Isotropic Layer Research Articles

Atomic layer etching of Al2O3 with NF3 plasma fluorination and trimethylaluminum ligand exchange

In this study, a cyclic isotropic plasma atomic layer etching (ALE) process was developed for aluminum oxide that involves fluorination with NF3 plasma and ligand exchange with trimethylaluminum (TMA). The isotropic plasma ALE consists of two steps: fluorination and removal. During the fluorination step, the Al2O3 surface was fluorinated to AlOFx with NF3 plasma at 100 °C. The formation of the AlOFx layer was confirmed by x-ray photoelectron spectroscopy analysis, and the atomic fraction of fluorine on the surface was saturated at 25% after 50 s of plasma fluorination. The depths of the fluorinated layers were in the range of 0.79–1.14 nm at different plasma powers. In the removal step, the fluorinated layer was removed by a ligand exchange reaction with TMA at an elevated temperature range of 250–480 °C. The etch per cycle (EPC) was 0.20–0.30 nm/cycle and saturated after 30 s in the temperature range of 290–330 °C. No etching was observed below 250 °C, and the EPC increased in the temperature range of 250–300 °C during the removal step with the ligand exchange reaction and reached the maximum at 300 °C. Then, the EPC was significantly reduced at high temperatures, possibly due to TMA decomposition. The fluorine atomic fraction on the surface was reduced to 14% after the removal. In conclusion, Al2O3 was successfully etched at the atomic scale by the cyclic plasma ALE process. The average surface roughness of Al2O3 was reduced from 8.6 to 5.3 Å after 20 cycles of etching.

The study of sound transmission through sandwich cylindrical shells with circumferentially corrugated cores filled with porous materials

This paper presents an analytical study on the sound wave propagation across a sandwich cylindrical shell with a corrugated core filled with porous materials. The outer layer is subjected to oblique plane waves, and a subsonic flow is traveling in the exterior medium. To describe the porous medium, the extended full method (EFM) is employed, which calculates the displacement and stress fields across the layer. Next, the corrugated core is modeled as a series of translational and rotational springs, and the mass of the core is uniformly distributed on the inner and outer isotropic shells. Besides, the first-order shear deformation theory is used to model the dynamic response of the isotropic layers. The proposed formulation is validated by comparing the current approach to previous studies on the proposed literature. The vibroacoustic effects of various parameters, such as porosity, types of the porous materials, the thickness of the corrugated core, structural damping factor, incident angle, and Mach number of the external flow, are analyzed. Also, the sound insulation capability of the structure with and without the porous medium is carefully studied.

On elastic clamping boundary conditions in plate models describing detaching bilayers

Elastic clamping boundary conditions are derived, which describe root rotations and root displacements in plate models used to analyze detaching bimaterial layers subjected to arbitrary end loadings. The elasticity technique uses the reciprocity theorem and J-integral calculations and is applicable to isotropic and orthotropic bimaterial layers of different thicknesses, also with extreme elastic constants and mismatch. Explicit closed form expressions for all clamping coefficients are derived for bimaterial isotropic layers with mid-thickness cracks and zero second Dundurs’ parameter; the derivation relies on existing solutions for energy release rate and local fields. Closed form expressions are derived for the most relevant coefficients in homogeneous symmetric orthotropic layers and thin isotropic layers on isotropic half planes. The technique is applicable to general cases using analytical or numerical results for the energy release rate.

Appearing ZGV point in the first flexural branch of Lamb waves in multilayered plates

Appearing the zero group velocity (ZGV) point belonging to the first quasi flexural branch (A1) of Lamb waves propagating in the multilayered traction-free plates containing homogeneous isotropic layers is observed and analyzed; in contrast to the previously studied homogeneous isotropic plates admitting ZGV points that may belong to the higher flexural modes (A2, A3, …) and higher symmetric modes. The detected ZGV point in a multilayered traction-free plate leads to the transverse quasi resonance occurred at the lower frequency than the previously studied resonance associated with the first symmetric mode (S1) and especially higher symmetric and flexural modes. The analysis is done by the combined method comprising Cauchy sextic formalism and the exponential fundamental matrix method.

Omnidirectional nonreciprocal absorber realized by the magneto-optical hypercrystal.

