Local Strain Effects Research Articles

Strain-gradient induced topological transition in bent nanoribbons of the Dirac semimetal Cd3As2

Dirac semimetal is an ideal parent state to realize various exotic states of matters, such as quantum spin Hall state, Weyl semimetal phase and Majorana zero modes. Topological phase transition allows for the switching between these different topological states. Here, in this paper, we exhibit experimentally an effective approach of inducing topological phase transition in Cd3As2 nanoribbons, by applying a bending strain profile onto the sample. The local strain varies linearly from compression to tension through the cross-section of a bent nanoribbon. The strain gradient causes obvious lattice deformation and breaks the C4 rotational symmetry, thus opening an energy gap at the Dirac points and making the bulk gapful. When further increasing the strain strength, the local strain effect dominates over the symmetry-breaking effect, where spatially-varying band shift becomes prominent across the nanoribbon. Our results demonstrate the effect of strain gradient on the evolution of energy band structures, which should be valuable for further study of strain-mediated topological phase transition.

The Influence of Local Strain Distribution on the Effective Electrical Resistance of Carbon Black Filled Natural Rubber.

A monotonous relation between strain and measured electric resistance is highly appreciated in stretchable elastomer sensors. In real-life application the voids or technological holes of strained samples often induce non-homogeneous local strain. The present article focused on studying the effect of non-homogeneous local strain on measured direct current (DC) effective electric resistance (EER) on samples of natural rubber (NR), reinforced with 50, 60 and 70 phr of carbon black (CB). Samples were imparted geometrical inhomogeneities to obtain varied local strains. The resulting strain distribution was analyzed using Digital Image Correlation (DIC). EER exhibited a well-detectable influence of locations of inhomogeneities. Expectedly, the EER globally decreased with an increase in CB loading, but showed a steady increase as a function of strain for 50 and 60 phr over the complete testing protocol. Interestingly, for 70 phr of CB, under the same testing conditions, an alternating trend in EER was encountered. This newly observed behavior was explained through a novel hypothesis—“current propagation mode switching phenomenon”. Finally, experimentally measured EERs were compared with the calculated ones, obtained by summing the global current flow through a diversity of strain dependent resistive domains.

Effects of local stress, strain, and hydrogen content on hydrogen-related fracture behavior in low-carbon martensitic steel

The present study investigated the hydrogen-related fracture behavior of specimens with different stress concentration factors through microstructure observation, finite element (FE) simulation, and digital image correlation (DIC) analysis. The alloy studied was a simple model alloy (Fe-0.2C binary alloy) with fully martensite structure. When the hydrogen content was large (2.21 mass ppm (121 at ppm)), the crack initiation and propagation occurred along the prior austenite grain boundaries. Through the FE simulations, we found that the crack initiation sites corresponded to the region with high stress and high hydrogen content. Although the stress concentration factors were different, the stress level and the hydrogen content at the crack initiation sites were almost the same, indicating that the hydrogen-related intergranular fracture originated from stress-controlled decohesion at the prior austenite grain boundaries. For the specimen with small hydrogen content (0.41 mass ppm (22.5 at ppm)), the quasi-cleavage cracks formed at the surface of the notch root and propagated along the {011} planes. The FE simulations revealed that the plastic strains were maximum at the initiation sites of the quasi-cleavage cracks. Moreover, we confirmed that hydrogen enhanced the local plastic deformation by DIC analysis. As the local values of maximum principal stress, plastic strain, and hydrogen content at the initiation sites of the quasi-cleavage cracks were different depending on the stress concentration factor, the critical quantitative condition for the initiation of quasi-cleavage cracking was not simple compared to that of the case of intergranular cracking.

Study of the Influence of Local Strains of Lactobacillus on the Experimental Model of Ulcerative Colitis

The article is devoted to one of the most important effects of local strains of lactic acid bacteria - the detection of anti-inflammatory action. For this purpose, studies were conducted on an experimental model of ulcerative colitis caused in experimental animals (mice). The data proving that the effect of various probiotic bacteria is unequal are presented. The ability of probiotic lactic acid bacteria in vitro and in vivo systems to influence the production of pro - and anti-inflammatory cytokines, to stimulate antimicrobial, anti-inflammatory, and protective effects have been shown. It is shown that it is necessary to study the specific effect of local lactobacillus strains on anti-inflammatory properties for a more adequate, effective selection of probiotic drugs in the treatment of intestinal ulcers. Data have been presented proving the positive effects of probiotic bacteria on the wound key.

