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