Strain Tuning Research Articles

Reduction in thermal conductivity of monolayer MoS2 by large mechanical strains for efficient thermal management

Two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDC) have received extensive research interests and investigations in the past decade. In this research, we report the first experimental measurement of the in-plane thermal conductivity of MoS2 monolayer under a large mechanical strain using optothermal Raman technique. This measurement technique is direct without additional processing to the material, and MoS2’s absorption coefficient is discovered during the measurement process to further increase this technique’s precision. Tunable uniaxial tensile strains are applied on the MoS2 monolayer by stretching a flexible substrate it sits on. Experimental results demonstrate that, the thermal conductivity is substantially suppressed by tensile strains: under the tensile strain of 6.3%, the thermal conductivity of the MoS2 monolayer drops approximately by 62%. A serious of thermal transport properties at a group of mechanical strains are also reported, presenting a strain-dependent trend. It is the first and original study of 2D materials’ thermal transport properties under a large mechanical strain (> 1%), and provides important information that the thermal transport of MoS2 will significantly decrease at a large mechanical strain. This finding provides the key information for flexible and wearable electronics thermal management and designs.

Shape‐Reconfigurable Crack‐Based Strain Sensor with Ultrahigh and Tunable Sensitivity

AbstractIn the field of wearable electronics and human–machine interfaces, there is a growing need for highly sensitive and adaptable sensors capable of detecting a wide range of stimuli with high precision. Traditional sensors often lack the versatility to adjust their sensitivity for different applications. Inspired by the mechanosensory system of spiders, a shape‐reconfigurable crack‐based sensor with ultrahigh and tunable strain sensitivity based on the precise control of nanocrack formation on a shape memory polymer substrate is demonstrated. This design incorporates a line‐patterned substrate composed of a thermoplastic polyurethane (TPU) matrix and thermo‐responsive shape memory polymer, poly(lactic acid) (PLA), to form parallel nanocracks in a thin platinum film. This design achieves an ultrahigh gauge factor of 2.7 × 109 at 2% strain, significantly surpassing conventional sensors. The shape memory property of the TPU/PLA substrate enables tunable strain sensitivity according to the desired strain range, eliminating the need for multiple sensors. The sensor demonstrates exceptional capabilities in detecting subtle strains (as low as 0.025%), monitoring biological signals, and sensing acoustic waves (100–20 000 Hz) with a response time of 0.025 ms. This work represents a significant advancement toward strain sensors with both ultrahigh and tunable sensitivity.

Bioinspired Tunable Helical Fiber-Shaped Strain Sensor with Sensing Controllability for the Rehabilitation of Hemiplegic Patients.

Fiber-based strain sensors, as wearable integrated devices, have shown substantial promise in health monitoring. However, current sensors suffer from limited tunability in sensing performance, constraining their adaptability to diverse human motions. Drawing inspiration from the structure of the spiranthes sinensis, this study introduces a unique textile wrapping technique to coil flexible silver (Ag) yarn around the surface of multifilament elastic polyurethane (PU), thereby constructing a helical structure fiber-based strain sensor. The synergistic interaction between the elastic PU core and the outer helical Ag yarn enhances the mechanical strength and stretchability of the sensor, while the external helical Ag yarn offers high conductivity. By adjusting the spacing of Ag yarn coils on the surface of the fiber-based sensor, we achieve precise control over both sensing sensitivity and strain range. Specifically, experimental results show that with a pitch of 1.25 mm, the strain range reaches up to 150%, and the gauge factor (GF) is 2.6; when the pitch is adjusted to 5 mm, within a 60% strain range, the GF value significantly increases to 9.3. Based on these excellent performance metrics, we further apply the sensor as a conductor in ECG monitoring garments, successfully verifying its practicality in cardiac monitoring. Additionally, we developed a smart glove for hand function rehabilitation training, utilizing wireless signal transmission to promote hand function recovery in hemiplegic patients. The sensor is also capable of effectively monitoring respiratory rate and pulse, showing broad prospects in the fields of rehabilitation medicine and smart healthcare.

Phase Engineering of Giant Second Harmonic Generation in Bi2O2Se.

