bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Electron Microscopy Study of Second-Phase Particles in 7075 and 7475 Aluminum Alloys
Authors: Raghavan M. , Koo J. Y. , Steeds J. W. , Park B. K.
Published: June 2020

X-ray microanalysis and Convergent Beam Electron Diffraction (CBD) studies were conducted to characterize the second phase particles in two commercial aluminum alloys -- 7075 and 7475. The second phase particles studied were large (approximately 2-5μm) constituent phases and relatively fine ( ∼ 0.05-1μn) dispersoid particles, Figures 1A and B. Based on the crystal structure and chemical composition analyses, the constituent phases found in these alloys were identified to be Al7Cu2Fe, (Al,Cu)6(Fe,Cu), α-Al12Fe3Si, Mg2Si, amorphous silicon oxide and the modified 6Fe compounds, in decreasing order of abundance. The results of quantitative X-ray microanalysis of all the constituent phases are listed in Table I. The data show that, in almost all the phases, partial substitution of alloying elements occurred resulting in small deviations from the published stoichiometric compositions of the binary and ternary compounds.
Characterization of Si/CaF2/Si Epitaxial Films Grown By MBE
Authors: Lewis N. , Hall E. L. , Fathauer R. W. , Schowalter L.
Published: June 2020

There has been a large research effort throughout the electronics industry to develop epitaxial Si/insulator/Si structures for silicon-on-insulator (SOI) and 3-dimensional integrated circuit applications. Molecular beam epitaxy (MBE) is one promising method of producing these SOI structures. The use of CaF2 as an insulator is interesting because of the similarities in the Si (diamond cubic) and CaF2, (cubic fluorite) structures, where the lattice mismatch between these two materials is only 0.6% at room temperature. CaF2 also evaporates congruently during epitaxial growth by MBE, therefore, avoiding problems with the control of film stoichiometry. This paper describes the characterization of epitaxial Si overlayer and CaF2, insulator films which were grown on a (111) single crystal Si substrate.
High-Resolution Electron Microscopy Studies of Supported Platinum Particles on ZSM-5 Zeolites
Authors: N. Acosta , E. Dominguez
Published: June 2020

Supported small metallic particles (SMP) on zeolitic materials influence the catalytic properties of zeolites in several ways. Pt/ ZSM-5 containing 1.81 Pt in weight, were observed at high resolution conditions. The images of thin zeolite crystals were obtained and morphological and structural details were characterized. From the diffraction patterns some variations of the ratio c/a were found, caused possibly by local changes in Al concentration.

The metal particles were found mostly distributed on the support crystalline phase as well as in areas presenting some structural defects; however the population of small metallic particles was greater in the crystalline zones. In addition, some contrast differences between particles seating on the same zeolite crystal were observed. These effects are attributed to different orientations for a given number of particles having the same diameter but different contrast (see figures 1a and 1b, particles A and B). Another interesting aspect, is the relative “transparency” of some particles such that crystalline planes of the zeolite (i.e. support) are visible trough the metal particle without any apparent perturbation of crystalline planes below them (see picture 3a).
Structure Variations in Small Metal Particles
Authors: Barry J.C. , Gai P.L.
Published: June 2020

High resolution electron microscopy (HREM) is found to be a useful technique for the study of supported metal particles. However, with HREM, image detail in supported particles is often obscured by support contrast. Computer calculations have therefore been carried out for a model silver particle/amorphous alumina catalyst, to examine the effect of support thickness on particle image detail.

Model catalysts were prepared by evaporating Ag on amorphous alumina. The diffraction contrast and HREM images, recorded on a JEOL 200CX HREM, are shown in Figs. 1(a) and (b) respectively. It can be seen in the latter image that the edge definition is blurred in the presence of the amorphous support.

Image calculations were carried out using an Intellect 200 image analysis system for 55 atom particles of cuboctahedral and icosahedral shapes (energy calculations show that small clusters of 55 atoms are relatively stable 3) as well as for 309 atom cuboctahedral particles.
Current Applications of Lowicryl-K4M in Immunocytochemistry
Authors: Altman Lawrence G. , Schneider Barbara G. , Papermaster David S.
Published: June 2020

The introduction of Lowicryl-K4M as an embedding medium for immunoelectron microscopy has increased the number of options now available when attempting to localize antigenic sites on thin sections. Here we review some modifications of the manufacturer's original embedding protocol (5-6 days) by instituting changes that minimize antigen exposure to a number of potentially deleterious conditions while accelerating the entire process. Fixation and resin infiltration may be completed in three hours (room temp.) and block polymerization (0-4•) is often possible in less than 60 minutes. This rapid approach was tested for antigen preservation in Bufo marinus kidney (Na+,K+ ATPase alpha chain catalytic subunit) and retina (opsin) by comparing morphometric data (ferritin particles/μm2) against an alternate (intermediate) technique which employed the same rapid fixation/ dehydration/ Infiltration but with a more extended polymerization time of 2-3 days.
Reversible Embedment Cytochemistry: A New Method for Ultrastructural Imaging and Affinity Labeling of Tissue Sections
Authors: Gorbsky G. , Borisy G.G.
Published: June 2020

