bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymorphism of fiber cell junctions in mammalian lens
Authors: Costello M. Joseph , Al-Ghoul Kristin J. , Oliver Timothy N. , Lane C. Wesley , Wodnicka Magdalena , Wodnicki Pawel
Published: June 2020

Previous studies of junctional specializations between bovine lens fiber cells have indicated that pentalamellar profiles in isolated membranes correspond to gap junctions (GJs), undulating square array junctions (SAJs) and thin symmetric junctions (TSJs). We show here that this same junctional diversity occurs in the intact tissue and that the differences in thickness and staining patterns can be documented by density profiles from thin-section TEM images of in vivo and isolated membranes.

Fresh bovine lenses were mounted on edge and vibratome sectioned parallel the optic axis. Sections near the center were fixed (paraformaldehyde, glutaraldehyde, and tannic acid) for thin-section analysis or were dissected on a glass slide to select a group of fiber cells within a narrow region, such as the deep cortex about 2 mm from the lens surface. Membranes were isolated from this small fraction of cells using a new procedure, essentially, suspending in buffer, washing 30 min in 4M urea and pelleting at low speed in an AirFuge (Beckman).
Processing of high-resolution images of irradiated ceramics
Authors: Lewis M.E. , Qin L.C. , Sreeram A.N. , Hobbs L.W.
Published: June 2020

Mathematical morphology as an image processing and analysis tools is both a science and an art. The theory of mathematical morphology is rooted in topology, where a set-theoretic framework is the basis of binary morphology. Gray-scale morphology is an extension into the space of functions. This rigorous formulation has provided powerful transformations, operating directly on the information content of an image. However, it is up to the investigator’s creativity to devise the appropriate criteria for each problem at hand.

The main focus of the present study is the analysis of image contrast and the relationship with the underlying structure of the material. Image processing and analysis methods based on mathematical morphology were applied to high resolution micrographs of irradiated ceramics: electronirradiated tridymite and ion-irradiated lead pyrophosphate single crystal.

The interesting feature of these images is the presence of periodic, aperiodic and partially ordered structures, Fig.s la and 2a.
Standard formats for the exchange and storage of image data
Authors: Egerton R.F. , Bright D.S. , Davilla S.D. , Ingram P. , Kirkland E.J. , Kundmann M. , Lyman C.E. , Rez P. , Steele E. , Zaluzec N.J.
Published: June 2020

In microscopy, there is an increasing need for images to be recorded electronically and stored digitally on disk or tape. This image data can be shared by mailing these magnetic media or by electronic transmission along telephone lines (e.g. modem transfer) or special networks, such as Bitnet and Internet. In each case, the format in which the image is stored or transmitted must be known to the recipient in order to correctly recover all the information. Because there are many image formats to choose from, it would undoubtedly save misunderstanding and frustration if a group of individuals with similar interests and needs could agree upon a common format. The MSA Standards Committee has surveyed several formats which could be of particular interest to microscopists, with a view to making a recommendation to our community.

Our chief concern has been compatibility with existing software, combined with an adequate representation of the data, compactness of data storage (on disk) and reasonable rate of data transfer.
Determining chromatin structure by computer-aided image analysis
Authors: Olesen James B. , Heckman Carol A.
Published: June 2020

In the present research, we address the problem of how chromatin fibers are ordered in band and interband regions along the length of a Drosophila polytene chromosome. Our approach employs image processing as a preliminary step to amplify the image contrast. Then, computerized pattern recognition methods are used to study how the chromatin is arranged.

Polytene chromosomes were isolated from salivary glands and squashed on glass microscope slides. The slides were immersed in liquid nitrogen and the coverslips were removed with a razor blade. Small droplets of a polymer developed in our laboratory called HACH (a mixture of 2- hydroxyhexanedial, carbohydrazide and hydrazine) were then placed over individual chromosome spreads and the slides were left at 26°C overnight to allow for HACH polymerization. HACHembedded samples were removed from the slides, mounted on resin blocks, trimmed and thinsectioned at a thickness of approximately 100 nm. Sections were floated onto formvar-coated gold grids and viewed with a Zeiss 10C transmission electron microscope operated at 80kV.
Log-log scale roughness spectroscopy of surfaces
Authors: Fraundorf P. , Armbruster B.
Published: June 2020

