Crystal Orientation Angle Research Articles

High strength induced wide band gap formations in additively manufactured cubic metamaterial

Strength and band gap are the two basic physical features of the cubic metamaterial. How to design band gap characteristics with high strength of structure is the key for the further industrial application in vibration control of the cubic metamaterial. Here a cubic metamaterial is designed by optimal selection of crystal orientation angle to obtain wide band gaps with high strength. The prototype samples were fabricated using advanced additive manufacturing technology to tensile-pressure experiments and sine frequency sweep experiment, thereby demonstrating the validity of the obtained results. Results indicated that the normalized bandwidth of simple cubic (SC) metamaterials is 0.47 and the ultimate strength is 25.99 MPa. The normalized bandwidth is increased by 3.1 times and 47 times higher than that of the metamaterials of face-centered cubic (FCC) and body-centered cubic (BCC). Its ultimate strength is increased by 3.5 times and 6.7 times. The static simulation results revealed that the maximum mises stress values of SC, FCC, and BCC metamaterials were 1.71, 10.49, and 31.40 MPa respectively. The attenuation amplitude of the elastic wave measured by experiment is 80 dB, which is consistent with the simulation results. The bandwidths of cubic metamaterials exhibit a positive correlation with their strength. The variation in crystal orientation angles plays a crucial role in elucidating the underlying mechanism behind the positive correlation between the strength and the band gap. The further buckling analysis of SC metamaterial with high strength and wide bandgap characteristics reveals that the negative Poisson’s ratio structure experiences a reduction in bandwidth and strength as buckling deformation intensifies.

Wide spectral range guided-mode resonant grating designed for the wet etching process

We present wideband guided-mode resonant (GMR) gratings made of Si on a SiO2 substrate. Based on the base angle of the grating as the crystal orientation angle (54.74°) of Si, the design process of reflectors suitable for TM-polarized waves is demonstrated in the near-infrared (NIR) and mid-infrared (MIR) wavelengths. Benefiting from the mutual attraction and interaction of the two GMR modes, the bandwidth of reflectivity above 99% for the reflector under the NIR and MIR bands reaches 297 nm (from 1416 nm to 1713 nm) and 657 nm (from 3154 nm to 3811 nm), respectively. In addition, the effects of the incident light source state and the structural parameters on the performance of the reflector are analyzed in detail. The results show that the reflector will maintain good tolerance and stability during fabrication and use. This work will be compatible with the wet etching process in the microelectromechanical system, and the results can be extended to the design of broadband GMR reflectors in other wavelength bands.

Polarization-Dependent Anisotropy of LIPSSs' Morphology Evolution on a Single-Crystal Silicon Surface.

Utilizing the principle of laser-induced periodic surface structures (LIPSSs), this research delves into the morphological evolution of single-crystal silicon surfaces irradiated by a near-infrared picosecond laser through a scanning mode. With the increase in laser energy density, the nanostructure morphology on single-crystal silicon surfaces induced by incident lasers with different polarization directions sequentially produces high spatial-frequency LIPSSs (HSFLs) with a period of 220 nm ± 10 nm parallel to the laser polarization, low spatial-frequency LIPSSs (LSFLs) with a period of 770 nm ± 85 nm perpendicular to the direction of the polarization, and groove structures. Furthermore, by varying the angle between the laser polarization and the scanning direction, the study examined the combined anisotropic effects of the laser polarization scanning direction angle and the laser polarization crystal orientation angle on the genesis of LIPSSs on single-crystal silicon (100) surfaces. The experiments revealed polarization-related anisotropic characteristics in the morphology of HSFLs. It was found that when the polarization angle approached 45°, the regularity of the LSFLs deteriorated, the modification width decreased, and the periodicity increased. This is critical for the precise control of the LSFLs' morphology.

Research on the anisotropic mechanism of plastic behavior during tensile process of textured pure titanium

The presence of texture has an important influence on the deformation behavior of titanium. In this study, the anisotropy of the macro-mesoscopic deformation behavior of the material and its evolution with strain were systematically studied by uniaxial tensile test and electron backscatter diffraction (EBSD) technique. Based on the above results, the calculation formula of Schmid factor (SF) for each variant of the slip system expressed by the crystal orientation angle was derived, and the influence of initial texture and texture redirection on the activability of each deformation mode was explored. The impact of the ratios between the critical resolved shear stress (CRSS) of the three deformation modes on the predictions of the dominant deformation mode of yield was systematically assessed, using the CRSS as the standard. The initial yield mode of RD tensile is prismatic <a>slip, while TD tensile may be a combination of multiple slip modes. One of the primary reasons of the evolution of the basal split texture components is the activation of dislocation slip, while the twinning mainly plays a role in coordinating the deformation. According the Taylor axis analysis, the prismatic <a> slip is the primary deformation mode during RD and TD tensile, followed by pyramidal <a> slip, while the basal <a> slip is difficult to be activated or the activability decreases with the increase of strain.

