Anisotropic Layered Structures Research Articles

A novel method for determining the resistivity of compressed superconducting materials

The measurement of resistivity in a compressed material within a diamond anvil cell presents significant challenges. The high-pressure experimental setup makes it difficult to directly measure the size changes induced by pressure in the three crystallographic directions of the sample. In this study, we introduce a novel and effective method that addresses these technical challenges. This method is anticipated to offer a valuable foundation for high-pressure investigations on quantum materials, particularly those with anisotropic layered structures.

Transient and steady-state temperature rise in three-dimensional anisotropic layered structures in pump-probe thermoreflectance experiments

Recent developments of the pump-probe thermoreflectance methods (such as the beam-offset and elliptical-beam approaches of the time-domain and frequency-domain thermoreflectance techniques) enabled measurements of the thermal conductivities of in-plane anisotropic materials. Estimating the temperature rise of anisotropic layered structures under surface heating is critically important to make sure that the temperature rise is not too high to alias the signals in these experiments. However, a simple formula to estimate the temperature rise in three-dimensional (3D) anisotropic layered systems heated by a non-circular laser beam is not available yet, which is the main problem we aim to solve in this work. We first re-derived general formalisms of the temperature rise of a multilayered structure based on the previous literature work by solving the 3D anisotropic heat diffusion equation in the frequency domain. These general formalisms normally require laborious numerical evaluation; however, they could be reduced to explicit analytical expressions for the case of semi-infinite solids. We then extend the analytical expressions to multilayered systems, taking into account the effect of the top layers. This work not only enhances our understanding of the physics of temperature rise due to surface laser heating but also enables quick estimation of the peak temperature rise of 3D anisotropic layered systems in pump-probe thermoreflectance experiments and thus greatly benefits the thermoreflectance experiments in choosing the appropriate heating power intensity for the experiments.

Mixed boundary–transmission problems for composite layered elastic structures

We investigate mixed type boundary–transmission problems of the generalized thermo‐electro‐magneto‐elasticity theory for complex elastic anisotropic layered structures containing interfacial cracks. This type of problems is described mathematically by systems of partial differential equations with appropriate transmission and boundary conditions for six dimensional unknown physical field (three components of the displacement vector, electric potential function, magnetic potential function, and temperature distribution function). We apply the potential method and the theory of pseudodifferential equations and prove uniqueness and existence theorems of solutions to different type mixed boundary–transmission problems in appropriate Sobolev spaces. We analyze smoothness properties of solutions near the edges of interfacial cracks and near the curves where different type boundary conditions collide.

Guided wave field calculation in anisotropic layered structures using normal mode expansion method

The guided wave technique is commonly used in structural health monitoring as the guided waves can propagate far in the structures without much energy loss. The guided waves are conventionally generated by the surface-mounted piezoelectric wafer active sensor (PWAS). However, there is still lack of understanding of the wave propagation in layered structures, especially in structures made of anisotropic materials such as carbon fiber reinforced polymer (CFRP) composites. In this paper, the Rayleigh-Lamb wave strain tuning curves in a PWAS-mounted unidirectional CFRP plate are analytically derived using the normal mode expansion (NME) method. The excitation frequency spectrum is then multiplied by the tuning curves to calculate the frequency response spectrum. The corresponding time domain responses are obtained through the inverse Fourier transform. The theoretical calculations are validated through finite element analysis and an experimental study. The PWAS responses under the free, debonded and bonded CFRP conditions are investigated and compared. The results demonstrate that the amplitude and travelling time of wave packet can be used to evaluate the CFRP bonding conditions. The method can work on a baseline-free manner.

Layer-resolved absorption of light in arbitrarily anisotropic heterostructures

We present a generalized formalism to describe the optical energy flow and spatially resolved absorption in arbitrarily anisotropic layered structures. The algorithm is capable of treating any number of layers of arbitrarily anisotropic, birefringent, and absorbing media and is implemented in an open access computer program. We derive explicit expressions for the transmitted and absorbed power at any point in the multilayer structure, using the electric field distribution from a 4 $\times$ 4 transfer matrix formalism. As a test ground, we study three nanophotonic device structures featuring unique layer-resolved absorption characteristics, making use of (i) in-plane hyperbolic phonon polaritons, (ii) layer-selective, cavity-enhanced exciton absorption in transition metal dichalcogenide monolayers, and (iii) intersubband-cavity polaritons in quantum wells. Covering such a broad spectral range from the far-infrared to the visible, the case studies demonstrate the generality and wide applicability of our approach.