Photonic bandgap design is one of the most basic ways to effectively control the interaction between light and matter. However, the traditional photonic bandgap is always dispersive (blueshift with the increase of the incident angle), which is disadvantageous to the construction of wide-angle optical devices. Hypercrystal, the photonic crystal with layered hyperbolic metamaterials (HMMs), can strongly modify the bandgap properties based on the anomalous wavevector dispersion of the HMM. Here, based on phase variation competition between HMM and isotropic dielectric layers, we propose for the first time to design nonreciprocal and flexible photonic bandgaps in one-dimensional photonic crystals containing magneto-optical HMMs. Especially the zero-shift cavity mode and the blueshift cavity mode are designed for the forward and backward propagations, respectively. Our results show maximum absorption about 0.99 (0.25) in an angle range of 20-75 degrees for the forward (backward) incident light at the wavelength of 367 nm. The nonreciprocal omnidirectional cavity mode not only facilitates the design of perfect unidirectional optical absorbers working in a wide-angle range, but also possesses significant applications for all-angle reflectors and filters.

Диссипативные свойства трехслойных композитных структур. 2. Метод решения

Object and purpose of research. This paper discusses a three-layered plate made up by two rigid anisotropic layers and soft isotropic medium layer of viscoelastic polymer. Each of the two rigid layers is an anisotropic structure formed by a finite number of arbitrarily oriented orthotropic viscoelastic composite layers. The purpose of this work is to develop a numerical solution method for decaying vibration equations of three-layered unsupported rectangular plates. Materials and methods. The system of algebraic equations is constructed as per Ritz method using Legendre polyno-mials as coordinate functions. The first step is to find real solutions. To find complex natural frequencies of the system, their initial values are taken as real natural frequencies thus found, with subsequent calculation of complex frequencies as per the method of third-order iterations. Main results. This paper discusses the results of convergence analysis for a numerical solution of differential motion equations with respect to an unsupported rectangular three-layered plate with transversally isotropic rigid layers. The material for these rigid lay-ers is unidirectional carbon-reinforced plastic (CRP) with elastic dissipation properties, within the investigated range of frequencies and temperatures, independent on its vibration frequency. For the soft isotropic medium layer of viscoelastic polymer, temperature-frequency curve governing the real part of complex elasticity modulus and mechanical loss coefficient is taken into account. Validation of the mathematical model and the numerical solution method, the comparison of calculated and experimental natural frequencies and mechanical loss coefficients for the two variants of three-layered unsupported plate has demonstrated their good correlation. Conclusion. This paper suggests and validates the numerical solution method for decaying vibration equations of three-layered unsupported rectangular plate made up by two rigid monoclinic layers and soft isotropic medium layer of viscoelastic polymer.

Approximate structures of thermoelastic fields induced by a penny-shaped thermal-medium crack in a transversely isotropic layer

It is of practical significance to investigate thermoelastic fields at the front of a penny-shaped crack embedded in a material with finite thickness. The existing works always focus on numerical solutions of the derived integral equations and approximate solutions are seldom studied. In the present study, the problem of a penny-shaped crack in a transversely isotropic layer is addressed under uniform heat flow and mechanical loadings. The extended thermal-medium crack model with a nonlinear relation between heat flow of crack interior and crack opening displacement is used to capture the effect of heat conduction inside crack. The Hankel transform technique is applied to solve governing partial differential equations, then Fredholm integral equations of the second kind are derived. Applying integral kernel series expansion method, approximate solutions to the derived Fredholm integral equations are analyzed and determined. Approximate structures of thermoelastic fields around penny-shaped crack are further obtained. Theoretical analysis and numerical results are carried out to show the applicability of approximate solutions. The observations reveal that the determined approximate solutions have some significance to a practical engineering application. The advantages of the developed methods are to make approximate solutions visible, and some penny-shaped crack problems of thermo-piezoelectric and thermo-magnetoelectroelastic layers could be solved similarly.

Sedimentation of colloidal plate-sphere mixtures and inference of particle characteristics from stacking sequences

We investigate theoretically the effect of gravity on a plate-sphere colloidal mixture by means of an Onsager-like density functional to describe the bulk, and sedimentation path theory to incorporate gravity. We calculate the stacking diagram of the mixture for two sets of buoyant masses and different values of the sample height. Several stacking sequences appear due to the intricate interplay between gravity, the sample height, and bulk phase separation. These include the experimentally observed floating nematic sequence, which consists of a nematic layer sandwiched between two isotropic layers. The values of the thicknesses of the layers in a complex stacking sequence can be used to obtain microscopic information of the mixture. Using the thicknesses of the layers in the floating nematic sequence we are able to infer the values of the buoyant masses from the colloidal concentrations and vice versa. We also predict new phenomena that can be experimentally tested, such as a nontrivial evolution of the stacking sequence by increasing the sample height in which new layers appear either at the top or at the bottom of the sample.

