Nanoscale Strain Fields Research Articles

Automated analysis framework of strain partitioning and deformation mechanisms via multimodal fusion and computer vision

Simultaneously investigating strain partitioning and the underlying deformation mechanisms for both the grain interior and the grain boundary (GB) is essential for understanding the complex plastic deformation of hexagonal close-packed metals. To this end, an automated analysis framework based on high-resolution digital image correlation (HRDIC) and electron backscatter diffraction (EBSD) data fusion and computer vision, integrating nanoscale resolution and a large field of view, is proposed. This framework consists of: (1) HRDIC-EBSD data fusion; (2) Segmenting the strain field into individual grains each with a core and a mantle; (3) Data clustering of the Matrix and slip bands (SBs) for each grain; (4) Full slip system (SS) identification and SS assignment to the SBs. The capabilities of this framework were demonstrated on Mg-10Y during compression. The strain field data, which was segmented into different clusters, including grain mantle, grain core, Matrix, and SBs, was analyzed statistically and quantitatively. The pixel-based slip activity, which considers the SB morphology, was obtained from a statistical perspective. Inter-granular accommodating mechanisms, including GB strain, slip transfer, and GB sliding, were quantitatively analyzed. Overall, this analysis framework, which can be applied to other materials, can automatically and statistically evaluate both nanoscale strain fields and underlying intra- and inter-granular deformation mechanisms grain-by-grain. This work provides valuable experimental insights into plastic deformation and accommodation mechanisms for polycrystals.

Investigation of nanoscale strain fields induced by the L12–Al3Zr phase in Al–Zn–Mg–Cu alloys

Al–Zn–Mg–Cu alloys are widely used in aerospace as an advanced lightweight structural material. The precipitation of the nanoscale L12–Al3Zr phase enhances the mechanical properties of the alloy. This study employs scanning transmission electron microscopy and geometric phase analysis techniques to investigate the strain fields induced by the nanoscale L12–Al3Zr phase. The findings demonstrate that after the precipitation of the L12–Al3Zr phase, the strain within the L12–Al3Zr phase is negligible, and a coherent strain field is developed near the L12–Al3Zr/Al interface. Characterizing the coherent strain fields of the nanoscale L12–Al3Zr phase provides a valuable reference for optimizing the mechanical properties of Al alloys.

4D‐STEM Nanoscale Strain Analysis in van der Waals Materials: Advancing beyond Planar Configurations

Achieving nanoscale strain fields mapping in intricate van der Waals (vdW) nanostructures, like twisted flakes and nanorods, presents several challenges due to their complex geometry, small size, and sensitivity limitations. Understanding these strain fields is pivotal as they significantly influence the optoelectronic properties of vdW materials, playing a crucial role in a plethora of applications ranging from nanoelectronics to nanophotonics. Here, a novel approach for achieving a nanoscale‐resolved mapping of strain fields across entire micron‐sized vdW nanostructures using four‐dimensional (4D) scanning transmission electron microscopy (STEM) imaging equipped with an electron microscope pixel array detector (EMPAD) is presented. This technique extends the capabilities of STEM‐based strain mapping by means of the exit‐wave power cepstrum method incorporating automated peak tracking and K‐means clustering algorithms. This approach is validated on two representative vdW nanostructures: a two‐dimensional (2D) MoS2 thin twisted flakes and a one‐dimensional (1D) MoO3/MoS2 nanorod heterostructure. Beyond just vdW materials, the versatile methodology offers broader applicability for strain‐field analysis in various low‐dimensional nanostructured materials. This advances the understanding of the intricate relationship between nanoscale strain patterns and their consequent optoelectronic properties.

Planar defects and strain distributions in polycrystalline BaFe2As2 superconductors synthesized by mechanochemical methods

