bluuebunny/crossref_metadata_2025 huggingface dataset:
A new microscopy method to assess mass transfer during freezing in rat liver tissue slices
Authors: Raha D. , Pazhayannur P. , Bischof J. C.
Published: June 2020

In cryofixation of biological samples it is typically desirable to minimize or avoid ice crystals in the sample by one of several rapid cooling techniques. Using these techniques freezing rates of 1,000 -10,000 °C/s are commonly achieved at a cooling boundary. At these rates, cellular dehydration is typically absent, and intracellular ice crystals are so small as to be considered negligible within an “ice-free” zone typically ranging 5-25 μm into the sample from the cooling boundary. However, during medical applications of freezing including cryopreservation as well as cryosurgery, the rate of freezing is orders of magnitude less than the idealized freezing procedures used in cryofixation. During slower freezing at rates between 1 - 100 °C/min, significant water transport between the cells and the extracellular/vascular space of a tissue can occur. This dehydration affects how and where the ice will form in the tissue which in turn can influence the post-freeze viability and therefore the overall success of a medical freezing treatment. The purpose of this work is to obtain a more quantitative understanding and prediction of the biophysics of water transport in liver tissue during freezing.
An improved cryofixation technique for optimal orientation of Caenorhabditis elegans for cryosectioning and EPXMA
Authors: Roberts Edward , Wallace Nancy , Freedman Jonathan , LeFurgey Ann
Published: June 2020

INTRODUCTION: Plunge freezing into liquid cryogens has been frequently employed with success for cryofixation of biological specimens <lmm in size; however, positioning of cells or organisms with a precise orientation for subsequent cryosectioning is difficult. In these studies, a metal mirror cryofixation device, e.g. cryogun, has been tested to determine its applicability for cryofixation of small organisms such as nematodes or larval invertebrates with specific positioning. The objective of the experiments was to determine the optimum technique for rapid cryofixation and cryosectioning of the intestinal tract and lumen of the nematode Caenorhabditis elegans, prior to electron probe x-ray microanalysis (EPXMA) of subcellular elemental distribution.

METHODS: Freezing and sectioning quality obtained using plunge freezing into -190°C liquid propane (Figure la) was compared with that obtained with -196°C metal mirror fixation using the cryogun (PS 1000, Delaware Diamond Knives, Wilmington, DE)(Figure lb). C. elegans were grown in culture to the adult stage, and individual nematodes were placed on either (1) a wooden specimen stub compatible with the plunge freezing device (Figure 2a) or (2) a cryogun specimen mount (Figure 2b).
Advantages of Low Temperature SEM for Bacterial Studies
Authors: Roy Stéphane , Babic Isabelle , Watada Alley E. , Wergin William P.
Published: June 2020

The application of transmission electron microscopy (TEM) has greatly increased our understanding of structure-function relationships in bacteriology. However, to achieve further advancements investigators are seeking preparation procedures that would avoid the artifacts associated with conventional chemical fixation, dehydration and critical point drying or embedding. In our laboratory a field emission scanning electron microscope (SEM) was recently equipped with a cold stage. This combination of techniques, referred to as low temperature (LT) SEM, allowed us to examine frozen, fully hydrated biological specimens. The present investigation images bacteria that were cryofixed for LTSEM observations and then freeze-substituted for TEM observations. In addition an attempt was made to culture the samples that had been cryofixed and observed with LTSEM so that taxonomic identification and further microscopic observations could be made.

Bacteria used in this study were isolated from spinach leaves (variety New Jersey). LTSEM observations of cryofixed samples were performed on a Hitachi S-4100 field emission SEM equipped with an Oxford CT-1500HF Cryotrans System.
Contour-based segmentation and visualization of electron tomographic volumes
Authors: Marko M. , Leith A. , Buttle K. , Li Y.
Published: June 2020

Electron tomography is increasingly employed to obtain highly-detailed 3-D structural information from complex biological specimens, when such information cannot be obtained otherwise. Thick sections (ca. 0.25-3 μm), which require an intermediate- or high-voltage EM, are often used so that an appreciable portion of the structure of interest can be contained within the section. Because of this relatively large amount of material, volumes made by tomographic reconstruction are often filled with a tremendous amount of detail, not all of which is of interest. Often, in the absence of special stains, the structures of interest have low contrast compared to surrounding or adjoining structures. Typically, all the structures are embedded in the "ground cytoplasm", which has nonuniformlydispersed small structural elements that have the same density and spatial-frequency range as the structures of interest. In addition, the density of a given structure may vary within an image due to non-uniform staining. In these situations, the segmentation of the volume to isolate the interesting portions of the structure presents a formidable problem.
Stereo modeling of HVEM specimens by serial tilting and computer graphics
Authors: McIntosh J.R. , Stemple D.L. , Bishop William , Hannaway G.W.
Published: June 2020