2D materials with remarkable second-harmonic generation (SHG) hold promise for future on-chip nonlinear optics. Relevant materials with both giant SHG response and environmental stability are long-sought targets. Here, the enormous SHG from the phase engineering of a high-performance semiconductor, Bi2O2Se (BOS), under uniaxial strain, is demonstrated. SHG signals captured in strained 20 nm-BOS films exceed those of NbOI2 and NbOCl2 of similar thickness by a factor of 10, and are four orders of magnitude higher than monolayer-MoS2, resulting in a significant second-order nonlinear susceptibility on the order of 1 nmV-1. Intriguingly, the strain enables continuous adjustment of the ferroelectric phase transition across room temperature. An exceptionally large tunability of SHG, approximately six orders of magnitude, is achieved through strain modulation. This colossal SHG, originating from the geometric phase of Bloch wave functions and coupled with sensitive strain tunability in this air-stable 2D semiconductor, opens new possibilities for designing chip-scale, switchable nonlinear opticaldevices.

Uniaxial strain tuning of charge modulation and singularity in a kagome superconductor

Tunable quantum materials hold great potential for applications. Of special interest are materials in which small lattice strain induces giant electronic responses. The kagome compounds AV3Sb5 (A = K, Rb, Cs) provide a testbed for electronic tunable states. In this study, through angle-resolved photoemission spectroscopy, we provide comprehensive spectroscopic measurements of the electronic responses induced by compressive and tensile strains on the charge-density-wave (CDW) and van Hove singularity (VHS) in CsV3Sb5. We observe a tripling of the CDW gap magnitudes with ~ 1% strain. Simultaneously, changes of both energy and mass of the VHS are observed. Combined, this reveals an anticorrelation between the unconventional CDW order parameter and the mass of the VHS, and highlight the role of the latter in the superconducting pairing. The substantial electronic responses uncover a rich strain tunability of the versatile kagome system in studying quantum interplays under lattice variations.

Toward a Fundamental Understanding of Solid-Solid Interfaces in Hydrogen Fuel Cells and Water Electrolysis through First-Principles Based Modeling

To achieve Net-Zero Emissions by 2050, hydrogen and hydrogen fuel cells will play a significant role in powering vehicles. In this talk, I will show, through first-principles-based modeling, how to achieve rigorous modeling and a fundamental understanding of the solid-solid interface for the oxygen reduction reaction in hydrogen fuel cells and the hydrogen evolution and oxygen evolution reactions in water electrolysis. I will further show how the fundamental understanding paves the way toward developing both model and industrial electrocatalysts with significantly improved performance. Specifically, I will introduce the following three topics.[1] metal-metal interfaces: strain generation and strain tuning of epitaxial, stepped and free-standing platinum group metals for the oxygen reduction reaction in hydrogen fuel cells. (1, 2)[2] metal-oxide interfaces: stability and activity of monolayer oxide/Pt interface toward improving the hydrogen evolution reaction in the alkaline electrolysis.(3)[3] oxide-oxide interfaces: self-consistent modeling of active phases, reaction centers, and catalytic mechanisms of Ni- and Co-based layered double hydroxides for the oxygen evolution reaction in the alkaline electrolysis.(4-6)

Quasi-static compression response of a novel multi-step auxetic honeycomb with tunable transition strain

Auxetic honeycombs with multi-step deformation have received widespread attention due to their multifunctionality and superior mechanical properties. To improve the tunability of the auxetic honeycomb, a novel multi-step auxetic honeycomb (MSAH) is proposed by combining star-rhombic parts with crossed thin walls. MASH is characterized by multi-step deformation, and its stress-strain curve has three significant plateau stages. The strain during the transition between different deformation steps can be adjusted by designing unit cells with different geometrical parameters. In the compression process, the ordered contact of the cell walls of MASH is the critical reason for realizing the multi-step deformation. The quasi-static compression finite element model of MASH is established and verified by experiments. Quasi-static compression response and deformation mechanism of MASH are studied. Then, the effects of geometrical parameters on the compression response of MASH are investigated. The results show that the wall thickness has a greater effect on the compressive stress, and the cell-wall angle determines the deformation mode of MASH. Furthermore, the transition strain of MASH is theoretically analyzed and verified by numerical simulations. This study provides a reference for designing multi-step deformation honeycombs and applying multi-stage energy absorbers.

High-Entropy Selenides with Tunable Lattice Distortion as Efficient Electrocatalysts for Oxygen Evolution Reaction.

Developing stable and active electrocatalysts is crucial for enhancing the oxygen evolution reaction (OER) efficiency, which sluggish kinetics hinder sustainable hydrogen production. High entropy selenides (HESes) feature with random distribution of multiple metals cations and unique electronic and size effect of Se anion, allowing for precious regulation of their catalytic properties towards high OER activity. In this work, we report a series of high-entropy selenides catalysts with tunable lattice strain for electrocatalytic oxygen evolution. Electrochemical measurements show that the quinary (NiCoMnMoFe)Sex requires only 291 mV to reach 10 mA cm-2 and exhibits a superior stability with negligible current decay during 100 h's continuous operation. By combining experimental measurements and theoretical calculation, the study reveals that the lattice distortion, reflected by the local microstrain near the active site, plays a vital role in boosting the OER activity of HESes.

