Radiation damage to organic and inorganic specimens in the TEM

Two- and three-dimensional electron imaging of beam-sensitive specimens

Radiation damage is the main factor that determines the spatial resolution of TEM and STEM images of beam-sensitive specimens, its influence being well represented by a dose-limited resolution (DLR). In this review, DLR is defined and evaluated for both thin and thick samples, for all common imaging modes, and for electron-accelerating voltages up to 3 MV. Damage mechanisms are discussed (including beam heating and electrostatic charge accumulation) with an emphasis on recently published work. Experimental methods for reducing beam damage are identified and future lines of investigation are suggested.

Visualization of Cellulose Structures with Cesium Labeling and Cryo-STEM

Cellulose, a pivotal component of plant cell walls, is a widely studied biologically derived material with vast potential for numerous applications. However, visualizing the arrangement of individual cellulose molecules within hierarchical structures with electron microscopy has proven challenging due to the material's low contrast and high beam sensitivity. In this study, a novel approach is introduced that combines labeling of cellulose functional groups with high-contrast cesium counter cations (Cs+) in conjunction with atomic resolution scanning transmission electron microscopy (STEM) in annular dark-field (ADF) mode at cryogenic temperatures. This technique allows for the identification of individual sulfate groups attached to cellulose chains within cellulose nanocrystal hierarchies at Ångström resolution. Systematic comparison of experimentally obtained interatomic Cs+ distances with simulations potentially enables the localization of the labeled functional groups at the macromolecular level. The method has the potential to elucidate the polymer chain arrangements in nanoscale soft materials.

Commonsense and common nonsense opinions: PROSPECTS for further reducing beam damage in electron microscopy of radiation-sensitive specimens

Biological molecules are easily damaged by high-energy electrons, thus limiting the exposures that can be used to image such specimens by electron microscopy. It is argued here that many-electron, volume-plasmon excitations, which promptly transition into multiple types of single-electron ionization and excitation events, seem to be the predominant cause of damage in such materials. Although reducing the rate at which primary radiolysis occurs would allow one to record images that were much less noisy, many novel proposals for achieving this are unlikely to be realized in the near future, while others are manifestly ill-founded. As a result, the most realistic option currently is to more effectively use the available "budget" of electron exposure, i.e. to further improve the "dose efficiency" by which images are recorded. While progress in that direction is currently under way for both "conventional" (i.e. fixed-beam) and scanning EM, the former is expected to set a high standard for the latter to surpass.

Three-Dimensional Electron Microscopy of Chiral Nanoparticles: From Imaging to Measuring

The increasing interest in plasmonic nanoparticles with intrinsic chirality, i.e., reduced symmetry and strong optical activity, calls for characterization beyond qualitative imaging. In this context, three-dimensional electron microscopy (3D EM), which provides images containing information on the particles' surface and may even retrieve the explicit 3D shapes, is seeing exciting developments and applications. In this Mini-Review, we focus on scanning electron microscopy (SEM), electron tomography, and secondary electron electron-beam-induced current (SEEBIC). We highlight the recent advances in these 3D EM techniques and the analysis of their data that relate to chiral metallic nanoparticles. The study of shape-property relationships, in particular by quantitatively analyzing geometric chirality and informing electromagnetic simulations, is covered. New ways in which 3D characterization is revealing the growth pathways of the nanoparticles are also presented. Finally, we provide an outlook on future opportunities for 3D EM to further guide the understanding and development of (chiral) nanoparticles.

Fabrication of Multifarious Nanoparticles Inside a TEM: An In Situ Evaporation and Deposition Method

Revealing the surface effect of nanoparticles (NPs) is one of the key prerequisites for understanding their extraordinary properties at the nanometer scale. However, active NPs frequently suffer from surface oxidation and contamination, which hinders the realization of their delicate surface-related properties. Upon this issue, this paper develops an in situ evaporation and deposition (in-E&D) method inside a transmission electron microscope (TEM), by which NPs with ultra-clean surfaces can be controllably fabricated and examined. More than 12 types of materials, including Mg, Al, Cr, Mn, Ni, Cu, Zn, Ge, Ag, Sb, Pb, Bi, etc., have been demonstratively verified, and diverse NPs/nanorods have been obtained with featured structures, shapes, phases, etc. It is found that the electron beam-induced thermal effect and the vapor pressure of the precursor material are two decisive parameters for this in-E&D method. With appropriate settings, NP size, number density, and distribution can be designedly modulated. With alloyed/mixed precursors, the in-E&D method can be extended to fabricate binary and even more complex NPs in demand. It provides an effective chance to uncover the property and behavior of delicate NPs which are sensitive and prone to contamination during sample transfer.

A nanoscale chemical oscillator: reversible formation of palladium nanoparticles in ionic liquid

From the theory of chaos-to-order transitions to the origins of life on Earth, oscillating chemical reactions play a fundamental role in nature. This study demonstrates how chemical oscillators can exist at the nanoscale, bridging the gap between molecules and living cells. We identify three necessary conditions for nanoscale chemical oscillations: (i) a continuous energy flux; (ii) alternating fluxes of two chemical species with opposing effects-specifically, a reductant and an oxidant; and (iii) a redox-active metal. Irradiating palladium ions dissolved in benzyl imidazolium bromide ([BnMIm]+Br-) with a 200 keV electron beam meets these requirements, resulting in the oscillating, dendritic assembly of palladium nanoparticles. By encapsulating the solution inside carbon nanotubes, we can slow down the rate of chemical oscillations, allowing for real-time analysis at the individual nanoparticle level. Our results indicate that nanoparticles in liquids are far from the thermodynamic equilibrium during transmission electron microscopy (TEM) imaging, which is an important consideration for studying nanoparticles using in situ TEM methods or employing them for catalysis in the liquid phase.

Exploring guest species in zeolites using transmission electron microscopy: a review and outlook

Zeolites, with their well-defined microporous frameworks, accommodate diverse guest species, including metal ions, atoms, clusters, complexes, and organic molecules. Direct imaging of these species and their interactions with the framework is crucial for understanding their structural and functional roles. Transmission electron microscopy (TEM), particularly aberration-corrected scanning TEM (STEM), has become an indispensable tool, offering atomic-resolution real-space insights. This review summarizes key (S)TEM techniques for probing guest species in zeolites, with a focus on low-dose strategies to minimize beam damage. We discuss the principles, applications, and limitations of various imaging modalities and highlight recent advances in visualizing metallic and organic species. Finally, we explore future directions for (S)TEM in zeolite research, emphasizing the opportunities and challenges of in situ, three-dimensional, and cryogenic imaging for resolving host-guest interactions with greater precision.