EM specimens often contain 3-dimensional information that is lost during micrography on a single photographic film. Two images of one specimen at appropriate orientations give a stereo view, but complex structures composed of multiple objects of graded density that superimpose in each projection are often difficult to decipher in stereo. Several analytical methods for 3-D reconstruction from multiple images of a serially tilted specimen are available, but they are all time-consuming and computationally intense.
Visibility and stability of a 12-tungsten atom complex
Authors: Monson K. L. , Wall J. S. , Hainfeld J. F.
Published: June 2020

Although it is quite possible to visualize single heavy atoms in the STEM, the dose necessary to do so (∼1000 e/Å2) precludes their use as high resolution labels of biological samples, except in the special case of ordered arrays. We have previously evaluated a cluster compound consisting of 11 gold atoms in terms of visibility and stability and it has been functionalized and covalently linked to specific sites. Although the undecagold cluster will surely find continued use, it is fairly sensitive to beaminduced mass loss.
Survey of electronic imaging past, present, and future
Authors: Aikens R. , Sims G.
Published: June 2020

Since its inception in the 1920's, electronic imaging has evolved from placing a photocell behind a rotating disk with a spiral pattern of holes to solid-state sensors backed by powerful image-processing computers. In the early years, developments in electronics imaging were driven by the possibility of broadcasting images over the airwaves. A number of scientists attempted to adapt devices for television to other forms of electronic imaging. However, success in applying televison pickup tubes to high-performance imaging was minimal because of the high cost, low performance, and scarcity of large-scale computers.
Electron microscopy of frozen, hydrated RECA and its DNA complexes
Authors: Schmid M.F. , Rankert D.A. , Chang C.F. , Jeng T.-W. , Chiu W.
Published: June 2020

RecA is a multifunctional enzyme which plays a role in general recombination and in DNA repair in E. coli. It consists of 352 amino acids and has a molecular weight of 37,842. A portion of the amino terminal domain shows homology with the active sites of serine proteases and has been implicated as the active site for cleavage of the LexA repressor. It also exhibits a DNA-de-pendent ATPase activity. The protein forms helical filaments under certain conditions either alone or in complex with DNA. It is thought that the filaments play a significant physiological role in recombination events. However, the mechanism of this function is not yet clear. Electron microscopic studies on frozen hydrated filaments of RecA and RecA-DNA complexes may provide useful information about various functional states.
Quantitative digital x-ray imaging of frozen hydrated and dried cryosections
Authors: Saubermann A. J. , Heyman R. V.
Published: June 2020

Application of quantitative x-ray imaging to frozen hydrated (FH) tissue sections has presented a number of major problems including lack of a suitable algorithm which could deal effectively with hydrated specimen mass loss from radiation damage, low characteristic x-ray signal to background signal, and lack of a suitable method which would permit analysis and comparison of the same cryosection in both hydrated and dried state. Our algorithm, using hydrated then dried cryosections, eliminates the major problems associated with analysis of FH tissue sections. This algorithm is suitable for application to quantitative x-ray imaging and will provide quantitative elemental images in both wet and dry weight units as well as quantitative images of water fractions.
Water accumulation as a function of temperature on specimens in an electron microscope cold stage
Authors: Lamvik M.K. , Kopf D.A. , Davilla S.D. , Robertson J.D.
Published: June 2020

Last year we reported1 that there is a striking reduction in the rate of mass loss when a specimen is observed at liquid helium temperature. It is important to determine whether liquid helium temperature is significantly better than liquid nitrogen temperature. This requires a good understanding of mass loss effects in cold stages around 100K.
Single-particle averaging of purified us acetylcholinesterase
Authors: Morgan D. G. , Schrag J. D. , Olson S. , Schmid M. F. , Chiu W.
Published: June 2020

Acetylcholinesterase is an enzyme which plays an integral role in the normal function of cholinergic synapses. Hydrolysis by this enzyme of the neurotransmitter acetylcholine to choline and acetic acid readies the synapse for a response to the next signal. The objective of the present work is to define the size, shape and quaternary associations of the catalytic subunits of this enzyme.
3-D diffraction intensities of the crotoxin complex crystal
Authors: Prasad B.V.V. , Degn L.L. , Jeng T.-W. , Chiu W.
Published: June 2020

The crotoxin complex, a neurotoxin from the venom of the Brazilian rattlesnake, Crotalus durissus terrificus, forms thin crystals suitable for high resolution electron crystallography. These crystals grow to variable completions of the unit cell, making it difficult to merge the intensity data from different crystals. This difficulty is overcome by collecting as many electron diffraction patterns (EDP) as possible from a single crystal tilted from +60° to -60°. Several series of approximately twenty EDP's were collected using a Philips 400 equipped with a cold stage at MRC, Cambridge in Dr. R. Henderson's laboratory. We report here our progress in synthesizing a 3-D intensity data set from these series.
Computer-simulated density models of polymers of sickle hemoglobin
Authors: Bluemke David A. , Carragher Bridget , Josephs Robert , Potel Michael J.
Published: June 2020

