinum diselenide $(\mathrm{PtS}{\mathrm{e}}_{2})$, being a type-II Dirac semimetal, doped with electron and hole carriers has been investigated by first-principles calculations. It is found that the superconducting transition temperature ${T}_{\mathrm{c}}$ of pristine $\mathrm{PtS}{\mathrm{e}}_{2}$ is very low $(\ensuremath{\le}0.002$ K), making it infeasible as a practical superconductor. The electron doping is an effective way to increases the ${T}_{\mathrm{c}}$ of $\mathrm{PtS}{\mathrm{e}}_{2}$ to 2.15 K at $0.5{e}^{\ensuremath{-}}$ per unit cell. We further find that the mechanism of superconducting transition is the acoustic branch vibration mode softening rather than the Fermi surface nesting. Our results provide an important clue to increase superconducting temperature in the heavy transition-metal dichalcogenides and shed light on searching for new superconducting topological semimetals.

Generating electron coherence in quantum materials is essential in optimal control of many-body interactions and correlations. In a multidomain system this signifies nonlocal coherence and emergence of collective phenomena, particularly in layered 2D quantum materials possessing novel electronic structures and high carrier mobilities. Here we report nonlocal ac electron coherence induced in dispersed MoS2 flake domains, using coherent spatial self-phase modulation (SSPM). The gap-dependent nonlinear dielectric susceptibility χ(3) measured is surprisingly large, where direct interband transition and two-photon SSPM are responsible for excitations above and below the bandgap, respectively. A wind-chime model is proposed to account for the emergence of the ac electron coherence. Furthermore, all-optical switching is achieved based on SSPM, especially with two-color intraband coherence, demonstrating that electron coherence generation is a ubiquitous property of layered quantum materials.

The spinel-type LiMn1.90Mg0.05Si0.05O4 cathode materials were successfully synthesized by a citric acid-assisted sol–gel method. The sintering parameters such as sintering temperature and sintering time were investigated, and the crystal structures, morphologies, and chemical compositions of synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The results indicate that all the co-doped samples synthesized at different calcination temperatures possess the cubic spinel structure of LiMn2O4 with space group of Fd-3m and the average particle size increases with the extending of sintering time. The electrochemical performance of synthesized samples was studied by galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). Under the optimum sintering condition, the co-doped sample can deliver the initial discharge capacity of 136.2 mA h g−1 at 0.5 °C in the voltage range of 3.2–4.35 V with good capacity retention of 96.0 % after 100 cycles. When cycling at 55 °C, the optimal co-doped sample displays 91.3 % capacity retention after 20 cycles, compared to 58.6 % for the undoped sample. Most importantly, the addition of equimolar Mg2+ and Si4+ ions significantly enhances the rate performance, especially the capacity recovery performance as the charge–discharge rate restores to 0.2 from 10 °C.

The structural, elastic and electronic properties of CuYO2 have been investigated by the plane wave pseudopotential density functional theory (DFT) within the local density approximation (LDA) and the LDA + U methods. The strong on-site Coulomb repulsion of the localized Cu 3d electrons and Y 4d electrons are amended by LDA + U formalism, showing that the properties of CuYO2 are quite sensitive to the change of the value of U; the optimized choice of U is 6 eV plusing to the 3d state of the Cu atoms. Through the LDA + U correction, the calculated lattice constants, insulating gap and bulk modulus agree well with the available experimental and other theoretical data. Moreover, the anisotropies, the compressional and shear wave velocities, Young’s modulus, Poisson’s ratio, as well as the Debye temperature have been calculated for U = 6 eV, which are compared with those for U = 0 eV. It has been found that the predicted elastic constants, bulk modulus, shear modulus, acoustic velocities, anisotropy factor and Debye temperature of CuYO2 are slightly fluctuant with the increase of the U value. The calculated results also show that, the valence band of CuYO2 mainly composed of the 3d state of the Cu and the 2p state of the O, while the conduction band mainly composed of the 4d state of the Y.