In this study, the microstructure of polycrystalline Co-doped BaFe2As2 superconducting bulks was comprehensively analyzed. The synthesis process involved ball milling and subsequent spark plasma sintering (SPS). A strong correlation between the microstructure and synthesis conditions was observed. Specifically, when mechanochemical synthesis of raw metal powders was carried out at a ball milling energy (EBM) of 100 MJ/kg, the resulting Co-BaFe2As2 bulk contained nanograins with a high density of planar defects and exhibited a high critical current density (Jc) under both magnetic and self-fields. The findings suggest that planar defects are one of the influential factors on the superconducting properties. Atomic-resolution microstructural characterization revealed that the planar defects are parallel to (001) and exhibit distinctive atomic arrangements. Atomic-resolution elemental mappings displayed a remarkable barium concentration in planar defects and grain boundaries compared to the BaFe2As2 matrix. Local strain fields were also observed around planar defects, especially near their edges. These nanoscale strain fields could be considered as volumetric pinning centers, and effectively pin flux vortices in the random crystal orientation, thereby increasing Jc in the Fe-based superconducting bulk. Additionally, an extended investigation was performed to include a K-doped BaFe2As2 bulk that exhibits similar planar defects. Based on the results of the microstructural analysis, speculations were mode on the evolution process of the microstructure during the preparation of BaFe2As2 bulks.

Imaging Light-Induced Migration of Dislocations in Halide Perovskites with 3D Nanoscale Strain Mapping.

In recent years, halide perovskite materials have been used to make high-performance solar cells and light-emitting devices. However, material defects still limit device performance and stability. Here, synchrotron-based Bragg coherent diffraction imaging is used to visualize nanoscale strain fields, such as those local to defects, in halide perovskite microcrystals. Significant strain heterogeneity within MAPbBr3 (MA = CH3 NH3 + ) crystals is foundin spite of their high optoelectronic quality, and both 〈100〉 and 〈110〉 edge dislocations are identified through analysis of their local strain fields. By imaging these defects and strain fields in situ under continuous illumination, dramatic light-induced dislocation migration across hundreds of nanometers is uncovered. Further, by selectively studying crystals that are damaged by the X-ray beam, large dislocation densities and increased nanoscale strains are correlated with material degradation and substantially altered optoelectronic properties assessed using photoluminescence microscopy measurements. These results demonstrate the dynamic nature of extended defects and strain in halide perovskites, which will have important consequences for device performance and operational stability.

Structural characterization and nanoscale strain field analysis of α/β interface layer of a near α titanium alloy

Abstract In this article, the structural and nanoscale strain field of the α/β phase interface layer in Ti80 alloy were studied by using high-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). The α/β interface layer was observed in forged and different annealed Ti80 alloys, which is mainly composed of lamellar face-centered cubic (FCC) phase region and α′ + β region. The FCC phases between α and β phases show a twin relationship, and the twinning plane is ( 1 1 ¯ 1 ) (1\bar{1}1) . The orientation relationship of the β phase, the α phase, and the FCC phase is (110)β//(0001)α// ( 1 1 ¯ 1 ) (1\bar{1}1) FCC and [ 1 ¯ 11 \bar{1}11 ]β//[ 2 1 ¯ 1 ¯ 0 2\bar{1}\bar{1}0 ]α//[011]FCC. The nanoscale strain field of FCC + α and β + α′ regions was analyzed by using the GPA technology. The FCC + α region shows more significant strain gradient than the α′ + β region, and ε FCC > ε α, ε α′ > ε β. The influence of element addition on the formation mechanism of the FCC phase was discussed. The addition of Zr promotes the formation of the FCC phase by inducing lattice distortion and reducing the stacking fault energy of the α phase. In addition, the Al element forms an obvious concentration gradient around the interface layer during the cooling process of the alloy, which provides a driving force for the formation of the FCC phase.

Correlation of H Adsorption Energy and Nanoscale Elastic Surface Strain on Rutile TiO2(110)

Scanning tunneling microscopy (STM) has been used to obtain the aerial distribution of bridge-bonded hydroxyl groups (HOb) on a rutile TiO2(110) surface, modified with a well-defined nanoscale strain field. Our study makes use of earlier findings that 5–30 nm wide locally strained areas of the surface can be formed via low-energy Ar-ion bombardment combined with a thermal treatment. These strained areas appear as protrusions in the STM images, resulting from subsurface argon-filled cavities. Our STM images show that the local surface concentration of OHb groups is lower on the protrusions. This lowering of concentration has been interpreted as a reduction in the local H absorption energy, ΔE, a result similar to that observed on metals. In this paper, analysis of the reduction in this O–H bond energy across the surface shows a strong correlation between ΔEOH and the characteristic surface strain value, S. The ΔEOH values have been calculated through a subtraction of the contribution of the repulsive dipol...