We have developed a modeling system for generating density distributions of deoxyhemoglobin S (HbS) polymers that is based on the crystallographic atomic coordinates of HbS. Computed density projections depicting the particle structure may be compared to electron micrographs of negativelystained preparations of sickle hemoglobin. In this manner, image features may be quantitatively analyzed and related to the molecular arrangement of hemoglobin tetramers. Such computer-simulated models provide a structural approach that is able to link high-resolution x-ray diffraction data to electron microscopic studies of noncrystalline polymers of HbS.
Ionic channels for mechanoelectrical transduction and frequency tuning by vertebrate hair cells
Authors: Hudspeth A. J.
Published: June 2020

The electrical activity of vertebrate hair cells, including mechanoelectrical transduction, resonant frequency tuning, and synaptic transmission, results from the action of an ensemble of ionic channels. In an effort to understand how hair cells function as the sensory receptors of the internal ear, our research group is conducting in vitro investigations of the ionic channels of saccular hair cells from the bullfrog, Rana catesbeiana.

Mechanoelectrical transduction commences when stimuli, derived from sounds or accelerations, deflect the hair bundle, a cluster of enlarged microvilli termed stereocilia.
Endoneural organization of the vagal hepatic nerve
Authors: Prechtl J. C.
Published: June 2020

Behavioral and electrophysiological analyses in rats indicate that the hepatic branch of the vagus nerve is an important pathway for chemoreceptive information from the hepatic portal circulation. Since morphological data have not been available on the rat hepatic branch, previous experiments have been designed and interpreted on the assumption the this nerve is a relatively simple and homogeneous structure. Our recent findings indicate that the hepatic shows a more complex although reproducible organization.
A novel method for preventing collapse of air-dried specimens for heavy metal shadowing
Authors: Kessel M. , Buhle E. L. , Glavaris E. , Aebi U.
Published: June 2020

Heavy metal shadowing is one of the oldest and most useful methods of enhancing the contrast of biological molecules for visualization by electron microscopy. A critical step in this method is the dehydration of the specimen prior to metal shadowing without causing distortion and collapse of the structure and consequent loss of the three-dimensional information. Two methods commonly employed today are glycerol spraying/vaccuum evaporation and freeze-drying. While glycerol spraying is the easier method of the two, it does not significantly prevent collapse artifact during air-drying and thus is limited to single extended molecules. Freeze-drying minimizes the collapse artifact of flattening and distortion due to surface tension. Freeze-drying preparations suffer their own problems of thermal vibrations and possible contamination by a eutectic of remaining salts and proteins.
Reduction of spermatogonia and testosterone in rat testes flown on space lab-3
Authors: Philpott Delbert E. , Sapp W. , Williams C. , Fast T. , Stevenson J. , Black S.
Published: June 2020

Space Lab 3 (SL-3) was flown on Shuttle Challenger providing an opportunity to measure the effect of spaceflight on rat testes. Cannon developed the idea that organisms react to unfavorable conditions with highly integrated metabolic activities. Selye summarized the manifestations of physiological response to nonspecific stress and he pointed out that atrophy of the gonads always occurred. Many papers have been published showing the effects of social interaction, crowding, peck order and confinement. Flickinger showed delayed testicular development in subordinate roosters influenced by group numbers, social rank and social status. Christian reported increasing population size in mice resulted in adrenal hypertrophy, inhibition of reproductive maturation and loss of reproductive function in adults. Sex organ weights also declined. Two male dogs were flown on Cosmos 110 for 22 days. Fedorova reported an increase of 30 to 70% atypical spermatozoa consisting of tail curling and/or the absence of a tail.
A transmission electron microscopic study of porcine stratum corneum treated with topical applications of glycolipid
Authors: Laffoon J. , Lesch C. , Squier C. A.
Published: June 2020

The mammalian epidermis forms a differentiated surface layer termed the stratum corneum (sc) which represents the principal barrier. It is now known that the permeability barrier is located in the intercellular region of the sc and consists largely of neutral lipids derived from glycolipids that are aligned to form a highly hydrophobic structure. It is possible that this barrier might be augmented by topical application of pure glycolipid, which could diffuse through the regions between the squarnes. We have examined this possibility by treating the backskin of pigs with glycolipids and then preparing the tissue for examination with the transmission electron microscope (TEM).
Application of Scanning Electron Microscopy to paraffin-embedded plant tissues to study invasive processes of plant-pathogenic fungi
Authors: Kokko E. G. , Gaudet D. A.
Published: June 2020

Scanning electron microscopy (SEM) applied to paraffin-embedded tissue section is compared with the traditional techniques of light microscopy (LM) and surface SEM for the study of invasion by a plant-pathogenic fungus. SEM of paraffin-embedded sections of wheat leaves infected by Coprinus psychromorbidus consistently yielded high-quality micrographs showing three-dimensional views of both internal and external disease development processes. When the orientation of the specimen in the SEM is manipulated, the specimen can be viewed from different perspectives. The technique is simple and inexpensive and combines the advantages of great depth of focus and high resolution of the SEM with the simple preparatory techniques employed for light microscopy.
Interaction of 16S rRNA With Protein S4 - a first step to visualization of the assembly of the Escherichia Coli 30S Ribosomal Subunit by Stem
Authors: Mandlyan V. , Oostergetel G. T. , Wall J. S. , Hainfeld J. F. , Boublik M.
Published: June 2020

