Advanced Electron Microscopy Techniques Research Articles

Crystallization-driven tuneable lasing of perylene doped into the nematic liquid crystal

Versatile devices with tunable capabilities for controlling lasing wavelength and intensity are in high demand. Liquid crystals (LCs) exhibit immense potential for such applications, offering fine-tuning possibilities through external factors. On the other hand, laser technology is currently a research hotspot in optoelectronics, and also in practical applications. The recent market introduction of laser television marks a significant stride toward making such advanced technology accessible in every household. In synergy with laser pumping, the LCs unquestionably can be rediscovered. This study presents a comprehensive investigation into the crystallization phenomenon within a host-guest device, compact in size, free from moving parts, and integrating the liquid crystalline (LC) matrix doped with 3,4,9,10-tetra-(3-alcoxy-carbonyl)-perylene (THCP) dye. The focus lies in examining the influence of varying dye concentrations on multicolor fluorescence, lasing behavior, and device morphology. The systematic analysis of Random Lasing (RL) energy thresholds and the impact of DC voltage on light intensity modulation is demonstrated. Morphological changes were monitored in real-time using optical microscopy techniques, including crossed polarizer, and fluorescence imaging under 450 nm excitation. Utilizing advanced Transmission Electron Microscopy (TEM) techniques, we explore exceptional insights into our set of devices, providing novel information about the THCP crystallization process for the first time in the literature. To gain a comprehensive understanding of the crystal forming and molecular geometry we examined additionally the THCP dye, using X-ray diffraction and Raman spectroscopy. Furthermore, we showcase that varying the pumping energy enables multicolor tuning in the fabricated systems, presenting an attractive feature in the context of laser display technologies.

Visualizing Structure, Growth, and Dynamics of Li Dendrite in Batteries: From Atomic to Device Scales

AbstractThe growth of lithium (Li) dendrites, characterized by construction of internal Li substrate and surface solid electrolyte interphase (SEI), represents a significant hurdle for both liquid‐state and solid‐state Li batteries. To better understand the growth behaviors of these dendrites at atomic to device scale, advanced electron microscopy techniques have emerged as a valuable tool, providing high temporal and spatial resolutions for real‐time observations. In this review, the mechanistic aspects of growth of Li dendrites are delved first from both thermodynamic and kinetic perspectives. Then, a systematic overview of the state‐of‐the‐art in‐situ devices is provided that is developed for integration into electron microscopes, detailing the corresponding static and dynamic structures of Li dendrites. Additionally, the utilization of the non‐destructive cryogenic TEM technique is explored to classify and compare the local fine structure information of as‐formed Li deposits, which are influenced by various factors such as current density, temperature, electrolyte composition, solvents, and additives. Overall, this review article offers a comprehensive understanding of the physical origins associated with Li dendrites, spanning from atomic to device scales and encompassing both liquid and all‐solid‐state battery scenarios, then envisioning fundamental principles and strategies for optimizing batteries and overcoming the critical challenges posed by Li dendrites.

Recent progress about transmission electron microscopy characterizations on lithium-ion batteries

With the rapid development of portable electronics, new energy vehicles, and smart grids, ion batteries are becoming one of the most widely used energy storage devices, while the safety concern of ion batteries has always been an urgent problem to be solved. To develop a safety-guaranteed battery, the characterization of the internal structure is indispensable, where electron microscopy plays a crucial role. Based on this, this paper summarizes the application of transmission electron microscopy (TEM) in battery safety, further concludes and analyzes the aspects of dendrite growth and solid electrolyte interface (SEI) formation that affect the safety of ion batteries, and emphasizes the importance of electron microscopy in battery safety research and the potential of these techniques to promote the future development of this field. These advanced electron microscopy techniques and their prospects are also discussed.