The elastic, thermodynamic and electronic properties of LaF3 in tysonite structure have been investigated by density functional theory method within the frame of the local density approximation (LDA). The calculated lattice parameters of LaF3 under zero temperature and zero pressure are in good agreement with the experimental data. The calculated elastic constants also agree well with the available experimental data and other theoretical ones. The results show that the c axis of LaF3 is slight more incompressible than the a axis. It is mechanically stable up to 21 GPa. The pressure dependences of the elastic constants, Debye temperatures, Poisson’s ratio, sound velocity and mechanical stability of LaF3 have also been systematically investigated. Based on the quasi-harmonic approximation model, the thermodynamic properties of LaF3 have been studied. In the pressure range studied, the stability of the phonon is confirmed and its change tendency is revealed. The electronic structure calculations show that the tysonite phase of LaF3 is a direct band gap insulator with a value of 7.74 eV.

Carbon is a versatile element in the periodic table because of its ability to form various stable and metastable allotropes. In the present work, an orthorhombic carbon allotrope with ‘4-membered rectangles’ is predicated by Particle Swarm Optimization method at 0 GPa. Calculations indicate that this new phase is dynamically and mechanically stable although it has a high enthalpy. Its electronic and mechanical properties such as elastic constants, hardness, ideal tensile strength and shear strength are systematically studied. The results show that it is an indirect band gap crystal with a gap of 2.68 eV; in spite of its elastic anisotropy, the theoretical hardness of 76.2 GPa still makes it a potential superhard material; the obtained ideal tensile strength and shear strength are 69.0 GPa and 75.6 GPa, respectively, confirming its superhard character. The related microscopic deformation mechanisms are also detailedly analyzed through investigating the corresponding charge density, which reveals that the bonds arranged parallel to the b -axis are responsible for the breakdown of the crystal under the critical tension and shear deformations. These studies provide important information for the potential applications of the crystal once it is synthesized.

Band engineering of two-dimensional transition metal dichalcogenides (2D TMDCs) is of great significance with regard to both fundamental exploration and practical application. Here we report on a study of the band evolution of monolayer and bilayer TMDCs (WS2, WSe2, and MoS2) under vertical electric fields. Our results show that the electric field has a negligible influence on the bandgaps of monolayer TMDCs. For bilayer TMDCs, our results show that their intralayer direct bandgaps are also immune to the electric field. However, the indirect bandgaps of bilayer TMDCs can be effectively tuned by a vertical electric field. Interestingly, we find that the field tunability of the bandgap in bilayer WSe2 is much larger than those in bilayer WS2 and MoS2.

Based on first-principles calculations and theoretical analysis, we investigated various properties of pristine monolayer M2C (M = V, Nb, Ta). Firstly, we optimized the structures of monolayer M2C and computed the corresponding electronic band structures, the results show that they are metallic. And there exists Dirac points in the band structure, which make them may being potential candidates for investigating Dirac-physics-based applications. Secondly, we analyzed the phonon spectra combining with the corresponding projected phonon density of states of monolayer M2C. The results indicate that the three monolayers M2C are dynamically stable. The large energy gap between the optical phonon ZO and ZO' mode gets wider with the mass of translation metal increasing. Thirdly, the related thermodynamic properties, such as the Raman (E g, A 1g), infrared active (E u, A 2u) mode, Debye temperature, sound speed, temperature-dependent heat capacity, entropy, free energy and lattice thermal conductivity were also investigated. Finally, the planar elastic stiffness coefficients and other derived elastic properties of monolayer M2C were determined. We find that the Y s value of Nb2C and Ta2C is larger than that of monolayer Ti2C (130 N m-1). By using the uniaxial tensile, we obtained the stress-strain properties of monolayer M2C. The monolayer Ta2C has the strongest peak strength in the direction of armchair. Its maximum stress is 83GP at e arm = 0.19. Thus, those MXene materials can be considered as extremely stiff 2D materials.

