Biaxial Strain Research Articles

3D Woven Liquid Metals for Radio‐Frequency Stretchable Circuits

AbstractMechanically flexible and stretchable inductive coils are critical for enabling communication, sensing, and wireless power transfer capabilities in wearable electronics that conform to the body for healthcare and Internet of Things (IoT) applications. Leading stretchable conductors such as liquid metals (LMs) offer conformability but sacrifice electromagnetic performance compared with Cu wires, leading to lossy radio‐frequency (RF) characteristics. Here, a strategy leveraging multistranded 3D woven ‘litz’ transmission lines is presented to amplify the resonant RF performance of LM inductors. Through comprehensive simulations and experiments, it is discovered that interwoven LM litz wires boost the Quality Factor (Q) by 80% compared to standard liquid metal wires. A fabrication methodology is also demonstrated for stretchable coils that retain high Q (>30), outperforming the previously reported LM coils and maintaining 98% of their wireless transmission efficiency under up to 30% biaxial strain. Moreover, the versatility of this approach is showcased by 3D printing four‐terminal ‘choke’ inductors optimized for RF filtering and inductance tunability, overcoming the fabrication limitations of traditional planar printed electronics. These results offer valuable insights into the design and implementation of 3D‐printed inductors for a diverse suite of electromagnetic device applications.

Biaxial compressive failure criteria and constitutive model of high-strength geopolymer concrete after high temperature

This paper studies the effect of high temperatures (20℃, 200℃, 400℃, and 600℃) and stress ratios (σ2/σ3) (0.15, 0.3, 0.45, and 0.60) on biaxial compressive strength and strain development patterns of high-strength geopolymer concrete (HGPC). Experimental observations indicate that HGPC exhibits laminar damage similar to ordinary Portland concrete (OPC) before and after exposure to high temperatures, under biaxial compression. Unlike OPC, damage in HGPC initially passes through coarse aggregates at room temperature but shifts predominantly to the aggregate-mortar interface at 600℃. The biaxial compressive strength envelope of HGPC expands with rising temperatures. The increased multiple of biaxial compressive strength (σ3/fm) for HGPC at room temperature rises and then falls with increasing stress ratios, peaking at a stress ratio of 0.45 and surpassing the values for OPC and high-strength concrete (HSC). Before high temperature, the modulus of elasticity of HGPC is higher than that of OPC and decreases with increasing temperature, decreasing by about 45–60% for every 200°C increase, and the reduction is greater than that of OPC. The existing failure criterion is not suitable for HGPC after high temperature, this paper develops a new biaxial compression failure criterion for HGPC before and after high temperature based on Kupfer's criterion, taking into account the effect of temperature. The proposed failure criterion calculation results are well in agreement with the experimental data. A damage constitutive model for HGPC considering the effect of temperature and lateral pressure is also proposed, combining the Weibull distribution model for the ascending branch and a modified empirical model for the descending branch. This combined model effectively predicts the stress-strain relationship of HGPC under various temperature conditions.

Strain-dependent ultrafast carrier dynamics and spin–lattice interaction in LaMnO3 films

We investigate the ultrafast carrier dynamics and spin–lattice interaction in strained and unstrained LaMnO3 films via temperature-dependent femtosecond transient optical spectroscopy. The transient reflectivity measurements show two characteristic relaxation processes in both types of films, which are attributed to electron–phonon coupling and phonon-assisted spin–lattice interaction, respectively. The carrier dynamics and coupling between lattice and spin system are well described with the three-temperature model; the spin–lattice relaxation time constant is dominated by the temperature-dependent spin specific heat. Both the electron–phonon coupling and the spin–lattice interaction are enhanced in the strained film, as a result of the modified band structure and orbital ordering under biaxial compressive strain. Our results reveal the critical role of strain in the photo-induced dynamical interactions in LaMnO3.

