bluuebunny/crossref_metadata_2025 huggingface dataset:
Secretory activity of the gallbladder epithelium
Authors: MacPherson B. R. , Scott G. W.
Published: June 2020

Evidence of secretory activity in gallbladder epithelial cells has been accumulating since the initial TEM observation by Johnson et al. in the dog. The presence of mucocoeles in human gallbladder, as will as histochemically demonstrable apical material, has long suggested the secretion of mucoid substances by these cells. Apocrine-like secretory processes have been documented by various investigators in the dog, fetal human and rabbit, mouse, guinea pig, trout, tench and other teleosts using light microscopy, TEM and SEM. Fujita et al. have indicated their belief in various stages of a secretory cycle in the epithelial cells of rabbit gallbladder. Our continuing biliary research has noted the occurrence of surface alterations suggestive of this secretory activity in the gallbladder epithelium of the dog, rabbit and man.

Freshly excised tissue was rinsed in oxygenated Kreb's to remove excess mucoid and biliary deposits, pinned relatively flat on cork and floated face-down in either gluteraldehyde in Millionig's buffer (pH 7.4) or Karnovsky's buffered in 0.2M cacodylate (pH 7.4).
Induction of adhesion and spreading of Ehrlich ascite tumor cells in culture by dextran
Authors: E.C. Chew , T.K. Lam , H.J. Hou-Chan
Published: June 2020

Ehrlich ascites tumor (EAT) has been maintained in our laboratory for about ten years. It has been reported that under normal conditions, EAT cells attach very weakly and do not spread on substrata. Cieslak et al. discovered that EAT cells coated with dextran T-500 adhere and spread on glass in serum-free media. The present communication reports the fine structural changes of EAT in the process of adhesion and spread induced by dextran.

The EAT cells in ascitic fluid were collected from tumor-bearing mice and washed several times in DMEM medium. Dextran (MW.2,000,000), at a concentration of 5% was added to EAT cell suspension and cultured for 3 hours, 5 hours, 1 day and 3 days. Specimens were fixed in 2.5% glutaraldehyde for 1 hour at different time intervals after incubation, dehydrated, critical point dried and coated with gold. The coated specimens were examined with a Jeol JSM-35CF scanning electron microscope at 15 kV.
Evidence for extracellular matrix stimulation of neural crest cell migration
Authors: Jönsson L. , Löfberg J. , Mccoy Anita Nynäs
Published: June 2020

The purpose of this experiment was to study if extrinsic factors regulate initial neural crest cell migration. Recent experiments suggest that a crucial extrinsic factor may be the embryonic extracellular matrix (ECM).

The initiation of neural crest cell migration begins in the anterior trunk segments and follows gradually in more posterior ones. If the surrounding ECM has a migration-stimulating capacity, one would expect a decrease in the amount of ECM anterior-posteriorly at the initial migration stage.

Epidermal grafts from the 3rd trunk somite level of Stage 25 axolotl embryos (Ambystoma mexicanum) were transplanted to the 9th trunk somite level of Stage 25 embryos (Fig. 1). At Stage 25, initial migration is soon to begin at the 3rd trunk somite level. In the controls, epidermal grafts were transplanted between the 9th trunk somite levels of Stage 25 embryos. The operated embryos were incubated for 48 hr at 15°C, fixed and prepared for light microscopy studies.
Localization of IgA and IgG within granules in mucous cells of the human endocervical epithelium
Authors: Sowinski J.M. , Mackay R.L. , Nicosia S.V.
Published: June 2020

The human cervical canal is lined by three epithelial cell types: mucous, ciliated and reserve cells. The origin of immunoglobulins within the endocervix has not been clearly defined. In 1968, Pozzuoli et al presented immunoelectrophoretic and immunofluorescent evidence for the existence of IgA and IgG within both human cervical mucus and plasma cells which were present beneath the endocervical epithelium. Masson, Heremans and Ferin in 1969 analyzed pooled samples of cervical mucus by chromatography on DEAE-cellulose columns and were able to identify IgA and IgG as well as several other soluble proteins. In 1970 Lippes et al were able to identify IgA and IgG in the human cervix by immunocytochemical localization at the light microscopic level.

Using a direct peroxidase conjugated antisera to human IgA and IgG, we have been able to confirm the presence of these immunoglobulins at the ultrastructural level and to localize both IgA and IgG within the granules of endocervical mucous cells.
Ascospore germination in Eleutherascus (Pezizales)
Authors: Steffens W.L.
Published: June 2020

The fine-structural changes which immediately precede and then accompany germination in spores of most fungal classes have been described to some extent. Few however describe ultrastructure of germinating ascospores. A study of germinating ascospores of ELEUTHERASCUS PERUVIANUS was undertaken to determine the type of germination and to provide some much needed information on the ultrastructure of germination in the Operculate Discomycetes. Figure 1 shows the fully mature ascospore of E. PERUVIANUS before the onset of germination. Immediately prior to and during germination, the single haploid nucleus undergoes several mitotic divisions resulting in a multinucleate ascospore (fig 2). Additionally, there is a great decrease in density of the sporoplasm, with the integrity of all organelles being restored. Large membrane-bound vacuoles appear, and the once abundant oil droplets totally disappear. With the exception of the multiple nuclei, the sporoplasts remarkably resemble the newly delimited prospore stage of their earlier ontogeny (Steffens and Jones, Ms in review).
Intercelular adhesion of teratocarcinoma STEM cells
Authors: Grabel L. B. , Martin G. R. , Rosen S. D.
Published: June 2020