Laser powder bed fusion of pure copper electrodes

This study explores the fabrication and characterization of a pure copper electrode for an EDM equipment using laser powder bed fusion (LPBF) and comparing its performance with an original cast sample. The microstructural, mechanical, electrical, thermal, and corrosion characteristics of the samples were analyzed. The microstructure of the additively manufactured (AM) sample exhibited superior mechanical properties, with an 18 % increase in ultimate tensile strength and more than two times greater elongation in comparison with those of the cast sample. Moreover, the electrical and thermal conductivity coefficients of the AM sample were found to be consistent with industry standards as 5.52 × 107 S/m and 361 W/mK, respectively. Additionally, the potentiodynamic polarization corrosion test results of the AM sample further exhibited superior corrosion resistance in terms of the corrosion potential particularly in a 3.5 % NaCl environment. Advanced electron microscopy techniques were used to investigate the differences in the properties of the AM and cast samples and further shed light on the superior properties of the LPBF counterpart. Despite challenges in manufacturing pure copper components through LPBF, this study demonstrates the feasibility of producing a functional part that competes effectively with cast counterparts and excels in certain aspects.

Deep convolutional neural networks to restore single-shot electron microscopy images

Advanced electron microscopy techniques, including scanning electron microscopes (SEM), scanning transmission electron microscopes (STEM), and transmission electron microscopes (TEM), have revolutionized imaging capabilities. However, achieving high-quality experimental images remains a challenge due to various distortions stemming from the instrumentation and external factors. These distortions, introduced at different stages of imaging, hinder the extraction of reliable quantitative insights. In this paper, we will discuss the main sources of distortion in TEM and S(T)EM images, develop models to describe them, and propose a method to correct these distortions using a convolutional neural network. We validate the effectiveness of our method on a range of simulated and experimental images, demonstrating its ability to significantly enhance the signal-to-noise ratio. This improvement leads to a more reliable extraction of quantitative structural information from the images. In summary, our findings offer a robust framework to enhance the quality of electron microscopy images, which in turn supports progress in structural analysis and quantification in materials science and biology.

Advanced Electron Microscopy Characterisation of Al-O Coordination in Catalyst Supports

Performance of alumina supported catalyst systems are significantly affected by how the tetrahedral (Al-O4) and octahedral (Al-O6) coordination are mixed and blended with each other. Characterisation of Al-O coordination is thus important to understand how catalysts interact with alumina at the microscopic level. Here we report the application of two advanced electron microscopy techniques on Al-O coordination. The first technique is Electron Energy Loss Spectroscopy (EELS) that can reveal detailed electronic structure profile of Al valence band to analyse how Al is coordinated by oxygen. The second technique is Pair Distribution Function (PDF) based on Electron Diffraction (ED), employed to measure Al-O bond lengths associated with the coordination geometry.

Probing Oxidation-Driven Amorphized Surfaces in a Ta(110) Film for Superconducting Qubit.

Recent advances in superconducting qubit technology have led to significant progress in quantum computing, but the challenge of achieving a long coherence time remains. Despite the excellent lifetime performance that tantalum (Ta) based qubits have demonstrated to date, the majority of superconducting qubit systems, including Ta-based qubits, are generally believed to have uncontrolled surface oxidation as the primary source of the two-level system loss in two-dimensional transmon qubits. Therefore, atomic-scale insight into the surface oxidation process is needed to make progress toward a practical quantum processor. In this study, the surface oxidation mechanism of native Ta films and its potential impact on the lifetime of superconducting qubits were investigated using advanced scanning transmission electron microscopy (STEM) techniques combined with density functional theory calculations. The results suggest an atomistic model of the oxidized Ta(110) surface, showing that oxygen atoms tend to penetrate the Ta surface and accumulate between the two outermost Ta atomic planes; oxygen accumulation at the level exceeding a 1:1 O/Ta ratio drives disordering and, eventually, the formation of an amorphous Ta2O5 phase. In addition, we discuss how the formation of a noninsulating ordered TaO1-δ (δ < 0.1) suboxide layer could further contribute to the losses of superconducting qubits. Subsurface oxidation leads to charge redistribution and electric polarization, potentially causing quasiparticle loss and decreased current-carrying capacity, thus affecting superconducting qubit coherence. The findings enhance the comprehension of the realistic factors that might influence the performance of superconducting qubits, thus providing valuable guidance for the development of future quantum computing hardware.