Imaging the Progression of Radiolytic Damage in Molecular Crystals with Scanning Nanobeam Electron Diffraction

Almost every electron microscopy experiment is fundamentally limited by radiation damage. Nevertheless, little is known about the onset and progression of radiolysis in beam-sensitive materials. Here we apply ambient-temperature scanning nanobeam electron diffraction to record simultaneous dual-space movies of organic and organometallic nanocrystals at sequential stages of beam-induced radiolytic decay. We show that the underlying mosaic of coherently diffracting domains undergoes internal rearrangement as a function of accumulating electron fluence, causing the intensities of some associated Bragg reflections to fade nonmonotonically. Furthermore, we demonstrate that repeated irradiation at a single probe position leads to the isotropic propagation of delocalized radiolytic damage well beyond the direct footprint of the incident beam. We refer to these expanding tides of amorphization as "impact craters."

Imaging of Hydrated and Living Cells in Transmission Electron Microscope: Summary, Challenges, and Perspectives

Transmission electron microscopy (TEM) is well-known for performing in situ studies in the nanoscale. Hence, scientists took this opportunity to explore the subtle processes occurring in living organisms. Nevertheless, such observations are complex─they require delicate samples kept in the liquid phase, low electron dose, and proper cell viability verification methods. Despite being highly demanding, so-called "live-cell" experiments have seen some degree of success. The presented review consists of an exhaustive literature review on reported "live-cell" studies and associated subjects, including liquid phase imaging, electron radiation interactions with liquids, and methods for cell viability testing. The challenges of modern, reliable research on living organisms are widely explained and discussed, and future perspectives for developing these techniques are presented.

Native state structural and chemical characterisation of Pickering emulsions: A cryo-electron microscopy study

Transmission electron microscopy can be used for the characterisation of a wide range of thin specimens, but soft matter and aqueous samples such as gels, nanoparticle dispersions, and emulsions will dry out and collapse under the microscope vacuum, therefore losing information on their native state and ultimately limiting the understanding of the sample. This study examines commonly used techniques in transmission electron microscopy when applied to the characterisation of cryogenically frozen Pickering emulsion samples. Oil-in-water Pickering emulsions stabilised by 3 to 5 nm platinum nanoparticles were cryogenically frozen by plunge-freezing into liquid ethane to retain the native structure of the system without inducing crystallisation of the droplet oil cores. A comparison between the droplet morphology following different sample preparation methods has confirmed the effectiveness of using plunge-freezing to prepare these samples. Scanning transmission electron microscopy imaging showed that dry droplets collapse under the microscope vacuum, changing their shape and size (average apparent diameter: ∼342 nm) compared to frozen samples (average diameter: ∼183 nm). Cryogenic electron tomography was used to collect additional information of the 3D shape and size of the emulsion droplets, and the position of the stabilising nanoparticles relative to the droplet surface. Cryogenic energy dispersive X-ray and electron energy loss spectroscopy were used to successfully obtain elemental data and generate elemental maps to identify the stabilising nanoparticles and the oil phase. Elemental maps generated from spectral data were used in conjunction with electron tomography to obtain 3D information of the oil phase in the emulsion droplets. Beam-induced damage to the ice was the largest limiting factor to the sample characterisation, limiting the effective imaging resolution and signal-to-noise ratio, though careful consideration of the imaging parameters used allowed for the characterisation of the samples presented in this study. Ultimately this study shows that cryo-methods are effective for the representative characterisation of Pickering emulsions.

Understanding Electron Beam-Induced Chemical Polymerization Processes of Small Organic Molecules Using Operando Liquid-Phase Transmission Electron Microscopy

Electron beams evolved as important tools for modern technologies that construct and analyze nanoscale architectures. While electron-matter interactions at atomic and macro scales are well-studied, a knowledge gap persists at the molecular to nano level─the scale most relevant to the latest technologies. Here, we employ operando liquid-phase transmission electron microscopy supported by density functional theory calculations and a mathematical random search algorithm to rationalize and quantify electron beam-induced processes at the molecular level. By examining a series of small organic molecules, we identify critical physical and chemical parameters that dictate polymerization rates under continuous electron beam irradiation. Our findings offer a deeper understanding of electron beam-induced reactions, enabling the prediction of molecular reactivities from a classical chemistry perspective. These insights apply equally to other soft matter systems and, thus, are of fundamental interest to scientists and engineers who use electron beams to analyze or to manipulate nanoscale matter.

Correlated Structural and Optical Characterization of Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) plays a central role in nanoelectronics and nanophotonics. Moreover, hBN hosts room-temperature quantum emitters and optically addressable spins, making the material promising for quantum sensing and photonics. Despite significant investigation of the optical and structural properties of hBN, the role of contamination at surfaces and interfaces remains unexplored. We prepare hBN samples that are compatible with confocal photoluminescence (PL) microscopy, transmission electron microscopy (TEM), and atomic-force microscopy (AFM), and we use those techniques to quantitatively investigate correlations between fluorescent emission, flake morphology, and surface residue. We find that the microscopy techniques themselves induce changes in hBN's optical activity and residue morphology: PL measurements induce photobleaching, whereas TEM measurements alter surface residue and emission characteristics. We also study the effects of common treatments─annealing and oxygen plasma cleaning─on the structure and optical activity of hBN. The methods can be broadly applied to study two-dimensional materials, and the results illustrate the importance of correlative studies to elucidate factors that influence hBN's structural and optical properties.

A statistical approach for interplanar spacing metrology at a relative uncertainty below 10-4 using scanning transmission electron microscopy

Atomic-scale metrology in scanning transmission electron microscopy (STEM) allows to measure distances between individual atomic columns in crystals and is therefore an important aspect of their structural characterization. Furthermore, it allows to locally resolve strain in crystals and to calibrate precisely the pixel size in STEM. We present a method dedicated to the evaluation of interplanar spacing (d-spacing) based on an algorithm including curve fitting of processed high-angle annular dark-field STEM (HAADF STEM) signals. By examining simulated data of perovskite cubic SrTiO3, we confirm that our proposed method is unbiased, and the precision is better than the significant digit of the input value. Then, we study experimental data to learn how electron dose, sampling resolution, and statistical sampling affect the mean and precision values of d110. For single d-spacing measurements using a probe corrected STEM, we find that uncertainty ranges between 1 and 3 pm. Here, we measure numerous d-spacings in an automated and statistical approach, resulting in relative uncertainties in mean values ≤ 10-4. Thus, we propose to calibrate TEMs using this method as it enables measuring lattice parameters at uncertainties comparable to reports of x-ray diffraction measurements, but with a significantly lower sample volume, in this case ∼ 10-3 µm3.