Biaxial strain effects on electronic, transport, and thermoelectric properties of SnX[formula omitted] (X = Se, Te) and Janus SnSeTe 1T-monolayers

Biaxial strain in two-dimensional materials plays a crucial role in degenerating the valence and conduction bands, leading to energy dispersion in the band structure and causing changes in transport properties, such as carrier mobility, Seebeck coefficient, and electrical conductivity. Herein, we investigated the effects of biaxial strain on SnX2 (X = Se, Te) and the Janus SnSeTe 1T-monolayer using density functional theory, deformation potential, and semiclassical Boltzmann transport theory. Our findings reveal that the studied 1T-monolayers exhibit high and directionally isotropic electron mobility. Biaxial tensile strain has the effect of increasing the bandgap, predominantly reducing the effective mass of electrons while increasing that of holes. This results in an enhanced electron mobility along with a simultaneous reduction or increase in the concentration of electron carriers or holes, respectively. Especifically, in the case of the Janus SnSeTe 1T-monolayer, we observed a remarkable 68% increase in electron mobility, reaching a value of 1588 cm2V−1s−1. This increase contributes to higher thermoelectric performance due to elevated electrical conductivity and a simultaneous rise in the Seebeck coefficient when subjected to biaxial strain. Our study underscores that strain engineering is an effective strategy for achieving improved thermoelectric properties, particularly exemplified by the SnSeTe 1T-monolayer, which achieved a maximum value of 2.25 for n-type due the ultralow thermal conductivity of 0.359 Wm−1K−1 as result of strong phonon anharmonicity on acoustical and optical modes.

Softened membrane model for shear of ultra-high-performance concrete (SMM-UHPC)

Understanding the shear behavior of Ultra-High-Performance (UHPC) is crucial to prevent undesired responses that could be induced by diagonal shear cracks. Hence, the ability of analytical models to predict shear responses of UHPC members is of paramount importance, which is addressed in this paper by the Softened Membrane Model (SMM). Since the SMM is a two-dimensional shear modeling framework developed for reinforced concrete, a parametric investigation was conducted to assess its suitability for UHPC, namely SMM-UHPC. Through this assessment, a softening coefficient for the biaxial behavior of UHPC was developed and new constitutive laws were integrated in SMM. Comparisons with shear panel tests were used to evaluate the accuracy of SMM-UHPC and quantify the significance of key model parameters. Sensitivity analyses showed that the decomposition between biaxial and uniaxial strain fields, which is used in SMM to capture the Poisson effect, has a negligible influence on UHPC shear. Combining experimental and analytical data, the tensile localization strain was identified to be of most significance for predicting the shear stress-strain response of UHPC.

Electronic phase transformations and energy gap variations in uniaxial and biaxial strained monolayer VS[formula omitted] TMDs: A comprehensive DFT and beyond-DFT study

In the rapidly evolving field of 2D materials, transition metal dichalcogenides (TMDs) have emerged as compelling candidates for electronic applications. This study investigates the electronic structure of the H-phase monolayer VS2 belonging to TMD family and the influence of strain on its band structure through Density Functional Theory (DFT). We employ two different pseudopotential approximations and a suite of computational methods including DFT+U, GAUPBE, G0W0, and self-GW to provide a nuanced understanding of its electronic band structure. A highlight of the study is its focus on how both uniaxial and biaxial strains, ranging from -5% to +5%, affect the electronic properties of the H-phase monolayer VS2. Our comprehensive analysis reveals that these tensile strains significantly widen the energy gap, with uniaxial strains having a more pronounced effect than their biaxial counterparts. Additionally, we identify an intriguing phase transition from a semiconducting to a metallic state under compressive strains, this transition is attributed to both symmetry breaking and bond length variation in the uniaxial case, the bond length in biaxial. These key findings not only enrich our understanding of the intricate electronic behavior of monolayer VS2 under different strains but also pave the way for the design of innovative electronic devices using strain engineering.

The quantum spin Hall insulator with large bandgap in functionalized AlBi monolayer

The quantum spin Hall (QSH) insulator exhibits various interesting physical properties. Therefore, researchers have been seeking QSH insulators with large bandgaps suitable for room temperature applications. Here, based on first-principles calculations, we predict that the chlorine atom functionalized AlBi monolayer forms a topological insulator with a large bandgap (Eg = 0.215 eV). Chlorination and SOC effect induce AlBi(Cl)2 band inversion, and phonon spectra calculations demonstrate excellent dynamic stability for AlBi(Cl)2. The Z2 topological invariants, as well as the topological nontrivial edge states further confirm these findings. In addition, we applied the biaxial strains ranging from −5% to 5% to the monolayer, revealing a topological phase transition at −3%, resulting in the emergence of a normal insulator. These interesting features suggest that chlorinated AlBi is a promising material for room temperature spintronic devices.