A major research interest is the identification of the cell surface molecules responsible for the selective intercellular adhesion of various cell types. Initially it was believed that cell-cell adhesion was mediated by tissue specific lock and key molecules present on adjacent cells; a single molecular recognition system would be sufficient to generate the desired selectivity. In the past few years it has become apparent that although specific recognition molecules are certainly involved in mediating intercellular adhesion, the idea of each cell type having a single unique molecular system of recognition is an oversimplification. The available data suggest that multiple systems of adhesion function simultaneously in any given cell type, and that the same or similar molecules may be involved in adhesion within different tissues.

We have been studying the intercellular adhesion of teratocarcinoma stem cells, and review here evidence that at least two separable components are involved in their intercellular adhesion; one requiring the presence of divalent cations, and the other one involving recognition by a cell surface fucan/mannan specific lectin.
Low atomic number imaging of cells by electron energy loss spectroscopy
Authors: Leapman R.D. , Ornberg R.L.
Published: June 2020

Recent advances in electron microscopy and analytical electron microscopy now make it possible to obtain elemental images of biological samples. In particular, electron energy loss spectroscopy is sensitive to the low Z elements, carbon, nitrogen, and oxygen which constitute most of the mass of a cell. Since the relative numbers of these atoms vary from one cellular compartment to another, significant information should be contained in C, N, and O images. The resolution in such images will clearly depend on the susceptibility of biological compounds to radiation damage. In order to learn how low Z imaging can be applied to cell physiology, we have obtained and describe here some preliminary carbon and nitrogen maps of the well characterized bovine adrenal chromaffin cells.

Dissociated 3-day old bovine chromaffin cell cultures were quick frozen, freeze substituted in tetrahydrofuran, and embedded in Lowicryl HM20 resin as previously described. Energy loss images were obtained with recently developed instrumentation consisting of a Hitachi H700H TEM-5TEM and a magnetic sector electron spectrometer interfaced to a Digital Equipment Corporation PDP 11/60 and LSI 11/23 computer system. During image aquisition the computer steps the probe (∽10 nm dia.) across the sample and acquires several spectrum channels around selected core edges at each image point (pixel).
Negative staining versus rotational evaporation
Authors: Schmiady H. , Kreuzfeldt C. , Reuber E. , Tesche B.
Published: June 2020

This comparative study demonstrates the salient differences between the two most common methods of contrasting subcellular particles, using the 40S ribosomal subunit from saccharomyces cerevisiae as test specimen because its socalled beak-like L (left) and R (right) particle projections can be unequivocally distinguished.

The negative staining method produces images which are not artifact-free because it is a combination of fixation and chemical staining and, therefore, not neutral towards the object. For three-dimensional reconstruction it is unsatisfactory because:

(1) The affinity of the support film to the negative stain solution differs so greatly that sometimes undesired positive staining effects occur.

(2) The rendition of the structure depends on the embedding--that is, on the level of the negative stain; fluctuations in the level lead to a loss and/or change of the structure, and thus to difficulties in interpreting the stain distribution, especially when reconstruction of the object by means of tilt series is planned.
Electron crystal structure analysis of biomembrane lipids
Authors: Dorset Douglas L.
Published: June 2020

Because of the well-known sample crystallization difficulties which often hinder the X-ray crystal structure analysis of many long-chain lipids, Parsons and Nyburg were the first to attempt the crystallographic elucidation of a phospholipid structure using electron diffraction intensity data from more readily-available microcrystals. Subsequent electron diffraction studies of various lipids in this laboratory over the past decade have revealed a number of peculiar features of such data-particularly if these are expected to resemble X-ray data. These observations have led to a physically reasonable overview of the problem based on well-established diffraction theory and have permitted the derivation of useful analytical procedures for electron crystal structure determination. It is interesting to note that the appropriate procedure is dependent on the method used for specimen crystallization.

Lipid crystals grown from solution are typically plate-like with long alkyl chains packing with axes more or less perpendicular to the best developed crystal face ; an incident electron beam thus parallels the longest unit cell axis.
A neuronal mechanism for the control of latero-frontal ciliary activity in the fingernail clam, Musculium transversum
Authors: Paparo Anthony , Murphy Judith A. , Dean Robert
Published: June 2020

Extensive studies have dealt with the transport of particles on the gill of suspension feeding bivalves, but our knowledge of the mechanisms involved is still incomplete. There is, however, physiological evidence that each of the ciliated cell systems in bivalve molluscs may be individually controlled. Three types of ciliated cells are distinguished on the gill of fingernail clams: frontal (FC); latero-frontal (LFC); and lateral (LC).For the most part in studies involving ciliary control mechanisms, LFC are neglected. It is thus the purpose of this study to present data which begin to elucidate a neuronal mechanism for LFC control.