Defect Engineering for Photocatalysis: From Ternary to Perovskite Oxynitrides

AbstractExploiting defects and specific anion non‐stoichiometry in mixed‐anion semiconductors is a challenge that remains at the forefront of photocatalytic and photoelectrochemical water splitting research. The interplay between of oxygen and nitrogen defects in perovskite oxynitrides specifically creates exciting, yet complex, opportunities for optimizing phase stability, ionic conduction and anion order in these materials. In this Minireview we highlight the recent advances in defect engineering in oxynitride semiconductors, such as anion content/non‐stoichiometry, surface modification, cation doping and formation of anisotropic layered structures, on photocatalytic and photoelectrochemical water splitting. Avenues warranting further investigation are discussed.

Fast Calculation of Scattering in Planar Uniaxial Anisotropic Multilayers

In this paper, the generalized recursive formulations of the finite difference time domain (FDTD) for updating the electric and magnetic fields in the multi-layer anisotropic media are derived with a uniaxial perfectly matched layer. The stability condition of the proposed method is clearly analyzed and verified. Then this method is used to calculate the three-dimensional complex scattering fields in planar multilayered anisotropic microstructures with optical axis perpendicular to the layered interface and the scattering fields of arbitrary shape scatters in the anisotropic layered structures. The electric field induced by the sine dipole source is calculated in the spatial domain and the corresponding spectral domain results are achieved through Fourier transform. The scattering field of composite materials with submillimeter thicknesses used in the industrial engineering is calculated using a terahertz wave with operation frequency of 0.3 THz. Robustness of the derived formulations for the complex uniaxial anisotropic media is verified by comparing with the COMSOL software, which is based on FEM analysis. The comparison of memory and CPU time shows the efficiency of the proposed FDTD method. Finally, the scattering fields of different scatters buried in multilayer anisotropic media are studied. So it is expected to become an effective simulation tool for dealing with complex electromagnetic environment in the future, such as abnormal detection of aircraft coating materials and detection of hidden target and so on.

Generalised semi-analytical method for excitability curves calculation and numerical modal amplitude analysis for Lamb waves

The paper presents an efficient and exact method for the calculation of excitability curves and for the analysis of numerical models for guided waves. The proposed procedure makes use of the wave equation and through-thickness-only discretisation of anisotropic, layered plates to obtain the Lamb wave amplitude characteristics. Thereby, the method can be used for any arbitrarily selected anisotropic (layered structures, such as composites) material in a straightforward manner. A general framework for the proposed analysis is given, along with application examples. For this purpose, orthogonality conditions based on the reciprocity theorem are derived for the numerical model. Although the developed mathematical framework is verified and application examples are given based on the local interaction simulation approach for elastic waves propagation, the proposed methodology can easily be adopted for other numerical methods (eg, finite elements and cellular automata for elastodynamics). The method can also be used to study the influence of discretisation parameters on excitability curves estimates.

Extended Yeh’s method for optically active anisotropic layered media

We extend the original method of Yeh [J. Opt. Soc. Am.69, 742 (1979)JOSAAH0030-394110.1364/JOSA.69.000742] for calculating the reflection and transmission from anisotropic layered structures to media exhibiting not only dielectric, but also magnetic anisotropy, as well as optical activity. We likewise establish the relationship between the optical activity and gyration tensors from the two most used constitutive relations for optically active media and illustrate the extended Yeh's method on a practically important example.

General Elastic Surface Waves in Anisotropic Layered Structures

A solution of homogeneous equations of elasticity equations, which describes surface waves and is based on the summation of plane waves, is presented. Bibliography: 15 titles.