We investigate the structural and elastic properties of hexagonal Ce2O3 under pressure using LDA+U scheme in the frame of density functional theory (DFT). The obtained lattice constants and bulk modulus agree well with the available experimental and other theoretical data. The pressure dependences of normalized lattice parameters a/a0 and c/c0, ratio c/a, and normalized primitive volume V/V0 of Ce2O3 are obtained. Moreover, the pressure dependences of elastic properties and three anisotropies of elastic waves of Ce2O3 are investigated for the first time. We find that the negative value of C44 is indicative of the structural instability of the hexagonal structure Ce2O3 at zero temperature and 30 GPa. Finally, the density of states (DOS) of Ce2O3 under pressure is investigated.

The traditional thin dielectric sheet approximation (TDS) method models the electromagnetic scattering by thin dielectric sheet using surface integral equation. In this approximation, only the tangential current within the dielectric sheet is considered, and the vertical component is ignored. This article proposes a method that uses the volume integral equation solution to predict the vertical volume current and hence to improve the overall solution accuracy. The formulation is based on the hybrid surface (SIE) and volume integration equation (VIE) in which, the thin dielectric is modeled with SIE, and the thin layers are modeled by VIE. It is shown that the inclusion of the vertical current component does not increase memory and solution time. Numerical examples will be provided to demonstrate the effectiveness of this approach. © Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1978–1982, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23518

In practical applications, frequency-selective surfaces (FSSs) are finite, and sometimes even curved. In this paper, we present a hybrid volume-surface integral-equation approach to analyze the transmission and reflection characteristics of finite and curved FFS structures. The hybrid integral equations are established using the surface- and volume-equivalent principles. This approach has two advantages. One is the capability of modeling arbitrarily shaped FSS structures in detail, the other one allows us to easily apply the multilevel fast multiple algorithm to speed up the solution process. The scattering characteristics and frequency responses of several FSSs are analyzed. The simulation results show that for a finite-sized FSS, reducing the radius of curvature causes amplitude variation, frequency shift, and bandwidth change in the reflection and transmission responses. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 107–112, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20738

The rewarming process of cryopreserved organs using microwave technology is analyzed by numerical simulation. The FDTD (finite-difference time-domain) method is applied to calculate the electromagnetic field in a real microwave rewarming system, composed by a cylindrical resonant cavity, an antenna source, and a frozen rabbit-kidney phantom with temperature-dependent properties. The efficiency of the FDTD codes is improved by nonuniform grid techniques and parallel algorithms. Meanwhile, an apparent specific-heat method is introduced in the temperature-field calculation. Coupling the solutions of the two fields is realized by a formerly developed algorithm. The numerical results show that in the rewarming process of the rabbit kidney phantom, the warming rate can reach 300°–500°C/min, which may prevent devitrification, but the maximum temperature difference in the sample (18 mm in radius) can reach 15°C at the end, which may cause severe thermal stress. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 201–205, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20945

This paper discusses a special imaging reconstruction problem in which the object to be reconstructed resides in a homogeneous media but consists of a known part and an unknown part. The known part is combined with the homogeneous background media to form an inhomogeneous media. The dielectric permittivity profiles are reconstructed for the unknown part using the Born iteration (BI) method. Numerical examples demonstrate that this modified BI algorithm has faster convergence and higher accuracy than the regular BI method. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 91–95, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10684

Intrinsic valley polarization can be obtained in VSe2 monolayers with broken inversion symmetry and time reversal symmetry. First-principles investigations reveal that the magnitude of the valley splitting in magnetic VSe2 induced by spin–orbit coupling reaches as high as 78.2 meV and can be linearly tuned by biaxial strain. Besides conventional polarized light, hole doping or illumination with light of proper frequency can offer effective routes to realize valley polarization. Moreover, spin–orbit coupling in monolayer VSe2 breaks not only the valley degeneracy but also the three-fold rotational symmetry in band structure. The intrinsic and tunable valley splitting and the breaking of optical isotropy bring additional benefits to valleytronic and optoelectronic applications.

