Uniaxial Strain Research Articles

Study on superconductivity in Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}SC and Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{2}$$\\end{document}AsC MAX phases at various pressures

Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}SC and Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}AsC are among the identified superconducting MAX phases, both exhibiting a transition temperature Tc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {T}_{{c}}$$\\end{document} lower than 10 K. These compounds appear to belong to the conventional class of superconductors. By calculating the electron-phonon couplings of these materials, we have found that the predicted transition temperatures are approximately 6 K for Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}SC and 2 K for Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}AsC, closely matching the experimental findings. However, when subjected to pressure or strain, Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}SC and Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}AsC exhibit contrasting behaviors. While the transition temperature of Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}SC can be doubled by applying pressure up to 50 GPa, the transition temperature of Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}AsC significantly decreases under the same pressure. On the other hand, in the case of Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}AsC, a uniaxial tensile strain of approximately 2% along the c direction can enhance the compound’s transition temperature by about 40%. These results show that with the right pressure or strain, it is possible to increase superconducting transition temperature in the Nb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Nb}_{{2}}$$\\end{document}AC compounds.

Parameter determination of Johnson–Holmquist–Cook constitutive model and calibration for Indiana Limestone

In this study, a comprehensive parameter determination procedure for the Johnson–Holmquist–Cook (JHC) constitutive model is introduced, including calibration and validation processes for Indiana Limestone rocks. The procedure is conducted utilizing the existing physical and mechanical properties of Indiana Limestone. To obtain an accurate set of parameters for the JHC model for Indiana Limestone, an extensive dataset comprising mechanical and physical properties of Indiana Limestone rocks was initially compiled. The static mechanical tests incorporated uniaxial compression, triaxial compression, direct tensile, and uniaxial strain data, while the dynamic mechanical test data was primarily derived from the Split Hopkinson Pressure Bar experiments. Subsequently, the JHC constitutive model parameters were determined using existing literature data, employing statistical analysis, theoretical derivation, and numerical back analysis techniques. One of the damage parameters was determined through numerical post-peak behavior calibration of triaxial compression strength test results on experimental data. Finally, the accuracy of the determined parameters was validated by comparing the numerical and experimental results of both static and dynamic tests. This study effectively addresses the challenges associated with the numerical method using the JHC material model, such as the complex parameter determination process and the costly required tests, thereby preserving the efficiency and applicability of the numerical method.

Investigation of the electronic properties of a topological semimetal LaAuPb under uniaxial strain and hydrostatic pressure: A DFT approach

In this study, we utilized first-principles calculations to investigate the structural, electronic, mechanical, and vibrational properties of the topological semimetal LaAuPb. Our research delves into how uniaxial strain and hydrostatic pressure influence the electronic band structure of LaAuPb. We discovered that LaAuPb exhibits ductile behavior and maintains dynamic stability under various conditions. Upon introducing compressive strains of −6%, we observed a significant separation of degenerate states at the gamma point, which consequently led to the formation of a band gap. Similarly, the application of hydrostatic pressure at 16 GPa also resulted in the creation of a band gap by altering the electronic band structure. These findings suggest that both compressive strain and hydrostatic pressure can be effective in modulating the electronic properties of LaAuPb, potentially making it useful for applications requiring tunable electronic behavior. Conversely, when subject to tensile strain, no band gap formation was observed. Instead, there was a notable gradual overlap between the valence and conduction bands, indicating that tensile strain does not induce the same electronic separations as compressive strain or hydrostatic pressure. This asymmetrical response to different types of strain underscores the complex nature of LaAuPb's electronic properties and provides valuable insights for its potential use in electronic and mechanical applications. Overall, our findings contribute to the understanding of how external mechanical forces can be harnessed to control the electronic properties of topological semimetals like LaAuPb.