Unlocking the key role of bentonite fungal isolates in tellurium and selenium bioremediation and biorecovery: Implications in the safety of radioactive waste disposal

Research on eco-friendly bioremediation strategies for mitigating the environmental impact of toxic metals has gained attention in the last years. Among all promising solutions, bentonite clays, to be used as artificial barriers to isolate radioactive wastes within the deep geological repository (DGR) concept, have emerged as effective reservoir of microorganisms with remarkable bioremediation potential. The present study aims to investigate the impact of bentonite fungi in the speciation and mobility of selenium (Se) and tellurium (Te), as natural analogues 79Se and 132Te present in radioactive waste, to screen for those strains with bioremediation potential within the context of DGR. For this purpose, a multidisciplinary approach combining microbiology, biochemistry, and microscopy was performed. Notably, Aspergillus sp. 3A demonstrated a high tolerance to Te(IV) and Se(IV), as evidenced by minimal inhibitory concentrations of >16 and >32 mM, respectively, along with high tolerance indexes. The high metalloid tolerance of Aspergillus sp. 3A is mediated by its capability to reduce these mobile and toxic elements to their elemental less soluble forms [Te(0) and Se(0)], forming nanostructures of various morphologies. Advanced electron microscopy techniques revealed intracellular Te(0) manifesting as amorphous needle-like nanoparticles and extracellular Te(0) forming substantial microspheres and irregular accumulations, characterized by a trigonal crystalline phase. Similarly, Se(0) exhibited a diverse array of morphologies, including hexagonal, irregular, and needle-shaped structures, accompanied by a monoclinic crystalline phase. The formation of less mobile Te(0) and Se(0) nanostructures through novel and environmentally friendly processes by Aspergillus sp. 3A suggests it would be an excellent candidate for bioremediation in contaminated environments, such as the vicinity of deep geological repositories. It moreover holds immense potential for the recovery and synthesis of Te and Se nanostructures for use in numerous biotechnological and biomedical applications.

Resolving exit strategies of mycobacteria in Dictyostelium discoideum by combining high-pressure freezing with 3D-correlative light and electron microscopy.

The infection course of Mycobacterium tuberculosis is highly dynamic and comprises sequential stages that require damaging and crossing of several membranes to enable the translocation of the bacteria into the cytosol or their escape from the host. Many important breakthroughs such as the restriction of mycobacteria by the autophagy pathway and the recruitment of sophisticated host repair machineries to the Mycobacterium-containing vacuole have been gained in the Dictyostelium discoideum/M. marinum system. Despite the availability of well-established light and advanced electron microscopy techniques in this system, a correlative approach integrating both methods with near-native ultrastructural preservation is currently lacking. This is most likely due to the low ability of D. discoideum to adhere to surfaces, which results in cell loss even after fixation. To address this problem, we improved the adhesion of cells and developed a straightforward and convenient workflow for 3D-correlative light and electron microscopy. This approach includes high-pressure freezing, which is an excellent technique for preserving membranes. Thus, our method allows to monitor the ultrastructural aspects of vacuole escape which is of central importance for the survival and dissemination of bacterial pathogens.

From Multi- to Single-Hollow Trimetallic Nanocrystals by Ultrafast Heating.

Metal nanocrystals (NCs) display unique physicochemical features that are highly dependent on nanoparticle dimensions, anisotropy, structure, and composition. The development of synthesis methodologies that allow us to tune such parameters finely emerges as crucial for the application of metal NCs in catalysis, optical materials, or biomedicine. Here, we describe a synthetic methodology to fabricate hollow multimetallic heterostructures using a combination of seed-mediated growth routes and femtosecond-pulsed laser irradiation. The envisaged methodology relies on the coreduction of Ag and Pd ions on gold nanorods (Au NRs) to form Au@PdAg core-shell nanostructures containing small cavities at the Au-PdAg interface. The excitation of Au@PdAg NRs with low fluence femtosecond pulses was employed to induce the coalescence and growth of large cavities, forming multihollow anisotropic Au@PdAg nanostructures. Moreover, single-hollow alloy AuPdAg could be achieved in high yield by increasing the irradiation energy. Advanced electron microscopy techniques, energy-dispersive X-ray spectroscopy (EDX) tomography, X-ray absorption near-edge structure (XANES) spectroscopy, and finite differences in the time domain (FDTD) simulations allowed us to characterize the morphology, structure, and elemental distribution of the irradiated NCs in detail. The ability of the reported synthesis route to fabricate multimetallic NCs with unprecedented hollow nanostructures offers attractive prospects for the fabrication of tailored high-entropy alloy nanoparticles.

