Anisotropic Phenomena Research Articles

Anisotropic magnetic entropy change and magnetic critical behavior in van der Waals Fe3GaTe2

Fe3GaTe2, with intrinsic magnetism at ambient temperature and high perpendicular magnetic anisotropy, is a promising van der Waals material for 2D-materials-based spintronic devices. Herein, we report the anisotropic magnetocaloric effects and magnetic critical phenomena in Fe3GaTe2 single crystal. Owing to the large anisotropy, magnetic entropy change (−ΔSM) shows anisotropic character with −ΔSMmax of 1.67 J kg−1 K−1 along the c axis and 1.11 J kg−1 K−1 in the ab plane under field change of 5 T. The rotating ΔSM from the ab plane to the c axis reaches 0.67 J kg−1 K−1 at magnetic field of 5 T. By carefully fitting the −ΔSMmax and relative cooling power (RCP), we determine their relationships to be −ΔSMmax∝Hn (n = 0.694(1)) and RCP∝Hm (m = 1.301(3)) for the magnetic field along the c-axis. Further analysis of critical behavior near TC reveals critical exponents β = 0.41(1) at TC = 341.5(1) K, γ = 1.01(1) at TC = 341.6(3) K, and δ = 3.67(15) at TC = 340 K, indicating a three-dimensional complex magnetic exchange.

Validation of Fixed Ultrasonography for Achilles Tendon Assessment: A Reliability Study

Background: It is important to highlight the advantages of ultrasound in assessing muscular and tendinous behavior due to its non-invasive nature and capacity for dynamic studies. However, evaluating tendons via ultrasound can be challenging given the complexity of anisotropic phenomena related to collagen fiber arrangement. This study aims to validate the reliability of fixed ultrasound compared to manual acquisition in measuring Achilles tendon thickness. Method: Twenty participants, six men and fourteen women, were recruited. Ultrasound was used to measure the Achilles tendon’s thickness at two specific points (4 and 6 cm from the calcaneal insertion of the Achilles tendon). The measurements were conducted by two examiners, one with previous experience and another without. Results: The measurements at 6 cm from the calcaneal insertion showed α = 0.996, α = 0.998 for measurements at 4 cm using manual acquisition, and α = 0.997 for measurements with fixed ultrasound at rest. For the weight-bearing and ankle dorsiflexion measurements, the reliability was excellent (α = 0.999 and α = 1.000). Conclusions: The findings demonstrated excellent reliability in the ultrasound measurements of the Achilles tendon’s thickness, even when performed by different evaluators and under load-bearing conditions. This study suggests the clinical utility of assessing anatomical structures under load, enhancing ultrasound’s applicability beyond the examination table. It is concluded that fixed ultrasound acquisition exhibits excellent reliability in measuring the Achilles tendon’s thickness, offering potential benefits for precise diagnosis of pathologies, planning surgical interventions, and reducing possible errors related to operator variability.

An anisotropic eigenfracture approach accounting for mixed fracture modes in wooden structures by the Representative Crack Element framework

Finite Element analysis of anisotropic fracture phenomena in wood is a challenging task, particularly when dealing with intricate loading scenarios and mode-specific behavior. The appeal of energetically motivated approaches, such as the eigenfracture method, is that they enable simulation of fracture without prior knowledge of the crack path. The promising eigenfracture method has shown good numerical performance for isotropic materials, and this contribution showcases its application to anisotropic materials. Wood is one such anisotropic material and in this manuscript, the directional dependence of both elasticity and fracture evolution are incorporated into the eigenfracture approach. Further, the eigenfracture approach is used in conjunction with Representative Crack Elements (RCE), which permit accurate modeling of physical crack deformations. The governing equations are systematically derived and implemented into the Finite Element framework. By representative numerical examples, some advantages over the alternative phase-field method are demonstrated. Another highlight of this work is that it is possible to provide a realistic ratio of the energy release rates parallel to and perpendicular to the fiber direction in order to achieve physically accurate crack patterns. Additionally, the calculation effort is reduced, because the unknowns required to determine the crack kinematics can be solved analytically at the material level, a feature that also enables parallelization.

