Multiferroicity in two-dimensional III-V indium pnictide optoelectronic materials.

In isotropic materials, it is known that values of Poisson's ratio larger than one half are thermodynamically inadmissible, for such values would lead to negative strain energy under certain loads. Although a negative Poisson's ratio is not forbidden by thermodynamics, it is rare in crystalline solids. With the development of modem fiber reinforced composite materials, the effective Poisson's ratio of laminated fiber reinforced composites shows a peculiar behavior as it becomes larger than one half or less than zero. In this article, a study of negative in-plane Poisson's ratio for a general class of randomly-oriented composite laminates is presented. A simple random statistical analysis has been presented. It is demonstrated that composite laminates with negative in-plane Poisson's ratio could be achieved by using the specific values of independent elastic constants E1, E2, G12, and v12 in each lamina. Also, the influence of the lamina material properties to the negative in-plane Poisson's ratio of the composite laminates is presented. The results from this statistical analysis provide a set of general guidelines for designing composite laminates with a special character-the negative in-plane Poisson's ratio.

Two-dimensional (2D) atomic crystals have extraordinary electronic and photonic properties and hold great promise in the applications of photonic and optoelectronics. Here, we review some of our works about the spin-orbit interaction of light on the surface of 2D atomic crystals. First, we propose a general model to describe the spin-orbit interaction of light of the 2D free standing atomic crystal, and find that it is not necessary to involve the effective refractive index to describe the spin-orbit interaction. By developing the quantum weak measurements, we detect the spin-orbit interaction of light in 2D atomic crystals, which can act as a simple method for defining the layer numbers of graphene. Moreover, we find the transverse spin-dependent splitting in the photonic spin Hall effect exhibits a quantized behavior. Furthermore, the spin-orbit interaction of light for the case of air-topological insulator interface can be routed by adjusting the strength of the axion coupling. These basic finding may enhance the comprehension of the spin-orbit interaction, and find the important application in optoelectronic.

Motivated by the successful synthesis of 2D C2F diamanes [Bakharev, P.V. et al., Nat. Nanotechnol. 15, 59–66 (2020)], we have systematically investigated the structural stability, in-plane mechanical, optoelectronic, photocatalytic, piezoelectric, and thermoelectric properties of non-Janus and Janus diamanes monolayers named as C2H, C2F, C2Cl, C4HF, C4HCl and C4FCl. The structural stability is confirmed by cohesive energy, phonon dispersion spectra, and mechanical properties. The electronic properties has been calculated by HSE06 functional and the band gap are found to be 3.85, 5.64, 2.32, 4.16, 0.73 and 1.91 eV for C2H, C2F, C2Cl, C4HF, C4HCl and C4FCl, respectively. The hydrogen-containing non-Janus and Janus diamanes monolayers have a higher negative Poisson's ratio (NPR) and therefore are good auxetic materials. From the Poisson's ratio and Young's modulus of each configuration of non-Janus and Janus diamanes monolayer, anisotropic behavior was displayed. From the optical properties calculations, the refractive index values are around 1.5, which means that it will be a transparent monolayered materials. Also, C2Cl, C4HCl and C4FCl monolayers displayed high absorption spectra with an order of 105 cm−1 in the visible region, which shows great applications in optoelectronic devices. Additionally, the valence and conduction band-edge positions of 2D Janus and non-Janus diamanes of C2H, C2F, and C2Cl and C4HF monolayers have to straddle the redox potentials of water. It means that the photogenerated electrons and holes are sufficient to drive the overall water splitting. Whereas non-Janus diamanes C4HCl, and C4FCl monolayers displayed only water oxidation. The investigated in-plane piezoelectric coefficient has larger in non-Janus diamanes C4HF, C4HCl, and C4FCl monolayers. Therefore, it is very useful in the field of piezoelectric applications. From the thermoelectric properties, the non-Janus and Janus diamanes monolayers have great thermoelectric efficiency and were found to be 10.52 and 10.63% for C2H and C2F, respectively. Our results demonstrate the new class of 2D carbon-based monolayers has good auxetic materials as well as a wide range of applications in optoelectronics, piezoelectric, and thermoelectric fields.

Poisson’s ratio is one of the fundamental features of materials, reflecting the transverse strain response to the applied certain axial strain. The materials with a negative Poisson’s ratio, also known as auxetic materials, are rare in nature and attract lots of research interest because of their unusual mechanical behavior and extensive applications in mechanical nanodevices. Here, we proposed and studied a novel hyperbolic two-dimensional graphene-like structure (GLS) showing a negative Poisson’s ratio behavior by first-principles calculation. The thermodynamic, dynamic, lattice dynamic, and mechanical stabilities of the GLS were carefully studied. In addition, we also explored the electronic structure, mechanical characteristics, and optical-electronic characteristics. The GLS not only displays a negative Poisson’s ratio in certain directions but also shows low-gap semiconductor characteristics and superior electronic conductivity. It is a potential sunscreen material because of the outstanding reflection and absorption for ultraviolet and infrared light.