Electrode-stress-induced nanoscale disorder in Si quantum electronic devices

Disorder in the potential-energy landscape presents a major obstacle to the more rapid development of semiconductor quantum device technologies. We report a large-magnitude source of disorder, beyond commonly considered unintentional background doping or fixed charge in oxide layers: nanoscale strain fields induced by residual stresses in nanopatterned metal gates. Quantitative analysis of synchrotron coherent hard x-ray nanobeam diffraction patterns reveals gate-induced curvature and strains up to 0.03% in a buried Si quantum well within a Si/SiGe heterostructure. Electrode stress presents both challenges to the design of devices and opportunities associated with the lateral manipulation of electronic energy levels.

Femtosecond electron imaging of defect-modulated phonon dynamics.

Precise manipulation and control of coherent lattice oscillations via nanostructuring and phonon-wave interference has the potential to significantly impact a broad array of technologies and research areas. Resolving the dynamics of individual phonons in defect-laden materials presents an enormous challenge, however, owing to the interdependent nanoscale and ultrafast spatiotemporal scales. Here we report direct, real-space imaging of the emergence and evolution of acoustic phonons at individual defects in crystalline WSe2 and Ge. Via bright-field imaging with an ultrafast electron microscope, we are able to image the sub-picosecond nucleation and the launch of wavefronts at step edges and resolve dispersion behaviours during propagation and scattering. We discover that the appearance of speed-of-sound (for example, 6 nm ps−1) wavefronts are influenced by spatially varying nanoscale strain fields, taking on the appearance of static bend contours during propagation. These observations provide unprecedented insight into the roles played by individual atomic and nanoscale features on acoustic-phonon dynamics.

A high performance all-organic flexural piezo-FET and nanogenerator via nanoscale soft-interface strain modulation.

Flexural strain fields are encountered in a wide variety of situations and invite novel device designs for their effective use in sensing, actuating, as well as energy harvesting (nanogenerator) applications. In this work we demonstrate an interesting all-organic device design comprising an electrospun P(VDF-TrFE) fiber-mat built directly on a conducting PANI film, which is also grown on a flexible PET substrate, for flexural piezo-FET and nanogenerator applications. Orders of magnitude stronger modulation of electrical transport in PANI film is realized in this device as compared to the case of a similar device but with a uniform spin-coated P(VDF-TrFE) film. We find that in the flexural mode of operation, the interaction between the laterally modulated nanoscale strain field distributions created by the fibers and the applied coherent strain field strongly influences the carrier transport in PANI. The transport modulation is suggested to occur due to strain-induced conformational changes in P(VDF-TrFE) leading to changes in carrier localization-delocalization. We further show that the fiber-mat based device system also works as an efficient nanogenerator capable of delivering power for low power applications.

Nanoscale strain fields research of boundaries between B2 matrix and G.P. zone in Ni-Ti alloy thin films.

Ti-47at.%Ni alloy films were prepared by magnetron sputtering followed by 460°C for 40 minutes heat-treatment. The strain fields between B2 phase matrix and G.P. zone were mapped by a combination of high-resolution transmission electron microscopy and geometric phase analysis method. It was found that there is a compressive strain region parallel to the longitudinal axis of G.P. zone with 2 nm in width, −2.2% in average strain at the boundaries between B2 phase and G.P. zone.

Strain Field Mapping of Dislocations in a Ge/Si Heterostructure

Ge/Si heterostructure with fully strain-relaxed Ge film was grown on a Si (001) substrate by using a two-step process by ultra-high vacuum chemical vapor deposition. The dislocations in the Ge/Si heterostructure were experimentally investigated by high-resolution transmission electron microscopy (HRTEM). The dislocations at the Ge/Si interface were identified to be 90° full-edge dislocations, which are the most efficient way for obtaining a fully relaxed Ge film. The only defect found in the Ge epitaxial film was a 60° dislocation. The nanoscale strain field of the dislocations was mapped by geometric phase analysis technique from the HRTEM image. The strain field around the edge component of the 60° dislocation core was compared with those of the Peierls–Nabarro and Foreman dislocation models. Comparison results show that the Foreman model with a = 1.5 can describe appropriately the strain field around the edge component of a 60° dislocation core in a relaxed Ge film on a Si substrate.

