Development Of Transmission Electron Microscopy Research Articles

Quantum-Coherent Light-Electron Interaction in a Scanning Electron Microscope.

The last two decades experimentally affirmed the quantum nature of free electron wave packets by the rapid development of transmission electron microscopes into ultrafast, quantum-coherent systems. So far, all experiments were restricted to the bounds of transmission electron microscopes enabling one or two photon-electron interaction sites. We show the quantum coherent coupling between electrons and light in a scanning electron microscope, at unprecedentedly low, subrelativistic energies down to 10.4keV. These microscopes not only afford the yet-unexplored energies from ∼0.5 to 30keV providing the optimum electron-light coupling efficiency, but also offer spacious and easily configurable experimental chambers for extended, cascaded optical set ups, potentially boasting thousands of photon-electron interaction sites. Our results make possible experiments in electron wave packet shaping, quantum computing, and spectral imaging with low-energy electrons.

Atomic-resolution protein structure determination by cryo-EM.

Single-particle electron cryo-microscopy (cryo-EM) is a powerful method for solving the three-dimensional structures of biological macromolecules. The technological development of transmission electron microscopes, detectors and automated procedures in combination with user-friendly image processing software and ever-increasing computational power have made cryo-EM a successful and expanding technology over the past decade1. At resolutions better than 4Å, atomic model building starts to become possible, but the direct visualization of true atomic positions in protein structure determination requires much higher (better than 1.5Å) resolution, which so far has not been attained by cryo-EM. The direct visualization of atom positions is essential for understanding the mechanisms of protein-catalysed chemical reactions, and for studying how drugs bind to and interfere with the function of proteins2. Here we report a 1.25Å-resolution structure of apoferritin obtained by cryo-EM with a newly developed electron microscope that provides, to our knowledge, unprecedented structural detail. Our apoferritin structure has almost twice the 3D information content of the current world record reconstruction (at 1.54Å resolution3). We can visualize individual atoms in a protein, see density for hydrogen atoms and image single-atom chemical modifications. Beyond the nominal improvement in resolution, we also achieve a substantial improvement in the quality of the cryo-EM density map, which is highly relevant for using cryo-EM in structure-based drug design.

Transmission imaging on a scintillator in a scanning electron microscope

Large area electron microscopy (EM) imaging has long been difficult due to fundamental limits in throughput for conventional electron microscopes. New developments in transmission electron microscopy and multi-beam scanning electron microscopy (MBSEM) imaging have however made it possible to generate large EM datasets [1,2,3]. This article describes a transmission imaging technique that is suitable for a MBSEM as it allows for a relatively straightforward way of separating the signals generated by each beam. The technique places a thin (50nm-200nm) tissue section directly on top of a coated scintillator. The electrons that are transmitted through the section generate light in the scintillator which is collected by a high NA objective and imaged onto a photon detector. This article gives a model for the contrast-to-noise (CNR) and signal-to-noise (SNR) ratio that is to be expected for this imaging technique. These parameters were calculated using Monte-Carlo simulations. It was found that the CNR increases when decreasing landing energy and SNR increases with increasing landing energy. These two trends cause that there is an intermediate energy where imaging performance is best. The energy of this optimum was calculated for various levels of heavy metal staining, section thickness, coating material, coating thickness and light collection efficiency. The model was verified experimentally on a synthetic sample.