Understanding the mechanism of ribosome assembly and involvement in protein synthesis can be greatly facilitated by elucidation of its three-dimensional structure. The conformation, topography, and Interactions of ribosomal constituent proteins and RNAs can be directly studied by dedicated high resolution scanning transmission electron microscopy (STEM). The high (80%) efficiency in collection of scattered electrons in the dark-field mode makes 1t possible to visualize freezedried unstained specimens at low radiation dose (le/Å2); this minimizes many artifacts inherent in conventional transmission electron microscopy (staining, air-dry1ng, and radiation damage). In addition, the linear proportionality of the large-angle elastically scattered electrons to specimen mass thickness can be used for quantitative determination of molecular weight, mass distribution, and calculation of the apparent radius of gyration (RG), a parameter closely related to the threedimensional structure of the macromolecule.
Morphologic alterations in bacteroides fragilis following single and combinant beta-lactam exposure
Authors: Goheen Michael P. , Edmiston Charles E.
Published: June 2020

The synergistic activity of antimicrobial combinants against aerobic and facultative microorganisms has been well documented. in comparison, few studies have been performed using obligate anaerobic isolates and antimicrobial combinants. For this study clinical strains of Bacteroides fragilis(BF) were selected to investigate both single/combinant drug activity and cellular morphologic changes when BF is exposed to Imipenem (I), Piperacillin (P), Cefpimizole (C), Imipenem/Piperacillin (I+P), and Imipenem/Cefpimizole (I+C).
Quantitative analysis of the cooperativity of protein-nucleic acid interactions by electron microscopy
Authors: Hicks Pamela S. , Andrews Christopher L. , Bear David G.
Published: June 2020

It is common for sing1e-stranded nucleic acid finding proteins to bind polynucleotides cooperatively. The parameter ω is used to describe the component of the association binding constant that is due to cooperative interactions between protein molecules on the polynucleotide lattice; ω is 1 for noncooperative binding, while ω can be as high as 103-104for highly cooperative proteins such as bacteriophage T4 gene 32 protein. In the past, to has been determined by computer fitting of spectroscopic titration data. It has been suggested that electrom microscopy would provide a more direct method for estimation of the cooperativity parameter. An equation can be derived that relates the experimentally obtained average protein cluster size (at a specific protein/RNA saturation ratio) to ω. The only other parameter required for the calculation is the RNA binding site size obtained from stoichiometric titration measurements.
High-voltage Electron Microscopy of astroglial cell whole mounts
Authors: Turner J.N. , Shain W.G. , Madelian V. , Grassucci R.A. , Forman D.L.
Published: June 2020

Homogeneous cultures of astroglial cells have proved useful for studying biochemical, pharmacological, and toxicological responses of astrocytes to effectors of central nervous system function. LRM 55 astroglial cells, which were derived from a rat glioma and maintained in continuous culture, exhibit a number of astrocyte properties (1-3). Stimulation of LRM 55s and astrocytes in primary cell cultures with the beta-adrenergic agonist isoproterenol results in rapid changes of morphology. Studies with time lapse video light microscopy (VLM) and high-voltage electron microscopy (HVEM) have been correlated to changes in intracellular levels of c-AMP. This report emphasizes the HVEM results.
The ultrastructure of hepatocellular carcinomas in english sole (Parophrys vetulus) from puget sound
Authors: Stehr Carla
Published: June 2020

High prevalences of liver neoplasms have been found in English sole (Parophrys vetulus) from urban waterways of Puget Sound, Washington. Although the etiology of these neoplasms is not known, evidence suggests that chemical contaminants may be the causative agents. Electron microscopy studies were undertaken to investigate subcellular structures of hepatocellular carcinomas from these fish.

English sole were collected by otter trawl from several urban waterways of Puget Sound, Washington State. Grossly visible liver nodules were excised from freshly killed fish and divided for light and electron microscopy. Tissues for light microscopy were processed by standard histological procedures, and stained with Hematoyxlin and Eosin.
Regional variation in perineurial cell basal lamina thickness in nerves of diabetics
Authors: Beggs John L. , Johnson Peter C. , Watkins C. Jane
Published: June 2020

The perineurial sheath, composed of multiple layers of perineurial cells, plays an important role in maintaining an optimal endoneurial environment. Alterations in the perineurial sheath have an effect on nerve function and may play a role in the formation of neuropathy. Neuropathy is a common complication of diabetes mellitus (DM). Perineurial cell basal lamina (PCBL) thickening is associated with the diabetic syndrome and the degree of thickening is correlated with the duration of diabetes. The process of basal lamina (BL) thickening in capillaries as well as perineurial cells has been the subject of numerous studies. Some investigators have suggested that the process of BL thickening is directly related to altered metabolism, e.g. hyperglycemia. If hyperglycemia is directly related to PCBL thickening in the nerves of diabetics, it is likely that the degree of BL thickening would be relatively uniform thoughout the peripheral nervous system (PNS).
Sequential degranulation of eosinophils induced by antigen or autocoids in allergic humans
Authors: Sjoerdsma Kate W. , Metzger W. James
Published: June 2020

Eosinophils are important to the pathogenesis of allergic asthma, and are increased in bronchoalveolar lavage within four hours after bronchoprovocation of allergic asthmatic patients, and remain significantly increased up to 24 hours later. While the components of human eosinophil granules have been recently isolated and purified, the mechanisms of degranulation have yet to be elucidated.