Computational modeling of grain boundary segregation: A review

Nearly all metals, alloys, ceramics, and their associated composites are polycrystalline in nature, with grain boundaries that separate well-defined crystalline regions that influence materials properties. In all but the most pure elemental systems, intentional solutes or impurities are present and can segregate to, or less commonly away from, the grain boundaries, in turn influencing boundary behavior, their stability, and associated materials properties. In some cases, grain-boundary segregation can also trigger “phase-like” structural transitions that dramatically alter the essential nature of the boundary. With the development of advanced electron microscopy techniques, researchers can directly observe grain-boundary structures and segregation with atomic precision. Despite such spatial resolution, the underlying mechanisms governing grain-boundary segregation remain difficult to characterize. As a result, computational modeling techniques such as density functional theory, molecular dynamics, mesoscale phase-field, continuum defect theory, and others are important complementary tools to experimental observations for studying grain-boundary segregation behavior. These computational methods offer the ability to explore the underlying formation mechanisms of grain-boundary segregation, elucidate complex segregation behavior, and provide insights into solutions to effectively controlling microstructure.

Derivatives of Sri Lankan Vein Graphite: Atomic Scale Study of Graphene Oxide and Reduced Graphene Oxide

Aims: The present study examines the atomic-scale structures of Graphene Oxide (GO) and Reduced Graphene Oxide (RGO). Background: Electron microscopic studies on Sri Lankan vein graphite are considerably less; hence, this study focuses on the atomic-scale study of Sri Lankan vein graphite, using advanced electron microscopic techniques. Objective: The purpose of this research is to utilize the data obtained to explore the multidisciplinary characteristics of graphene to the maximum prospectively. Method: We report an atomic-scale study on Sri Lankan vein graphite (purest) derivatives using advanced electron microscopic techniques, including High-Resolution Transmission Electron Microscope (HRTEM), Scanning Transmission Electron Microscope (STEM), and Electron Energy Loss Spectroscopy (EELS). The present study examines the atomic-scale structures of Graphene Oxide (GO) and Reduced Graphene Oxide (RGO). Result: The results obtained exhibited an inter-atomic layer distance of 3.54 Å for RGO. The EELS study performed with the electron dose optimization for GO and RGO distinguished the differences in the C K edge with the oxygen functionalities. The XPS study confirmed the changes in oxygen functionalities obtained with EELS. Conclusion: The advanced electron microscopic techniques and other molecular spectroscopic analysis techniques allowed us to obtain a comprehensive study on Sri Lankan vein graphene-based structural and chemical features on an atomic scale.

Anisotropic Amorphization and Phase Transition in Na2 Ti3 O7 Anode Caused by Electron Beam Irradiation.

Na2 Ti3 O7 is considered one of the most promising anode materials for sodium ion batteries due to its superior safety, environmental friendliness, and low manufacturing cost. However, its structural stability and reaction mechanism still have not been fully explored. As the electron beam irradiation introduces a similar impact on the Na2 Ti3 O7 anode as the extraction of Na+ ions during the battery discharge process, the microstructure evolution of the materials is investigated by advanced electron microscopy techniques at the atomic scale. Anisotropic amorphization is successfully observed. Through the integrated differential phase contrast-scanning transmission electron microscopy technique and density functional theory calculation, a phase transition pathway involving a new phase, Na2 Ti24 O49 , is proposed with the reduction of Na atoms. Additionally, it is found that the amorphization is dominated by the surface energy and electron dose rate. These findings will deepen the understanding of structural stability and deintercalation mechanism of the Na2 Ti3 O7 anode, providing new insight into exploring the failure mechanism of electrode materials.

Probing the Interface Evolution in Co‐sintered All‐Phosphate Cathode‐Solid Electrolyte Composites

