bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of Single Particle Methods to Reconstruct Helical Reca and F-Actin Filaments
Authors: Egelman EH , Orlova A , Yu X
Published: July 2020

RecA has been the most intensively studied enzyme in homologous genetic recombination. Actin is one of the most abundant and conserved eukaryotic proteins, and is central to muscle contraction, cell motility, and the control of cell shape. Both form helical filaments, and we have been studying both for many years, primarily using negatively stained specimens. We and others have used cryo-EM of frozen-hydrated RecA and F-actin samples, but the resolution obtained by this method is actually worse than that obtained from negatively stained specimens. The criterion for resolution that we have used is the match with an atomic model for F-actin, since this is a much better standard than statistical measures such as Fourier ring correlations or phase residuals, which can only measure the internal consistency of the data.

F-actin is a flexible structure, both with respect to bending and torsional motions of subunits. The RecA filament is 10 times more flexible than F-actin. The bending of RecA and F-actin require that images be straightened, and the ability of a user to fit a spline function to the filament axis limits the precision of the method. The method is only valid for small perturbations from a rigid rod, and thus will introduce artifacts for real filaments. In order to straighten filament images obtained in ice, one needs sufficient contrast (obtained by a large defocus) to be able to apply such algorithms. The torsional motions of the actin subunits, which may be as large as 5-6° per subunit, limit the resolution that can be obtained as one averages over long lengths.
Imaging Considerations for Cryo-Tomography of Organelles and Whole Cells at High Accelerating Voltage
Authors: Marko M , Hsieh C-E , Mannella CA , McEwen BF
Published: July 2020

Cryo-electron tomography can be used to obtain highly-detailed 3-D reconstructions of micrometer-sized biological structures which are unfixed, unstained and embedded in vitreous ice. Important practical considerations for acquiring the requisite tilt-series images are the choice of electron dose and defocus value, and the effects of contamination and ice thickness.

It is essential to reduce the total dose enough to prevent excessive ice radiolysis and damage to the specimen itself. To reduce the dose, a sensitive cooled CCD camera and microscope automation system are all but required. Because the specimens are thick, it is advantageous to use a high accelerating voltage, and/or energy filtering to reduce inelastic scattering. At high accelerating voltage, it is important to keep the dose high enough so that the signal is above the “scintillator noise” generated by the interaction of the high-energy electrons with the phosphor scintillator of the CCD camera. Initial test reconstructions indicate that scintillator noise, unlike electron shot noise, cannot be mitigated using dose fractionation. Fortunately, we find that large objects embedded in a thick (ca. 1 μm) vitrified ice layer are more resistant to beam damage (as well as charging) compared to smaller objects embedded in ice 100-200nm thick.
FESEM and Cryo-Techniques in the Study of Marine Diatom A. Longipes
Authors: Chen Ya , Wang Yan , Gretz Michael
Published: July 2020

Field emission scanning electron microscopy (FESEM) provides a direct view of a biological sample with high spacial resolution. Combining FESEM with cryo-techniques, macromolecular structures have been obtained from single SEM image successfully (Hermann & Müller, 1992; Chen et al., 1995, 1997). This protocol is now applied to study the extracellular matrix of the diatom A. longipes.

Stalk, which is originated from the terminal region of diatom cells, consists of 3 regions: a surfaceadhered pad, a shaft that separates the cell from the substratum, and a ring-like collar (Fig. 1). Investigating the structure and function of the stalk will help to understand the adhesion and interaction of diatom with the external environment. The extracellular matrix of diatom is highly hydrated, it is difficult to preserve them for EM. It will be easily extracted and collapse during specimen preparation (e.g. fixation, dehydration). In order to preserver the stalk structures close to their native condition and observer them with high fidelity, cryo-preparation techniques are implemented. Cryo-technique is widely used in the plant biology. However, to our knowledge, it has not been used in the diatom research.
Nuclear Envelope and Nuclear Pore Complex Dynamjcs in vitro, Visualised by FEISEM
Authors: Allen TD , Cotter LA , Cronshaw JM , Wilson KL , Goldberg MW
Published: July 2020

As the defining structure in eukaryote cells, the nuclear envelope is completely dismantled and reformed within an hour or so at each cell division (open mitosis). In yeast and some insect tissues, closed mitosis occurs, in which the nuclear envelope is maintained largely intact throughout chromosome separation. Use of cell free systems has allows us access to the mechanisms of cell division and NE dynamics in vitro by FEISEM (Field Emission In Lens Scanning Electron Microscopy. We have used demembranated Xenopus sperm heads as a source of DNA, which is incubated in an extract of Xenopus egg cytoplasm, where it becomes assembled into a normal nucleus with functional nuclear envelope (1-4). DNA replication proceeds under normal cell cycle controls, followed by an in vitro mitosis in suitable conditions. The cytoplasmic extract can be separated into membrane and soluble fractions that can be supplemented with, or depleted of, specific proteins. Inhibitors and other effectors can be.added to modulate both assembly and transport (5). Using the lectin WGA we have depleted Xenopus cytoplasmic extract of the major nucleoporins, CAN, Nup 98 and p62 and their associated proteins, whose removal effectively inhibits three aspects of nuclear formation, namely NPC formation, nuclear growth, and the reorganisation of the DNA in the depleted nuclei. Adding back these eluted nucleoporins restores normality with respect to nuclear growth, DNA reorganisation and NPC assembly. Current work involves purification of complexes containing these proteins by HPLC to allow add back of the complexes singly and in combination, to characterise their individual roles in NPC assembly, structure and transport (Figures 1,2,3).
High-Pressure Frozen Mouse Lung: Cryo Scanning Electron Microscopy
Authors: Bastacky Jacob , Walther Paul , Goerke Jon , Clausnitzer Eve , Lee Charles , Müller Martin
Published: July 2020