Multimodal Approach Reveals the Symmetry-Breaking Pathway to the Broken Helix in EuIn2As2

Understanding and manipulating emergent phases, which are themes at the forefront of quantum-materials research, rely on identifying their underlying symmetries. This general principle has been particularly prominent in materials with coupled electronic and magnetic degrees of freedom, in which magnetic order influences the electronic band structure and can lead to exotic topological effects. However, identifying symmetry of a magnetically ordered phase can pose a challenge, particularly in the presence of small domains. Here we introduce a multimodal approach for determining magnetic structures, which combines symmetry-sensitive optical probes, scattering, and group-theoretical analysis. We apply it to EuIn2As2, a material that has received attention as a candidate axion insulator. While first-principles calculations predict this state on the assumption of a simple collinear antiferromagnetic structure, subsequent neutron-scattering measurements reveal a much more intricate magnetic ground state characterized by two coexisting magnetic wave vectors reached by successive thermal phase transitions. The proposed high- and low-temperature phases are a spin helix and a state with interpenetrating helical and Néel antiferromagnetic order termed a “broken helix,” respectively. Employing a multimodal approach, we identify the magnetic structure associated with these two phases of EuIn2As2. We find that the higher-temperature phase is characterized by a variation of the magnetic moment amplitude from layer to layer, with the moment vanishing entirely in every third Eu layer. The lower-temperature structure is similar to the broken helix, with one important difference: Because of local strain, the relative orientation of the magnetic structure and the lattice is not fixed. Consequently, the symmetry required to protect the axion phase is not generically protected in EuIn2As2, but we show that it can be restored if the magnetic structure is tuned with uniaxial strain. Finally, we present a spin Hamiltonian that identifies the spin interactions that account for the complex magnetic order in EuIn2As2. Our work highlights the importance of a multimodal approach in determining the symmetry of complex order parameters. Published by the American Physical Society 2024

Predicting the band gap of kinked Mo6S6 nanowires based on band folding theory

Transition-metal chalcogenide (TMC) nanowires are an important building block for semiconductor components, which is conducive to the miniaturization and integration for nano-electronic devices and optoelectronic functional devices. Here, using density-functional theory (DFT) methods, we unveil intriguing electronic properties of kinked Mo6S6 nanowires (Mo6S6-NWs.) The results demonstrate that the shorter kinked Mo6S6 nanostructures exhibit distinct semiconductor behavior compared to the intrinsic Mo6S6-NWs, with the band gap being highly dependent on the length of the intrinsic Mo6S6-NWs between the kinks. Importantly, the band gap of kinked Mo6S6-NWs can be predicted by the band-folding theory, and the predicted value is extremely close to the actual calculated value. In addition, under uniaxial tension and compression strain, the band gap of long kinked Mo6S6-NWs changes within a narrow range, indicating their excellent electronic stability. This is mainly attributed to the small contribution of Mo/S atoms in the kinked part to valence band maximum (VBM) and conduction band minimum (CBM). Our work provides a useful theoretical insight for electronic properties of kinked Mo6S6-NWs, which open up the possibility of tailoring the properties of TMC nanowires, providing an ideal candidate material for the construction of flexible nanodevices.

Competition between d-wave superconductivity and magnetism in uniaxially strained Sr2RuO4

The pairing symmetry of Sr2RuO4 is a long-standing fundamental question in the physics of superconducting materials with strong electronic correlations. We use the functional renormalization group to investigate the behavior of superconductivity under uniaxial strain in a two-dimensional realistic model of Sr2RuO4 obtained with density functional theory and incorporating the effect of spin-orbit coupling. We find a dominant dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{{{{\\rm{x}}}}}^{2}-{{{{\\rm{y}}}}}^{2}}$$\\end{document} superconductor mostly hosted by the dxy-orbital, with no other closely competing superconducting state. Within this framework, we reproduce the experimentally observed enhancement of the critical temperature under strain and propose a simple mechanism driven by the density of states to explain our findings. We also investigate the competition between superconductivity and spin-density wave ordering as a function of interaction strength. By comparing theory and experiment, we discuss constraints on a possible degenerate partner of the dx2−y2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{{{{{\\rm{x}}}}}^{2}-{{{{\\rm{y}}}}}^{2}}$$\\end{document} superconducting state.

