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Amorphous silicates in meteoritic samples are significant as potential surviving interstellar dust from the formation of the Solar System. Amorphous silicate-rich grains called GEMS, glass with embedded metal and sulfides, are abundant in anhydrous interplanetary dust particles and some ultracarbonaceous Antarctic micrometeorites that have high presolar grain abundances. Some GEMS within these objects have been confirmed to be presolar. GEMS-like material, consisting of amorphous silicate with opaque inclusions, has been identified in the matrices of some primitive meteorites. We use specialized thin specimen preparation and transmission electron microscopy methods to compare the GEMS-like material in Paris (CM) and Acfer 094 (ungrouped) chondrites with GEMS in anhydrous, chondritic interplanetary dust particles. Specifically, we compared the amorphous silicate morphology, degree of partial ordering, elemental composition and dominant iron oxidation state. We find that the amorphous silicates in the GEMS-like materials in Paris and Acfer 094 show incipient ordering and are Fe-rich and highly oxidized, while those in GEMS are fully amorphous, Fe-poor, and anhydrous. From examination of various formation routes for the amorphous silicates, we conclude that the GEMS-like material in Paris and Acfer 094 is not GEMS and that it is unlikely that GEMS-like material accreted as primary amorphous material that retained its original amorphous structure since accretion. We also conclude that the presence of GEMS-like amorphous silicates in chondrite matrix is not a reliable indicator for high degrees of primitivity or pristinity since even mild, complex alteration processes may significantly alter silicate structure. Finally, we propose searches for presolar amorphous silicates in chondrite matrix samples that have been precharacterized by transmission electron microscopy methods to enable direct comparisons of presolar amorphous silicate abundances.

Structure and chemistry of metal/metal-oxide interfaces are critical for many catalytic processes and sensing. Pristine interfaces of Pt and γ-Al2O3 were fabricated using high-energy ion implantation and thermal processing. Amorphous regions of alumina develop in single crystal α-alumina during Pt+ implantation and an 800 °C thermal treatment crystalizes amorphized alumina to γ-Al2O3 and allows Pt ions to precipitate within the developing γ-alumina, yielding Pt nanoparticle tetrahedra terminated by {111} surfaces. The phase of alumina that developed and the distribution, morphology, and orientation of Pt nanoparticles was determined using x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy and scanning transmission electron microscopy.

Summary The reticular synthesis of covalent organic frameworks (COFs), extended porous two-dimensional (2D) or three-dimensional (3D) networks held together by strong, highly directional chemical bonds, has thus far been restricted to small, shape-persistent, molecular building blocks. Here, we demonstrate the growth of crystalline 2D COFs from a polydisperse macromolecule derived from single-layer graphene, bottom-up synthesized quasi-one-dimensional (1D) graphene nanoribbons (GNRs). X-ray scattering and transmission electron microscopy reveal that 2D sheets of GNR-COFs self-assembled at a liquid-liquid interface stack parallel to the layer boundary and exhibit an orthotropic crystal packing. Liquid-phase exfoliation of multilayer GNR-COF crystals gives access to large-area (>105 nm2) bilayer and trilayer cGNR-COF films. The functional integration of extended 1D materials into crystalline COFs greatly expands the structural complexity and the scope of mechanical and physical materials properties accessible through a deterministic reticular bottom-up approach.

Summary Porous graphitic framework (PGF) is a two-dimensional (2D) material that has emerging energy applications. An archetype contains stacked 2D layers, the structure of which features a fully annulated aromatic skeleton with embedded heteroatoms and periodic pores. Due to the lack of a rational approach in establishing in-plane order under mild synthetic conditions, the structural integrity of PGF has remained elusive and ultimately limited its material performance. Here, we report the discovery of the unusual dynamic character of the C=N bonds in the aromatic pyrazine ring system under basic aqueous conditions, which enables the successful synthesis of a crystalline porous nitrogenous graphitic framework with remarkable in-plane order, as evidenced by powder X-ray diffraction studies and direct visualization using high-resolution transmission electron microscopy. The crystalline framework displays superior performance as a cathode material for lithium-ion batteries, outperforming the amorphous counterparts in terms of capacity and cycle stability.