Gill preps were isolated with an intact nerve supply in a dish which was placed in a holder fastened to an adjustable stage of a microscope. In fields of view of 50 gill filaments, ciliary motility, chemical perfusion and electrical stimulation were observed and/or performed.
Nuclear microtubular invaginations in acute lymphoblastic leukemia cells
Authors: Ahearn M.J. , Yee G.S. , Trujillo J.M.
Published: June 2020

Intranuclear "mitochondrion-like" bodies have been described in the neoplastic cells of both the Sezary syndrome and mycosis fungoides. (2) These cytoplasmic structures are hypothesized to be trapped in the nucleus during mitotic division and to represent another example of the abnormalities of the Sezary cell.

We have recently observed identical nuclear inclusions in lymphoblasts from pediatric acute lymphocytic leukemia (ALL) patients, Figs. 1 and 2. In each instance, the malignant cells represent an abnormal variant of thymus-derived lymphocytes. They display a common feature in the pronounced maturation asynchrony between the nucleus and the cytoplasm. Our continuing studies of ALL blasts have revealed the presence of an apparent longitudinal and cross-sectional presentation of the "mitochondrionlike" body, Fig. 3. In this conformation, the similarity between the structure's outer membranes and the double-walled nuclear membrane becomes apparent.
EM study of leptomeninges on a patient with metastatic melanoma
Authors: Lim B. S.
Published: June 2020

LB is a Caucasian male with a diagnosis of hebephrenic Schizophrenia. He was first hospitalized from 1923 to 1928 then eloped. On his return in 1941, he helped with the ward work. From 1963 through 1967 he was given Thorazine 300 to 600 mg/day to control his psychotic behavior. The medication was then stopped for unknown reason. Sometime before his death a malignant tumor of the eye was discovered; the patient refused surgery. At the time of autopsy, multiple tumors in the skin, various organs and the calvarium were noted. There were also very small demarcated black areas seen in the leptomeninges. Light microscopy study of the brain revealed focal atrophy of the left optic tract and focal fibrosis of leptomeninges of the left temporal lobe. However, no pigment were detected in histological sections of the leptomeninges. A section from one of the black areas was taken for electron microscopic examination. This work is to reveal the presence of melanosomes in leptomeninges and to discuss possible links between phenothiazines and melanin synthesis.
Strategies for error reduction in high-magnification stereoscopic measurements based on error equation calculations
Authors: Ruben George C. , Marx Kenneth A.
Published: June 2020

We have used freeze-fracture TEM to visualize toroidal shaped spermidine Calf Thymus DNA complexes. DNA collapsed into these complexes represents an in vitro model system for the packaging of double stranded DNA in bacteriophage and virus heads. Both freeze fracture TEM and biochemical data support a circumferential DNA winding model for DNA organization in the hydrated torus. To better understand this microscopic DNA organization we made stereoscopic measurements of surface DNA topology in high-resolution eucentric tilt views of freeze-etch, single direction shadowed, low Pt-C metal (9Å) replicas. Here we calculate and discuss the error magnitude associated with these modern high-magnification stereoscopic measurements. Freeze fracture TEM was performed on spermidine-condensed Calf Thymus DNA samples as previously described. Micrographs (105 x with a JEM 100 CX) were printed at 2.5 x 105 for measurement with a floating-mark stereometer (SB 190 Mirror Stereoscope, Cartographic Eng. Ltd.). Figure 1 shows the DNA torus we made measurements on.
Recent projects at the Madison HVEM
Authors: Pawley James , Ris Hans , Neuberger Damian
Published: June 2020

Efforts to obtain <2nm resolution from covalently bonded samples in the TEM using low-dose techniques have varied the embedding medium (glucose, ice) and the specimen temperature but not the beam voltage. HVEM provides an increase in permissable sample thickness, a wider contrast transfer function, a larger specimen area for the introduction of the necessary cold stage and, possibly, a reduction in radiation damage. A concerted effort to investigate these potential advantages was initially hampered by various practical difficulties such as lower film sensitivity at 1 MeV, poor instrumental resolution, low contrast of the viewing screen image and lack of a minimum exposure system. How, a film incorporating a 10-20μm NTB-3 emulsion has been found to be almost as effective for these studies at 1 MeV as normal EM films are at 100 kV. We have also improved our instrument performance (.2 nm from Au, axial ilium.) and added a sensitive TV camera with attached, averaging image memory which has greatly improved focussing accuracy at all magnifications Furthermore, flexible circuitry to permit minimal exposure techniques is now operational and a high resolution cold stage is nearing completion.
Actin and RNA identification in the rat chromatoid body by means of protein A-gold and RNAse-gold techniques
Authors: Armbruster B. L. , Walt H.
Published: June 2020