Transmission electron microscopy analysis of Co3O4 degradation induced by electron irradiation

This study presents an investigation into the electron beam damage phenomenon of Co3O4 under transmission electron microscopy (TEM). It was found that after irradiation at a dose rate of 6.78 × 106 e/nm2s, Co3O4 crystals exhibited surface reconstruction and faceting features. Electron energy loss spectroscopy (EELS) analysis indicates that the damage process initiates with the desorption of oxygen anions, which subsequently leads to a reduction in the valence state of cobalt cations and corresponding atomic rearrangement. High resolution TEM (HRTEM) reveals that surface faceting, which has an epitaxial relationship with the bulk, could help maintain the crystal lattice of face-centered cubic (fcc) Co3O4 despite Co-O bond breakage upon beam exposure. With a finely focused electron beam, the hole drilling effect was observed. The structural degradation is proposed to arise from inelastic damage that induced partial desorption of oxygen anions and rearrangement of valence-reduced cobalt cations to epitaxially grow on the surface, suggesting an interplay between irradiation damage and material restructuring. The relative phase stability of Co3O4, combined with its interfacial structure developed upon irradiation, are beneficial to magnetic loss and interfacial polarization loss, thereby rendering Co3O4 a promising candidate as an effective EMW absorber.

Control of Grain Boundary Formation in Atomically Resolved Nanocrystalline Carbon Monolayers: Dependence on Electron Energy

In this study, we explore the dynamics of grain boundaries in nanocrystalline carbon monolayers, focusing on their variation with electron beam energy and electron dose rate in a spherical and chromatic aberration-corrected transmission electron microscope. We demonstrate that a clean surface, a high-dose rate, and a 60 keV electron beam are essential for precise local control over the dynamics of grain boundaries. The structure of these linear defects has been evaluated using neural network-generated polygon mapping.

Electron Microscopy Reveals Inhomogeneous Adsorption of Iodine and Concurrent Defect Formation in a Metal-Organic Framework

Adsorption behaviors are typically examined through adsorption isotherms, which measure the average adsorption amount as a function of partial pressure or time. However, this method is incapable of identifying inhomogeneities across the adsorbent, which may occur in the presence of strong intermolecular interactions of the adsorbate. In this study, we visualize the adsorption of molecular iodine (I2) in the metal-organic framework material MFM-300(Sc) using high-resolution scanning transmission electron microscopy (STEM). Our observations demonstrate that, counterintuitively, I2 adsorption in MFM-300(Sc) occurs in an inhomogeneous manner, regardless of the I2 uptake level. Even at adsorption saturation, corresponding to an average of 23 iodine atoms per unit cell, MOF channels with significantly varying iodine contents─from nearly empty to densely filled─coexist. Image simulations suggest that the most densely packed I2 may locally form the previously proposed triple-helix structure, corresponding to up to 142 iodine atoms per unit cell. Furthermore, STEM imaging reveals that I2 adsorption can induce the formation of structural defects, such as edge dislocations and stacking faults, within the MOF framework. These defects persist even after the complete removal of I2 molecules. Additionally, we have developed a surfactant-capping strategy to minimize the release of adsorbed I2 from MFM-300(Sc) and validated its effectiveness using STEM imaging.

A tale of two transfers: characterizing polydimethylsiloxane viscoelastic stamping and heated poly bis-A carbonate transfer of hexagonal boron nitride

Two-dimensional (2D) materials have many applications ranging from heterostructure electronics to nanofluidics and quantum technology. In order to effectively utilize 2D materials towards these ends, they must be transferred and integrated into complex device geometries. In this report, we investigate two conventional methods for the transfer of 2D materials: viscoelastic stamping with polydimethylsiloxane (PDMS) and a heated transfer with poly bis-A carbonate (PC). We use both methods to transfer mechanically-exfoliated flakes of hexagonal boron nitride onto silicon nitride (SiNx) substrates and characterize the resulting transfers using atomic force microscopy (AFM), aberration-corrected scanning transmission electron microscopy (AC-STEM) and electron energy loss spectroscopy (EELS). We find that both transfer methods yield flakes with significant and comparable residue (within the limitations of our study on eight samples). Qualitative interpretation of EELS maps demonstrates that this residue is comprised of silicon, carbon and oxygen for both transfer methods. Quantitative analysis of AC-STEM images reveals that the area covered in residue is on average, slightly lower for PDMS transfers (31 % ± 1 %), compared to PC transfers (41 % ± 4 %). This work underscores the importance of improving existing transfer protocols towards applications where cleaner materials are critical, as well as the need for robust methods to clean 2D materials.

Real-Time Observation of Polymer Fluctuations During Phase Transition Using Transmission Electron Microscope

Measuring molecular dynamics improves understanding of the structure-function relationships of materials. In this study, we present a novel technique for observing material dynamics using transmission electron microscopy (TEM), in which the gold nanoparticles are employed as motion probes for tracing the polymer dynamics in real space. A thin layer of polymer materials was generated on the 2 μm diameter holes of Quantifoil grids, and gold nanoparticles were dispersed on the membrane surface. By tracking the movement of gold nanoparticles from a series of TEM images taken under continuous temperature control, we obtained mean squared displacement (MSD) curves. The dynamics of poly{2-(perfluorooctyl)ethyl acrylate} (PC8FA) and poly(stearyl acrylate) (PSA) were analyzed. In the temperature-dependent analysis of the MSD, sharp peaks were observed for both PC8FA and PSA at positions corresponding to their melting and crystallization temperatures. These results demonstrate the capability of TEM to provide valuable insights into the dynamics of polymer materials, highlighting its potential for widespread application in materials sciences.

Unravelling complex mechanisms in materials processes with cryogenic electron microscopy

Investigating nanoscale structural variations, including heterogeneities, defects, and interfacial characteristics, is crucial for gaining insight into material properties and functionalities. Cryogenic electron microscopy (cryo-EM) is developing as a powerful tool in materials science particularly for non-invasively understanding nanoscale structures of materials. These advancements bring us closer to the ultimate goal of correlating nanoscale structures to bulk functional outcomes. However, while understanding mechanisms from structural information requires analysis that closely mimics operation conditions, current challenges in cryo-EM imaging and sample preparation hinder the extraction of detailed mechanistic insights. In this Perspective, we discuss the innovative strategies and the potential for using cryo-EM for revealing mechanisms in materials science, with examples from high-resolution imaging, correlative elemental analysis, and three-dimensional and time-resolved analysis. Furthermore, we propose improvements in cryo-sample preparation, optimized instrumentation setup for imaging, and data interpretation techniques to enable the wider use of cryo-EM and achieve deeper context into materials to bridge structural observations with mechanistic understanding.

Graphene-Assisted Electron-Based Imaging of Individual Organic and Biological Macromolecules: Structure and Transient Dynamics

Characterizing the structures, interactions, and dynamics of molecules in their native liquid state is a long-existing challenge in chemistry, molecular science, and biophysics with profound scientific significance. Advanced transmission electron microscopy (TEM)-based imaging techniques with the use of graphene emerged as promising tools, mainly due to their performance on spatial and temporal resolution. This review focuses on the various approaches to achieving high-resolution imaging of individual molecules and their transient interactions. We highlight the crucial role of graphene grids in cryogenic electron microscopy for achieving Ångstrom-level resolution for resolving molecular structures and the importance of graphene liquid cells in liquid-phase TEM for directly observing dynamics with subnanometer resolution at a frame rate of several frames per second, as well as the cross-talks of the two imaging modes. To understand the chemistry and physics encoded in these molecular movies, incorporating machine learning algorithms for image analysis provides a promising approach that further bolsters the resolution adventure. Besides reviewing the recent advances and methodologies in TEM imaging of individual molecules using graphene, this review also outlines future directions to improve these techniques and envision problems in molecular science, chemistry, and biology that could benefit from these experiments.

