Large Tensile Strain Research Articles

Properties of (001) NaNbO3 films under epitaxial strain: A first-principles study

First-principles calculations are performed to investigate and analyze properties of (001) thin films made of the most complex perovskite system, namely, $\mathrm{Na}\mathrm{Nb}{\mathrm{O}}_{3}$ (NNO), and are subject to epitaxial strain. In particular, an energy-versus-misfit strain phase diagram is constructed and reveals the existence of three different ground states for different strain regimes. For large compressive strain and up to moderate tensile strain, a monoclinic $Cc$ phase occurred, with its polarization and axis of antiphase tilting both rotating within a ($\overline{1}10$) plane with the magnitude of the strain. For large tensile strain, a ferroelectric orthorhombic state of $Pmc{2}_{1}$ symmetry emerges with polarization lying along the [110] in-plane direction together with an octahedral tilting adopting the ${a}^{\ensuremath{-}}{a}^{\ensuremath{-}}{c}^{+}$ pattern and an antiferroelectric vector associated with the reciprocal zone-border $X$ point. Finally, in between and for a narrow region of strain, a complex ground state is found. It has orthorhombic $Pca{2}_{1}$ symmetry, for which a complex tilting pattern coexists with polarization pointing along the [001] out-of-plane direction and antiferroelectric displacement associated with the $\mathrm{\ensuremath{\Delta}} k$ point located halfway between the zone-center $\mathrm{\ensuremath{\Gamma}}$ and zone-border $X$ point. Ferroelectric, antiferroelectric, and antiferrodistortive properties are also reported and discussed as a function of misfit strain.

Structural correlation with the electrochemical properties of carbon nano-spheres/polyaniline nanocomposite films

Structural, morphological and electrical properties of the CNS/PANI composite have been studied as a function of composition of CNS. Morphological analysis by FESEM and TEM indicates an enhanced interaction between PANI and CNS as the CNS increases forming larger aggregated interconnected matrix network of CNS having hetero-structured molecular phases of sp2 and sp3. Raman spectroscopy reveals the presence of large tensile strain on the G and D bands of the CNS/PANI composite. Increase in the CNS percentage is seen to relax this large amount of strain. Electrochemical analysis of these composite structures as an active electrode gives a highest specific capacitance of 1470 Fg−1 for CNS/PANI composite with 75% of CNS with high cyclic stability.

Self-Assembly of Ge and GaAs Quantum Dots under Tensile Strain on InAlAs(111)A

Quantum dots that store large tensile strains represent an emerging research area. We combine experiments and computational modeling to investigate the self-assembly of Ge and GaAs tensile-strained quantum dots (TSQDs) on In0.52Al0.48As(111)A. Comparing these two nominally similar material systems highlights how differences in adatom kinetics leads to distinct features of Ge and GaAs TSQD self-assembly. The energy barrier to diffusion of Ge adatoms is higher than that for Ga adatoms, while forming a stable island requires six Ge atoms and four Ga atoms. Unusually, these critical cluster sizes do not increase as we raise the substrate temperature. Radial distribution scaling shows that both Ge and GaAs TSQDs preferentially nucleate at a particular distance from their neighbors. This deeper understanding of the physics of Ge(111) and GaAs(111)A TSQD self-assembly will enable researchers to more effectively tailor these nanostructures to specific optoelectronic applications.

Integration of silicon nitride waveguide in Ge-on-insulator substrates for monolithic solutions in optoelectronics

This work presents a novel process to manufacture advanced Germanium-On-Insulator with integrated Silicon Nitride (GOIN) stripes as light waveguide for Ge photonic devices. Through the integration of GOIN stripes, larger tensile strain could be imposed to the bonded Ge layer which may could be used to tailor the bandgap of Ge material for short wave length infrared application. The successful fabrication of advanced GOIN substrate makes the opportunity for monolithic integration of high-performance Ge-based high mobility transistors with photonic components where silicon nitride is the waveguide with low optical loss.