Optical interferometry, confocal light microscopy, stereopair scanning electron microscopy, scanning tunneling microscopy, and scanning force microscopy, can produce topographic images of surfaces on size scales reaching from centimeters to Angstroms. Second moment (height variance) statistics of surface topography can be very helpful in quantifying “visually suggested” differences from one surface to the next. The two most common methods for displaying this information are the Fourier power spectrum and its direct space transform, the autocorrelation function or interferogram. Unfortunately, for a surface exhibiting lateral structure over several orders of magnitude in size, both the power spectrum and the autocorrelation function will find most of the information they contain pressed into the plot’s origin. This suggests that we plot power in units of LOG(frequency)≡-LOG(period), but rather than add this logarithmic constraint as another element of abstraction to the analysis of power spectra, we further recommend a shift in paradigm.
Visualization of the anionic sites in the cell wall of apple fruit using a cationic colloidal gold probe
Authors: Roy Stéphane , Conway William S. , Watada Alley E. , Pooley Christopher D. , Wergin William P.
Published: June 2020

The ripening of fleshy fruits involves a softening process that consists of biochemical changes in the cell wall and leads to cell separation. Calcium is an important constituent of the cell wall and plays roles in maintaining the firmness of fruit and in reducing postharvest decay. The modification of cell wall strength is believed to be influenced by calcium that interacts with acidic pectic polymers to form crossbridges. This study examined how the frequency and distribution of anionic binding sites in the cell walls of apple fruit were influenced by calcium infiltration.

Mature “Golden Delicious” apple fruits were pressure infiltrated with either H2O or a 4% solution of CaCl2and the pericarp was sampled and processed according to standard procedures. Cationic poly-Llysine colloidal gold complex was used in a one-step procedure to visualize anionic sitesin muro. Observations were performed with light microscopy, following silver intensification, and with transmission electron microscopy.
Electron microscopy of the changes in the sperm head curvature of the palm squirrel (Funambulus Penanti)
Authors: Bawa S. R. , Bawa R. , Bains H. K.
Published: June 2020

Examination of ultrathin sections of the spermatozoa recovered from the epididymis of the Indian palm squirrel (Funambulus penanti) indicates that the sperm head undergoes changes in its curvature during epididymal transit.

Testis and epididymis of an adult male squirrel were dissected and small pieces of tissue fixed in 2.0% glutaraldehyde in 0.1 M phosphate buffer and post-fixed in osmium tetroxide. After dehydration in graded acetone the material was embedded in Araldite. Ultrathin sections were cut on a Reichert Jung Ultracut, picked-up on copper grids, stained with Reynold’s lead citrate-uranyl acetate and examined with a JEOL 1200 EX transmission electron microscope.

Ultrathin sections of the caput epididymal spermatozoa reveal that their plasma membrane is adherent to the underlying acrosome (Figure 1). When these spermatozoa reach the corpus epididymis the plasma membrane surrounding the head becomes ruffled (Figure 2). The lifting-up of the plasma membrane around the head is restricted to the posterior bend of the acrosome.
Ultrastructural change of the cell membranes on myocardium following treatment with H2O2
Authors: Oguro Tatsuo , Aihara Kaoru , Aida Kuniharu , Asano Goro , Ashraf Muhammad
Published: June 2020

It has been suggested that hydrogen peroxide (H2O2) is indirectly associated with postischemicreperfusion injury of the heart. Previously, we reported that the heart was not damaged when perfused with exogenously generated superoxide anions. However, H2O2 which is a dismutation product of superoxide anion severely affected the heart structure and function, and the combined effects of H2O on membrane lipid and proteins result in the formation of membranous bleb.

In this study, we evaluated the ultrastructural changes of the cell membranes in isolated rat hearts and cultured myocytes following treatment with exogenous H2O2. In the isolated hearts, 300μM H2O2 was perfused for 15 min and in the isolated cultured myocytes an equal amount of H2O2 was added to the culture medium for 30 min. This dosage of H2O2 was found to be injurious to the heart in our previous study. In the isolated cultured myocytes, 300μM H2O2 was added to the medium for 30 min.
Human melanocytes transfer pigment to epidermal keratinocytes after grafting of a cultured skin substitute to athymic mice
Authors: Harriger M. Dana , Boyce Steven T.
Published: June 2020