We obtained blood from two volunteers who had a history of allergic rhinitis and asthma and a positive skin test (5x5mm wheal) to Alternaria and Ragweed. Eosinophils were obtained using a modification of the method described by Roberts and Gallin.
Reflection electron microscopy of surfaces
Authors: Lehmpfuhl G. , Uchida Y.
Published: June 2020

In surface science the direct imaging of the surface topography of single crystals is of great interest for the investigation of surface-changing processes. Imaging can be done in transmission electron microscopy (TEM) as well as in reflection electron microscopy (REM) using a diffracted beam with surface-sensitive intensity. Surface steps of atomic height can be imaged with both methods. The highest resolution is obtainable only in transmission; however, for the investigation of surface treatments, the reflection method from bulk single crystals is more suitable, even with a lack of resolution, since the thin TEM specimens are often not mechanically stable against surface treatments. With this technique the initial stage of epitaxy, the influence of surface reactions, corrosion etc. on the surface topography can be investigated. The application of REM requires that two important conditions be met, one concerning the specimen itself. Due to the small angle of observation the image is foreshortened.
The effects of strain and strain rate on residual microstructures in copper
Authors: Stevens M. F. , Follansbee P. S.
Published: June 2020

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.
Investigation of shock-wave deformation history from recovered structure
Authors: Mogilevsky M.A. , Bushnev L.S.
Published: June 2020

Single crystals of Al were loaded by 15 to 40 GPa shock waves at 77 K with a pulse duration of 1.0 to 0.5 μs and a residual deformation of ∼1%. The analysis of deformation structure peculiarities allows the deformation history to be re-established.

After a 20 to 40 GPa loading the dislocation density in the recovered samples was about 1010 cm-2. By measuring the thickness of the 40 GPa shock front in Al, a plastic deformation velocity of 1.07 x 108 s-1 is obtained, from where the moving dislocation density at the front is 7 x 1010 cm-2. A very small part of dislocations moves during the whole time of compression, i.e. a total dislocation density at the front must be in excess of this value by one or two orders. Consequently, due to extremely high stresses, at the front there exists a very unstable structure which is rearranged later with a noticeable decrease in dislocation density.
Microstructural development of rapidly solidified, phase-separated SiO2-Al2O3 glass
Authors: Taglialavore A. P. , Kriven W. M. , Risbud S. H.
Published: June 2020

A metastable miscibility gap has been shown to exist oyer much of the SiO2(s) -mullite(s) phase field by various indirect methods. The various proposed boundaries of this liquid-liquid immiscibility region, however, significantly disagree in their widths and critical point positions. The overall aim of our research is to directly determine the miscibility gap boundaries by using TEM/EDS on suitably equilibrated phases of rapidly solidified SiO2-Al2O3 glass. Rapid solidification by roller quenching (∼106°C/sec) and by ice- water quenching (~1035°C/sec) was used so that a wide range of compositions could be studied. SiO2-Al2O3 melts with more than ∼30 wt% Al2O3 readily crystallize when slowly cooled. A suitable microstructure for EDS requires homogeneous phases that are separated by sharp interfaces, and are large enough to withstand beam damage. In an attempt to meet these requirements, the as-quenched glass microstructures were developed by annealing for various times at suitable temperatures.
Tem studies of partially crystallized Y-Si-Al-O-N glasses
Authors: Rai R.S. , Dinger T.R. , Thomas G.
Published: June 2020

Although Si3N4 has many attractive refractory properties some limitations occur due to intergranular oxynitride glass phases that result from liquid phase sintering with oxide additions. Hence it is of fundamental and technical importance that a more detailed understanding of such glasses and possible crystallization behavior is obtained.

This research is being done on a series of compositions of Y-Si-Al-O-N which can be made as glasses and subsequently heat treated to promote crystallization. Here the results of crystallization (of glass Y.26Si.30Al.11ON.11) leading to Y2Si2O7 crystals of different forms is described. Specimens for electron microscopic observations were prepared by ion milling followed by a thin layer of carbon and examined by conventional TEM, CBED, EDXS and at atomic resolution in the Berkeley ARM.
Polytypic intergrowths in barium polytitanate dielectric ceramics
Authors: Davies P. K.
Published: June 2020

Over the past ten years several new ceramic materials have been developed for incorporation in high quality microwave integrated filters. A suitable ceramic dielectric microwave resonator material must have low loss in the microwave region, a low temperature coefficient of dielectric constant, and a high dielectric constant, typically 35-40. Most of the research conducted on the ceramic systems has focused upon phases in the BaO-TiO2 system. Many of the barium polytitanates have dielectric properties suited toward their use in microwave filters. Ba2Ti9O2O and BaTi4O9 are used commercially in the communications industry, and BaTi5O11 may also be a potential candidate for use in these systems.
HRTEM of hexagonal, rhombohedral and Monoclinic(?) Graphite
Authors: Barry J.C. , Buseck P.R.
Published: June 2020