Photonic Vitrimer Elastomer with Self‐Healing, High Toughness, Mechanochromism, and Excellent Durability based on Dynamic Covalent Bond

AbstractVitrimers, with their unique dynamic covalent bonds, possess attractive self‐healability and mechanical robustness, providing an intriguing opportunity to construct functional soft materials. However, their potential for function recovery, especially optical function, is underexplored. Harnessing the synergistic effect of photonic crystals and vitrimers, a novel photonic vitrimer with light regulating and self‐healing capabilities is presented. The resulting photonic vitrimer exhibits a large tensile strain (>1000%), high toughness (21.2 kJ m−3), bright structural color, and mechanochromism. Notably, the structural color remains constant even after 10 000 stretching/releasing cycles, showing superior mechanical stability, creep‐resistance, and excellent durability. More importantly, the exchange of dynamic covalent bonds imparts the photonic vitrimer with a self‐healing ability (>95% efficiency), enabling the recovery of its optical function. Benefiting from the above merits, the photonic vitrimer has been successfully used as a sensor for human motion detection, which demonstrates visualized interactive sensibility even after self‐repairing. This material design provides a general strategy for optical functionalization of vitrimers. The photonic vitrimer elastomers present great potential as resilient functional soft materials for diverse flexible devices and a novel optical platform for soft robotics, smart wearable devices, and human‐machine interaction.

Multifunctional carbon fiber reinforced multilayered metastructure with broadband microwave absorption and effective mechanical resistance

AbstractMetastructure is an innovative structure form to improve broadband microwave absorption. However, without reliable mechanical properties, it is difficult to apply metastructure absorbers in realistic application scenarios. Herein, a multifunctional carbon fiber reinforced multilayered metastructure (CFRMM) is proposed and fabricated through the principles of multiscale design, gradient structure design, and metastructure design. The multiwall carbon nanotube (MWCNT)/carbonyl iron (CI)/epoxy resin(EP) nano lossy composite was integrated with the patterned resistive films (PRF) to form a gradient metastructure. Carbon fiber (CF) cloth was incorporated into the structure to enhance mechanical resistance. The CFRMM achieves −10 dB absorption bandwidth in frequency bands of 2‐4.3 GHz and 7.02‐18 GHz with maximum absorption of −17.4 dB. The −9 dB absorption bandwidth was covered in the full band 2‐18 GHz. The CFRMM exhibits excellent mechanical properties with equivalent tensile strength and flexural strength of 75.77 and 408.43 MPa, respectively. The large tensile fracture strain of 24% reveals the good toughness of the metastructure. Broadband microwave absorption and effective load bearing integrated in one structure make the CFRMM more promising for applications in the future.

Twinning‐induced large tensile strains in directionally-solidified Fe100−xGax oligocrystals

Fe100−xGax alloys require highly textured samples for optimal magnetostrictive performance, which is often accomplished through directional solidification. In this study, we measure the mechanical properties of commercial Fe81.6Ga18.4 oligocrystals using sub-sized tensile specimens and digital image correlation (DIC). While many samples fractured around 360 MPa (the literature yield/tensile stress), most had discontinuous yielding as low as 186 MPa. Many of the samples also exhibited surprisingly large tensile strains, up to 5%, with substantial specimen-to-specimen variability. In all specimens, DIC showed high strain bands that develop at very defined angles, in agreement with electron back-scattered diffraction, which revealed significant deformation twinning.

