Biaxial In-plane Research Articles

Probing n-ZnMgO/p-Si nanowire junctions: Insights into composition, strain, and defects via Raman spectroscopy and electrical measurements

This article focuses on investigating physical properties of n-ZnMgO/p-Si heterojunctions containing ZnMgO nanowires (NWs) with ZnMgO/ZnO/ZnMgO quantum wells (QWs) grown by molecular beam epitaxy. Detailed analysis of chemical composition, crystal lattice strain, and defects in the structures was conducted via Raman spectroscopy, deep level transient spectroscopy (DLTS), and capacitance-versus-temperature characteristics, C(T). Additionally, current-voltage (I-V) curves were included to demonstrate the rectifying properties of the studied n-ZnMgO/p-Si NW junctions. The samples varied in the thicknesses of the ZnO QWs and the ZnMgO barriers. Raman spectra provided information on strain within the crystal lattice of the nanowires. The values of the biaxial in-plane strain were calculated for the selected samples, and the origin of this strain was discussed in detail. A broadened part of spectrum in the range of 480-600cm-1 was ascribed to the contribution of A1LO mode, which is associated with lattice defects such as oxygen vacancies, zinc interstitials, or their complexes. The presence of deep traps in the junctions was revealed by the DLTS method. Measurements of C(T) characteristics of the p-n junctions disclosed the presence of deep-level traps in the structures as well.

Three-dimensional elastoplastic post-buckling analysis of porous FG plates resting on Winkler/Pasternak foundation using meshless RRKPM

This paper presents a three-dimensional (3D) analysis of the elastoplastic post-buckling behavior of porous functionally graded (FG) plates resting on Winkler/Pasternak foundations under uniaxial and biaxial in-plane loadings using an enhanced meshless approach. The principle of virtual work is used to derive the governing equations, and 3D nonlinear Green–Lagrange strains are considered. Plastic deformation is modeled employing the Prandtl–Reuss flow law and the isotropic hardening von Mises criterion. A novel meshless radial basis reproducing kernel particle approach is used to obtain the discretized system of equations. The Newton–Raphson method, coupled with the arc-length technique, is used to compute post-buckling paths of porous FG plates. Numerical assessments show that post-buckling paths are significantly influenced by porosity parameter, porosity distribution, foundation parameters, material gradient, plate thickness, loading ratio, and boundary conditions (BCs).

High-speed and high-precision measurement of biaxial in-plane displacements: tens of nanometers principle error suppression in microprobe sensors

When the microprobe sensor is faced with the demand of high-speed biaxial displacement measurement, due to the characteristics of phase generated carrier (PGC) technology, accompanying optical intensity modulation (AOIM) and unfavorable phase modulation depth (PMD) will bring about the tens of nanometer cyclic nonlinear errors, further hindering high-speed and high-precision measurement. Herein, a light source intensity stabilization system based on semiconductor optical amplifier (SOA) feedback control is achieved to eliminate the error caused by AOIM in the presence of high-frequency and large-amplitude laser modulation. Based on this, the reasons for large nonlinear errors in biaxial measurements and the inability to ensure the stability of the accuracy of multiple measurement axes are methodically examined, and an effective nonlinear error elimination methodology based on the normalized amplitude correction of active temperature scanning is proposed. The continuity and linearity of the temperature scanning are also discussed. The performed experiments show that the above approach is capable of reducing the displacement demodulation error from the nanometer scale to the sub-nanometer scale. Further, the nonlinear error is reduced to within 0.1 nm for both measurement axes and the performance becomes consistent. The dual-axis measurement resolution of the microprobe sensor reaches 0.4 nm and the measurement speed is better than 1.2 m/s with the standard deviation of lower than 0.5 nm.

Multi-interpolation Method to Linearize Stress Path in Cruciform Specimen for In-Plane Biaxial Test

Multi-interpolation Method to Linearize Stress Path in Cruciform Specimen for In-Plane Biaxial Test

Atomically Thin Semiconductor TiPtGe and Heterostructure of β-Antimonene/TiPtGe: A First-Principles Study

Half-Heusler intermetallic compounds have been an important subject of interest in the field of semiconductors for years, but have been studied more for their bulk structure and rarely for their two-dimensional structure. Here, a novel two-dimensional semiconductor material with the chemical formula TiPtGe and an indirect bandgap of 1.27 eV has been developed on the basis of first-principles calculations. Significantly, it could be transformed from an indirect to a direct bandgap semiconductor under small biaxial in-plane strain. Given the similar lattice parameters and symmetry with the single-element two-dimensional material antimonene, we have attempted to form a vertical heterostructure of the two. The calculated results show that the heterostructure can be transformed from an indirect to a direct bandgap by increasing the number of TiPtGe layers. Further calculated results of the optical properties show that increasing the number of TiPtGe layers in the heterostructure could significantly improve the absorption efficiency in the visible region. This provides a new possibility for the application of antimonene in optoelectronic devices.