Graphite exists in both hexagonal and rhombohedral forms. Usually about 5% of well-crystallised graphite, natural or synthetic, is of the rhombohedral form. In previous HRTEM studies on carbonization and graphitization only the (0002) spacings (d = 3.36Å) were resolved. In order to study the relationship between the hexagonal and rhgmbohedral phases directly, it is necessary to resolve the (100) (d = 2.13Å) and the (101) (d = 2.03Å) spacings. This study is concerned with graphite of less than perfect crystallinity. Compared to perfectly crystallised graphite, these samples have a smaller crystallite size and more diffuse diffraction spots. The samples were studied at 400kV in a 4000EX TEM (top entry, ±15° double-tilt, Cs= 1.0mm, structure resolution limit = 1.7Å).
Lattice parameter measurements of SiC materials using CBED Holz lines
Authors: Hangas J. , Shinozaki S. , Donlon W.T.
Published: June 2020

Lattice parameter measurements of 6H and 4H polytypes of SiC with various additions were desired to determine if any change occurred with the addition of different sintering aids. The systems studied were the Al-B-SiC system and BeO-SiC system. Lattice parameters have been reported for 6H from a=.3073 to .3081nm, and c=1.508 to 1.511nm, and for 4H a=.3073nm and c=1.0053nm and in one solid solution study variations in c were observed from 1.0082 to 1.0088nm.
High-resolution microscopy of silicon carbide
Authors: Yang C.H. , Mitchell T.E. , Youngman R.A.
Published: June 2020

Silicon carbide, because of its excellent thermal, chemical and mechanical properties, has many applications as high-temperature structural components ranging from adiabatic engines to semiconducting devices. From a scientific point of view, SiC is also a prominent example of a material which crystallizes in polytypic modifications. TEM has been used extensively to study the microstructure of those polytypes. In the present study HREM has been used to study three types of SiC: (1) α-SiC single crystal plates from the pure central core of the Acheson process, (2) VLS-grown β-SiC whiskers, and (3) α-SiC polycrystals sintered with small additions of B4C and C. Observations were conducted on a JEM 200CX microscope with a point-to-point resolution -2.4Å. This resolution is insufficient to distinguish Si and C positions; this requires a resolution of 1.4Å, as shown in Fig. 1(a) which is a weak-phase object projection along [1120] of 6H α-SiC. The equivalent HREM image in Fig. 1(b) shows the zig-zag ABCACB atomic stacking of 6H but not the individual atom positions.
Recrystallization behavior of ion beam modified α-Al2O3
Authors: Sklad P. S.
Published: June 2020

The importance of Al2O3 as a technological material is demonstrated by its use in such widely varying fields as energy production and conversion, catalysis, primary metal production, and communications. Properties of interest include room temperature and elevated temperature strength and fracture toughness, hardness and wear resistance, chemical stability in aggressive environments, high surface area and thermal stability, adhesion of thin metallic films, and dimensional stability. Many of the properties of critical interest are surface controlled.

Until recently charged particle techniques have been used primarily to investigate the radiation damage behavior of Al2O3. However, in the last few years ion beam techniques have been used extensively as a means to modify the near-surface properties of Al2O3. One aspect of this work involves the use of ion implantation to produce an amorphous phase on a single crystal α-Al2O3 substrate and the investigation of the recrystallization behavior during post implantation annealing.
Dislocations and strengthening in ordered Ni4Mo
Authors: Kao H. P. , Vasudevan K. , Brooks C. R.
Published: June 2020

In the Ni-20 at pet Mo alloy, when the ordered Ni4Mo phase (β) forms from the the disordered, fee phase (α) by heat treatment below the critical temperature (868°C), a complex array of domains is created. With aging, considerable strengthening occurs (e.g., hardness may double), but the alloy becomes quite brittle (e.g., <4% elongation), fracturing along the former α high-angle grain boundaries. Some studies have been reported of the dislocation structure of deformed Ni4Mo, but conflicting explanations have been given for the strengthening. In order to better understand the strengthening mechanism, we have made TEM observations of the dislocation structure in aged (725 and 850°C) samples that were undeformed and deformed either by rolling, tensile straining or in situ in the TEM straining stage.
Structure and microanalysis of laser-melted Tl high-speed tool steel
Authors: Kusinski J. , Bielicki T.A. , Thomas G.
Published: June 2020

Laser melting (LM) is currently of interest as a means of improving the wear properties of high-speed tool steels (HSS). The rapid solidification rates obtainable after LM are expected to produce microstructural refinement and high homogeneity which are beneficial to mechanical properties. However a detailed understanding of the laser-hardening of HSS through LM of the surface remains to be obtained.

