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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Dramatic influence of Dy{sup 3+} doping on strain and domain structure in lead-free piezoelectric 0.935(Na{sub 1/2}Bi{sub 1/2})TiO{sub 3}−0.065BaTiO{sub 3} ceramics

An electric-field induced giant strain response and doping level dependent domain structural variations have been studied in the dysprosium (Dy{sup 3+})-modified 0.935(Na{sub 1/2}Bi{sub 1/2})TiO{sub 3}-0.065BaTiO{sub 3}(xDy : NBBT) ceramics with the doping levels of 0%, 0.5%, 1%, and 2%. X-ray diffraction and Raman spectroscopy analyses not only demonstrates the change in ionic configurations induced by Dy{sup 3+} doping, but also shows the local crystal symmetry for x ≥ 0.5% doping levels to deviate from the idealized cubic structure. Piezoresponse force microscopy measurement exhibits the presence of an intermediate phase with orthorhombic symmetry at the critical Dy{sup 3+} doping level of 2%. Moreover, at this doping level, a giant recoverable nonlinear strain of ∼0.44% can be observed with high normalized strain (S{sub max}/E{sub max}) of 728 pm/V. At the same applied field, the strain exhibits a 175% increase than that of NBBT ceramic. Such a large strain stems from the varying coherence lengths of polar nanoregions (PNRs) and an unusual reversible 90° domain switching caused by the symmetry conforming property of point defects, where the restoring force is provided by unswitchable defects. The mechanism reveals a new possibility to achieve large electric-field strain effect for a wide range of ferroelectric systems, which can lead to applications in novel “on-off” actuators.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Intersubband energies in strain-compensated InGaN/AlInN quantum well structures

Intersubband transition energies in the conduction band for strain-compensated InGaN/AlInN quantum well (QW) structures were investigated as a function of strain based on an effective mass theory with the nonparabolicity taken into account. In the case of an InGaN/AlInN QW structure lattice-matched to GaN, the wavelength is shown to be longer than 1.55 μm. On the other hand, strain-compensated QW structures show that the wavelength of 1.55 μm can be reached even for the QW structure with a relatively small strain of 0.3 %. Hence, the strain-compensated QW structures can be used for telecommunication applications at 1.55 μm with a small strain, compared to conventional GaN/AlN QW structure.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Enhancement of piezoelectric constants induced by cation-substitution and two-dimensional strain effects on ZnO predicted by density functional perturbation theory

Using density functional perturbation theory, we investigated the effect of various substitutional dopant elements and in-plane strain on the piezoelectric properties of ZnO. The piezoelectric stress constant e{sub 33} of doped ZnO was found to depend on the formal charge of the substitutional dopant. By decomposing the piezoelectric stress constant e{sub 33} into the individual atomic contributions, the change in the piezoelectric properties was found to originate from a change in the coupling between the atomic displacement and the strain. Furthermore, we found that in-plane tensile strain along the a axis, which is specific to the thin film, can enhance the piezoelectric constant of ZnO. A phase transition from wurtzite to h-BN-type structure was found to occur with increasing in-plane tensile. The piezoelectric strain constant d{sub 33} was predicted to reach ∼200 pC/N for 2.78 at. % V-substituted ZnO at 5.5% in-plane strain, just before the phase transition. These theoretical results suggest that the piezoelectric constant of ZnO can be enhanced by controlling the in-plane strain via selection of the substrate material and dopant element.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Structural anisotropy results in strain-tunable electronic and optical properties in monolayer GeX and SnX (X = S, Se, Te)

Using first-principles calculations, the structural and electronic properties of group-IV monochalcogenide monolayers are investigated. It is demonstrated that all the monolayers employed here possess moderate indirect bandgaps. In-plane elastic stiffness calculation demonstrates the structural anisotropy in these materials, further resulting in anisotropic response to in-plane strains in their electronic properties and anisotropic optical properties. The bandgaps of GeX and SnX monolayers can be linearly reduced by applied in-plane compressive strains and the semiconductor-to-metal transition can be realized under large compressive strains; while tensile strains exert less influence on the electronic properties in comparison to compressive strains. Some monolayers will experience indirect-to-direct bandgap transition when subjected to proper strains. A further insight into the variation of bandgaps of these monolayers can be obtained from the changing band edges.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Strain-engineering the anisotropic electrical conductance in ReS{sub 2} monolayer