AbstractTo achieve cohesive interfaces of solid components in next‐generation Li‐ion batteries (LIBs) composed of oxide cathodes and solid electrolytes (SEs) high‐temperature sintering is necessary which leads to material degradation and phase decompositions. Thermochemically compatible components can address these issues. In this work, advanced electron microscopy techniques are employed to investigate the structural and chemical evolution taking place at the interfaces between a LiFePO4 (LFP) cathode and an in‐house optimized Li1.3Al0.3Ti1.7(PO4)3 (LATP) SE co‐sintered between 650 °C – 850 °C. While the LFP particles exhibit excellent structural stability, the LATP particles phase transforms at elevated temperatures. At 650 °C, FeLi anti‐site defect is observed at the LFP grain boundaries. Between 750 and 850 °C, the LATP (R‐3c) transforms into two orthorhombic phases (Pbca and Pbcn) of the type Li1.3+xAl0.3FexTi1.7‐x(PO4)3 depending on Fe substitution while forming the cohesive interfaces. The discharge capacity of the composite decreases from 148 mAh g−1 at 650 °C to 130 mAh g‐1 at 850 °C confirming that the new phases are still electrochemically active. This study provides a spatially resolved insight into the formation of cohesive interfaces highlighting the advantage of employing components with similar anionic structures for further improvements in LIBs.

New insights into the microstructure of M2 high-speed steel

In this work, the microstructure of the heat-treated AISI M2 high-speed steel of different initial structural states, wrought and as-cast, was investigated in detail down to the atomic scale, using advanced electron microscopy techniques. Significantly different amount of the secondary carbide particles of a size up to 300 nm in the microstructure of both steels was established and described. In the tempered matrix, the formation of the ultrafine sub-grains with a size in the range of 3–15 nm and the substructure of the α-Fe consisting of nano-sized elongated plates about 200–300 nm in length and 7–30 nm in thickness were proven. Fine dispersions of the secondary hardening carbides along the matrix sub-grain boundaries and inside the carbide clusters were thoroughly investigated and identified as vanadium-rich MC carbide. Extremely fine precipitates at the boundaries of the nano-sized elongated plates in the substructure of the tempered α-Fe were revealed in both steels. The precipitates, regularly dispersed in the tempered matrix and containing carbon, were enriched primarily in iron, molybdenum, chromium, vanadium, and, to a lesser extent, in tungsten, as proven by the combined EDX and EELS analysis. At the atomic scale, the precipitates were found to be mostly disordered solids without a crystalline structure. However, some of the precipitates exhibited traces of crystalline structure, which likely corresponds to Fe21(W,Mo)2C6 phase.

A Stunt of Sustainability: Artificial humic substances can generate and stabilize single Fe(0) species on mineral surfaces.

Iron species are omnipresent in fertile soils and contribute to biological and geological redox processes. Here, we show by advanced electron microscopy techniques that an important, but previously not considered iron species, single atom Fe(0) stabilized on clay mineral surfaces, is contained in soils when humic substances are present. As the concentration of neutral iron atoms is highest under frost logged soil conditions, their formation can be attributed to the action of a then reductive microbiome. The Fe0/Fe2+ couple is with -0.04 Volt standard potential highly suited for natural environmental remediation and detoxification, and its occurrence can help to explain the sustained auto-detoxification of black soils.

Gram-Scale Continuous Flow Synthesis of Silver-on-Silica Patchy Nanoparticles with Widely Tunable Resonances for Plasmonics Applications

Extensive research has been conducted on colloids that incorporate nanostructured noble metals, motivated in particular by their highly tunable optical properties. However, the lack of approaches that offer reproducibility, tunability, and scalable production is limiting their exploitation in many application areas. Here, we present an innovative process for the controlled formation of silver patches on silica nanospheres using gold nanocrystal seeds. The synthesis of the seeds and their attachment in very small numbers to the silica spheres is achieved without employing any surfactants, stabilizers, or linker molecules. Using advanced transmission electron microscopy techniques, we show that electroless deposition of nanostructured silver occurs at the introduced seeds and leads to a central protrusion from the metal patches not observed in earlier, seed-free work. We demonstrate that both seeding and growth processes can be achieved in millimixer flow reactors. With this simple and scalable approach, we provide compelling evidence for the use of seeds in producing targeted morphology and function. Specifically, patch size and optical properties can be tailored in a predictive manner by adjusting the density of seeds on the silica nanospheres as well as reagent concentrations during growth. As a result, our process can be used to obtain colloidal dispersions with localized surface plasmon resonance peaks anywhere in the range 400 to nearly 1300 nm. We confirm the scalability of our method by operating the growth process for around 70 min. Apart from changes in the first few minutes, the product properties remained rather stable and over a gram of high quality silver patch-coated silica could be recovered. Our approach opens up exciting new avenues for plasmonics applications, which typically require large amounts of nanoparticles with specifically designed optical properties. These include color and IR pigments, photocatalysts, and as light management components in optoelectronic devices like photovoltaic cells.

