Explore the vast range of titles available.

Twinning, on par with dislocations, is critically required in plastic deformation of hexagonal close-packed crystals at low temperatures. In contrast to that in cubic-structured crystals, twinning in hexagonal close-packed crystals requires atomic shuffles in addition to shear. Though the twinning shear that is carried by twinning dislocations has been captured for decades, direct experimental observation of the atomic shuffles, especially when the shuffling mode is not unique and does not confine to the plane of shear, remains a formidable challenge to date. Here, by using in-situ transmission electron microscopy, we directly capture the atomic mechanism of the$$\\left\\{11\\bar{2}1\\right\\}$$11 2 ¯ 1 twinning in hexagonal close packed rhenium nanocrystals. Results show that the$$\\left\\{11\\bar{2}1\\right\\}$$11 2 ¯ 1 twinning is dominated by the ( b 1/2 , h 1/2 ) twinning disconnections. In contrast to conventional expectations, the atomic shuffles accompanying the twinning disconnections proceed on alternative basal planes along 1/6$$\\left\\langle 1\\bar{1}00\\right\\rangle$$1 1 ¯ 00 , which may be attributed to the free surface in nanocrystal samples, leading to a lack of mirror symmetry across the$$\\left\\{11\\bar{2}1\\right\\}$$11 2 ¯ 1 twin boundary.

Surface passivation, a desirable natural consequence during initial oxidation of alloys, is the foundation for functioning of corrosion and oxidation resistant alloys ranging from industrial stainless steel to kitchen utensils. This initial oxidation has been long perceived to vary with crystal facet, however, the underlying mechanism remains elusive. Here, using in situ environmental transmission electron microscopy, we gain atomic details on crystal facet dependent initial oxidation behavior in a model Ni-5Cr alloy. We find the (001) surface shows higher initial oxidation resistance as compared to the (111) surface. We reveal the crystal facet dependent oxidation is related to an interfacial atomic sieving effect, wherein the oxide/metal interface selectively promotes diffusion of certain atomic species. Density functional theory calculations rationalize the oxygen diffusion across Ni(111)/NiO(111) interface, as contrasted with Ni(001)/NiO(111), is enhanced. We unveil that crystal facet with initial fast oxidation rate could conversely switch to a slow steady state oxidation.

Transmission electron microscopy (TEM) is widely used as an imaging modality to provide high-resolution details of subcellular components within cells and tissues. Mitochondria and endoplasmic reticulum (ER) are organelles of particular interest to those investigating metabolic disorders. A straightforward method for quantifying and characterizing particular aspects of these organelles would be a useful tool. In this protocol, we outline how to accurately assess the morphology of these important subcellular structures using open source software ImageJ, originally developed by the National Institutes of Health (NIH). Specifically, we detail how to obtain mitochondrial length, width, area, and circularity, in addition to assessing cristae morphology and measuring mito/endoplasmic reticulum (ER) interactions. These procedures provide useful tools for quantifying and characterizing key features of sub-cellular morphology, leading to accurate and reproducible measurements and visualizations of mitochondria and ER.

Energy-filtering transmission electron microscopy (TEM) and bright-field TEM can be used to extract local sample thickness $t$ and to generate two-dimensional sample thickness maps. Electron tomography can be used to accurately verify the local $t$. The relations of log-ratio of zero-loss filtered energy-filtering TEM beam intensity ($I_{{\\rm ZLP}}$) and unfiltered beam intensity ($I_{\\rm u}$) versus sample thickness $t$ were measured for five values of collection angle in a microscope equipped with an energy filter. Furthermore, log-ratio of the incident (primary) beam intensity ($I_{\\rm p}$) and the transmitted beam $I_{{\\rm tr}}$ versus $t$ in bright-field TEM was measured utilizing a camera before the energy filter. The measurements were performed on a multilayer sample containing eight materials and thickness $t$ up to 800 nm. Local thickness $t$ was verified by electron tomography. The following results are reported: • The maximum thickness $t_{{\\rm max}}$ yielding a linear relation of log-ratio, $\\ln ( {I_{\\rm u}}/{I_{{\\rm ZLP}}})$ and $\\ln ( {I_{\\rm p}}/{I_{{\\rm tr}}} )$, versus $t$. • Inelastic mean free path ($\\lambda _{{\\rm in}}$) for five values of collection angle. • Total mean free path ($\\lambda _{{\\rm total}}$) of electrons excluded by an angle-limiting aperture. • $\\lambda _{{\\rm in}}$ and $\\lambda _{{\\rm total}}$ are evaluated for the eight materials with atomic number from $\\approx$10 to 79. The results can be utilized as a guide for upper limit of $t$ evaluation in energy-filtering TEM and bright-field TEM and for optimizing electron tomography experiments.