High-pressure facilitates freezing of biological specimens: pressurizing to 2000 bar before cooling retards growth and reduces size of ice crystals in the specimen. Although the lung is 80% air and is generally difficult to freeze, we report here good cellular ultrastructure in high-pressure frozen lung when: 1) the lung is allowed to collapse (empty of air) prior to sampling, or 2) air-filled lung is allowed to compress during pressurization in the high-pressure freezer prior to freezing or 3) airspaces are filled with relatively incompressible fluorocarbon liquid.

Small Balb mice (28-30g) were anaesthetized and ventilated via endotracheal tube. The chest was opened and a 2mm diameter disk of lung at the thin anterior margin of the right lung was clamped between two aluminum tophats (200μm wells), sealing in air. In other experiments, the lung was allowed to collapse to 0 cm water transpulmonary pressure prior to clamping. In the third series of experiments, air was gradually replaced with fluorocarbon liquid (FC5312, 3M, Minneapolis MN) and the lung inflated with liquid to functional residual capacity. The top hat assembly containing the sealed lung was transferred to the high-pressure freezer (HPM 010, Bal-Tec, Balzers, Lichtenstein) where they were pressurized and frozen.
Time-Dependent Structural Changes in Porcine Stratum Corneum Following an Electroporating Pulse
Authors: Gallo SA , Sen A , Hensen ML , Chow B , Hui SW
Published: July 2020

Electroporation has been used to permeabilize the skin to enhance the transdermal delivery of molecules. The mechanism is generally believed to be based on the temporary breakdown and permeabilization of the stratum corneum by the applied pulsed electric field. The kinetics of recovery are believed to be in the millisecond range. However, no structural changes within this time scale have been observed.

We studied the morphological changes to heat stripped porcine stratum corneum following an electroporating pulse by time-resolved freeze fracture electron microscopy. Pulses at a supraelectroporation threshold of 80 volts and 300 μsec were applied across the stratum corneum with a pair of copper plate electrodes, which also served as cooling contacts. The pulse timing was accomplished through the time-of-flight of a trigger bar attached to the plunging rod holding the sample.. The trigger bar passes through two optical switches. As the sample was propelled towards the liquid propane coolant container, the first switch triggered the pulse generator and the second marked the precise time at which the sample was frozen. The sample was pulsed at set times of 0.5 ms, 12ms, 5 sec, 60 sec, and 300 sec before freezing.
Bugscope: a Sustainable Web-Based Telemicroscopy Project for K-12 Classrooms
Authors: Potter CS , Carragher B , Ceperley M , Conway C , Grosser B , Hanlon J , Hoyer C , Kisseberth N , Robinson S , Sapp J , Soskin P , Stone D , Thakkar U , Weber D
Published: July 2020

Bugscope is a new educational project in the World Wide Laboratory. The World Wide Laboratory provides Web browser based control of scientific imaging instrumentation using the Internet [1]. Providing K-12 classrooms with web based remote access to sophisticated scientific imaging systems was initially demonstrated by us in 1996 in the Chickscope project [2,3]. Chickscope allowed students to study chicken embryo development using a remotely controlled magnetic resonance imaging (MRI) system from their classrooms. While the Chickscope project was highly successful, the resources required to provide operational support for the remote imaging aspects of the project for a small number of classrooms were enormous and the project was not sustainable. The Bugscope project builds on the methods developed and the lessons learned from the Chickscope project. The primary goal is to demonstrate that relatively low cost, sustainable access to an environmental scanning electron microscope (ESEM) can be made available to K-12 classrooms to examine arthropods.

Methods: Classrooms use a standard web browser over the Internet to control and acquire images from a Philips XL-30FEG ESEM. The architecture to support remote acquisition is shown in fig. 1. The client/server control architecture for the ESEM remote control server is based on the emScope control library [4].
From 3-D Light Microscopic Images to Quantitative Insight
Authors: Roysam B , Can A , Shen H , Al-Kofahi K , Turner JN
Published: July 2020

This presentation will describe a common core set of widely applicable image analysis techniques for automated quantitative analysis of volumetric microscope image data. Volumetric (as distinct from stereoscopic) three-dimensional (3-D) Microscopy is a rapidly maturing field offering the ability to image thick (compared to the depth of field) specimens using a variety of instrumentation techniques, and producing arrays of brightness values in three spatial dimensions. Also well developed are methods to correct the acquired images for a variety of physical effects including blur and attenuation.