Differentiating spermatids display various forms of motility, the most obvious being microtubule-dynein motivated flagellar movements. Recent studies have demonstrated the presence of contractile proteins, in mammalian germinal epithelium, and some organelle movements seem to be based on an actin-myosin mechanism. Chromatoid bodies, found in the spermatocytes and spermatids of many animals, show directed movements around spermatid nuclei during differentiation. Although this phenomenon has been described frequently, the underlying motive force was not established. As the chromatoid body moves along the nuclear envelope towards the region of the differentiating acrosome, it established contact to intranuclear material through nuclear pore complexes. It has been postulated that nucleocytoplasmic RNA transport is a major function of the chromatoid body. Whereas light microsopic histochemical studies suggested the presence of RNA in this organelle, similar results were not found at the ultrastructural level. More recent studies by means of high resolution autoradiography supported that conclusion that the organelle contains long-lived messenger RNA for use in late spermiogenesis.
Electron microscopy of rabbit FC crystals
Authors: Grant Robert A. , Degn Laura L. , Chiu Wah , Robinson John
Published: June 2020

Proteolytic digestion of the immunoglobulin IgG with papain cleaves the molecule into an antigen binding fragment, Fab, and a compliment binding fragment, Fc. Structures of intact immunoglobulin, Fab and Fc from various sources have been solved by X-ray crystallography. Rabbit Fc can be crystallized as thin platelets suitable for high resolution electron microscopy. The structure of rabbit Fc can be expected to be similar to the known structure of human Fc, making it an ideal specimen for comparing the X-ray and electron crystallographic techniques and for the application of the molecular replacement technique to electron crystallography. Thin protein crystals embedded in ice diffract to high resolution. A low resolution image of a frozen, hydrated crystal can be expected to have a better contrast than a glucose embedded crystal due to the larger density difference between protein and ice compared to protein and glucose. For these reasons we are using an ice embedding technique to prepare the rabbit Fc crystals for molecular structure analysis by electron microscopy.
Structural investigation of frozen-hydrated Omp C specimens prepared by the fatty acid monolayer technique
Authors: Chang Chung-Fu , Glaeser Robert M.
Published: June 2020

Omp C (M.W. ∽36,000) is one of the major proteins in the outer membrane of E. coli. Trimeric Omp C forms a pore allowing small hydrophilic molecules to diffuse across the membrane. Specimens we have studied are prepared by reconstituting purified Omp C trimers with lipid A (the core structure of the outer membrane 1ipopolysaccharide). These specimens form 2-D periodic arrays with a size of ∽0.5 μm on edge.

Initial structural investigations on negatively stained Omp C specimens have been reported by Grano et al. We now present a preliminary structural analysis of frozen-hydrated Omp C, using specimens prepared by a modification of the stearic-acid monolayer technique of Hayward et al. Stearate monolayers can successfully "squeeze out" the bulk water on the surface of the EM grid only at relatively high concentrations of Ca++ and high pH. In the current study, we replaced the stearic acid with behenic acid, CH3(CH2)20COOH, which can adhere to a suitably prepared EM grid from a subphase of distilled water.
Double periodic component in the cell wall of a square-shaped halobacterium
Authors: Kessel Martin
Published: June 2020

Halobacterial walls are known to be composed of glycoprotein subunits usually arranged in a hexagonal array as seen by shadow casting of the cell surface. The recent description of a Halobacterium having a unique square shape has enabled us to obtain negatively stained images of organisms sampled directly from their natural habitat. The views most commonly observed are those of cells lying on their flat surface thus presenting a confusing image of the superposition of the upper and lower cell surfaces.The superposition effect may be resolved in the optical diffraction pattern which shows the periodic components of the image to lie on two separate lattices rotated relative to each other by an arbitrary angle. Separate views of the upper and lower cell walls may be obtained by applying a fourier filter to the image transform. We have used a digital filter based on the indexing of the reciprocal lattices as seen in the digital power spectrum.
Electron microscopic localization of sulfated glycosaminoglycans and proteoglycans in pleomorphic adenomas
Authors: Lam Ronald
Published: June 2020

Although “myoepithelial” cells in pleomorphic adenomas have been implicated by several ultrastructural studies as responsible for the production of myxomatous and chondroid stroma, the cellular source of stromal glycosaminoglycans and proteoglycans has yet to be demonstrated histochemically by electron microscopy.

Three major salivary gland pleomorphic adenomas were examined by electron microscopy after fixation in 2.5% glutaraldehyde and in 0.2% ruthenium red-glutaraldehyde. Routine ultrastructural preparations revealed a spectrum of cells with epithelial and mesenchymal features. The mesenchymal cells in the myxoid region displayed intracytoplasmic 70-80Å microfilaments, prominent Golgi complex, RER, and secretory vesicles. The fine structural appearance with ruthenium red stained tissue was similar to that of routine preparations. However, with ruthenium red staining, proteoglycans of the myxoid stroma could be visualized as numerous extracellular 250-500Å polygonal matrix granules with fine projecting filaments (Fig. 1A). Similar positive ruthenium red stained intracellular granules were observed within the cytoplasmic vacuoles of the mesenchymal cells, a feature not present in cells with epithelial differentiation (Fig. 1B).
Fibril-like structures in preparations of scrapie prions purified from hamster brain
Authors: McKinley M. P. , Bolton D. C. , Prusiner S. B.
Published: June 2020

