bluuebunny/crossref_metadata_2025 huggingface dataset:
A bacterial S-layer: separation of double lattices, correlation averaging and 3D reconstruction
Authors: Hegerl R. , Cejka Z. , Baumeister W.
Published: June 2020

Two major questions concerning the results of 3D reconstruction are: 1) The effects of the interaction between specimen and specimen support and 2) the effects of stain level and stain distribution. These questions were approached using the S-layer of the bacterium Clostridium thermohydrosulphuricum which in the electron microscope is usually doubled upon itself. From these specimens independent 3D reconstructions of the upper and lower layers were made and compared with each other.
A comparison of isolated and in situ thick filaments from smooth muscle
Authors: Buhle E.L. , Somlyo A.V. , Somlyo A.P.
Published: June 2020

Early ultrastructural studies of smooth muscle are consistent with the sliding filament mechanism of contraction. Myosin filaments are stable structures in situ and can be found in both relaxed and contracted muscle. Actin filaments can be decorated with SI subfragments of myosin to show a polarity similar to the Z-lines of skeletal muscle. The work presented here is a comparison of isolated thick filaments from relaxed chick amnion with thick filaments obtained in situ from longitudinal thin sections (∽50nm thick) of rabbit portal vein in rigor.
Polymorphic phase transition of a membrane protein - analysis of continuous diffuse electron diffraction intensity
Authors: Dorset Douglas L. , Massalski Andrew K.
Published: June 2020

Matrix porin, the ompF gene product of E. coli, has been the object of a electron crystallographic study of its pore geometry in an attempt to understand its function as a membrane molecular sieve. Three polymorphic forms have been found for two-dimensional crystals reconstituted in phospholipid, two hexagonal forms with different lipid content and an orthorhombic form coexisting with and similar to the hexagonal form found after lipid loss. In projection these have been shown to retain the same three-fold pore triplet geometry and analyses of three-dimensional data reveal that the small hexagonal and orthorhombic polymorphs have similar structure as well as unit cell spacings.
Inexact reconstruction with added noise
Authors: Mu C. , Shao Z.
Published: June 2020

An inexact reconstruction technique (IRT) has recently been developed which allows a 3-D object to be reconstructed using a very limited number of views. The object is assumed to be adequately represented by a binary (Boolean) distribution of mass.

This method has been successfully applied to a biological object using only three views at 45° intervals. The IRT method has been improved with regard to speed and accuracy and has been extended to the special case where three mutually orthogonal views can be obtained.
Morphology of mitochondria in a teleost, salmo gairdneri
Authors: Henderson V. , Song M. J.
Published: June 2020

Mitochondria have been observed at the ultrastructural level as spherical, oval, or sausagelike. Mitochondria average 0.3 to 1.0 um in diameter and 1.0 to 10.0 μm in length. Mitochondria may exceed these dimensions under certian physiological or pathological conditions. The number of mitochondria may reflect the metabolic condition of cells. Cells with high ATP demands display a large number of mitochondria. High energy requirements characterize muscles in both vertebrates and invertebrates. It has been established that yeast cells have but a single mitochondrion. This investigation was designed to ascertain if the numerous mitochondrial profiles represent a single mitochondrion in vertebrate cells.
Freeze-dried surface replicas of tobacco pectin gels and noncutinized lower epidermal cell surfaces compared
Authors: Ruben George C. , Bokelman Gordon H. , Sun Howard H.
Published: June 2020

Pectic polysaccharides play an important role in the extracellular matrix of land plant tissues. Pectins are found in primary cell walls and in the connecting region between cells, the middle lamella. These polysaccharides are thought to function as a binding material within cell walls and between cells. Pectins contain galacturonosyl residues as a major constituent and varying amounts of neutral sugar residues. A portion of the galacturonosyl residues are methyl-esterlfted. Calcium salts of pectin are thought to be present in primary cell walls and middle lamella. The structure of the calcium bond between interfiber galacturonosyl residues has been suggested by x-ray fiber diffraction work. The pectic acid unit cell indicates that the galacturonosyl residue as viewed down the chain axis is roughly 7.2 x 6.8Å along the two crystallographlc a and b axes. One or two waters of hydration can Increase this size by 3-6Å In freeze-etched preparations or an associated calcium Ion can Increase Its cross-sectional dimensions by about 2Å.
High-voltage electron microscopy of unsectioned human lung alveolar walls
Authors: Bastacky Jacob
Published: June 2020

The lung presents a very thin tissue barrier (0.2 μm) to gas exchange with alveolar walls on the order of 10 ym thick. We found the highly energetic (1.5 MeV) beam of the high voltage electron microscope (HVEM) able to penetrate whoiemount unsectioned alveolar walls. Thus, it is possible to simultaneously image the two surfaces of the wall and the internal contents of the wall. The result resembles a high-resolution scanning electron microscope (SEM) surface image with a superimposed transmission electron microscope (TEM) image of internal structure. The composite image resembles a freeze fracture image; however, this technique has the advantage that the specimen is still present.
A comparison of frozen-hydrated/unstained and dried/negatively stained specimen preparation for electron microscopy: Ferritin and apoferritin
Authors: Massover William H.
Published: June 2020