An anisotropic full-network model with damage surface for the Mullins effect in filled rubbers

The Mullins effect is a highly anisotropic damage phenomenon exhibited by filled rubbers among other soft materials. When filled rubbers are subjected to uniaxial tension, their apparent stiffness drops in the direction of stretching but is essentially unaltered in the transverse directions. However, micromechanical full-network models where Mullins softening is described at the level of individual chains often predict that uniaxial deformations induce transverse softening in addition to softening in the stretching direction. Moreover, these approaches typically require the storage of damage state variables for each chain, which is computationally expensive. Taking an alternative approach, we present a full-network model for the Mullins effect where the damage state is described by a single macroscopic damage tensor from which the damage state in each direction can be calculated. The evolution of damage is specified through damage surfaces and damage flow rules, which depend on the directions of principal stretches. The model is shown to reproduce experimental data for filled rubbers sequentially subjected to uniaxial tension in different directions. The model is also implemented in the finite element software ABAQUS as a user subroutine UMAT to illustrate the suitability of the model to simulate non-homogeneous deformation states.

Anisotropic Icephobic Mechanisms of Textured Surface: Barrier or Accelerator?

Icing has been seen as an economic and safety hazard due to its threats to aviation, power generation, offshore platforms, etc., where passive icephobic surfaces with a surface texturing design have the potential to address this problem. However, the intrinsic icephobic principles associated with the surface textures, energy, elasticity, and hybrid effects are still unclear. To explore the anisotropic wettability, ice nucleation, and ice detaching behaviors, a series of textured poly(dimethylsiloxane) (PDMS)-based coatings with various texture orientations were proposed through a simple stamping method with surface functionalization. The anisotropic hydrophobic/icephobic phenomena and mechanisms were discovered from wettability evaluation, experimentally studied by icing/deicing experiments, and finally verified by microscopic numerical simulations. One-way analysis of variance (one-way ANOVA analysis) was used to analyze the effect of surface textures on hydrophobic/icephobic properties, which assisted in understanding anisotropic phenomena. Typical anisotropic ice nucleation and growth on the textured coatings were clarified using in situ environmental scanning electron microscope (ESEM) characterization. The ice/coating interfacial stress responses were studied by numerical stimulation at the microscopic level, further verifying the localized, amplified, and propagated stress at the ice/coating interface. The theoretical anisotropic responses, barrier effect, and accelerating effect were verified to interpret the anisotropic wettability and icephobicity, depending on the specific surface conditions. This study revealed the basics of the anisotropic icephobic mechanisms of textured icephobic surfaces, further facilitating the R&D of passive icephobic surfaces.

Precursory Signs of Large Forbush Decreases in Relation to Cosmic Rays Equatorial Anisotropy Variation

Forbush decreases are usually characterized by increased values of cosmic ray anisotropy. The precursory signs, i.e., pre-increases and especially pre-decreases of the cosmic ray intensity, are highly anisotropic phenomena that ordinarily forewarn of such events. Two Cosmic Ray Groups from the National and Kapodistrian University of Athens (NKUA) and the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation of the Russian Academy of Sciences (IZMIRAN) have been investigating the existence of precursory signs preceding Forbush decreases in relation to different solar phenomena, interplanetary parameters, and geomagnetic conditions. In this study, large Forbush decreases (magnitude > 5%) accompanied by geomagnetic storms (i.e., geomagnetic index Dst < −100 nT and 5 ≤ Kp-index ≤ 9) and characterized by an equatorial anisotropy 1 h before the onset of the event (Axyb, %) less than 0.8% were examined regarding precursors. In total, 50 events with the aforementioned features were selected and analyzed from the IZMIRAN’s Forbush Effects and Interplanetary Disturbances database concerning the time period from 1969 until 2023. The Ring of Stations method, which depicts the cosmic ray variations for various asymptotic longitudes in relation to time, was applied on each event. The results revealed that clear signs of pre-decreases were not present for the majority of the events. Since particularly strong events were considered, most of them still showed some precursory signs, albeit mainly weak. Despite this, the value of Axyb = 0.8% proves to be a good threshold for the manual selection of FDs with well-expressed precursors.