Conventional epoxy and acrylic embedding procedures for electron microscopy involve infiltration into tissues of resin monomers that are subsequently polymerized and covalently crosslinked. During the polymerization and crosslinking reactions, tissue structure and antigenicity may be compromised by heat generation and by covalent modification of chemical subgroups within the tissue. In contrast, reversible embedment cytochemistry is a physical embedding procedure involving no chemical polymerization or covalent crosslinking reactions. In the procedure we have developed, fully polymerized polymethylmethacrylate was dissolved in dichloromethane and inflitrated into fixed and dehydrated tissue culture cells or tissues. The dichloromethane was allowed to evaporate at room temperature leaving the tissues embedded in plastic. Because polymethylmethacrylate is a hard, hydrophobic plastic, sections of from 30 nm to 1000 nm were reliably cut by conventional means using glass or diamond knives fitted with water troughs. Moreover, because polymethylmethacrylate is composed of linear polymers that are not covalently crosslinked, the plastic was easily reextracted from the sections by immersion in acetone.
Simultaneous Ultramicrotomy of Multiple Areas and Examination of Ribbons on One New Grid
Authors: Chien K. , Van de Velde R. , Heusser R.
Published: June 2020

The localization of an area of interest for ultramicrotomy within a tissue block is usually determined by first surveying large thick sections under the light microscope. Yang has shown that multiple areas from a large block face can be vertically divided for sequential sectioning. By applying a simple and direct technique, two or more areas of interest from the same block can be sectioned simultaneously and examined on one grid for ultrastructural studies.

Depending on the size and distance between the areas that are going to be sectioned, there are several possible approaches:

1.

Two Small Areas Widely Separated. Since the entire surface of the block is in one plane after thick sectioning, it is possible to rotate the block and trim selected areas into two trapezoids so that their leading and trailing edges are parallel to the knife edge. If their combined total areas do no exceed the average area routinely sectioned, the two trapezoids can be cut simultaneously and two ribbons formed (fig.1).
Uranyl Acetate En Bloc Staining to Complement Diagnostic Electron Microscopic Evaluation of Muscle Biopsies
Authors: R.C. Caughey , U.P. Kalyan-Raman
Published: June 2020

Uranyl acetate en bloc staining is known to improve overall contrast and membrane preservation and removes glycogen from tissues. This staining procedure complements diagnostic electron microscopic evaluation by enhancing ultrastructural details. The ultrastructural structures enhanced are basement and plasma membranes, mitochondrial membrane and cristae, sarcoplasmic reticulum and T-tubule system. We wanted to study the usefulness of this technique over the conventional method in the study of muscle biopsy. Ultrastructurally, thirty muscle biopsies submitted to our Electron Microscopic Lab were routinely fixed in 2.5% glutaraldehyde and 1% 0S04, dehydrated in a graded series of ethanols, and embedded in Epon 812. Half of the blocks were processed and evaluated with post uranyl acetate/lead citrate staining. The other half were processed and evaluated by en bloc 0. 5% uranyl acetate/Walpole's buffer after 0S04 and before ethanol dehydration. The en bloc half were also stained with post uranyl acetate/lead citrate.
The 3-Dimensional Molecular Structure of the Actin Filament Revisited
Authors: Aebi U. , Millonig R. , Salvo H.
Published: June 2020

To date, most 3-D reconstructions of undecorated actin filaments have been obtained from actin filament paracrystal data (for refs, see 1,2). However, due to the fact that (a) the paracrystals may be several filament layers thick, and (b) adjacent filaments may sustantially interdigitate, these reconstructions may be subject to significant artifacts. None of these reconstructions has permitted unambiguous tracing or orientation of the actin subunits within the filament. Furthermore, measured values for the maximal filament diameter both determined by EM and by X-ray diffraction analysis, vary between 6 and 10 nm. Obviously, the apparent diameter of the actin filament revealed in the EM will critically depend on specimen preparation, since it is a rather flexible supramolecular assembly which can easily be bent or distorted. To resolve some of these ambiguities, we have explored specimen preparation conditions which may preserve single filaments sufficiently straight and helically ordered to be suitable for single filament 3-D reconstructions, possibly revealing molecular detail.
Evaluation of Staple Impressions in the Scanning Electron Microscope
Authors: Basu S.
Published: June 2020

Use of the scanning electron microscope (SEM) for examination of tool marks, paricularly firing pin impressions of semi-automatic pistols, selected shotguns and rifles, is well documented. It was the intent of this investigation to apply SEM to staplers, in order to examine if the impressions on the shoe-ends of staples using a particular stapler possessed persisting defects with repeated tackings, and whether these defects can be used as “individual characteristics” in order to be able to identify the source of a staple on tacked papers from a list of eight staplers of different makes and models (Swingline® 747 and 27, ASCO® 40 and ACE® 102). The effects of pre-existing marks, which are usually existent as parallel striations on staples, and the different forms (100% round, 100% round with sharp points and chisel points) of staples on the resulting impression were examined by using different brands of staples (Swingline® standard No. S.F.-1, Swingline® R. W.-35, Bostitch® standard, and ACE® 2025).
Torus Circumference and Thickness Parameters From a Linear DNA Size Series Suggest How Toruses Self-Assemble
Authors: Ruben George C. , Marx Kenneth A.
Published: June 2020