Effective preparative procedures for converting wet macromolecular samples into the frozen-hydrated state via vitrification have been developed recently [1], It is not yet clear whether the electron microscopy of unstained vitrified specimens (cryo-EM) [1,2] is to be preferred over the traditional approach of using negative staining since each method has both advantages and disadvantages [1-3]. The present report describes a comparative evaluation of specimens prepared by vitrification or by negative staining, using the well-characterized metalloprotein, ferritin, as a test object.
Techniques for cryoultramicrotomy of propane jet frozen biological samples
Authors: Craig B. , Hawkey L. , LeFurgey A.
Published: June 2020

Ultra-rapid freezing followed by cryoultramicrotomy is essential for the preservation of diffusible elements in situ within cells prior to scanning transmission electron microscopy and quantitative energy dispersive x-ray microanalysis. For cells or tissue fragments in suspension and for monolayer cell cultures, propane jet freezing provides cooling rates greater than 30,000°C/sec with regions up to 40μm in thickness free of significant ice crystal formation. While this method of freezing has frequently been applied prior to freeze fracture or freeze substitution, it has not been widely utilized prior to cryoultramicrotomy and subsequent x-ray microanalytical studies. This report describes methods devised in our laboratory for cryosectioning of propane jet frozen kidney proximal tubule suspensions and cultured embryonic chick heart cells, in particular a new technique for mounting frozen suspension specimens for sectioning. The techniques utilize the same specimen supports and sample holders as those used for freeze fracture and freeze substitution and should be generally applicable to any cell suspension or culture preparation.
C-propeptide of type ii procollagen; a protein associated with cartilage mineralization
Authors: Lee E.R. , Poole A.R.
Published: June 2020

A matrix protein has been identified in both calcifying and noncalcifying cartilage during development, and named chondrocalcin. The concentration of this protein is greatly increased in calcifying cartilage and it appears in the matrix when and where mineralization occurs. Amino acid sequencing has recently shown that chondrocalcin is identical to the C-propeptide of type II procollagen. Type II procollagen is a high molecular weight precursor of type II collagen and it is characterized by amino (NH2) and carboxy (C) propeptide extensions. These nonhelical extensions are normally cleaved extracellularly by proteinases to give the collagen molecule. To investigate the synthesis, secretion and matrix distribution of the C-propeptide, particularly during mineralization, this protein has been localized at the EM level with immunogold techniques.
Ultrastructure of sudden death syndrome, a new disease in soybeans
Authors: Bozzola John J. , Yopp John , Krishnamani M.R.S. , Richardsonv John , Klubek Brian
Published: June 2020

Sudden Death Syndrome (SDS), a potentially devastating disease of soybeans, was first recognized in Arkansas in the 1970's. Diseased plants first show small interveinal chlorotic spots that progress to brown, necrotic blotches within five to ten days. Tissues around the major veins remain dark green until the late stages when leaf abscission, vascular discoloration and seed pod abortion occur. The disease is most severe during the later reproductive stages of the soybean plant and following a climatic sequence of warm, dry weather followed by a sudden cold, wet period. No organisms have conclusively implicated as causal organisms, although species of Fusarium, Macrophomina, Rhizoctonia and Cercospora fungi have been isolated from diseased plants.
A comparative study of nematosomes in rat autonomic and sensory ganglia
Authors: Jones H. B.
Published: June 2020

Nematosomes are cytoplasmic organelles that are encountered occasionally in the perikarya of many vertebrate neurons and less commonly in a variety of other cell types. The structure of nematosomes in autonomic ganglion neurons differs significantly from that in sensory ganglion neurons. The aim of this study was to investigate the relationship between nematosomes and other cell organelles and thereby gain some insight into their function.
Effect of Sms 201-995, a long-acting somatostatin analog, on the morphology of a growth hormone-secreting pituitary adenoma causing acromegaly: A histologic, immunohistochemical, ultrastructural and morphometric study
Authors: Kovacs K. , Horvath E. , Asa S.L. , Lietz D. , George S.R. , Cross E.G. , Burrow G.N.
Published: June 2020

Treatment of acromegalic patients with somatostatin is a logical approach, since growth hormone (GH) cell adenomas possess somatostatin receptors and somatostatin is known to inhibit GH release. Because of short duration of its action, therapy with natural somatostatin is ineffective in patients with acromegaly. I has been shown recently that SMS 201-995, a long-acting somatostatin analog, reduces blood GH levels and ameliorates clinical signs and symptoms in GH excess. We report here morphologic findings in a pituitary GH cell adenoma removed by surgery from a 36-year-old acromegalic woman after 10 days of SMS 201-995 therapy. Treatment resulted in reduction of blood GH levels.
Paracrystalline arrays in human muscle: HVEM study
Authors: Turner J.N. , Collins D.N.
Published: June 2020