Spin-orbit effects in ferroelectric PbTiO3 under tensile strain

We report a study based on first-principles calculations complemented by a tight-binding approach and a $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ model of the spin-orbit effects in epitaxially strained $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$. The imposed biaxial tensile strain allows us to rotate the electrical polarization of $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ from out-of-plane to in-plane directions through structural phase transitions between a tetragonal, monoclinic, and orthorhombic phase. It is found that Ti $d$-state conduction bands exhibit two strong Rashba-like spin-splitting parameters of (1) 0.39 eV \AA{} at a tensile strain $\ensuremath{\eta}=1.55$% due to a polarization rotation in the monoclinic phase and (2) 1.08 eV \AA{} under large tensile strain of 3.8% due to band anticrossing in the orthorhombic phase. Remarkably, we also identified the presence of a quasipersistent spin texture for the band with a ${d}_{yz\ensuremath{-}zx}$ character in the orthorhombic phase. We then conclude that using strain could be an interesting way to tune the spin-orbit effects in ferroelectric materials with technological interests.

Processing and characterization of novel Ce0.8Sm0.1Bi0.1O2-δ-BaCe0.8Sm0.1Bi0.1O3-δ (BiSDC-BCSBi) composite electrolytes for intermediate-temperature solid oxide fuel cells

Ce0.8Sm0.1Bi0.1O2-δ-BaCe0.8Sm0.1Bi0.1O3-δ (BiSDC-BCSBi) composites are fabricated as novel electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Both dramatically enhanced sinterability and electrical performance are obtained due to the Bi doping. BiSDC-BCSBi composites are densified at as low as 1200 °C, allowing a decrease of 350 °C compared with Ce0.8Sm0.2O2-δ-BaCe0.8Sm0.2O3-δ (SDC-BCS) composites. The optimal electrical conductivity of BiSDC-BCSBi electrolytes measured at 600 °C in humid air reaches up to 27.97 mS cm−1, almost 6 times higher than that of SDC-BCS electrolytes (3.91 mS cm−1 in humid air), which is mainly attributed to their lower sintering temperature, more uniform microstructure, larger tensile strains, and higher concentrations of O–H groups and oxygen vacancies. The electrolyte-supported single cell with BiSDC-BCSBi electrolyte displays a peak power density of 397 mW cm−2 at 600 °C using humid hydrogen as fuel and ambient air as oxidant. These results imply that BiSDC-BCSBi composites have a great application prospect for IT-SOFCs.

Analysis of stress distribution in microfabricated germanium with external stressors for enhancement of light emission

In the field of silicon photonics, germanium (Ge) is an attractive material for monolithic light sources. Tensile strain is a promising means for Ge based light sources due to enhancing direct band gap recombination. We investigated strain engineering in Ge using silicon nitride (SiNx) stressors. We found that microfabricated Ge greatly improves the tensile strain because SiNx on the Ge sidewalls causes a large tensile strain in the direction perpendicular to the substrate. Tensile strain equivalent to an in-plane biaxial tensile strain of 0.8% at maximum was applied, and the PL emission intensity was improved more than five times at the maximum.

(Invited) Heteroepitaxy and Strain Engineering of Germanium-Silicon-Tin Ternary Alloy Semiconductor Thin Films for Energy Band Design

Ternary alloy semiconductor of germanium-silicon-tin (GeSiSn) has attracted for electronic and optoelectronic applications, because this group-IV alloy material provides energy band engineering independent on the lattice constant like group III-V compound semiconductors [1]. In addition, GeSiSn/Ge(Sn) heterostructure realizes type-I energy band alignment with a sufficiently large band offset at both conduction and valence band edges with no or very small lattice mismatching [2,3], and that is preferable for effective carrier confinement for light emitting devices and high mobility transistors. On the other hand, there are still challenges for crystal growth with strain and band engineering of group-IV ternary alloy semiconductor thin films. GeSn is one of promising candidates for optoelectronic applications since it realizes direct transition group-IV semiconductor. GeSn with an in-plane lattice constant larger than Ge is better to enhance the emission efficiency, as the conduction band edge of the gamma-valley lowers than that of the L-valley with large lattice constant and/or in-plane tensile strain. Thus, a buffer layer such as GeSiSn with a lattice constant sufficiently larger than Ge is required to obtain direct transition GeSn thin films, and lattice-constant engineering technology of buffer and GeSn layers should be developed with well-controlled strain relaxation technique. Recently, we explored effective strain engineering technique of GeSiSn ternary alloy epitaxial layers on Ge and Si substrate to obtain much larger in-plane lattice constant. We investigated the effect of low-temperature growth of Ge buffer layer on the strain relaxation of GeSiSn layer [4,5]. Also, we examined the ion implantation technique into substrate to enhance the strain relaxation of GeSiSn epitaxial layers grown on Ge substrate [6]. We can achieve GeSiSn epitaxial layers with the enhancement of strain relaxation and the lattice constant larger than Ge, although the crystalline quality of these epitaxial layers should be still improved. We previously reported that the strain direction as compressive and tensile ones is significantly influence of GeSiSn epitaxial layers [7]. The control of strain structure and its relaxation process is keys to obtain high crystalline quality of GeSiSn and GeSn heteroepitaxial layers for improving the electronic and optoelectronic properties of group-IV heterostructures.

