bluuebunny/crossref_metadata_2025_split huggingface dataset:
A TEM characterization of precipitates evolution and their effect on the grain-growth behavior of gas atomized superalloy A-286
Authors: Shin Keesam 
Published: June 2020

It is generally accepted that the refined grain size and stable grain boundaries observed in rapid-solidification-processed (RSP) materials are due to the fine precipitates produced during and after the processing. This is based on the observation of the materials after consolidation of the powders. Though there is little doubt that the as-atomized powder structure is crucial for the understanding of the consolidated sample, there are few studies of the powder. This is mainly because of the difficulty in preparation of thin electron-transparent samples.The most common method of powder sample preparation uses two or three different embedding materials whose polishing conditions are usually not identical. In this study, a monolayer of powder was gold coated, electroplated with nickel, and then electropolished. Electropolishing provided a nice and smooth surface without any surface artifact. In this study, as-atomized and heat treated powders were studied by TEM (JEOL JEM 200CX) and STEM (VG HB501). Because of the fineness of the defects involved, TEM observation is crucial.
Room temperature deformation and stress-induced phase transformation in Laves phase Fe2Zr
Authors: Liu Yaping , Allen Samuel M. , Livingston James D. 
Published: June 2020

Laves phases have three structures: Cubic C15 (MgCu2), hexagonal C14 (MgZn2) and dihexagonal C36 (MgNi2). Their high-temperature deformability has been studied by many investigators. But the study of their room-temperature deformation is very limited. By such studies, it may be possible to enhance the room-temperature deformability of Laves phases.In the present study, arc-melted samples of Fe-10 at% Zr, containing α-Fe and Fe2Zr Laves phase, were annealed at 1190°C for 48 hr and then compressed at 0.001 inch/min to strains of 46∼48% at room temperature. The 0.2% offset yield stress is about 75 kg/mm2. Micrographs revealed dislocation structures in α-Fe and cracks in proeutectic Fe2Zr after deformation. X-ray diffraction patterns show that the crystal structure of Fe2Zr is mainly C36 before deformation. After compression, the C15 peaks, which overlap other peaks in the pattern, increase in intensity, as seen in Fig. 1. This demonstrates that a phase transformation occurred as a result of deformation. The detail and mechanism of the transformation were studied by TEM. A characteristic banded structure which was rarely found in undeformed sample was frequently observed in the compressed Fe2Zr particles, as shown in Fig. 2. Electron diffraction patterns and high-resolution TEM showed that these bands have a C15 structure with a {111} plane parallel to the basal plane of C36 structure in the adjacent parts of a particle. Fig. 3 is a high-resolution TEM picture showing the stacking sequence of the close-packed planes of the particle containing the C15 band in Fig. 2. It has a ABCABC stacking sequence in the central part (C15) and ABAC on the two sides (C36). Inside the C15 band there are many stacking faults on {111} planes. A twinned region (C15T) is also seen to the right of the C15 region.
Precipitation in Al-Li-Zr alloys
Authors: Vanderwalker D.M. 
Published: June 2020

Aluminum-lithium alloys have a low density and high strength to weight ratio. They are being developed for the aerospace industry.The high strength of Al-Li can be attributed to precipitation hardening. Unfortunately when aged, Al-Li aquires a low ductility and fracture toughness. The precipitate in Al-Li is part of a sequence SSSS → Al3Li → AlLi A description of the phases may be found in reference 1 . This paper is primarily concerned with the Al3Li phase. The addition of Zr to Al-Li is being explored to find the optimum in properties. Zirconium improves fracture toughness and inhibits recrystallization. This study is a comparision between two Al-Li-Zr alloys differing in Zr concentration.Al-2.99Li-0.17Zr(alloy A) and Al-2.99Li-0.67Zr (alloy B) were solutionized for one hour at 500oc followed by a water quench. The specimens were then aged at 150°C for 16 or 40 hours. The foils were punched into 3mm discs. The specimens were electropolished with a 1/3 nitric acid 2/3 methanol solution. The transmission electron microscopy was conducted on the JEM 200CX microscope.
High-resolution TEM of Cr-Gd and Co-Gd multilayers
Authors: Bertero Gerardo A. 
Published: June 2020