2D Green’s functions for an elastic layer on a rigid support loaded by an internal point force

The problem of a homogeneous isotropic elastic layer resting on a rigid base and loaded by an internal point force is analytically investigated under plane strain conditions. The displacement field is sought as the superposition of a fundamental solution (doublet state) and a homogeneous solution which allows satisfying the boundary conditions at the upper and lower boundaries of the layer. The displacement field is represented through convergent Fourier integral transforms. Once the closed form solution in the transformed domain is found, the displacement and stress fields are assessed by numerical inversion of transforms. Results concerning both the displacements and stresses for different positions of the load application point are reported and compared to FEM solution, finding very good agreement. The solutions obtained for horizontal and vertical point forces define the Green’s functions for the layer, which can be used to describe the mechanical interaction between the layer and an embedded body. As a striking application, the interaction between an elastic layer and an embedded laterally loaded wall or diaphragm is finally addressed, finding the contact pressure and, in turn, the internal forces in the diaphragm.

Plasma atomic layer etching for titanium nitride at low temperatures

Isotropic plasma atomic layer etching (ALE) was developed for titanium nitride (TiN) through a three-step process: plasma oxidation, plasma fluorination, and thermal removal at low temperatures. In the plasma oxidation step, TiN was oxidized to form a titanium oxide (TiO2) layer with O radicals generated from O2 plasma at 100 °C. The TiO2 thickness was found to be saturated with plasma after an exposure time of 300 s, and the saturated thickness increased from 0.29 to 1.23 nm with increasing temperature and RF power. In the plasma fluorination step, the TiO2 layer was converted to titanium oxyfluoride (TiO2−xFx) with F radicals generated in the CF4 plasma at 100 °C. The F atomic fraction on the surface was found to be saturated at 12%, with RF powers below 15 W in the fluorination step. The process temperature was increased during the removal step, and the TiO2−xFx formed by plasma fluorination was completely removed above 150 °C. The removal rates of TiN ranged from 0.24 to 1.71 nm/cycle by controlling the thickness of the TiO2 layer determined earlier. The average surface roughness of TiN decreased from 1.27 to 0.26 nm after 50 cycles of the ALE process. This work demonstrated that plasma oxidation and fluorination with thermal removal can remove TiN at the atomic scale at low temperatures for atomic-scale three-dimensional devices.

Residual stress analysis of electrodeposited thick CoMnP monolayers and CoMnP/Cu multilayers

Residual stress in electroplated hard magnetic layers is crucial to the stability and durability in end applications. We electrodeposited highly HCP (002) textured CoMnP hard magnetic layers on copper substrate. We characterized and compared the residual stresses of mono- and multi-layered configurations using sin2ψ X-ray diffraction (XRD) for the apparent crystallite stress (σXRD), and curvature measurement methods for the macro-stress (σf). Intermediate Cu layer having a fixed thickness of 1.4 μm was introduced as a stress reliever for the multilayered CoMnP/Cu through sequential electrodeposition. In multilayers, thickness of all single magnetic layers was added to around ~20 μm similar to that of a monolayer. The surface morphology, layer composition and microstructure remain the same regardless of individual CoMnP single layer thickness. XRD results of ϕ-scan and ψ-scan depict the transversely isotropic CoMnP layers are under an equi-biaxial stress status, making a simplified analytical solution of sin2ψ method. The residual stresses measured by XRD sin2ψ method have been correlated with those acquired by curvature method. Increasing the number of layers from 2, 3 to 6 in the CoMnP/Cu multilayers reduces the σXRD by 8.3%, 25%, 33%, respectively; while the σf by 7.7%, 15% and 23%, respectively, as compared to those of the CoMnP mono-layer. These reductions are attributed to the released strain energy due to soft interlayer confinement and stacking fault formation. Elaborated includes unambiguous understandings of residual stress and microstructures for the electrodeposited CoMnP layers.