A new approach to achieving strong ferroelectric properties in TiN/Hf0.5Zr0.5O2/TiN devices

In this paper, we propose a method to improve the performance of TiN/Hf0.5Zr0.5O2 (HZO)/TiN Nano-capacitors used in memory devices. Instead of direct fabrication of the TiN/HZO/TiN device, our method involves an intermediate step in which W metal is used as a capping material to induce a large in-plane tensile strain during rapid thermal annealing, resulting in a total suppression of the monoclinic phase and the appearance of the ferroelectric phase. Consequently, after removing the W capping electrode through an etching process and the post-deposition of a TiN top electrode at room temperature, a high remnant polarization of approximately 40 μC cm−2 and a 65% increase of coercive field were obtained. Moreover, the leakage current was reduced by an order of magnitude compared to the normal TiN/HZO/TiN capacitor; this result is attributed to the presence (absence) of the W/HZO (TiN/HZO) top interface during thermal annealing. The formation of a TiO x interfacial layer at elevated temperatures, which pulls oxygen from the HZO layer, resulting in the formation of oxygen vacancies, is the main cause of the high leakage current through the TiN/HZO/TiN stacks. It was confirmed that the re-capped TiN/HZO/TiN capacitor has a comparable endurance to a normal capacitor. Our results offer the re-capping process as a promising approach to fabricating HfO2-based ferroelectric memory devices with various electrode materials.

Strain-Engineered Metal-to-Insulator Transition and Orbital Polarization in Nickelate Superlattices Integrated on Silicon.

Epitaxial growth of SrTiO3 (STO) on silicon greatly accelerates the monolithic integration of multifunctional oxides into the mainstream semiconductor electronics. However, oxide superlattices (SLs), the birthplace of many exciting discoveries, remain largely unexplored on silicon. In this work, LaNiO3 /LaFeO3 SLs are synthesized on STO-buffered silicon (Si/STO) and STO single-crystal substrates, and their electronic properties are compared using dc transport and X-ray absorption spectroscopy. Both sets of SLs show a similar thickness-driven metal-to-insulator transition, albeit with resistivity and transition temperature modified by the different amounts of strain. In particular, the large tensile strain promotes a pronounced Ni orbital polarization for the SL grown on Si/STO, comparable to that reported for LaNiO3 SL epitaxially strained to DyScO3 substrate. Those results illustrate the ability to integrate oxide SLs on silicon with structure and property approaching their counterparts grown on STO single crystal, and also open up new prospects of strain engineering in functional oxides based on the Si platform.