Thin film multilayered structures have assumed significant technological importance. In particular, several have proven adequate for magneto-optic recording applications in which vertical magnetization, large coercivities and a large Kerr rotation effect are needed. In this regard, Co-Gd and Cr-Gd, among others, are candidate systems and specifically Gd-Co has already been used with some success.In the present work, HRTEM was performed on sputter-deposited Cr-Gd and Co-Gd multilayers. These two systems are expected to show contrasting behavior which may affect the long term magneto-optic performance of the multilayer. Cr and Gd are almost totally immiscible, suggesting a large positive heat of mixing. Conversely, Co and Gd form a large number of intermetallic phases and show a deep eutectic at 60 at.% Gd indicating a negative, and possibly large, heat of mixing. Thus, a tendency for intermixing and solid state amorphization is expected for the Co-Gd system and not so for Cr-Gd. These considerations may be of importance since thermal stability is required for magneto-optical applications where the magnetic media is subjected to local thermal cycling during the magnetic writing process.
A HREM study of the interfaces between TiO2 precipitates and the Al2O3 matrix in star sapphire
Authors: Xiao S.Q. , Heuer A. H. , Pirouz P. 
Published: June 2020

The asterism, or star effect, present in star sapphire (Ti-doped A12O3) single crystals is known to arise from the needle-like rutile(r) (TiO2) precipitates in the sapphire(s) matrix. The specific orientation relationship between the precipitates and the matrix is {100}r//{0003}s and <011>r//<1010>s . In this work we report a HREM study of the rutile/sapphire interface.The cross-section perpendicular to the needle axis of a very small precipitate, which is coherent, or has just one misfit dislocation at its interface, is a rhombus; the precipitate/matrix interface (habit plane) is {111}r{1123}s. As the coherency break down and misfit dislocations are introduced into the interface, the shape of the cross-section becomes nearly square; the two orthogonal interfaces are {100}r//0003}s and {011}r//{1120}s. Larger precipitates show rectangular interfaces elongated along the {100}r//{0003}s interface (Fig.l). A regular array of misfit dislocations with Burger vector b = 1/3<0001>S are present at the {011}r//{1120}s interface, the mean distance between every two adjacent 1/3<0001>S misfit dislocations being 8.7 nm which compensates exactly the 5.9% lattice mismatch estimated from the lattice constants of these two structures. Similarly, a regular array of misfit dislocations with Burgers vector b = 1/3<1010>S at the {100}r//{0003}s interface compensates the 4.5% lattice mismatch at that interface.
Diffraction from interfaces
Authors: Eaglesham D.J. 
Published: June 2020

A wide variety of approaches have been used to study diffraction from interfaces and thereby gain information on the structure or chemistry at the interface. In this paper the various techniques will be reviewed and a few examples will be used to illustrate the methods.Techniques for studying interfaces can be broadly divided into cross-section and plan-view approaches, and further classified according to whether the information to be extracted lies on the coincident site lattice or at some intermediate position (i.e. whether diffraction will determine a rigid body shift or a full reconstructed interface structure). While cross-section diffraction studies have been shown to be extremely powerful in elucidating a number of problems, we will concentrate here on plan-view methods. The reasoning for this is that cross-section diffraction retains many of the drawbacks to cross-sectional HREM (small field of view, indeterminate averaging and above all increased specimen preparation damage) and has substantially reduced signal, whereas plan-view diffraction can give us access to unique information on both local and long-range variations in the interface.
Morphology and orientation of ultrafine Y2O3 precipitates in YBa2Cu3O7-x thin films
Authors: Lu P. , Zhao J. , Chern C.S. , Li Y.Q. , Gallois B. , Norris P. , Kear B. , Cosandey F. 
Published: June 2020

Yttrium-rich YBa2Cu3O7-x (YBCO) thin films grown by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD), have been reported to have high critical current densities (Jc) of > l×106A/cm2 at 77K. Electron microscopy has been used to understand how excess Y is incorporated into thin film microstructures without affecting their superconducting properties. In this work, we report identification of small Y2O3 precipitates, their morphologies and orientation relationships in YBCO thin films.Details of thin film growth process have been reported elsewhere. The films were examined both in planar and in cross-sectional view by electron microscopy. TEM samples were prepared by conventional mechanical polishing and ion milling techniques. An ISI-002B high resolution electron microscope with a resolution limit of ∼0.18 nm at 200keV was used for observations.
EM studies of reduction and oxidation behavior of model heterogeneous catalysts
Authors: Yao Nan , Meitzner G. D. , Fung S. C. , Disko M. M. , Behal S. K. , McHenry J. , Sinfelt J. H. 
Published: June 2020