Paracrystalline arrays, most often found beneath the sarcolemma membrane in the region of the nucleus, have been observed in postmortem human muscle tissue. Periodic arrangements of glycogen characterize the arrays, and similar arrays have been reported in muscle of patients with nemaline myopathy. When the glycogen is dissolved a fibrillar network with the same periodicities remains. Individual arrays show a variety of morphologies and symmetries. This work optimises the observation of the fibrillar arrays in semi-thick sections observed in the highvoltage electron microscope (HVEM).
A multislice approach to the rheed and rem simulation
Authors: Peng L.M. , Cowley J.M.
Published: June 2020

The multislice method of calculating dynamical diffraction is based on the physical optics theory of Cowley and Moodie, which has been shown is equivalent to the quantum theory, back scattering being neglected. This method is capable of the calculation of RHEED diffraction amplitudes and the REM image simulation provided that the surface structure and surface potential have been properly modeled.

The procedure for RHEED and REM calculations used her,e is basically the same as the conventional multislice calculation. The periodic continuation assumption has been employed to include the desired model surface (Fig. 1). A large dimension normal to the surface must be used so that there is no interference between these extended unit cells. The choice of the specimen thickness depends on the competition between the requirements for short computing time and larger model surface required to simulate the real equilibrium diffraction processes.
SREM observation of the interaction between the in-situ deposited Pd small particles and MgO cleavage surface
Authors: Ou H.-J.
Published: June 2020

The understanding of the interactions between the small metallic particles and ceramic surfaces has been studied by many catalyst scientists. We had developed Scanning Reflection Electron Microscopy technique to study surface structure of MgO hulk cleaved surface and the interaction with the small particle of metals. Resolutions of 10Å has shown the periodic array of surface atomic steps on MgO. The SREM observation of the interaction between the metallic particles and the surface may provide a new perspective on such processes.
Atomic structure imaging of the Si/SiO2 interface with high-resolution electron microscopy
Authors: Batstone J.L. , Gibson J.M. , White Alice.E. , Short K.T.
Published: June 2020

High resolution electron microscopy (HREM) is a powerful tool for the determination of interface atomic structure. With the previous generation of HREM's of point-to-point resolution (rpp) >2.5Å, imaging of semiconductors in only <110> directions was possible. Useful imaging of other important zone axes became available with the advent of high voltage, high resolution microscopes with rpp <1.8Å, leading to a study of the NiSi2 interface. More recently, it was shown that images in <100>, <111> and <112> directions are easily obtainable from Si in the new medium voltage electron microscopes. We report here the examination of the important Si/Si02 interface with the use of a JEOL 4000EX HREM with rpp <1.8Å, in a <100> orientation. This represents a true structural image of this interface.
High-resolution electron microscopy of Cu2O surfaces
Authors: Castano V. , Krakow W.
Published: June 2020

In non-UHV microscope environments atomic surface structure has been observed for flat-on for various orientations of Au thin films and edge-on for columns of atoms in small particles. The problem of oxidation of surfaces has only recently been reported from the point of view of high resolution microscopy revealing surface reconstructions for the Ag2O system. A natural extension of these initial oxidation studies is to explore other materials areas which are technologically more significant such as that of Cu2O, which will now be described.
High-resolution studies of interfaces in materials science
Authors: Carpenter R.W.
Published: June 2020

Structure and composition of interfaces span a wide range in materials science, from grain boundaries to interphase interfaces. Silicon-silicon oxide and various si1 icon-si 1icide interfaces are the most intensively studied to date. In favorable cases where misfit strain is very small and flat boundaries can be examined in cross-section to satisfy the projection approximation, as in nickel silicide-silicon interfaces, the interface bond structure can be determined. In most other cases interfaces are neither homogeneous or flat, and it is useful to also apply microbeam diffraction and spectroscopy to interfacial analysis. For small unit cell crystals, i.e. metals, intermediate voltage HREM is necessary. In this note applications to ion implantation in silicon, composite interfaces, and precipitation in metallic alloys are illustrated.
The effect of residual strain on twinning in shock-loaded copper
Authors: Gray G.T.
Published: June 2020

Under shock-loading, twinning is observed in metals that do not twin under conventional loading conditions, for example copper and nickel where the stacking fault energy is about 78 and 128 ergs/cm2, respectively. Contradictions in the published data on the twinning stress in copper (from 1.6 GPa in thin films to 14.5-20 GPa in bulk specimens suggest differences associated with experimental techniques. This study examines the role of residual plastic strain (eres) on the deformation substructures, particularly twinning, in shock-roaded copper.
TEM visualization of surface replicated acid and base catalyzed sol-gel glasses
Authors: Ruben George C. , Shafer Merrill W.
Published: June 2020

