In-plane Negative Poisson's Ratio Research Articles

A novel two-dimensional sp-sp2-sp3 hybridized carbon nanostructure with a negative in-plane Poisson ratio and high electron mobility

A novel two-dimensional (2D) semiconducting carbon allotrope is proposed by inserting alkyne into tetrahexcarbon. This new carbon allotrope consists of tetra-rings and acetylenic linkages and is called TAL-carbon. To the best of our knowledge, this is the first 2D carbon allotrope composed of sp-sp2-sp3 hybridized carbon atoms. Due to its unique puckered structure, TAL-carbon is the fourth 2D carbon material with an intrinsic in-plane negative Poisson ratio (NPR) reported after graphene, penta-graphene, and tetrahexcarbon. Materials with NPR exhibit a wide range of potential applications in biomedicine, aerospace industries, and precision instruments. TAL-carbon has an indirect band gap of 1.614 eV. At room temperature, it exhibits high in-plane electron mobility of up to ~3.5 × 104 cm2V−1s−1, which is 30 times higher than monolayer black phosphorus and two orders of magnitude higher than monolayer MoS2. The phonon dispersion curves and in-plane elastic constants indicate that TAL-carbon is dynamically and mechanically stable. Its equibiaxial strain limit reaches 13.7%, similar to that of graphene. An ab initio molecular dynamics (AIMD) simulation demonstrates that TAL-carbon is thermally stable at 300 K and 1000 K. The results show that TAL-carbon is a promising 2D auxetic material for applications in nanomechanics and nanoelectronics.

A Novel Hyperbolic Two-Dimensional Carbon Material with an In-Plane Negative Poisson's Ratio Behavior and Low-Gap Semiconductor Characteristics.

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.

Modulation of multi-directional auxeticity in hybrid origami metamaterials

A novel origami metamaterial with programmable multi-directional auxeticity is proposed by hybridizing the concept of re-entrant honeycomb with the Miura pattern. Normal Miura-based origami metamaterials have been widely shown to exhibit negative in-plane Poisson's ratio. However, negative out-of-plane Poisson's ratio cannot be realized in these set of materials, essentially limiting their capability for prospective applications in many multi-functional devices and systems. Here we propose a hybrid Miura-based metamaterial that can show both in-plane and out-of-plane negative Poisson's ratios. More interestingly, we are able to program the Poisson's ratios to have mild to extreme auxeticity and map their mutual interaction as a function of the microstructural configuration. Besides the single-layer meta-sheets, we have shown that a class of multi-layer stacked metamaterial with uniform and graded configurations can be developed to achieve multi-objective functional goals. Theoretical and experimental analyses are combined in this paper to demonstrate the concepts of modulating multi-directional Poisson's ratios. The fundamental mechanics of the proposed origami based metamaterial being scale-independent, this novel class of deployable hybrid materials can be directly transferred for application in a range of milli-, micro-, and nanometer-size systems, essentially opening avenues for the design of energy absorbers, sensors, actuators, medical stents, catalysis, drug delivery systems, adaptive wings for next-generation of aircrafts and other deployable mechanical and electronic systems at multiple length-scales.

Two-Dimensional Square-A2B (A = Cu, Ag, Au, and B = S, Se): Auxetic Semiconductors with High Carrier Mobilities and Unusually Low Lattice Thermal Conductivities.

Using evolutionary structure search combined with ab initio theory, we investigate the electronic, thermal, and mechanical properties of two-dimensional (2D) A2B (A = Cu, Ag, Au, and B = S, Se) auxetic semiconductors. Two types of structures are found to have low energy, namely, s(I/II)-A2B, which have direct bandgaps in the range 1.09-2.60 eV and high electron mobilities. Among these semiconductors, Cu2B and Ag2B have light holes with 2 orders of magnitude larger mobility than the heavy holes, up to 9.51 × 104 cm2 V-1 s-1, giving the possibility of achieving highly anisotropic hole transport with the application of a uniaxial strain. Due to the ionic bonding nature, s-A2B structures have unusually low lattice thermal conductivities down to 1.5 W m-1 K-1 at 300 K, which are quite promising for new generation thermoelectric devices. Besides, s-A2B structures show extraordinary flexibility with ultralow Young's moduli (down to 20 N/m), which are lower than most previously reported 2D materials. Moreover, under strain along the diagonal direction, five of the structures have in-plane negative Poisson's ratios.