Thermal stability of rhombohedral α- and monoclinic β-Ga2O3 grown on sapphire by liquid-injection MOCVD

We investigate the thermal stability of single-phase undoped epitaxial rhombohedral α- and bi-axially-symmetric, monoclinic β-Ga2O3 thin films grown on sapphire substrates by liquid-injection metalorganic chemical vapor deposition (LI-MOCVD) by means of in-situ high-temperature X-ray diffraction (HT-XRD) and room temperature (RT) cathodoluminescence (CL). Ga2O3 layers were vacuum annealed up to 1100 °C, while monitoring the respective 303‾0 and 6‾03 reflections of α- and β-phase Ga2O3. α-Ga2O3 layers were found to withstand the vacuum annealing at 700 °C/20 min, 750 °C/10 min, and 800 °C/8 min without notable degradation, however an indication of reversible biaxial in-plane compressive strain was observed for annealing temperatures close to 800 °C. Annealing at temperatures above 825 °C led to complete layer degradation and partial phase transformation to (010) β-Ga2O3. β-Ga2O3 layers showed no notable degradation or structural changes after the annealing at 1100 °C/30 min, however an indication of reversible biaxial in-plane tensile strain was observed for prolonged annealing at 1100 °C. RT CL spectra revealed the Ga2O3 emission consisted of several distinctive luminescence bands (red, green, blue, and two UV bands). Relatively weak but distinctive signal maxima with energy close to the expected bandgap energies of α- and β-Ga2O3, at 5.3 and 5.0 eV, respectively, were observed and attributed to their near band-edge (NBE) emissions.

Quantifying Alignment Deviations for the In-Plane Biaxial Test System via a Shape-Optimised Cruciform Specimen.

The loading coaxiality of an in-plane biaxial test system and the structure of a cruciform specimen markedly affect the test results. However, due to the lack of methods for correcting the loading coaxiality and designing the cruciform specimen, the data scatter of the test results of the in-plane biaxial test systems varies from the laboratory to different tests. To quantify the loading coaxiality of the in-plane biaxial test system, we first developed a model to calculate alignment deviations with strain distribution of the shape-optimised cruciform specimen with Automated Machine Learning (AutoML). Our results demonstrated that 99.2% (54,536 of 54,976) of the quantified errors are less than 5%. Quantifying alignment deviations for an in-plane biaxial test system has been solved. The quantified method of alignment deviations could enhance the reliability of test data, improve assembly efficiency, and aid in constructing failure criteria of materials under biaxial stress.

Strain and lattice vibration mechanisms in GaN-AlxGa1-xN nanowire structures on Si substrate

In this work we use Raman scattering and X-ray diffraction (XRD) techniques to examine strain and lattice vibration mechanisms in self-assembled GaN-AlxGa1-xN nanowire (NW) structures grown by plasma-assisted molecular beam epitaxy on Si(111) substrate. The samples consisted of GaN NW parts overgrown by AlxGa1-xN segments with the nominal Al content x = 0.1, 0.25, 0.5, 0.75 and 1. The non-resonant Raman spectra revealed phonon modes originating from the Si substrate as well as from GaN and AlN. By analysing frequency position of the GaN-like and AlN-like E2high vibration modes as well as of GaN-like A1LO mode, we were able to study chemical composition and strain in NWs, as well as lattice vibrations mechanisms, such as: temperature effects, phonon confinement and phonon-plasmon interaction. All these factors were considered and analysed within this work to explain the observed phonon modes shifts. The biaxial in-plane strain in the NWs was calculated based on the estimated E2high Raman lines shifts with respect to that of bulk GaN and bulk AlN. XRD studies supplemented Raman measurements by the analysis of micro-strain in GaN-AlxGa1-xN NW structures. Based on the XRD reciprocal space maps the in-plane and out-of-plane strain values were estimated. The results obtained from XRD were in a good agreement with those derived from Raman measurements.