Tunable electronic structure and optical properties of GaN monolayer via substituted doping and strain

In this study, the stability, optical properties and electronic structure of transition metal (TM) (Cr, Mn, Fe) doped GaN monolayers is investigated within the first-principles calculation methods. Additionally, the influence of biaxial strain on the aforementioned system is explored. The results demonstrate that substitutional doping effectively adjusts the electronic structure of GaN monolayer, enhancing its performance. The TM-doped GaN monolayer structures exhibit strong dynamic stability: doping with Cr and Fe bring magnetic properties, while Mn doping results in a half-metallicity property. In terms of optical absorption, the GaN:Mn system exhibits significant absorption in the infrared region, while GaN:Cr and GaN:Fe systems show stronger absorption in the visible light and ultraviolet regions compared to the pristine GaN monolayer. Under the biaxial strain from −3% to +12%, with increments of 3%, the band gap types of GaN:Cr, GaN:Fe, and GaN:Mn systems undergo minimal changes, with gradual reduction in gap values. Meanwhile, the optical absorption of doped systems exhibits systematic growth and redshift, particularly evident in the infrared-visible-ultraviolet spectral regions for the GaN:Mn system. These results indicate the controllability and variability of two-dimensional GaN materials, providing new avenues for the potential use of GaN as a material for optoelectronic devices.

The interlayer magnetic interaction in the CrI$_3$/CrSe$_2$ heterostructure

Abstract Based on first-principles calculations, we systematically studied the stacking energy and interlayer magnetic interaction of the heterobilayer composed of CrI$_3$ and CrSe$_2$ monolayers. We found that the stacking order plays a crucial role in the interlayer magnetic coupling. Among all possible stacking structures, the AA-stacking is the most stable heterostructure, exhibiting interlayer antiferromagnetic interactions. Interestingly, the interlayer magnetic interaction can be effectively tuned by biaxial strain. A 4.3% compressive strain would result in a ferromagnetic interlayer interaction in all stacking orders. These results reveal the magnetic properties of CrI$_3$/CrSe$_2$ heterostructure, which is expected to be applied to spintronic devices.

Comparative first principles investigation on the structural, optoelectronic and vibrational properties of strain-engineered graphene-like AlC3, BC3 and C3N monolayers

Three cardinal two-dimensional semiconductors viz., AlC3, BC3 and C3N, closely resembling the graphene structure, are intriguing contenders for emerging optoelectronic and thermomechanical applications. Starting from a critical stability analysis, this density functional theory study delves into a quantitative assessment of structural, mechanical, electronic, optical, vibrational and thermodynamical properties of these monolayers as a function of biaxial strain (ε) in a sublinear regime (−2%⩽ε⩽4%) of elastic deformation. The structures with cohesive energies slightly smaller than graphene, manifest exceptional mechanical stiffness, flexibility and breaking stress. The mechanical parameters have been deployed to further cultivate acoustic attributes and thermal conductivity. The hexagonal structures with mixed ionic-covalent molecular bonds have indirect electronic band-gap and work-function acutely sensitive to ε . Dispersions of optical dielectric function, energy loss, refractive index, extinction coefficient, reflectivity, absorption coefficient and conductivity are deciphered in the UV–Vis–NIR regime against strain, where particular frequency bands featuring high polarization, dissipation, absorbance or reflectance are identified. Phonon band-structure and density of states testify dynamic stability in the ground state for all systems except the compressed ones. A comprehensive group theoretical analysis is performed to cultivate rotational; infrared and Raman-active modes, and the nature of molecular vibrations is delineated. The red-shifting of phonon bands and E2g/A1g Raman peaks with increasing ε , associates estimation of Grüneisen parameter. Finally, strain-induced alterations of thermodynamic quantities such as entropy, enthalpy, free energy, heat capacity and Debye temperature are studied, followed by a molecular dynamics-based stability assessment under canonical ensemble.

