Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO3-Bi(Mg0.5Ti0.5)O3 relaxor dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High-resolution, synchrotron X-ray diffraction indicated a globally cubic structure (Pm3̅m), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along < 100 > and < 110 > zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2–5 nm. Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.

Intentionally disordered metal–organic frameworks (MOFs) display rich functional behaviour. However, the characterisation of their atomic structures remains incredibly challenging. X-ray pair distribution function techniques have been pivotal in determining their average local structure but are largely insensitive to spatial variations in the structure. Fe-BTC is a nanocomposite MOF, known for its catalytic properties, comprising crystalline nanoparticles and an amorphous matrix. Here, we use scanning electron diffraction to first map the crystalline and amorphous components to evaluate domain size and then to carry out electron pair distribution function analysis to probe the spatially separated atomic structure of the amorphous matrix. Further Bragg scattering analysis reveals systematic orientational disorder within Fe-BTC’s nanocrystallites, showing over 10° of continuous lattice rotation across single particles. Finally, we identify candidate unit cells for the crystalline component. These independent structural analyses quantify disorder in Fe-BTC at the critical length scale for engineering composite MOF materials.

Nine halloysite nanotubes (HNTs) have been examined using scanning electron microscopy (SEM), atomic force microscopy (AFM) and (cross-sectional) transmission electron microscopy (TEM) to evaluate details of their external and internal morphologies. The samples span morphologies within the cylindrical to prismatic-polygonal framework proposed by Hillier et al. (2016). The ‘carpet roll’ model assumed in the conceptualization of most technological applications of HNTs is shown to be far too simplistic. Both cylindrical and prismatic forms have abundant edge steps traversing their surfaces that, by analogy with plates of kaolinite, correspond to prism faces. The mean value for the diameter of the central lumen of the tubes is 12 nm. Numerous slit-like nanopores, with diameters up to 18 nm, also occur between packets of layers, particularly in prismatic forms at the junction between a central cylindrical core and outer packets of planar layers. These pores expose aluminol and siloxane surfaces, but unlike the lumen, which is assumed only to expose an aluminol surface, they do not extend along the entire length of the nanotube. Edge steps seen most clearly by AFM correspond in height to the packets of layers seen in TEM. TEM cross-sections suggest that tube growth occurs by accretion of a spiralled thickening wedge of layers evolving from cylindrical to polygonal form and reveal that planar sectors may be joined by either abrupt angular junctions or by short sections of curved layers. A more realistic model of the internal and external morphologies of HNTs is proposed to assist with understanding of the behaviour of HNTs in technological applications.

Insight into the nucleation, growth and phase transformations of calcium sulphate could improve the performance of construction materials, reduce scaling in industrial processes and aid understanding of its formation in the natural environment. Recent studies have suggested that the calcium sulphate pseudo polymorph, gypsum (CaSO 4 ·2H 2 O) can form in aqueous solution via a bassanite (CaSO 4 ·0.5H 2 O) intermediate. Some in situ experimental work has also suggested that the transformation of bassanite to gypsum can occur through an oriented assembly mechanism. In this work, we have exploited liquid cell transmission electron microscopy (LCTEM) to study the transformation of bassanite to gypsum in an undersaturated aqueous solution of calcium sulphate. This was benchmarked against cryogenic TEM (cryo‐TEM) studies to validate internally the data obtained from the two microscopy techniques. When coupled with Raman spectroscopy, the real‐time data generated by LCTEM, and structural data obtained from cryo‐TEM show that bassanite can transform to gypsum via more than one pathway, the predominant one being dissolution/reprecipitation. Comparisons between LCTEM and cryo‐TEM also show that the transformation is slower within the confined region of the liquid cell as compared to a bulk solution. This work highlights the important role of a correlated microscopy approach for the study of dynamic processes such as crystallisation from solution if we are to extract true mechanistic understanding.