Supported metal heterogeneous catalysts, such as Pt/γ-Al2O3, are used for reforming reactions in which saturated hydrocarbons, in petroleum naphtha, are converted to aromatics with a much higher anti-knock quality for automotive fuel. Reforming is now one of the most important industrial applications of catalysts. The platinum on alumina catalyst was developed in the 1950s, and remains in use around the world.The mechanisms of deactivation of alumina-based catalysts are still not well understood, since their deactivation on oil is accompanied, or rapidly followed, by massive carbon deposition which prevents inspection by chemisorption. In order to fully understand the general loss of activity for supported metal catalysts during operation, investigations of the atomic structure and the chemical composition for both working and model catalyst systems have been performed using high resolution transmission electron microscopy (HRTEM). Morphological and chemical changes of small catalytic particles distributed on the top surface of a porous alumina and impregnated within a porous alumina have been compared.
UHV-TEM imaging and diffraction study of Cu-Au on Si(111)
Authors: Xu P. , Marks L. D. 
Published: June 2020

It has been demonstrated that ultra-high vacuum transmission electron microscopy is a powerful technique in solving surface atomic structures. During some recent work while we were testing surface imaging modes using the Si(111)-7×7 surface, we accidentally contaminated the surface by sputtering copper and some gold from the specimen holder onto the silicon. This paper presents the results of transmission electron diffraction and imaging studies of this surface.Experiments were performed in a Hitachi UHV H-9000 300 keV electron microscope with a stable operation pressure of 1x10-10 Torr. Attached to the microscope is a UHV surface science chamber for in situ sample preparation. A thin sample of silicon (111) (P doped to 80 ohm-cm) was mechanically polished, dimpled, and ion-beam thinned before being transferred into the surface science chamber. The sample was then ion beam sputter cleaned using 3-4 Kv argon ions and annealed to about 600°C using an electron gun (4-5 Kv, 2-3 Ma). Later tests indicated that the ion gun was not centered around the 3 mm disk and a part of the sample surface was covered by the sputtered materials from the sample holder. EDX results from a Hitachi HF-2000 analytical microscope showed that the deposited layer consisted of about 70% Cu and 30% Au.
DNA complexed with RECA protein
Authors: Egelman Edward H. , Yu Xiong 
Published: June 2020

We have been using electron microscopy and computed image analysis to understand the structure of the helical polymer that the RecA protein from E. coli forms on DNA. Recent work has adressed the following points:1) RecA binds an ATP analog, ATP-γ-S, and hydrolyzes this analog several thousand times more slowly than ATP is hydrolyzed by RecA. We have shown that structural transitions may be seen within RecA filaments on the same time scale (several hours) on which ATP-γ-S is being hydrolyzed, and several lines of evidence suggest that these conformational changes are due to the RecA ATPase. We have therefore been able to directly visualize these motions, using image analysis of bundles of RecA filaments.
Structure of spliceosomal UsnRNPs
Authors: Lührmann Reinhard , Behrens Sven-Erik , Kastner Berthold 
Published: June 2020

The major snRNPs, Ul, U2, U4/U6 and U5, are essential trans-acting factors in the pre-mRNA splicing process. They assemble with a pre-mRNA and a number of other non-snRNP splicing factors prior to the splicing reaction to form an active spliceosome. We are interested in investigating the biochemical composition of UsnRNPs and their ultrastructure as well as their function in splicing. In HeLa cell nuclear extracts the spliceosomal UsnRNPs exhibit differential association behaviour depending on the salt concentration. Thus, at high salt (420 mM) the majority of the Ul, U2, U4/U6 snRNPs migrates on sucrose gradients at 10-12S, while U5 snRNP sediments at 20S. Under in vitro splicing conditions (i.e. at about 100 mM salt), U5 and U4/U6 snRNPs form a 25 S [U4/U6.U5]tri-snRNP-complex and U2 snRNPs sediment at about 17 S.We have isolated the various types of UsnRNPs under native conditions using mainly immunoaffinity chromatography procedures. Today we can distinguish more than 35 distinct snRNP proteins. They can be grouped into two classes. The first class comprises eight common snRNP proteins which are present in each of the spliceosomal UsnRNPs. In addition, the individual snRNPs contain snRNP-specific proteins. These include three (70k, A, C) for the 12 S Ul snRNP, two (A′, B″ for the 12 S U2 snRNP, an additional eight for the 17 S U2 snRNP and eight for the 20 S U5 snRNP. The 25 S [U4/U6.U5]tri-snRNP-complex contains, in addition to the common proteins and the U5-specific proteins, a third group of six proteins which are essential for the stable formation of the tri-snRNP-complex. Thus, the different S-values of a particular snRNP particle result from differences in the population of snRNP-specific proteins associated with that particle.
Observation of neuronal activity using real-time voltage-sensitive dye imaging
Authors: Kauer John S. , Cinelli Angel , Wellis David , White Joel 
Published: June 2020