Two-dimensional IV–VI materials with in-plane negative Poisson's ratio and anisotropic carrier mobility

Two-dimensional (2D) semiconductors with novel mechanical behaviors and electronic features are highly sought for a variety of potential applications.

A new family of two-dimensional ferroelastic semiconductors with negative Poisson's ratios.

Two-dimensional (2D) materials with both ferroelasticity and negative Poisson's ratios have attracted intensive interest, but it is very rare to have both ferroelasticity and negative Poisson's ratios in a single material. Directional positive and negative Poisson's ratios in a switchable ferroelastic dielectric may enable non-destructive readout in ferroelastic data storage. Herein, we propose 14 kinds of stable 2D semiconductors: AB monolayers (A = Sc, Y, La; B = N, P, As, Sb, Bi) based on first-principles calculations. The band gaps of AB monolayers cover a wide range from 0.69 eV to 2.15 eV. Mechanical analysis reveals that these materials are flexible and 12 of 14 are predicted to possess an in-plane negative Poisson's ratio (NPR). Moreover, 10 of these 14 systems possess an out-of-plane NPR. More encouragingly, all AB monolayers are identified as 2D ferroelastic materials with reversible strains of around 5.94% to 20.30%. The ferroelastic switching barriers, mechanical properties and electronic structures of these materials are discussed in detail. Such outstanding properties make the AB monolayers very promising as switchable anisotropic 2D materials for nanoelectronics and micromechanical applications.

Auxetic B4N Monolayer: A Promising 2D Material with in-Plane Negative Poisson's Ratio and Large Anisotropic Mechanics.

Auxetic materials, known with negative Poisson's ratio, are highly desirable for many advanced applications, but the candidates are rather scarce, especially at low dimension. Motivated by the re-entrant structure that often exposes negative Poisson's ratio, we predict a two-dimensional (2D) planar B4N monolayer as a promising auxetic material with unusual in-plane negative Poisson's ratio within the framework of density functional theory calculations. B4N monolayer also exhibits a highly emerged mechanical anisotropy, characterized by Young's modulus and Poisson's ratio. In addition, this monolayer shows superior mechanical flexibility in ideal tensile strength and critical strain values. The phonon dispersion calculations and ab initio molecular dynamics simulations further demonstrate that this monolayer also owns excellent dynamical and thermal stabilities. The fantastic mechanical properties coupled with robust structural stability render the auxetic B4N monolayer promising for future nanomechanical devices.

Predicting Novel 2D MB2 (M = Ti, Hf, V, Nb, Ta) Monolayers with Ultrafast Dirac Transport Channel and Electron-Orbital Controlled Negative Poisson's Ratio.

Three-dimensional diborides MB2, featured in stacking the M layer above the middle of the honeycomb boron layer, have been extensively studied. However, little information on the two-dimensional counterparts of MB2 is available. Here, by means of evolutionary algorithm and first-principles calculations, we extensively studied the monolayer MB2 crystal with M elements ranging from group IIA to IVA covering 34 candidates. Our computations screened out eight stable monolayers MB2 (M = Be, Mg, Fe, Ti, Hf, V, Nb, Ta), and they exhibit Dirac-like band structures. Dramatically, among them, groups IVB-VB transition-metal diboride MB2 (M = Ti, Hf, V, Nb, Ta) are predicted to be a new class of auxetic materials. They harbor in-plane negative Poisson's ratio (NPR) arising mainly from the orbital hybridization between M d and Boron p orbitals, which is distinct from previously reported auxetic materials. The unusual NPR and the Dirac transport channel of these materials are applicable to nanoelectronics and nanomechanics.