This paper describes an electron-microscopic investigation of a conventionally-hardened Tl (0.85C/18.5W/4.2Cr/1.2V) HSS which was surface-melted to a depth of 300 um using 1ms pulses from a 7J neodymium laser with an incident diameter of 0.4 mm. The samples were subsequently tempered at 500°C, 600°C, and 700°C for 2 hours. The melted layer showed the highest hardness gain over the unmelted substrate after tempering at 700°C (1050 and 500 uHV respectively).
Characterizatiom of spinodally decomposed Fe-30.1% Cr-9.9% Co: Part 2
Authors: Spooner S. , Horton L. L. , Miller M. K.
Published: June 2020

Characteristic distances describing the scale of the spinodal microstructure obtained from Transmission Electron Microscopy (TEM), Atom Probe Field Ion Microscopy (APFIM), and Small Angle Neutron Scattering (SANS) are described and compared. These techniques provide a view of the microstructure either directly in real space or indirectly in reciprocal space. The material and its general microstructure are described in Part 1, elsewhere in these proceedings. Only the decomposition of the ferrite phase into a modulated isotropic microstructure consisting of a chromium-enriched α' phase and an iron-rich a phase is considered in this presentation.
Identification of Ni3B precipitates in annealed electroless nickel films
Authors: Kitchen D. R.
Published: June 2020

Electroless nickel plating is a process which depends upon the autocatalytic reduction of nickel cations by a suitable reducing agent in an aqueous solution. In this paper electroless nickel is a nickel-boron alloy. Most previous work has involved nickel-phosphorous alloys, however, very little work has been carried out on Ni-B which is the subject of the current work. The microstructure of as-plated and aged electroless nickel-boron thin films, used as the lead frame finish for dual-in-line integrated circuit packages, has been studied by high resolution transmission electron microscopy. In this work the boride phase in the nickel matrix of the annealed plate was identified and characterized.
Two “improvements” for Philips 400 series microscopes
Authors: Greene A. E. , Eades J. A.
Published: June 2020

The optimum size for the disks in a convergent-beam pattern is when the disks just touch. This provides the maximum area of useful pattern indside the disks and avoids the loss of information where they overlap. In a standard transmission microscope, the size of the disk is selected by the size of the condenser aperture. This provides only a few possible settings with rather coarse steps.

We have modified Philips EM420 and EM400T microscopes to provide a continuous variation of the convergence of the incident illumination. This is accomplished by adding a control to vary the ‘Mini’ lens current. The mini lens is located inside the objective lens upper pole piece and by reversal of its magnetic flux, gives the objective lens system two distinct operating characteristics.
A simple method for performing scanned TEM on a JEOL 200CX
Authors: Colijn H. , Clark W.A.T.
Published: June 2020

Computer analysis of TEM images and diffraction patterns has generally required the use of a video camera and frame storage. However, one can achieve the same result with a simple and inexpensive modification to the JEOL ASD system. With this modification, the ASD unit can collect TEM images and diffraction patterns rastered over the existing STEM detector. This modified ASD system can also use our existing x-ray analysis system (TN-2000) with digital beam control (DBC) to acquire images or diffraction patterns for computer analysis at a resolution of up to 512x512 pixels.

Without having a video camera and frame store, one is limited to using STEM for collecting digital images. Scanned TEM allows many more options. Because the specimen is viewed in TEM mode, it is easy to adjust the camera length and magnification and to set up the desired imaging conditions. It is also significantly easier to obtain diffraction patterns using scanned TEM than using STEM methods.
A metrology electron microscope system
Authors: Hembree G. G.
Published: June 2020

An electron microscope system has been constructed which is capable of calibration-quality dimensional measurements from 0.5 to 150 μm. This system was designed to certify one dimensional calibration artifacts for micrometrology instruments. Examples of these artifacts include stage micrometers for microscope magnification calibration and polystyrene latex for flow-through particle sizing instrumentation.

The principle of operation of the instrument is similar to that of an ordinary optical measuring microscope. The electron beam is fixed in position and acts as the reference point. The measured object is translated beneath the electron beam on an electromechanically scanned stage. The displacement of the stage is determined by a commercial optical intei— ferometric measurement system. Therefore the metric of the system is directly traceable to the wavelength standard. One of the electron output signals from the specimen is stored synchronously with the data output from the interferometer by a dedicated minicomputer system. Subsequent analysis of the electron intensity profile is used to determine the measured size of the object.
Image modelling for SEM-based metrology
Authors: Joy David C.
Published: June 2020

Much of the success of the scanning electron microscope (SEM) can be attributed to the fact that the images that it produces appear similar to those seen by our eyes. Consequently the interpretation of SEM micrographs is perceived as a straightforward process. Although this casual approach works well enough for many qualitative purposes, when the SEM is to be used to make precise dimensional measurements of micron-sized features, such as resist strips or conductor pads, then more care must be paid to the details of image formation.