Colossal Strain Tuning of Ferroelectric Transitions in KNbO3 Thin Films.

Strong coupling between polarization (P) and strain (ɛ) in ferroelectric complex oxides offers unique opportunities to dramatically tune their properties. Here colossal strain tuning of ferroelectricity in epitaxial KNbO3 thin films grown by sub-oxide molecular beam epitaxy is demonstrated. While bulk KNbO3 exhibits three ferroelectric transitions and a Curie temperature (Tc) of ≈676K, phase-field modeling predicts that a biaxial strain of as little as -0.6% pushes its Tc >975K, its decomposition temperature in air, and for -1.4% strain, to Tc >1325K, its melting point. Furthermore, a strain of -1.5% can stabilize a single phase throughout the entire temperature range of its stability. A combination of temperature-dependent second harmonic generation measurements, synchrotron-based X-ray reciprocal space mapping, ferroelectric measurements, and transmission electron microscopy reveal a single tetragonal phase from 10 K to 975K, an enhancement of ≈46% in the tetragonal phase remanent polarization (Pr),and a ≈200% enhancementin its optical second harmonic generation coefficients over bulk values. These properties in a lead-free system, but with properties comparable or superior to lead-based systems, make it an attractive candidate for applications ranging from high-temperature ferroelectric memory to cryogenic temperature quantum computing.

Essential role for HSP40 in asexual replication and thermotolerance of malaria parasites.

Plasmodium falciparum, the parasite responsible for nearly all cases of severe malaria, must survive challenging environments to persist in its human host. Symptomatic malaria is characterized by periodic fevers corresponding to the 48-hour asexual reproduction of P. falciparum in red blood cells. As a result, P. falciparum has evolved a diverse collection of heat shock proteins to mitigate the stresses induced by temperature shifts. Among the assortment of heat shock proteins in P. falciparum, there is only one predicted canonical cytosolic J domain protein, HSP40 (PF3D7_1437900). Here, we generate a HSP40 tunable knockdown strain of P. falciparum to investigate the biological function of HSP40 during the intraerythrocytic lifecycle. We determine that HSP40 is required for malaria parasite asexual replication and survival of febrile temperatures. Previous reports have connected proteotoxic and thermal stress responses in malaria parasites. However, we find HSP40 has a specific role in heat shock survival and does not mitigate the proteotoxic stresses induced by artemisinin or proteosome inhibition. Following HSP40 knockdown, malaria parasites have a cell cycle progression defect and reduced nuclear replication. Untargeted proteomics reveal HSP40 depletion leads to a multifaceted downregulation of DNA replication and repair pathways. Additionally, we find HSP40 knockdown sensitizes parasites to DNA replication inhibition. Overall, these studies define the specialized role of the J domain protein HSP40 in malaria parasites during the blood stages of infection.

Multilayer Bionic Tunable Strain Sensor with Mutually Non‐Interfering Conductive Networks for Machine Learning‐Assisted Gesture Recognition

AbstractFlexible strain sensors capable of acquiring tiny mechanical signals and attaching to various irregular surfaces are becoming prevalent in physiological measurement, soft robotics, and human‐machine interaction. However, the advancement of flexible strain sensors is substantially impeded by the intrinsic compromise between sensitivity and the range of detectable signals. Inspired by the multilayer structure of nacre in nature, a carbon nanotubes (CNTs)/graphene (GR)/graphene (GR)/thermoplastic polyurethane (TPU) mat (CGGTM) is prepared by electrospinning and high‐pressure spraying technology. By designing a multilayer structure with mutually non‐interfering conductive networks, the resulting CGGTM possesses a low detection limit (0.05% strain), high sensitivity (gauge factor, GF > 152537), large detection range (up to 364% strain), fast response/recovery time (80 ms/100 ms), and excellent cyclic durability (up to 1000 cycles). Furthermore, the CGGTM also exhibits satisfactory triboelectric performances when assembled into a triboelectric nanogenerator (TENG, 3 × 3 cm2), including high triboelectric output (open‐circuit voltage Voc = 135.4 V, short‐circuit current Isc = 1.25 µA) and power density (88 mW m−2), enabling reliable power supply, self‐powered sensing, and pulse monitoring capability. Finally, CGGTM is successfully applied to the collection of biological signals and multi‐gesture motion recognition assisted by machine learning algorithms, which holds promise for intelligent interaction with gestures in the future.