Root rotations and root displacements in bimaterial layers and thin films

An elasticity technique to derive compliance coefficients describing crack tip root rotations and displacements in end-loaded, bimaterial, isotropic and orthotropic layers has been recently proposed in Ustinov and Massabò (Int. J. Solids Struct., 2022). The coefficients define the boundary conditions which account for the near tip deformations when using beam (plate) theories to describe the detached layers. The coefficients, collected into 6x6 compliance matrices, relate crack tip kinematic variables describing relative displacements and rotations between the detached and intact parts, and six elementary crack tip loadings, which combine to describe general end loadings. The steps necessary to use the coefficients in the solution of statically determined problems, when the forces acting on the layer are known through equilibrium, is presented here with reference to classical fracture mechanics specimens.

Gamma-convergence results for nematic elastomer bilayers: relaxation and actuation

We compute effective energies of thin bilayer structures composed of soft nematic elastic liquid crystals in various geometrical regimes and functional configurations. Our focus is on elastic foundations composed of an isotropic layer attached to a nematic substrate where order-strain interaction results in complex opto-mechanical instabilities activatedviacoupling through the common interface. Allowing out-of-plane displacements, we compute Gamma-limits for vanishing thickness which exhibit spontaneous stress relaxation and shape-morphing behaviour. This extends the plane strain modelling of Cesana and Leon Baldelli [Math. Models Methods Appl. Sci.(2018) 2863-2904], and shows the asymptotic emergence of fully coupled active macroscopic nematic foundations. Subsequently, we focus on actuation and compute asymptotic configurations of an active plate on nematic foundation interacting with an applied electric field. From the analytical standpoint, the presence of an electric field and its associated electrostatic work turns the total energy non-convex and non-coercive. We show that equilibrium solutions are min-max points of the system, that min-maximising sequences pass to the limit and, that the limit system can exert mechanical work under applied electric fields.

An Experimental Investigation of the Failure Mechanism of Simulated Transversely Isotropic Layers of Concrete and Soil

An Experimental Investigation of the Failure Mechanism of Simulated Transversely Isotropic Layers of Concrete and Soil

BENDING PROPERTIES OF A FUNCTIONALLY GRADED POLYMERIC COMPOSITE REINFORCED WITH A HYBRID NANOMATERIAL

In this paper, functionally graded polymer hybrid nanocomposites have been produced by silica (SiO2) nanoparticles and alumina (Al2O3) nanoparticles distributed in a matrix of epoxy during the ultra-sonication via hand lay-up method. The variation in nanoparticles volume fraction (Vf.) has been given in the thickness direction for reaching the gradation. Each layer has a thickness of 1.2 mm through various concentrations of nanoparticles and is sequentially cast in acrylic moulds to fabricate the graded composite sheet with a 6 mm thickness. To fabricate the functionally graded layers, various concentrations of different nanoparticles (1.5% SiO2, 1% SiO2, epoxy, 2% Al2O3 and 3% Al2O3) have been used for tensile and compressive testing each isotropic layer of functionally graded material (FGM). The mechanical property that was studied for pure epoxy, isotropic and FGM was the flexural resistance. The flexural properties of FGM, isotropic nanocomposite (1% SiO2 + 2% Al2O3) and pristine epoxy, for evaluating their mechanical properties, including flexural stress-strain criteria and flexural Young's modulus, were determined via a Three-point bending test, with loading from the side of silica and alumina for the hybrid-FGM and at one side for the isotropic hybrid nanocomposite and pristine epoxy. The mechanical properties (tensile and compression) and the density of every layer were obtained for the epoxy resin and nanocomposites. They can benefit from the Finite Element Analysis (FEA) of the Three-point bending test via the Design Modeler (ANSYS workbench). The results of experiments were confirmed via building a detailed 3D FE model. Also, the advanced deformation results from the FE model were found in good agreement with the experimental outcomes.

Surface alteration driven bi-functional catalytic activity of alkali niobate-N doped graphene composite for exalted oxygen electrochemistry

In this work, we establish that surface reconstruction, oxygen vacancies —specifically those located on the catalyst surface, and high crystallinity can be effective in tuning the catalytic activity of perovskite oxides. We report a high-performance electrocatalyst with an orthorhombic perovskite structure (NaNbO3), having an anisotropic surface layer and high crystallinity that exhibits superior activity and durability for the bi-functional oxygen electrochemistry compared to that of a similar perovskite composition with an isotropic surface layer and low crystallinity. The improvement in the electrocatalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is mainly attributed to the formation of an easy diffusion path on the surface layer due to the ionic movements, enhanced intrinsic activity of the catalytic sites resulting from the higher crystallinity, high oxygen vacancies and a large electrochemically active surface area. The sole key parameter in achieving all the acquired characteristics is the annealing temperature. We believe that the straightforward method of bringing the desired combination of properties by just tweaking the annealing temperature is handy and energy-efficient, and hence easily adoptable.