Elemental mapping of human teeth enamel, dentine and cementum in view of their microstructure

This paper presents a detailed analysis to directly compare the morphology and chemistry of human tooth layers using advanced scanning electron microscopy (SEM) techniques together with supporting data from energy dispersive spectroscopy (EDS) measurements. The aim of this study was to visualise and evaluate the structural and microanalytical differences of the mineralised hard tissues of human teeth. The extracted sound teeth without any pathologies were divided into the following groups: incisors, canines, premolars, and molars. Tooth samples were broken vertically to preserve the primary structures and to visualise individual tooth tissues. Specimens were also used to find variations in the elemental composition of tissues for different tooth groups. The average thickness of the enamel in the tooth groups studied was 1.1 mm and the average width of the enamel prisms was 4.2 µm, with the highest values observed for molars. The analysis of the chemical composition of the enamel showed that Ca and P were among the predominant elements. The average dentine thickness was 1.87 mm, with the highest values determined for molars, and the lowest for canines. The width of the dentinal tubules was less than 2 µm, for molars being significantly smaller. The analysis of the chemical composition of the dentine showed the highest O content of the all tooth tissues analyzed, while a lower P and Ca content was observed compared to the enamel. The cementum thickness averaged 0.14 mm, with the highest values observed for molars and the lowest for incisors. The analysis of the chemical composition of the cementum showed the lowest average O and P content, and the highest average C and N content, compared to the enamel and the dentine. Increasingly accurate imaging and analysis of dental hard tissue structures provides the opportunity for multifactorial evaluation in terms of their clinical application.

The role of the strengthening phases on the HAZ liquation cracking in a cast Ni-based superalloy used in industrial gas turbines

This work presents the influence of microstructural constituents on liquation crack formation in the cast Ni-based superalloy, René 108. The investigation was divided into three parts: characterisation of the material's microstructure in pre-weld condition, hot ductility studies and analysis of liquation cracking induced by the gas tungsten arc welding process. Using advanced electron microscopy techniques it is shown that the base material in pre-weld condition is characterised by a complex microstructure. The phases identified in René 108 include γ matrix, γ' precipitates, MC and M23C6 carbides, and M5B3 borides. Based on Gleeble testing, it was found that René 108 is characterised by high strength at elevated temperatures with a maximum of 1107 MPa at 975 °C. As a result of constitutional liquation, the superalloy’s strength and ductility were significantly reduced. The nil strength temperature was equal to 1292 °C, while the nil ductility temperature was 1225 °C. The low ductility recovery rate (32.1), ratio of ductility recovery (36.2) and hot cracking factor (Rf = 0.05) values confirmed the low weldability of Renѐ 108. In the heat-affected zone (HAZ) induced by welding, constitutional liquation of mainly γ' precipitates, with a contribution of M23C6 carbides and M5B3 borides, was observed. The thin non-equilibrium liquid film, which formed along high-angle grain boundaries, led to crack initiation and their further propagation during cooling. The eutectic γ–γ' re-solidification products are visible on the crack edges.

Exploring the Nanoscale Origin of Performance Enhancement in Li1.1Ni0.35Mn0.55O2 Batteries Due to Chemical Doping

AbstractDespite significant potential as energy storage materials for electric vehicles due to their combination of high energy density per unit cost and reduced environmental and ethical concerns, Co‐free lithium ion batteries based on layered Mn oxides presently lack the longevity and stability of their Co‐containing counterparts. Here, a reduction in this performance gap is demonstrated via chemical doping, with Li1.1Ni0.35Mn0.54Al0.01O2 achieving an initial discharge capacity of 159 mAhg−1 at C/3 rate and a corresponding capacity retention of 94.3% after 150 cycles. The nanoscale origins of this improvement are subsequently explored through a combination of advanced diffraction, spectroscopy, and electron microscopy techniques, finding that optimized doping profiles lead to an improved structural and chemical compatibility between the two constituent sub‐phases that characterize the layered Mn oxide system, resulting in the formation of unobstructed lithium ion pathways between them. A structural stabilization effect of the host compound is also directly observed near the surface using aberration corrected scanning transmission electron microscopy and integrated differential phase contrast imaging.