Strain tuning of vestigial three-state Potts nematicity in a correlated antiferromagnet

Strain tuning of vestigial three-state Potts nematicity in a correlated antiferromagnet

Small compressive strain tuning of α-TeO2 and β-TeO2 polymorphs: Electronic, linear, and nonlinear optical properties from first-principles calculations

This study examines the effects of 2 % compressive strain on the structural, electronic, and optical properties of α-TeO2 and β-TeO2 polymorphs. α-TeO2’s bandgap increases from 3.64 eV to 3.70 eV, while β-TeO2’s decreases from 3.632 to 3.53 eV. Lattice parameters uniformly reduce in α-TeO2, but vary dissimilarly in β-TeO2. PDOS analysis shows O-2p and Te-5p states dominate near the band edges. Optical behavior is anisotropic, with enhanced polarizability and refractive indices under strain. Nonlinear optical properties improve with increased strain, especially the non-linear susceptibility components, which are relevant for second-harmonic generation. Born Effective Charges show increased Te polarization and reduced oxygen polarization, impacting dielectric response.

Autonomous Sensing Architected Materials

AbstractIntegrating autonomous sensing materials into future applications necessitates developing advanced multiscale multiphysics predictive models. This study introduces an experimentally informed predictive framework for autonomous sensing architected materials, combining theoretical and computational methodologies. By incorporating stress‐dependent electrical resistivity through anisotropic piezoresistive constitutive effects, alongside considering material, geometric, and contact nonlinearities, the proposed multiscale model captures the architecture‐dependent piezoresistive responses of lattice composites produced via additive manufacturing of polyetherimide (PEI)/carbon nanotube (CNT) nanoengineered feedstock. The PEI/CNT composite exhibits exceptional strength (105 MPa), stiffness (3368 MPa), and strain sensitivity (gauge factor ≈13), translating into remarkable piezoresistive characteristics for the PEI/CNT lattice composites, surpassing existing works (gauge factor ≈3 to 11). This multiscale finite element model accurately predicts both macroscopic piezoresistive responses and the influence of architectural and topological variations on electric current paths, validated via infrared thermography analysis. Additionally, an Ashby chart for the gauge factor of PEI/CNT lattice composites suggests their prediction through a scaling law similar to mechanical properties, underscoring the tunable strain and damage sensitivity of these materials. The combined experimental, theoretical, and numerical findings offer critical insights into optimizing piezoresistive composites through architected design, with profound implications for smart orthopedics, structural health monitoring, sensors, batteries, and other multifunctional applications.

Cryogenic Digital Image Correlation as a Probe of Strain in Iron-Based Superconductors

Abstract Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors. However, accurately characterizing anisotropic strain can be challenging and complex. Here, we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method. Compared with other methods such as high-resolution X-ray diffraction, strain gauge, and capacitive sensor, digital image correlation offers a non-contact, full-field measurement approach, acting as an optical virtual strain gauge that provides high spatial resolution. The results measured on detwinned BaFe2As2 are quantitatively consistent with the distortion measured by X-ray diffraction and neutron Larmor diffraction. These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains, facilitating the application of uniaxial strain tuning in the study of quantum materials.

Unraveling magneto-elastoresistance in the Dirac nodal-line semi-metal ZrSiSe

Quantum materials are often characterized by a marked sensitivity to minute changes in their physical environment, a property that can lead to new functionalities and thereby, to novel applications. One such key property is the magneto-elastoresistance (MER), the change in magnetoresistance (MR) of a metal induced by uniaxial strain. Understanding and modeling this response can prove challenging, particularly in systems with complex Fermi surfaces. Here, we present a thorough analysis of the MER in the nearly compensated Dirac nodal-line semi-metal ZrSiSe. Small amounts of strain (0.27%) lead to large changes (7%) in the MR. Subsequent analysis reveals that the MER response is driven primarily by a change in transport mobility that varies linearly with the applied strain. This study showcases how the effect of strain tuning on the electrical properties can be both qualitatively and quantitatively understood. A complementary Shubnikov-de Haas oscillation study sheds light on the root of this change in quantum mobility. Moreover, we unambiguously show that the Fermi surface consists of distinct electron and hole pockets revealed in quantum oscillation measurements originating from magnetic breakdown.

