Modern Electron Microscopes Research Articles

Electronic tweezers for magnesium oxide nanoparticles

Abstract In this work, we present recent findings regarding the linear momentum transferred from swift electrons, like those typically used in Scanning and Transmission Electron Microscopy, to a magnesium oxide nanoparticle. We performed full-retarded numerical calculations based on Classical Electrodynamics formalism considering the interaction of a single fast electron, which is a good approximation due to the small electric current (tens of pA) involved in modern electron microscopes, with a spherical magnesium oxide nanoparticle. As previously calculated for plasmonic nanoparticles, our results also show that the linear momentum transfer can be either attractive or repulsive for a magnesium oxide nanoparticle, depending on the relevant parameters of the problem: the distance between the electron and the nanoparticle and the electron’s speed. Interestingly, we found that the magnitude of the linear momentum transferred to the nanoparticle lies in the same range as for gold and aluminum nanoparticles. These theoretical results pave the way to consider the possibility of implementing electronic tweezers to manipulate not only metallic nanoparticles.

Restructuring in high burnup UO2 studied using modern electron microscopy

Modern electron microscopy techniques were used to conduct a thorough study of an irradiated urania fuel pellet microstructure to attempt at an understanding of high burnup structure formation in this material. The fuel was irradiated at low power to high burnups in a light water reactor, proving ideal for this purpose. Examination of grain size and orientation with strict spatial selectivity across the fuel pellet radius allowed for capturing the progression of the restructuring process, from its onset to full completion. Based on this information, the polygonization mechanism was shown to be responsible for restructuring, involving formation of low-angle grain boundaries with their initiation occurring at the original high-angle grain boundaries of the as-fabricated pellet and at the gas bubble-matrix interfaces. The low-angle character of boundaries between the subdivided grains disappeared in the fully developed high burnup structure, likely due to creep deformation in the pellet.

A Way to New Smart Materials – Hierarchical 3D Structures Produced Via Self-Organization of Nanowires

Galina Strukova, Gennady Strukov The beauty of these pictures is intriguing and fascinating by its asymmetric, exquisite and intricate pattern. What is it? Is it a product of a novel computer program or photographs of fine creations of nature? Neither statement is true. In fact, these are not pictures, but images of metal samples made with an electron microscope. Only some color is added to the images to emphasize their resemblance to natural objects of our macroworld: seashells, jelly-fish, leaves of exotic plants. The size of the samples is varied in micron scale. They are produced via self-organization of nano-sized (millionth of a millimeter) wires growing on porous membranes under the action of electric current pulses. This is how such volumetric (3D) sculptures are described in scientific journals [1- 3] along with the experimental conditions for their reproduction, i.e., the conditions of the process (electrolyte composition, porous membrane, pulsed current mode) are specified, when growing nanowires organize themselves in an inexplicable fashion into “sculptures” that show perfect resemblance to natural creations. The authors have managed to isolate and photograph them with a modern electron microscope. Besides, they have proved that the internal structure of this metallic “seashells” is a volumetric multilayer network woven by nano-sized wires. Such antenna-like samples are expected to find application in nanotechnology as new materials for different applications. Now we produce such “sculptures” from various metals “by order”, examine their magnetic properties, study their interaction with plasma and focused electron beam, look for a field of their application and admire their elegant forms. However, it is still a riddle. Why do they so closely resemble shells and leaves? Does this mysterious self-organization have anything in common with formation of plant leaves and seashells? [1] J of Bionic Engineering 10 (2013) 368–376 [2] Materials Today 16 (2013) 98–99 , [3] Materials Letters, 128 (2014) 212-215. Figure 1

Collection efficiency and acceptance maps of electron detectors for understanding signal detection on modern scanning electron microscopy.

Collection efficiency and acceptance maps of typical detectors in modern scanning electron microscopes (SEMs) were investigated. Secondary and backscattered electron trajectories from a specimen to through-the-lens and under-the-lens detectors placed on an electron optical axis and an Everhart-Thornley detector mounted on a specimen chamber were simulated three-dimensionally. The acceptance maps were drawn as the relationship between the energy and angle of collected electrons under different working distances. The collection efficiency considering the detector sensitivity was also estimated for the various working distances. These data indicated that the acceptance maps and collection efficiency are keys to understand the detection mechanism and image contrast for each detector in the modern SEMs. Furthermore, the working distance is the dominant parameter because electron trajectories are drastically changed with the working distance.