Negative Poisson's ratio in 2D life-boat structured crystals.

Two-dimensional auxetic materials with negative Poisson's ratio expand in response to a tensile strain in cross-section. Such counter-intuitive behaviours have been mainly ascribed to concave structures with ideal rigid ball-stick models. Here, based on first-principles calculations, we systematically analyze the mechanical behaviours of three life-boat structured two-dimensional (2D) materials and report two new auxetic materials: δ-arsenic and δ-graphane. The calculated Poisson's ratio values are correlated with Young's modulus, cohesive energy, and valence shell electron pair repulsion of isostructures. Combining with previous research, we provide a self-consistent explanation of the origin of the 2D in-plane negative Poisson's ratio and an algorithmic route to discover new auxetic materials by comparing the energy restored in bond rotation and stretch.

Electronic and mechanical properties of few-layer borophene

We report first principle calculations of electronic and mechanical properties of few-layer borophene with the inclusion of interlayer van der Waals (vdW) interaction. The anisotropic metallic behaviors are preserved from monolayer to few-layer structures. The energy splitting of bilayer borophene at $\Gamma$ point near the Fermi level is about 1.7 eV, much larger than the values (0.5--1 eV) of other layered semiconductors, indicating much stronger vdW interactions in metallic layered borophene. In particular, the critical strains are enhanced by increasing the number of layers, leading to much more flexibility than that of monolayer structure. On the one hand, because of the buckled atomic structures, the out-of-plane negative Poisson's ratios are preserved as the layer-number increases. On the other hand, we find that the in-plane negative Poisson's ratios disappear in layered borophene, which is very different from puckered black phosphorus. The negative Poisson's ratio will recover if we enlarge the interlayer distance to 6.3 $\mbox\AA$, indicating that the physical origin behind the change of Poisson's ratios is the strong interlayer vdW interactions in layered borophene.

Negative Poisson's ratio and high-mobility transport anisotropy in SiC6 siligraphene.

The diverse forms of silicon carbides lead to versatile properties, but an auxetic allotrope at zero pressure has never been reported. Here, using first-principles calculations we propose a two-dimensional (2D) auxetic silicon carbide material, namely SiC6 siligraphene. The plausibility of the SiC6 siligraphene is verified by the low formation energy, positive phonon spectrum and high mechanical stability. The unique framework of sp2 carbon and sp3 silicon atoms leads to unusual in-plane negative Poisson's ratios and electronic properties superior to both graphene and silicene. SiC6 siligraphene possesses a natural band gap of 0.73 eV and a high carrier mobility. The theoretical mobility in the order of 104 cm2 V-1 s-1 for electrons along the [1[combining macron]10] direction is comparable to the hole mobility in black phosphorene, whereas the hole transport along the [110] direction is blocked. Both the electronic band structure and carrier mobility of the SiC6 siligraphene can be tuned by applying external strain. A possible synthetic route is also proposed. The exotic properties make SiC6 siligraphene a versatile and promising 2D material for applications in nanomechanics and nanoelectronics.

Phase transformation in two-dimensional covalent organic frameworks under compressive loading.

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.

Theoretical discovery of novel two-dimensional VA-N binary compounds with auxiticity.