In this paper the static and dynamic performances of sandwich structures with in-plane negative Poisson's ratio core are investigated from an analytical point of view. The cellular material theory is applied to calculate the orthotropic mechanical properties of re-entrant cell honeycomb cores which shows negative Poisson's ratio values. This special geometrical layout of the cells allows an higher out-of-plane shear modulus compared to the one of regular honeycombs. The laminate orthotropic plate theory with shear correction factors is applied in order to describe the static and dynamic behaviour of symmetric sandwich plates with different core to sheet thickness ratios. Comparisons are made with analogous structures with regular honeycomb. The maximum deflections due to uniform pressure and buckling loads are enhanced, while the natural frequencies show a slight enhancing for some parameters of the cells.

Metal halide HgI2 monolayer with auxetic property and photocatalysis application

As a new class of two-dimensional (2D) materials, 2D covalent organic frameworks (COFs) are proven to possess remarkable electronic and magnetic properties. However, their mechanical behaviours remain almost unexplored. In this work, taking the recently synthesised dimethylmethylene-bridged triphenylamine (DTPA) sheet as an example, we investigate the mechanical behaviours of 2D COFs based on molecular dynamics simulations together with density functional theory calculations. A novel phase transformation is observed in DTPA sheets when a relatively large in-plane compressive strain is applied to them. Specifically, the crystal structures of the transformed phases are topographically different when the compressive loading is applied in different directions. The compression-induced phase transformation in DTPA sheets is attributed to the buckling of their kagome lattice structures and is found to have significant impacts on their material properties. After the phase transformation, Young's modulus, band gap and thermal conductivity of DTPA sheets are greatly reduced and become strongly anisotropic. Moreover, a large in-plane negative Poisson's ratio is found in the transformed phases of DTPA sheets. It is expected that the results of the compression-induced phase transformation and its influence on the material properties observed in the present DTPA sheets can be further extended to other 2D COFs, since most 2D COFs are found to possess a similar kagome lattice structure.

In this paper a novel class of core material for sandwich structures is analyzed from an analytical and numerical point of view. Honeycombs with re-entrant cell geometry present negative in-plane Poisson's ratio coefficients, with an increase of bending stiffness compared to the one of hexagonal honeycomb cores. Due to the orthotropic mechanical properties of this kind of core material it is possible to employ the formulations of laminated orthotropic plates in order to describe the vibroacoustic behavior of simply supported sandwich plates. The natural frequencies of these laminates are sensitive to the geometrical parameters of the core cells. As an example application, an infinite cylindrical sandwich shell in contact with exterior and interior fluid flow is examined. An improvement of transmission loss factors is observed, suggesting a possible use of these cores in acoustic insulation. Damping properties are modeled taking into account the complex modulus of the core material. Two models are examined, one with full viscoelastic core and the other with a free-layer symmetrical beam geometry in order to describe the walls of the core cells. Both cases show a significant increase of the storage moduli of the cores compared to the ones of a regular honeycomb.

Effect of negative Poisson's ratio on the postbuckling behavior of axially compressed FG-GRMMC laminated cylindrical shells surrounded by an elastic medium

Abstract

Materials normally get thinner when stretched (positive Poisson’s ratio) and expand when heated (positive thermal expansion coefficients). However, not all systems behave in this way and systems (materials or structures) which defy common expectation and become wider when stretched (negative Poisson’s ratios, NPR, commonly referred to as auxetic) or contract when heated (negative thermal expansion, NTE) do exist and are now well documented. Materials exhibiting one of these unusual properties are known to be very useful in various practical applications. For example it has been shown that the presence of a negative Poisson’s ratio gives auxetic materials various enhanced physical characteristics over their conventional counterparts ranging from increased indentation resistance and a natural ability to form dome-shaped surfaces to improved acoustic damping properties. Similarly, negative thermal expansion materials can be extremely useful in various applications, such as in the manufacture of composites exhibiting some pre-determined thermal expansion coefficients since the presence of a component with negative thermal expansion lowers the overall thermal expansion of a composite. Although in recent years considerable progress and developments were made in the distinct fields of NPR and NTE, so far, research on systems which could exhibit both of these anomalous properties simultaneously is still in its infancy. Nevertheless, it is known that NTE and NPR are not mutually exclusive properties and in fact, single-crystalline polyacetylene networks (hypothetical carbon allotropes, which so far have not been synthesised) have been predicted to exhibit both properties. Here we will show how existing knowledge on systems exhibiting negative Poisson’s ratios and negative thermal expansion can be combined to produce a novel and easily constructible system which can exhibit both negative properties simultaneously. In particular, we note that as we have recently shown, the construct made from beams connected as illustrated in Fig. 1(a) can exhibit NPR since when it is uniaxially stretched, the beams will flex as illustrated in Fig. 1(b) with the net effect that the triangles rotate relative to each other to produce a more open structure (the ‘‘rotating triangles’’ effect, resulting in negative Poisson’s ratios of 1 in-plane if the triangles are equilateral. In such systems, the straight beams of length 2l can either be welded together or connected through the use of ‘‘pin joint’’-type connections at ends and centres of the beams (corresponding to the vertices of the triangles) where the axes of the ‘‘pin joints’’ are orthogonal to the plane of the structure. The use of such ‘‘pin joints’’ is possible since the formation of the triangles reduces the degrees of freedom of the system and give the structure its characteristic shear rigidity. The presence of these triangles also provide us with a route for turning this auxetic structure into one which can also exhibit negative thermal expansion since as recently proposed, equilateral triangles constructed in such a way that their base is made from a material with a thermal expansion coefficient being at least four times that of the other two sides will get shorter when heated (the ‘‘shortening of triangles’’ mechanism). In fact, it has been shown that dh, the change in height h when the equilateral triangle in Fig. 2 is subjected to a temperature change dT is given by:

Two-dimensional (2D) atomic crystals have triggered significant excitement due to their rich physics as well as potential industrial applications. The possibility of a molecular counterpart with scalable processability and superior performance is intriguing from both fundamental and applied perspectives. Here, we present the freestanding 2D molecular charge-transfer bis(ethylenedithio)tetrathiafulvalene-C60 crystals prepared by a modified Langmuir–Blodgett method, with precisely controlled few-layer thickness and centimeter-scale lateral dimension. The interconversion of intrinsic excited process, the long-range ordering and anisotropic stacking arrangement of the molecular layered crystals generate external stimuli responsive behaviors and anisotropic spin-charge conversion with magnetic energy conversion ability, as well as a superior UV photosensitivity. Moreover, the 2D freestanding crystals demonstrate superior magneto-electrical properties. These results suggest that a new class of 2D atomically thin molecular crystals with novel electronic, optical and magnetic properties have great potential for spintronic, energy and sensor applications.

Phosphorene, a monolayer of elemental phosphorus, has emerged as one of the most significant two-dimensional (2D) atomic crystals in the post-graphene era, as a potential candidate for semiconductor industry, nanotechnology, optoelectronics, and nanomedicine. However, the toxicological effects of this material toward different biomolecules remain elusive. In this article, we perform all-atom molecular dynamics simulations to decipher the effect of interaction and adsorption of two dimeric proteins, namely the HIV-1 integrase and the λ6–85 repressor protein on black phosphorene (BPn). It is revealed that upon purely noncovalent adsorption “on the top” of the BPn surface, the secondary structure of the proteins remains conserved, maintaining all the inter- and intraresidue interactions. In addition, the dimeric structure of the proteins does not dissociate into individual monomeric units, thereby inflicting insignificant to no nanotoxicity. However, if the protein–nanomaterial interaction occurs from an orientation where the edge of the 2D material is directed toward the dimer interface and the axis of dimerization of the protein is perpendicular to the plane of the material, a “clean cut” of the dimer is highly probable, wherein individual monomers are structurally not perturbed. The process of BPn edge-induced dimer cleavage is highly favorable as the Gibbs free energy change accompanying the process is negative for both of the dimeric proteins. Thus, BPn is expected to show orientation-dependent nanotoxicity toward dimeric proteins. For monomeric proteins, however, the extent of nanotoxicity would be significantly milder, and the 2D material may be used as a “molecular scissor” for the nondisruptive cleavage of dimeric proteins.

H2 atmosphere is often involved in growth and application of two-dimensional (2D) atomic crystals, and it is of great importance to understand interaction of the 2D materials with H2 molecules. Here, a full graphene layer and a full hexagonal boron nitride (h-BN) layer grown on Pt(111) were exposed to H2 atmosphere, which were investigated by in situ near ambient pressure X-ray photoelectron spectroscopy and quasi in situ ultraviolet photoelectron spectroscopy. We confirm the occurrence of hydrogen intercalation of the graphene and h-BN overlayers in ambient pressure H2. The hydrogen intercalation in 0.1 Torr H2 at room temperature and hydrogen desorption in 0.1 Torr H2 at 200 °C are fully reversible on the graphene/Pt(111) and h-BN/Pt(111) surfaces. Furthermore, hydrogen desorption on the graphene/Pt(111) and h-BN/Pt(111) surfaces was found to happen at lower temperature than that on the Pt(111) surface due to the graphene and h-BN cover effect.

A decade of intense research on two-dimensional (2D) atomic crystals has revealed that their properties can differ greatly from those of the parent compound. These differences are governed by changes in the band structure due to quantum confinement and are most profound if the underlying lattice symmetry changes. Here we report a high-quality 2D electron gas in few-layer InSe encapsulated in hexagonal boron nitride under an inert atmosphere. Carrier mobilities are found to exceed 103 cm2 V-1 s-1 and 104 cm2 V-1 s-1 at room and liquid-helium temperatures, respectively, allowing the observation of the fully developed quantum Hall effect. The conduction electrons occupy a single 2D subband and have a small effective mass. Photoluminescence spectroscopy reveals that the bandgap increases by more than 0.5 eV with decreasing the thickness from bulk to bilayer InSe. The band-edge optical response vanishes in monolayer InSe, which is attributed to the monolayer's mirror-plane symmetry. Encapsulated 2D InSe expands the family of graphene-like semiconductors and, in terms of quality, is competitive with atomically thin dichalcogenides and black phosphorus.