Traditionally ceramics have been shaped from powders and densified at temperatures close to their liquid point. New processing methods using various types of sols, gels, and organometallic precursors at low temperature which enable densificatlon at elevated temperatures well below their liquidus, hold the promise of producing ceramics and glasses of controlled and reproducible properties that are highly reliable for electronic, structural, space or medical applications. Ultrastructure processing of silicon alkoxides in acid medium and mixtures of Ludox HS-40 (120Å spheres from DuPont) and Kasil (38% K2O &62% SiO2) in basic medium have been aimed at producing materials with a range of well defined pore sizes (∼20-400Å) to study physical phenomena and materials behavior in well characterized confined geometries. We have studied Pt/C surface replicas of some of these porous sol-gels prepared at temperatures below their glass transition point.
Microstructure characterization of non-stoichiometric dicalcium silicates doped with aluminum oxide
Authors: Chan C. J. , Kriven W. M. , Young J. F.
Published: June 2020

Dicalcium silicate is a major component of portland cement. The high temperature polymorph (eg. the β form) is more reactive than the low temperature (γ) form. There are reports that the high temperature polymorphs can be stabilized by varying the stoichiometry (CaO/SiO2 ratio) or by addition of dopants. Excess lime in solid solution is claimed to improve the reactivity of stabilized β-Ca2SiO2. In our study we re-examine the stabilizing effect of CaO/SiO2 non-stoichiometry and Al2O3 doping.
Transmission Electron Microsopy of oxidized UO2 spent fuel
Authors: Thomas L. E. , McCarthy J. M. , Gilbert E. R.
Published: June 2020

The possibility that spent fuel from commercial light-water reactors (LWRs) may be stored for extended periods before reprocessing or permanant disposal has led to interest to its oxidation behavior in air. Oxidation weight gain tests at 150 to 250°C indicate that spent LWR fuel oxidizes 10 to 100 times more rapidly than unirradiated UO2, but is much slower to break up into U3O8 powder. To gain insight into the mechanisms that control oxidation in spent fuel, pre- and post oxidation samples were examined by transmission electron microscopy.
TEM characterization of proton-exchanged LiNbO3 optical waveguides
Authors: Lee W. E.
Published: June 2020

An optical waveguide consists of a several-micron wide channel with a slightly different index of refraction than the host substrate; light can be trapped in the channel by total internal reflection.

Optical waveguides can be formed from single-crystal LiNbO3 using the proton exhange technique. In this technique, polished specimens are masked with polycrystal1ine chromium in such a way as to leave 3-13 μm wide channels. These are held in benzoic acid at 249°C for 5 minutes allowing protons to exchange for lithium ions within the channels causing an increase in the refractive index of the channel and creating the waveguide. Unfortunately, optical measurements often reveal a loss in waveguiding ability up to several weeks after exchange.
Strain contrast in SiC whisker reinforced Al2O3
Authors: Angelini P. , Mader W.
Published: June 2020

Whisker reinforced ceramic materials offer the potential for increased fracture toughness and fracture strength. Residual stresses resulting from differences in thermal expansion properties of the matrix and the whisker can develop during cooling and affect mechanical properties. TEH strain contrast of large inclusions has previously been observed for nearly spherical particles of ZrO2 in Al2O3 matrix grains. The formation of strain contrast oscillations was explained and a quantitative analysis of strains around ZrO2 inclusions in Al2O3 was performed. The present research is concerned with characterizing by TEM the strain field present in Al2O3 reinforced with SiC whiskers.
In situ observation of the martensitic transformation in (Mg,Y)-PSZ
Authors: Lee R-R.
Published: June 2020

Partially-stabilized ZrO2 (PSZ) ceramics have considerable potential for advanced structural applications because of their high strength and toughness. These properties derive from small tetragonal ZrO2 (t-ZrO2) precipitates in a cubic (c) ZrO2 matrix, which transform martensitically to monoclinic (m) symmetry under applied stresses. The kinetics of the martensitic transformation is believed to be nucleation controlled and the nucleation is always stress induced. In situ observation of the martensitic transformation using transmission electron microscopy provides considerable information about the nucleation and growth aspects of the transformation.
Dislocations at low temperatures in brittle ceramics
Authors: Veyssière P. , Castaing J.
Published: June 2020

Brittleness is a feature common to many ceramic materials at low temperature. However, in some cases, they remain ductile as, for instance, crystals with the rocksalt structure which can be deformed down to 4.2 K: their properties are very similar to those of metals and will not be described in the present paper (for a review, see). Usually, macroscopic strain can be obtained only at temperatures larger than 0.5 TM, where TM is the melting temperature. The resulting microstructures consist in networks where dislocation climb is shown by TEM to have played an extensive role. Nevertheless, despite the active atomic diffusion pointed out in the high temperature experiments, what controls the transition between ductility and brittleness is probably not related to the rate of matter transport. Rather, the reasons for this transition rely on crystal structure and chemical bonding, which are of prime importance in the choice of Burgers vectors and slip plane, in the mobility of dislocations...
Recent trends in high-resolution electron microscopy
Authors: Smith David J.
Published: June 2020