Unravelling nonclassical beam damage mechanisms in metal-organic frameworks by low-dose electron microscopy

Recent advances in direct electron detectors and low-dose imaging techniques have opened up captivating possibilities for real-space visualization of radiation-induced structural dynamics. This has significantly contributed to our understanding of electron-beam radiation damage in materials, serving as the foundation for modern electron microscopy. In light of these developments, the exploration of more precise and specific beam damage mechanisms, along with the development of associated descriptive models, has expanded the theoretical framework of radiation damage beyond classical mechanisms. We unravel, in this work, the nonclassical beam damage mechanisms of an open-framework material, i.e. UiO-66(Hf) metal-organic framework, by integrating low-dose electron microscopy and ab initio simulations of radiation induced structural dynamics. The physical origins of radiation damage phenomena, spanning across multiple scales including morphological, lattice, and molecular levels, have been unequivocally unveiled. Based on these observations, potential alternative mechanisms including reversible radiolysis and radiolysis-enhanced knock-on displacement are proposed, which account for their respective dynamic crystalline-to-amorphous interconversion and site-specific ligand knockout events occurring during continuous beam radiation. The current study propels the fundamental understanding of beam damage mechanisms from dynamic and correlated perspectives. Moreover, it fuels technical innovations, such as low-dose ultrafast electron microscopy, enabling imaging of beam-sensitive materials with uncompromised spatial resolution.

Diffusion distribution model for damage mitigation in scanning transmission electron microscopy

Despite the widespread use of Scanning Transmission Electron Microscopy (STEM) for observing the structure of materials at the atomic scale, a detailed understanding of some relevant electron beam damage mechanisms is limited. Recent reports suggest that certain types of damage can be modelled as a diffusion process and that the accumulation effects of this process must be kept low in order to reduce damage. We therefore develop an explicit mathematical formulation of spatiotemporal diffusion processes in STEM that take into account both instrument and sample parameters. Furthermore, our framework can aid the design of Diffusion Controlled Sampling (DCS) strategies using optimally selected probe positions in STEM, that constrain the cumulative diffusion distribution. Numerical simulations highlight the variability of the cumulative diffusion distribution for different experimental STEM configurations. These analytical and numerical frameworks can subsequently be used for careful design of 2- and 4-dimensional STEM experiments where beam damage is minimised.

In Situ Transmission Electron Microscopy of Electrocatalyst Materials: Proposed Workflows, Technical Advances, Challenges, and Lessons Learned

In situ electrochemical liquid phase transmission electron microscopy (LP-TEM) measurements utilize micro-chip three-electrode cells with electron transparent silicon nitride windows that confine the liquid electrolyte. By imaging electrocatalysts deposited on micro-patterned electrodes, LP-TEM provides insight into morphological, phase structure, and compositional changes within electrocatalyst materials under electrochemical reaction conditions, which have practical implications on activity, selectivity, and durability. Despite LP-TEM capabilities becoming more accessible, in situ measurements under electrochemical reaction conditions remain non-trivial, with challenges including electron beam interactions with the electrolyte and electrode, the lack of well-defined experimental workflows, and difficulty interpreting particle behavior within a liquid. Herein a summary of the current state of LP-TEM technique capabilities alongside a discussion of the relevant experimental challenges researchers typically face, with a focus on in situ studies of electrochemical CO2 conversion catalysts is provided. A methodological approach for in situ LP-TEM measurements on CO2R catalysts prepared by electro-deposition, sputtering, or drop-casting is presented and include case studies where challenges and proposed workflows for each are highlighted. By providing a summary of LP-TEM technique capabilities and guidance for the measurements, the goal is for this paper to reduce barriers for researchers who are interested in utilizing LP-TEM characterization to answer their scientific questions.

Exploring Biomineralization Processes Using In Situ Liquid Transmission Electron Microscopy: A Review

Liquid transmission electron microscopy (TEM) is a newly established technique broadly used to study reactions in situ. Since its emergence, complex and multifaceted biomineralization processes have been revealed with real-time resolution, where classical and non-classical mineralization pathways have been dynamically observed primarily for Ca and Fe-based mineral systems in situ. For years, classical crystallization pathways have dominated theories on biomineralization progression despite observations of non-traditional routes involving precursor phases using traditional- and cryo-TEM. The new dynamic lens provided by liquid TEM is a key correlate to techniques limited to time-stamped, static observations - helping shift paradigms in biomineralization toward non-classical theories with dynamic mechanistic visualization. Liquid TEM provides new insights into fundamental biomineralization processes and essential physiological and pathological processes for a wide range of organisms. This review critically reviews a summary of recent in situ liquid TEM research related to the biomineralization field. Key liquid TEM preparation and imaging parameters are provided as a foundation for researchers while technical challenges are discussed. In future, the expansion of liquid TEM research in the biomineralization field will lead to transformative discoveries, providing complementary dynamic insights into biological systems.

Evaluating Cryo-TEM Reconstruction Accuracy of Self-Assembled Polymer Nanostructures

Cryogenic transmission electron microscopy (cryo-TEM) combined with single particle analysis (SPA) is an emerging imaging approach for soft materials. However, the accuracy of SPA-reconstructed nanostructures, particularly those formed by synthetic polymers, remains uncertain due to potential packing heterogeneity of the nanostructures. In this study, the combination of molecular dynamics (MD) simulations and image simulations is utilized to validate the accuracy of cryo-TEM 3D reconstructions of self-assembled polypeptoid fibril nanostructures. Using CryoSPARC software, image simulations, 2D classifications, ab initio reconstructions, and homogenous refinements are performed. By comparing the results with atomic models, the recovery of molecular details is assessed, heterogeneous structures are identified, and the influence of extraction location on the reconstructions is evaluated. These findings confirm the fidelity of single particle analysis in accurately resolving complex structural characteristics and heterogeneous structures, exhibiting its potential as a valuable tool for detailed structural analysis of synthetic polymers and soft materials.