Melanocytes are pigment-synthesizing cells intercalated among the basal keratinocytes along the dermal-epidermal junction of the skin. Through production of melanin, melanocytes generate skin pigmentation that provides the ultraviolet barrier in the epidermis. Melanosomes are very electron-dense, membrane-bound organelles that package and transfer pigment throughout the epidermis. Melanocytes transfer melanosomes to nearby keratinocytes in the basal layer of the epidermis. The mechanism of pigment transfer may involve either the fusion and breakdown of plasma membranes of both melanocyte and keratinocyte, establishing cytoplasmic communication, or phagocytosis of melanosome containing dendritic processes by the keratinocyte. Most melanosomes within keratinocytes are degraded by lysosomal enzymes as the cells differentiate and move upward. However, some keratinocytes retain melanosomes into the stratum corneum. Melanocytes are identified in light micrographs by their palely staining cytoplasm, ovoid nucleus, and cytoplasmic granules (Figs. 1,3) and in electron micrographs by the absence of keratin filaments and presence of melanosomes (Figs. 2,4,5,6).
Adrenal and vagus modulation of cisplatin-induced gastric emptying and ulceration
Authors: Aggarwal Surinder K.
Published: June 2020

Cisplatin is a most valuable broad spectrum antineoplastic drug available for the treatment of testicular and ovarian cancers. It has several severe toxic side effects of which gastrointestinal and nephrotoxicity are the major dose limiting. It also induces hypocalcemia and Hypomagnesemia that have been demonstrated to effect the secretory activity of the neurohypophysis and the parathyroid glands. In rats cisplatin treatment causes stomach bloating and ulceration that can be ablated by daily injections of calcium just before the treatment and during the treatment or using vagotomy. Adrenalectomy has also been shown to prevent ulceration. Present study is an effort to determine the effect of cisplatin on morphological and cytochemical changes in the neuromuscular interactions of the stomach smooth muscle and the adrenal glands before and after vagotomy.

Male Wistar rats [Crl:(WI)BR] weighing 200-300 g were given intraperitoneal injection of 9 mg/kg in 0.85% saline. Alternate group of animals received in addition daily injections of calcium (1 ml of 1.3% calcium chloride).
SEM comparison between dentin surfaces etched with acid agents and dentin surfaces irradiated with laser
Authors: Silberman Jaime , Vargas Marcos , Denehy Gerald
Published: June 2020

Preliminary research has indicated that laser etching may create a roughened dentin surface similar to that produced by enamel acid etching. Localized melting and recrystallization produce fungiform projections on dentinal surfaces. Consequently, this surface may present potential for bonding composite resin restorations. The purpose of this investigation was to compare using SEM and dentin topography that results from both acid etching and laser treatment, and also make comparisons between the effectiveness of various laser exposure parameters. In addition, a shear bond strength pilot study was done to corroborate the SEM results.

Forty-two molars were collected and randomly divided into six groups. Dentin surfaces were prepared by horizontal section through the middle third of the teeth crown and finished with 600-grit paper. Five of the groups were laser treated with LX-20 CO2 surgical laser. The dentin treatments of each group were as follows: Group #1: Dentin etched with 10% Maleic Acid, Group #2: Dentin irradiated with CO2 laser at 2W mode 5, Group #3: Dentin etched with 10% Maleic acid and 3W mode 5 and then etched with 10% Maleic acid, Group #5: Dentin irradiated at 3W mode 7, Group #6: Dentin irradiated at 3W mode 9.
Microanalysis of silicate glass films grown on α-Al2O3 by pulsed-laser deposition
Authors: Mallamaci Michael P. , Bentley James , Barry Carter C.
Published: June 2020

Glass-oxide interfaces play important roles in developing the properties of liquid-phase sintered ceramics and glass-ceramic materials. Deposition of glasses in thin-film form on oxide substrates is a potential way to determine the properties of such interfaces directly. Pulsed-laser deposition (PLD) has been successful in growing stoichiometric thin films of multicomponent oxides. Since traditional glasses are multicomponent oxides, there is the potential for PLD to provide a unique method for growing amorphous coatings on ceramics with precise control of the glass composition. Deposition of an anorthite-based (CaAl2Si2O8) glass on single-crystal α-Al2O3 was chosen as a model system to explore the feasibility of PLD for growing glass layers, since anorthite-based glass films are commonly found in the grain boundaries and triple junctions of liquid-phase sintered α-Al2O3 ceramics.

Single-crystal (0001) α-Al2O3 substrates in pre-thinned form were used for film depositions. Prethinned substrates were prepared by polishing the side intended for deposition, then dimpling and polishing the opposite side, and finally ion-milling to perforation.
A vacuum modification for the philips CM30 electron microscope
Authors: Evans N. D. , Bentley J. , Fisher A T.
Published: June 2020