Isogeometric shape optimization of missing rib auxetics with prescribed negative Poisson’s ratio over large strains using genetic algorithm

This paper presents an isogeometric shape optimization framework using genetic algorithm to design 2D auxetic structures with prescribed Poisson’s ratio over large tensile or compressive strains in the nonlinear deformation regime. The design domain is parametrized using NURBS to allow smoother shape variation of the structure and enable accurate fabrication of the optimized structures. The versatility of the framework is illustrated through the optimization of a missing rib structure with four ligaments under different loading conditions. The manufacturability of specimens using the NURBS and PolyJet 3D printing technology is also shown. The first example focuses on achieving constant negative Poisson’s ratio up to -0.7 within the applied tensile strain of 50% under plane stress condition. As auxetics experiments under large compressive strain are rarely performed and published, the second example demonstrates the optimization for compressive loading. The Poisson’s ratio determined from experiments matches well with the numerical results. The experiments highlight that for very flexible materials, deformation under self-weight and contacts between adjacent unit cells are significant factors in compression, and further investigations are needed.

Behavior of FRP Ring-Confined CFST columns under axial compression

Although concrete-filled steel tube (CFST) columns have been widely accepted in applications, they suffer deterioration due to various reasons. On the other hand, the concrete and the steel in CFST columns subjected to compression are not perfectly bonded at the initial loading stage. To this end, fiber-reinforced polymer (FRP) rings are proposed to strengthen the CFST columns in the present study. By strengthening CFST columns with FRP rings, it is expected that their nominal yield strength is increased and the strengthened CFSTs exhibit a monotonic ascending load–strain behavior under compression. An experimental study on axial compressive behavior of FRP ring-confined CFST (FRCCFST) columns is carried out and the effects of the FRP type, the FRP ring thickness (0, 2, 3, 4 layers) and the FRP ring clear spacing (40, 80, 120 mm) on the axial compressive behavior of FRCCFST columns are investigated in this study. The experimental results show that FRP rings substantially enhance the ultimate load capacity and slightly enhance the yield strength of CFST columns. The ultimate axial strain of polyethylene terephthalate (PET) FRP ring-confined specimens is much better than that of CFRP ring-confined specimens due to the large ultimate tensile strain of PET FRP. The ultimate stress and strain of concrete in CFST specimens are obtained and compared with those provided by existing stress–strain models to examine their accuracy and capability.

A model for rubber elasticity

A constitutive equation for rubber-like materials is developed using the left stretch tensor. This process starts with a model for hyperelastic solids based on a separable energy function. This model accurately fits extensional data for vulcanized natural rubber until the onset of hysteresis at intermediate strains. Better predictions outside the hyperelastic range are obtained by directly modifying this constitutive equation to describe limited extensibility. The resulting model accurately fits biaxial, planar, and uniaxial extension data for a variety of rubber-like materials using three constants. This model also predicts simple shear results derived from planar extension data and characterizes inflation of spherical membranes for elastomers and soft tissue. A final modification accurately describes hardening associated with crystallization at large tensile strains.

Toughening a superstrong carbon crystal: Sequential bond-breaking mechanisms

A complex orthorhombic carbon allotrope in $Pbam$ symmetry with 32 atoms in its unit cell, thus termed $Pbam$-32 carbon, was recently predicted [C. Y. He et al., Phys. Rev. Lett. 121, 175701 (2018)]. Its crystal structure comprises alternating fivefold, sixfold, and sevenfold carbon rings and exhibits reduced bonding anisotropy compared to diamond, raising the prospects of finding a superstrong material with distinct and favorable mechanical properties. Here we report findings from first-principles calculations that reveal peculiar stress-strain relations in $Pbam$-32 carbon. The obtained stress responses under various tensile and shear strains display outstanding characteristics contrasting those of traditional superhard materials like diamond and cubic boron nitride ($c$-BN). The $Pbam$-32 carbon undergoes structural deformations that produce highly isotropic stress responses under a wide variety of large tensile and shear strains, showcasing unprecedented nearly degenerate stress-strain curves along multiple deformation paths extended over ultralarge, including full-range, strains up to the bond-breaking points. These deformation modes impede or even suppress the graphitization process commonly seen in highly strained diamond and $c$-BN crystals while still sustaining large peak stresses comparable to those in diamond. Most notably, we find conspicuous bond-weakening and -breaking mechanisms stemming from bonding symmetry reduction in $Pbam$-32 carbon. At large tensile strains, a sequential bond elongation process occurs, generating a more ductile deformation past the peak stress; at large shear strains, the crystal structure goes through a similar sequential bond elongation process and, interestingly, transforms into a distinct three-dimensional network containing mixed $s{p}^{2}$ and $s{p}^{3}$ bonding states, suppressing the usual graphitization process. These more gradual bonding-state changes in the severely strained $Pbam$-32 carbon improve ductility and toughness in this superstrong carbon crystal. These insights elucidate mechanisms for toughening superstrong covalent crystals via microstructural arrangements, which shed light on rational design and development of a distinct class of superstrong materials that exhibit more isotropic mechanical responses with improved toughness under diverse loading conditions.