Commonly, what is of interest is the best-possible visualization of thick specimens. The next step, increasingly being considered in view of growing computational resources, and progress in image analysis techniques, seeks to quantify many of the processes and effects being studied. In some mainstream fields, such quantitation is essential. For instance, various assays for substance testing in pharmaceutical and chemical industries involve quantitative end points. As an illustration, the Draize assay for ocular irritancy testing of drugs and biochemical products for human use requires counting of live and dead cells that stain differently. Another example is the mouse lymphoma test that requires a 3-D counting of bacterial colonies. Neurobiological assays require morphometry, as well as quantification of changes in neurons as a function of time and various applied stimuli such as drugs, heat, and radiation. Angiogenesis assays require quantification of changes in vascular morphometry. Computerized image analysis is a powerful tool for extracting quantitative data from 3-D images for statistical analysis.
Scanning Electron Microscopy at a Distance: A Nuts-and-Bolts Discussion
Authors: Barlow S B
Published: July 2020

Not everyone can afford to own and operate a scanning electron microscope. Everyone can, however, access images and instruments in a variety of ways, depending on the objective. Remote access capability is a result of recent developments in desktop computers, software, and the World Wide Web. Some of these developments and some suggestions for future resource development will be reviewed here.

With the arrival of commercially available, digitally controlled SEMs in the 1980s, it became possible to control microscope operation with a desktop computer and the appropriate software. By connecting a desktop computer to the microscope via the Internet or dedicated data lines such as ATMs, remote control of microscopes became a reality. Although analog microscopes are not as readily controllable over the Internet, their video data stream is easily captured, digitized, and dispatched to remote observers using low-cost consumer video conferencing programs. These approaches enable users at one location to observe their samples in a microscope located elsewhere. However, transfer rates over the Internet fluctuate wildly depending on network traffic, at times making remote access or control almost impossible. Dedicated data lines ensure a relatively stable transfer rate, but at a significantly higher cost.
50 Years of EPMA / Today’s and Tomorrow’s Instruments.
Authors: Conty C
Published: July 2020

The Sepia years. 1951. Castaing’s thesis(1) : Genesis of a Non-Destructive and truly Quantitative Microanalysis method. 1958. The beginning of commercial microprobes : Early instruments had no computers and were lacking special analyzing crystals, but overall they were well designed. Modern features we are familiar with today, such as light element analysis, field emission gun, Energy Dispersive analysis, analysis of insulated material and scanning analysis, although not widely implemented, were discussed in scientific reviews even then(2) 1963. One of my early personal experience: The daring job of obtaining Castaing’s acceptance for his Cameca-buih EPMA at the University of Paris/Orsay.

From early models to present microprobes Early microprobes were developed, after WWII, in a world driven by metallurgy. They had few WD spectrometers, usually at low take off angle. However, the need for light element analysis and the fast growing use of EPMA in geology have sent the manufacturers back to the drawing board. Why ? The design of modern microprobes was a compromise between light optics, electron optics and higher take off angle X-ray spectrometry. There were three possible designs of X-ray path geometry : X-rays through the(final) lens, X-rays through the gap of the lens, X-rays outside the lens, hence three suppliers arose based on these concepts.

Present and future EPMA improvements. As in the initial era of EPMA newer applications will point the direction in which the electron microprobe of the future should evolve.
Minimally Invasive (ENERGY) Dispersive Analytical Spectroscopy (MIDAS). The Golden Touch for In-Situ X-Ray Microanalysis of Bulk Bio-Organic Samples
Authors: Echlin Patrick
Published: July 2020

The matrix of bio-organic samples is composed primarily of carbon, hydrogen, oxygen and nitrogen. Dispersed within this matrix there is a wide spectrum of other elements whose local concentration can be measured in situ by x-ray spectroscopy. The analysis continues to present a challenge because most samples are highly hydrated, beam sensitive and of low density. In light of these restrictions there is only one sensible approach to the use of an analytical procedure which depends on the intereaction of high energy beam electrons with a labile specimen. Samples must be prepared by the least invasive preparative procedure and irradiated with the minimum amount of energy in order to obtain the maximun amount of chemical information. Low temperature sample preparation and low voltage electron beam instruments are central to these processes. By way of example, a brief description will be given of an on-going biological investigation which makes full use of these processes.
Quantitative Elemental Analysis of Heavy Metal Exposed Cells of Synechococcus Leopoliensis Using Regular and Overplus Cells: An Energy Disspersive X-Ray Spectroscopy Study
Authors: Goldberg JJ , Jensen TE
Published: July 2020

It has previously been shown that microbial polyphosphate bodies are the main sites of metal sequestration. In our present study, we have exposed Synechococcus leopoliensis, grown to log phase and to overplus phase, to five different heavy metals, Al, Cu, Cd, Pb, and Zn, independently. The cells were analyzed using the STEM mode of a transmission electron microscope in conjunction with a PGT IMIX energy dispersive x-ray spectrometer.

Cells of Synechococcus leopoliensis were grown for two weeks at 21°C on a 12-hour light/dark cycle in modified Fizgerald’s medium The second cell type were the overplus cells, which were grown as previously described. The cells were exposed to 100PPM of each metal for two hours, then were fixed and embedded in EPON according to Luff’s procedure.