Shape compensation for carbon fiber thermoplastic composite stamp forming

Shape compensation of tooling for stamp forming of carbon fiber thermoplastic laminated composites is described as a process wherein the virtual twin, FORM3D is utilized to determine the tooling geometry required to produce the desired part geometry in a single step process. FORM3D is a physics-based virtual twin that incorporates anisotropic phenomena including transient heat transfer, thermoviscoelasticity, thermoelastic and crystallization shrinkage, and polymer crystallization and melting kinetics. This procedure for determining the compensated tool geometry is illustrated for a composite laminate constructed of AS4/PEKK prepreg, supplied by Solvay Thermoplastic Composites, for a quasi-isotropic layup of variable thickness and double curvature: major radius of curvature of 1556.7 mm and minor radius of curvature of 75.7 mm. The resulting, compensated shape was shown to agree with the desired geometry within ±0.25 mm.

Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex.

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

Experimental and numerical investigation of the yield point phenomenon and strain partitioning behavior in a dual-phase steel with lamellar structure

Severe rolling techniques show potential for enhancing the strength and ductility of metallic materials, but the resulting microstructural anisotropy affects the mechanical behavior. The study investigated the anisotropic yield point phenomenon (YPP) and strain partitioning behavior in a dual-phase steel with ultrafine lamellar structure, fabricated through severe cold- and warm-rolling procedures. Experimental results show that tensile specimens aligned parallel to the rolling direction exhibit YPP and higher ductility, while those oriented normal to the rolling direction show continuous yielding behavior and decreased ductility. Using Digital Image Correlation techniques, we studied the evolution of the strain distribution on the surface of the gauge segment, revealing that the strain within the Lüders band was almost constant during the Lüders band propagation. Strain-induced martensitic transformation (SIMT) was observed within the Lüders band and the volume fraction of martensite keeps almost constant during the Lüders band propagation. Numerically, we integrated the mechanisms of SIMT and YPP into a dislocation density-based J2 plasticity constitutive framework. Simulated tensile tests indicate a smaller Lüders strain resulted from the initial higher strain hardening rate. Additionally, SIMT suppresses local instability and therefore promotes the stable propagation of Lüders bands. Simulations verify that the lamellar orientation and SIMT significantly affect the strain hardening rate and void growth. Our findings provided a new perspective on the intrinsic mechanism of the anisotropic YPP and ductility in lamellar dual-phase steels.

Wandering principal optical axes in van der Waals triclinic materials

Nature is abundant in material platforms with anisotropic permittivities arising from symmetry reduction that feature a variety of extraordinary optical effects. Principal optical axes are essential characteristics for these effects that define light-matter interaction. Their orientation – an orthogonal Cartesian basis that diagonalizes the permittivity tensor, is often assumed stationary. Here, we show that the low-symmetry triclinic crystalline structure of van der Waals rhenium disulfide and rhenium diselenide is characterized by wandering principal optical axes in the space-wavelength domain with above π/2 degree of rotation for in-plane components. In turn, this leads to wavelength-switchable propagation directions of their waveguide modes. The physical origin of wandering principal optical axes is explained using a multi-exciton phenomenological model and ab initio calculations. We envision that the wandering principal optical axes of the investigated low-symmetry triclinic van der Waals crystals offer a platform for unexplored anisotropic phenomena and nanophotonic applications.

Chemical Vapor Deposition of a Single-Crystalline MoS2 Monolayer through Anisotropic 2D Crystal Growth on Stepped Sapphire Surface.