The ultrastructure and biochemical composition of the scrapie agent, an infectious particle which causes a degenerative disease of the central nervous system in sheep and goats, has remained elusive for decades. Progress in its purification has shown that the infectivity of the agent depends upon a protein(s). The term “prion” was introduced to reflect the unusual molecular characteristics of the infectious agent. In purified fractions highly enriched for the scrapie prion, we have found rod shaped, fibril-like structures. The purified fractions were prepared using two different procedures: one used sarkosyl gel electrophoresis and the other employed sucrose gradient centrifugation. In these same purified fractions we have also identified a protein of molecular weight 27,000 to 30,000. This protein is unique to fractions purified from scrapie infected brains. The biophysical behavior of the scrapie associated protein parallels that observed for the infectious prion: under nondenaturing conditions both the protein and the prion are resistant to degradation by proteases at 37° for 30 min.
Computer Simulation of the Imaging of Atomic Defects in Metals
Authors: Fields P. M. , Cowley J. M.
Published: June 2020

Localized defects in metals, such as vacancies and interstitials, should have scattering powers for electrons comparable with those of the single heavy atoms which have been imaged in recent years by use of high resolution electron microscopes. It should therefore be possible to obtain appreciable contrast from such defects with current lOOkV electron microscopes. However in order to distinguish the intensity variations due to these defects from those due to specimen surface structure, contamination or other causes, it may be necessary to use the improved resolution of high voltage microscopes so that the characteristic shapes of the defects and their local strain fields can be recognized.

In order to test these speculations, we have made computer calculations of the images and diffraction patterns to be expected from split interstitials in thin crystals of gold and aluminum for bright-field and dark-field imaging with a lOOkV microscope with an objective lens having Cs = 1.8mm and for a l000kV microscope, Cs = 1.8mm.
Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry
Authors: Lally J. S. , Lee R. J.
Published: June 2020

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.

Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.
Clustering of Atomic Defects in Copper during In situ Annealing in the High-Voltage Electron Microscope
Authors: Jäger W.
Published: June 2020

The migration of atomic defects (interstitials, vacancies) introduced by electron irradiation of metals at low temperatures during subsequent thermal annealing may lead to mutual annihilation, to annihilation at sinks, or to an agglomeration of atomic defects of the same species into clusters. In the past this has been investigated in copper mainly by resistivity experiments and diffuse x-ray scattering methods. In-situ annealing experiments in a high-voltage electron microscope may yield additional information about the formation and nature of clusters and therefore may contribute to the understanding of the annealing stages in metals. This paper summarizes the most important results of a detailed investigation of the formation of clusters in copper during in-situ annealing between 10K and 470 K.

Thin copper foils (nominal purity 99.999%, foil thickness,~200nm) were irradiated with 650 keV electrons at 10 K to a total dose of 8 x 1019e cm-2 in a Hitachi HU 650 microscope equipped with a helium-cooled specimen stage.
Near-Surface Formation of Dislocation Loops in Electron-Irradiated Al-Mg
Authors: Westmacott K. H.
Published: June 2020

In studies of metal foils electron irradiated in a high voltage electron microscope it is found that after a short incubation period, interstitial loops nucleate in the center of the foils and grow under continued irradiation until eventually a network is formed. Stereomicroscopy has confirmed that loops are unable to nucleate within ~0.2μ of the surface. This is because the surfaces act as good sinks for the point defects and prevent the attainment of the necessary supersaturation for loop nucleation. In the present work on Al-ll%Mg quite different behavior has been observed depending on the condition of the foil surfaces prior to the irradiation. All the irradiations were done on electropolished discs at 650 kV in the Berkeley HVEM.
An Application of High Brightness LAB6 Cathode Gun to JEM-100CX
Authors: Yonezawa Akira , Nakagawa Seiichi , Suzuki Mikio
Published: June 2020

The LaB6 cathode gun, which is noted for its high brightness and long life, is highly expected to improve the image quality of CTEM,STEM and secondary electron images. But, in order that the LaB6 gun may stably attain its maximum performance, it is necessary to solve big prblems concerning the vacuum pressure around the tip and with tip holding and heating.

Here, we shall introduce excellent data and CTEM and secondary electron images, obtained by a clean high vacuum EM, the JEM-100CX with aid of a LaB6 emitter assembly1)commercialized as an option for the JSM-35. The instrument also used a high resolution scanning device, ASID-4D to obtain the secondary electron images. The JEM-100CX can easily attain, even in the gun chamber, a 10-7 torr clean high vacuum which is high enough for a LaB6 tip, because it employs the “CASCADE” differential pumping system2). We shall discuss the gun assembly.
Image Acquisition and Storage Via a Computer Driven STEM
Authors: Butler Jeffrey
Published: June 2020