For x-ray analysis, cells of interest were first located using the TEM mode. The microscope was then switched to the STEM mode.
Observing the Chemical State of Elements With Z=21 To 28 From L Alpha1 To L L Ratios With Energy Dispersive Spectroscopy (EDS)
Authors: Sandborg A , Anderhalt R
Published: July 2020

It is well known that chemical bonding affects elemental x-ray emission spectra. The spectra of low atomic number elements show energy shifts which depend on the bonding of the element. To observe these shifts, a high resolution wavelength dispersive (WDS) x-ray spectrometer is required. Intensity variations of the L series can be observed with an EDS system which also show chemical effects.

The L Alphal and the L L radiations are produced from a vacancy in the L III shell. Normally the L L line is about 5 to 6% of the intensity of the L Alphal line. However, in the atomic number range of Z=21 to 28, it is easily observed that the L L line becomes more intense. The L Alphal is no longer present at Z=20. These intensity changes are due to the outer electron shells of these atoms being unfilled. The L Alphal comes from the L3-M5 transition, while the L L comes from L3-M1 transition. The M5 (3d level) of the M shell is partially filled for Z=21 to 28; empty for Z<21and full for Z> 28. Holliday observed a Ti LL which was 17% greater than the Ti L Alphal.
Microstructural Evaluation and Quantitative Analysis in the Unleaded Solder Joint
Authors: Duh JG , Lee YG , Wu FB
Published: July 2020

Solder joints provide mechanical and electronic connections between solders and components for various levels in microelectronic package. However, due to different thermal expansion coefficients and elastic modulus of the associated materials, solder joints are susceptible to fatigue degration, microcracks and fracture. The solder joint reliability is, therefore, critical in the evalution of the joint quality. Recently, the employment of lead-free solder is attractive due to the environmental concern of the Pb-containing solder. Hence, the investigation on the unleaded solder joint is of practical importance in the field of microelectronic package.

Intermetallic compounds (IMC), which form and grow between solders and metallizations, are considered to be a source of mechanical weakness for its brittleness and different coefficient of thermal expansion from the metallization or the solder.
Incoherent Stem Imaging at 1.5 Å Resolution With A 200 Kv FEGTEM
Authors: James EM , Browning ND
Published: July 2020

Here we demonstrate sub- 1.5 Å resolution in compositionally sensitive high-angle annular dark-field (HAADF) (“Z-contrast”) imaging. For the first time this has been achieved on a 200 kV field-emission transmission electron microscope (FEGTEM), the JEOL JEM-2010F. With a Gatan imaging filter, this type of instrument is then capable of both analytical imaging and electron energy-loss spectroscopy at similar spatial resolution as in the 300 kV dedicated STEM.

The Z-contrast imaging technique has a spatial resolution given by the size of the electron probe. When used to image periodic specimens and their defects, the effective incoherent nature of the Z-contrast method leads to higher resolution for given lens Cs, higher sensitivity to atomic number and easier qualitative image interpretation than in HRTEM.In practice, the ability to form a small (atomic resolution) probe depends on the brightness of the electron source, and achieving low enough levels of mechanical and electrical instabilities that otherwise incoherently broaden the probe.
Analysis of Diffraction Contrast as A Function of Energy Loss in Energy Filtering Transmission Electron Microscope (EFTEM) Imaging and Possible Implications on High-Resolution Compositional Mapping
Authors: Moore KT , Howe JM
Published: July 2020

The dependence of diffraction contrast on electron energy loss is an important relationship that needs to be understood because of its potential effect on energy-filtering transmission electron microscope (EFTEM) images. Often when either a two-window jump-ratio image or a three-window elemental map is produced diffraction contrast is not totally eliminated and contributes to the intensity of the final EFTEM image. Background removal procedures often are unable to completely account for intensity changes due to dynamical effects (i.e., elastic scattering) that occur between images acquired at different energy losses, leaving artifacts in the final EFTEM image.

In this study, the relationship between diffraction contrast and electron energy loss was investigated by obtaining EFTEM images of a bend contour in aluminum in 100 eV increments from 0 to 1000 eV (Fig. 1). EFTEM images were acquired a JOEL 2010F FEG TEM with a Gatan imaging filter (GIF) at a microscope magnification of 8 kX using a 1 eV/pixel dispersion, 2X binning (512 x 512) and exposure times ranging from 0.25 s for 0 eV energy loss up to 132 sec for 1000 eV energy loss.
Segregation of Silicon in Metal-Alumina Composites
Authors: Hashimoto RY , Menon ESK , Fox AG
Published: July 2020

A common impurity in polycrystalline commercial alumina is Si since silica is often added as a sintering aid. There have been several studies on impurities in alumina, and substantial degree of grain boundary segregation has been found to occur. Alumina-metal composites have found several applications especially in the electronic industry and consequently systems such as alumina-copper have been studied exhaustively. However, the role of impurities in metal-alumina composites has not been fully explored. Studies of Pt-alumina composites has shown that silicon is present at the interface of vacuum, diffusion bonded samples. Our earlier studies have shown that Si indeed segregates to the triple junctions and grain boundaries in alumina and in alumina-copper composites, often Si segregates to the metal-ceramic interfaces as well. This investigation concentrates on the distribution of silicon in copper-alumina in comparison to aluminum-alumina composites.