The recent advent of high-resolution electron microscopes (HREMs) capable of resolving sub-2-Ångstrom detail on a routine basis has led to an enormous increase in the range of materials which can be usefully studied. Not only is it possible to resolve individual atomic columns in low index zones of most common metals but observations of semiconductors, for example, are no longer restricted to the traditional [110] zone, thereby making it feasible at last to obtain two-dimensional information about surfaces, interfaces and other planar defects. There is a worldwide upsurge of interest in the capabilities of these machines and the so-called medium-voltage (300-400kV) HREMs are selling rapidly despite their considerable expense. Our objective here is to provide a brief and selective overview of the latest applications and likely trends in HREM studies of materials - further details can be found elsewhere in these proceedings. No attempt is made to review instrumentation developments since they are being considered separately.
Superfluid cryostage for high-resolution electron microscopy
Authors: Fujiyoshi Y.
Published: June 2020

Structural study using electron microscopy is indispensable in the fields of physics, chemistry and biology because electron microscopy provides structural images from only small regions of a specimen. The high sensitivity of structure analysis in electron microscopy, however, results in the inevitable problem of irradiation damage in biological and organic materials. Many methods have been tried to reduce the irradiation damage, for example, by raising accelerating voltage, developing high sensitivity recording systems, cooling specimen temperature, etc. Cryoprotection may be the most promising method available for reducing damage at present. The cryoprotection effect from room temperature to liquid helium temperature has interested many researchers for about 15 years, although it is still open to controversy. Recently, the International Experimental Study Group made an interesting attempt to resolve the problem of the cryoprotection factor by cooling specimens in electron microscopes in independent experiments, as closely coordinated as possible with one another. In that paper, although the critical doses measured in each laboratory agree satisfactorily at room temperature, no agreement among the values was observed at very low temperatures.
Identification of HCP ε phase in β CoAl phase of CoCrAl(Y) Alloys
Authors: Caola John R.
Published: June 2020

Superalloy components for use at high temperatures generally require a coating to provide adequate oxidation resistance. An important group of these state-of-the-art MCrAlY coatings is based on the Co-Cr-Al system. The CoCrAl alloys contain two major phases:α(a Co-rich solid solution) and β (based on CoAl). The composition, morphology and distribution of phases are important factors in the behavior of the coatings. This study reports the results of one step in the identification of the phases present within the β-phase using TEM in CoCrAl-type alloys formed both by casting and by coating onto a superalloy substrate by electron beam physical vapor deposition (EBPVD).
Microstructural investigation of temper embrittlement in 2.25% Cr-1%Mo steels with and without La additions
Authors: Burke M.G. , Garcia C. I. , DeArdo A. J.
Published: June 2020

Lanthanide (rare earth) metal additions to 2.25% Cr-1% Mo steels have been found to alleviate the material's susceptibility to temper embrittlement. To elucidate the manner by which such additions impart immunity to temper embrittlement, analytical electron microscopy (AEM) and atom probe field-ion microscopy (APFIM) have been employed to study the microstructures of tempered 2.25% Cr-1% Mo steels containing tramp elements with and without lanthanum additions.

Thin-foil and carbon extraction replica specimens were prepared from the heat-treated 2.25% Cr-1% Mo steels. These samples were examined in a JEOL 200CX Temscan at 200 kV. Alloy carbides were identified by electron diffraction and STEM qualitative energy dispersive x-ray analysis.
Precipitate coarsening during hot-compression testing of NiAl + 2 at.% Nb
Authors: Sherman W. M. , Vedula K. M.
Published: June 2020

The strength to weight ratio and oxidation resistance of NiAl make this ordered intermetallic, with some modifications, an attractive candidate to compete with many superalloys for high temperature applications. Recent studies have shown that the inherent brittleness of many polycrystalline intermetallics can be overcome by micro and macroalloying. It has also been found that the high temperature mechanical properties of NiAl can be enhanced through the addition of Nb by powder metallurgical techniques forming a dispersed second phase through interdiffusion in a polycrystalline matrix. A drop in the flow stress is observed however in a NiAl-2 at.% Nb alloy after 0.2 % strain during constant strain rate hot compression testing at 1025°C. The object of this investigation was to identify the second phase and to determine the cause of the flow stress drop.
Improvements on the gaseous detector device
Authors: Danilatos G.D.
Published: June 2020

The possibility of placing the specimen in a gaseous medium in the environmental SEM (ESEM) has created novel ways for detection of signals from the beam-specimen interactions. It was originally reported by Oanilatos that the ionization produced by certain signals inside the conditioning medium can be used to produce images. The aim of this report is to demonstrate some of the improvements on the system that have occurred thereafter.

Two straight thin wires are aligned horizontally along a direction normal to the direction of the two scintillator backscattered electron (BSE) detectors reported elsewhere. The free end tips of the wires are about 5 mm apart halfway between the specimen and the pressure limiting aperture (specimen distance = 1.5 mm). The other end of each wire makes contact with the input of a separate preamplifier, two of which are built inside a shielding aluminum stub. With such a design, interference noise from the input cables is avoided.
Magnetic microstructure imaging by secondary electron spin polarization analysis
Authors: Hembree G. G. , Unguris J. , Celotta R. J. , Pierce D. T.
Published: June 2020

Recent research has shown that the low energy secondary electrons generated from ferromagnetic material are spin polarized. The secondary electron polarization yields a signal which is directly proportional to the magnitude and direction of the magnetization within the volume of material in which the electrons were generated. This signal can be used in a scanning electron microscope to image the microstructure of magnetic domains on the surface of ferromagnetic materials.