Three-dimensional indoor radio-wave propagation is accurately modeled by solving the volume electric-field integral equation (VEFIE). The integral equation is discretized by the method of moments (MoM), in which the building walls, ceilings, floors, as well as any internal obstacles are represented by a collection of small volumetric cells. This discretization is capable of modeling a 3-D room structure to fine details. The solution to the MoM matrix equation is facilitated by the multilevel fast multipole algorithm (MLFMA), which significantly reduces memory requirements and CPU time. Numerical examples are shown to demonstrate the accuracy of the solution and the capability of modeling dielectric structures of nearly realistic sizes. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 168–175, 2001.

A combined solution of an electromagnetic (EM)-wave equation and head transfer equation is presented to analyze the microwave rewarming process of cryopreserved tissues. The solution process starts with an initial temperature of the tissue. The EM-field distribution inside the tissue is determined first by solving hybrid surface-volume integral equations. This solution provides a thermal source term for the heat-transfer equation. A finite-difference scheme is then applied to solve the heat-transfer equation, which determines the temperature distribution inside the tissue for the next time step. Since the tissue's electrical characteristics (/spl epsiv/ and /spl sigma/) are functions of temperature, their values are then updated based on the new temperature distribution. The iteration continues until a termination condition is satisfied. This combined iterative solution of wave equation and heat-transfer equation allows one to model the complex rewarming process. Numerical results are presented to demonstrate the application of the combined analysis approach.

FISC (Fast Illinois solver code), co-developed by the Center for Computational Electromagnetics, University of Illinois, and DEMACO, is designed to compute the RCS of a target described by a triangular-facet file. The problem is formulated using the method of moments (MoM), where the Rao, Wilton, and Glisson (1982) basis functions are used. The resultant matrix equation is solved iteratively by the conjugate gradient (CG) method. The multilevel fast multipole algorithm (MLFMA) is used to speed up the matrix-vector multiplication in the CG method. The complexities for both the CPU time per iteration and the memory requirements are of O(Nlog N), where N is the number of unknowns. A 2.4-million unknown problem is solved in a few hours on the SGI GRAY origin 2000 at NCSA of the University of Illinois at Urbana-Champaign.

An accurate and efficient technique called the thin-stratified medium fast-multipole algorithm (TSM-FMA) is presented for solving integral equations pertinent to electromagnetic analysis of microstrip structures, which consists of the full-wave analysis method and the application of the multilevel fast multipole algorithm (MLFMA) to thin stratified structures. In this approach, a new form of the electric-field spatial-domain Green's function is developed in a symmetrical form which simplifies the discretization of the integral equation using the method of moments (MoM). The patch may be of arbitrary shape since their equivalent electric currents are modeled with subdomain triangular patch basis functions. TSM-FMA is introduced to speed up the matrix-vector multiplication which constitutes the major computational cost in the application of the conjugate gradient (CG) method. TSM-FMA reduces the central processing unit (CPU) time per iteration to O(N log N) for sparse structures and to O(N) for dense structures, from O(N/sup 3/) for the Gaussian elimination method and O(N/sup 2/) per iteration for the CG method. The memory requirement for TSM-FMA also scales as O(N log N) for sparse structures and as O(N) for dense structures. Therefore, this approach is suitable for solving large-scale problems on a small computer.

The recursive T -matrix algorithm is applied to Monte Carlo simulations of multiple scattering by random distribution of dielectric spheres. The method is a fast algorithm for calculating the exact solution of Maxwell's equations for a large number of scattering objects. The extinction rate is calculated by averaging over many realizations. The computed results are compared with those from analytic approximations, namely, the quasi-crystalline approximation.