Auxetic materials, which possess a negative Poisson's ratio (NPR), have been a hot topic in materials science research. Through atomistic simulations, we theoretically rediscover a few novel two-dimensional (2D) VA-nitride (VA-N) binary compounds with δ-phosphorene-like structures. The structures in the δ-phase (except for δ-PN) exhibit better stability in terms of energy, thermodynamics, and mechanics with respect to their counterparts in the α- and β-phases. The structures in the δ-phase show semiconducting behaviors with direct band gaps falling in the visible light region. Interestingly, most structures in the α- and δ-phases (except for δ-BiN) exhibit large in-plane NPRs and excellent mechanical properties. The maximum NPR occurs along the zigzag (x) direction for the δ-phases and along the diagonal direction for the α-phases. Particularly, for α- and δ-SbN, the NPRs are -0.628 and -0.296, respectively. δ-SbN can sustain tensile strains of up to 22% and 35% with maximum stresses of 12.1 and 9.8 GPa in the zigzag and armchair directions, respectively. In addition, the transverse response can reach up to 6.6% at a strain of ∼18% along the armchair (y) direction for δ-SbN, which is considerably higher than those of other 2D auxetic materials. Our results reveal that 2D VA-N binary compounds have potential applications in designing 2D electromechanical and optoelectronic devices.

Auxetics and Other Systems of Anomalous Characteristics

Auxetics and Other Systems of Anomalous Characteristics

Sign-tunable Poisson's ratio in semi-fluorinated graphene.

Poisson's ratio is a fundamental property of a material which reflects the transverse strain response to the applied axial strain. Negative Poisson's ratio is allowed theoretically, but is rare in nature. Besides the discovery and tailoring of bulk auxetic materials, recent studies have also found a negative Poisson's ratio in nanomaterials, while their negative Poisson's ratio is mainly based on conventional rigid mechanical models as bulk auxetic materials. In this work, we report the existence of in-plane negative Poisson's ratio in a two-dimensional convex structure of newly synthesized semi-fluorinated graphene by using first-principles calculations. In addition, the sign of the Poisson's ratio can be tuned by the applied strain. Interestingly, we find that this unconventional negative Poisson's ratio cannot be explained by conventional rigid mechanical models but originates from the enhanced bond angle strain over the bond strain due to chemical functionalization. This new mechanism of auxetics extends the scope of auxetic nanomaterials and can serve as design principles for future discovery and design of new auxetic materials.

In-plane elasticity of a novel auxetic honeycomb design

Abstract This work presents a novel negative Poisson's ratio honeycomb design composed by two parts (a re-entrant hexagonal component and a thin plate part) that provide separate contributions to the in-plane and out-of-plane mechanical properties. The re-entrant hexagons provide the in-plane negative Poisson's ratio, the in-plane compliance and the out-of-plane compressive strength, while the thin plate part connecting the re-entrant hexagonal section bears the large out-of-plane flexibility. This paper focuses on the in-plane mechanical properties of the auxetic cellular structure. Theoretical models related to the in-plane uniaxial tensile modulus, the shear modulus, and the Poisson's ratios have been built and validated using the finite element techniques. The in-plane behavior of the honeycomb has also been investigated against the geometrical parameters of the unit cell using a parametrical analysis. The theoretical and numerical models illustrate good agreement and show the potential of its application in morphing structures. We also provide a benchmark of the auxetic configuration proposed in this work against negative Poisson's ratio topologies from open literature.

Investigation of shape memory alloy honeycombs by means of a micromechanical analysis

Shape memory alloy (SMA) honeycombs are promising new smart materials which may be used for light-weight structures, biomedical implants, actuators and active structures. In this study, the behavior of several SMA honeycomb structures is investigated by means of a continuum-based thermomechanically coupled micromechanical analysis. To this end, macroscopic inelastic stress–strain responses of several topologies are investigated, both for pseudoelasticity and for shape memory effect. It was found that the triangular topology exhibits the best performance. In addition, the initial transformation surfaces are presented for all possible combinations of applied in-plane stresses. A special two-phase microstructure that is capable of producing an overall negative coefficient of thermal expansion is suggested and studied. In this configuration, in which one of the phases is a SMA, residual strains are being generated upon recovery. Here, the negative coefficient of thermal expansion appears to be associated with a larger amount of residual strain upon recovery. Furthermore, a two-dimensional SMA re-entrant topology that generates a negative in-plane Poisson's ratio is analyzed, and the effect of the full thermomechanical coupling is examined. Finally, the response of a particular three-dimensional microstructure is studied.

