Functional Materials Under Stress: In Situ TEM Observations of Structural Evolution

The operating conditions of functional materials usually involve varying stress fields, resulting in structural changes, whether intentional or undesirable. Complex multiscale microstructures including defects, domains, and new phases, can be induced by mechanical loading in functional materials, providing fundamental insight into the deformation process of the involved materials. On the other hand, these microstructures, if induced in a controllable fashion, can be used to tune the functional properties or to enhance certain performance. In situ nanomechanical tests conducted in scanning/transmission electron microscopes (STEM/TEM) provide a critical tool for understanding the microstructural evolution in functional materials. Here, select results on a variety of functional material systems in the field are presented, with a brief introduction into some newly developed multichannel experimental capabilities to demonstrate the impact of these techniques.     

Dislocation distributions in monocrystalline nickel‐based superalloys subjected to thermo‐mechanical fatigue with and without hold times

The characteristics of dislocation configurations under thermo‐mechanical fatigue cycling were investigated in [001] oriented nickel‐based single‐crystal superalloys. Thermo‐mechanical fatigue tests were performed on TMS‐75 (without hold time) and TMS‐82 (with hold time) superalloys. The specimens were subsequently studied by transmission electron microscopy under two‐beam conditions. In TMS‐75 superalloy, cross‐slipping is the main characteristic for the low number of dislocations. In TMS‐82 superalloy, more complex process of dislocation configurations has been demonstrated in detail, involving five stages: after the first stress relaxation, after the first tensile plastic deformation, after the second stress relaxation, after 30 cycles and after rupture. In addition, for TMS‐82 superalloy, there is a reversible movement behaviour of stacking faults that occur in compression and disappear in tension. After rupture, the number of dislocation is related to the hold time. Longer hold time could generate a higher degree of stress relaxation and produce more dislocations with climbing characteristic.     

Polymer‐Mediated Nanoparticle Assembly: Structural Control and Applications

Nanoparticle–polymer composites are diverse and versatile functional materials, with applications ranging from electronic device fabrication to catalysis. This review focuses on the use of chemical design to control the structural attributes of polymer‐mediated assembly of nanoparticles. We will illustrate the use of designed particles and polymers to create nanocomposites featuring interesting and pragmatic structures and properties. We will also describe applications of these engineered materials.     

Cryo‐EM‐On‐a‐Chip: Custom‐Designed Substrates for the 3D Analysis of Macromolecules

The fight against human disease requires a multidisciplinary scientific approach. Applying tools from seemingly unrelated areas, such as materials science and molecular biology, researchers can overcome long‐standing challenges to improve knowledge of molecular pathologies. Here, custom‐designed substrates composed of silicon nitride (SiN) are used to study the 3D attributes of tumor suppressor proteins that function in DNA repair events. New on‐chip preparation strategies enable the isolation of native protein complexes from human cancer cells. Combined techniques of cryo‐electron microscopy (EM) and molecular modeling reveal a new modified form of the p53 tumor suppressor present in aggressive glioblastoma multiforme cancer cells. Taken together, the findings provide a radical new design for cryo‐EM substrates to evaluate the structures of disease‐related macromolecules.     

Investigation of Ba<Subscript>2-x</Subscript>Sr<Subscript>x</Subscript>TiO<Subscript>4</Subscript>: Structural aspects and dielectric properties

Investigation of solid solution of barium-strontium orthotitanates of the type, Ba_2-x Sr _x TiO₄ (0 ≤x≤ 2), show that pure phases exist only for the end members, Ba₂TiO₄ and Sr₂TiO₄, crystallizing in the β-K₂SO₄ and K₂NiF₄ structures, respectively. The intermediate compositions (till≥ 1) lead to a biphasic mixture of two Ba₂TiO₄-type phases (probably through a spinodal decomposition) with decreasing lattice parameters, indicating Sr-substitution in both the phases. Forx > 1, Sr₂TiO₄ along with a secondary phase is obtained. The dielectric constant and dielectric loss were found to decrease with Sr substitution till the nominal composition ofx = 1. However, pure Sr₂TiO₄ shows higher dielectric constant compared to the solid solution composition. Sr₂TiO₄ shows very high temperature stability of the dielectric constant.     