The chronicles of coronaviruses: the bronchitis, the hepatitis and the common cold

Coronaviruses first appeared as chicken virus that cause respiratory disease. Historical reconsideration tells that coronavirus infection originated in the early 20th century. The first definitive account of the infection was given by Arthur Schalk and Merle Fawn in 1931 as a “new respiratory disease of baby chicks.” Leland Bushnell and Carl Brandly established virus as the causative agent in 1933 and was called infectious bronchitis virus (IBV), which eventually became the coronavirus type species. An apparently unrelated viral infection was discovered from laboratory mice in 1949 as JHM that caused encephalomyelitis and another in 1951 as mouse hepatitis virus (MHV). Study in the 1960s of viruses causing common colds in humans revealed unusual human viruses (designated B814 and 229E as the sample codes). Development of transmission electron microscopy enabled structural visualisation for the first around time ­and with startling revelation – IBV, MHV, B814 and 229E were fundamentally the same virus having characteristic halo around the spherical viral core, a reminisce of solar corona for which they get a new name, coronaviruses, in 1968. The available historical records are incomplete and sometimes inaccurately represented, and this article attempt to mend the flaws whilst giving a more detailed account.

Imaging reactive surface water

Surface Microscopy Recent developments in transmission electron microscopy (TEM) have enabled imaging of single atoms, but adsorbed gas molecules have proven more challenging because of a lack of sufficient image contrast. Yuan et al. adsorbed water and carbon dioxide (CO2) on a reconstructed nanocrystalline anatase titanium dioxide (TiO2) surface that has protruding TiO3 ridges every four unit cells, which provide regions of distinct contrast. Water adsorption on this surface during environmental TEM experiments led to the formation of twinned protrusions. These structures developed dynamic contrast as the water reacted with coexposed CO2 to form hydrogen and carbon monoxide. Science , this issue p. [428][1] [1]: /lookup/doi/10.1126/science.aay2474

Transmission electron microscopy of cellulose. Part 1: historical perspective

Following the first electron micrographs of cotton in 1940, the development of transmission electron microscopy applied to native cellulose has been evolving in a series of successive advances. At first, faced with the weak contrast of the early images, the operators had to use specific electron-dense contrasting agents to reveal the ultrastructure of their samples. It was thus found that all native celluloses consisted of microfibrils, with some size variations depending on the sample origin. Following this, a major advance was achieved when the electron microscopes could be adjusted with low electron doses, allowing the recording of diffraction diagrams from the electron beam-sensitive cellulose samples. Under these conditions, one could obtain information of cellulose itself and not, as before, of the contrasting agent. This important development applied to microdiffraction conditions revealed that some large cellulose microfibrils could yield spot diagrams typical of single crystals. Their recording led to a decisive progress for resolving the molecular and crystal structure of the two cellulose allomorphs, cellulose Iα and Iβ. Using various combinations of diffracted beams to create the images, the so called “diffraction contrast images” could then be developed. These micrographs showed many aspects of the crystalline core of cellulose, including spectacular high-resolution images showing the molecular planes of cellulose in their crystalline environment. Today, electron diffraction, diffraction contrast imaging and low-dose electron microscopy have become major tools to follow the effect of various physical, chemical and biochemical processes at the cellulose crystalline level.

Introduction to high-resolution cryo-electron microscopy

For many years two techniques have dominated structural biology - X-ray crystallography and NMR spectroscopy. Traditional cryo-electron microscopy of biological macromolecules produced macromolecular reconstructions at resolution limited to 6-10 Å. Recent development of transmission electron microscopes, in particular the development of direct electron detectors, and continuous improvements in the available software, have led to the "resolution revolution" in cryo-EM. It is now possible to routinely obtain near-atomic-resolution 3D maps of intact biological macromolecules as small as ~100 kDa. Thus, cryo-EM is now becoming the method of choice for structural analysis of many complex assemblies that are unsuitable for structure determination by other methods.