The capacity for crystals to adsorb elements and molecules is a function of the structures of their crystal faces and the relative proportions of those faces. More importantly, this study shows that the surface structure of crystal faces is affected by their surface roughness and is the dominant factor controlling the absorption site density. In a continuation of the study of synthetic goethites with varying single crystal size distributions, two more synthetic goethites with intermediate sizes were analyzed by Brunauer-Emmett-Teller (BET) and atomic-resolution scanning transmission electron microscopy (STEM) to determine the effects of crystal size on their shape, atomic-scale surface roughness, and ultimately on their total surface site density. Results show that surface roughness scales directly with the size [or inversely with the specific surface area (SSA)] of synthetic goethites in the SSA range of 40-75 m2/g. This surface roughness, in turn, increases the total site density over ideal atomically smooth crystals. The total site density of synthetic goethite increases from a combination of decreasing crystal length/width ratio and increasing surface roughness.

Complex, electron-beam sensitive systems include organic crystals, polymers, hybrid organic-inorganic materials, some inorganic materials such as hydrates, as well as multiphase solid/liquid and solid/gas systems. Arguably they constitute the majority of systems of current interest across a wide range of scientific and engineering disciplines. We review the use of analytical transmission electron microscopy (TEM) for the characterisation of such beam-sensitive materials and complex, multiphase systems in-situ or close to their native state. Such materials are prone to damage by radiolysis which cannot be eliminated or switched off, requiring TEM analysis to be done within a dose budget so as to achieve an optimum dose-limited resolution and reliable, artefact-free results [1]. We highlight the importance of determining the damage sensitivity of a particular system in terms of characteristic changes that occur on irradiation under both an electron fluence and flux. We discuss the choice of electron beam accelerating voltage and detectors for optimizing resolution and outline the different strategies employed for low-dose microscopy in relation to the damage processes in operation. In particular, we discuss the use of scanning TEM (STEM) techniques for maximizing information content from high-resolution imaging and spectroscopy of materials and the use of cryogenic sample preservation methods. As an example, we describe studies of crystallization processes in the calcium sulfate system using a correlated approach: a combination of liquid cell TEM (LCTEM), in-situ Raman spectroscopy and cryogenic TEM (cryo-TEM). Recent studies have suggested that the calcium sulfate polymorph gypsum (CaSO 4

New approaches for the engineering of the 3D microstructure, pore modality, and chemical functionality of hierarchically porous nanocarbon assemblies are key to develop the next generation of functional aerogel and membrane materials. Here, interfacially driven assembly of carbon nanotubes (CNT) is exploited to fabricate structurally directed aerogels with highly controlled internal architectures, composed of pseudo-monolayer, CNT microcages. CNT Pickering emulsions enable engineering at fundamentally different length scales, whereby the microporosity, mesoporosity, and macroporosity are decoupled and individually controlled through CNT type, CNT number density, and process energy, respectively. In addition, metal nanocatalysts (Cu, Pd, and Ru) are embedded within the architectures through an elegant sublimation and shock-decomposition approach; introducing the first approach that enables through-volume functionalization of intricate, pre-designed aerogels without microstructural degradation. Catalytic structure-function relationships are explored in a pharma-important amidation reaction; providing insights on how the engineered frameworks enhance catalyst activity. A sophisticated array of advanced tomographic, spectroscopic, and microscopic techniques reveal an intricate 3D assembly of CNT building-blocks and their influence on the functional properties of the enhanced nanocatalysts. These advances set a basis to modulate structure and chemistry of functional aerogel materials independently in a controlled fashion for a variety of applications, including energy conversion and storage, smart electronics, and (electro)catalysis.

Appropriate graphitisation of a carbon steel may provide an alternative route to developing more simply and inexpensively alloyed machining steels which are more recyclable than those which are currently available. The extent of crystallinity of graphite particles formed during a graphitisation anneal of an experimental carbon steel was studied by Raman spectroscopy. It is demonstrated that it was possible to record the progress of graphitisation with annealing time as well as to determine which starting microstructural conditions, either ferrite-pearlite, bainite or martensite, formed the most highly crystalline graphite particles during annealing. During a machining operation the graphite should act as an internal lubricant at the chip/tool interface and thus the extent of crystallinity may influence the final machinability of the steel, or effectively, optimisation of the heat treatment. It was revealed by the Raman spectra that the crystallinity of the graphite particles formed was strongly affected by the starting microstructures as well as the graphitising anneal periods. For a similar annealing time, a better degree of crystallinity was observed in graphite particles formed from a ferrite-pearlite starting microstructure rather than bainite and martensite starting microstructures. However, crystallinity could be gradually improved with increasing annealing time from all three of the starting microstructures examined.