Recently, a step-flow growth mode has been proposed to break the inherent molybdenum disulfide (MoS2) crystal domain bimodality and yield a single-crystalline MoS2 monolayer on commonly employed sapphire substrates. This work reveals an alternative growth mechanism during the metal-organic chemical vapor deposition (MOCVD) of a single-crystalline MoS2 monolayer through anisotropic 2D crystal growth. During early growth stages, the epitaxial symmetry and commensurability of sapphire terraces rather than the sapphire step inclination ultimately govern the MoS2 crystal orientation. Strikingly, as the MoS2 crystals continue to grow laterally, the sapphire steps transform the MoS2 crystal geometry into diamond-shaped domains presumably by anisotropic diffusion of ad-species and facet development. Even though these MoS2 domains nucleate on sapphire with predominantly bimodal 0 and 60° azimuthal rotation, the individual domains reach lateral dimensions of up to 200 nm before merging seamlessly into a single-crystalline MoS2 monolayer upon coalescence. Plan-view transmission electron microscopy reveals the single-crystalline nature across 50 μm by 50 μm inspection areas. As a result, the median carrier mobility of MoS2 monolayers peaks at 25 cm2 V-1 s-1 with the highest value reaching 28 cm2 V-1 s-1. This work details synthesis-structure correlations and the possibilities to tune the structure and material properties through substrate topography toward various applications in nanoelectronics, catalysis, and nanotechnology. Moreover, shape modulation through anisotropic growth phenomena on stepped surfaces can provide opportunities for nanopatterning for a wide range of materials.

Sub-preferential rotational wave beaming in structurally rhombus re-entrant honeycombs

Rotational waves frequently manifest in micro-structured materials and are often coupled with classical shear or longitudinal wave modes. In this study, a distinctive isolated optical branch, exhibiting very high polarization index related to joint rotation motion, is found in dispersion diagram of elastic wave propagation in structurally rhombus re-entrant honeycomb (SSRH). Through an analysis of group velocity, we further explore the wave beaming of the rotational wave propagation within the SRRH, and intriguingly, observe the emergence of sub-preferential wave beaming occurring along the short diagonal directions. This dynamic anisotropic phenomenon stems from the intricate interplay between wave frequency and structural topology. To elucidate the underlying dynamic anisotropy of rotational waves, we propose a simple rigid-spring model and derive a modulation function that precisely captures the intricate frequency-structure coupling behavior. The obtained modulation function unveils the formation of sub-preferential directions of the rotational wave within the SRRH.

Ultrafast optical properties and applications of anisotropic 2D materials

Abstract Two-dimensional (2D) layered materials exhibit strong light-matter interactions, remarkable excitonic effects, and ultrafast optical response, making them promising for high-speed on-chip nanophotonics. Recently, significant attention has been directed towards anisotropic 2D materials (A2DMs) with low in-plane crystal symmetry. These materials present unique optical properties dependent on polarization and direction, offering additional degrees of freedom absent in conventional isotropic 2D materials. In this review, we discuss recent progress in understanding the fundamental aspects and ultrafast nanophotonic applications of A2DMs. We cover structural characteristics and anisotropic linear/nonlinear optical properties of A2DMs, including well-studied black phosphorus and rhenium dichalcogenides, as well as emerging quasi-one-dimensional materials. Then, we discuss fundamental ultrafast anisotropic phenomena occurring in A2DMs, such as polarization-dependent ultrafast dynamics of charge carriers and excitons, their direction-dependent spatiotemporal diffusion, photo-induced symmetry switching, and anisotropic coherent acoustic phonons. Furthermore, we review state-of-the-art ultrafast nanophotonic applications based on A2DMs, including polarization-driven active all-optical modulations and ultrafast pulse generations. This review concludes by offering perspectives on the challenges and future prospects of A2DMs in ultrafast nanophotonics.