Impact of uniaxial cyclic stretching on matrix-associated endothelial cell responses

Uniaxial cyclic stretching plays a pivotal role in the fields of tissue engineering and regenerative medicine, influencing cell behaviors and functionality based on physical properties, including matrix morphology and mechanical stimuli. This study delves into the response of endothelial cells to uniaxial cyclic strain within the geometric constraints of micro-nano fibers. Various structural scaffold forms of poly(l-lactide-co-caprolactone) (PLCL), such as flat membranes, randomly oriented fiber membranes, and aligned fiber membranes, were fabricated through solvent casting and electrospinning methods. Our investigation focuses on the morphological variation of endothelial cells under diverse geometric constraints and the mechanical-dependent release of nitric oxide (NO) on oriented fibrous membranes. Our results indicate that while uniaxial cyclic stretching promotes endothelial cell spreading, the anisotropy of the matrix morphology remains the primary driving factor for cell alignment. Additionally, uniaxial cyclic stretching significantly enhances NO release, with a notably stronger effect correlated to the increasing strain amplitude. Importantly, this study reveals that uniaxial cyclic stretching enhances the mRNA expression of key proteins, including talin, vinculin, rac, and nitric oxide synthase (eNOS).

An open-source membrane stretcher for simultaneous mechanical and structural characterizations of soft materials and biological tissues

The ability to simultaneously measure material mechanics and structure is central for understanding their nonlinear relationship that underlies the mechanical properties of materials, such as hysteresis, strain-stiffening and -softening, and plasticity. This experimental capability is also critical in biomechanics and mechanobiology research, as it enables direct characterizations of the intricate interplay between cellular responses and tissue mechanics. Stretching devices developed over the past few decades, however, do not often allow simultaneous measurements of the structural and mechanical responses of the sample. In this work, we introduce an open-source stretching system that can apply uniaxial strain at a submicron resolution, report the tensile force response of the sample, and be mounted on an inverted microscope for real-time imaging. Our system consists of a pair of stepper-based linear motors that stretch the sample symmetrically, a force transducer that records the sample tensile force, and an optically clear sample holder that allows for high-magnification microscopy. Using polymer samples and cellular specimens, we characterized the motion control accuracy, force measurement robustness, and microscopy compatibility of our stretching system. We envision that this uniaxial stretching system will be a valuable tool for characterizing soft and living materials.

The geomechanical response of the Gulf of Mexico Green Canyon 955 reservoir to gas hydrate dissociation: A model based on sediment properties with and without gas hydrate

Gas hydrate is commonly found concentrated in sand- and silt-rich reservoirs and these are thought to have great potential as an energy resource. To evaluate this potential, it is critical to understand their in-situ stress state and their behavior during production. We explore the geomechanical behavior of sandy silt sediments from a hydrate reservoir at Green Canyon GC 955, deep-water Gulf of Mexico without hydrate and compare these results to previous work on the same sandy silty sediments with hydrate present. Previous results from hydrate-bearing sediments at GC 955 using intact specimens show that the ratio of lateral to axial effective stress under uniaxial strain (K0) is strongly time-dependent and over long timescales approaches 1 (isostatic stress state). New results from sediments without hydrate using reconstituted specimens reveal that K0 is 0.51 and independent of time and stress. The reservoir without hydrate is approximately three times more compressible than with hydrate. In addition, we find that hydrate-free sediments have a normalized creep rate of Cα/Cc of about 0.028 at all stress levels, whereas hydrate bearing sediments exhibit a decrease in Cα/Cc with stress. We use these observations to present a new geomechanical model that describes how stress and porosity evolve during production of the hydrate reservoir. The key insight in our proposed model is that the sediment skeleton and gas hydrate phases share any applied external load in proportion to their relative stiffnesses. The model results predict that hydrate-bearing sediments are stiffer than gas hydrate-free sediments and that K0 reduces dramatically after gas hydrate dissociation, as is observed. At GC 955, a 5 MPa depressurization is needed to cause gas hydrate dissociation. This change in pore pressure increases the vertical and horizontal effective stresses from 3.8 to 8.8 MPa and 3.8–4.4 MPa, respectively. The dramatic vertical effective stress increase will cause significant compaction (7%) and perturb stresses near the wellbore. These experimental observations and the load-sharing model presented have the potential to underpin a new generation of hydrate reservoir simulation models, which may drive more effective production approaches.