The exceptional physical properties and unique layered structure of two-dimensional (2D) materials have made this class of materials great candidates for applications in electronics, energy conversion/storage devices, nanocomposites, and multifunctional coatings, among others. At the center of this application space, mechanical properties play a vital role in materials design, manufacturing, integration and performance. The emergence of 2D materials has also sparked broad scientific inquiry, with new understanding of mechanical interactions between 2D structures and interfaces being of great interest to the community. Building on the dramatic expansion of recent research activities, here we review significant advances in the understanding of the elastic properties, in-plane failures, fatigue performance, interfacial shear/friction, and adhesion behavior of 2D materials. In this article, special emphasis is placed on some new 2D materials, novel characterization techniques and computational methods, as well as insights into deformation and failure mechanisms. A deep understanding of the intrinsic and extrinsic factors that govern 2D material mechanics is further provided, in the hopes that the community may draw design strategies for structural and interfacial engineering of 2D material systems. We end this review article with a discussion of our perspective on the state of the field and outlook on areas for future research directions. The elastic properties, in-plane failures, fatigue performance, interfacial shear/friction, and adhesion behaviors of 2D materials are summarized. Novel characterization techniques and computational methods are discussed. Intrinsic and extrinsic factors that govern 2D material mechanics are further provided. The challenges and perspectives in the field of 2D materials mechanics are outlined.

Transmission electron microscopy (TEM) provides direct structural information on nano‐structured materials and is popular as a characterization tool in soft matter and supramolecular chemistry. However, technical aspects of sample preparation are overlooked and erroneous image interpretations are regularly encountered in the literature. There are three most commonly used TEM methods as we derived from literature: drying, staining and cryo‐TEM, which are explained here with respect to their application, limitations and interpretation. Since soft matter chemistry relies on a lot of indirect evidence, the role of TEM for the correct evaluation of the nature of an assembly is very large. Mistakes in application and interpretation can therefore have enormous impact on the quality of present and future studies. We provide helpful background information of these three techniques, the information that can and cannot be derived from them and provide assistance in selecting the right technique for soft matter imaging. This essay warns against the use of drying and explains why. In general cryo‐TEM is by far the best suited method and many mistakes and over‐interpretations can be avoided by the use of this technique. The most popular electron microscopy methods for soft and supramolecular systems are reviewed with respect to their possibilities and limitations. Drying is highly discouraged, because it causes unpredictable structures and artefacts. Staining preserves the structure better, but inner details are obscured. Although one should be aware of artefacts such as ice contamination, cryo‐electron microscopy is the method of choice.

The strain rate sensitivity ( m ) of (Ni 0.92 Zr 0.08 ) 100 − x Al x (0 ≤ x ≤ 4 at.%) eutectic with varying average lamellae thickness (λ w ) in the range of 39–275 nm has been investigated in the strain rate range of 8 × 10 −5 and 8 × 10 −3 s −1 at room temperature. The microstructure of the nano-/ultrafine eutectic composites (NECs) is comprised of alternate lamellae of fcc γ-Ni and Ni 5 Zr along with 20–31 vol% γ-Ni dendritic phase. The m value of all the investigated NECs lies between 0.0080 and 0.0102, whereas the activation volume ( V *) has been estimated to be between 29.7 b 3 and 49.8 b 3 . High-resolution transmission electron microscopy studies confirm the dislocation-mediated plastic flow including dislocation–lamellae interaction, and their pile-up at the interface, which result in the narrow variation of m for a wide range of λ w due to its interlocked lamellar microstructure. A mathematical model has been developed to correlate the m with λ w for the experimented NECs with wide microstructure length scale and solute content.

Metal–organic frameworks (MOFs) are crystalline nanoporous materials with great potential for a wide range of industrial applications. Understanding the nucleation and early growth stages of these materials from a solution is critical for their design and synthesis. Despite their importance, the pathways through which MOFs nucleate are largely unknown. Using a combination of in situ liquid-phase and cryogenic transmission electron microscopy, we show that zeolitic imidazolate framework-8 MOF nanocrystals nucleate from precursor solution via three distinct steps: 1) liquid–liquid phase separation into solute-rich and solute-poor regions, followed by 2) direct condensation of the solute-rich region into an amorphous aggregate and 3) crystallization of the aggregate into a MOF. The three-step pathway for MOF nucleation shown here cannot be accounted for by conventional nucleation models and provides direct evidence for the nonclassical nucleation pathways in open-framework materials, suggesting that a solute-rich phase is a common precursor for crystallization from a solution.