Study of elastoplastic deformation and crack evolution mechanism of single-crystal ice during uniaxial compression using 3D digital image correlation

Single-crystal freshwater ice was subjected to uniaxial compression tests with different strain rates and crystal orientations, and the real-time full-field deformation and strain were measured by the three-dimensional digital image correlation (3D DIC) method. The mechanism of elastoplastic deformation and crack evolution of single-crystal ice is discussed based on the basal slip. The maximum compressive strength appeared when the crystal orientation (angle between the C-axis and loading direction) θ=0°/90°. When 45°<θ<90°, an inclined bearing layer appeared and caused the specimen to rotate simultaneously. When 0°<θ⩽45°, the vertical compressive stress was sequentially transmitted through the basal plane, two diagonal expansions to the sidewall appeared. The failure mode and compressive strength of ice exhibited a ductile–brittle transition. The strength was positively correlated with the strain rate below the ductile–brittle transition range. The stress concentration at the crack tip was released through basal slip, inhibiting crack propagation, which showed multi-crack ductile failure. When in the ductile–brittle transition range, the cracks could grow stably, leading to axial splitting failure. When the strain rate was higher, the crack tip could not grow stably, producing inclined cracks and resulting in spalling or axial splitting failure, and the ice exhibited a brittle failure mode.

Application of a new grain boundary technology for quasi-single crystalline silicon ingots

A new functional grain boundary group (FGBG) technology was employed to generate quasi-single crystalline silicon ingots with a high single crystalline area ratio. Fabrication of the FGBG structure was achieved and special grain boundaries were formed between adjacent seed crystal strips with 〈100〉 crystal orientation, with a 30° crystal orientation angle between the special grain boundaries. The influence of FGBG on the evolution of grains, dislocation, and surface morphology was analyzed by photoluminescence and electron back-scattered diffraction. FGBG effectively suppressed the side polycrystalline grains (spontaneous nucleation on the crucible wall) intrusion at the early stage of solidification. Additionally, when the crystal growth height was increased, FGBG acted as a barrier layer for the external polycrystalline grains under the control of an appropriate horizontal temperature gradient and slightly convex solid–liquid interface shape, preventing most of the polycrystalline grains around the ingot from growing into the crystal, and blocking the dislocations generated by polycrystalline grains near the grain boundary. The application of this FGBG technology will greatly improve the quality of quasi-single crystalline silicon ingots with a weight of 1400 kg (G7).

Взаимная трансформация световых волн при встречном взаимодействии на отражательной голографической решетке в кристалле Bi-=SUB=-12-=/SUB=-SiO-=SUB=-20-=/SUB=- среза (001)

The features of energy exchange during the contra-directional mixing of two linearly polarized light waves in a cubic photorefractive Bi12SiO20 piezocrystal of (001)-cut are analyzed. The dependences of the relative intensity of the signal wave on the azimuth of its polarization at the entrance to the crystal during mixing with the reference wave polarized in the plane of incidence are theoretically studied for various crystal orientation angles. The dependence of the relative intensity of the signal wave on the azimuth of its polarization is experimentally studied for the cases when the vector amplitudes of light waves propagating in the crystal are parallel and perpendicular to each other. The calculation is based on the numerical solution of the coupled waves equations with and without taking into account the self-diffraction of the light waves by the reflection holographic grating recorded in the crystal. Based on a comparison of theoretical and experimental data, the influence of self-diffraction on the mutual transformation of light waves during their contra-directional mixing is analyzed. The limits of applicability of the static grating and the dynamic grating approximations for solution of the coupled waves equations are determined.