Sensory systems are confronted with the problem of taking “information” in the outside world and encoding and manipulating it in forms that can be used in the neuronal world. A major challenge is to document how the transition between these worlds takes place (transduction) and, once it has taken place, how the data are manipulated by neural circuits (integration). Since the brain is an intrinsically parallel device, carrying out many functions simultaneously, it would appear as important to record brain activity in a similarly parallel manner as to record events in single cells and membranes. Optical recording of neuronal events offers a first step toward thing to observe events that are distributed among the cells and processes of a neuronal network.In the sense of smell odors appear to be encoded by activity distributed across many neurons at each level of the system studied so far, from the sensory cells in the nose to the pyramidal cells in prepyriform cortex (for review see). Thus, to elucidate how the molecular properties of odorants are represented by neurons it is probably necessary to observe the patterns of distributed activation. The distribution of activity across many neuronal elements, in contrast to representing odor molecules by dedicated “labelled lines”, confers redundancy and fault tolerance on a system that is crucial for complex behaviors that underly survival for many animals species, as well as providing flexibility for being sensitive to large numbers of compounds.
The distribution of “capsaicin-sensitive” nerve fibers in the lymphatic wall
Authors: Fruschelli C. , Guarna M. , Pucci A.M. , Alessandrini C. , Crestini F. 
Published: June 2020

In a previous paper we have shown that guinea pig mesentery lymph collectors possess not only autonomic nerve fibers containing classical neurotransmitters but also peptidergic ones. These nerve fibers are sensitive to the depletory action of capsaicin, and are likely to be sensory in nature.Therefore the aim of this study was to evaluate the effects of capsaicin of the nerve fibers of the lymphatic wall by ultrastructural methods and to study the distribution of the “capsaicin sensitive” nerve fibers in the lymphatic vessel wall.
Jansky-Bielschowsky syndrome, a lysosomal disease: First diagnosed cash in Oman
Authors: Buhl Line , Muirhead David 
Published: June 2020

There are four lysosomal diseases of which the neuronal ceroid lipofuscinosis is the rarest. The clinical presentation and their characteric abnormal ultrastructure subdivide them into four types. These are known as the Infantile form (Santavuori-Haltia), Late infantile form (Jansky-Bielschowsky), Juvenile form (Batten-Spielmeyer-Voght) and the Adult form (Kuph's).An 8 year old Omani girl presented wth myclonic jerks since the age of 4 years, with progressive encephalopathy, mental retardation, ataxia and loss of vision. An ophthalmoscopy was performed followed by rectal suction biopsies (fig. 1). A previous sibling had died of an undiagnosed neurological disorder with a similar clinical picture.
Role of PKC isozyme III (γ) in water transport in amphibian urinary bladder
Authors: Mia A.J , Oakford L.X. , Thompson P.D. , Ning Z.H. , Yorio T. 
Published: June 2020