Bandgap engineering and enhanced optical properties of Hf3X2O2 (X = N, P, As) novel 2D MXene structures using first-principles study

Two-dimensional (2D) MXenes, having comparable transport properties like graphene and a wide spectrum application, are often limited to being used in optoelectronics due to metallic bandgap. Here, by employing density functional theory we report the bandgap engineering and tuning optoelectronic properties through modulating the anions of novel 2D spinel Hf3X2O2 (X = N, P and As) MXenes structures and show that the material class can be among the few semiconducting MXenes. Phonon spectra and cohesive energies confirm that these structures are dynamically stable and chemically exothermic. Modulating anions X = N, P, and As in Hf3X2O2, the electronic bandgaps are found ∼0.46 eV for N, metallic for P, and ∼48 meV for As atoms, suggesting the semiconducting, metallic, and semi-metallic MXenes. The biaxial strains are incorporated to tune the features: In the Hf3N2O2 structure, the bandgap is increased with both compressive and tensile strains, while for the Hf3As2O2 structure, the gap decreased at the GGA-PBE level. For Hf3P2O2 structures, the bandgaps are all metallic irrespective of pristine or biaxial strain. Spin–orbit coupling SOC+GGA reveals that Hf3N2O2 is highly spin responsive while Hf3As2O2 shows semi-metal-to-metallic bandgap transition for pristine as well as biaxial strained conditions. From optical properties analysis, optical absorptions are found located in the visible spectral regions that are also highly receptive to biaxial strains. These properties we have unleashed for the novel Hf3X2O2 (X = N, P, As) semiconducting MXene, thus, show the potentiality of the utilization of the material class in nanoelectronics and optoelectronics applications.

Efficient Modulation of Schottky to Ohmic Contact in MoSi2N4/M3C2 (M = Zn, Cd, Hg) van der Waals Heterostructures.

A strong Fermi level pinning (FLP) effect can induce a large Schottky barrier in metal/semiconductor contacts; reducing the Schottky barrier height (SBH) to form an Ohmic contact (OhC) is a critical problem in designing high-performance electronic devices. Herein, we report the interfacial electronic features and efficient modulation of the Schottky contact (ShC) to OhC for MoSi2N4/M3C2 (M = Zn, Cd, Hg) van der Waals heterostructures (vdWHs). We find that the MoSi2N4/M3C2 vdWHs can form a p-type ShC with small SBH with the calculated pinning factor S ≈ 0.8 for MoSi2N4/M3C2 contacts. These results indicate that the FLP effect can be effectively suppressed in MoSi2N4 contact with M3C2. Moreover, the interfacial properties and SBH of MoSi2N4/Zn3C2 vdWHs can be effectively modulated by a perpendicular electric field and biaxial strain. In particular, an efficient OhC can be achieved in MoSi2N4/Zn3C2 vdWHs by applying a positive electric field of 0.5 V/Å and strain of ±8%.

Asymmetric optical properties and bandgap shift of pre-strained flexible ZnO films

Strain engineering has been extensively explored to modulate the various intrinsic properties of flexible inorganic semiconductor films. However, experimental characterization of tensile and compressive strain-induced modulation of optoelectronic properties and their differences has not been easily implemented in flexible inorganic semiconductor films. Herein, the strain-dependent structural, optical, and optoelectronic properties of flexible ZnO films under pre-tensile and pre-compressive strains are systemically investigated by a Mueller matrix ellipsometry-based quantitative characterization method combined with x-ray diffraction and first-principle calculation. With extended prestress-driven deposition processing under bi-direction bending modes, pre-tensile and pre-compressive strains with symmetric magnitudes can be achieved in flexible ZnO films, which allows precise observation of the strain-driven asymmetric modulation of optoelectronic properties. When the applied prestrain varies approximately equally from 0% (baseline) to −0.99% (compression) and 1.07% (tensility), respectively, the relative changes for the c-axis lattice constant are 0.0133 and 0.0104 Å, respectively. Meanwhile, the dependence factors of the bandgap energy on the pre-compression and pre-tensile strains were determined as −0.0099 and −0.0156 eV/%, respectively, and the complex refractive index also presents an asymmetric varying trend. With the help of the strain–stress analysis and the first-principle calculation, the intriguing asymmetric strain-optical modulation effect could be attributed to the biaxial strain mechanism and the difference in the deformation potential between the two prestrain modes. These systematic investigation consequences are thus promising as a basis for the booming applications of the flexible inorganic semiconductor ensemble.