We have incorporated a new compact spin polarization analyzer into a commercial UHV SEM. A schematic diagram of the apparatus is shown in Fig. 1. The secondary electrons are extracted from the sample and are then focused into a hemispherical energy analyzer which filters out the high energy electrons.
Tunneling images of reconstructed semiconductor surfaces
Authors: Griffith J. E.
Published: June 2020

The study of reconstructed surfaces has been dominated by diffraction and ion beam techniques that are sensitive to the regular structure of the reconstruction. These techniques tend to emphasize the properties of perfect lattices. The tunneling microscope offers a different perspective on these surfaces by revealing images of local defects in the reconstruction. Steps, missing atoms, and extra atoms are all easily imaged. Images of defects give us new information about the reconstructions and about the properties of the microscope itself. The tunneling microscope is also capable of inducing defects in a reconstructed surface.
Electron detection modes and their relation to linewidth measurement in the Scanning Electron Microscope
Authors: Postek M. T.
Published: June 2020

The basic premise underlying the use of the scanning electron microscope (SEM) for linewidth measurement for semiconductor research and production applications is that the video image acquired, displayed, and ultimately measured reflects accurately the structure of interest. It should be understood that not all the secondary electrons detected originate at the point of impact with the primary electron beam. Those that do are referred to as Type I electrons. Some of the signal is contributed by re-emergent backscattered electrons creating secondary electrons at the surface of the sample (Type II electrons) and at the final lens polepiece (Type III electrons). Other signal contributions include line-of-sight backscattered electrons and other sources particular to each instrument (Type IV electrons). The effects of these four types of contributions to the actual image or linewidth measurement have not been fully evaluated. In measurement applications, error due to the actual location of signal origination will not affect pitch measurements as the errors cancel. However, in linewidth measurement, the errors are additive and thus give twice the edge detection error to the measured width. The basic intent of this work is to demonstrate the magnitude of these errors relative to the mode of signal detection at a variety of beam acceleration voltages.
Imaging and diffraction modes in Scanning Transmission Electron Microscopy
Authors: Cowley J. M. , Glaisher R. , Lin J. A. , Ou H.-J.
Published: June 2020

Some of the most important applications of STEM depend on the variety of imaging and diffraction made possible by the versatility of the detector system and the serial nature, of the image acquisition. A special detector system, previously described, has been added to our STEM instrument to allow us to take full advantage of this versatility. In this, the diffraction pattern in the detector plane may be formed on either of two phosphor screens, one with P47 (very fast) phosphor and the other with P20 (high efficiency) phosphor. The light from the phosphor is conveyed through a fiber-optic rod to an image intensifier and TV system and may be photographed, recorded on videotape, or stored digitally on a frame store. The P47 screen has a hole through it to allow electrons to enter a Gatan EELS spectrometer. Recently a modified SEM detector has been added so that high resolution (10Å) imaging with secondary electrons may be used in conjunction with other modes.
Software pattern recognition applied to nanodiffraction patterns from a STEM instrument
Authors: Fan G.Y. , Cowley J.M.
Published: June 2020

In recent developments, the ASU HB5 has been modified so that the timing, positioning, and scanning of the finely focused electron probe can be entirely controlled by a host computer. This made the asynchronized handshake possible between the HB5 STEM and the image processing system which consists of host computer (PDP 11/34), DeAnza image processor (IP 5000) which is interfaced with a low-light level TV camera, array processor (AP 400) and various peripheral devices. This greatly facilitates the pattern recognition technique initiated by Monosmith and Cowley. Software called NANHB5 is under development which, instead of employing a set of photo-diodes to detect strong spots on a TV screen, uses various software techniques including on-line fast Fourier transform (FFT) to recognize patterns of greater complexity, taking advantage of the sophistication of our image processing system and the flexibility of computer software.
Site occupations in L12 ordered alloys by axial electron channeling microanalysis
Authors: Bentley J.
Published: June 2020

Lattice site location of alloying additions to A3B-type ordered alloys with the L12 structure is important for alloy development, but ion channeling and X-ray diffraction techniques require single crystal specimens. The ALCHEMI technique is applicable to polycrystalline specimens but provides only qualitative results on the site occupancy in L12 A3B alloys. Quantitative analysis by standard planar channeling ALCHEMI is complicated by the absence of lattice planes containing only B atoms. Since certain zone axes, including <001> and <111>, contain columns of A atoms well separated from columns of B atoms, the ALCHEMI method has been extended to use zone axis channeling conditions. Further, the procedure has been simplified to use spectra recorded from two orientations - an appropriate channeling zone axis and a “random” non-channeling condition typically 2-5° from the zone. The concentration CX of element X on the B sites is given by Cx = {R(X/A) - 1}/{R(B/A) - 1}, where R(X/A) = (NX/NA)zone/(NX/NA)random, ete., and NX, NA, NB are the characteristic X-ray intensities of elements X, A, and B.
Electron microscopy of transient annealed polysilicon films
Authors: Krause S.J. , Wilson S.R. , Gregory R.B. , Paulson W.M.
Published: June 2020