A system for the collection, recording, transferring and processing of digitized real-time image data has been built for use in conjunction with a JEM- 100B electron microscope equipped with an ASID scanning attachment. Display, comparison and processing of images is facilitated through an ETEC Vistascan, while the third basic unit of hardware is a DEC PDP-11/20 minicomputer, as shown in the block diagram, Fig. 1. To link these units together, several interfaces have been designed for the purposes of driving the scan and video signals over the physical distance separating these devices and to decode control pulses, multiplexed with video signals, fed to the microscope and Vistascan from the PDP-11. The implementation of the Vistascan and the capacity for recording image data on magnetic tape exist as important variations from a previously reported system (1).
In situ Investigation of Field and Temperature Effects on the Surface of Metal Tips
Authors: Colliex C. , Sudraud P. , Van de Walle J.
Published: June 2020

For the achievement of high brightness ion sources, field evaporation, desorption and ionization effects constitute very attractive solutions (1,2). All theses mechanisms are promoted in a very small area on the apex of metal tips. The interpretation of field ionization images is often made uncertain because of the lack of accurate information concerning the topography and the crystallographic structures of the emitter.

Several authors (3,4,5) have associated electron microscope visualization of tungsten tips either with CTEM (at standard or high voltages) or with SEM, with the study of field emission or ionization patterns. But very few of these works have coupled these observations to the determination of the fundamental parameters (electric field, tip temperature) which control the emission. For instance, in the scanning microscope, the thermally emitted electrons disturb heavily the working conditions preventing from dynamic in-situ observations.
Lattice Imaging of Grain Boundary Precipitation Reactions
Authors: Gronsky R. , Thomas G.
Published: June 2020

Materials and Molecular Research Division, Lawrence Berkeley Laboratory and Department of Materials Science and Mineral Engineering, University of California, Berkeley, California 94720.

Grain boundaries are known to catalyze a wide variety of solid state phase transformations which drastically affect metallurgical properties. The study of these reactions has traditionally required transmission electron microscopy, particularly when the transformation products are only partially developed. In the present paper, an application of lattice fringe imaging to the study of grain boundary reactions in Al-Zn alloys is described. The technique has proven to be far superior to conventional TEM methods in providing information on not only the detailed structural configuration of lattice planes at boundaries, but also the compositional changes, to within ∽10Å of the boundary plane, accompanying the transformations.
The Strain Dependent Accommodation Behaviour of Extrinsic Grain Boundary Dislocations
Authors: Jones A.R. , Ralph B.
Published: June 2020

Previous work on a fully austenitic stainless steel has shown that the nucleation and growth of Niobium Carbide (NbC) particles at grain boundaries can be substantially affected by deformation introduced prior to ageing (1). The present investigation which is, in part, an extension of the above work was instigated to examine the accommodation behaviour of extrinsic grain boundary dislocations as a function of deformation and temperature. The alloy investigated contained 20% chromium, 25% nickel, 0.6% niobium, 0.02% carbon + nitrogen, balance iron. Solution treated specimen material was cold rolled by 2%, 5% and 13% prior to annealing for times between 5 and 15 minutes at temperatures ranging from 650°C to 1000°C.

Figures la and b show typical grain boundaries in the as-worked 2% and 5% materials; extrinsic dislocations appearing as linear features in the grain boundaries. However, grain boundaries in specimen material deformed by 13% contained such large numbers of these defects that the clear resolution of the individual dislocations was frequently impossible.
Characterization Of Flaws Produced By Mechanical Grinding Of Si3N4
Authors: Tighe Nancy J.
Published: June 2020

The flexure strength of silicon nitride is related to the size of flaws at or below the surface. These flaws typically are cracks which nucleate at ground surfaces or at internal inclusions. One crack from the population of flaws grows under the applied stress and causes failure. Recent mechanical testing experiments in this laboratory showed that high temperature (1200°C) exposure can either increase or decrease the strength of silicon nitride depending on the time of exposure and the testing temperature (1). Because this material oxidized readily at 1200°C, both oxidation and heat treatment changed the flaw population. The change in flaw population can be determined after nature of the initial population is established.

The initial flaw population produced by grinding is being characterized by examining thin foils made from silicon nitride samples which had different surface treatments.
Direct Observation of Crystalline Ordering In Naturally Graphitized Carbon Produced by Low Grade Metamorphism
Authors: McKee Thomas R. , Buseck Peter R.
Published: June 2020

Sediments commonly contain organic material which appears as refractory carbonaceous material in metamorphosed sedimentary rocks. Grew and others have shown that relative carbon content, crystallite size, X-ray crystallinity and development of well-ordered graphite crystal structure of the carbonaceous material increases with increasing metamorphic grade. The graphitization process is irreversible and appears to be continous from the amorphous to the completely graphitized stage. The most dramatic chemical and crystallographic changes take place within the chlorite metamorphic zone.

The detailed X-ray investigation of crystallite size and crystalline ordering is complex and can best be investigated by other means such as high resolution transmission electron microscopy (HRTEM). The natural graphitization series is similar to that for heat-treated commercial carbon blacks, which have been successfully studied by HRTEM (Ban and others).
Crystal Structures Of L-Nb205 AND L-Ta205
Authors: Iijima Sumio
Published: June 2020

Although structures of tantalum pentoxides have been extensively studied, they have not been fully understood because of the complex nature of their X-ray diffraction patterns. In this study we made some observations on crystals of L-Ta2O5 and L-Nb2O5 using a high resolution electron microscope. The latter structure has been believed to be isostructural with L-Ta2O5. The samples were prepared by Dr. Roth at NBS and were parts of the products used for determining phase relationships in niobium pentoxides (1) and the Ta2O5-Ta2WO8 system (2).