The metal-ceramic composites were prepared by diffusion bonding 99.99% pure metal foils sandwiched in between commercially available sintered alumina (∼99.5% pure) substrates for several hours in vacuum.
Electron Beam Induced Damage of GaN And Changes in EELS
Authors: Eustis TJ , Silcox J
Published: July 2020

GaN-based materials hold promise for electronic and optical applications. Lacking a suitable lattice matched substrate, microstructural investigation by electron microscopy has become an important player in the development of these materials. Electron microscopy investigations vary from standard defect analysis, to polarity determination, to evaluation of electronic structure. To date, no evidence of electron beam damage has been reported.

For this experiment, the beam current from the Cornell University VG501 lOOkV STEM was approximately 0.3nA. During acquisition of multiple PEEL spectra of the N K-edge, the intensity of the core loss decreased and eventually disappeared due to electron beam induced damage. Damage is a function of dose. Thus observation of damage is dependent upon magnification and thickness, i.e., electron dose and fractional change in signal.
A Method for Determining the Volume Fraction of Sub-Micron Particulates in Aluminum Alloys Using Energy Filtered Transmission Electron Microscopy (EFTEM)
Authors: Steele D , Ball M , Lloyd DJ
Published: July 2020

The microstructure and mechanical properties of alloy systems are known to be influenced by the size and distribution of sub-micron dispersoids through boundary pinning and Orowan strengthening. Explaining and accurately predicting the behaviour of these systems relies in part on the measurement of the volume fraction of the second phase precipitates. The transmission electron microscope (TEM) provides the necessary resolving power to measure the dispersoids of interest, and when coupled to Electron Energy Loss Spectroscopy (EELS) based filtering systems, the thickness of the observed volumes can be determined using the log-ratio technique.

A series of nominally AA5754 alloys with increasing Manganese content (0%, 0.2%, 0.5%, 0.8%) was used to evaluate the method. The data was collected using a Philips FEGSTEM equipped with a Gatan Imaging Filter (GIF). A series of images were collected from each of a number of contiguous fields in each specimen. These included an unfiltered image, an image collected from the zero-loss region of the transmitted spectrum, and a filtered image generating sufficient precipitate contrast to allow subsequent spatial measurement. Using a filtered image, the contribution of diffuse scattered electrons is minimized, thus enabling the analysis of thicker regions.
The Use of ELNES for Microanalysis
Authors: Craven AJ , MacKenzie M
Published: July 2020

The performance of many materials systems depends on our ability to control the distribution of atoms on a nanometre or sub-nanometre scale within those systems. This is as true for steels as it is for semiconductors. A key requirement for improving their performance is the ability to determine the distribution of the elements resulting from processing the material under a given set of conditions. Analytical electron microscopy (AEM) provides a range of powerful techniques with which to investigate this distribution. By combining information from different techniques, many of the ambiguities of interpretation of the data from an individual technique can be eliminated. The electron energy loss near edge structure (ELNES) present on an ionisation edge in the electron energy loss spectrum reflects the local structural and chemical environments in which the particular atomic species occurs. Thus it is a useful contribution to the information available. Since a similar local environment frequently results in a similar shape, ELNES is useful as a “fingerprint”.
Some Things Never Change - The Microcrystallite Story After 25 Years
Authors: Gibson JM , Treacy MMJ , Voyles PM
Published: July 2020

When I (JMG) began my Ph.D. studies under the supervision of Archie Howie in 1975, he was still licking his wounds over one of the very few apparently incorrect publications[l] of his career. I am proud that our recent work has shown that, far from being wrong, Archie and Lee Rudee were actually 25 years before their time. It was in the early 1970’s that electron microscopy instrumentation reached the performance level that was adequate to resolve the interplanar spacings in elemental materials, such as the semiconductors silicon and germanium. It immediately became of interest to examine the structure of amorphous silicon and germanium, in the expectation that direct imaging could resolve the old controversy between micro-crystallite and random network structural models. Porai-Koschits was the first to suggest that amorphous materials comprised extremely small crystalline domains (microcrystals), in contrast Zachariasen[2] proposed that a continuous random network was a better description of glassy materials.
Quantitative Valence-Loss Spectroscopy of Carbon Nanostructures
Authors: Stöeckli T , Wang ZL , Bonard J-M , Stadelmann P , Châtelain A
Published: July 2020

Carbon tubes or spheres synthesized by arc-discharge are usually mixed with other byproducts, prohibiting direct measurements of their physical properties by the well established optical techniques because a large quantity of pure specimen is required. Electron energy-loss spectroscopy (EELS) is a unique technique that can be applied to probe the electronic structure of a single carbon tube or sphere. In this paper, the classical dielectric response theory is applied to calculate the EELS spectra acquired from a graphitic carbon sphere at various impact parameters. Graphite is an anisotropic dielectric medium whose dielectric function is described by a tensor. A graphitic carbon sphere is composed of concentric graphitic shells whose dielectric tensor in the spherical geometry, under the local response approximation, is given by (Figure 1)

where are the dielectric function of graphite for an electric field perpendicular and parallel, respectively, to the c axis. In the non-relativistic approximation, the surface excitation is calculated by [1]
Structure and Composition of Supported Pt-Sn Electrocatalysts
Authors: Radmilovic V , Richardson T , Chen SJ , Ross PN
Published: July 2020