Influence of Al x Ga1−x N nucleation layers on MOVPE-grown zincblende GaN epilayers on 3C-SiC/Si(001)

The suitability of Al x Ga1−x N nucleation layers (NLs) with varying Al fraction x for the metal organic vapour phase epitaxy of zincblende GaN on (001) 3C-SiC was investigated, using x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray diffraction. The as-grown NLs exhibited elongated island structures on their surface, which reduce laterally into smaller, more equiaxed islands with increasing AlN composition. During high-temperature annealing in a mixture of NH3 and H2 the nucleation islands with low Al fraction ripened and increased in size, whereas this effect was less pronounced in samples with higher Al fraction. The compressive biaxial in-plane strain of the NLs increases with increasing AlN composition up to x = 0.29. GaN epilayers grown over NLs that have low Al fraction have high cubic zincblende phase purity and are slightly compressively strained relative to 3C-SiC. However, those samples with a measured Al fraction in the NL higher than 0.29 were predominantly of the hexagonal wurtzite phase, due to formation of wurtzite inclusions on various {111} facets of zb-GaN, thus indicating the optimal Al composition for phase-pure zb-GaN epilayer growth.

Possible way to achieve anomalous valley Hall effect by piezoelectric effect in a GdCl2 monolayer

Ferrovalley materials can achieve manipulation of the valley degree of freedom with intrinsic spontaneous valley polarization introduced by their intrinsic ferromagnetism. A good ferrovalley material should possess perpendicular magnetic anisotropy (PMA), valence band maximum (VBM)/conduction band minimum (CBM) at valley points, strong ferromagnetic (FM) coupling and proper valley splitting. In this work, the monolayer $\mathrm{GdCl_2}$ is proposed as a potential candidate material for valleytronic applications by the first-principles calculations. It is proved that monolayer $\mathrm{GdCl_2}$ is a FM semiconductor with the easy axis along out of plane direction and strong FM coupling. A spontaneous valley polarization with a valley splitting of 42.3 meV is produced due to its intrinsic ferromagnetism and spin orbital coupling (SOC). Although the VBM of unstrained monolayer $\mathrm{GdCl_2}$ is away from valley points, a very small compressive strain (about 1\%) can make VBM move to valley points. We propose a possible way to realize anomalous valley Hall effect in monolayer $\mathrm{GdCl_2}$ by piezoelectric effect, not an external electric field, namely piezoelectric anomalous valley Hall effect (PAVHE). This phenomenon could be classified as piezo-valleytronics, being similar to piezotronics and piezophototronics. The only independent piezoelectric strain coefficient $d_{11}$ is -2.708 pm/V, which is comparable to one of classical bulk piezoelectric material $\alpha$-quartz ($d_{11}$=2.3 pm/V). The biaxial in-plane strain and electronic correlation effects are considered to confirm the reliability of our results. Finally, the monolayer $\mathrm{GdF_2}$ is predicted to be a ferrovalley material with dynamic and mechanical stabilities, PMA, VBM at valley points, strong FM coupling, valley splitting of 47.6 meV, and $d_{11}$ of 0.584 pm/V.

Band Alignment in Monolayer Boron Phosphide with Janus MoSSe Heterobilayers under Strain and Electric Field

Recent studies have revealed that Janus structures and heterobilayers made from them might have properties superior to those of two-dimensional (2D) materials. We construct 2D monolayer boron phosphide (MBP)/$\mathrm{Mo}\mathrm{S}\mathrm{Se}$ and $\mathrm{Mo}\mathrm{S}\mathrm{Se}$/MBP heterobilayers and describe comprehensively their optoelectronic properties in the presence of biaxial in-plane and uniaxial out-of-plane strain and the effects of electric fields using first-principles methods. The electronic bands of both MBP/$\mathrm{Mo}\mathrm{S}\mathrm{Se}$ and $\mathrm{Mo}\mathrm{S}\mathrm{Se}$/MBP heterobilayers display a peculiarity in the direct gap, with different band-gap values in the pristine forms. Remarkably, it is shown that different varieties of band alignments are induced for different orders of the van der Waals (vdW) heterobilayers. Electric fields and in-plane and out-of-plane strain give rise to important changes in the electronic and optical properties. The band alignments can transform from type I to type II under the influence of an electric field and strain. The main absorption peaks of pristine forms of both heterobilayers have in the visible region (approximately 2.67 eV), while in the presence of biaxial strain are redshifted. Since the absorption peaks of the pristine forms of the heterobilayers are in the visible region, the heterobilayers recommended here can be used in photovoltaic applications, and the presence of effects of external electric fields and strain promises functional optoelectronic devices.

Morphologies of compressed active epithelial monolayers.