According to the X-ray data both structures have orthorhombic unit cells with a = 6.2, b = 29.3, c = 3.9Å. The structures are based on the U03-type and the b spacings are nearly 8 times those of the subcell. Electron diffraction (E.D.) patterns of L-Nb2O5 and L-Ta3O5 crystals showing a*-b* reciprocal sections confirmed generally the results of X-ray works (Figs, la and lc).
Image Contrast Of Amorphous Carbonaceous Materials
Authors: Iijima Sumio
Published: June 2020

We have previously reported a method for preparing extremely thin films of graphite single crystals for use as support films (1). Usefulness of these films, in particular, for obtaining high resolution images of phase objects, was demonstrated by imaging (with bright field mode of CTEM) surface steps with heights of less than 10Å on graphite films (2) and also single atoms of tungsten (3). In this study using the same graphite substrates we have made some observations of amorphous materials to understand the image contrasts in terms of microstructure.

Although image contrasts of thin evaporated carbon films, even if prepared as thin as possible, do not show measurable dependence on film thicknesses, we chose as test objects the extremely thin films of contamination which grew discontinuously on the substrate films during specimen observation (4). Image contrasts of these films were then compared with those of known structures such as surface steps and a single layer of graphite crystal.
High Voltage Electron Phase Microscopy With Crystal Supports
Authors: Hines R. L
Published: June 2020

The use of single crystal support films to produce high contrast images of phase objects has been discussed by Hines and Howie (1). When a phase object such as a biological molecule or a latex sphere is located on top of a strongly diffracting crystal support, the crystal support acts like a phase plate. Dark field, shadow or phase contrast images may be formed depending upon the exact crystal diffraction conditions and thickness. An objective aperture is used to exclude the diffracted beams so that the image is formed only with the bright field beam and the electrons scattered by the object. For simplicity in analysis, 0.11 micron diameter latex spheres are used as objects and are supported on graphite crystals about 0.1 microns thick. The graphite crystal preparation is described elsewhere (2). The latex sphere suspension is sprayed onto the graphite with a glass nebulizer after the graphite has been made hydrophilic by subjecting it to a glow discharge.
Microstructural Changes in 900°C Heat Treated Ti-6A1-4V After Deformation
Authors: Imam M. Ashraf , Fraker Anna C. , Gilmore Charles M.
Published: June 2020

It has been shown that the mill annealed form of Ti-6A1-4V has improved fatigue resistance after it has been heat treated at 900°C for 10 minutes and water quenched, some of the increased fatique strength of this material may result from microstructural adjustments to deformation. The present study deals with the general microstructure of the material and specifically with that of the martensite before fatigue, at the fracture surface after fatigue and at distances away from the fracture surface. In addition, microstructural changes which are brought about by annealing this heat treated material at 500°C for 8 hours are discussed.

Thin foil specimens were prepared from bulk materials by spark cutting and planing. This was followed by electropolishing in a solution of 62.5% methanol, 31% butanol and 6.5% of 70% perchloric acid at 13.9 volts at -40°C. Fatigue testing was conducted at ±0.020 shear strain with a constant axial stress of 2.12 x 107 N/M2.
On the Microstructure of Step Quenched and Tempered AISI 4340 Steel
Authors: Khan K.H. , Kannan V.C.
Published: June 2020

It has been shown by earlier workers1that when AISI 4340 steel is quenched from 1200°C, the martensite formed exhibits packets of laths containing dislocations and auto-tempered ∊-carbide inside the laths and thin films of stabilized austenite retained between the parallel lath interfaces. In the present report, we present TEM observations made on specimens of AISI 4340 steel which were step-quenched and then tempered. The heat treatment was: 1200°C/1 hr→ 1100°C/1 hr→ oil quench —tempered at 200° C/l hr. Electron transparent samples were prepared by double jet electropolishing using standard solutions and the thin foils were observed at 100KV in a Hitachi HU 11B electron microscope. Figures 1 and 2 show the microstructures obtained from these samples. One can discern the presence of lath martensite A as well as "blocky" martensite B in these two micrographs. The blocky martensite was mainly observed adjacent to prior austenite grain boundaries.
The Fine Microstructure of a Mechanically Alloyed Oxide Dispersion Strengthened Solid Solution
Authors: Marti Jordi , Stulga John E. , Tien John K.
Published: June 2020

A recent development in powder metallurgy technology, known as mechanical alloying (1), can find applications in alloys which cannot be manufactured by conventional processes, due to high melting temperatures, chemical incompatibility of constituents in the melt, or high reactivity. The process has been utilized in the production of a nickel-base superalloy and a nickel-base solid solution which contain dispersions of fine and inert oxide particles for high temperature strength. As part of a study of the creep and stress rupture behavior of these alloys, the as-received and crept microstructures have been examined using the transmission electron microscope. This note discusses the fine-scale microstructure of the mechanically alloyed oxide dispersion strengthened (ODS) nickel-base solid solution.