Large stress-induced anisotropy in soft magnetic films for synthetic spin valves

We obtain a large in-plane magnetic uniaxial anisotropy in the soft magnetic Fe60Co20B20 (FeCoB) thin films prepared by rotational sputtering. The anisotropy field (Ha) of 75 to 175 Oe was found in the films with wide ranged thickness from 2.5 to 100 nm, which was attributed to the magnetoelastic energy in association with anisotropic tensile stress. This stress-induced anisotropy has outstanding thermal stability that survives up to 350 °C in the annealing process. The similar large uniaxial anisotropy can be realized in other soft magnetic thin films, such as Fe, Co, Ni, FeCo, and NiFe, with the same synthesis technique. The anisotropic FeCoB film was used as a free layer in a synthetic spin valve. A linear resistance change against external field with a range wider than ±100 Oe together with a significantly reduced coercivity of ∼1.1 Oe (∼8.5 Oe in the case with isotropic free layer) was observed in the transfer curve. The results of this work not only confirm the feasibility of films with large stress-induced magnetic anisotropy as a functional layer in spin-valve devices but also demonstrate a simple synthesis route to induce the magnetic anisotropy, which provides an additional control parameter for the spintronic device design.

An analytical model for dynamic response of geosynthetic reinforced embankment system under traffic load

To make a more accurate prediction for the dynamic response of geosynthetic reinforced embankment (GRE) system under traffic load, an analytical model is developed based on the theory of elastodynamics, and the analytical solution of this model is also presented. In this new model, the pavement structure is simplified as an infinitely long Euler-Bernoulli beam, while the embankment fill, the foundation soil and the geosynthetic reinforced cushion are described by the theory of elastodynamics, which is quite different from the existing GRE models. Furthermore, the reinforced layer is modeled as a transversely isotropic layer, so that the anisotropic characteristic of the reinforced layer could be taken into consideration. The model is coupled through the appropriate boundary and interface conditions. After that, the model is solved analytically based on the integral transform technique and the theory of differential equations. The parametric studies show that the load velocity has a significant influence on the response of the system. A critical velocity is found and as the load velocity approaches this point, the response of the system dramatically increases. Additionally, the influence of the transversely isotropic property, as well as the thickness of the reinforced layer are also investigated.

Naturally occurring van der Waals heterostructure lengenbachite with strong in-plane structural and optical anisotropy

Lengenbachite is a naturally occurring layered mineral formed with alternating stacks of two constituent PbS-like and M2S3-like two-dimensional (2D) material layers due to the phase segregation process during the formation. Here, we demonstrate to achieve van der Waals (vdW) heterostructures of lengenbachite down to a few layer-pair thickness by mechanical exfoliation of bulk lengenbachite mineral. The incommensurability between the constituent isotropic 2D material layers makes the formed vdW heterostructure exhibit strong in-plane structural anisotropy, which leads to highly anisotropic optical responses in lengenbachite thin flakes, including anisotropic Raman scattering, linear dichroism, and anisotropic third-harmonic generation. Moreover, we exploit the nonlinear optical anisotropy for polarization-dependent intensity modulation of the converted third-harmonic optical vortices. Our study establishes lengenbachite as a new natural vdW heterostructure-based 2D material with unique optical properties for realizing anisotropic optical devices for photonic integrated circuits and optical information processing.

Surface Love-type waves propagating through viscoelastic functionally graded media.

This paper deals with the solution of the model equations, which describes the propagation of the surface Love-type waves in a waveguide structure consisting of a lossy isotropic inhomogeneous layer placed on a viscoelastic homogeneous substrate. The paper points to the possibility of using the triconfluent Heun differential equation to solve the model equation. The exact analytical solution within the inhomogeneous layer is expressed by the triconfluent Heun functions. The exact solutions are general in the sense that only the internal parameters of the triconfluent Heun functions can change the spatial dependencies of the material parameters in the inhomogeneous layer's thickness direction. Based on the comparison, the limits of the WKB method applicability are discussed. It is further demonstrated that substrate losses affect the dispersion characteristics only to a small extent. Using examples in which the surface layer is represented by functionally graded materials, it was shown that the distance between the modes can be influenced through those materials.