Certain double stranded DNA bacteriophage and viruses are thought to have their DNA organized into large torus shaped structures. Morphologically, these poorly understood biological DNA tertiary structures resemble spermidine-condensed DNA complexes formed in vitro in the total absence of other macromolecules normally synthesized by the pathogens for the purpose of their own DNA packaging. Therefore, we have studied the tertiary structure of these self-assembling torus shaped spermidine- DNA complexes in a series of reports. Using freeze-etch, low Pt-C metal (10-15Å) replicas, we have visualized the microscopic DNA organization of both calf Thymus( CT) and linear 0X-174 RFII DNA toruses. In these structures DNA is circumferentially wound, continuously, around the torus into a semi-crystalline, hexagonal packed array of parallel DNA helix sections.
E.M. Autoradiography of Crayfish Androgenic Gland
Authors: Tichenor Paula J.
Published: June 2020

The androgenic gland is near the terminal region of the vas deferens in most crustaceans. It secretes a hormone responsible for male sexual characteristics. Eyestalk ablation, or destalking, is known to cause androgenic gland stimulation. Previous experimental and E.M. evidence is equivocal as to whether the hormone is a steroid or a protein; hence, this investigation.

Three groups of 6 experimental (bilateral eyestalk extirpation) and 6 non-destalked controls were selected from 36 reproductive Form I male Orconectes sp. crayfish. The three groups were given the following regimes 6 days after destalking the experimental animals: (1) 2UCi/g animal weight L-amino acid-3H; (2) 0.76UCi/g Uridine-5-3H; and (3) same regime as group (2) followed by specimen incubatitfn with 0.2 mg/ml ribonuclease Type I-A.
Imaging Properties of the Soft X-Ray Photon
Authors: Sayre D.
Published: June 2020

Introduction. The soft x-ray photon (0.1-lkeV, wavelength l-10nm) is now available for the first time in large numbers, thanks to several new radiation sources (see below). This particle offers important new opportunities in the imaging of unprocessed biological structures, including intact biological cells in the natural and even living state.

Basic properties. We begin by examining the basic properties of the particle which give it its special imaging characteristics.

1.

The reaction cross-section level of its principal imaging reaction, photoelectric absorption (Fig. 1). This cross-section, at 105- 106 barns/atom, is excellently matched to the thickness of the biological cell. The other principal imaging reactions in use today (scattering of 100keV electrons in electron microscopy, and coherent scattering of 0.15nm photons in x-ray crystallography; see Fig. 1) are best suited to cellular sections or substructures, and to macroscopic ordered specimens (crystals), respectively.

2.

The strong dependence of its reaction cross-section on Z (Fig. 1). For example, the 2.4nm photon images biological structures in the presence of water, due to its low reactivity with hydrogen and oxygen. In general, good image contrast is obtained without specimen processing, even for biological materials.
X-Ray Contact Imaging: the Technique
Authors: Feder R. , Mayne-Banton V.
Published: June 2020

Until recently, instruments used to image small biological objects directly have involved the use of light microscopy or electron microscopy. Presently, the use of x-rays has emerged as another probe to investigate details in biological specimens. X-rays can be used either by using an x-ray “lens”, which will be discussed by others at this symposium or by a direct contact “print” of the object on a special emulsion. This latter method is what will be discussed in this paper.

The object to be ‘photographed’ is prepared on a substrate and then placed in contact with a resist such as poly- methyl-methacrylate (PMMA). This polymer has the property that when it is exposed to x-rays and then placed in a solution of methyl isobutyl ketone (MIBK) it will 'develop’ depending on the number of x-ray photons absorbed in the PMMA. This three dimensional relief structure is actually a photon density map of the specimen.
Effects of Platelet-Activating Factor on Leukocyte Adhesion in the Guinea Pig Aorta
Authors: Melden Mary Kay , Van Valen Ronald G. , Saunders Robert N. , Handley Dean A.
Published: June 2020

Platelet-activating factor (PAF) is a potent mediator of immune anaphylaxis. In a dose-dependent manner, PAF can induce such effects as thrombocytopenia, neutropenia, hypotension, bronchoconstriction, hemoconcentration, and negative inotropic cardiac effects. By intradermal or intravenous injection, PAF has been shown to induce blood vessel hyperpermeability resulting in extravasation of plasma, leukocyte adhesion and subsequent diapedesis. However, most studies of endothelial-leukocyte interactions have been limited to small vessels. We have examined the effects of PAF on endothelial structure and leukocyte involvement in the guinea pig aorta.
Microthrombi in Human Atherogenesis: A Sem Report
Authors: Spurlock Ben O. , Chandler A. B.
Published: June 2020

The response to injury hypothesis for the pathogenesis of atherosclerosis as outlined by Ross and associates focuses on three major events: 1) that lesions of athero sclerosis are initiated in response to some form of injury to the arterial endothelium; 2) that focal sites of injury permit circulating blood elements; i.e., platelets, monocytes and lipoproteins to adhere to the subendothelial connective tissue; 3) that adherent platelets release platelet derived growth factor (PDGF) from their granules and lead to the proliferation of smooth muscle cells in the intima. if there is early repair of the endothelial surface the process ceases; if however, the connective tissue components remain exposed to the circulating elements there is a continuation of the process with progressive smooth muscle cell proliferation and development of an atherosclerotic plaque.
Nonasbestos Ferruginous Bodies in Man
Authors: Dodson R. F. , O'Sullivan M. , Corn C. J. , Williams M. G. , Hurst G. A.
Published: June 2020