The alloy has a nominal chemical composition in weight percent of Ni - 20Cr - 0.5Ti - 0.3A1 with O.6Y2O3oxide particles.
Annealing Temperature and Grain Size Effect on the Grain Boundary Ledge (Density) Structure in Nickel
Authors: Venkatesh Eswarahalli
Published: June 2020

In recent years many researchers have shown great interest in understanding the structure of grain boundaries1,2 and their influence on the mechanical properties of metals and alloys3-5. It has been shown that the structure of grain boundaries can be changed by appropriate thermomechanical treatments6. There are many experimental parameters that can influence the grain boundary ledge structure. The influence of annealing temperature and grain size are considered here.

In the present work, pure (99.98%) nickel sheet mill rolled (hot) to 0.022 in. thick was used. One batch of sample was cut and rolled to 40% reduction in thickness and annealed at 800-1125°K in argon,and air cooled to achieve a constant grain size of 50 μm in all samples. A second set of samples was cut and rolled 10-70% reduction in thickness and similarly annealed at 800-1325°K so as to obtain different samples with grain size of 2, 30, 50, and 150 μm.
Metallurgical Problems with Orthopaedic Joint Prostheses
Authors: Jendrzejewski John P. , Paulson Gary G.
Published: June 2020

Metallic joint prosthetic devices are used to replace the skeletal structure of the human body which has been destroyed by disease or accident. These surgical implants are intended to remain in place for the rest of the patients' life, but often they fail. Subsequent removal and replacement is both expensive and painful. We have had the opportunity to examine numerous joint prosthetic devices which have fractured in use. The scanning electron microscope and energy dispersive X-ray spectrometer used in conjunction with conventional metallography have proven very useful for these failure analyses.

The primary failure mode of joint prostheses is metal fatigue. Shown in Figure 1 is a femoral component of a hip prosthesis which failed in the stem portion. Fractographic analysis reveals that reverse bending stresses initiated fatigue cracks at the distal and proximal portion of the stem as pointed out in Figure 2.
Void Growth in the Early Stages of Electromigration
Authors: Lloyd J. R. , Nakahara S.
Published: June 2020

Recently, a TEM study has shown that a high density(l010 to 1012/cm2) of small(<50A) voids are present in both as-deposited(l), and annealed(2) evaporated gold films. Using the defocus contrast technique, Lloyd and Nakahara(1) were able to make void size measurements which allowed a systematic study of the dependence of void formation on deposition parameters.

In order to study the role of pre-existing voids in electromigration(EM) damage, ^lOOOA-thick gold films with initial void densities of lO10and1011/cm2 were obtained by evaporation onto KC1 substrates held at 280°C and 80°C, respectively. This choice of substrate temperatures was based on our previous study (l) of the effect of deposition parameters on void density.

All films studied were found to contain many small voids which were revealed with the use of defocus contrast. EM-induced void growth was studied by comparing two films deposited onto a substrate held at 80°C during the same evaporation.
Brittle Grain Boundary Fracture in Iridium
Authors: Rohr D. L. , Hecker S. S. , Murr L. E.
Published: June 2020

Iridium is a most interesting fee metal with a high melting point (2443°C) and extremely high elastic moduli (Young's modulus of 76 million psi). Single crystals of Ir fail by brittle cleavage and polycrystalline Ir fails by brittle intergranular fracture at temperatures below 1000°C. We have previously shown that both modes of fracture are intrinsic and not impurity related. (1)

The present study was undertaken to study the grain boundary structure of Ir by transmission electron microscopy. Sheet specimens of Ir-0.3%W (used in space nuclear power applications) were recrystallized at temperatures above 1300°C. Thin foils were prepared by spark planing and electropolishing with an acidified CaCl2 solution in a jet polisher and were examined in a JEOL 200 B electron microscope operated at 200 kv.

We examined a large number of foils and found the most interesting grain boundary features to be ledges (2) (Fig. la).
Structural Defects in Polycrystalline Silicon and Their Effect on Solar Cell Efficiency
Authors: Narayan J.
Published: June 2020

Although extensive electron microscope studies of defect structures in silicon single crystals have been made, it appears that little or no attention has been given to the defect structures in polycrystalline silicon (Polysil) because it has been used almost exclusively as a source material subjected to further purification and growth into device grade single crystals. There is current interest in Polysil for fabrication of less expensive solar cells; however, improvement in the electrical properties will be necessary in order to achieve reasonable solar cell efficiency. Since most structural defects degrade the electrical properties of both p- and n-type silicon, the characterization of their structures will provide a basis for selection of better material and/or processes for reducing defect densities. The present work is part of a program which includes the evaluation and development of Polysil as a solar cell material. The observations reported here were made on Polysil obtained from Texas Instruments and Monsanto and are believed to be more or less representative of the structures observed in other Polysil material.