Polycrystalline silicon, commonly used as an interconnect and as a gate material in many integrated circuits, is ion implanted and annealed to reduce its resistivity. We previously characterized the effects of transient annealing on the structure and electrical properties of ion implanted polycrystalline silicon and found that grain growth occurred by an interfacial energy controlled mechanism which resulted in increased grain size and reduced resistivity. In this work we are reporting on structural changes in films subjected to a treatment of transient preannealing, ion implantation, and transient post-annealing.
Direct casting of SBS block copolymers on supported grids for TEM study
Authors: Spontak R.J.
Published: June 2020

Transmission electron microscopy (TEM) has been used successfully in studying the microstructures resulting from microphase-separated block copolymers consisting of polystyrene (S) and polybutadiene (B). Difficulty, however, arises in the sample preparation stage, in which specimens ranging 50-100 nm thick are required. Such specimens can be obtained by either cutting ultrathin sections from a bulk sample or by dissolving the polymer in a suitable solvent and casting the solution to form an ultrathin film. Many methods exist for preparing such films, and almost all share one common feature: the cast film is floated on a clean fluid (e.g., water) surface. In some cases, the film is first cast on a carboncoated glass slide and scored prior to the flotation step so that small sections may be picked up by TEM grids. To avoid (a) casting the copolymer onto a flotation medium, which may inadvertently affect the microstructure orientation, (b) excessive handling of the cast film, and (c) exposing a hygroscopic copolymer (e.g., siloxane polyimide polymers) to a water surface, a method of casting copolymer films directly onto supported TEM grids is presented here.
TEM recombination studies of dislocations in indium phosphide
Authors: Myhajlenko S. , Hutchinson H. J. , Steeds J. W.
Published: June 2020

We have reported the use of transmission electron microscopy (TEM) with simultaneous cathodoluminescence (CL) for the study of defects in opto-electronic semiconductors such as InP and ZnSe. The effect of individual dislocations on the efficiency of the near band edge luminescence was investigated; the main observation reported for InP was the quenching at some dislocations of the exciton-related emission. No correlation was found between dislocation type and luminescence behaviour. Further, during the course of this work, a better appreciation has been gained of factors which are important in transmission CL studies, for example, the effects of excitation, strain, surface recombination, electric fields and optical interference. We describe some of them here and new results from dislocation groups in InP.
Localized ion milling of metallic and ceramic TEM specimens
Authors: Fisher A. T. , Bentley J.
Published: June 2020

The utility of localized ion milling in the preparation of metallic and ceramic specimens for TEM and AEM is being evaluated from the standpoint of optimizing procedures and identifying limitations and milling characteristics. The equipment used was a Gatan model 645 precision ion milling system (PIMS). This device is a scanning ion beam instrument with which selected areas of a sample can be imaged by either secondary electron or secondary ion signals and selectively ion milled in a small region within the imaged area. The 1 to 10 keV ion beam can be focussed to a 2 μm spot. Specimens are thinned without removing them from the electron microscope specimen holder.
Microstructural characterization of sol-gel derived PbTiO3 thin films
Authors: Budd K. D. , Dey S. K. , Payne D. A.
Published: June 2020

A process has been developed for the fabrication of continuous, crack-free layers, of a series of compositions in the PbO-La2O3-TiO2-ZrO2 system. These layers were formed by spin-casting solutions of complex alkoxides onto platinum, silicon, silica, and a variety of substrates. The dried layers were amorphous gels which could be densified and converted to ceramic films at relatively low temperatures (e.g., 350-500°C). Gellation was caused by the condensation polymerization of alkoxide molecules, and was initiated by hydrolysis of the alkoxy groups. Gel structures were manipulated by controlling hydrolysis conditions (catalyst and amount of water) in an effort to control pyrolysis behaviour, optimize microstructures, and minimize firing temperatures. Lower processing temperatures increased the compatibility with substrates such as Si wafers. Structural control was possible because the polymerization reactions become site-specific under certain hydrolysis conditions. As discussed below, microstructures of thin films were influenced considerably by both the type of catalyst, and by interactions with silicon substrates.
An IBM PC-based system for generating three-dimensional reconstructions from serial electron micrographs
Authors: Kinnamon ohn C. , Young Stephen J. , Sherman Terri A.
Published: June 2020

ne of the common problems confronting the morphologist is the elucidation f the three-dimensional (3-D) nature of biological structures from twoimensional micrographs. Serial section analysis can alleviate this problem omewhat, but it becomes increasingly difficult to mentally reconstruct tructures encompassing more than a few sections. For the past decade, the se of computers has been applied to the generation of 3-D reconstructions rom serial micrographs. Until recently, however, the costs of both ardware and software for 3-D reconstructions have been prohibitively xpensive for most laboratories.
Evaluation of sectioning techniques for Electron Microscopic analyses of low-density polyethylene foams
Authors: McCarthy P. L. , Price C. W.
Published: June 2020

