108,473 research outputs found
Polytypism and Unexpected Strong Interlayer Coupling of two-Dimensional Layered ReS2
The anisotropic two-dimensional (2D) van der Waals (vdW) layered materials,
with both scientific interest and potential application, have one more
dimension to tune the properties than the isotropic 2D materials. The
interlayer vdW coupling determines the properties of 2D multi-layer materials
by varying stacking orders. As an important representative anisotropic 2D
materials, multilayer rhenium disulfide (ReS2) was expected to be random
stacking and lack of interlayer coupling. Here, we demonstrate two stable
stacking orders (aa and a-b) of N layer (NL, N>1) ReS2 from ultralow-frequency
and high-frequency Raman spectroscopy, photoluminescence spectroscopy and
first-principles density functional theory calculation. Two interlayer shear
modes are observed in aa-stacked NL-ReS2 while only one interlayer shear mode
appears in a-b-stacked NL-ReS2, suggesting anisotropic-like and isotropic-like
stacking orders in aa- and a-b-stacked NL-ReS2, respectively. The frequency of
the interlayer shear and breathing modes reveals unexpected strong interlayer
coupling in aa- and a-b-NL-ReS2, the force constants of which are 55-90% to
those of multilayer MoS2. The observation of strong interlayer coupling and
polytypism in multi-layer ReS2 stimulate future studies on the structure,
electronic and optical properties of other 2D anisotropic materials
On the stable discretization of strongly anisotropic phase field models with applications to crystal growth
We introduce unconditionally stable finite element approximations for
anisotropic Allen--Cahn and Cahn--Hilliard equations. These equations
frequently feature in phase field models that appear in materials science. On
introducing the novel fully practical finite element approximations we prove
their stability and demonstrate their applicability with some numerical
results.
We dedicate this article to the memory of our colleague and friend Christof
Eck (1968--2011) in recognition of his fundamental contributions to phase field
models.Comment: 20 pages, 8 figure
Influence of elastic anisotropy on the shapes of ellipsoidal blisters and stress field around the blisters in solid materials
Ishii Akio. Influence of elastic anisotropy on the shapes of ellipsoidal blisters and stress field around the blisters in solid materials. AIP Advances 13, 125024 (2023); https://doi.org/10.1063/5.0182632.To address the embrittlement challenges posed by gas blisters in anisotropic materials, the stable shape of constant-pressure blisters in anisotropic materials (hexagonal, tetragonal, and rhombohedral) was energetically investigated based on continuum theory (micromechanics), considering the blister as Eshelby’s ellipsoidal inclusion. The non-negligible change in the blister shape was confirmed in terms of the anisotropic factor η ≡ C3333/C1111. Although the spherical shape of the blister is preferable for isotropic and cubic materials (η = 1), the x3 normal penny and capsule shapes were theoretically confirmed to be the most stable ones for η > 1 and η < 1, respectively. The penny and capsule shape blisters generate larger stress fields around themselves than the sphere shape blisters, thus inducing crack formation. The embrittlement due to the gas (typically hydrogen or helium) inside the blister for the anisotropic materials was more significant than isotropic and cubic embrittlement
Infrared dichroism of gold nanorods controlled using a magnetically addressable mesophase
Gold nanorods have unique optical properties, which make them promising
candidates for building nano-structured materials using a "bottom-up" strategy.
We formulate stable bulk materials with anisotropic optical properties by
inserting gold and iron oxide nanorods within a lamellar mesophase.
Quantitative measurements of the order parameter by modelling the absorbance
spectra show that the medium is macroscopically aligned in a direction defined
by an external magnetic field. Under field, the system exhibits significant
absorption dichroism in the infrared range, at the position of the longitudinal
plasmon peak of the gold nanorods (about 1200 nm), indicating strong
confinement of these particles within the water layers of the lamellar phase.
This approach can yield soft and addressable optical elements
Energy conserving Anisotropic Anhysteretic Magnetic Modelling for Finite Element Analysis
To model ferromagnetic material in finite element analysis a correct
description of the constitutive relationship (BH-law) must be found from
measured data. This article proposes to use the energy density function as a
centrepiece. Using this function, which turns out to be a convex function of
the flux density, guarantees energy conservative modelling. The magnetic field
strength can be seen as a derivative with respect to the flux density.
Especially for anisotropic materials (from lamination and/or grain orientation)
this method has advantages. Strictly speaking this method is only valid for
anhysteretic and thermodynamically stable material
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