Ferruginous bodies (FBs) in human lung tissue are generally accepted as a marker for asbestos exposure. However, a limited number of “pseudoasbestos” bodies with cores of elastin fibers, diatornaceous earth, carbon fibers, or sheet silicates have been reported in humans. An unusual case was referred to our laboratory after a lung biopsy, containing numerous FBs by light microscopy, was used as a basis for inferring asbestos related disease. Some of the FBs contained cores inconsistent with those normally seen in asbestos bodies and many others were indistinguishable. The patient's case history indicated he had indeed worked in a dusty environment but no asbestos exposure was noted. Tissue (0.05 gm) was digested and collected on a 0.2 μm Nuclepore filter. The sample was analyzed and found to contain 73,000FBs/gm. Many of the cores were nonanalyzable by scanning electron microscopy and x-ray energy dispersive analysis because they were completely covered by the ferruginous coating.
Freeze-Drying-Embedding Method of Specimens For Analysis of Diffusible Elements by Electron Spectroscopic Imaging
Authors: Simon G.T. , Spitzer E.
Published: June 2020

Electron spectroscopic imaging (ESI), developed in the last decade by F. P. Ottensmeyer and his group is one of the most sensitive electron microscopic analytical techniques available today. Spatial resolutions of 0.5.m and mass resolution of 50 atoms or less can be achieved. The limitations of ESI resides in the fact that only very thin specimens (20nm in thickness) can be used. It is therefore impossible to analyze frozen-dried or frozen hydrated sections.

The primary concern in analyzing diffusible elements is their extraction and translocation during processing. Already existing freeze-drying embedding techniques have been modified. Quick freezing is by far the fixation method of choice. The type of coolant and the entrance velocity are of critical importance. Vitrification layers of 25-30 microns can be obtained by plunging small fragments of tissue into liquid propane at an entrance velocity of more than 6.4 m/s.
Microwave Acceleration of the Metallization and Intensification of Cytochemical and Immunocytochemical Reaction Products with Silver Methenamine
Authors: Hanker J. , Pierce J. , Rustioni A. , Borowitz M. , Chandler D. , Yates P. , Giammara B.
Published: June 2020

Intensification of the staining of cytochemical reaction products for light microscopy, or of their electron opacity and conductivity for electron and scanning electron microscopy, is frequently achieved by treatment with silver compounds. Most of these procedures require numerous steps and/or long exposure to ultraviolet or heat to achieve sufficient metallization of the reaction product. Brinn showed that histological staining with a number of silver techniques widely employed in the pathology laboratory could be significantly accelerated by the application of microwave (MW) energy. This was attributed to increased molecular movement of metal across the tissue resulting from virtually instantaneous heating of the silver solution.
Processing Immunoperoxidase Labeled Cell Monolayers and Cryostat Sesctions For Electron Microscopy
Authors: Chien K. , Van de Velde R. , Shintaku I.P. , Sassoon A.F.
Published: June 2020

Immunoelectron microscopy of neoplastic lymphoma cells is valuable for precise localization of surface antigens and identification of cell types. We have developed a new approach in which the immunohistochemical staining can be evaluated prior to embedding for EM and desired area subsequently selected for ultrathin sectioning.

A freshly prepared lymphoma cell suspension is spun onto polylysine hydrobromide- coated glass slides by cytocentrifugation and immediately fixed without air drying in polylysine paraformaldehyde (PLP) fixative. After rinsing in PBS, slides are stained by a 3-step immunoperoxidase method. Cell monolayer is then fixed in buffered 3% glutaraldehyde prior to DAB reaction. After the DAB reaction step, wet monolayers can be examined under LM for presence of brown reaction product and selected monolayers then processed by routine methods for EM and embedded with the Chien Re-embedding Mold. After the polymerization, the epoxy blocks are easily separated from the glass slides by heatingon a 100°C hot plate for 20 seconds.
Films That Wet Without Glow Discharge
Authors: Wall J.S. , Hainfeld J.F. , Chung K.D.
Published: June 2020

Mass measurements with the Scanning Transmission Electron Microscope (STEM) provide a direct link between biochemistry and the information in the dark field STEM image of an unstained biological specimen. Total mass of a complex mass of individual components, mass per unit length, mass per unit area, or change in mass distribution following biochemical treatment, are easily determined.

Accuracy and preparation requirements have been described elsewhere. In the past year, we have made significant progress in specimen preparation, developing a “wet film” technique which eliminates the need for glow discharge treatment of grids. The method is similar to the Valentine technique but uses minute quantities of specimen. A thin carbon film is evaporated under UHV conditions onto freshly cleaved rock salt. The thin carbon is floated off the rock salt onto distilled water and a titanium grid with a thick, holey carbon film laid on top of it. After a few minutes, the grid is picked up from above by grasping its edge with a tweezer and turned over so that the adhering drop of water is facing upward.
The Hierarchic Order of Intermediate Filament Structure and Assembly
Authors: Aebi U. , Glavaris E.C. , Eichner R.
Published: June 2020