Intrinsic room-temperature ferromagnetism in two-dimensional ternary transition metal tellurides CrX2Te4 (X = Al, Ga, and In)

A tremendous amount of research has witnessed the exploration of two-dimensional (2D) materials with intrinsic ferromagnetism and diverse physical properties. However, the low Curie temperature and deficient magnetic anisotropy hinder their practical applications in nanoscale spintronics. Based on first-principles calculations, we propose a new family of 2D ternary transition metal tellurides, CrX2Te4 (X = Al, Ga, and In), with both structural and magnetic stabilities at room temperature. Our calculations demonstrate that the 2D CrX2Te4 crystal exhibits the intrinsic 100% spin-polarized half-metallic feature with spin-up metallic and spin-down semi-conducting properties. With the remarkable magnetic moment of 4 μB per Cr atom, both 2D CrAl2Te4 and CrGa2Te4 crystals perform robust ferromagnetism with the out-of-plane magnetic anisotropy, while the 2D CrIn2Te4 crystal prefers the in-plane easy magnetization axis. The Monte Carlo simulation based on the 2D Heisenberg model shows that the critical Curie temperatures of the 2D CrAl2Te4, CrGa2Te4, and CrIn2Te4 crystals could reach 466, 431, and 536 K, respectively. Moreover, the magnetic exchange strength and magnetic anisotropy could be further enhanced by the in-plane biaxial strain. The novel electronic and magnetic features promote 2D CrX2Te4 (X = Al, Ga, and In) crystals as a new family of two-dimensional intrinsic ferromagnetic materials for next-generation advanced spintronics.

A hyperelastic hydrogel with an ultralarge reversible biaxial strain.

Hyperelastic materials exhibit a nonlinear elastic response to large strains, whereas hydrogels typically possess a low elastic range due to the nonuniform cross-linking and limited chain segments among cross-links. We developed a hyperelastic hydrogel that possesses a broader elastic range by introducing a reversible pearl-necklace structure, in which beads are connected by strings. The subnanometric beads can efficiently unfold and refold under cyclic mechanical strains; thus, the hydrogel can rapidly recover after being stretched to an areal strain of more than 10,000%. Additionally, the hydrogel can quickly heal from minor mechanical damages such as needle punctures and cuts. These advancements make our ionic hydrogels ideal for multifunctional pneumatic gripper materials; they simultaneously offer an ultralarge gripping range, self-sensing capabilities, and fast healing abilities.

The strain regulated physical properties of PbI2/g-C3N4 for potential optoelectronic device

The van der Waals (vdW) heterostructures of Z-scheme PbI2/g-C3N4 with an indirect bandgap have gained much attention in recent years due to their unique properties and potential applications in various fields. However, the optoelectronic characteristics and strain-modulated effects are not yet fully understood. By considering this, six stacking models of PbI2/g-C3N4 are proposed and the stablest structure is selected for further investigation. The uniaxial and biaxial strains (−10%–10%) regulated band arrangement, charge distribution, optical absorption in the framework of density functional theory are systematically explored. The compressive uniaxial strain of −8.55% changes the band type from II→I, and the biaxial strains of −7.12%, −5.25%, 8.91% change the band type in a way of II→I→II→I, acting like the ‘band-pass filter’. The uniaxial strains except −10% compressive strain, and the −6%, −4%, 2%, 4%, 10% biaxial strains will enhance the light absorption of PbI2/g-C3N4. The exerted strains on PbI2/g-C3N4 generate different power conversion efficiency ( ηPCE ) values ranging from 3.64% to 25.61%, and the maximum ηPCE is generated by −6% biaxial strain. The results of this study will pave the way for the development of new electronic and optoelectronic materials with customized properties in photocatalytic field and optoelectronic devices.