Bimetallic alloy particles supported on high-surface area carbon are widely used as electrode materials. Because of their stability, Pt-Sn alloys are of particulate interest for a variety of applications. Although the reasons for the superior properties of these catalysts are not fully understood, the dispersion, structure, and compositional homogeneity of the alloy clusters, are clearly important factors in determining their catalytic activity. In order to identify the composition and structure of Pt-Sn base nanoparticles, various characterization techniques, mainly X-ray diffraction (XRD) and transmission electron microscopy (TEM) [1], have been applied. However, very often conflicting conclusions regarding to the structure of Pt-Sn particles have been reported. The focus of the present work is to examine a commercially available carbon supported bimetallic Pt-Sn catalyst, with a nominal Pt:Sn wt. ratio of 2:1 (500N and 900N samples) and 3:1 (E270 sample), using high resolution electron microscopy (HREM), electron and X-ray diffraction techniques, and microchemical analysis by energy dispersive X-ray spectroscopy (EDS).
Characterization of Ceramics Using Electron Backscatter Diffraction in the SEM
Authors: Michael JR
Published: July 2020

The technique of electron backscatter diffraction (EBSD) in the scanning electron microscope is becoming a standard technique for the characterization of materials. EBSD has evolved into a tool that can determine the orientation of a crystalline area of interest or the technique can be used for the identification of unknown phases from their composition and crystallography. The application of the technique to ceramic materials has demonstrated the many advantages of this technique over classical x-ray diffraction techniques or electron diffraction in the TEM.

EBSD patterns are obtained by illuminating a highly tilted sample (>45° from horizontal) with a stationary electron beam. Electrons that are backscattered from the sample may satisfy the condition for channeling (or diffraction) and produce images that contain bands of increased and decreased intensity that are equivalent to channeling patterns. The patterns are imaged by placing a phosphor screen near the sample and imaging the screen with either TV rate or a slow scan CCD camera.
Electron Microscopy of Hierarchical Materials
Authors: Blanford CF , Stein A , Carter CB
Published: July 2020

Recent innovations in materials chemistry have allowed the preparation of “hierarchical” ceramic and polymer materials that possess features on several different size scales. One of the newest hierarchical materials are ceramics that exhibit a three-dimensional ordered array of half-micron voids. These macroporous structures are synthesized from a liquid ceramic precursor and a polymer colloidal crystal template. This template is extracted by either thermal or chemical methods leaving a structure such as the porous zirconia particle shown in Fig. 1. The final structure of these materials may be thought of as the opposite of opal: the spheres here are the voids. Ordered arrays of dielectric material like these could potentially be used as photonic crystals that interact with visible light. For the microscopist, these materials create new opportunities to study interrelated aspects such as templating, crystallization, and phase transformations.

Transmission electron microscopy (TEM) was carried out on a Philips CM30 TEM equipped with a LaB6 filament and operating at 300 kV.
Effect of Correction of the 3-Fold Astigmatism on HREM Lattice Imaging With Information Below 100 Pm
Authors: Wang YC , Fitzgerald A , Nelson EC , Song C , O’Keefe MA , Kisielowski C
Published: July 2020

High resolution electron microscopes with field emission sources opened the possibility to investigate solids on a 100 pm range. Either electron holograpy can be applied or an information limit that may even extend into a region below 100 pm can be exploited to reach this goal [1]. However, lens aberrations such as the three-fold astigmatism often complicate an image interpretation in the 100 pm range or even make it impossible [2]. On the other hand, there is growing need to understand physical processes at a mono-atomic level in order to further develop artificially structured materials such as nano-crystals, ceramic coatings or semiconductors. Commonly, such materials contain light elements like C, N, or O with bond lengths that are shorter than a typical 180 pm point resolution of a high resolution, electron microscope. The carbon-carbon distance of 150 pm is the shortest bond length value in crystalline solids. Moreover, any projection of a diamond lattice along a low index zone axis for lattice imaging leads to a reduced C-C distance.
Use of Electron Diffraction for Determining the Orientation of Rapid Thermally Annealed Lead Zirconate Titanate Thin Film On (111) Pt Coated Si Substrate
Authors: Cheng SC , Su T , Trolier-McKinstry S
Published: July 2020

Lead zirconate titanate (PZT) is a perovskite-staictured material which is ferroelectric over most of the solid solution and which exhibits a range of electrical and electromechanical properties depending on the Zr/Ti ratio. Thin film PZT is currently being developed for piezoelectric actuators, ferroelectric memory devices and pyroelectric detectors. The ferroelectric properties and microstructures of the PZT films depend upon numerous processing parameters.In this research, sol-gel PZT films crystallized by rapid thermal annealing at 700°C for 30 seconds were investigated. A modification of the procedure described by Budd, Dey and Payne was utilized for the solution preparation. The electrodes/substrates which have been used for the deposition of PZT are Pt/Ti/SiO,/Si. The approximate thicknesses of Pt, Ti and SiO2 layers are 150 nm, 20 nm and 1000 nm, respectively. Transmission electron microscopy (TEM) was used to reveal the microstructure of the films, including the interfacial characteristics, grain sizes and domain structures. Cross sectional specimens were prepared by the following procedures.
Microstructure of Yba2Cu3O7 Thick Films by Post Annealing of the Precursor by High Rate E-Beam Deposition On SrTiO3 Substrates
Authors: Wu Lijun , Zhu Yimei , Suenaga M , Sabatini RL
Published: July 2020