Tutorial on In Situ and Operando (Scanning) Transmission Electron Microscopy for Analysis of Nanoscale Structure-Property Relationships

In situ and operando (scanning) transmission electron microscopy [(S)TEM] is a powerful characterization technique that uses imaging, diffraction, and spectroscopy to gain nano-to-atomic scale insights into the structure-property relationships in materials. This technique is both customizable and complex because many factors impact the ability to collect structural, compositional, and bonding information from a sample during environmental exposure or under application of an external stimulus. In the past two decades, in situ and operando (S)TEM methods have diversified and grown to encompass additional capabilities, higher degrees of precision, dynamic tracking abilities, enhanced reproducibility, and improved analytical tools. Much of this growth has been shared through the community and within commercialized products that enable rapid adoption and training in this approach. This tutorial aims to serve as a guide for students, collaborators, and nonspecialists to learn the important factors that impact the success of in situ and operando (S)TEM experiments and assess the value of the results obtained. As this is not a step-by-step guide, readers are encouraged to seek out the many comprehensive resources available for gaining a deeper understanding of in situ and operando (S)TEM methods, property measurements, data acquisition, reproducibility, and data analytics.

From Beam Damage to Massive Reaction Amplification under the Electron Microscope: An Ionization-Induced Chain Reaction in Crystals of a Dewar Benzene

Electron microscopy in its various forms is one of the most powerful imaging and structural elucidation methods in nanotechnology where sample information is generally limited by random chemical and structural damage. Here we show how a well-selected chemical probe can be used to transform indiscriminate chemical damage into clean chemical processes that can be used to characterize some aspects of the interactions between high-energy electron beams and soft organic matter. Crystals of a Dewar benzene exposed to a 300 keV electron beam facilitate a clean valence-bond isomerization radical-cation chain reaction where the number of chemical events per incident electron is amplified by a factor of up to ca. 90,000.

Grain and Domain Microstructure in Long Chain N-Alkane and N-Alkanol Wax Crystals

Waxes comprise a diverse set of materials from lubricants and coatings to biological materials such as the intracuticular wax layers on plant leaves that restrict water loss to inhibit dehydration. Despite the often mixed hydrocarbon chain lengths and functional groups within waxes, they show a propensity for ordering into crystalline phases, albeit with a wealth of solid solution behavior and disorder modes that determine chemical transport and mechanical properties. Here, we reveal the microscopic structure and heterogeneity of replica leaf wax models based on the dominant wax types in the Schefflera elegantissima plant, namely C31H64 and C30H61OH and their binary mixtures. We observe defined grain microstructure in C31H64 crystals and nanoscale domains of chain-ordered lamellae within these grains. Moreover, nematic phases and dynamical disorder coexist with the domains of ordered lamellae. C30H61OH exhibits more disordered chain packing with no grain structure or lamellar domains. Binary mixtures from 0-50% C30H61OH exhibit a loss of grain structure with increasing alcohol content accompanied by increasingly nematic rather than lamellar chain packing, suggesting a partial but limited solid solution behavior. Together, these results unveil the previously unseen microstructural features governing flexibility and permeability in leaf waxes and outline an approach to microstructure analysis across agrochemicals, pharmaceuticals, and food.

Mechanism of Electron-Beam-Induced Structural Degradation in ZIF-8 and its Electron Dose Tolerance

Zeolitic-imidazolate frameworks (ZIFs) are crystalline microporous materials with promising potential for gas adsorption and catalysis application. Further research advances include studies on integrating ZIFs into nanodevice concepts. In detail for the application, e.g., electron-beam-assisted structural modifications or patterning, there is a need to understand potential structural degradation processes caused by such electron beams. Advanced transmission electron microscopy (TEM) has demonstrated its ability to study structures at the nanoscale. Here, we systematically investigated electron-beam-induced loss in crystallinity in ZIF-8 under various experimental conditions, using as measure the attenuation of the relative intensity and the relative displacement of electron diffraction Bragg planes with increasing cumulative electron dose. The {110} Bragg planes reflect the overall stability of the ZIF-8 unit-cell structure, while the {431} Bragg planes assess the stability of its micropore structure. We considered a relative loss of Bragg plane intensity of 37% as the threshold for determining the critical electron dose, which varied for different Bragg planes, with 35.6 ± 8.4 e-Å-2 for {110} and 11.4 ± 3.0 e-Å-2 for {431}. However, the critical dose per breakage of N-Zn bonds in a ZnN4 tetrahedra per different Bragg plane was found to be ∼3 e-Å-2, which indicates continuous, simultaneous breakage of N-Zn bonds throughout the crystal, confirming radiolysis as the dominant damage mechanism. In addition, we investigated the effects of TEM experiment parameters, including acceleration voltage, electron dose rate, cryogenic sample temperature, in situ sample drying, and change in conductivity of the sample substrate (e.g., graphene). Our results unravel the degradation mechanisms in ZIF-8 and provide threshold parameters for maximizing resolution in electron-beam-assisted experiments and processes.

Understanding, Mimicking, and Mitigating Radiolytic Damage to Polymers in Liquid Phase Transmission Electron Microscopy

Advances in liquid phase transmission electron microscopy (LP-TEM) have enabled the monitoring of polymer dynamics in solution at the nanoscale, but radiolytic damage during LP-TEM imaging limits its routine use in polymer science. This study focuses on understanding, mimicking, and mitigating radiolytic damage observed in functional polymers in LP-TEM. It is quantitatively demonstrated how polymer damage occurs across all conceivable (LP-)TEM environments, and the key characteristics and differences between polymer degradation in water vapor and liquid water are elucidated. Importantly, it is shown that the hydroxyl radical-rich environment in LP-TEM can be approximated by UV light irradiation in the presence of hydrogen peroxide, allowing the use of bulk techniques to probe damage at the polymer chain level. Finally, the protective effects of commonly used hydroxyl radical scavengers are compared, revealing that the effectiveness of graphene's protection is distance-dependent. The work provides detailed methodological guidance and establishes a baseline for polymer degradation in LP-TEM, paving the way for future research on nanoscale tracking of shape transitions and drug encapsulation of polymer assemblies in solution.

Atomic resolution scanning transmission electron microscopy at liquid helium temperatures for quantum materials

Fundamental quantum phenomena in condensed matter, ranging from correlated electron systems to quantum information processors, manifest their emergent characteristics and behaviors predominantly at low temperatures. This necessitates the use of liquid helium (LHe) cooling for experimental observation. Atomic resolution scanning transmission electron microscopy combined with LHe cooling (cryo-STEM) provides a powerful characterization technique to probe local atomic structural modulations and their coupling with charge, spin and orbital degrees-of-freedom in quantum materials. However, achieving atomic resolution in cryo-STEM is exceptionally challenging, primarily due to sample drifts arising from temperature changes and noises associated with LHe bubbling, turbulent gas flow, etc. In this work, we demonstrate atomic resolution cryo-STEM imaging at LHe temperatures using a commercial side-entry LHe cooling holder. Firstly, we examine STEM imaging performance as a function of He gas flow rate, identifying two primary noise sources: He-gas pulsing and He-gas bubbling. Secondly, we propose two strategies to achieve low noise conditions for atomic resolution STEM imaging: either by temporarily suppressing He gas flow rate using the needle valve or by acquiring images during the natural warming process. Lastly, we show the applications of image acquisition methods and image processing techniques in investigating structural phase transitions in Cr2Ge2Te6, CuIr2S4, and CrCl3. Our findings represent an advance in the field of atomic resolution electron microscopy imaging for quantum materials and devices at LHe temperatures, which can be applied to other commercial side-entry LHe cooling TEM holders.