Optical and electrical characterization of WS2 multilayer on flexible PET substrate

WS2 is two-dimensional layered material which the electronic band gap is dependent on the number of layers. From application point of view, the WS2 few layers are good candidate for nano scale flexible electronics . In this study, the WS2 number of layers is modified using liquid phase exfoliation method. The blue shift of WS2 supernatant absorption peaks suggested the change of layer thickness compare to the non-exfoliated one. This supernatant is further deposited on Polyethylene terephthalate (PET) to create a flexible multilayer WS2 thin films. The morphology and the content of the thin film are confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), respectively. The Raman and photoluminescence spectroscopy show typical characteristics of WS2 multilayers which are dominated by W-S vibrations, exciton contributions, as well as the local defect and strain effects. Furthermore, the electrical characterization reveals the robustness of the WS2 electronic properties again the mechanical stretching. This study highlights the abundant optical and electrical characterization of WS2 multilayer which are applicable for flexible electronic devices.

Effect of load-induced local mechanical strain on peri-implant bone cell activity related to bone resorption and formation in mice: An analysis of histology and strain distributions

The purpose of this study was to investigate the effect of load-induced local mechanical strain on bone cell activity of peri-implant bone in mice. Titanium implants were placed in the maxillae of 13-week-old male C57BL/6J mice and subjected to intermittent 0.15 N, 0.3 N, or 0.6 N loads for 30 min/day for 6 days. The animals were sacrificed 2 days after the final loading. Unloaded mice were used as controls. An animal-specific three-dimensional finite element model was constructed based on morphological data retrieved from in vivo microfocus computed tomography for each mouse to calculate the mechanical strain distribution. Strain distribution images were overlaid on corresponding histological images of the same site in the same animal. The buccal cervical region of the peri-implant bone was predetermined as the region of interest (ROI). Each ROI was divided by four strain intensity levels: 0–20 με, 20–60 με, 60–100 με, and ≥100 με, and the bone histomorphometric parameters were analyzed by the total area of each strain range for all loaded samples. The distance between the calcified front and calcein labeling as a parameter representing the mineral apposition rate was significantly greater in the areas with strain intensity ≥100 με than in the area with strain intensity <100 με, suggesting that the bone formation activity of osteoblasts was locally enhanced by a higher mechanical strain. However, the shrunken osteocytes and the empty osteocyte lacunae were significantly lower in the highest strain area, suggesting that osteoclastogenesis was more retarded in higher strain areas than in lower strain areas. The histomorphometric parameters were not affected geometrically in the unloaded animals, suggesting that the load-induced mechanical strain caused differences in the histomorphometric parameters. Our findings support the hypothesis that bone cell activity related to bone resorption and formation is local strain-dependent on implant loading.

The effect of localized strain on the electrical characteristics of curved carbon nanotubes

Carbon nanotubes (CNTs) are the emerging alternative for silicon for developing miniatured electromechanical devices in the More than Moore's era. But, the inconsistent pitch distances among the aligned CNTs have limited their outstanding performances. Except for the intertube overlapping, the curved morphology is an important but often ignored factor for the attractive CNTs under van der Waals interaction. Here, we have synthesized a clean and curved CNT structure with a definite curvature radius by introducing micro perturbation. Electrical measurement has demonstrated that the curved structure will limit the on/off ratio by orders of magnitude but can maintain a high output delivery in transistors. This is attributed to the resistance induced by the localized strain and the extra current delivery capability of the inner walls, which can be well explained by the energy band diagram model. Among the curved CNTs, incommensurate double walled CNTs of higher diameter difference are the optimal candidates for delivering a high current output by limiting intertube charge transfer. Our demonstrations and analysis have highlighted the importance of controlling both the chiral structures and morphology of CNTs for the applications of high-performance carbon-based electronics.