Elementary Green function as an integral superposition of Gaussian beams in inhomogeneous anisotropic layered structures in Cartesian coordinates

Elementary Green function as an integral superposition of Gaussian beams in inhomogeneous anisotropic layered structures in Cartesian coordinates

Influence of structure on the ultralow friction of layered coatings deposited via ion-beam sputtering

The influence of technology on the properties of thin films with anisotropic layered structures is investigated. Electron diffraction and electron microscopy investigations of the structure, as well as the testing of tribotechnical properties, are performed. It is established that a deposited wear-resistant sublayer and doped coating materials enhance the durability to a considerable extent and create ultralow friction. A generalized model of dissipationless mass transfer, which does not involve resistance forces affecting motion, is developed. Ultralow friction, superconductivity, and superfluidity are found to be cognate phenomena related to the phase transition of particles at the critical value of a characteristic parameter (overcoming the potential barrier). In the case of dissipationless motion without resistance forces, the energy-efficient arrangement of particles in the crystal lattice is their location in the van der Waals space of layered systems, where the phenomena under study can be predicted.

The study of electronic states in highly anisotropic layered structures with stage ordering

The study of electronic states in highly anisotropic layered structures with stage ordering

Synthetic magnetic field effects on neutral bosonic condensates in quasi-three-dimensional anisotropic layered structures

We discuss a system of dilute Bose gas confined in a layered structure of stacked square lattices (slab geometry). A derived phase diagram reveals a non-monotonic dependence of the ratio of tunneling to on-site repulsion on the artificial magnetic field applied to the system. The effect is reduced when more layers are added, which mimics a two- to quasi-three-dimensional geometry crossover. Furthermore, we establish a correspondence between anisotropic infinite (quasi three-dimensional) and isotropic finite (slab geometry) systems that share exactly the same critical values, which can be an important clue for choosing experimental setups that are less demanding, but still leading to the identical results. Finally, we show that the properties of the ideal Bose gas in a three-dimensional optical lattice can be closely mimicked by finite (slab) systems, when the number of two-dimensional layers is larger than ten for isotropic interactions or even less, when the layers are weakly coupled.

Gaussian beams in inhomogeneous anisotropic layered structures

Summary Gaussian beams concentrated close to rays of high-frequency seismic body waves propagating in an inhomogeneous anisotropic layered structure are studied. The amplitude proflles of the Gaussian beam along the plane perpendicular to the ray and along the plane perpendicular to the slowness vector are Gaussian. The Gaussian proflle is controlled by the 2 £ 2 complex-valued matrix M of the second derivatives of the travel-time fleld at any point of the ray. The matrix M can be simply determined at any point of the ray if the ray-propagator matrix along the ray is known and if the value of M is specifled at a selected point of the ray. The ray-propagator matrix can be determined by dynamic ray tracing along the ray. In inhomogeneous anisotropic medium, the dynamic ray tracing can be performed alternatively in several coordinate systems: in global Cartesian coordinates, in ray-centred coordinates and in wavefront orthonormal coordinates. In addition, also simplifled dynamic ray tracing in global Cartesian coordinates can be used, which reduces the number of equations of the dynamic ray tracing system. The derived expressions for the Gaussian beams are applicable to general 3-D inhomogeneous layered structures of arbitrary anisotropy (specifled by upto 21 independent position-dependent elastic moduli). Possible simpliflcation of the procedure are outlined.

Dielectric tensor measurement from a single Mueller matrix image

A technique for measuring dielectric tensors in anisotropic layered structures, such as thin films of biaxial materials, is demonstrated. The ellipsometric data are collected in a quasi-monochromatic Mueller matrix image acquired over a large range of incident and azimuthal angles by illuminating a very small area on the sample with a focused beam from a modulating polarization state generator. After the beam interacts with the sample, the reflected and/or transmitted light is collected using an imaging polarization state analyzer. An image of the exit pupil of a collection objective lens is formed across a CCD such that each pixel collects light from a different angle incident on the sample, thus acquiring ellipsometric data at numerous incident angles simultaneously. The large range of angles and orientations is necessary to accurately determine dielectric tensors. The small but significant polarization aberrations of the low-polarization objective lenses used to create and collect the focused beams provide a significant challenge to accurate measurement. Measurements are presented of a thin-film E-type polarizer and a stretched plastic biaxial film.