We demonstrate a characterisation protocol for quantifying nanostructural features associated with heterogeneous graphene nanosheets, including the lateral dimension, thickness and defect density of flakes produced by liquid phase exfoliation methods. The underlying basis for the protocol is a cross correlation between high resolution electron probe-based techniques and lower resolution but higher throughput photon probe-based characterisation methods. Using statistical data analysis we are able to develop a practical characterisation protocol that provides access to the precision and accuracy of the various graphene characterisation techniques. We have shown that the lateral dimension and thickness of heterogeneous graphene flakes can be rapidly quantified via optical mapping techniques. The defect densities within graphene samples can be accessed via Raman micro-spectroscopy. Based on the high throughput photon probe-based characterisation method, statistically representative data for heterogeneous graphene nanosheets can be obtained. Such information can be used to differentiate between inhomogeneous graphene samples in large length scales and thus can be useful for optimising graphene synthesis processes.

SummaryFormulation processing of organic crystalline compounds can have a significant effect on drug properties, such as dissolution rate or tablet strength/hardness. Transmission electron microscopy (TEM) has the potential to resolve the atomic lattice of these crystalline compounds and, for example, identify the defect density on a particular crystal face, provided that the sensitivity of these crystals to irradiation by high‐energy electrons can be overcome. Here, we acquire high‐resolution (HR) lattice images of the compound furosemide using two different methods: low‐dose HRTEM and bright‐field (BF) scanning TEM (STEM) scanning moiré fringes (SMFs). Before acquiring HRTEM images of furosemide, a model system of crocidolite (asbestos) was used to determine the electron flux/fluence limits of low‐dose HR imaging for our scintillator‐based, complementary metal‐oxide semiconductor (CMOS) electron camera by testing a variety of electron flux and total electron fluence regimes. An electron flux of 10 e−/(Å2 s) and total fluence of 10 e−/Å2 was shown to provide sufficient contrast and signal‐to‐noise ratio to resolve 0.30 nm lattice spacings in crocidolite at 300 kV. These parameters were then used to image furosemide which has a critical electron fluence for damage of ≥10 e−/Å2 at 300 kV. The resulting HRTEM image of a furosemide crystal shows only a small portion of the total crystal exhibiting lattice fringes, likely due to irradiation damage during acquisition close to the compound's critical fluence. BF‐STEM SMF images of furosemide were acquired at a lower electron fluence (1.8 e−/Å2), while still indirectly resolving HR details of the (001) lattice. Several different SMFs were observed with minor variations in the size and angle, suggesting strain due to defects within the crystal. Overall BF‐STEM SMFs appear to be more useful than BF‐STEM or HRTEM (with a CMOS camera) for imaging the crystal lattice of very beam‐sensitive materials since a lower electron fluence is required to reveal the lattice. BF‐STEM SMFs may thus prove useful in improving the understanding of crystallization pathways in organic compounds, degradation in pharmaceutical formulations and the effect of defects on the dissolution rate of different crystal faces. Further work is, however, required to quantitatively determine properties such as the defect density or the amount of relative strain from a BF‐STEM SMF image.