The effects of local strain on the cubic Li7La3Zr2O12(001)/Li(001) interface: A first-principles study

Cubic Li7La3Zr2O12 (c-LLZO) is considered as one of the promising electrolytes for all-solid-state lithium-ion batteries, owing to its high Li ionic conductivity and chemical stability against Li anode. The c-LLZO/Li interface, as a Li-ion transport structure which affects the charge-discharge cycle of Li metal batteries, remains to be fully understood at present, especially on the atomic-level. Here, we present a first-principles study to explore the stability of the c-LLZO/Li interface and Li transport across the c-LLZO/Li interface. The interaction between Li slab and c-LLZO slab is attractive, which is confirmed to be physical adsorption by the density of state. Some vacancies are introduced into the Li layer to release the local strain at the interface. There is negligible change in the interface energy with the introduction of vacancies, meaning the local strain has little effect on the stability of the interface. The diffusion energy barriers of Li across the c-LLZO/Li interface are in the range of 0.17 to 0.36 eV, which are greatly influenced by the local strain. Such low diffusion energy barriers indicate the c-LLZO/Li interface is in favor of fast lithium ion conduction.

Effects of local shear strain on the zigzag graphene nanoribbon with a topological line defect

Abstract First-principles density functional theory calculations are performed to study the effects of local shear strain on the structural, mechanical and electronic properties of zigzag graphene nanoribbon with a topological line defect (LD-ZGNR). By changing the nanoribbon width N (N is the number of zigzag chains in the left or right ribbons of the topological line defect) and deformation positions, the optimal position is obtained. The mechanical properties of the LD-ZGNR such as stress-strain curves exhibit nonlinear behavior with strain, and the shear modulus is strongly dependent on the nanoribbon width N and deformation positions. Furthermore, the strong interactions among atoms of the LD-ZGNR under local shear strain induce dramatic changes to the electronic properties of the system. This work reveals mechanism of LD-ZGNR under local shear strain, and provides new idea and more accurate data for the design and application of graphene flexible elastic electronic devices.

Rapid polarization mapping in ferroelectrics using Fourier masking.

Ferroelectric materials, and more specifically ferroelectric domain walls (DWs) have become an area of intense research in recent years. Novel physical phenomena have been discovered at these nanoscale topological polarization discontinuities by mapping out the polarization in each atomic unit cell around the DW in a scanning transmission electron microscope (STEM). However, identifying these features requires an understanding of the polarization in the overall domain structure of the TEM sample, which is often a time-consuming process. Here, a fast method of polarization mapping in the TEM is presented, which can be applied to a range of ferroelectric materials. Due to the coupling of polarization to spontaneous strain, we can isolate different strain states and demonstrate the fast mapping of the domain structure in ferroelectric lead titanate (PTO). The method only requires a high-resolution TEM or STEM image and is less sensitive to zone axis or local strain effects, which may affect other techniques. Thus, it is easily applicable to in-situ experiments. The complimentary benefits of Fourier masking with more advanced mapping strategies and its application to other materials are discussed. These results imply that Fourier masked polarization mapping will be a useful tool for electron microscopists in streamlining their analysis of ferroelectric TEM samples. LAY DESCRIPTION: This paper addresses a problem that often occurs when looking at a ferroelectric material in the Transmission Electron Microscope (TEM). Ferroelectric samples are interesting because they form tiny areas inside themselves with arrow of charge in each one. The thinner the sample, the smaller these regions, called "domains" become. These arrows of charge point in different directions in each domain of the sample. The boundary where these domains meet have interesting properties to study in a TEM but it's important to figure out which way the arrows point in the domains around the boundary. What causes the arrows in the different domains is tiny shifts of different atoms in unit cell away from their neutral position, usually because they're being squeezed by pressure from the domains nearby. The problem is that these tiny atoms moving are difficult to measure and see where the charged arrow is pointing, often it's hard to know how many different domains are even in the sample and where they begin. This paper discusses a method called "Fourier masking" to quickly see what's going on in the overall TEM sample, where the domains are and roughly where the arrows point. It does this by looking at the spacings of the atoms from a magnification where you can just about see the lines of atoms. In lead titanate the unit cell is a rectangle and the arrow always points in line with the long side of the rectangle. The Fourier masking lets you see which direction the long side of the rectangular unit cell is pointing in different parts of your TEM image. The big advantage is that it takes about two minutes to do and uses software that almost every TEM already has. That lets the TEM user quickly know where the domains are in their TEM samples and roughly which way the arrows of charge are pointing. Then they can choose the most interesting features focus on for higher resolution analysis.