Using a three-dimensional active vertex model, we numerically study the shapes of strained unsupported epithelial monolayers subject to active junctional noise due to stochastic binding and unbinding of myosin. We find that while uniaxial, biaxial, and isotropic in-plane compressive strains do lead to the formation of longitudinal, herringbone pattern, and labyrinthine folds, respectively, the villus morphology characteristic of, e.g., the small intestine appears only if junctional tension fluctuations are strong enough to fluidize the tissue. Moreover, the fluidized epithelium features villi even in the absence of compressive strain provided that the apico-basal differential surface tension is large enough. We analyze several details of the different epithelial forms including the role of strain rate and the modulation of tissue thickness across folds. Our results show that even unsupported, non-patterned epithelia can form nontrivial morphologies.

Magnetization Dynamics and Spin Wave Excitation in Strain-Mediated Multiferroic Heterostructures With the Interfacial Dzyaloshinskii-Moriya Interaction

The effect of the interfacial Dzyaloshinskii-Moriya interaction (i-DMI) on the magnetization dynamics induced by strain is described within the framework of micromagnetic simulations taking into the magnetoelastic coupling between the spin and strain in multiferroic heterostructures. In this magnetized system, biaxial in-plane strain act on the perpendicular magnetization without bias magnetic field is introduced. As the micromagnetic simulation results have shown, the lateral magnetization dynamics and spin wave were excited with the i-DMI induced intrinsic magnetization tilting along the nanostrip width direction. It is found that the excitation strain field could generate a quantized width mode with odd mode numbers. In addition, our simulation reveals that the excitation field with higher frequency generates two spin wave modes with a different mean free path. Our works, therefore, show the potential of using a strain with the presence of i-DMI as the perspective for integrating spin wave emitters into future logic or computing devices and hinting at possible technological applications in strain-controlled spintronic systems.

Strong extrinsic chirality in biaxial hyperbolic material α-MoO3 with in-plane anisotropy.

Chirality has always been a hot research topic because it possesses potential applications in polarization optics, chemical and biosensing. In the previous works, intrinsic chirality has been extensively explored, but its development is limited due to the complexity in fabrication of chiral metamaterials. Therefore, there is an urgent need to simplify fabrication and design of compact devices with chiral response. Extrinsic chirality has shown great potential because it can be realized in nonchiral anisotropic planar structures with low-cost fabrication techniques. In this paper, the extrinsic chirality of biaxial hyperbolic material $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ with in-plane anisotropy has been investigated. By analyzing the effect of thickness of $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film, the angle of incidence, azimuth angle, and wavelength of incidence on the circular dichroism (CD), the maximum CD can reach 0.77. This strong extrinsic chirality of the $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film results from the mutual orientation of the $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film and the incident light. In addition, $\alpha {\text -}{\rm{Mo}}{{\rm{O}}_3}$ film can still maintain strong extrinsic chirality when the azimuthal angle ranges from approximately 20°-57° and the angle of incidence is from 55°-80°.

Relationship between Transport Anisotropy and Nematicity in FeSe

The mechanism behind the nematicity of FeSe is not known. Through elastoresitivity measurements it has been shown to be an electronic instability. However, so far measurements have extended only to small strains, where the response is linear. Here, we apply large elastic strains to FeSe, and perform two types of measurements. (1) Using applied strain to control twinning, the nematic resistive anisotropy at temperatures below the nematic transition temperature Ts is determined. (2) Resistive anisotropy is measured as nematicity is induced through applied strain at fixed temperature above Ts. In both cases, as nematicity strengthens the resistive anisotropy peaks about about 7%, then decreases. Below ~40 K, the nematic resistive anisotropy changes sign. We discuss possible implications of this behaviour for theories of nematicity. We report in addition: (1) Under experimentally accessible conditions with bulk crystals, stress, rather than strain, is the conjugate field to the nematicity of FeSe. (2) At low temperatures the twin boundary resistance is ~10% of the sample resistance, and must be properly subtracted to extract intrinsic resistivities. (3) Biaxial inplane compression increases both in-plane resistivity and the superconducting critical temperature Tc, consistent with a strong role of the yz orbital in the electronic correlations.

Two-dimensional intrinsic ferrovalley GdI2 with large valley polarization

Manipulation of the valley degree of freedom provides a novel paradigm in quantum information technology. In this work, through first principles calculations, we demonstrate that monolayer $\mathrm{Gd}{\mathrm{I}}_{2}$ is a promising candidate material for valleytronic applications. Monolayer $\mathrm{Gd}{\mathrm{I}}_{2}$ can be easily exfoliated from bulk, and it is spontaneously valley polarized with a giant splitting of 149 meV due to its intrinsic ferromagnetism and large spin orbital coupling. The anomalous valley Hall effect could be realized in monolayer $\mathrm{Gd}{\mathrm{I}}_{2}$ by an appropriate external electric field. Furthermore, the valley polarization feature is stable against the biaxial in-plane strain. Our findings provide an extraordinary and potential material platform for experimental studies and practical applications in the emergent field of valleytronics.