Nanostructured ferritic alloys (NFAs) contain an ultra-high density of 2–4 nm fcc pyrochlore Y2Ti2O7 nano-oxides (NOs) embedded in a bcc Fe-14Cr ferritic matrix. Characterization of helium interactions with NOs and associated Fe-Y2Ti2O7 interfaces is important to the development of structural materials for nuclear fusion and fission applications. A benchmark 14YWT NFA was first annealed to coarsen the NOs, then insoluble helium was implanted at 700 °C to produce a high number density of bubbles. High-resolution scanning transmission electron microscopy characterization shows two dominant Fe-Y2Ti2O7 crystallographic orientation relationships (cube-on-edge and cube-on-cube). The smallest NOs (≈ 2 nm) are associated with the smaller bubbles (≈ 1.5 nm), while some of the largest NOs (> 6 nm) have larger, and sometimes multiple, bubbles. NO corner {111} facets are the preferred sites for He bubble nucleation. A refined sequence of events for He trapping and bubble formation is presented. These observations offer new insight on He management in NFAs, and provide a foundation for detailed modeling studies.

Large superelastic deformation in ferroelastic-ferroelectrics (FMs) is a complex phenomenon involving multiple mechanisms operating simultaneously. Understanding how these mechanisms contribute corporately is critical to apply this useful property to the intrinsically brittle FMs, which can therefore display both excellent functional and mechanical performance. Here, we have directly observed and quantitatively analyzed in situ in a transmission electron microscope the three main mechanisms of twinning domain, phase transformation and mobile point defect contributing to extremely large superelastic deformation in single-crystal BaTiO3 (5.0% strain) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (10.1% strain). Our results reveal the hierarchical origin of large recoverable strain in “brittle” FMs.

Nanobeam electron diffraction strain mapping has been used to measure the strain evolution in stainless steel under in situ deformation. As the amount of deformation increases, the leading dislocation of a planar slip band leaves behind a residual strain in the form of a small lattice expansion. Dislocation analysis confirmed that the dislocations involved were type. While the characteristic residual strain of planar slip has often been observed, it has never before been directly measured. Our results provide a view into the dynamic mechanisms of planar slip, and showcase the possibilities of multidimensional in situ imaging.

Scanning nanobeam electron diffraction strain mapping is a technique by which the positions of diffracted disks sampled at the nanoscale over a crystalline sample can be used to reconstruct a strain map over a large area. However, it is important that the disk positions are measured accurately, as their positions relative to a reference are directly used to calculate strain. In this study, we compare several correlation methods using both simulated and experimental data in order to directly probe susceptibility to measurement error due to non-uniform diffracted disk illumination structure. We found that prefiltering the diffraction patterns with a Sobel filter before performing cross correlation or performing a square-root magnitude weighted phase correlation returned the best results when inner disk structure was present. We have tested these methods both on simulated datasets, and experimental data from unstrained silicon as well as a twin grain boundary in 304 stainless steel.

In this work, the accuracy of geometric phase analysis (GPA) on aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (Cs-corrected HAADF-STEM) images for lattice strain measurement at heterogeneous interfaces has been systematically investigated. Starting with an ideal crystal lattice of synthetic images, and then experimental HAADF images of a single-crystal lattice, we have quantitatively evaluated the inherent GPA processing artifacts and experimental errors due to STEM scanning distortions. Our results suggest that, with a properly chosen Fourier mask size and strain profile direction/width, 1 pm accuracy can be achieved for GPA strain quantification in the STEM fast-scan direction with a spatial resolution of 3 /SrTiO 3 (LAO/STO) and the relaxed SrTiO 3 /MgO (STO/MgO). Interestingly, GPA strain mapping reveals a novel secondary relaxation mechanism in the LAO/STO heterostructures. Essential limitations in GPA are also discussed using the example of a FeSe 0.5 Te 0.5 (FST)/SrTiO 3 heterointerface. Although we focus on the interfacial lattice strain in this paper, the approaches for strain error estimation and the fundamental discussions on line profiles can also be applied, with some modifications, to other nanostructures.