Mutual transformation of the light waves by contra-directional mixing on reflection holographic grating in Bi-=SUB=-12-=/SUB=-SiO-=SUB=-20-=/SUB=- crystal of (001)-cut

The features of energy exchange during the contra-directional mixing of two linearly polarized light waves in a cubic photorefractive Bi 12 SiO 20 piezocrystal of (001)-cut are analyzed. The dependences of the relative intensity of the signal wave on the azimuth of its polarization at the entrance to the crystal during mixing with the reference wave polarized in the plane of incidence are theoretically studied for various crystal orientation angles. The dependence of the relative intensity of the signal wave on the azimuth of its polarization is experimentally studied for the cases when the vector amplitudes of light waves propagating in the crystal are parallel and perpendicular to each other. The calculation is based on the numerical solution of the coupled waves equations with and without taking into account the self-diffraction of the light waves by the reflection holographic grating recorded in the crystal. Based on a comparison of theoretical and experimental data, the influence of self-diffraction on the mutual transformation of light waves during their contra-directional mixing is analyzed. The limits of applicability of the static grating and the dynamic grating approximations for solution of the coupled waves equations are determined. Keywords: Photorefractive crystal, reflection holographic grating, coupled wave equations, self-diffraction.

A deep learning augmented genetic algorithm approach to polycrystalline 2D material fracture discovery and design

The gestalt of computational methods including physics-based molecular dynamics simulations, data-driven machine learning (ML) models, and biologically-inspired genetic algorithms affords a powerful toolbox for tackling materials mechanism discovery and design problems. Here, we leverage these methods to investigate the complex multidimensional problem of polycrystalline 2D material fracture. We focus first on graphene and in doing so, demonstrate a practical workflow for exploring the structural dependencies of fracture energy. Despite training our ML model on exclusively single crystal fracture in increments of 10° orientations, we can identify a crack branching mechanism responsible for high bicrystal toughness centered at initial crystal orientation angles of 19° and 41°. These high peaks span only a few degrees in range and are completely overlooked by a search with stride 10°. Furthermore, we can discover qualitative physical phenomena such as collective fracture branch termination and extract quantitative trends relating angular dispersion and mis-orientation angles of crystal grains to fracture energy. None of these complex polycrystalline behaviors were presented in the training data, and the predictive power of the model ultimately allows us to expeditiously generate polycrystalline graphene structures with bespoke fracture paths, a task with great implications in industrial design applications and mechanism discovery. Furthermore, the approach is not limited to graphene specifically, as we demonstrate by retraining the model for another more complex 2D material—MoS2—and achieve polycrystalline fracture predictions of comparable accuracy.

Anisotropic two-photon absorbers measured by the Z-scan technique and its application in laser beam shaping

We investigate anisotropic two-photon absorption (TPA) effects in a cubic-symmetry crystal excited by scalar and vectorial optical fields. First, we present the anisotropic TPA coefficient, which depends on the anisotropy coefficient, the dichroism coefficient, the crystal orientation angle, and the ellipticity of the polarized ellipse. Second, we develop the elliptically polarized light Z-scan technique for characterizing anisotropic two-photon absorbers, which is demonstrated experimentally. Last, we present the laser beam shaping of vectorial optical fields with Gaussian intensity distribution into a flat-top profile through anisotropic TPA effects. It is shown that the anisotropic TPA offers a new avenue to manipulate the intensity distribution of the polarization-structured light field, which may find interesting applications in beam shaping, optical limiting, and photodetection.

Phase‐field‐crystal study on deformation behavior of nanoscale monocrack system in the ductile‐to‐brittle transition region

AbstractPhase‐field‐crystal method is applied to study deformation behavior in the ductile‐to‐brittle transition region of the nanoscale monocrack system in this work. The influence of temperature, crystal orientation angle, and crack shape on the deformation behavior is investigated. Temperature can induce fracture mode change, while crystal orientation angle and crack shape can only affect the specific evolutionary behavior. In the ductile region, if the orientation of a vertex is approximately aligned with a certain close‐packed direction, crack extends shortly in cleavage mode at this vertex, which means cleavage crack propagation can be promoted in a particular range of crystal orientation angle. Additionally, the influence of crack shape is achieved by varying the orientation relationship between crack and lattice structure. In the brittle region, crystal orientation angle impacts on the specific cleavage evolution process, and crack shape can promote or hinder plastic deformation by affecting stress concentration.

Anisotropic nonlinear Kerr media: Z-scan characterization and interaction with hybridly polarized beams.