In the solution of an integral equation using the conjugate gradient (CG) method, the most expensive part is the matrix-vector multiplication, requiring O(N2) floating-point operations. The fast multipole method (FMM) reduced the operation to O(N15). In this article we apply a multilevel algorithm to this problem and show that the complexity of a matrix-vector multiplication is proportional to N (log(N))2. © 1994 John Wiley & Sons, Inc.

We develop a new algorithm to expedite the matrix-vector multiplication in using the conjugate gradient method to solve the linear algebraic equation of scattering by a cluster of particles. We compare this method of solving the scattering problem with two other methods. One is our previously developed method, called recursive aggregate T-matrix method. The second one is the direct use of the conjugate gradient method. Our new method is shown to have reduced computational complexity as well as memory requirement compared to the use of the conjugate gradient directly to solve the linear algebraic equation of scattering. © 1993 John Wiley & Sons, Inc.

A new algorithm is proposed to solve the volume integral equation whereby the scatterer is first divided into N subscatterers. Smaller problems are nested within larger problems using the Huygens equivalence principle. The resultant algorithm has reduced computational complexity whose CPU time is proportional to N1.5. © 1993 John Wiley & sons, Inc.

A feast recursive algorithm is used to compute the scattering properties of a finite array of strip gratings on a dielectric slab. this algorithm has a computational complexity of O(N log/sup 2/ N) for one incident angle and O(N/sup 2/ log N) for N incident angles. It uses plane wave basis for expanding the incident wave and the scattered wave. The scattered wave is expanded in terms of a Sommerfeld-type integral with spectral distribution along a vertical branch cut, rendering its expansion very efficient. To validate the scattering solution obtained using the recursive algorithm, comparisons with the method of moments are illustrated. The current distributions on the strips and scattering patterns are both presented. Since this algorithm has reduced computational complexity and is fast compared to other conventional methods, it can be used to analyze very large strip arrays. Scattering solution of a 50-wavelength wide strip is illustrated. >

In this work, the realization of AlxGa1−xAs/GaAs two‐step barrier diode is presented. Experimental observation on the current–voltage characteristics of the two‐step barrier diode is reported. At both room temperature and 77 K, it shows a strong negative differential resistance under forward bias while no similar phenomenon was observed under reverse bias. Such an asymmetric current–voltage characteristic would open the possibility of negative differential resistance in an ac field in the absence of a dc bias. Theoretical simulation and experimental current–voltage characteristics are compared and discussed.

[1] The surface integral equation approach and the hybrid surface-volume integral equation approach are compared for solving the problem of electromagnetic scattering by conducting objects with dielectric coating. The surface integral equation is formulated by the PMCHW method, and it is efficient for modeling bulk material scattering. The hybrid surface-volume integral equation approach is better conditioned for the volume scattering problems. For a special class of problems in which the dielectric coating is electrically thin (one to two grid sizes), the numbers of unknowns needed by the two approaches are of the same order, and the surface-volume integral equation approach converges significantly faster than the pure surface integral equation approach. Several numerical examples are given, and the results showed good agreements with the above statement.

[1] A high-order method of moment solution with quadrature-point-based sampling is presented for the solution of the volume electric field integral equation for the scattering of inhomogeneous dielectric bodies. The proposed scheme efficiently allows for the material profile to be inhomogeneous within a curvilinear cell. It is demonstrated that the method leads to exponential convergence in both the radar cross section (RCS) and the volume current density. It is also demonstrated that the method can be more efficient than surface field integral equation formulations for thin-material scattering.