Rhenium disulfide (ReS{sub 2}) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1 T (Re in octahedral coordination) phase. The reduced symmetry in ReS{sub 2} leads to in-plane anisotropy in various material properties. In this work, we performed a comprehensive first-principle computational study of strain effect on the anisotropic mechanical and electronic properties of ReS{sub 2} monolayers. We found that the anisotropic ratio in electron mobility along two principle axes is 2.36 while the ratio in hole mobility reaches 7.76. The study of strain applied along different directions shows that the elastic modulus is largest for out-of-plane direction, and the strain along a-direction induces indirect bandgap while strain along b- or c-direction does not. In addition, the carrier mobility can be significantly improved by the c-direction tensile strain. This study indicates that the ReS{sub 2} monolayer has promising applications in nanoscale strain sensor and conductance-switch FETs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Distinctive mapping of strain and quantum size effects using depth-resolved photoluminescence in ZnO nanoneedles

In order to locate the spatially resolved influence of the strain, carrier localization, and quantum size effect (QSE) in tapered ZnO nanoneedles (NNs), the photoluminescence (PL) was measured as a function of the incident laser angle θ from 0{sup ∘} (normal to a surface) to 85{sup ∘}. With increasing θ, the excitation point is spatially restricted along the axis of the NNs and varies from the ZnO buffer/sapphire interface to the tips of the NNs. In this way, we identified a strain-induced blue-shift of 25.3 meV at the ZnO buffer/sapphire interface, which corresponds to a tensile strain of 0.319%. The influence of strain and the concomitant indications of carrier localization decreased as the excitation point moved to a higher location along the NNs with increasing θ whereas the QSE revealed an abrupt blue-shift near the tips of the NNs. Furthermore, time-resolved PL measurement as a function of the excitation angle was used to distinguish the strain effect from the QSE. We observed two spatially competing tendencies: (1) the decay times are influenced by the increase in the interfacial strain and (2) the decay times are influenced by the decrease in the diameter-dependent QSE near the tips of the tapered ZnO NNs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

An atomistic investigation of the effect of strain on frictional properties of suspended graphene

We performed molecular dynamics (MD) simulations of a diamond probe scanned on a suspended graphene to reveal the effect of strain on the frictional properties of suspended graphene. The graphene was subjected to some certain strain along the scanning direction. We compared the friction coefficient obtained from different normal loads and strain. The results show that the friction coefficient can be decreased about one order of magnitude with the increase of the strain. And that can be a result of the decreased asymmetry of the contact region which is caused by strain. The synthetic effect of potential energy and the fluctuation of contact region were found to be the main reason accounting for the fluctuation of the friction force. The strain can reduce the fluctuation of the contact region and improve the stability of friction.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Electromodulation spectroscopy of direct optical transitions in Ge{sub 1−x}Sn{sub x} layers under hydrostatic pressure and built-in strain

Unstrained Ge{sub 1−x}Sn{sub x} layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge{sub 0.97}Sn{sub 0.03} layers with built-in compressive (ε = −0.5%) and tensile (ε = 0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photoreflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge{sub 1−x}Sn{sub x} layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2 ± 0.2 meV/kbar, which is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge{sub 1−x}Sn{sub x} alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge{sub 0.97}Sn{sub 0.03} with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge{sub 1−x}Sn{sub x} layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electronic origin of strain effects on solute stabilities in iron

Nonuniform strain fields might induce the segregation of alloying solutes and ultimately lead to the mechanical performance degradation of body-centered-cubic (bcc) Fe based steels serving in extreme environments, which is worthy of investigation. In this paper, two typical volume-conserving strains, shear strain (SS) and normal strain (NS), are proposed to investigate the strain effects on solute stabilities in bcc iron by first-principles calculations. For solutes in each transition metal group, the calculated substitution energy change due to SS exhibits a linear dependence on the valence d radius of the solutes, and the slope decreases in an exponential manner as a function of the absolute difference between the Watson's electronegativity of iron and the averaged value of each transition metal group. This regularity is attributed to the Pauli repulsion between the solutes and the nearest neighboring Fe ions modulated by the hybridization of valence d bands and concluded to be originated from the characteristics of valence d bonding between the transition-metal solutes and Fe ions under SS. For main-group and post transition-metal solutes, the considerable drop of substitution energy change due to NS is concluded to be originated from the low-energy side shift of the widened valence s and p bands of the solutes. Our results indicate that the stabilities of substitutional solutes in iron under volume-conserving strain directly correlate with the intrinsic properties of the alloying elements, such as the valence d radius and occupancy, having or not having valence s and p bands.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Thermal stability and relaxation mechanisms in compressively strained Ge{sub 0.94}Sn{sub 0.06} thin films grown by molecular beam epitaxy

Strained Ge{sub 1-x}Sn{sub x} thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge{sub 0.94}Sn{sub 0.06} films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge{sub 0.94}Sn{sub 0.06} films grown by molecular beam epitaxy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Strain effects on Auger–Meitner recombination in silicon