In Situ Scanning Probe Microscopy Nanomechanical Testing

AbstractScanning probe microscopy (SPM) has undergone rapid advancements since its invention almost three decades ago. Applications have been extended from topographical imaging to the measurement of magnetic fields, frictional forces, electric potentials, capacitance, current flow, piezoelectric response and temperature (to name a few) of inorganic and organic materials, as well as biological entities. Here, we limit our focus to mechanical characterization by taking advantage of the unique imaging and force/displacement sensing capabilities of SPM. This article presents state-of-the-art in situ SPM nanomechanical testing methods spanning (1) probing the mechanical properties of individual one-dimensional nanostructures; (2) mapping local, nanoscale strain fields, fracture, and wear damage of nanostructured heterogeneous materials; and (3) measuring the interfacial strength of nanostructures. The article highlights several novel SPM nanomechanical testing methods, which are expected to lead to further advancements in nanoscale mechanical testing and instrumentation toward the exploration and fundamental understanding of mechanical property size effects in nanomaterials.

Infrared nanoscopy of strained semiconductors

Knowledge about strain at the nanometre scale is essential for tailoring the mechanical and electronic properties of materials. Flaws, cracks and their local strain fields can be detrimental to the structural integrity of many solids. Conversely, the controlled straining of silicon can be used to improve the performance of electronic devices. Here, we demonstrate that infrared near-field microscopy allows direct, non-invasive mapping and a semiquantitative analysis of residual strain fields in polar semiconductor crystals with nanometre-scale resolution. Our experiments with silicon carbide crystals yield optical images of nanoindents showing strain features as small as 50 nm and the evolution of nanocracks. In addition, by imaging nanoindents in doped silicon, we provide experimental evidence for plasmon-assisted near-field imaging of free-carrier properties in nanoscale strain fields. Near-field infrared strain mapping provides possibilities for nanoscale material and device characterization, and could become a tool for nanoscale mapping of the local free-carrier mobility in strain-engineered semiconductors.

Geometric Phase Analysis of Nano-Scale Strain Fields Around 90° Domains in PbTiO3/SrTiO3 Epitaxial Thin Film

AbstractThe nano-scale strain fields analysis around 90° domains and misfit dislocations in PbTiO3/SrTiO3 001 epitaxial thin film has been conducted using the geometric phase analysis (GPA) combined with high angle annular dark field - scanning transmission electron microscopy (HAADF-STEM). The films typically possess a-c mixed domain configuration with misfit dislocations. The PbTiO3 layer was formed from the two layer: the upper 200 nm layer shows the typical a- and c- mixed domain configuration where the a-domains are several tens nm in width; the bottom 100 nm layer shows the different domain configuration that the width is several nm. In the latter case, a-domains are terminated within the film and are short in length. On the other hand, the bottom of a-domains does not contact the film/substrate interface. It keeps away from the interface, and there is completely c-domain layer under a-domains. The HAADF-STEM-GPA shows that the strain fields around an a-domain and a misfit dislocation interact each other: the tensile strain field and lattice plane bending fit together. This result indicates that the a-domain originates from the misfit dislocation.

Micromagnetics and micromechanics of Ni-Mn-Ga actuation

An analytic model is described that accounts for the nanoscale strain field that defines the twin-boundary width and energy density as well as the interaction of a 90° domain wall with such a twin boundary. These parameters are being used as input to micromagnetic calculations of the domain-wall profile perturbed by the twin-boundary strain field. Further, application of a magnetic field can displace the domain wall from a pinned twin boundary with the Zeeman energy being stored elastically in the domain-wall anisotropy energy.

Straining Effects in Silica-Filled Elastomers Investigated by Atomic Force Microscopy: From Macroscopic Stretching to Nanoscale Strainfield

Abstract Understanding the way fillers can reinforce elastomers requires, among other things, requires a precise description of the behavior of filler aggregates when a macroscopic strain is applied. In this study, Atomic Force Microscopy was used to investigate samples of SBR and PDMS filled with silica. The samples were stretched uniaxially at different strain values (up to 145%) and imaged by Atomic Force Microscopy. The distances between aggregates were followed at the different strains, which allowed calculation of the local strains and comparison of the values obtained with the macroscopic strain value. The main results are (i) that the strain field is highly heterogeneous, depending on the local concentration of filler and (ii) that the strain undergone by elastomer chains can be very high locally, in the regions where distances between aggregates are very short.