Ch 1. INTRODUCTION - What is EELS?. Interaction of electrons with matter. Basics of the TEM. Comparison of EELS in TEM with other spectroscopies. Conclusions. References and useful general texts on TEM, EELS and related techniques. Ch 2. THE EEL SPECTRUM - The primary transmitted electron signal. Historical development. Basic components of an EEL spectrum. Basic physics. Summary of analytical uses. References. Ch 3. EELS INSTRUMENTATION AND EXPERIMENTAL ASPECTS - The electron spectrometer. Coupling a magnetic spectrometer to the microscope. Spectral recording. Energy filtered imaging. Choice of experimental conditions for EELS. Specimen parameters. Summary of experimental setup and data. Acquisition procedures for EELS. Summary of data correction procedures for EELS. References and further reading. Ch 4. LOW LOSS SPECTROSCOPY - Quantification of sample thickness. Quantitative aspects of low loss data. Experimental aspects of EELS low loss measurements. Conclusions. References and further reading. Ch 5. ELEMENTAL QUANTIFICATION - Quantification of EEL spectra. Background removal. Determination of the ionization cross-section. Final quantification step. Summary of the quantification procedure. Summary of experimental quantification parameters. Accuracy and detection sensitivity of EELS. Quantification and comparison with EDX in the TEM. References and further reading. Ch 6. FINE STRUCTURE ON INNER SHELL IONIZATION EDGES (ELNES/EXELFS) - Origin of edge fine structure. Determination of co-ordinations. Determination of valencies. Determination of bond lengths. Experimental aspects of ELNES/EXELFS measurements. Conclusions. References and further reading. Ch 7. EELS IMAGING. INTRODUCTION TO EELS IMAGING AND ENERGY FILTERING - Summary of energy-filtering techniques. Procedure for EFTEM elemental mapping. Experimental parameters in EFTEM. Correlation of elemental maps. General strategy for EFTEM elemental analysis. Experimental procedure for EFTEM image acquisition and processing. Comparison of EFTEM and spectrum imaging methods. Energy-filtered tomography. Conclusions. references and further reading. Ch 8. ADVANCED EELS TECHNIQUES IN THE TEM -Orientation dependency in EELS. Spatially resolved measurements. Electron Compton scattering. Reflection mode and surface measurements. References and further reading. Ch 9. CONCLUSIONS - Further reading. Further resources.

Progress in the implementation of nanoparticles for therapeutic applications will accelerate with an improved understanding of the interface between nanoparticle surfaces and the media they are dispersed in. We examine this interface by analytical scanning transmission electron microscopy and show that incorrect specimen preparation or analysis can induce an artefactual, nanoscale, calcium phosphate-rich, amorphous coating on nanoparticles dispersed in cell culture media. We report that this ionic coating can be induced on five different types of nanoparticles (Au, BaTiO3, ZnO, TiO2 and Fe2O3) when specimen preparation causes a significant rise in pH above physiological levels. Such a pH change reduces ionic solubility in the suspending media to permit precipitation of calcium phosphate. Finally, we demonstrate that there is no indication of a calcium-phosphorus-rich coating on BaTiO3 nanoparticles suspended in culture media when prepared without alteration of the pH of the suspending media and imaged by cryo-STEM. Therefore we recommend that future reports utilising nanoparticles dispersed in cell culture media monitor and report the pH of suspensions during sample preparation.

The ability to synthesize plasmonic nanomaterials with well-defined structures and tailorable size is crucial for exploring their potential applications. Gold nanoplates (AuNPLs) exhibit appealing structural and optical properties, yet their applications are limited by difficulties in thickness control. Other challenges include a narrow range of tunability in size and surface plasmon resonance, combined with a synthesis conventionally involving cytotoxic cetyltrimethylammonium (CTA) halide surfactant. Here, a one-step, high-yield synthesis of single-crystalline AuNPLs is developed, based on the combined use of two structure-directing agents, methyl orange and FeBr3, which undergo preferential adsorption onto different crystalline facets of gold. The obtained AuNPLs feature high shape homogeneity that enables mesoscopic self-assembly, broad-range tunability of dimensions (controlled thickness from approximate to 7 to approximate to 20 nm, accompanied by modulation of the edge length from approximate to 150 nm to approximate to 2 mu m) and plasmonic properties. These merits, coupled with a preparation free of CTA-halide surfactants, have facilitated the exploration of various uses, especially in bio-related areas. For example, they are demonstrated as biocompatible photothermal agents for cell ablation in NIR I and NIR II windows. This work paves the way to the innovative fabrication of anisotropic plasmonic nanomaterials with desired attributes for wide-ranging practical applications.