We study the effects of compressive and tensile biaxial strain on direct and phonon-assisted Auger–Meitner recombination (AMR) in silicon using first-principles calculations. We find that the application of strain has a non-trivial effect on the AMR rate. For most AMR processes, the application of strain increases the AMR rate. However, the recombination rate for the AMR process involving two holes and one electron is suppressed by 38% under tensile strain. We further analyze the specific phonon contributions that mediate the phonon-assisted AMR mechanism, demonstrating the increased anisotropy under strain. In conclusion, our results indicate that the application of tensile strain increases the lifetime of minority electron carriers in p-type silicon and can be leveraged to improve the efficiency of silicon devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Improved experimental and diagnostic techniques for dynamic tensile stress–strain measurement with a Kolsky tension bar

Kolsky tension bar experiments were improved for dynamic tensile stress–strain measurements with higher fidelity and minimal uncertainties. The difficulties associated with specimen gripping, relatively short gage section, and geometric discontinuity at the bar ends all compromise the accuracy of the traditional strain measurement method in a Kolsky tension bar experiment. Here in this study, an improved three-channel splitting-beam laser extensometer technique was developed to directly and independently track the displacement of the incident and transmission bar interfaces. By adopting a dual-channel configuration on the incident bar side, the resolution and measurement range of this laser extensometer were coordinated between the two channels to provide highly precise measurement at both small and large strains under high strain-rate loading condition. On the transmission bar side an amplified channel, similar to that used on the incident bar side, was adopted to measure the transmission bar displacement with high resolution. With this novel design, a maximum resolution of approximately 500 nm can be obtained for the bar displacement measurement, which corresponds to a strain of 0.0079% for a specimen with 6.35 mm gage length. To further improve the accuracy, a pair of lock nuts were used to tighten the tensile specimen to the bars in an effort not only to prevent the specimen from potential pre-torsional deformation and damage during installation, but also to provide better thread engagement between the specimen and the bar ends. As a demonstration of this technique, dynamic tensile stress–strain response of a 304L stainless steel was characterized with high resolution in both elastic and plastic deformations.

42 ENGINEERING↗
DOE OSTI2018

Microstrip patch antenna for simultaneous strain and temperature sensing

A patch antenna, consisting of a radiation patch, a dielectric substrate, and a ground plane, resonates at distinct fundamental frequencies that depend on the substrate dielectric constant and the dimensions of the radiation patch. Since these parameters change with the applied strain and temperature, this study investigates simultaneous strain and temperature sensing using a single antenna that has two fundamental resonant frequencies. The theoretical relationship between the antenna resonant frequency shifts, the temperature, and the applied strain was first established to guide the selection of the dielectric substrate, based on which an antenna sensor with a rectangular radiation patch was designed and fabricated. A tensile test specimen instrumented with the antenna sensor was subjected to thermo-mechanical tests. Experiment results validated the theoretical predictions that the normalized antenna resonant frequency shifts are linearly proportional to the applied strain and temperature changes. As a result, an inverse method was developed to determine the strain and temperature changes from the normalized antenna resonant frequency shifts, yielding measurement uncertainty of 0.4 °C and 17.22 μϵ for temperature and strain measurement, respectively.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2017

Strain control of composite superconductors to prevent degradation of superconducting magnets due to a quench: II. High-strength, laminated Ag-sheathed Bi-2223 tapes

In article I of this series, we described a spiral coil quench technique for probing the influence of the superconductor stress and strain state during normal operation on its margin to degradation during a quench and applied to a Bi-2212 round wire. Here we extend this technique to study the failure mechanisms and limits of high-strength Bi-2223 tapes experiencing a quench while carrying a large current in a high magnetic field. In contrast to Bi-2212 magnets made via a wind-and-react technique for which bending strains can be ignored, Bi-2223 magnets are made with a react-and-wind technique for which bending strain is significant. The critical tensile stress of Bi-2223 tapes (type HT-NX) decreases from >440 MPa for straight samples to 185 MPa after being bent to a diameter D of 50 mm. For HT-NX tapes with D = 50 mm, the quench degradation limit, measured using maximum allowable temperature during a quench T allowable , is greater than 300 K for axial tensile stress ${\sigma }_{a}$ < 94 MPa; it decreases with increasing tensile axial stress ${\sigma }_{a}$ nonlinearly, dropping to 230 K for ${\sigma }_{a}$ = 125 MPa. T allow able $({\sigma }_{a})$ experimental data at D = 50 mm is consistently predicted by a general strain model that assumes that quench degradation in NX/Bi-2223 is driven by axial tensile strain in Bi-2223 filaments exceeding the irreversible strain limit. The T allowable $({\sigma }_{a})$ is then predicted for various D including D = 80 mm important for NMR magnets. In conclusion, the given T allowable $(D,{\sigma }_{a})$ is easy to use and important for finding the balance between operation stress, and therefore magnetic field generation efficiency, and operation margin when designing a superconducting magnet using Bi-2223 tapes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Strain-engineered optoelectronic properties of 2D transition metal dichalcogenide lateral heterostructures