The uniaxial compressive strength of concrete: revisited

This paper re-examines common notions and conventions regarding the compressive strength of concrete in general and of the uniaxial compressive strength of concrete in particular. A distinction is introduced between the strength of the specimen and the strength of the concrete as a material, and the commonly measured and adopted strength is shown to be the specimen’s strength, wrongly interpreted as the material’s strength. the two major damage modes of concrete specimens (with the formation of either longitudinal cracks or shear bands) are discussed. Such failure modes are wrongly considered as features of concrete behavior in uniaxial compression, but this is not the case. Longitudinal cracking is due to lateral expansion (Poisson’s effect) and occurs at a relatively low applied load in absence of friction at specimen’s top and bottom boundaries. Shear failure (accompanied by the formation of an inclined shear band) is related to the shear envelope parameters that are related to the concrete mixture, but the applied ultimate pressure is not the concrete uniaxial compressive strength. Hence, though caused by applied compressive loading, these failure modes are little/hardly related to the concrete material intended as the ultimate uniaxial stress (strength) corresponding to a maximum value of the uniaxial compressive strain. Using the shear envelope parameters has been proven to yield a very good prediction of the applied compressive loading of the specimen in the limit state, as a demonstration that the applied pressure at specimen’s failure resulting from the formation of inclined fracture bands is the specimen’s failure strength, and not the material’s compressive strength! Reasons are given against the existence of a uniaxial compressive strength failure for concrete, and a piece of evidence in this direction is provided by concrete specimens subjected to pure hydrostatic compression, that do not fail at all. The entire issue requires, therefore, a deep revisiting and re-thinking, to provide correct measures for representing concrete response under compression in analysis and design.

The impacts of spin–orbit coupling and strain on transverse dynamical spin susceptibility in undoped phosphorene: Kane–Mele model study

We present the behaviors of dynamical transverse spin susceptibilities of undoped phosphorene monolayer using the Green’s function approach in the context of Kane–Mele model Hamiltonian. Such dynamical spin susceptibility is proportional to inelastic cross section of neutron beam from the layer. Specially, the effects of magnetic field and spin–orbit coupling strength on the spin excitation modes of phosphorene monolayer are investigated via calculating correlation function of spin density operators. Our results show the increase of magnetic field leads to move the magnetic excitation energy to higher values. Also, the intensity of peaks in inelastic cross section reduces with increase of magnetic field. We also show that applying both uniaxial and biaxial strains causes to decrease the intensity of peaks in dynamical spin susceptibility. Finally the effects of both compressive and tensile strains on frequency dependence of dynamical spin structure factor of phosphorene layer are studied. Moreover, the frequency positions of spin excitation mode of phosphorene layer have been investigated due to the effects of spin orbit coupling strength in details.

Band gap crossover and symmetry breaking in strained monolayer MoS2

Transition metal dichalcogenides are of considerable interest and understanding the impact of strain on their band gap is essential for tailoring their electronic properties. Experimental studies on MoS2 monolayers have identified the accurate band gap and the strain levels at which direct to indirect band gap crossover occurs. However, density functional theory (DFT) based calculations often fail to reproduce these experimental results. Also, the previous theoretical studies mainly focused on the band gap prediction. We have identified the optimal functional which accurately predicts both the band gap and the band crossover. The broken symmetry is also observed for uniaxial strain, leading to valley polarization and topological effects.

Biaxial Tensile Strain Enhances Electron Mobility of Monolayer Transition Metal Dichalcogenides.

Strain engineering can modulate the properties of two-dimensional (2D) semiconductors for electronic and optoelectronic applications. Recent theory and experiments have found that uniaxial tensile strain can improve the electron mobility of monolayer MoS2, a 2D semiconductor, but the effects of biaxial strain on charge transport are not well characterized in 2D semiconductors. Here, we use biaxial tensile strain on flexible substrates to probe electron transport in monolayer WS2 and MoS2 transistors. This approach experimentally achieves ∼2× higher on-state current and mobility with ∼0.3% applied biaxial strain in WS2, the highest mobility improvement at the lowest strain reported to date. We also examine the mechanisms behind this improvement through density functional theory simulations, concluding that the enhancement is primarily due to reduced intervalley electron-phonon scattering. These results underscore the role of strain engineering in 2D semiconductors for flexible electronics, sensors, integrated circuits, and other optoelectronic applications.