Alkali-based CO2 sorbents were prepared from a novel material (i.e., Laminaria hyperborea). The use of this feedstock, naturally containing alkali metals, enabled a simple, green and low-cost route to be pursued. In particular, raw macroalgae was pyrolyzed at 800 °C. The resulting biochar was activated with either CO2 or KOH. KOH–activated carbon (AC) had the largest surface area and attained the highest CO2 uptake at 35 °C and 1 bar. In contrast, despite much lower porosity, the seaweed-derived char and its CO2-activated counterpart outweighed the CO2 sorption performance of KOH–AC and commercial carbon under simulated post-combustion conditions (53 °C and 0.15 bar). This was ascribed to the greater basicity of char and CO2–AC due to the presence of alkali metal-based functionalities (i.e., MgO) within their structure. These were responsible for a sorption of CO2 at lower partial pressure and higher temperature. In particular, the CO2–AC exhibited fast sorption kinetics, facile regeneration and good durability over 10 working cycles. Results presented in the current article will be of help for enhancing the design of sustainable alkali metal-containing CO2 captors.

We review the use of transmission electron microscopy (TEM) and associated techniques for the analysis of beam sensitive materials and complex, multiphase systems in-situ or close to their native state.We focus on materials prone to damage by radiolysis and explain that this process cannot be eliminated or switched off, requiring TEM analysis to be done within a dose budget to achieve an optimum dose-limited resolution.We highlight the importance of determining the damage sensitivity of a particular system in terms of characteristic changes that occur on irradiation under both an electron fluence and flux by presenting results from a series of molecular crystals.We discuss the choice of electron beam accelerating voltage and detectors for optimising resolution and outline the different strategies employed for low dose microscopy in relation to the damage processes in operation.In particular, we discuss the use of scanning TEM (STEM) techniques for maximising information content from high resolution imaging and spectroscopy of minerals and molecular crystals.We suggest how this understanding can then be carried forward for in-situ analysis of samples interacting with liquids and gases, provided any electron beam-induced alteration of a specimen is controlled or used to drive a chosen reaction.Finally, we demonstrate that cryo-TEM of nanoparticle samples snap frozen in vitreous ice can play a significant role in benchmarking dynamic processes at higher resolution.

The concept of representative imaging and analysis is a significant challenge in characterisation and is one of vital importance when examining (cid:212)real-world(cid:213) samples, which are often multi-component, complex systems. This is especially evident with nanoparticles, which have increasing applications in strategically important fields, from healthcare to energy generation. When appropriately engineered nanoparticles can be the central and active component of a product, e.g. as agents for MRI contrast enhancement or the UV block in suncream.

In this paper the chemical interaction between catalyst and support has been studied to understand the observed different growth rate of CNTs in our previous paper. Both pure MgO and Mg(NO3)2 . 6H2O as sources of the MgO catalyst support and Fe2(SO4)3 · xH2O as the source of the Fe catalyst, were employed. A Fe catalyst supported on MgO has been synthesized using the wet impregnation method followed by calcination. To compare the catalyst grain size and its distribution, the sample were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and BET specific surface area (SSA) measurement and X-ray photoelectron spectroscopy (XPS). XPS technique have utilized complementary to demonstrate the existence of chemical interaction between MgO support and Fe catalyst. Results revealed that the type of precursor used to prepare the support has a significant influence on the morphology of the support and the associated distribution of the Fe catalysts. The highest yield of MgFe2O4 phase was obtained using a pure MgO precursor which after calcination results in a homogenous distribution of nano-sized Fe particles over the support surface

Abstract2D metal nanomaterials offer exciting prospects in terms of their properties and functions. However, the ambient aqueous synthesis of atomically‐thin, 2D metallic nanomaterials represents a significant challenge. Herein, freestanding and atomically‐thin gold nanosheets with a thickness of only 0.47 nm (two atomic layers thick) are synthesized via a one‐step aqueous approach at 20 °C, using methyl orange as a confining agent. Owing to the high surface‐area‐to‐volume ratio, abundance of unsaturated atoms exposed on the surface and large interfacial areas arising from their ultrathin 2D nature, the as‐prepared Au nanosheets demonstrate excellent catalysis performance in the model reaction of 4‐nitrophenol reduction, and remarkable peroxidase‐mimicking activity, which enables a highly sensitive colorimetric sensing of H2O2 with a detection limit of 0.11 × 10−6 m. This work represents the first fabrication of freestanding 2D gold with a sub‐nanometer thickness, opens up an innovative pathway toward atomically‐thin metal nanomaterials that can serve as model systems for inspiring fundamental advances in materials science, and holds potential across a wide region of applications.