Increasing of Aceh’s patchouli production with technology of bio-fertilizer local specific mycorrhizal strains in Entisols

Aceh’s patchouli is one of the superior local commodities, and its growth and yield could be improved in various means. One way to increase the patchouli production can be done by using bio-fertilizer mycorrhizal local strain. The purpose of this research was to study effect of bio-fertilizer mycorrhizal local specific strain on the growth and yield of patchouli in Entisols. We conducted two experiment. The first experiment was the propagation technique of mycorrhizae on Entisols soil and the second experiment the test of the fertilizer on a greenhouse pot scale for the growth of patchouli seedlings. The research was arranged by a non-factorial randomized block design with three replications. The investigated factor was the bio-fertilizer mycorrhizal from local specific strain with four levels, i.e. M0 (without mycorrhizae), M1 (Glomus mosseae) M2 (Gigaspora sp) and M3 (Mixing between Glomus mosseae and Gigaspora sp). The variety of patchouli used in this study was the Tapak Tuan variety. The observed parameters were seedling height and seedling diameter of patchouli at 45, 60 days after planting; additionally the parameter of patchouli yields consist of number of leaves, number of branches and weight of leaves were observed at 90 days after planting, and root colonization by mycorrhizae. The results showed that mixed mycorrhizal strains between Glomus mosseae + Gigaspora sp contributed to the best marks for increasing growth and yield of seedling patchouli in Entisolss. The similar trend result was also found in the root colonization by mycorrhizae. The strain of mycorrhizal of Gigaspora sp application was not effective for increasing the growth and yield of Aceh’s patchouli in Entisols.

Quenched nematic criticality and two superconducting domes in an iron-based superconductor

The nematic electronic state and its associated critical fluctuations have emerged as a potential candidate for the superconducting pairing in various unconventional superconductors. However, in most materials their coexistence with magnetically ordered phases poses a significant challenge in determining their importance. Here, by combining chemical and hydrostatic physical pressure in FeSe0.89S0.11, we access a nematic quantum phase transition isolated from any other competing magnetic phases. From quantum oscillations in high magnetic fields, we trace the evolution of the Fermi surface and electronic correlations as a function of applied pressure and detect a Lifshitz transition that separates two distinct superconducting regions. One emerges from the nematic phase with a small Fermi surface and strong electronic correlations, while the other one has a large Fermi surface and weak correlations that promotes nesting and stabilization of a magnetically ordered phase at high pressures. The absence of mass divergence at the nematic quantum phase transition suggests that the nematic fluctuations could be quenched by the strong coupling to the lattice or local strain effects. A direct consequence is the weakening of superconductivity at the nematic quantum phase transition in the absence of magnetically driven fluctuations. Using sulfur doping and pressure, the authors separate the nematic and magnetic phase transitions in FeSe. They find that a Lifshitz transition sits between two independent superconducting domes where nematic critical fluctuations remain finite.

Direct Visualization of Local Spin Transition Behaviors in Thin Molecular Films by Bimodal AFM.

Thin films of the molecular spin-crossover complex [Fe(HB(1,2,4-triazol-1-yl)3 )2 ] undergo spin transition above room temperature, which can be exploited in sensors, actuators, and information processing devices. Variable temperature viscoelastic mapping of the films by atomic force microscopy reveals a pronounced decrease of the elastic modulus when going from the low spin (5.2 ± 0.4 GPa) to the high spin (3.6 ± 0.2 GPa) state, which is also accompanied by increasing energy dissipation. This technique allows imaging, with high spatial resolution, of the formation of high spin puddles around film defects, which is ascribed to local strain relaxation. On the other hand, no clustering process due to cooperative phenomena was observed. This experimental approach sets the stage for the investigation of spin transition at the nanoscale, including phase nucleation and evolution as well as local strain effects.