Enhancing Layer-Engineered Interlayer Exciton Emission and Valley Polarization in van der Waals Heterostructures via Strain.

Layer-engineered interlayer excitons from heterostructures of transition-metal dichalcogenides (TMDCs) exhibit a rich variety of emissive states and intriguing valley spin-selection rules, the effective modulation of which is crucial for excitonic physics and related device applications. Strain or high pressure provides the possibility to tune the energy of the interlayer excitons; however, the reported emission intensity is substantially quenched, which greatly limits their practical application in optoelectronic devices. Here, via applying uniaxial strain based on polyvinyl alcohol (PVA) encapsulation technique, we report enhanced layer-engineered interlayer exciton emission intensity with largely modulated emission energy in WSe2/WS2 heterobilayer and heterotrilayer. Both momentum-direct and momentum-indirect interlayer excitons were observed, and their emission energies show an opposite shift tendency upon applied strain, which agrees with our DFT calculations. We further demonstrate that intralayer and interlayer exciton states with low phonon interactions can be modulated through the mechanical strain applied to the PVA substrate at low temperatures. Due to strain-induced breaking of the 3-fold rotational symmetry, we observe the enhanced valley polarization of interlayer excitons. Our study contributes to the understanding and modulation of the optical properties of interlayer excitons, which could be exploited for optoelectronic device applications.

Unveiling a New 2D Semiconductor: Biphenylene-Based InN.

The two-dimensional (2D) materials class earned a boost in 2021 with biphenylene synthesis, which is structurally formed by the fusion of four-, six-, and eight-membered carbon rings, usually named 4-6-8-biphenylene network (BPN). This research proposes a detailed study of electronic, structural, dynamic, and mechanical properties to demonstrate the potential of the novel biphenylene-like indium nitride (BPN-InN) via density functional theory and molecular dynamics simulations. The BPN-InN has a direct band gap energy transition of 2.02 eV, making it promising for optoelectronic applications. This structure exhibits maximum and minimum Young modulus of 22.716 and 22.063 N/m, Poisson ratio of 0.018 and -0.008, and Shear modulus of 11.448 and 10.860 N/m, respectively. To understand the BPN-InN behavior when subjected to mechanical deformations, biaxial and uniaxial strains in armchair and zigzag directions from -8 to 8% were applied, achieving a band gap energy modulation of 1.36 eV over tensile deformations. Our findings are expected to motivate both theorists and experimentalists to study and obtain these new 2D inorganic materials that exhibit promising semiconductor properties.

Ferroelectric Order Evolution in Freestanding PbTiO3 Films Monitored by Optical Second Harmonic Generation.

The demand for low-dimensional ferroelectric devices is steadily increasing, however, the thick substrates in epitaxial films impede further size miniaturization. Freestanding films offer a potential solution by eliminating substrate constraints. Nevertheless, it remains an ongoing challenge to improve the stability in thin and fragile freestanding films under strain and temperature. In this work, the structure and ferroelectric order of freestanding PbTiO3 (PTO) films are investigated under continuous variation of the strain and temperature using nondestructive optical second harmonic generation (SHG) technique. The findings reveal that there are both out-of-plane and in-plane domains with polarization along out-of-plane and in-plane directions in the orthorhombic-like freestanding PTO films, respectively. In contrast, only out-of-plane domains are observed in the tetragonal epitaxial PTO films. Remarkably, the ferroelectricity of freestanding PTO films is strengthened under small uniaxial tensile strain from 0% up to 1.66% and well-maintained under larger biaxial tensile strain up to 2.76% along the [100] direction and up to 4.46% along the [010] direction. Moreover, a high Curie temperature of 630K is identified in 50nm thick freestanding PTO films by wide-temperature-range SHG. These findings provide valuable understanding for the development of the next-generation electronic nanodevices with flexibility and thermostability.

Electronic Transport Modulation in Ultrastrained Silicon Nanowire Devices.