Sign Change of Poisson's Ratio for Carbon Nanotube Sheets

Most materials shrink laterally like a rubber band when stretched, so their Poisson's ratios are positive. Likewise, most materials contract in all directions when hydrostatically compressed and decrease density when stretched, so they have positive linear compressibilities. We found that the in-plane Poisson's ratio of carbon nanotube sheets (buckypaper) can be tuned from positive to negative by mixing single-walled and multiwalled nanotubes. Density-normalized sheet toughness, strength, and modulus were substantially increased by this mixing. A simple model predicts the sign and magnitude of Poisson's ratio for buckypaper from the relative ease of nanofiber bending and stretch, and explains why the Poisson's ratios of ordinary writing paper are positive and much larger. Theory also explains why the negative in-plane Poisson's ratio is associated with a large positive Poisson's ratio for the sheet thickness, and predicts that hydrostatic compression can produce biaxial sheet expansion. This tunability of Poisson's ratio can be exploited in the design of sheet-derived composites, artificial muscles, gaskets, and chemical and mechanical sensors.

Exploration of high and negative Poisson's ratio elastomer‐matrix laminates

AbstractElastomer‐matrix composites show promise for high Poisson's ratio and negative Poisson's ratio (auxetic) applications due to high orthotropy. There are approximately five orders of magnitude between the axial stiffness of high modulus graphite fibres and the stiffness of low durometer elastomers. Although the maximum Poisson's ratio for isotropic elastomers is 0.5, it is easily shown that inplane Poisson's ratios twice unity can be obtained with a graphite/epoxy angle‐ply laminate at 25°. Chou and others have predicted inplane Poisson's ratios greater than 7 for certain cord‐rubber combinations. Peel previously predicted inplane Poisson's ratios higher than 32 and less than –60. Preliminary experimental results have produced inplane Poisson's ratios as high as 14. Certain combinations of un‐balanced highly orthotropic laminates may also produce inplane negative Poisson's ratios. Inplane Poisson's ratios, experimentally obtained from two laminate configurations with approximately the same axial stiffness are compared. A symmetric, balanced laminate produced an inplane Poisson's ratio of 3.7; while an unbalanced laminate with an equivalent axial stiffness produced an average inplane Poisson's ratio of –1.5. Certain high and negative Poisson's ratio elastomer‐matrix laminates appear to have quasi anti‐symmetric relationships about 0°, although laminate designers may consider dual angle‐ply laminates to be the more likely counterpart to the unbalanced dual angle auxetic laminates. Unbalanced symmetric laminates experience significantly more inplane shear deformation when axially loaded than their balanced counterparts. The high shear may be desirable for damping applications, but less desirable otherwise. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of hexagonal chiral structure for morphing airfoil concept

In this paper a concept of hexagonal chiral honeycomb is proposed as a truss-like internal structure for adaptive wing box configurations. In contrast with classical centresym-metric cellular structures like rectangular or hexagonal grids, the proposed honeycomb did not present inversion symmetry, and featured an in-plane negative Poisson's ratio behaviour. The cellular structure considered exhibited this Poisson's ratio behaviour under a large range of strain. A set of numerical (finite element, FE) simulations have been carried out in order to correct the initial theoretical predictions to take into account axial, shear and elastic deformations of all elements composing the unit cell when subjected to uniaxial loading. The homogenized linear elastic mechanical properties were then introduced in an FE wing box model of a racecar wing coupled to a panel code to simulate unidirectional static fluid—structure coupling between the wing box and the flow surrounding the airfoil. The cellular solid proposed as the internal layout of the wing box allowed conforming deformations with the external flow, giving a variation of the camber line and trailing edge displacement, and acting as an aileron