Effect of grain orientation and local strains on void growth and coalescence in titanium

Ductile fracture has been extensively studied in metals with weak mechanical anisotropy such as copper and aluminum. The fracture of more anisotropic metals, especially those with a hexagonal crystal structure (e.g. titanium), remains far less understood. This paper investigates the ductile fracture process in commercially pure titanium (CP-Ti) with particular emphasis on the influence of grain orientation and local state of strain on void growth. An experimental approach was developed to directly relate the growth of a void in three dimensions to its underlying grain orientation. Grain orientation was obtained by electron back scattered diffraction on void-containing CP-Ti sheets prior to their diffusion bonding. Changes in void dimensions were measured during in-situ straining within an x-ray tomography system. The strong influence of the embedded grain orientation and that of its neighbors on void growth rate and coalescence has been experimentally quantified. Finite element crystal plasticity simulations that take into account both grain orientation and the local strain state were found to predict the experimental void growth. Grains where basal slip dominates show the largest void growth rates because they are closer to a plane strain condition that favors void growth and coalescence.

(Invited) A Review of Defects in 2D Metal Dichalcogenides: Doping, Alloys, Interfaces, Vacancies and Their Effects in Catalysis & Optical Emission

Two-dimensional transition metal dichalcogenides (TMDs) such as MoS2 and WS2 hold great promise for many novel applications. Recent years have therefore witnessed tremendous efforts on large scale manufacturing of these 2D crystals. A long-standing puzzle in the field is the effect of different types of defects in their electronic, magnetic, catalytic and optical properties. In this presentation an overview of different defects in transmission metal di-chalcogenides (TMDs) will be presented [1,2]. We will first focus on: 1) defining the dimensionalities and atomic structures of defects; 2) pathways to generating structural defects during and after synthesis and, 3) the effects of having defects on the physico-chemical properties and applications. We will also emphasize doping and allowing monolayers of MoS2 and WS2, and their implications in electronic and thermal transport. We will also describe the catalytic effects of edges, vacancies and local strain observed in MoxW(1-x)S2 monolayers by correlating the hydrogen evolution reaction (HER) with aberration corrected scanning transmission electron microscopy (AC-HRSTEM) [3]. Our findings demonstrates that it is now possible to use chalcogenide layers for the fabrication of more effective catalytic substrates, however, defect control is required to tailor their performance. By studying photoluminescence spectra, atomic structure imaging, and band structure calculations, we also demonstrate that the most dominating synthetic defect—sulfur monovacancies in TMDs, is responsible for a new low temperature excitonic transition peak in photoluminescence 300 meV away from the neutral exciton emission [4]. We further show that these neutral excitons bind to sulfur mono-vacancies at low temperature, and the recombination of bound excitons provides a unique spectroscopic signature of sulfur mono-vacancies [4]. However, at room temperature, this unique spectroscopic signature completely disappears due to thermal dissociation of bound excitons [4]. Finally, hetero-interfaces in TMDs, will be studied and discussed by AC-HRSTEM and optical emission.

TFET inverter static and transient performances in presence of traps and localized strain

This paper investigates the digital circuit-level performance of an inverter realised with n- and p-type tunnel field-effect transistors (TFETs) integrated on the same InAs/Al0.05Ga0.95Sb tech nology platform in the presence of interface traps and localized strain. The TFET-based inverter is simulated for two different IOFF values, namely 100 nA/μm and 10 pA/μm to target both high-performance and low-power applications. Based on 3D full-quantum simulations, interface traps induce a significant degradation of the voltage gain, noise margin and transient performance despite the better subthreshold slope. The effect of localized strain at the source/channel heterojunction caused by lattice mismatch, while being beneficial in terms of on-current, is unable to recover the circuit-level performance of the ideal case. The device with traps and localized strain is able to outperform the ideal one only in terms of switching transients for IOFF=10 pA/μm.