Compared with their bulk counterparts, 2D materials can sustain much higher elastic strain at which optical quantities such as bandgaps and absorption spectra governing optoelectronic device performance can be modified with relative ease. Using first-principles density functional theory and quasiparticle GW calculations, we demonstrate how uniaxial tensile strain can be utilized to optimize the electronic and optical properties of transition metal dichalcogenide lateral (in-plane) heterostructures such as MoX 2 /WX 2 (X = S, Se, Te). We find that these lateral-type heterostructures may facilitate efficient electron–hole separation for light detection/harvesting and preserve their type II characteristic up to 12% of uniaxial strain. Based on the strain-dependent bandgap and band offset, we show that uniaxial tensile strain can significantly increase the power conversion efficiency of these lateral heterostructures. Our results suggest that these strain-engineered lateral heterostructures are promising for optimizing optoelectronic device performance by selectively tuning the energetics of the bandgap.

2D materials↗
DOE OSTI2024

Tuning superconductivity and spin-vortex instabilities in CaKFe 4 As 4 through in-plane antisymmetric strains

Lattice strains of appropriate symmetry have served as an excellent tool to explore the interaction of superconductivity in the iron-based superconductors with orthorhombic-nematic and stripe spin-density-wave (SSDW) order. In this Letter, we contribute to a broader understanding of the coupling of strain to superconductivity and competing normal-state orders by studying CaKFe 4 As 4 under large, in-plane strains of B 1 g and B 2 g symmetry. In contrast to the majority of iron-based superconductors, pure CaKFe 4 As 4 exhibits superconductivity with a relatively high transition temperature of T c ∼ 35 K in proximity of a noncollinear, tetragonal, hedgehog spin-vortex crystal (SVC) order. Through experiments and calculations, we demonstrate an anisotropic in-plane strain response of T c and the favored SVC configuration in CaKFe 4 As 4 . This supports a scenario, in which the change in spin fluctuations dominates the strain response of superconducting T c . Overall, by suggesting moderate B 2 g strains as an effective parameter to change the stability of SVC and SSDW, we outline a pathway to a unified phase diagram of iron-based superconductivity. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Strain annealing of SiC nanoparticles revealed through Bragg coherent diffraction imaging for quantum technologies

The crystalline strain properties of nanoparticles have broad implications in a number of emerging fields, including quantum and biological sensing in which heterogeneous internal strain fields are detrimental to performance. Here we used synchrotron-based Bragg coherent x-ray diffraction imaging (BCDI) to measure three-dimensional lattice strain fields within individual 3C-SiC nanoparticles, a candidate host material for quantum sensing, as a function of temperature during and after annealing up to 900 degrees C. We observed pronounced homogenization of the initial strain field at temperatures above 500 degrees C, and we find that the surface layers and central volumes of the nanoparticles reduce strain at similar rates, suggesting a uniform healing mechanism. Thus, we attribute the observed strain homogenization to activation of mobile point defects that annihilate and improve the overall quality of the crystal lattice. This work also establishes the feasibility of performing BCDI at high temperatures (up to 900 degrees C) to map structural hystereses relevant to the processing of quantum nanomaterials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Switchable orbital polarization and magnetization in strained LaCo O 3 films

Strain engineering of epitaxial heterostructures offers opportunities to control the orbital degree of freedom by lifting the degeneracy of e g states. In this work, we show that the orbital occupation in LaCoO 3 (LCO) films can be switched between two degenerate e g bands with epitaxial strain. The orbital polarization of nearly -100% (or 100%) is controlled by depleting occupation of the d x2-y2 (or d( 3z2-r2 ) orbital entirely in LCO for large compressive (or moderate tensile) strain. The change of electronic configuration associated with the spin-state transition modulates the magnetization of strained LCO films. Under compressive strain, LCO films exhibit a small magnetization without long-range ferromagnetic ordering. With tensile-strain increases, the magnetization of LCO films increases and reaches the maximum value when the bonding angle (Co-O-Co) is close to 180° and the in-plane bond length (Co-O) is unstretched. Our results highlight the role of octahedral distortion and spin-state crossover in tailoring the magnetic properties of cobaltite thin films, indicating an attractive route to deliberately control the orbital polarization that can be tuned to maximize the functionality of oxide heterostructures.

36 MATERIALS SCIENCE↗