Strain-induced hierarchical ripples in MoS2 layers investigated by atomic force microscopy

Strain engineering plays a vital role in controlling the physical properties of two-dimensional (2D) materials. However, the nanomechanical behavior of atomically thin 2D crystals under strain has not been completely understood. Here, strain-induced hierarchical ripple nanostructures in triangular MoS2 flakes were investigated by advanced atomic force microscopy and optical spectral measurements. The hierarchical nanoripples exhibited a threefold radial pattern, and their mechanical, electronic, and optical spectra characteristics were significantly modified due to the suffering from large tensile strain. Structure evolution of these hierarchical nanoripples was further discussed based on the geometry and thickness of MoS2 flakes, and we attributed the curtain effect at the limit of a single atomic layer. Our study will be beneficial in designing nanomechanical structures and prototype electromechanical devices with 2D materials.

In situ measurement of phase transformations and residual stress evolution during welding using spatially distributed fiber-optic strain sensors* *This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide

Welding of high-strength steels can result in large tensile strains as the base metal and filler material cool from their molten state. To combat these large tensile strains, low-transformation-temperature (LTT) metal fillers have been proposed. These fillers undergo a martensitic phase transformation at a lower temperature which can ultimately reduce the tensile strain or can even introduce compressive strain adjacent to the weld metal. However, the process for optimizing the composition of the LTT material, as well as various weld parameters for each unique weld geometry, can be quite expensive, especially if the acceptance criterion requires using neutrons, x-ray beams, or destructive techniques to characterize residual stresses. This work describes a simple, low-cost method for quantifying residual stresses and phase transformations in situ during welding. Spatially distributed fiber-optic sensors were bonded to a cast iron plate, along with tack-welded thermocouples, to measure temperature and strain during multiple passes with LTT filler metals. Results show that the fiber-optic sensors can successfully resolve compressive strain adjacent to the weld region caused by the martensitic phase transformations in the LTT filler material.

Ligament size dependency of strain hardening and ductility in nanoporous gold

Nanoporous (NP) metals with ligament sizes up to a few tens of nm show exceptional mechanical properties such as high strength and stiffness per weight. While their elasticity and yield strength have been the subject of numerous studies, less is known about the plastic deformability of these materials under large compressive and tensile strains. In this study, the effect of ligament size is investigated using large-scale atomistic simulations to probe the elastic response, plastic response, and deformation mechanisms of nanoporous gold under uniaxial compression and tension to strains in excess of 60 percent. This paper explores the full range of the material response under uniaxial loading, focusing on the modifications to strain hardening under compression and ductility and delayed failure under tension. It was found that the elastic modulus experiences a compression-tension asymmetry that decreases with ligament size increase. Under compression, strain hardening is found to be ligament size dependent. This size dependency can be explained by the coupling effect of the change in surface area to solid volume ratio evolution and defects accumulation. Under tension, the material shows higher ductility with ligament size increase causing a delay in failure. This is attributed to differences in dislocation density. The results reported in this work will help in evaluating the effect of ligament size on the material response, and eventually enhance the design of novel nanoporous foams with tailored mechanical response.