Evaporation of Gold on NaCl Surfaces as a Way To Control Spatial Distribution of Nanoparticles: Insights on the Shape and Crystallographic Orientation

Herein, the growth of Au nanoparticles on NaCl surfaces as a way to control their spatial distribution is explored, giving new insights into the shape and relative orientation of the resulting nanoparticles through modern electron microscopy techniques. Their morphological features depending on the geometry of the NaCl surface site they nucleated on are described in detail. Also, hitherto unreported small but systematic angular deviations in the range of 1–4° from the exact epitaxial orientation were observed. A theoretical approach based on straightforward elastic energy considerations and yet capable of accounting for the experimental results was developed. The production of metallic nanoparticles is a fundamental subject in the development of nanotechnology, and the fine control of the shape and spatial distribution is an important issue for the applicability of nanoparticles. Furthermore, in spite of the extensive research on this topic, some key features such as the precise mechanism controlling particle shape and particle-substrate orientation are still not well understood as evidenced by the results of this work. Thus, a clear understanding of the role played by the diverse factors involved in epitaxial growth is required to produce nanoparticles with finely tailored properties.

Maximum usable thickness revisited: Imaging dislocations in Si by modern high-voltage scanning transmission electron microscopy

We have quantitatively evaluated the usable thickness of specimens in scanning transmission electron microscopy (STEM) at 1 MV using a wedge-shaped Si(110) single crystal including artificially introduced high-density dislocations. The width of dislocation images was employed as a criterion for the quantitative evaluation of usable thickness. Superior usable thickness in STEM than in TEM was found; the obtained results were 14.7 µm for STEM and 5.8 µm for TEM. In particular, in STEM, dislocations can be observed as thin lines with 10–15 nm width in the thickness range up to 10 µm. The latest high-voltage STEM is useful for imaging crystal defects in thick semiconductors.

Identification of a new injection system

Type 6 Secretion To interact with other cells, bacteria use contractile machines that function similarly to membrane-puncturing bacteriophages. The so-called type 6 secretion system (T6SS) functions from inside a bacterial cell. Bock et al. used modern electron microscopy methods and functional

In situ architecture, function, and evolution of a contractile injection system.

Contractile injection systems mediate bacterial cell-cell interactions by a bacteriophage tail-like structure. In contrast to extracellular systems, the type 6 secretion system (T6SS) is defined by intracellular localization and attachment to the cytoplasmic membrane. Here we used cryo-focused ion beam milling, electron cryotomography, and functional assays to study a T6SS in Amoebophilus asiaticus The in situ architecture revealed three modules, including a contractile sheath-tube, a baseplate, and an anchor. All modules showed conformational changes upon firing. Lateral baseplate interactions coordinated T6SSs in hexagonal arrays. The system mediated interactions with host membranes and may participate in phagosome escape. Evolutionary sequence analyses predicted that T6SSs are more widespread than previously thought. Our insights form the basis for understanding T6SS key concepts and exploring T6SS diversity.

Joint denoising and distortion correction of atomic scale scanning transmission electron microscopy images

Nowadays, modern electron microscopes deliver images at atomic scale. The precise atomic structure encodes information about material properties. Thus, an important ingredient in the image analysis is to locate the centers of the atoms shown in micrographs as precisely as possible. Here, we consider scanning transmission electron microscopy (STEM), which acquires data in a rastering pattern, pixel by pixel. Due to this rastering combined with the magnification to atomic scale, movements of the specimen even at the nanometer scale lead to random image distortions that make precise atom localization difficult. Given a series of STEM images, we derive a Bayesian method that jointly estimates the distortion in each image and reconstructs the underlying atomic grid of the material by fitting the atom bumps with suitable bump functions. The resulting highly non-convex minimization problems are solved numerically with a trust region approach. Existence of minimizers and the model behavior for faster and faster rastering are investigated using variational techniques. The performance of the method is finally evaluated on both synthetic and real experimental data.