Strain engineering of PtMn alloy enclosed by high-indexed facets boost ethanol electrooxidation

Surface strain engineering has proven to be an efficient strategy to enhance catalytic properties of platinum (Pt)-based catalysts for electrooxidation reactions. Herein, the S-doped PtMn concave cubes (CNCs) enclosed with high index facets (HIFs) and regulatable surface strain are successfully fabricated by two steps hydrothermal method. The S element with electrophilic property can modify the near-surface of PtMn nanocrystals, altering the electronic structure of Pt to effectively regulate the adsorption/desorption of intermediates in the ethanol electrooxidation reaction (EOR). The PtMnS1.1 catalyst with optimal surface strain delivered extraordinary catalytic performance on EOR in acidic media, with a specific activity of 2.88 mA/cm2 and mass activity of 1.10 mA/μgPt, which is 4.1 and 2.2 times larger than that of state-of-the-art Pt/C catalyst, respectively. Additionally, the PtMnS1.1 catalyst also achieve excellent catalytic properties in alkaline electrolyte for EOR. The results of kinetic studies indicated that the surface strain and modified electronic structure can degrade the activation energy barrier during the process of EOR, which is beneficial for enhance the reaction rate. This work provides a promising approach to construct highly efficient electrocatalysts with tunable surface strain effects for clean energy electro-chemical reactions.

Determination of the dynamic Young's modulus of quantum materials in piezoactuator-driven uniaxial pressure cells using a low-frequency AC method.

We report on a new technique for measuring the dynamic Young's modulus, E, of quantum materials at low temperatures as a function of static tuning strain, ϵ, in piezoactuator-driven pressure cells. In addition to a static tuning of stress and strain, we apply a small-amplitude, finite-frequency AC (1Hz ≲ ω ≲ 1000Hz) uniaxial stress, σac, to the sample and measure the resulting AC strain, ϵac, using a capacitive sensor to obtain the associated modulus E. We demonstrate the performance of the new technique through proof-of-principle experiments on the unconventional superconductor Sr2RuO4, which is known for its rich temperature-strain phase diagram. In particular, we show that the magnitude of E, measured using this AC technique at low frequencies, exhibits a pronounced nonlinear elasticity, which is in very good agreement with previous Young's modulus measurements on Sr2RuO4 under [1 0 0] strain using a DC method [Noad etal., Science 382, 447-450 (2023)]. By combining the new AC Young's modulus measurements with AC elastocaloric measurements in a single measurement, we demonstrate that these AC techniques are powerful in detecting small anomalies in the elastic properties of quantum materials. Finally, using the case of Sr2RuO4 as an example, we demonstrate how the imaginary component of the modulus can provide additional information about the nature of ordered phases.

Superconductivity in Freestanding Infinite-Layer Nickelate Membranes.

The observation of superconductivity in infinite-layer nickelates has attracted significant attention due to its potential as a new platform for exploring high-Tc superconductivity. However, thus far, superconductivity has only been observed in epitaxial thin films, which limits the manipulation capabilities and modulation methods compared to two-dimensional exfoliated materials. Given the exceptionally giant strain tunability and stacking capability of freestanding membranes, separating superconducting nickelates from the as-grown substrate is a novel way to engineer the superconductivity and uncover the underlying physics. Herein, this work reports the synthesis of the superconducting freestanding La0.8Sr0.2NiO2 membranes ( ), emphasizing the crucial roles of the interface engineering in the precursor phase film growth and the quick transfer process in achieving superconductivity. This work offers a new versatile platform for investigating superconductivity in nickelates, such as the pairing symmetry via constructing Josephson tunneling junctions and higher Tc values via high-pressure experiments.

Integration of 3D printing with acoustic-assisted assembly of nanomaterials for tunable strain sensors

This study reports a novel methodology for the development of tunable strain sensors by leveraging 3D printing for structural designs and nanomaterial assembly for functional layer coating. We utilized material extrusion (MEX) to print sensor substrates using composite ink of polydimethylsiloxane (PDMS) and silica nanoparticles. MEX allows us to create a non-uniform strain distribution of the sensor substrate by designing alternating wide and thin strips with different mechanical properties along the stretching direction. Then, we assembled nanometer-thick graphene flakes on the surface of the substrate using an acoustic-assisted dip-coating method to construct strain sensors. The graphene network on the narrow strips will experience large deformation leading to significantly increased resistance. By fixing the width of wide strips and tailoring the width ratio of the wide strip over narrow strips (r), the gauge factor can be controlled from 8.53 (r = 1:1) to 33.15 (r = 16:1). Also, by printing the narrow strips with softer PDMS, the sensitivity of the sensor can be further increased. The research pioneers the integration of 3D printing and nanomaterial assembly for strain sensors. More importantly, it paves the way for the generic design of flexible electronics and other hybrid systems of polymer and nanomaterials.