Two types of electron signal, backscattered (BS) and secondary (SE), are usually available in an SEM. In many respects quantitative image interpretation is more straightforward for backscattered than for secondary electrons because Monte Carlo trajectory tracing techniques can be employed to compute the expected variation of signal with beam position.
Computer-aided orientation relationship determination in non-cubic systems
Authors: Porter J. R.
Published: June 2020

Classical electron diffraction techniques for determining the orientations of grains within a polycrystalline material are time consuming. However, many of the steps involved in the process of indexing a convergent beam diffraction (CBED) pattern, eliminating the 180° ambiguity and establishing an axis-angle pair orientation relationship are ideally suited to microcomputer assistance, especially when working with non-cubic systems. The procedure described is an off-line technique applied to a study of alpha alumina, for which extensive electron diffraction data has recently been compiled.
K, L, M, and N core shell ionization cross sections for ELS
Authors: Skiff W.M. , Lin S.H. , Carpenter R.W.
Published: June 2020

Calculated core shell ionization cross sections are useful for elemental and chemical microanalysis using electron energy loss spectroscopy (ELS). We have recently derived analytical expressions for K, L, M, and N shell ionization cross sections in solids, that can be easily evaluated with a mini-computer. Here we briefly describe the theoretical model and give a preliminary comparison of the results with experiment.

The ionization cross section was evaluated using the 1st Born approximation and the single-electron transition model. The initial core shell state was taken as a hydrogen-like atomic orbital with an effective nuclear charge (Z*). The final ionization state was taken as a normalized plane wave, which ignores the target potential.
Very thin foil thickness measurement by energy loss microspectroscopy
Authors: Carpenter R.W. , Jang Peter R.T.
Published: June 2020

A simple experimental method for quantitative determination of foil thickness in very thin regions used for HREM and microanalysis under the single scattering or thin film approximations would be very useful and timely. Most current methods rely on diffraction and are applicable only to crystalline materials, with a lower thickness limit of about ξg, or are difficult to apply to very thin foils. Energy loss microspectrscopy avoids most of these difficulties. This note reports first applications of the method to wedge foils of silicon and austenitic stainless steel.
Retrieval of the single loss spectrum with Johnson-Spence method
Authors: Weng Xudong
Published: June 2020

A method using fourier transform and logarithm for the retrieval of the single scattering electron energy loss spectrum from the experimental multiple data has been described and used previously. However, the uniqueness of this method is proved only under an additional assumption that no energy gain processes occur as the incident electron pass through the specimen. This proof is adopted in the later review papers. In this paper we prove the uniqueness without such an assumption, although in comparison with the energy loss processes, the energy gain processes usually have negligible differential cross sections, provided the relaxation times for the excitation inside the specimen are short enough with respect to the amount of energy loss. Also we shall compare deconvolution methods for the low loss region.
Microdiffraction's Contribution to Microcharacterization
Authors: Eades J. A.
Published: June 2020

The Present

The most fully developed area of application of microdiffraction is the characterization of the specimen's crystal structure. Convergent-beam diffraction from a region of crystal, that has no defects (and, in the case of b, is free from strain), provides the following information:

a) Unit cell. From a single short camera length pattern, it is generally possible to determine the unit cell of an unknown phase.

b) Symmetry. The crystal point group and space group can be determined from a small number of patterns at major zone axes.

c) Fingerprints. Standard patterns can be used to identify the same phase whenever it is subsequently observed.

d) Strain. HOLZ lines can be used to measure local strain or lattice parameter variation.

e) Thickness. Fringes in dark-field patterns can be used to measure crystal thickness.
High-resolution analytical electron microscopy (HRAEM) study of LaCo5 intermetallic catalysts
Authors: Wang Z. L. , Colliex C. , Paul-Boncour V. , Percheron-Guegan A.
Published: June 2020

Intermetal1ic compounds, such as LaCo5, have been used as active and selective catalysts in chemical reaction involving (CO,H2) mixtures. The general understanding regarding these catalysts is that the observed activation is associated with a partial transformation of the intermetallic component into a metal-support system. The macroscopic study of LaCo3 by use of synchrotron radiation absorption measurements (EXAFS and XANES data analysis) largely support this hypothesis. In this work, the microscopic structure of these catalysts has been studied by HRAEM.
Non-porous oxide particles as model supports for heterogeneous catalysts
Authors: Datye A. K. , Logan A. D.
Published: June 2020

Transmission electron microscopy is a valuable characterization tool for studying heterogeneous catalysts. On a supported metal catalyst. TEM allows one to determine the nature of the dispersed phase (particle size, composition and habit) and it's structural relationship with the support (epitaxial growth). There is also a great deal of interest in understanding the three dimensional structure of the metal particles and the degree of interfacial interaction (wetting of the oxide, contact angle etc.). For instance, the phenomenon of strong metal support interaction (SMSI) in Pt/Ti02 catalysts has been associated with the metal particles assuming a raft-like or “pill box” morphology. In order to study questions such as these, it would be desirable to image the metal crystallites edge-on. with the electron beam parallel to the oxide surface. However, on conventional oxide supports, the metal particles tend to lie on the flat terraces of the oxide and therefore only a projection of the particle on the oxide surface can usually be seen. Figure 1 shows an example of a Ru/MgO catalyst prepared on a puratronic MgO support.