The fast multipole method is an effective way to expedite iterative solutions of integral equations for electrodynamic and elastodynamic problems. Iterative solvers, such as the conjugate gradient method, require matrix vector multiplies, and for dense matrices, these matrix-vector multiplies constitute the predominant computational cost as well as requiring a large memory. The fast multipole method is based on the translation of multipoles from one coordinate system to another, which is achieved by using translation matrices. However, the mere use of translation matrices does not reduce the computational cost nor the memory requirement for dynamic problems involving surface scatterers. For such problems, the crucial step in the fast multipole method is the diagonalization of the translation operators. The translation matrix for the three dimensional Helmholtz wave equation has been successfully diagonalized using an alternative and succinct method. The method reveals the relationship between the translation matrices and their representation of the translation group. A diagonalization is expected under a plane-wave basis for the representation since a plane-wave basis forms an irreducible representation for the translation group. Hence, the diagonalization of the translation matrices from the spherical harmonic representation can be viewed as a series of similarity transforms. The result can be used in the fast multipole method and the multilevel fast multipole method where multiple scattering involves interaction between multipoles.

A fast far-field approximation (FAFFA) is developed to estimate the RCS of conducting scatterers. This method accounts for the interaction between subscatterers in two ways, depending on the electrical distance between the subscatterers. The interactions of subscatterers separated by a large electrical distance are computed in three stages: (1) aggregation, which computes the total field at a group center due to the subscatterers of the group; (2) translation, which translates the field from one group center to another; and (3) disaggregation, which distributes the field in a group center to each subscatterer in the group. Two strategies are employed to accelerate the computation in the above three stages. One is the use of far-field approximation to simplify the computation in the translation stage; the other is the use of interpolation and smoothing techniques, which reduces the complexity of aggregation and disaggregation. The overall computational complexity for a matrix-vector multiplication is of the order of N1.33, and the memory requirement is of order N. Numerical results show that this method can predict a RCS that is very close to exact solution, and that the method can be applied to objects with very large electrical sizes. © 1995 John Wiley & Sons. Inc.

A truncated, nonuniform, finite array of strips does not have a closed-form solution. Using translational symmetry, a recursive algorithm that calculates the scattering solution with N log2 N computational complexity is described. The current distribution for the Hz polarization shows small-length-scale oscillations not present in the Ez polarization.

The stacked, self-assembled and vertically aligned quantum dot superlattices are fabricated by alternating growth of substrate and epitaxial materials, the stress/strain fields in the buried quantum dots can influence their optical and piezoelectric properties and mechanical stability. The distributions of stresses, strains, hydrostatic strains and biaxial strains in buried strain self-assembled Ge/Si semiconductor quantum dot are investigated based on the theory of anisotropy elasticity and also compared with those of free-standing quantum dot. The sameness and difference of the stresses/strains between the buried and the free-standing quantum dots, and the influence of cap layer on the stress/strain fields in quantum dots are given.

The dependence of total strain energy of a pyramidal self-assembled Ge/Si semiconductor quantum dot on the aspect ratio, is investigated. The free energy consisting of the strain energy and surface energy is defined, and used to study the equilibrium shape of the systems. The results show that the strain energy of thesystem decreases with the increasing aspect ratio, and under the requirement ofminimum total free energy, the quantum dot with a given volume will take a particular height-to-width aspect ratio,i.e.the equilibrium aspect ratio. Meanwhile, the distributions of the stress, hydrostatic strain and biaxial strain are presented. These can serve as a basis for interpretation of experiments on strain self-assembled quantum dots.

A Brownian motion theory of hopping mobility has been formulated based on the one-dimensional hopping conduction model between localized states. The probability of hopping in the direction of the applied electric field and the duration of the hop between the localized states are assumed to be field dependent and thermally activated. The general form of the Brownian motion mobility model fitted well with the time of flight results measured in the low field regime and for most part of the mobility data extracted from the space charge limited conduction applied to tris-(8-oxyquinolato) aluminum (Alq3) in higher field regime. The Brownian motion model can be modified in order to account for the dependence of charge mobility in the higher electric field regime and at higher temperatures. The variation of charge mobility with applied electric field was fitted using the Brownian motion theory. The hopping time and the hopping distance were extracted from the fit and found to be about 3ps and 0.9nm, respectively ...