Cryo-fixation and associated developments in transmission electron microscopy: a cool future for nematology

At present, the importance of sample preparation equipment for electron microscopy represents the driving force behind major breakthroughs in microscopy and cell biology. In this paper we present an introduction to the most commonly used cryo-fixation techniques, with special attention paid towards high-pressure freezing followed by freeze substitution. Techniques associated with cryo-fixation, such as immunolocalisation, cryo-sectioning, and correlative light and electron microscopy, are also highlighted. For studies that do not require high resolution, high quality results, or the immediate arrest of certain processes, conventional methods will provide answers to many questions. For some applications, such as immunocytochemistry, three-dimensional reconstruction of serial sections or electron tomography, improved preservation of the ultrastructure is required. This review of nematode cryo-fixation highlights that cryo-fixation not only results in a superior preservation of fine structural details, but also underlines the fact that some observations based on results solely obtained through conventional fixation approaches were either incorrect, or otherwise had severe limitations. Although the use of cryo-fixation has hitherto been largely restricted to model organisms, the advantages of cryo-fixation are sufficiently self-evident that we must conclude that the cryo-fixation method is highly likely to become the standard for nematode fixation in the near future.

Setting up a nanolab inside a transmission electron microscope for two-dimensional materials research

Abstract

Strain mapping of semiconductor specimens with nm-scale resolution in a transmission electron microscope

The last few years have seen a great deal of progress in the development of transmission electron microscopy based techniques for strain mapping. New techniques have appeared such as dark field electron holography and nanobeam diffraction and better known ones such as geometrical phase analysis have been improved by using aberration corrected ultra-stable modern electron microscopes. In this paper we apply dark field electron holography, the geometrical phase analysis of high angle annular dark field scanning transmission electron microscopy images, nanobeam diffraction and precession diffraction, all performed at the state-of-the-art to five different types of semiconductor samples. These include a simple calibration structure comprising 10-nm-thick SiGe layers to benchmark the techniques. A SiGe recessed source and drain device has been examined in order to test their capabilities on 2D structures. Devices that have been strained using a nitride stressor have been examined to test the sensitivity of the different techniques when applied to systems containing low values of deformation. To test the techniques on modern semiconductors, an electrically tested device grown on a SOI wafer has been examined. Finally a GaN/AlN superlattice was tested in order to assess the different methods of measuring deformation on specimens that do not have a perfect crystalline structure. The different deformation mapping techniques have been compared to one another and the strengths and weaknesses of each are discussed.

Measuring three-dimensional positions of atoms to the highest accuracy with electrons

Abstract Recent developments in transmission electron microscopy (TEM) have pushed lateral spatial resolution to well below 1 A. For selected perfect crystal structures, this allows atomic columns to be identified along several crystallographic orientations. Measuring the three-dimensional position of every atom within a TEM specimen, called by some the holy grail of electron microscopy, seems therefore within reach. In this paper, we will discuss recent approaches to this problem and present our own dose-efficient approach that is based on the direct inversion of multiple electron scattering within the sample and that can be applied to various coherent detection schemes, such as high-resolution TEM, confocal scanning TEM, or ptychography. One particular advantage of this approach is that data for only a very limited range of specimen tilt angles is required, and that it can handle the highly dynamical scattering associated with lower electron beam energy.

Direct observation of Pt nanocrystal coalescence induced by electron-excitation-enhanced van der Waals interactions

Nanocrystal coalescence has attracted paramount attention in nanostructure fabrication in the past decades. Tremendous endeavor and progress have been made in understanding its mechanisms, benefiting from the development of transmission electron microscopy. However, many mechanisms still remain unclear, especially for nanocrystals that lack a permanent dipole moment standing on a solid substrate. Here, we report an in situ coalescence of Pt nanocrystals on an amorphous carbon substrate induced by electron-excitationenhanced van der Waals interactions studied by transmission electron microscopy and first principles calculations. It is found that the electron-beam-induced excitation can significantly enhance the van der Waals interaction between Pt nanocrystals and reduce the binding energy between Pt nanocrystals and the carbon substrate, both of which promote the coalescence. This work extends our understanding of the nanocrystal coalescence observed in a transmission electron microscope and sheds light on a potential pathway toward practical electronbeam-controlled nanofabrication.