Receptor‐Mediated Cellular Uptake of Folate‐Conjugated Fluorescent Nanodiamonds: A Combined Ensemble and Single‐Particle Study

Fluorescent nanodiamonds (FNDs) are nontoxic and photostable nanomaterials, ideal for long‐term in vivo imaging applications. This paper reports that FNDs with a size of ≈140 nm can be covalently conjugated with folic acid (FA) for receptor‐mediated targeting of cancer cells at the single‐particle level. The conjugation is made by using biocompatible polymers, such as polyethylene glycol, as crosslinked buffer layers. Ensemble‐averaged measurements with flow cytometry indicate that more than 50% of the FA‐conjugated FND particles can be internalized by the cells (such as HeLa cells) through receptor‐mediated endocytosis, as confirmed by competitive inhibition assays. Confocal fluorescence microscopy reveals that these FND particles accumulate in the perinuclear region. The absolute number of FNDs internalized by HeLa cells after 3 h of incubation at a particle concentration of 10 µg mL^?1 is in the range of 100 particles per cell. The receptor‐mediated uptake process is further elucidated by single‐particle tracking of 35‐nm FNDs in three dimensions and real time during the endocytosis.     

In Situ Probing of the Particle‐Mediated Mechanism of WO3‐Networked Structures Grown inside Confined Mesoporous Channels

Nanocasting, using ordered mesoporous silica or carbon as a hard template, has enormous potential for preparing novel mesoporous materials with new structures and compositions. Although a variety of mesoporous materials have been synthesized in recent years, the growth mechanism of nanostructures in a confined space, such as mesoporous channels, is not well understood, which hampers the controlled synthesis and further application of mesoporous materials. Here, the nucleation and growth of WO₃‐networked mesostructures within an ordered mesoporous matrix, using an in situ transmission electron microscopy heating technique and in situ synchrotron small‐angle X‐ray scattering spectroscopy, are probed. It is found that the formation of WO₃ mesostructures involves a particle‐mediated transformation and coalescence mechanism. The liquid‐like particle‐mediated aggregation and mesoscale transformation process can occur in ≈10 nm confined mesoporous channels, which is completely unexpected. The detailed mechanistic study will be of great help for experimental design and to exploit a variety of mesoporous materials for diverse applications, such as catalysis, absorption, separation, energy storage, biomedicine, and nanooptics.     

Bismuthene Metallurgy: Transformation of Bismuth Particles to Ultrahigh‐Aspect‐Ratio 2D Microsheets

Ultrathin bismuth exhibits promising performance for topological insulators due to its narrow band gap and intrinsic strong spin–orbit coupling, as well as for energy‐related applications because of its electronic and mechanical properties. However, large‐scale production of 2D sheets via liquid‐phase exfoliation as an established large‐scale method is restricted by the strong interaction between bismuth layers. Here, a sonication method is utilized to produce ultrahigh‐aspect‐ratio bismuthene microsheets. The studies on the mechanism excludes the exfoliation of the layered bulk bismuth and formation of the microsheets is attributed to the melting of spherical particles (r = 1.5 µm) at a high temperature—generated under the ultrasonic tip—followed by a recrystallization step producing uniformly‐shaped ultrathin microsheets (A = 0.5–2 µm², t: ≈2 nm). Notably, although the preparation is performed in oxygenated aqueous solution, the sheets are not oxidized, and they are stable under ambient conditions for at least 1 month. The microsheets are used to construct a vapor sensor using electrochemical impedance spectroscopy as detection technique. The device is highly selective, and it shows long‐term stability. Overall, this project exhibits a reproducible method for large‐scale preparation of ultrathin bismuthene microsheets in a benign environment, demonstrating opportunities to realize devices based on bismuthene.