Recently, considerable efforts have been made in developing a fabrication procedure for YBa2 Cu3O7-δ superconducting films on a metallic substrate tape for electrical power applications. The central issue is to develop a method, which can produce the tape in sufficiently long lengths at a commercially viable cost. One possible approach is the so-called BaF2 post-deposition annealing process, which involves deposition of an unreacted mixture of a BaF2 -Y-Cu-O layer on a substrate by electron beam evaporation method, followed by heat-treatment of the layer in a mixed-gas atmosphere of a low partial pressure O2, saturated H2 O, and N2. To fabricate thick and long films, it is important to understand the effects of the heat-treatment parameters on the. structure and the properties. Here, we report our structural analysis of the films annealed at different temperatures.

The films annealed at 725°C, 750°C and 800°C have a similar phase assemblage which are composed ofYBa2 Cu3O7-δ and Y2O3, CuO and Ba-Ti-Sr-O precipitates, as shown in fig. la.
TEM Microstuctural Characterization of a 2091 (Al-Li-Mg-Zr) Alloy Subjected to Welding Operations
Authors: de Macedo MCS , Solórzano IG
Published: July 2020

For over two decades considerable effort has been directed towards the development of Al-Li base alloys with the objective of replacing conventional high aluminum alloys, due to the fact that lithium additions cause substantial reduction in density accompanied by significant increase in the elastic modulus, implying, therefore, in appreciable improvement in the specific properties of the resulting alloys. These properties depend on the miscrostucture evolution during heat treatment or welding cycle. The microstructure of the commercial Al-Li systems is complex due to the addition of alloying elements, which increases the number of the allowed stable and metastable phases. During the thermo-mechanical processing of the 2091 alloy, the probable metastable are δ’, GPB zones and S’, the stable phases are S, T2 and the high temperature R (1-3). Further, the Zr precipitates the Al3Zr. The present study deals with the microstructure evolution of welded joints of the 2091 alloy studied by transmission electron microscopy, TEM.
Formation of Γ Phase on Hot-Dip Galvanized Coating Steel Sheet after Various Heat Treatment
Authors: Lin Yuli , Lin Hwang-Che
Published: July 2020

Among those intermetallic phases in Zn-Fe system formed in the hot-dip galvanized coating and/or galvanneal coating, the microstructure of Γ phase was the least mentioned. The Γ phase form in the coating layer is usually too thin to observe by a microscope. However, it has been reported that the performance of coating is closely related to the microstructure of Γ phase. Tokunaga et al. has reported that the cracks were generated from the Γ layer or Γ+δ layer. Y.Lin et al. demonstrates that coherent interface forms between Γ and steel interface on annealed electrogalvanized steel sheets indicating that failure would not occur at this interface.

Samples used in this study were lab-made hot-dip galvanized steel sheets. To investigate the microstructure of coating, especially the Γ phase layer, specimens were heated to create the designed layer interface. It was found that the heat-treated conditions ranged from 700°C to 750°C for one hour was appropriate to observe the nucleation and growth of Γ phase layer.
Imaging Dislocations in Duplex Tial Using Electron Channeling Contrast
Authors: Ng BC , Bieler TR , Crimp MA
Published: July 2020

Electron channeling contrast imaging (ECCI), performed using a scanning electron microscope, has been used to observe dislocations in bulk TiAl with a duplex microstructure. The ECCI technique is based on the dependence of the back-scattered electron (BSE) yield (of the incident beam orientation) on the crystal lattice and defect orientation near the specimen surface. This allows nearsurface defects to be imaged in bulk specimens [1, 2]. ECCI was carried out in a Camscan 44FE FEG-SEM operated at 25 kV using a beam divergence of ∽8 mrad and a beam current of ∽ 2nA. Specimens were observed at a working distance of approximately 11 mm. To record the BSE signal, the microscope was fitted with an annular (four quadrant) silicon diode detector array attached to the final lens pole-piece, resulting in a solid angle collection of approximately ∽0.6 π str. Images were recorded as 32 frame averages using ∽1.1 frames/sec.
Cross-Sectional Transmission Electron Microscopy Sample Preparation Using Focus Ion Beam Machine and Wedge Technique
Authors: Li Du , Zhou Rose , Zanoya Rob
Published: July 2020

As features on an IC chip become smaller than the resolution power of an optical microscope and of the size of the grinding particles, the trend for preparing cross-sectional transmission electron microscopy (TEM) samples at specific locations (bits) is moving towards using a focused ion beam (FIB) machine. Details on how to use a FIB machine to prepare cross-sectional TEM samples have been outlined in many references.The general procedure is to first mark the specific location (bit) in the FIB machine and then grind the sample down to about 20 microns, 10 microns on each side of the feature of interest. After grinding, the sample is mounted on a pre-cut TEM grid and thinned with the FIB to about 0.1 micron in the region containing the feature of interest. There are several disadvantages to this method. First, the sample goes into the FIB machine at least twice—once for FIB marks on the location and once again for the final thinning.
Defect Analysis and Process Development of Microelectronics Devices Using Focused Ion Beam and Energy Filtering Transmission Electron Microscopy.
Authors: Pantel R , Mascarin G , Auvert G
Published: July 2020