Electron-Beam Writing of Atomic-Scale Reconstructions at Oxide Interfaces

The epitaxial growth of complex oxides enables the production of high-quality films, yet substrate choice is restricted to certain symmetry and lattice parameters, thereby limiting the technological applications of epitaxial oxides. In comparison, the development of free-standing oxide membranes gives opportunities to create novel heterostructures by nonepitaxial stacking of membranes, opening new possibilities for materials design. Here, we introduce a method for writing, with atomic precision, ionically bonded crystalline materials across the gap between an oxide membrane and a carrier substrate. The process involves a thermal pretreatment, followed by localized exposure to the raster scan of a scanning transmission electron microscopy (STEM) beam. STEM imaging and electron energy-loss spectroscopy show that we achieve atomically sharp interface reconstructions between a 30-nm-thick SrTiO3 membrane and a niobium-doped SrTiO3(001)-oriented carrier substrate. These findings indicate new strategies for fabricating synthetic heterostructures with novel structural and electronic properties.

Atomic Fabrication of 2D Materials Using Electron Beams Inside an Electron Microscope

Two-dimensional (2D) materials have garnered increasing attention due to their unusual properties and significant potential applications in electronic devices. However, the performance of these devices is closely related to the atomic structure of the material, which can be influenced through manipulation and fabrication at the atomic scale. Transmission electron microscopes (TEMs) and scanning TEMs (STEMs) provide an attractive platform for investigating atomic fabrication due to their ability to trigger and monitor structural evolution at the atomic scale using electron beams. Furthermore, the accuracy and consistency of atomic fabrication can be enhanced with an automated approach. In this paper, we briefly introduce the effect of electron beam irradiation and then discuss the atomic structure evolution that it can induced. Subsequently, the use of electron beams for achieving desired structures and patterns in a controllable manner is reviewed. Finally, the challenges and opportunities of atomic fabrication on 2D materials inside an electron microscope are discussed.

Reaction-diffusion study of electron-beam-induced contamination growth

A time-dependent reaction-diffusion model was elaborated to better understand the dynamical growth of contamination on surfaces illuminated by an electron beam. The goal of this work was to fully describe the flow of hydrocarbon molecules, denoted as contaminants, and their polymerization in the irradiated area with the number of parameters reduced to a minimum necessary. It was considered that the diffusion process of contaminants is driven by the gradient of their surface density generated by the impact of a circular homogeneous electron beam. The contribution of the residual gas atmosphere in the instrument was described by the tendency to reestablish the initial equilibrium surface density of contaminants before irradiation. The four unknown parameters of the model, the electron interaction cross-section, the diffusion coefficient, the initial surface density of contaminants, and the frequency of the supply of contaminants from the residual gas atmosphere were determined by comparing the modeled contamination growth with experimental results. The experiments were designed such that the influence of the single parameters could be unequivocally separated. To follow the dynamical evolution of the system and to generate time-resolved distinct experimental data, successive contamination measurements were performed at short time intervals up to 20 min. The local height and shape of the grown contamination were quantified by evaluating high-angle annular dark-field (HAADF) scanning-transmission- electron-microcopy (STEM) image intensities and corresponding Monte-Carlo simulations. Our model also applies to nonhomogeneous initial conditions like the reduced local surface density of contaminants after previous beam-showering. The dynamic analyses of this process might provide hints regarding the relative size of the contaminant molecules and also indicate some measures for the reduction of contamination growth.

Low-dose electron microscopy imaging for beam-sensitive metal-organic frameworks

Metal-organic frameworks (MOFs) have garnered significant attention in recent years owing to their exceptional properties. Understanding the intricate relationship between the structure of a material and its properties is crucial for guiding the synthesis and application of these materials. (Scanning) Transmission electron microscopy (S)TEM imaging stands out as a powerful tool for structural characterization at the nanoscale, capable of detailing both periodic and aperiodic local structures. However, the high electron-beam sensitivity of MOFs presents substantial challenges in their structural characterization using (S)TEM. This paper summarizes the latest advancements in low-dose high-resolution (S)TEM imaging technology and its application in MOF material characterization. It covers aspects such as framework structure, defects, and surface and interface analysis, along with the distribution of guest molecules within MOFs. This review also discusses emerging technologies like electron ptychography and outlines several prospective research directions in this field.

Electron beam and thermal stabilities of MFM-300(M) metal-organic frameworks

This work reports the thermal and electron beam stabilities of a series of isostructural metal-organic frameworks (MOFs) of type MFM-300(M) (M = Al, Ga, In, Cr). MFM-300(Cr) was most stable under the electron beam, having an unusually high critical electron fluence of 1111 e- Å-2 while the Group 13 element MOFs were found to be less stable. Within Group 13, MFM-300(Al) had the highest critical electron fluence of 330 e- Å-2, compared to 189 e- Å-2 and 147 e- Å-2 for the Ga and In MOFs, respectively. For all four MOFs, electron beam-induced structural degradation was independent of crystal size and was highly anisotropic, although both the length and width of the channels decreased during electron beam irradiation. Notably, MFM-300(Cr) was found to retain crystallinity while shrinking up to 10%. Thermal stability was studied using in situ synchrotron X-ray diffraction at elevated temperature, which revealed critical temperatures for crystal degradation to be 605, 570, 490 and 480 °C for Al, Cr, Ga, and In, respectively. The pore channel diameters contracted by ≈0.5% on desorption of solvent species, but thermal degradation at higher temperatures was isotropic. The observed electron stabilities were found to scale with the relative inertness of the cations and correlate well to the measured lifetime of the materials when used as photocatalysts.

in situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies (V O ⋅ ⋅ ). Notwithstanding its significance, behaviors of the defective structure andV O ⋅ ⋅ in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (Ce0.88Gd0.12O2-δ) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massiveV O ⋅ ⋅ rearrangement are stimulated and visualized in situ with sub-Å resolution. Electron dose rate is identified as a pivotal factor in modulating the phase transition, and both theV O ⋅ ⋅ concentration and the orientation of the newly formed phase can be altered via electron beam. Our results provide indispensable insights for understanding and refining the microscopic pathways of phase transition as well as defect engineering, and could be applied to other similar functional oxides.