In situ experimental mechanics of nanomaterials at the atomic scale

Sub-micron and nanostructured materials exhibit high strength, ultra-large elasticity and unusual plastic deformation behaviors. These properties are important for their applications as building blocks for the fabrication of nano- and micro-devices as well as for their use as components for composite materials, high-strength structural and novel functional materials. These nano-related deformation and mechanical behaviors, which are derived from possible size and dimensional effects and the low density of defects, are considerably different from their conventional bulk counterparts. The atomic-scale understanding of the microstructural evolution process of nanomaterials when they are subjected to external stress is crucial for understanding these ‘unusual’ phenomena and is important for designing new materials, novel structures and applications. This review presents the recent developments in the methods, techniques, instrumentation and scientific progress for atomic-scale in situ deformation dynamics on nanomaterials, including nanowires, nanotubes, nanocrystals, nanofilms and polycrystalline nanomaterials. The unusual dislocation initiation, partial-full dislocation transition, crystalline–amorphous transitions and fracture phenomena related to the experimental mechanics of the nanomaterials are reviewed. Current limitations and future aspects using in situ high-resolution transmission electron microscopy of nanomaterials are also discussed. A new research field of in situ experimental mechanics at the atomic scale is thus expected. The properties of a material depend not only on its composition but also on the exact arrangement of its atoms. In particular, nanostructured materials such as nanotubes, nanocrystals or polycrystalline materials are much stronger and more elastic than their bulk counterparts and exhibit different plastic deformations, making them suitable for a variety of applications. Lihua Wang and co-workers review how recent developments in transmission electron microscopy (TEM) techniques enable materials scientists to characterize, at the atomic scale, both the chemical composition of a nanomaterial and its deformation dynamics under stress and strain, in situ, and in real time. Some possible pitfalls and challenges remain — for example, over-irradiation with the TEM electron beam may damage the sample studied, and observations must typically be carried out under vacuum — but such detailed characterization provides a good understanding of the mechanisms at play. It therefore holds promise for the control of the mechanical, but also chemical and physical, properties of nanostructured materials through the application of stress or strain. Nanostructured materials always exhibit high strength, ultra-large elasticity and unusual plastic deformation behaviors. The atomic-scale understanding of the microstructure evolution process of nanomaterials when they are subjected to external stress is crucial for understanding these ‘unusual’ phenomena and is important for designing new materials and applications. In situ transmission electron microscopy (TEM) experiments provide the possibility for direct observation of the deformation mechanisms at the atomic scale. This review presents the recent developments of techniques and scientific progress for the atomic-scale in situ TEM deformation dynamics on nanomaterials. Current limitations and future aspects are also discussed.

Imaging electron detectors for low-voltage TEM

There is an increasing effort for the development of transmission electron microscopes operating at accelerating voltages of less that 100 kV, down to 20 kV. This work aims to clarify if the technology of conventional indirect scintillator-CCD cameras is suitable to record images formed with electrons of such low energy and how its performance compare to that of novel direct silicon imaging detectors. The performance of these imaging detectors is discussed in terms of modulation transfer function and detective quantum efficiency. It is demonstrated that whilst the performance of conventional scintillator-CCDs improves as the electron energy is dropped, it then peaks at 70 keV and then drops again. Optimum imaging performance at even lower energies is expected for the novel directly exposed detectors, which are capable of near 100% detective quantum efficiency at very low electron energies.

Chromatic correction: a revolution in electron microscopy?

When the development of correctors started in the 1970s, chromatic correction was already the main goal. The first corrector that could improve the resolution of an electron microscope was a chromatic corrector for a scanning electron microscope. Within the last three decades, the development of transmission electron microscopes (TEMs) was to a large extent driven by the attempt to improve the resolution in the presence of chromatic aberration. The major technical developments were high acceleration voltages, highly excited objective lenses with short focal length and field emission guns. Meanwhile, chromatic correction has reached the TEM world. Now, the question arises as to whether chromatic correction will make some of the aforementioned developments obsolete for high-resolution TEM, thereby opening up new imaging possibilities, which are nowadays prevented by instrument constraints. We show some examples for a 0.1 nm resolution TEM with unconventional microscope designs: very low voltages, far-field objective lenses and inexpensive electron guns.