In this work, we explore the effect of ultrahigh tensile strain on electrical transport properties of silicon. By integrating vapor-liquid-solid-grown nanowires into a micromechanical straining device, we demonstrate uniaxial tensile strain levels up to 9.5%. Thereby the triply degenerated phonon dispersion relation at the Γ-point of silicon disentangle and the longitudinal phonon modes are used to precisely determine the extent of mechanical strain. Simultaneous electrical transport measurements showed a significant enhancement in the electrical conductance. Aside from considerable reduction of the Si bulk resistivity due to strain-induced band gap narrowing, comparison with quasi-particle GW calculations further reveals that the effective Schottky barrier height at the electrical contacts undergoes a substantial reduction. For these reasons, nanowire devices with ultrastrained channels may be promising candidates for future applications of high-performance silicon-based devices.

Three-dimensional model for cyclic, rate-independent and compressible response of aluminium

A three-dimensional rate-independent framework consistent with thermodynamics is presented to study the dissipative response of metals. The entropy inequality is transformed into equality by introducing a non-negative, continuous rate of dissipation function. The constitutive relation that relates the Hencky strain and Cauchy stress is parametrized by replacement stress, instead of the plastic strain, for reasons discussed. The evolution equation for the replacement stress is obtained such that among the possible processes, the one that maximizes the rate of dissipation is realized so that thermodynamic equilibrium is achieved in the shortest possible time. Appropriate 3D constitutive functions to model aluminium are prescribed for the dissipation function and a Gibbs-like potential. The variation of the transverse strain as a function of the uniaxial strain differs between the present formulation and classical plasticity. Consistent with some of the experimental observations, the material tends to be compressible in the present formulation during plastic deformations. Thus, further experimental investigations are required to choose the appropriate constitutive relation.

Ultrasensitive Mechanical Sensor Using Tunable Ordered Array of Metallic and Insulating States in Vanadium Dioxide

Abstract Detecting tiny deformations or vibrations, particularly those associated with strains below 1%, is essential in various technological applications. Traditional intrinsic materials, including metals and semiconductors, face challenges in simultaneously achieving initial metallic state and strain-induced insulating state, hindering the development of highly sensitive mechanical sensors. Here we report an ultrasensitive mechanical sensor based on a strain-induced tunable ordered array of metallic and insulating states in the single-crystal bronze-phase vanadium dioxide [VO2(B)] quantum material. It is shown that the initial metallic state in the VO2(B) flake can be tuned to the insulating state by applying a weak uniaxial tensile strain. Such a unique property gives rise to a record-high gauge factor of above 607970, surpassing previous values by an order of magnitude, with excellent linearity and mechanical resilience as well as durability. As a proof-of-concept application, we use our proposed mechanical sensor to demonstrate precise sensing of the micro piece, gentle airflows and water droplets. We attribute the superior performance of the sensor to the strain-induced continuous metal-insulator transition in the single-crystal VO2(B) flake, evidenced by experimental and simulation results. Our findings highlight the potential of exploiting correlated quantum materials for next-generation ultrasensitive flexible mechanical sensors, addressing critical limitations in traditional materials.

A DFT study for improving the thermoelectric efficiency in AB bilayer phosphorene using uniaxial strain

Phosphorene is a two-dimensional (2D) semiconductor material that has attracted a lot of interest in several fields of applications. The anisotropic character of this new category of materials allows the tunability of electrical, optical, thermal, and other properties by the application of fields or forces. In the present work, using density functional theory (DFT) with the hybrid functional and Boltzmann transport equation, electronic properties, phonon dispersion and thermoelectric properties were calculated for AB bilayer phosphorene. To study the effect of the layer deformation on the thermoelectric properties of phosphorene, uniaxial tensile and compressive strain along the armchair and the zigzag direction was applied. The results revealed that AB bilayer phosphorene under a uniaxial tensile strain of 3 % along the armchair direction improve the thermoelectric properties, giving rise to a significant increase of the figure of merit to ZT = 1.24 at n-type doping. The increase of ZT upon uniaxial deformation corresponds to an increase of 110 % with respect to ZT of the unstrained AB bilayer phosphorene structure (ZT = 0.59 at 300 K).