Five different classes of intermediate-sized filaments (IFs) have been identified in differentiated eukaryotic cells: vimentin in mesenchymal cells, desmin in muscle cells, neurofilaments in nerve cells, glial filaments in glial cells and keratin filaments in epithelial cells. Despite their tissue specificity, all IFs share several common attributes, including immunological crossreactivity, similar morphology (e.g. about10nm diameter - hence ‘10-nm filaments’) and the ability to reassemble in vitro from denatured subunits into filaments virtually indistinguishable from those observed in vivo. Further more, despite their proteinchemical heterogeneity (their MWs range from 40 kDa to 200 kDa and their isoelectric points from about 5 to8), protein and cDNA sequencing of several IF polypeptides (for refs, see 1,2) have provided the framework for a common structural model of all IF subunits.
Structural and Chemical Studies of Pathological Fibers in Human Neurofibrillary Degeneration
Authors: Kosik K.S. , Duffy L.K. , Bakalis S. , Abraham C. , Selkoe D.J.
Published: June 2020

The major structural lesions of the human brain during aging and in Alzheimer disease (AD) are the neurofibrillary tangles (NFT) and the senile (neuritic) plaque. Although these fibrous alterations have been recognized by light microscopists for almost a century, detailed biochemical and morphological analysis of the lesions has been undertaken only recently. Because the intraneuronal deposits in the NFT and the plaque neurites and the extraneuronal amyloid cores of the plaques have a filamentous ultrastructure, the neuronal cytoskeleton has played a prominent role in most pathogenetic hypotheses.

The approach of our laboratory toward elucidating the origin of plaques and tangles in AD has been two-fold: the use of analytical protein chemistry to purify and then characterize the pathological fibers comprising the tangles and plaques, and the use of certain monoclonal antibodies to neuronal cytoskeletal proteins that, despite high specificity, cross-react with NFT and thus implicate epitopes of these proteins as constituents of the tangles.
Neurofilament Sidearms, Proteolysis and Phosphorylation
Authors: Eagles P.A.M. , Hopkins J.M. , Rao R. , Chin T.K.
Published: June 2020

The neurofilament is a dominant component of the cytoskeleton in many nerve cells. This is particularly true of the giant nerve fibres from the marine fan worm Myxicola infundibulum where these filaments constitute about 70% of the total protein in the axoplasm. The neurofilaments here are composed primarily of two almost identical polypeptides with mol.wts. on SDS gels of around 170k and 160k, together with fifteen minor polyptpeptides (Fig.2a). These minor polypeptides are anchored in the filament backbone and are thought to be generated after cleavage of the major components by proteolysis in vivo. A likely candidate for this activity is a naturally occurring protease that needs Ca2+ in the millimolar range for activation.
Early Electron Microscopy remembered through the candle light of history
Authors: Newberry Sterling
Published: June 2020

As nearly as we have been able to ascertain, three very early programs to make a true Electron microscope arose in this hemisphere independently and concurrently. That is to produce instruments with demountable vacuum systems and means for interchanging specimens. Washington University in St. Louis was one of the three. The author is grateful for this opportunity to describe the Washington University work.

Washington University was a likely place for a beginning in electron microscopy. In the first quarter of the century it had risen to prominence in many fields especially physics, biology and medicine and close communication existed between them. The physics department had direct lineage from J. J. Thompson and W. H. Bragg and close ties with Chicago and Berkeley. The biology department had strong connections with Woods Hole, while the medical school staff included “people from the four comers of the earth” and it had a close association with the Rockefeller Medical Institute.
Solving the mechanisms responsible for organelle behavior in vivo by same-cell correlative light and electron microscopy
Authors: Rieder Conly L.
Published: June 2020

The behavior of many cellular components, and their dynamic interactions, can be characterized in the living cell with considerable spatial and temporal resolution by video-enhanced light microscopy (video-LM). Indeed, under the appropriate conditions video-LM can be used to determine the real-time behavior of organelles ≤ 25-nm in diameter (e.g., individual microtubules—see). However, when pushed to its limit the structures and components observed within the cell by video-LM cannot be resolved nor necessarily even identified, only detected. Positive identification and a quantitative analysis often requires the corresponding electron microcopy (EM).
An atomic resolution study of a carbide phase in platinum
Authors: Witcomb M.J. , O'Keefe M.A. , Echer CJ. , Nelson C. , Turner J.H. , Dahmen U. , Westmacott K.H.
Published: June 2020

Under normal circumstances, Pt dissolves only a very small amount of interstitial carbon in solid solution. Even so, an appropriate quench/age treatment leads to the formation of stable Pt2C {100} plate precipitates. Excess (quenched-in) vacancies play a critical role in the process by accommodating the volume and structural changes that accompany the transformation. This alloy system exhibits other interesting properties. Due to a large vacancy/carbon atom binding energy, Pt can absorb excess carbon at high temperatures in a carburizing atmosphere. In regions rich in carbon and vacancies, another carbide phase, Pt7C which undergoes an order-disorder reaction was formed. The present study of Pt carburized at 1160°C and aged at 515°C shows that other carbides in the PtxC series can be produced.
The effect of thermal exposure on precipitation of Ti3Al(C,N) in Ti-48Al-IV-0.2C
Authors: Donlon W.T. , Dowling W.E. , Cambell C.E. , Allison J.E.
Published: June 2020

Titanium aluminides are attractive candidates for high temperature structural applications because of their high strength to weight ratio at elevated temperatures. The microstructure of these alloys consists of γ-TiAl (distorted L10 structure) , plus α2-Ti3Al (ordered DO19 structure). Varying the heat treatment temperature and cooling rate of these alloys alters the volume fraction and distribution of the γ and α2 phases. This has significant effects on the room temperature ductility. In addition, precipitation of carbides has been observed during high temperature exposure. The effect of these precipitates on the mechanical properties has yet to be determined.