First principles study of helium cluster induced local strain effects near the oxygen-enriched nanoclusters in Fe-based alloys

First principles theory calculations have been conducted to investigate the helium cluster interaction with various oxygen-enriched local atomic structures in the iron matrix. The helium atom displays strong affinity to the oxygen:vacancy pair. The helium formation energy reduces with the tensile strain and increases with the compressive strain. The iron matrix is hardened under the compressive strain and softened under the tensile strain, regardless of the local atomic structures. Under zero strain condition, the iron matrix elasticity is not sensitive to the size of embedded helium cluster, due to the dual effects of the local strain field induced by the helium cluster. On one hand, the helium cluster induces softening effect due to the stretching of the local atomic structure. On the other hand, the helium cluster induces the hardening effect due to the compression of the surrounding iron matrix.

Structural and vibrational properties of SnxGe1-x: Modeling and experiments

The effects of the composition and macroscopic strain on the structural properties and lattice vibrations of SnxGe1-x solid solutions (SSs) are investigated numerically, employing Tersoff empirical inter-atomic potentials, and experimentally. The calculations provide statistical distributions of bond lengths, pair correlation function, and vibrational Raman spectra of the SSs. Using this approach, we are able to evaluate the tin-content-dependent shifts due to the local environment (i.e., changes in the atomic mass and bond stiffness) and strain effects in the calculated Raman spectra and compare them to experimental data. The relative importance of the composition dependent effects of the local environment and strain for epitaxial layers of GeSn solid solutions is analysed.

Suppression of atomic vacancies via incorporation of isovalent small ions to increase the stability of halide perovskite solar cells in ambient air

The degradation of perovskite solar cells in the presence of trace water and oxygen poses a challenge for their commercial impact given the appreciable permeability of cost-effective encapsulants. Point defects were recently shown to be a major source of decomposition due to their high affinity for water and oxygen molecules. Here, we report that, in single-cation/halide perovskites, local lattice strain facilitates the formation of vacancies and that cation/halide mixing suppresses their formation via strain relaxation. We then show that judiciously selected dopants can maximize the formation energy of defects responsible for degradation. Cd-containing cells show an order of magnitude enhanced unencapsulated stability compared to state-of-art mixed perovskite solar cells, for both shelf storage and maximum power point operation in ambient air at a relative humidity of 50%. We conclude by testing the generalizability of the defect engineering concept, demonstrating both vacancy-formation suppressors (such as Zn) and promoters (such as Hg). Despite their high efficiencies, perovskite solar cells still suffer from degradation issues that impede their practical deployment. Saidaminov et al. explore the effect of local lattice strain on vacancy formation and show that careful choice of dopants plays a key role, enhancing the device stability.

Giant Enhancement of Magnetostrictive Response in Directionally-Solidified Fe83Ga17Erx Compounds.

We report, for the first time, correlations between crystal structure, microstructure and magnetofunctional response in directionally solidified [110]-textured Fe83Ga17Erx (0 < x < 1.2) alloys. The morphology of the doped samples consists of columnar grains, mainly composed of a matrix phase and precipitates of a secondary phase deposited along the grain boundary region. An enhancement of more than ~275% from ~45 to 170 ppm is observed in the saturation magnetostriction value (λs) of Fe83Ga17Erx alloys with the introduction of small amounts of Er. Moreover, it was noted that the low field derivative of magnetostriction with respect to an applied magnetic field ( for Happ up to 1000 Oe) increases by ~230% with Er doping ( 0.045 ppm/Oe; 0.15 ppm/Oe). The enhanced magnetostrictive response of the Fe83Ga17Erx alloys is ascribed to an amalgamation of microstructural and electronic factors, namely: (i) improved grain orientation and local strain effects due to deposition of Er in the intergranular region; and (ii) strong local magnetocrystalline anisotropy, due to the highly anisotropic localized nature of the 4f electronic charge distribution of the Er atom. Overall, this work provides guidelines for further improving galfenol-based materials systems for diverse applications in the power and energy sector.