The interaction of intense laser with matter gives rise to a variety of novel nonlinear optical effects, reflects the nonlinear optical property of a material, and modulates the light propagation behavior. Herein, we investigate anisotropic Kerr nonlinearities induced by both scalar and vectorial optical fields. Firstly, we present the anisotropic third-order nonlinear refraction indexes related to left-hand and right-hand components, which depend on the ellipticity, the dichroism coefficient, the anisotropy coefficient, as well as the crystal orientation angle. Secondly, we develop the elliptically polarized light Z-scan technique for characterizing third-order nonlinear susceptibility tensor in anisotropic nonlinear Kerr media, which is demonstrated experimentally. Lastly, with the known nonlinear optical parameters, we numerically study both the vectorial self-diffraction behaviors and spin angular momentum (SAM) characteristics of hybridly polarized beams induced by an anisotropic Kerr nonlinearity. It is shown that the anisotropic Kerr nonlinearity offers a new approach to manipulate the polarization-structured light field, which has potential applications in SAM manipulation, three-dimensional crystal orientation, and polarization-sensitive detection and sensing.

Effect of degree of strain relaxation on polarization charges of GaN/InGaN/GaN hexagonal and triangular nanowire solar cells

The innovative contribution of this paper is to derive polarization charges in hexagonal and triangular GaN/InGaN/GaN core/shell/shell nanowire solar cells considering effect of degree of strain relaxation (R) and appropriate stiffness coefficients. The crystal orientation angle, φ and non-linear effect of spontaneous polarization are tailored with strain calculations for a better precision of polarization charges in nanowire type devices. The article also formulated the effect of polarization charges while InGaN layers are grown above or below GaN layer in both types of nanowires depending on the lattice expansion or compression. The model accounts an innovative concept of polarization charges distribution with respect to growth of crystal orientation and strain relaxation. It is observed that nanowire solar cell with triangular geometry could be good enough for efficient generation of power as compared to hexagonal nanowire solar cell. This concept of one triangular nanowire solar cell exhibits an efficiency of 3.18% with 90.34% fill factor under 1 Sun AM1.5 illumination with 20% ‘In’ composition.

Twist-Angle-Dependent Optoelectronics in a Few-Layer Transition-Metal Dichalcogenide Heterostructure.

Lattice matching has been supposed to play an important role in the coupling between two materials in a vertical heterostructure (HS). To investigate this role, we fabricated a heterojunction device with a few layers of p-type WSe2 and n-type MoSe2 with different crystal orientation angles. The crystal orientations of WSe2 and MoSe2 were estimated using high-resolution X-ray diffraction. Heterojunction devices were fabricated with twist angles of 0, 15, and 30°. The I- V curve of the sample with the twist angle of 0° under the dark condition showed a diodelike behavior. The strong coupling due to lattice matching caused a well-established p-n junction. In cases of 15 and 30° samples, the van der Waals gap was built because of lattice mismatching, which resulted in the formation of a potential barrier. However, when the light-emitting diode light of 365 nm (3.4 eV) was illuminated, it was possible for excited electrons and holes to jump beyond the potential barrier and the current flowed well in both forward and reverse directions. The effects of the twist angle were analyzed by spectral responsivity and external quantum efficiency, where it was found that the untwisted HS exhibited higher sensitivity under IR illumination, whereas the twisting effect was not noticeable under UV illumination. From photoluminescence and Raman spectroscopy studies, it was confirmed that the twisted HS showed a weak coupling because of the lattice mismatch.

Identification of crystal orientation for turbine blades with anisotropy materials

A novel approach to identify the crystal orientation of turbine blades with anisotropy materials is proposed. Based on enhanced mode basis, with the main advantages of its efficiency, accuracy and general applicability, the blade vibration mode of each order is linearly constructed by several specified mode shapes, which are obtained from the considered turbine blade with specified crystal orientations correspondingly. Then, a surrogate model based on Kriging method is introduced for constructing the condensed perturbed matrix of stiffness in order to improve the efficiency even further. The constructed surrogate model allows to perform the modal analysis of turbine blades with arbitrary crystal orientations in higher efficiency, due to the fact that the elements of condensed perturbed matrix of stiffness are considered in construction of the surrogate model rather than concerning the perturbation of all the elements of the initial stiffness matrix for the blade. Genetic algorithm is finally employed to optimize the defined fitness functions in order to identify the crystal orientation angles of turbine blades. Several corresponding examples demonstrated the accuracy, efficiency and general applicability of the proposed method.