Patterning damage mechanisms for two-dimensional crystalline polymers and evaluation for a conjugated imine-based polymer

High-quality patterning determines the properties of patterned emerging two-dimensional (2D) conjugated polymers and is essential for potential applications in future electronic nanodevices. However, the most suitable patterning method for 2D polymers has yet to be determined because we still do not have a comprehensive understanding of their damage mechanisms by visualizing the structural modification that occurs during the patterning process. Here, the damage mechanisms during patterning of 2D polymers, induced by various patterning methods, are unveiled based on a systematic study of structural damage and edge morphology in an imine-based 2D polymer (polyimine). Patterning using a focused electron beam, focused ion beam (FIB) and mechanical carving is evaluated. The focused electron beam successively introduces a sputtering effect, knock-on displacement damage and massive radiolysis with increasing electron dose from9.46×107electrons nm-2to1.14×1010electrons nm-2. Successful patterning is enabled by knock-on damage but impeded by carbon contamination beyond a critical sample thickness. A FIB creates current-dependent edge morphologies and extensive damage from ion implantation caused by the tail of the unfocused beam. A precisely controlled tip can tear the polyimine film through grain boundaries and hence create a patterning edge with suitable edge roughness for certain application scenarios when beam damage is avoided. Taking structural damage and the resulting quantitative edge roughness into consideration, this study provides a detailed instruction on the proper patterning techniques for 2D crystalline polymers and paves the way for tailored intrinsic properties and device fabrication using these novel materials.

In-situ imaging of heat-induced phase transition in a two-dimensional conjugated metal-organic framework

Atomically-resolved in-situ high-resolution transmission electron microscopy (HRTEM) imaging of the structural dynamics in organic materials remains a major challenge. This difficulty persists even with aberration-corrected instruments, as HRTEM images necessitate a high electron dose that is generally intolerable for organic materials. In this study, we report the in-situ HRTEM imaging of heat-induced structural dynamics in a benzenehexathiol-based two-dimensional conjugated metal-organic framework (2D c-MOF, i.e., Cu3(BHT)). Leveraging its hydrogen-free structure and high electrical conductivity, Cu3(BHT) exhibits high electron beam resistance. We demonstrate atomic resolution imaging at an 80 kV electron accelerating voltage using our Cc/Cs-corrected SALVE instrument. However, continuous electron irradiation eventually leads to its amorphization. Intriguingly, under heating in a MEMS holder, the Cu3(BHT) undergoes a phase transition to a new crystalline phase and its phase transition, occurring within the temperature range of 480 °C to 620 °C in dependence on the electron beam illumination. Using HRTEM and energy-dispersive X-ray mapping, we identify this new phase as CuS. Our findings provide insights into the mechanisms governing structural transitions in purposefully engineered structures, potentially pivotal for future endeavours involving the production of metal oxide/sulfide nanoparticles from MOF precursors.

Electrified Operando-Freezing of Electrocatalytic CO2 Reduction Cells for Cryogenic Electron Microscopy

The ability to freeze and stabilize reaction intermediates in their metastable states and obtain their structural and chemical information with high spatial resolution is critical to advance materials technologies such as catalysis and batteries. Here, we develop an electrified operando-freezing methodology to preserve these metastable states under electrochemical reaction conditions for cryogenic electron microscopy (cryo-EM) imaging and spectroscopy. Using Cu catalysts for CO2 reduction as a model system, we observe restructuring of the Cu catalyst in a CO2 atmosphere while the same catalyst remains intact in air at the nanometer scale. Furthermore, we discover the existence of a single valence Cu (1+) state and C-O bonding at the electrified liquid-solid interface of the operando-frozen samples, which are key reaction intermediates that traditional ex situ measurements fail to detect. This work highlights our novel technique to study the local structure and chemistry of electrified liquid-solid interfaces, with broad impact beyond catalysis.

Event-responsive scanning transmission electron microscopy

An ever-present limitation of transmission electron microscopy is the damage caused by high-energy electrons interacting with any sample. By reconsidering the fundamentals of imaging, we demonstrate an event-responsive approach to electron microscopy that delivers more information about the sample for a given beam current. Measuring the time to achieve an electron count threshold rather than waiting a predefined constant time improves the information obtained per electron. The microscope was made to respond to these events by blanking the beam, thus reducing the overall dose required. This approach automatically apportions dose to achieve a given signal-to-noise ratio in each pixel, eliminating excess dose that is associated with diminishing returns of information. We demonstrate the wide applicability of our approach to beam-sensitive materials by imaging biological tissue and zeolite.

Influence of magnetic field on electron beam-induced Coulomb explosion of gold microparticles in transmission electron microscopy

In this work we instigated the fragmentation of Au microparticles supported on a thin amorphous carbon film by irradiating them with a gradually convergent electron beam inside the Transmission Electron Microscope. This phenomenon has been generically labeled as "electron beam-induced fragmentation" or EBIF and its physical origin remains contested. On the one hand, EBIF has been primarily characterized as a consequence of beam-induced heating. On the other, EBIF has been attributed to beam-induced charging eventually leading to Coulomb explosion. To test the feasibility of the charging framework for EBIF, we instigated the fragmentation of Au particles under two different experimental conditions. First, with the magnetic objective lens of the microscope operating at full capacity, i.e. background magnetic field B=2 T, and with the magnetic objective lens switched off (Lorenz mode), i.e. B=0 T. We observe that the presence or absence of the magnetic field noticeably affects the critical current density at which EBIF occurs. This strongly suggests that magnetic field effects play a crucial role in instigating EBIF on the microparticles. The dependence of the value of the critical current density on the absence or presence of an ambient magnetic field cannot be accounted for by the beam-induced heating model. Consequently, this work presents robust experimental evidence suggesting that Coulomb explosion driven by electrostatic charging is the root cause of EBIF.

Elemental quantification using electron energy-loss spectroscopy with a low voltage scanning transmission electron microscope (STEM-EELS)

Electron beam damage in electron microscopes is becoming more and more problematic in material research with the increasing demand of characterization of new beam sensitive material such as Li based compounds used in lithium-ion batteries. To avoid radiolysis damage, it has become common practice to use Cryo-EM, however, knock-on damage can still occur in conventional TEM/STEM with a high-accelerating voltage (200-300 keV). In this work, electron energy loss spectroscopy with an accelerating voltage of 30,20 and 10 keV was explored with h-BN, TiB2 and TiN compounds. All Ti L2,3, N K and B K edges were successfully observed with an accelerating voltage as low as 10 keV. An accurate elemental quantification for all three samples was obtained using a multi-linear least square (MLLS) procedure which gives at most a 5 % of standard deviation which is well within the error of the computation of the inelastic partial-cross section used for the quantification. These results show the great potential of using low-voltage EELS which is another step towards a knock-on damage free analysis.