Real space maps of atomic transitions

Considering the rapid technical development of transmission electron microscopes, we investigate the possibility to map electronic transitions in real space on the atomic scale. To this purpose, we analyse the information carried by the scatterer's initial and final state wave functions and the role of the different atomic transition channels for the inelastic scattering cross section. It is shown that the change in the magnetic quantum number in the transition can be mapped. Two experimental set-ups are proposed, one blocking half the diffraction plane, the other one using a cylinder lens for imaging. Both methods break the conventional circular symmetry in the electron microscope making it possible to detect the handedness of electronic transitions as an asymmetry in the image intensity. This finding is of important for atomic resolution energy-loss magnetic chiral dichroism (EMCD), allowing to obtain the magnetic moments of single atoms.

Close Look to the Nanoworld

One of the first high-performance Libra 200 FE-type electron microscopes (Carl Zeiss SMT AG) was inaugurated on 1st December 2005 in Munster. The one day-event took place at the lecture hall 2 of the IGI-physics building, University of Munster, Germany. Professor K. Urban (Research Centre Julich, Head of IFF-Institute and Ernst Ruska-Centre for Microscopy) contributed to the colloquium by an excellent lecture. He reviewed the imaging limitations in transmission electron microscopy with a detailed look on the aberration correction. The second lecture was held by Professor F. Hofer, Austrian Centre for Electron Microscopy and Nanoanalysis, Graz University of Technology. New developments in transmission electron microscopy were discussed in his outstanding presentation.

New Developments in Transmission Electron Microscopy for Nanotechnology

AbstractFor Abstract see ChemInform Abstract in Full Text.

New Developments in Transmission Electron Microscopy for Nanotechnology

AbstractHigh‐resolution transmission electron microscopy (HRTEM) is one of the most powerful tools used for characterizing nanomaterials, and it is indispensable for nanotechnology. This paper reviews some of the most recent developments in electron microscopy techniques for characterizing nanomaterials. The review covers the following areas: in‐situ microscopy for studying dynamic shape transformation of nanocrystals; in‐situ nanoscale property measurements on the mechanical, electrical and field emission properties of nanotubes/nanowires; environmental microscopy for direct observation of surface reactions; aberration‐free angstrom‐resolution imaging of light elements (such as oxygen and lithium); high‐angle annular‐dark‐field scanning transmission electron microscopy (STEM); imaging of atom clusters with atomic resolution chemical information; electron holography of magnetic materials; and high‐spatial resolution electron energy‐loss spectroscopy (EELS) for nanoscale electronic and chemical analysis. It is demonstrated that the picometer‐scale science provided by HRTEM is the foundation of nanometer‐scale technology.

In-Situ Ion Milling in the Transmission Electron Microscope (TEM) Outlook to a New Preparation Technique

Recent developments in transmission electron microscopy put high demands on specimen preparation. in general the imaging quality is not limited by the performance of the microscope but by the quality of the specimen. in order to achieve a spatial resolution of 0.1 nm in HRTEM undamaged samples with a thickness below 10 nm are required. in energy filtering analytical electron microscopy (EFTEM), a constant specimen thickness over large areas and very low contamination is needed.Conventional ion-milling techniques for TEM specimen preparation are essentially blind. Thus, it is left to chance whether the specimen detail of interest is suitable for TEM-imaging (many specimen areas are too thick). Another problem is the reaction of the specimen with the atmosphere during the transfer from the preparation stage to the microscope, which makes it very difficult to obtain the clean specimen surfaces that are needed in analytical EFTEM. Especially in high-resolution electron microscopy and electron holography the formation of amorphous oxidation and contamination layers on otherwise crystalline materials may seriously reduce the quality of high resolution images of the crystal structure.