Figure 1 shows the general microstructure that was used for this investigation. TEM foils were prepared by electropolishing using 5% perchloric, 35% 1-butanol, 60% methanol at -40°C. No precipitates were found following heat treatment in the γ+α phase field. Samples approximately 20 mm square were thermally exposed to temperatures between 625° and 1000°C for times between 1 and 2000 hours.
HVEM of crystallization of amorphous TiNi shape memory films
Authors: Moberly Warren J. , Busch John , Johnson David
Published: June 2020

TiNi alloys, well-known for their shape memory properties that arise due to a martensitic transformation, have recently been considered for application as thin film actuators. Although various methods of thin film preparation have been considered, deposition via d.c. magnetron ion sputtering provides for reproducible film formation as well as possible integration of a TiNi film as a micromachine with a semiconductor device. When sputter deposited at room temperature, the as-deposited films have an amorphous structure. These films can be bent into a particular macroscopic shape prior to crystallization, thereby setting the parent (memory) shape. When used as thin film actuators, TiNi shape memory alloys are quite cost efficient, as compared to the prohibitive manufacturing costs typical when producing bulk shape memory devices. In addition, thin film shape memory devices may be cooled much more quickly than a bulk part, and reversible transformation cycles are achieved in only milliseconds. Applications being considered for these shape memory thin films are as microactuators in optical storage devices and as microvalves in portable gas chromatographs.
New phases in the Al-Co-Cu alloy system : Marked variations from the “true” decagonal phase
Authors: Ramani Atul S. , Giannuzzi Lucille A. , Carim Altaf H. , Bitler William R. , Howell Paul R.
Published: June 2020

The decagonal phase in the Al-Co-Cu alloy system was first discovered by He et al. We shall call this phase the “true” decagonal phase (TD) phase because it is the one most commonly observed in the Al-Co-Cu alloy system. It is well known that quasicrystalline phases such as the TD phase contain the phason defect peculiar to incommensurate phases that causes subtle variations from perfect decagonal symmetry. In this paper we report on the existence of new phases in the Al-Co-Cu alloy system, that are related to the TD phase but yet show marked variations from the TD phase. These variations are too drastic to be caused by phason defects alone.

Figure 1(a) is a selected area diffraction pattern (SADP) recorded from a TD phase single “crystal” showing near perfect decagonal (tenfold) symmetry. This SADP agrees very well with the first published SADP of the TD phase in Al-Co-Cu that also shows almost perfect decagonal symmetry. In a previous paper we have reported several kinds of deviations from perfect decagonal symmetry, but none of these deviations involved the observation of perfect pentagonal (fivefold) symmetry. Figure 1(b) is an SADP recorded from a phase in Al-Co-Cu that exhibits perfect pentagonal symmetry instead of the expected decagonal symmetry. This breakdown of true tenfold symmetry into true fivefold symmetry is caused by unequal intensities of equal and opposite reflections. This example is a clear violation of Friedel's law, which states that the intensities of equal and opposite diffraction vectors must be equal.
HREM observations of internetallic alloy formation in Pt-Sn thin films
Authors: Dufner D.C.
Published: June 2020

The general goal of this research is to clarify mechanisms of solid state reactions at the atomic level as a step in the rationalization of macroscopic reaction behavior in solids. A study of intermetallic alloy formation resulting from interdiffusion of metals in thin films can be made by HREM. In this work, reactions between Pt and Sn in thin films are studied to elucidate mechanisms for structural and compositional changes during the interdiffusion process.

Thin films of Pt and Sn used in this study were prepared by the two-film method introduced by Shiojiri. Few hundred angstroms of Pt were vacuum-deposited onto holey carbon films mounted on TEM grids. Sn films with an average thickness of 200Å were created by evaporation at rates of 15-30 Å/sec onto air-cleaved KBr substrates. The Sn films were wet-stripped and collected on the holey Pt grids. Figure 1 shows a cross-section schematic of a Pt-Sn couple. While this two-film arrangement did not allow observations of the actual reaction interface, microtomy was used to produce cross-sections.
Effect of processing temperature on interfacial layer formation in SiC fiber-reinforced glass-ceramic composites
Authors: Shin Hyun-Ho , Berta Yolande , Speyer Robert F.
Published: June 2020