Birefringence in one-dimensional finite photonic bandgap structure

The spectral and dispersive behaviors of anisotropic layered structures forming a one-dimensional polarization-dependent photonic bandgap are discussed. The finite dimension of the structure is taken into account. Interesting field-localization properties are found when the optical axes of layers are not aligned each with each other, i.e., principal axes of layers are rotated with respect to each other. The field-localization behavior is also discussed through a suitable definition of density of modes for the anisotropic layered structure. A discussion about the behavior of the dispersion law for such a finite periodical structure is also presented.

A unified formalism using effective surface permittivity to study acoustic waves in various anisotropic and piezoelectric multilayers.

A unified formalism is presented that uses the effective surface permittivity (ESP) to study surface acoustic waves (SAW) in layered substrates and guided waves in layered plates. Based on known mathematical tools, such as ordinary differential equation and transfer matrix, a generalized surface impedance (GSI) concept is developed and exploited to investigate the acoustic propagation in various anisotropic and piezoelectric layered structures. The ESP function, originally defined for the surface of a homogeneous and semi-infinite piezoelectric substrate, is extended to both the top surface of and an interface in a layered half space, as well as to either surface of a finite-thickness plate. General ESP expressions for all mentioned configurations are derived in terms of an equivalent GSI matrix. It is shown that, when using the appropriate GSI matrices, the same form of the ESP expressions applies no matter whether the structure is a homogeneous half space alone or coated with a layered plate or a layered plate alone. GSI matrices are explicitly given in terms of the bulk partial mode solutions for a substrate and via the transfer matrix for a plate. Modified GSI matrices for structures consisting of both a plate and a substrate are also specified. Analytical development is fully detailed to suit program implementation. To illustrate its versatility, the formalism is also applied to two-substrate configurations, allowing one to analyze guided waves in a plate sandwiched between and interfacial waves existing along the boundary of two different media. Numerical examples are given to illustrate the spectrum features that the ESP shows for various structures. Deduced ESP expressions allow one to locate directly all piezoelectrically active waves in any structure including at least one piezoelectric layer. Acoustic modes that are not piezoelectrically active and those in non-piezoelectric materials can be also obtained by using the intermediate results, such as derived GSI matrices.

Zero-field polarized neutron optics and new possibilities

Some possibilities of the use of magnetically anisotropic layered structures are pointed out. Remanent supermirrors that require no field for saturation have recently been developed in several laboratories. Zero-field polarizers are unique in forming polarized beams and for analysis of polarization. Zero-field 3D polarizer made of two remanent benders magnetized in mutually perpendicular directions is suggested. Such a device used as analyzer will allow 3 components of the polarization vector to be measured without any magnetic systems, spin flippers or spin turners. In principle, one can work with polarized neutrons without any external magnetic fields in the whole region of the instrument (zero-field instrumentation).

Acoustoelastic effect in anisotropic layered structures

Mechanical stress alters the velocity of acoustic waves, a phenomenon known as AE (acoustoelastic) effect, which is of particular importance for the wave propagation in layered heterostructures. In order to calculate the AE effect of layered systems in the presence of stress we extended the transfer-matrix method for acoustic wave propagation by considering the change of the density, the influence of residual stress, and the modification of the elastic stiffness tensor by residual strain and by third-order constants. The generalized method is applied to the calculation of the angular dispersion of the AE effect for transverse bulk modes and surface acoustic waves on the Ge(001) crystal cut. The AE effect is found to depend significantly on the propagation direction and can even change sign. The maximum velocity change occurs for transversally polarized waves propagating parallel to the [110] direction. For the layered Ge/Si(001) system the AE effect is investigated for Love modes propagating in the [100] and [110] directions. The AE effect increases rapidly with increasing layer thickness and reaches almost its maximum value when the wave is still penetrating into the unstressed substrate. For higher-order Love modes the increase of the AE effect is even steeper and, furthermore, can reach higher values.