Electrical, optical and mechanical properties of monolayer MoTe2 for applications in wearable optoelectronic devices

Transition metal dichalcogenides (TMDs) have excellent optical and mechanical properties and have potential application value in wearable optoelectronic response devices. MoTe2, a representative material of TMDs, is studied by first-principles calculation in this paper. The results show that the MoTe2 monolayer has a direct band gap of 1.110eV, which has a strong light absorption capacity and can produce a high concentration of photogenerated charge carriers after light absorption. The material is soft and exhibits the unique mechanical properties of layered materials. The effects of biaxial strain and defects on the properties of the materials were analyzed. The results show that the biaxial compression strain can enhance the light absorption curve of the material, enhance the light absorption of the photogenerated carrier, and expand the range of its energy distribution. The tensile strain decreases the value of the photon absorption curve and decreases the range of energy distribution of photogenerated carriers. The Mo vacancy defect increases the absorption curve value in the low energy region and broadens the optical response range of the material. The two types of vacancy defects both induce a ‘discrete’ distribution of photogenerated carriers. The Mo vacancy significantly affects the elastic modulus and anisotropy properties of the material, resulting in the material changing from ductile to brittle. When Mo vacancy is added, the spatial distribution of the elastic modulus of the material also changes greatly. Therefore, MoTe2 has potential application in flexible optoelectronic devices, and its performance can be controlled by strains and defects.

A hybrid density functional study of tensile-induced changes in phonon dispersion, electronic structure and optical absorption of bilayer BN for optoelectronic applications

The electronic, phonon dispersion and optical properties of bilayer BN have been investigated with density functional theory (DFT) calculations. Interestingly, applying the biaxial strain of 4% converts the indirect band gap of bilayer BN to a direct band gap. We show that the interaction between the BN layers results in the removal of two-fold degeneracy and separation of ZA and ZO phonon modes near the Γ point. Across the entire range of applied biaxial tensile strains, the bilayer BN exhibits a dynamically stable behavior. The phonon bandgap of bilayer BN decreases under tensile strain. The bilayer BN has strong adsorption in the UV region and the optical absorption peaks are red-shifted by applying the tensile strain. These findings are essential for the strain engineering of bilayer BN and future fabrication of flexible electronic and optoelectronic devices.

Effect of strain on the hysteresis loop of PbTiO3 nanoporous

Spontaneous polarisation of ferroelectric materials has been widely applied in electronic components such as random access memory, sensor, and transducer. Among ferroelectric materials, PbTiO3 (PTO) is one of the dominant materials because it has a large spontaneous polarisation value and can operate stably at high temperatures. PTO has been studied in many different structures such as thin film, nanowire, nanodot, nanodisk, and nanotube. In order to clarify the strain effect on the hysteresis loop of PTO nanoporous, the author investigated the effect of mechanical deformation on porous structure PTO materials using calculations based on the core-shell model. The obtained results show that the hysteresis loop is expanded under the compression of the biaxial strain (x, y) and the tensile of the uniaxial strain (z). On the contrary, the loop is shrunk under the tensile of biaxial strain (x, y) and the compression of uniaxial strain (z). Besides, in the study, spontaneous polarisation distribution and regression function of hysteresis loop area - strain of PbTiO3 nanoporous is discussed as well.

Phonon and electronic properties of semiconducting silicon nitride bilayers

The two-dimensional (2D) IV-V semiconductors have attracted much attention due to their fascinating electronic and optical properties. In this work, we predicted three phases of silicon nitrides, denoted α-Si2N2, β-Si2N2, and γ-Si4N4, respectively. Both α-Si2N2 and β-Si2N2 consist of two buckled SiN sheets, and γ-Si4N4 consists of two puckered SiN sheets. It is challenging to transform between α-Si2N2 and β-Si2N2 because of the high energy barrier. The three dynamically stable bilayers are semiconductors with fundamental indirect band gaps from 0.25 eV to 2.92 eV. As expected, only the s and p orbitals contribute to the electronic states, and the pz orbitals dominate near the Fermi level. Furthermore, insulator-metal transitions occur in α-Si2N2 and β-Si2N2 under the biaxial strain of 16 %. These materials perhaps have potential applications in microelectronics and spintronics.