Development of In-plane Biaxial Compression Test Method for Thin Sheet and Investigation of SD Effect under Biaxial Stress Condition

The accuracy of the finite element simulation (FE simulation) of press forming has improved as a result of sophisticated material modelling using data of the various experiments such as uniaxial compression, biaxial tension, and in-plane cyclic loading tests. However, the biaxial compression test of sheet material has never been reported lowing to the difficulty in buckling suppression, and differences between material behavior under biaxial tension and that under biaxial compression have not yet been discussed. In this paper, the biaxial compression test of sheet material using special tools to suppress buckling and a specimen shape that leads to uniform deformation in the measurement area is proposed mainly on the basis of FE simulation. The special tool has a urethane plate where the tool come into contact with the measurement area of the specimen to prevent damage of the strain gauges. Absolute values of compressive stresses during plastic work measured by the biaxial compression test were larger than tensile stresses during the same plastic work measured by the biaxial tension test. Similar results observed in uniaxial tension and compression tests are known as the strength differential (SD) effect.

Buckling Response Analysis of Laminated Plates Subjected to Localised Bi-axial In-plane Compressive Loading

Laminated composite plates are well known structural member since last four decades because of its high stiffness and strength to weight ratio. Usually this type of structural members is subjected to partial biaxial loading during their functioning. For better safety and stability of structure, analysis of these structural member in that condition of loading is necessary. In this present analysis buckling response of laminated composite plates under biaxial partial in-plane loading is examined and effect of various parameters like aspect ratio, stacking sequence, fiber orientation and plate thickness ratio of nondimensionalised critical buckling load (NCBL) are revealed. A MATLAB program is developed higher order shear deformation theory based on finite element method for buckling analysis of laminated composite plate. Efficiency of the program is checked by comparing the result of the present work with that of already published which shows good favour of later one.

Static and dynamic analyses of graphene-reinforced aluminium-based composite plate in thermal environment

The enhanced thermo-mechanical static and dynamic behaviors are investigated for the functionally graded graphene nanoplatelet reinforced aluminium-based (GRA) composite plate. The partial differential governing equations of motion for the static and dynamic analyses of the GRA composite plate are obtained based on the first-order shear deformation plate theory, von Karman nonlinear geometric relationship and Hamilton's principle. Numerical simulations are finished through using the differential quadrature (DQ) method and direct iterative process. Three different distribution patterns of the graphene nanoplatelets (GPLs) are considered, including the uniform distribution pattern, U pattern, and functionally graded (FG) patterns of X and O patterns. For the static analyses, the thermal buckling and post-buckling behaviors of the GRA composite plate subjected to the uniaxial or biaxial in-plane loads are discussed with varying the boundary conditions. For the dynamic behaviors, the thermal linear and nonlinear vibrations of the GRA composite plate are analyzed in details. The numerical results demonstrate that there are remarkable distinctions among the thermo-mechanical behaviors of the GRA composite plates with three different GPL distribution patterns. The present investigations are significant to the optimal design and practical applications of the GRA composite plate, especially in the thermal environment.

Analysis of laminated composite plates based on different shear deformation plate theories

A finite strip formulation was developed for buckling and free vibration analysis of laminated composite plates based on different shear deformation plate theories. The different shear deformation theories such as Zigzag higher order, Refined Plate Theory (RPT) and other higher order plate theories by variation of transverse shear strains through plate thickness in the parabolic form, sine and exponential were adopted here. The two loaded opposite edges of the plate were assumed to be simply supported and remaining edges were assumed to have arbitrary boundary conditions. The polynomial shape functions are applied to assess the in-plane and out-of-plane deflection and rotation of the normal cross-section of plates in the transverse direction. The finite strip procedure based on the virtual work principle was applied to derive the stiffness, geometric and mass matrices. Numerical results were obtained based on various shear deformation plate theories to verify the proposed formulation. The effects of length to thickness ratios, modulus ratios, boundary conditions, the number of layers and fiber orientation of cross-ply and angle-ply laminates were determined. The additional results on the same effects in the interaction of biaxial in-plane loadings on the critical buckling load were determined as well.