1. Introduction.

With continuing reductions in semiconductor device dimensions high spatial resolution physical and chemical analysis techniques will be more and more required for defect analysis and process development in the microelectronics field. Transmission Electron Microscopy (TEM) analysis is now extensively used thanks to the fast Focused Ion Beam (FIB) specimen preparation technique which has furthered its development. Recently, we have shown the advantages of adding Electron Energy Loss Spectroscopy (EELS) to FIB-TEM analysis for semiconductor process characterization. In this paper we extend the EELS technique using FIB sample preparation to Energy Filtering TEM (EFTEM) observations. The EFTEM analysis allows high-resolution compositional mapping using spectroscopic imaging of core level ionization edges3. We show some applications of FIB-EFTEM to defect analysis and process development.

2. Experimental details.

The FIB system is a MICRION model 9500 EX using a gallium ion beam of 50 keV maximum energy with a 5 nm minimum spot diameter.
Novel Preparation of Precision Planar TEM Specimens for Integrated Circuits Using Dual-Beam Focused Ion Beam
Authors: Ma Zhiyong , Davies Brian , Brandt Jeremy , Baker Brian , Headley Karen , Miner Barbara
Published: July 2020

Preparation of precision planar TEM specimen for failure analysis in microelectronics industry has become increasingly difficult as the critical dimensions of integrated circuits (ICs) continue to shrink down to deep sub-micron regime. Accurate defect localization and endpoint control of specimen final thinning are critical steps leading to successful specimens and defect characterization. Conventional dimple and ion-mill method becomes inadequate for this class of specimen preparation due to poor optical imaging resolution, non-planar polishing, lack of flexible ion beam control and in situ process monitoring for endpoint control. These problems are exacerbated by the high density and a wide range of materials found in IC device structures. In this paper we present a novel method employing dual-beam focused ion beam (FIB) which significantly improves upon these difficulties.
A New Specimen Preparation Technique for Metallographic Evaluation of Lead and Lead Alloys
Authors: Vahaaho JM , Zieliński PA
Published: July 2020

Preparation of lead and lead alloy specimens for metallographic examination is more difficult than preparation of the majority of other metals and their alloys. The troublesome difference is that lead and lead alloys are soft (lead has a Vickers hardness of 4-5 [1,2]), and therefore readily develop a cold-worked surface layer and disturbances in the subsurface layers during mechanical polishing. The specimen softness also allows embedding of the abrasive particles. If not removed, these mechanically introduced artifacts obscure the true structure of the specimen, and in some cases could develop a pseudostructure, especially if excessive frictional heat is involved [1]. Usually etchpolishing, consisting of cycles of alternately etching, polishing, and microscopic examination, is required to remove the above artifacts. This treatment either might not completely remove these artifacts or it might overetch the sample. In addition, etching could introduce its own artifacts, such as tarnishing, etching pits, or both.
Boron Substrates for Particulate X-Ray Microanalysis
Authors: S.Windsor Eric , E.Newbury Dale , D.Kessler John , H.Chi Peter
Published: July 2020

Sample substrates for x-ray microanalysis of particles should be chemically simple and composed of low atomic number elements. Substrates meeting these requirements will generate a minimum number of low energy x-ray peaks that should not interfere with spectra generated by the particles of interest. Elemental carbon fulfills these requirements and carbon planchets are used for the majority of work involving x-ray microanalysis of particles. When particles of interest are carbonaceous, alternate substrates must be sought. Beryllium planchets have traditionally been used for the analysis of carboncontaining particles. However, concerns about beryllium toxicity along with regulations from the Occupational Safety and Health Administration (OSHA) have resulted in diminished use of beryllium as a substrate material. These toxicity issues prompted us to explore the possibility of using elemental boron as a substrate for microanalysis of carbon-containing particles.

Elemental boron is available from chemical supply houses and the material we purchased was in the form of irregularly shaped pieces, approximately 3 cm in the longest dimension.
A Reactor for “Ex-Situ” TEM Catalyst Characterization
Authors: Kliewer CE , Disko MM , Soled SL , DeMartin GJ
Published: July 2020

The microstructural and chemical characterization of catalysts is not only integral to their initial development but also to understanding and controlling their behavior over time. To better elucidate the morphology of these materials and relate physical properties to catalytic properties (e.g., activity, selectivity, etc.), “ex-situ” methods for studying catalysts under reactive conditions have been developed.

Because conventional transmission electron microscopy (CTEM) is conducted under high vacuum conditions, it is difficult to replicate the exact chemical environment of a catalyst (e.g., high pressure, variable gas mixtures, etc) within the TEM. Consequently, most analyses focus on comparing “fresh” and “spent” materials. In general, this methodology provides useful structural information albeit with limitations associated with the comparison of dissimilar regions and the effects of sampling inhomogenieties.