Smarter than an iPhone: the emergence of the modern electron microscope

Smarter than an iPhone: the emergence of the modern electron microscope

A Way to New Smart Materials – Hierarchical 3D Structures Produced Via Self-Organization of Nanowires

The beauty of these pictures is intriguing and fascinating by its asymmetric, exquisite and intricate pattern. What is it? Is it a product of a novel computer program or photographs of fine creations of nature? Neither statement is true. In fact, these are not pictures, but images of metal samples made with an electron microscope. Only some color is added to the images to emphasize their resemblance to natural objects of our macroworld: seashells, jelly-fish, leaves of exotic plants. The size of the samples is varied in micron scale. They are produced via self-organization of nano-sized (millionth of a millimeter) wires growing on porous membranes under the action of electric current pulses. This is how such volumetric (3D) sculptures are described in scientific journals [1- 3] along with the experimental conditions for their reproduction, i.e., the conditions of the process (electrolyte composition, porous membrane, pulsed current mode) are specified, when growing nanowires organize themselves in an inexplicable fashion into “sculptures” that show perfect resemblance to natural creations. The authors have managed to isolate and photograph them with a modern electron microscope. Besides, they have proved that the internal structure of this metallic “seashells” is a volumetric multilayer network woven by nano-sized wires. Such antenna-like samples are expected to find application in nanotechnology as new materials for different applications. Now we produce such “sculptures” from various metals “by order”, examine their magnetic properties, study their interaction with plasma and focused electron beam, look for a field of their application and admire their elegant forms. However, it is still a riddle. Why do they so closely resemble shells and leaves? Does this mysterious self-organization have anything in common with formation of plant leaves and seashells? [1] J of Bionic Engineering 10 (2013) 368–376 [2] Materials Today 16 (2013) 98–99 , [3] Materials Letters, 128 (2014) 212-215. Figure 1

The sleeping beauty kissed awake: new methods in electron microscopy to study cellular membranes

Electron microscopy (EM) for biological samples, developed in the 1940-1950s, changed our conception about the architecture of eukaryotic cells. It was followed by a period where EM applied to cell biology had seemingly fallen asleep, even though new methods with important implications for modern EM were developed. Among these was the discovery that samples can be preserved by chemical fixation and most importantly by rapid freezing without the formation of crystalline ice, giving birth to the world of cryo-EM. The past 15-20 years are hallmarked by a tremendous interest in EM, driven by important technological advances. Cryo-EM, in particular, is now capable of revealing structures of proteins at a near-atomic resolution owing to improved sample preparation methods, microscopes and cameras. In this review, we focus on the challenges associated with the imaging of membranes by EM and give examples from the field of host-pathogen interactions, in particular of virus-infected cells. Despite the advantages of imaging membranes under native conditions in cryo-EM, conventional EM will remain an important complementary method, in particular if large volumes need to be imaged.

Graphite oxidation and SEM as a tool for microstructural investigation

The microstructure of graphite and its oxidation have been individually investigated at length. When any catalytic impurities are removed from graphite, oxidative attack takes place preferentially from the exposed edges, or active sites of graphite crystallites. This provides valuable insights regarding the underlying crystallography and fundamental structure of graphite which are not immediately evident from a raw topographical examination using, for example, microscopy. Using new techniques, such as field emission guns and sensitive detectors, modern scanning electron microscopes are capable of operating down to a few hundred volts. When surface features and effects are being considered this is absolutely critical as the low voltages imply low sample penetration of the electrons, thus the true surface morphology of the material can be resolved. In combination, these methods provide a valuable technique for investigating the microstructures found in graphite. The approach has been applied to natural graphite but is even more relevant to synthetic graphite and therefore nuclear materials, which have an exceedingly complex microstructure. The revealed structural qualities can be related to the manufacturing processes in order to gain additional insights into the material and uncover potential options for improving the properties.

Current status and prospects of X-ray microscopy

Design and main constructive features of a new combined device for X-ray electron and X-ray microscopy for nanometer diagnostics are considered in relation to the current status of modern X-ray and electron microscopy.

Complementary High Spatial Resolution Methods in Materials Science and Engineering

This review features the potential of modern high spatial resolution methods in materials science and engineering by presenting a selection of scientific examples covering bulk materials, as well as hard coatings, semiconductors, and mesoporous thin films. Complementary techniques are employed to study microstructure and/or texture and stresses in multiphase Mo‐, Al‐, and Mg‐base alloys, in several nitride‐ and boride‐based hard coatings, in silicon, as well as in mesoporous silica films. Although far from being comprehensive, the chosen examples aim at underlining the importance of modern electron microscopy based methods and of scattering/diffraction techniques at large scale neutron and synchrotron radiation facilities for modern materials research. In addition, atom probe tomography, Raman scattering and atomic force microscopy are also highlighted.