Vasopressin stimulated water flow across renal epithelia is thought to occur through a V2 receptor coupled to adenylcyclase. The increase in water flow occurs as a result of a fusion of water channels with the apical membrane and is indicative of an increase in membrane capacitance following hormone addition.What controls the cycling of water channels and their insertion into the membrane is uncertain. Our laboratory has demonstrated that renal epithelia as well as amphibian urinary bladder membranes, contain a vasopressin V1 receptor which upon activation results in the breakdown of phosphoinositide and the formation of inositol triphosphate and diacylglycerol, the latter an activator of protein kinase C (PKC). The initiation of transepithelial water flow also appears to involve V1 receptors and possibly activation of PKC. To test this hypothesis, we have been using activators of PKC, such as phorbol esters and mezerein, as pharmacological tools to determine if PKC activation results in similar physiological responses as the hormone. Several PKC isozymes, upon activation, are known to be translocated to the apical membrane as visualized by FITC immunofluorescence. Previously, we reported co-localization of PKC subtypes I (γ) and II (β) in toad urinary bladders using monoclonal antibodies and protein A-gold probes. This report includes the localization of PKC subtype III (α) and its distribution pattern using immunogold labeling.
EM localization of chromaffin cell ATPase
Authors: Kriho V. , Pappas G. D. 
Published: June 2020

During exocytosis of the chromaffin granules, ATP is released. ATP can then be hydrolyzed by the ecto-ATPases of the plasma membrane to provide adenosine for reuptake or for activation of P1purinoceptors. Chromaffin granule membranes also possess ATPase activity. This activity is linked to the uptake of catecholamines from the cytoplasm into the membrane-bound granule compartment.In this report we combine EM cytochemistry and immunogold labelling to provide further evidence for the presence of ATPase on both the plasma membrane and granule membranes of bovine chromaffin cells in culture.
Convergent-beam electron diffraction studies of domains in tetragonal phase of lead zirconate titanate ceramics
Authors: Dass M.L.A. 
Published: June 2020

Lead zirconate titanate Pb(ZrxTi(1-x))O3(PZT) ceramics are ferroelectrics formed as solid solutions between PbTiO3and PbZrO3. Among the different phases in the ferroelectric state, the primary ones are the Ti+4rich tetragonal phase and the Zr+4rich rhombohedral phase. The coexistence of both T and R phases at the boundary composition has been reported using the convergent beam electron diffraction method. In an attempt to characterize the ferroelectric domains in the different phases, a study on the tetragonal phase is reported here, as such an analysis is useful in identifying the phases at the phase boundary.The ceramic used in this study was prepared by conventional ceramic processing and the composition of the sample examined was Pb(Zr0.55Ti0.45)O3. The structure has been found to be tetragonal with lattice parameters a=4.0155Å and c=4.1033Å using X-ray diffraction studies of powder samples.
Microstructure of MBE Grown Al/Gaas [100] schottky contacts
Authors: Kiely C. J. , Cherns D. 
Published: June 2020

The Aℓ/GaAs contact system is used in microwave field effect transistors, but to date, little systematic TEM characterization of the contact microstructure has been performed. There are three possible epitaxial configurations of Aℓ on GaAs [100].[100]Aℓ; Aℓ [100] ||GaAs[100], Aℓ [010] ||GaAs[011]
[110]Aℓ; Aℓ [110] ||GaAs[100], Aℓ [110]||GaAs[011]
[110]R Aℓ; Aℓ[110] ||GaAs[100], Aℓ [001] ||GaAs [011]The interfacial atomic structure of Aℓ[100] ||GaAs[100] has been investigated previously using a CBED technique on plan view specimens. this paper we study the distribution of the various Aℓ orientations as a function of initial GaAs surface reconstruction and film thickness. The misfit dislocation structure of [100] Aℓ/[100] GaAs has been characterized by weak beam microscopy. Also, lattice images from cross-sectional samples are presented. The samples studied were MBE grown and subsequent electrical characterization showed them all to have Schottky barrier heights (SBH) of 0.77eV and excellent rectifying properties over a large temperature range.
Application of WACBED to superlattice structures in compound semiconductors
Authors: McKernan S. 
Published: June 2020

Superlattice structures are now routinely grown in compound semiconductors, with superlattice periodicities ranging from a few angstroms to several hundred angstroms. The structures consist of alternating layers of compound semiconductor which have different chemical composition. The composition of the layers may be chosen to provide a relatively large lattice mismatch for a strained layer superlattice, or to provide lattice matching for good epitactic growth. The chemical difference may be large, as in AIAs/GaAs for example or may be represent only a change in concentration of substitutionally doped material. In all of these materials it is important to characterize the material of the individual layers as well as the interface between these layers.Microscopy of these materials has been performed in real space, using both high resolution and diffraction contrast techniques, and in reciprocal space. The thin cross section specimens used in these investigations are affected by stress relaxation at the interfaces which can result in bending of the atomic planes near the interface.