The high fracture toughness and non-catastrophic fracture behavior of fiber-reinforced ceramic matrix composites are due to the weak interfacial shear strength between fiber and matrix, permitting fiber-matrix sliding during failure. In SiC fiber-reinforced glass or glass-ceramic composites, such low interfacial shear strength is obtained by the presence of a carbon-rich interfacial layer. This provides a path for crack propagation, fiber pull-out, and fiber delamination during fracture. Hence, these composites have demonstrated very high fracture toughness (critical stress intensity factor of ∼ 17 MPam1/2) and high fracture strength (3 to 4 times larger than that of monolithic glass or glass-ceramics). The carbon-rich interfacial layer in these glass or glass-ceramic composites is formed by oxidation of the SiC fiber by the oxide matrix during hot pressing. Its thickness is governed by hot pressing time, temperature, and pressure. In our results on Nicalon SiC fiber-reinforced lithium aluminosilicate glass-ceramic composites, hot pressing temperature governed not only the thickness of the interfacial layer, but also the phases residing within it. In this paper, the effect of hot pressing temperature on the phases formed in the interfacial area is described.
EM study of phase transformation in zinc coatings
Authors: Drewien C. A.
Published: June 2020

Electrodeposited iron-zinc alloy (EZA) coatings, used for barrier and galvanic corrosion protection of steel by the automotive industry, are deposited under conditions, which give rise to small grain sizes and non-equilibrium phases. Subsequent processing of automotive body panels requires a paint bake cycle of 175 °C for 30 minutes. The as-deposited microstructure has not been investigated by TEM due to difficulty of sample preparation, and information on the effect of heat treatment upon EZA coatings is lacking. In this study, the as-deposited microstructure of a 6 w/o Fe EZA coating is investigated with electron microscopy, and in-situ heating in the TEM is used to observe the thermal stability of the microstructure.

A 6 w/o bulk iron content EZA coating was electrodeposited from a chloride bath onto a steel surface. The 7 μm thick coating was removed from the substrate, and three mm disks, punched from the material, were electropolished at 30-40 V in a room temperature, aqueous chromic-acetic acid mix. Samples were imaged with a JEOL 6300 FEG-SEM operated with an accelerating voltage of 1 keV and with a Philips 430 EM under an operating voltage of 250 keV.
Microstructure of BSCCO-Ag composites made by floating-zone method
Authors: Ikuhara Y. , Suzuki T. , Ikuhara Y.H. , Michishita K. , Takahashi K. , Kubo Y.
Published: June 2020

To develop applications of oxide superconductors,in addition to the enhancement of the critical current density (Jc), improving their mechanical properties is also important. The Bi-oxide superconductors are intrinsically brittle because of clevage in the basal plane. We have found that doping by Ag is very effective in improving the mechanical properties of Bi-oxide superconductor without decreasing its Jc. In this study,the microstructure of BSCCO-Ag was observed by transmission electron microscopy (TEM) in order to clarify the relationship of microstructure to mechanical properties.

BSCCO-Ag composites were fabricated by floating zone (FZ) method. The critical temperature(Tc) and Jc were 89K and 3000A/cm2, respectively. The mechanical properties were measured by three-point bend test and indentation fracture measurements. A JEOL 4000FX (400kV) was used to analyze the microstructure.
On the optimum hole concentration, nanostructure and superconductivity in Bi-cuprate ceramics
Authors: Subramanian M. A. , Gai P. L.
Published: June 2020

Many outstanding questions about optimum hole concentrations, hole doping mechanisms and complex structural issues in Bi-Sr-Ca-Cu-O high temperature superconductor system could be addressed by their study in the undoped system, and by cationic substitution able to modify the anion stoichiometry of the system, in various reducing and oxidizing environments. Such critical studies in different environments are very limited. A number of studies exist in the system, in which the role and concentrations of charge carriers in oxide superconductivity are discussed by correlating Tc with in-plane Cu-O bond lengths, or with substitutional contents. However, most of the work relates to samples treated in air or oxygen where overdoping of holes in the CuO2 sheet can occur due to excess oxygen.
STEM BSE imaging and Monte Carlo simulation of α-β microstructures in NbTi superconductors
Authors: Headley T. J. , Michael J. R. , Greulich F. A. , Carr M. J. , Seuntjens J. M.
Published: June 2020

High current density NbTi multifilamentary superconductors have α-β microstructures tailored by thermo-mechanical processing involving interspersed cold drawing and heat treatment. A final heat treatment in the two-phase α-β field controls the volume fraction of α-Ti precipitates and subsequent cold drawing refines the scale of the microstructure to a level that optimizes flux pinning properties which affect critical current density (Jc). The volume fraction, particle size, shape and spacing of α-Ti precipitates present after the final heat treatment are important parameters of interest, and should be measurable by image analysis techniques if suitable images were available.
Simulation and interpretation of image contrast and diffuse scattering of tweed structure
Authors: Zhu Yimei , Cai Z.X. , Suenaga M. , Welch D.O.
Published: June 2020

The so-called tweed structure exhibits a roughly periodic lenticular-domain image (Fig.l) associated with the streaking of diffuse scattering around the fundamental reflections in an electron diffraction pattern (Fig.2(c)). Tweed was observed in high Tc oxides YBa2(Cu1-xMx)3O7-δ (M = Fe, Co, Al, x≥0.03; M = Cu, δ∼0.6-0.8), as well as in some binary alloys, which usually show statistical fluctuation in their composition or in an order parameter.

Although tweed has long been studied, crystallographic aspects of tweed modulation is not well understood. To shed light on the details of the structure, we performed simulations both on the tweed image and diffuse scattering, based on our TEM observations of YBa2(Cu1-xMx)3O7-δ
Controlled hot-stage experiments in the HREM with active drift compensation and 2Å lattice resolution
Authors: Boyes E D , Hanna L , Gai P L
Published: June 2020

An electronic system has been developed to compensate electronically, with <2Å lattice resolution, for the image shift due to specimen and/or stage drift in the HREM. A simple system has been highly effective in compensating for the drift which has long limited many scientifically important but technically demanding applications of TEM in both the physical and biological sciences. It has facilitated controlled hot stage experiments with full HREM resolution.