A Multicore Path to Connectomics-on-Demand

The current design trend in large scale machine learning is to use distributed clusters of CPUs and GPUs with MapReduce-style programming. Some have been led to believe that this type of horizontal scaling can reduce or even eliminate the need for traditional algorithm development, careful parallelization, and performance engineering. This paper is a case study showing the contrary: that the benefits of algorithms, parallelization, and performance engineering, can sometimes be so vast that it is possible to solve "cluster-scale" problems on a single commodity multicore machine. Connectomics is an emerging area of neurobiology that uses cutting edge machine learning and image processing to extract brain connectivity graphs from electron microscopy images. It has long been assumed that the processing of connectomics data will require mass storage, farms of CPU/GPUs, and will take months (if not years) of processing time. We present a high-throughput connectomics-on-demand system that runs on a multicore machine with less than 100 cores and extracts connectomes at the terabyte per hour pace of modern electron microscopes.

Structural Study of Heterogeneous Biological Samples by Cryoelectron Microscopy and Image Processing.

In living organisms, biological macromolecules are intrinsically flexible and naturally exist in multiple conformations. Modern electron microscopy, especially at liquid nitrogen temperatures (cryo-EM), is able to visualise biocomplexes in nearly native conditions and in multiple conformational states. The advances made during the last decade in electronic technology and software development have led to the revelation of structural variations in complexes and also improved the resolution of EM structures. Nowadays, structural studies based on single particle analysis (SPA) suggests several approaches for the separation of different conformational states and therefore disclosure of the mechanisms for functioning of complexes. The task of resolving different states requires the examination of large datasets, sophisticated programs, and significant computing power. Some methods are based on analysis of two-dimensional images, while others are based on three-dimensional studies. In this review, we describe the basic principles implemented in the various techniques that are currently used in the analysis of structural conformations and provide some examples of successful applications of these methods in structural studies of biologically significant complexes.

Reflections on the value of electron microscopy in the study of heterogeneous catalysts.

Electron microscopy (EM) is arguably the single most powerful method of characterizing heterogeneous catalysts. Irrespective of whether they are bulk and multiphasic, or monophasic and monocrystalline, or nanocluster and even single-atom and on a support, their structures in atomic detail can be visualized in two or three dimensions, thanks to high-resolution instruments, with sub-Ångstrom spatial resolutions. Their topography, tomography, phase-purity, composition, as well as the bonding, and valence-states of their constituent atoms and ions and, in favourable circumstances, the short-range and long-range atomic order and dynamics of the catalytically active sites, can all be retrieved by the panoply of variants of modern EM. The latter embrace electron crystallography, rotation and precession electron diffraction, X-ray emission and high-resolution electron energy-loss spectra (EELS). Aberration-corrected (AC) transmission (TEM) and scanning transmission electron microscopy (STEM) have led to a revolution in structure determination. Environmental EM is already playing an increasing role in catalyst characterization, and new advances, involving special cells for the study of solid catalysts in contact with liquid reactants, have recently been deployed.

Ultrafast Electron Diffraction Tomography for Structure Determination of the New Zeolite ITQ-58.

In this work a new ultrafast data collection strategy for electron diffraction tomography is presented that allows reducing data acquisition time by one order of magnitude. This methodology minimizes the radiation damage of beam-sensitive materials, such as microporous materials. This method, combined with the precession of the electron beam, provides high quality data enabling the determination of very complex structures. Most importantly, the implementation of this new electron diffraction methodology is easily affordable in any modern electron microscope. As a proof of concept, we have solved a new highly complex zeolitic structure named ITQ-58, with a very low symmetry (triclinic) and a large unit cell volume (1874.6 Å3), containing 16 silicon and 32 oxygen atoms in its asymmetric unit, which would be very difficult to solve with the state of the art techniques.

Exploring Boltzmann-Factor Distributions of Precipitation-Nuclei in the TEM.

For nucleation in the solid-state, modern electron microscopes may allow one to examine pre-critical cluster distributions down to the size-scale of a single misplaced atom. A very specific challenge of this sort arises in the gigascale silicon integrated-circuit device industry, surrounding the important roles that oxygen in Czochralski silicon can play. We indicate here in particular that the number densities and sizes of precritical SiOx clusters in as-grown wafers, as estimated by elementary means, should be possible to quantify with modern techniques, provided that challenges associated with surface noise and thickness estimation can be overcome.