An anisotropic damage model for finite strains with full and reduced regularization of the damage tensor

AbstractThe modeling of damage as an anisotropic phenomenon enables the consideration of arbitrarily oriented microcracks at the material point level. Yet, the incorporation of material softening into structural simulations still requires a regularization of for example, the degrading variable. There exist different possibilities for a regularization in case of anisotropic damage with varying numbers of nonlocal degrees of freedom corresponding to for example, the symmetric integrity tensor , the principal traces of the damage tensor or a scalar damage hardening variable. Here, we propose a finite strain formulation with a symmetric second order damage tensor of which all six independent components are regularized with a corresponding nonlocal degree of freedom. Due to the significant increase in computational cost caused by the full regularization of the damage tensor, alternative approaches for a reduced regularization with fewer nonlocal degrees of freedom are discussed. Thereafter, the results of a numerical example using the model with full regularization are presented.

Troubleshooting spectral artifacts from biplate retarders for reliable Stokes spectropolarimetry.

Polarimetry is generally used to determine the polarization state of light beams in various research fields, such as biomedicine, astronomy, and materials science. In particular, the rotating quarter-wave plate polarimeter is an inexpensive and versatile option used in several single-wavelength applications to determine the four Stokes parameters. Extending this technique to broadband spectroscopic measurements is of great scientific interest since the information on light polarization is highly sensitive to anisotropic phenomena. However, the need for achromatic polarizing elements, especially quarter-wave plates, requires special attention in their modeling. In this study, we implemented a rotating retarder spectropolarimeter for broadband measurements using a commercially available quasi-achromatic biplate retarder over the visible range. Here, we present a comprehensive approach for troubleshooting this type of spectropolarimeter through the observation of artifacts stemming from the standard single-plate retarder model. Then, we derive a more suitable model for a quasi-achromatic retarder consisting of a biplate junction. This new biplate model requires knowledge of the intrinsic dispersive properties of the biplate, namely the equivalent retardance, fast axis tilt, and rotatory angle. Hence, in this study, we also show a self-consistent methodology to determine these biplate properties using the same polarimeter apparatus so that accurate Stokes parameters can be determined independently. Finally, the comparison of data generated with the standard single-plate and new biplate models shows a significant improvement in the measurement precision of the investigated polarization states, which confirms that remodeling the retarder for reliable spectropolarimetry is necessary.

Electronic and optical properties of new Pentagonal Janus PtXY (X, Y=S, Se, Te; X [formula omitted] Y) monolayers: A DFT study

In this work, we investigate a new phase of two-dimensional Janus PtXY (X, Y = S, Se, Te; X ≠ Y) monolayers named pentagonal (Penta-PtXY) using the first-principles calculations. We found that Penta-PtXY monolayers are semiconductors with an indirect band gap of 1.69 eV, 1.52 eV, and 1.43 eV for Penta-PtSSe, Penta-PtSTe, and Penta-PtSeTe, respectively, that is reduced with the inclusion of spin–orbit coupling. These structures are dynamically stable as their phonon dispersions showed no soft phonon frequencies. The investigation of the optical properties revealed that monolayers Penta-PtXY have in-plane anisotropic optical properties with higher absorption spectra along the y-direction. Moreover, the maximum absorption occurs in the ultraviolet (UV) region, therefore, they can harvest UV and visible photons more effectively. This combination of properties makes these materials attractive for fundamental studies of anisotropic phenomena in 2D materials and may enable novel optoelectronic and nanotechnology applications.

Anisotropic Topological Anderson Transitions in Chiral Symmetry Classes.