Over an extended period of time (>15s) which is fully adequate to record a high resolution image photographically or electronically, most drift of either the stage or the specimen can be approximated to a constant and relatively slow rate along a straight line path segment. With the new system the drift characteristic is video analyzed and an inverse correction ramp derived from a 12-bit DAC or external analog function generator is applied to existing post-specimen electrical image shift coils to stabilize the image position at the TEM camera. Image stabilization is also necessary for high quality data recording by digital processing of multiple (e.g. 256 or more) TV frames for an equivalent exposure time of several (8.5) seconds. This is the main data recording method for the dynamic experiments and with it low dose techniques can be used to minimize the beam damage effects which otherwise can be a serious problem in many HREM applications.
High-resolution imaging of ceramics
Authors: Carter C. Barry , McKernan Stuart
Published: June 2020

Ceramic materials have now been studied for many years using high-resolution transmission electron microscopy (HRTEM). The technique has had a major impact on our understanding of both the solid-sate chemistry of the materials themselves and the interfaces and defects present in the materials. The development of both aspects of the field have progressed in parallel as summarized in Figure 1. It is the purpose of this paper to review the current status and assess the needs for future studies.

HRTEM is uniquely suited for examining the chemistry and structure of ceramic materials on the local scale. Although it does not directly give information on the chemical composition of these materials, it does provide information on the local crystal structure which can, in turn, be used to infer the local crystal chemistry. A particularly clear illustration of such an application is shown in Figure 2 where a small particle with the spinel structure has grown inside a matrix of olivine as a result of internal oxidation of the matrix. The selected-area diffraction pattern confirmed the FCC nature of the particle although due to its small size, the diffraction spots were all considerably elongated.
Applications of HREM to the structural analysis of crystalline interfaces
Authors: Dahmen U. , Thangaraj N. , Lours P.
Published: June 2020

The investigation of the atomic structure of crystalline interfaces by HREM has recently become more prominent because of greatly improved resolution of modern electron microscopes, better means of sample preparation and wider availability of more generally applicable atomistic simulation procedures. As a result, a number of recent investigations have reported new and interesting features of crystalline interfaces and compared them with models based on atomistic, crystallographic or elastic theories. Examples of such features are stand-off dislocations in metal-ceramic and ceramic-ceramic interfaces, structural multiplicity of grain boundaries, solute segregation to selected facets, grain boundary microfaceting and dissociation and elastic distortion fields around interfacial ledges.
Characterization of structural units in tilt grain boundaries
Authors: McKernan Stuart , Carter C. Barry
Published: June 2020

General tilt grain boundaries can be viewed in terms of small structural units of varying complexity. High-resolution electron microscope (HREM) images of these boundaries in many materials show this repetitive similarity of the atomic structure at the boundary plane. The structure of particular grain boundaries has been examined for several special cases and commonly observed configurations include symmetric tilt grain boundaries and asymmetric tilt grain boundaries with one grain having a prominent, low-index facet. Several different configurations of the boundary structure may possibly occur, even in the same grain boundary. There are thus many possible ways to assemble the basic structural units to form a grain boundary. These structural units and their distribution have traditionally been examined by high-resolution electron microscopy. The images of the projection of the atomic columns (or the tunnels between atomic columns) providing a template for constructing “ball-and-stick ” models of the interface.
Principle and practice of high-resolution imaging with a field-emission TEM
Authors: Otten Max T. , Coene Wim M.J.
Published: June 2020

High-resolution imaging with a LaB6 instrument is limited by the spatial and temporal coherence, with little contrast remaining beyond the point resolution. A Field Emission Gun (FEG) reduces the incidence angle by a factor 5 to 10 and the energy spread by 2 to 3. Since the incidence angle is the dominant limitation for LaB6 the FEG provides a major improvement in contrast transfer, reducing the information limit to roughly one half of the point resolution. The strong improvement, predicted from high-resolution theory, can be seen readily in diffractograms (Fig. 1) and high-resolution images (Fig. 2). Even if the information in the image is limited deliberately to the point resolution by using an objective aperture, the improved contrast transfer close to the point resolution (Fig. 1) is already worthwhile.
A HREM study of V/Al2O3 interface
Authors: Ikuhara Y. , Pirouz P. , Heuer A. H. , Yadavalli S. , Flynn C. P.
Published: June 2020

The interface structure between vanadium and the R-plane of sapphire (α-Al2O3) was studied by conventional and cross-sectional high resolution electron microscopy (HREM) to clarify the atomic structure of the interface.

A 57 nm thick vanadium film was deposited on the (1102) (R) plane of sapphire by molecular beam epitaxy (MBE) at a substrate temperature of 920 K in a vacuum of 10-10torr. The HREM observations of the interface were done from three directions: two cross-sectional views (parallel to [0221]Al2O3 and [1120]Al2O3) and a plan view (parallel to [2201]Al2O3) by a top-entry JEOL 4000EX electron microscope (400 kV).