Structural Complexities in Sodium Ion Conductive Antiperovskite Revealed by Cryogenic Transmission Electron Microscopy

We use low-dose cryogenic transmission electron microscopy (cryo-TEM) to investigate the atomic-scale structure of antiperovskite Na2NH2BH4 crystals by preserving the room-temperature cubic phase and carefully monitoring the electron dose. Via quantitative analysis of electron beam damage using selected area electron diffraction, we find cryogenic imaging provides 6-fold improvement in beam stability for this solid electrolyte. Cryo-TEM images obtained from flat crystals revealed the presence of a new, long-range-ordered supercell with a cubic phase. The supercell exhibits doubled unit cell dimensions of 9.4 Å × 9.4 Å as compared to the cubic lattice structure revealed by X-ray crystallography of 4.7 Å × 4.7 Å. The comparison between the experimental image and simulated potential map indicates the origin of the supercell is a vacancy ordering of sodium atoms. This work demonstrates the potential of using cryo-TEM imaging to study the atomic-scale structure of air- and electron-beam-sensitive antiperovskite-type solid electrolytes.

Direct Imaging of the Crystalline Domains and Their Orientation in the PS-b-PEO Block Copolymer with 4D-STEM

The arrangement of crystalline domains in semicrystalline polymers is key to understanding how to optimize the nanostructured morphology for enabling better properties. For example, in polystyrene-b-poly(ethylene oxide) (PS-b-PEO), the degree of crystallinity and arrangement of the crystallites within the PEO phase plays a crucial role in determining the physical properties of the electrolyte. Here, we used four-dimensional scanning transmission electron microscopy to directly visualize the crystal domains within the PEO-rich region of the PS-b-PEO block copolymer and show the relative angle of the domain with respect to the PEO-PS interface. As demonstrated here, our analysis method is applicable to other electron-beam sensitive materials, especially semicrystalline polymers, to unveil their local phase condition and distribution.

Quantifying the Growth Kinetics of Lithium Metal Reduced from Solid Ionic Conductors

Investigating the growth kinetics of Li metal in solid-state batteries is crucial to both a fundamental understanding and practical application. Here, by directly observing the formation of Li metal from Ta-doped Li6.4La3Zr1.4Ta0.6O12 (LLZTO) in a transmission electron microscope, the growth kinetics is analyzed quantitatively. The growth kinetics of Li deposits shows a cubic-curve characteristic for LLZTO with Li-source-free. Instead, a linear growth process is observed with Li-source supplied. The impact of the illuminating electron dose rate on the growth kinetics is clarified, indicating that even low dose rates (1-3 e-/Å2/s) could affect Li growth, highlighting the significance of controlling dose rates. Furthermore, a new pathway for the formation of Li metal from Li-containing materials utilizing the field-emission effect is reported. This work has implications on the failure mechanism in solid batteries by using limited Li anodes and opens pathways for regulating Li growth in LLZTO at various scenarios, which can also extend to other ionic conductors.

Microscopic chemical characterization of epoxy resin with scanning transmission electron microscopy - electron energy-loss spectroscopy

The structural characterization of epoxy resins is essential to improve the understanding on their structure-property relationship for promising high-performance applications. Among all analytical techniques, scanning transmission electron microscopy-electron energy-loss spectroscopy (STEM-EELS) is a powerful tool for probing the chemical and structural information of various materials at a high spatial resolution. However, for sensitive materials, such as epoxy resins, the structural damage induced by electron-beam irradiation limits the spatial resolution in the STEM-EELS analysis. In this study, we demonstrated the extraction of the intrinsic features and structural characteristics of epoxy resins by STEM-EELS under electron doses below 1 e-/Å2 at room temperature. The reliability of the STEM-EELS analysis was confirmed by X-ray absorption spectroscopy and spectrum simulation as low- or non-damaged reference data. The investigation of the dependence of the epoxy resin on the electron dose and exposure time revealed the structural degradation associated with electron-beam irradiation, exploring the prospect of EELS for examining epoxy resin at low doses. Furthermore, the degradation mechanisms in the epoxy resin owing to electron-beam irradiation were revealed. These findings can promote the structural characterization of epoxy-resin-based composites and other soft materials.

Cinematographic study of stochastic chemical events at atomic resolution

The advent of single-molecule atomic-resolution time-resolved electron microscopy (SMART-EM) has created a new field of 'cinematic chemistry,' allowing for the cinematographic recording of dynamic behaviors of organic and inorganic molecules and their assembly. However, the limited electron dose per frame of video images presents a major challenge in SMART-EM. Recent advances in direct electron counting cameras and techniques to enhance image quality through the implementation of a denoising algorithm have enabled the tracking of stochastic molecular motions and chemical reactions with sub-millisecond temporal resolution and sub-angstrom localization precision. This review showcases the development of dynamic molecular imaging using the SMART-EM technique, highlighting insights into nanomechanical behavior during molecular shuttle motion, pathways of multistep chemical reactions, and elucidation of crystallization processes at the atomic level.

Atomic-Scale Imaging of Clay Mineral Nanosheets and Their Supramolecular Complexes through Electron Microscopy: A Supramolecular Chemist's Perspective

Recent advancements in electron microscopy techniques have revolutionized the ability to directly visualize and understand the intricate world of supramolecular chemistry. This paper provides a concise overview of a study delving into the atomic-scale imaging of monolayer clay mineral nanosheets and their associated supramolecular complexes. The imaging is conducted by harnessing the power of aberration-corrected scanning transmission electron microscopy (STEM). Clay mineral nanosheets, with their anionic charge and ultrathin thickness (of 1 nm), serve as a stable Coulombic host material for cationic guest molecules through electrostatic interactions, facilitating exceptional stability and control during observation. By incorporation of heavy-metal atom markers coordinated within the target molecules, high-angle annular dark field STEM enables a clear visualization of these supramolecular complexes. This approach helps to overcome the limitations of graphene-based systems and expands the possibilities of atomic-scale imaging of nonperiodic molecular assemblies formed by weak supramolecular interactions. The fusion of electron microscopy techniques with the principles of supramolecular and material chemistry offers exciting opportunities for studying the structure, behavior, and properties of complex supramolecular systems. It sheds light on the intricate molecular architectures and design principles governing these systems. This study showcases the immense potential of electron microscopy in supramolecular chemistry and invites researchers from various disciplines to explore the transformative possibilities of atomic-scale imaging in the field.

Understanding the Electron Beam Resilience of Two-Dimensional Conjugated Metal-Organic Frameworks

Knowledge of the atomic structure of layer-stacked two-dimensional conjugated metal-organic frameworks (2D c-MOFs) is an essential prerequisite for establishing their structure-property correlation. For this, atomic resolution imaging is often the method of choice. In this paper, we gain a better understanding of the main properties contributing to the electron beam resilience and the achievable resolution in the high-resolution TEM images of 2D c-MOFs, which include chemical composition, density, and conductivity of the c-MOF structures. As a result, sub-angstrom resolution of 0.95 Å has been achieved for the most stable 2D c-MOF of the considered structures, Cu3(BHT) (BHT = benzenehexathiol), at an accelerating voltage of 80 kV in a spherical and chromatic aberration-corrected TEM. Complex damage mechanisms induced in Cu3(BHT) by the elastic interactions with the e-beam have been explained using detailed ab initio molecular dynamics calculations. Experimental and calculated knock-on damage thresholds are in good agreement.