We study quantum phase transitions of three-dimensional disordered systems in the chiral classes (AIII and BDI) with and without weak topological indices. We show that the systems with a nontrivial weak topological index universally exhibit an emergent thermodynamic phase where wave functions are delocalized along one spatial direction but exponentially localized in the other two spatial directions, which we call the quasilocalized phase. Our extensive numerical study clarifies that the critical exponent of the Anderson transition between the metallic and quasilocalized phases, as well as that between the quasilocalized and localized phases, are different from that with no weak topological index, signaling the new universality classes induced by topology. The quasilocalized phase and concomitant topological Anderson transition manifest themselves in the anisotropic transport phenomena of disordered weak topological insulators and nodal-line semimetals, which exhibit the metallic behavior in one direction but the insulating behavior in the other directions.

Temperature-Driven Anisotropic Mg2+ Doping for a Pillared LiCoO2 Interlayer Surface in High-Voltage Applications.

High-voltage lithium cobalt oxide (LiCoO2) has the highest volumetric energy density among commercial cathode materials in lithium-ion batteries due to its high working voltage and compacted density. However, under high voltage (4.6 V), the capacity of LiCoO2 fades rapidly due to parasitic reactions of high-valent cobalt with the electrolyte and the loss of lattice oxygen at the interface. In this study, we report a temperature-driven anisotropic doping phenomenon of Mg2+ that results in surface-populated Mg2+ doping to the side of the (003) plane of LiCoO2. Mg2+ dopants enter the Li+ sites, lower the valence state of Co ions with less hybridization between the O 2p and Co 3d orbitals, promote the formation of surface Li+/Co2+ anti-sites, and suppress lattice oxygen loss on the surface. As a result, the modified LiCoO2 demonstrates excellent cycling performance under 4.6 V, reaching an energy density of 911.2 Wh/kg at 0.1C and retaining 92.7% (184.3 mAh g-1) of its capacity after 100 cycles at 1C. Our results highlight a promising avenue for enhancing the electrochemical performance of LiCoO2 by anisotropic surface doping with Mg2+.

Reflective Spin–Orbit Geometric Phase from Planar Isotropic Interface

AbstractManipulating angular momentum of light relies on the change of geometric phase in anisotropic nanostructures or optical interface phenomena. Spin–orbit interactions demonstrated in normal incidence at a planar isotropic interface are conditioned by Brewster reflection, limited to the light beam with a single radial frequency in the k‐space. This study demonstrates a geometric (Pancharatnam–Berry) phase that overcomes Brewster angle limitations providing high variability in the modulation of light reflected from a planar isotropic interface. The examined geometric phase stems from the reflection anisotropy imitating the structural anisotropy of photoaligned liquid crystals and photonic metasurfaces. Using a geometric‐phase modulation of tightly focused light reflected from a glass slab, three modes of spin to orbital angular momentum conversion are demonstrated. The discovered reflective spin–orbit interaction allows for design of a double‐helix focusing sensor to be used in microscopy imaging for precise depth measurements (accuracy 109 nm and precision 7 nm in the range of 8 µm). Experiments with a focused astigmatic beam prove that a glass plate can perform very complex modulation of the geometric phase using illumination structuring. The results thus provide the foundation for the design of low‐cost geometric‐phase systems relying on the space‐variant reflection anisotropy.

Nonlinear and Anisotropic Ion Transport in Black Phosphorus Nanochannels.

Two-dimensional material nanochannels with molecular-scale confinement can be constructed by Van der Waals assembly and show unexpected fluid transport phenomena. The crystal structure of the channel surface plays a key role in controlling fluid transportation, and many strange properties are explored in these confined channels. Here, we use black phosphorus as the channel surface to enable ion transport along a specific crystal orientation. We observed a significant nonlinear and anisotropic ion transport phenomenon in the black phosphorus nanochannels. Theoretical results revealed an anisotropy of ion transport energy barrier on the black phosphorus surface, with the minimum energy barrier along the armchair direction approximately ten times larger than that along the zigzag direction. This difference in energy barrier affects the electrophoretic and electroosmotic transport of ions in the channel. This anisotropic transport, which depends on the orientation of the crystal, may provide new approaches to controlling the transport of fluids.