Characterization of the sensitivity of piezoelectric resonant pressure/force sensor with a new automatic device

ABSTRACTA fully automated novel apparatus for the characterization of the sensitivity of piezoelectric resonant pressure/force sensor is proposed. The force-frequency effect of piezoelectric resonant sensors is the correlation between the force applied on the crystal resonator and the relative response resonant frequency shift of the resonator to the applied force. The force-frequency effect is closely related to the sensitivity of the pressure/force sensors. The new apparatus has been designed and fabricated to automatically measure the force-frequency relation at different azimuth angles ψ and force sensitivity coefficient Kf m.s/N which relates to parameters such as crystal geometry (diameter, thickness), orientation angle, and force direction (azimuth angle ψ). PI control is utilized for the automated measurement of force-frequency relation in crystal resonator. In addition, a lead screw mechanism is designed to yield precise linear motion of the clamp and minimize the backlash of the moving parts. As a result, the apparatus can automatically apply force on the crystal, measure the corresponding output frequency shift and yield the force-frequency relation graph. It also has a better force resolution and is simpler to adjust for force alignment. Moreover, the measurement time is reduced and the measurement result is more accurate. In order to validate this novel automated loading device, experiment tests on samples have been performed, and a comparison of the experiment outcomes with peers' measurement results shows a good agreement.

Crystal orientation-dependent mechanical property and structural phase transition of monolayer molybdenum disulfide

By performing molecular dynamics simulations, we investigate the mechanical property and structural phase transition in monolayer molybdenum disulfide (MoS2) with different crystal orientations under uniaxial tensions systematically. The results show that both the mechanical property and structural phase transition are strongly dependent on the crystal orientation, specifically, for some crystal orientation angles lower than about 20°, the structural phase transition takes place with the plastic deformation; for other crystal orientation angles, plastic deformation cannot occur. Further studies have found that plastic deformation results from irreversible changes of the angles between the bonds, rather than the variation of bond length. Young's modulus increases while ultimate strength and fracture strain decrease with the increase of the crystal orientation angle. The critical strain at which the first structural phase transition occurs increases with the increase of the crystal orientation angle. The plastic deformation and the irreversible structural transition almost linearly increase with the decrease of the crystal orientation angle.

Architecture of crossed-lamellar bivalve shells: the southern giant clam (Tridacna derasa, Röding, 1798).

Tridacna derasa shells show a crossed lamellar microstructure consisting of three hierarchical lamellar structural orders. The mineral part is intimately intergrown with 0.9 wt% organics, namely polysaccharides, glycosylated and unglycosylated proteins and lipids, identified by Fourier transform infrared spectrometry. Transmission electron microscopy shows nanometre-sized grains with irregular grain boundaries and abundant voids. Twinning is observed across all spatial scales and results in a spread of the crystal orientation angles. Electron backscatter diffraction analysis shows a strong fibre texture with the [001] axes of aragonite aligned radially to the shell surface. The aragonitic [100] and [010] axes are oriented randomly around [001]. The random orientation of anisotropic crystallographic directions in this plane reduces anisotropy of the Young's modulus and adds to the optimization of mechanical properties of bivalve shells.

A new apparatus for the measurement of force-frequency effect of crystal resonators

Abstract We describe an apparatus for the measurement of the force-frequency effect of crystal resonators. The force-frequency effect is the correlation between the force put on the crystal resonator and the relative resonant frequency of the resonator to the input force. The new apparatus has been designed and manufactured to measure the force sensitivity coefficient K f (m s/N), which relates to parameters such as crystal geometry, orientation angle, and force direction (azimuth angle). The new loading device has a better force resolution and is simpler to adjust for force alignment than traditional level-loading devices. In order to validate this new loading device, sample experiment tests have been performed, and a comparison of the experiment outcomes with peers’ measurement results show a good agreement.

Equilibrium diamond‐like carbon nanostructures with cubic anisotropy: Elastic properties

AbstractDiamond‐like carbon nanostructures with cubic anisotropy made by joining fullerene‐like molecules of different types via valence bonds are studied by means of molecular dynamics simulations. The considered structures are interesting because they include both‐ and‐hybridized carbon atoms, which lead to their distinct properties compared to the structures with one type of hybridization. Seven diamond‐like carbon phases having different shapes of structural units and/or different ways of their connection are studied in the present work. For the relaxed equilibrium structures, the engineering elastic constants (Poisson's ratio, Young's modulus, and shear modulus) are calculated as the functions of the crystal orientation angles. Extreme values of the elastic constants are reported. It is shown that two of the considered diamond‐like structures have negative Poisson's ratio and can be regarded as the partial auxetics. According to the results of the present study, elastic properties of the bulk diamond‐like carbon structures can vary considerably depending on their structure.Diamond‐like carbon nanostructures