Cell sizes of low-density polyethylene foams in the range of 0.5 to 5μm are most conveniently measured by SEM analyses. Unfortunately, the cell walls are relatively weak and fragile membranes that either collapse or are severely distorted by conventional surface preparation and sectioning techniques. Sectioning damage can be circumvented to some extent by freeze fracturing. However, fractures tend to propagate through the weakest structural features, they can be associated with severe deformation, even at liquid nitrogen temperatures, and they frequently do not yield planar surfaces for reliable statistical measurements. Therefore, alternate sectioning techniques were evaluated. The most promising techniques are vibrotome sectioning and ultramicrotomy. These techniques are compared with freeze fracturing using SEM examinations of carbon-coated specimens prepared from the same batch of foam.
Specimen preparation, cryotransfer and microscope parameters for cold-stage work in SEM and application for the physical and biological sciences
Authors: Sargent J.A.
Published: June 2020

The availability of equipment which enables frozen-hydrated material to be viewed over prolonged periods in the SEM has greatly extended the versatility of the instrument and permitted more precise interpretation of the data obtained from it. Artifacts associated with chemical fixation are avoided and soluble components are retained which might otherwise be removed by solvents used for dehydration or critical point drying. In addition the shrinkage which frequently occurs during freeze drying is avoided. Two further advantages of cryo preservation can be invaluable: rapid cooling of motile specimens instantly arrests movement and the immobilization of diffusible compounds and ions enables X-ray microanalysis to be performed with confidence.

The speed with which specimens are cooled is not critical if only surface features are to be studied. However, the examination of internal structure demands that ice crystal growth be minimised. Devices are available to maximise cooling rates using a variety of cryogens and specimen transfer to the SEM cold stage is achieved simply and effectively.
Molecular microscopy: Theoretical possibilities and experimental realities
Authors: Sidles John A.
Published: June 2020

It is interesting to imagine a world in which microscopy had never been invented. What techniques would scientists use to study cell structure? Lack of microscopy would not prevent research.... instead scientists would study cells using indirect means; e.g. by homogenizing, filtering, and centrifuging cells. After much work, they would be able to demonstrate that cells are surrounded by membranes, and contain nuclei carrying genetic information. All aspects of cell structure could be studied in this indirect way.

Biomedical researchers would not feel particularly handicapped by the lack of microscopy. Rather they would compete for access to the newest and most ingenious filtering devices. In this hypothetical world, it would not be readily apparent that instrument technology was a crucial medical/scientific issue.

It is arguably the case that we live in a similar world, and that (from a clinical perspective) we need a microscope technology that can image 3D biomolecular structure with the subangstrom spatial resolution that is required for the rational design of drugs and vaccines.

The highest-resolution techniques for determining 3D molecular structure are x-ray crystallography and mutidimensional NMR analysis. However, neither of these techniques can properly be called “microscopy”.
Effect of brefeldin A (BFA) on the unique surface coat of pulmonary intravascular macrophages (PIMs) of sheep: Ultrastructural and cytochemical study
Authors: Singh Baljit
Published: June 2020

The PIM of sheep, calf, goat and horse has a characteristic ultrastructural feature in the form of a unique, heparin sensitive, globular surface coat present around the plasma membrane with an intervening electron lucent space of 32-40 nm. We previously showed the active involvement of this surface coat in the phagocytosis of tracer material like monastral blue and cationized ferritin. The surface coat is capable of reconstitution in vivo following disruption with heparin. The present study was aimed to investigate whether PIM is the source of surface coat or not. In the recent years the BFA has been extensively used to understand the secretory pathways in the cells because of its ability to cause a rapid and reversible block to the anterograde transport of proteins from the endoplasmic reticulum to the Golgi.

Sheep (n=6) were weighed, their plasma volume was calculated indirectly and based on which a sufficient single intravenous dose of BFA was given so as to reach a concentration of 4-5 microgram/ml of plasma.
Identification of cytoplasmic tubular structures in Pneumocystis carinii
Authors: Goheen Michael P. , Bartlett Marilyn S. , Smith James W.
Published: June 2020

Pneumocystis carinii (PC) is an extracellular organism which frequently causes pneumonia in immunocompromised patients. In the United States more than 60% of patients with acquired immunodeficiency syndrome (AIDS) have at least one episode of PC pneumonia. The earliest published ultrastructural study of PC was undertaken by Dickmann et al. in 1954. A few articles which studied the ultrastructure of PC continued to appear in the German medical literature in the late 1950’s and early 1960’s. With the development of immunosuppressive chemotherapy for cancer patients and in later years the onslaught of the AIDS epidemic, the ultrastuctural literature concerned with PC has expanded. The internal morphology of PC has proved to be difficult to preserve and although extensively examined questions remain concerning the intracellular contents of PC. In this study we report the presence of cytoplasmic tubular structures (CTS) in PC. These structures have been identified in hepatocytes of Chimpanzees infected with non-A,non-B hepatitis and in the lymphocytes of humans with adult T-cell leukemia or AIDS.