For the Philips CM30 (or earlier EM430), the large surface area in the gun, the relatively poor pumping speed at the base of the gun, and the use of the same 100 l/s ion getter pump (IGP) for the column and gun, all lead to a significant degradation of gun vacuum (and slow recovery) following the gas burst involved in specimen exchange, even with extended pumping in the airlock. Since the vacuum quality in the gun is important for LaB6 filament life and high voltage stability, we adopted a conservative approach to the maximum pressure Pc allowed for the application of high voltage or filament emission; we chose an IGP reading of 22 (5 × 10−5 Pa). Delays of ~15 min typically occurred following specimen insertion. To avoid these problems the vacuum system has been modified. The goals were threefold: (1) To increase the pumping speed at the gun. The conductance of the original 600-mm-long vacuum line with three 90° elbows and a valve (V5) results in a pumping speed of < 10 l/s at the base of the emission chamber and a routine pressure of 3 × 10−5 Pa (1.5 × 10−7 torr).
Ultrastructural localization of fibronectin in process of serial intimal regeneration
Authors: Ishiwata Toshiyuki , Yokoyama Munehiro , Asano Goro
Published: June 2020

Intimal injury is considered as one of the initiation factors of atherosclerosis and intimal thickening. However the morphological elucidation after intimal injury is not so clear. On the other hand, fibronectin is a glycoprotein that play an important role in cell adhesion, migration, spreading, and differentiation. This study was designed to examine the mechanism of serial intimal regeneration after intimal injury and the localization of fibronectin using scanning and transmission electron microscope.

Male Wistar rats, weighing 400g were used and endothelial denudation was produced by the modified methods of Baumgartner. A deflated vascular balloon catheter( 1.5F, DOW CORNING , Corp.) was introduced into the thoracic aorta, then inflated up to 2.5mm in diameter, and passed through the aorta three times to a length of 2.5cm. The animals were sacrificed at 15min, 3,7,14 and 28 days after denudation. For electron microscopic examination, the tissues were fixed in 2.5% glutaraldehyde in 0.1M phosphate buffer, treated with 1% osmium tetroxide in phosphate buffer, and dehydrated in a graded ethanol series.
Application of electron tomography to elucidate the 3D architecture of diverse asymmetric biological specimens
Authors: McEwen Bruce F.
Published: June 2020

Electron tomography refers to the use of tomographic reconstruction methods to obtain three-dimensional (3D) information from transmission electron microscopy (TEM). This is accomplished by tilting the sample over a wide angular range with 180° being ideal, but 120° to 140° more typical due to limitations imposed by the geometry of most TEM specimens. If symmetry is present in the sample then the full angular range is not required. Furthermore, if the specimen is present as identical units, either in crystalline arrays or as single particles, the different tilts can be collected from different specimens and hence spare the total electron dose on any given particle. However, many important biological specimens are large, asymmetric objects which, due to their size, are not found as identical individual units. For such cases, the only recourse is to collect all the views from a single copy of the object, generally using a single axis tilt geometry.
Tailoring microstructures of materials through biomimetics
Authors: Sarikaya Mehmet , Aksay Ilhan A.
Published: June 2020

Biomimetics involves investigation of structure, function, and methods of synthesis of biological composite materials. The goal is to apply this information to the design and synthesis of materials for engineering applications.

Properties of engineering materials are structure sensitive through the whole spectrum of dimensions from nanometer to macro scale. The goal in designing and processing of technological materials, therefore, is to control microstructural evolution at each of these dimensions so as to achieve predictable physical and chemical properties. Control at each successive level of dimension, however, is a major challenge as is the retention of integrity between successive levels. Engineering materials are rarely fabricated to achieve more than a few of the desired properties and the synthesis techniques usually involve high temperature or low pressure conditions that are energy inefficient and environmentally damaging.

In contrast to human-made materials, organisms synthesize composites whose intricate structures are more controlled at each scale and hierarchical order.
Microstructural characterization using x-ray diffraction imaging
Authors: Black David R.
Published: June 2020

X-ray diffraction imaging, also known as x-ray topography, is a powerful tool to study the defect microstructure of single crystals. As the name implies, this technique is based on recording an image of the diffracted x-ray beam from a crystal. Contrast in the image results from point-to-point variation in the diffracted intensity through the crystal. An example of a diffraction image is shown in figure 1. That this image is in some way a topographic representation of the sample can be seen in the impression of differing elevations and textures in different parts of the image. However, since this image is a result of diffraction from the sample the interpretation of the image is much more complex.

Diffraction contrast is usually separated into two types: mosaic contrast and extinction contrast. Mosaic contrast occurs for crystals considered to be formed from a collection of small perfect crystal blocks. These blocks have a well defined rocking curve width, the angular range over which they will diffract, and may be slightly misoriented with respect to each other and/or may have different lattice spacing.
Scanned probe microscopy in biology
Authors: Fisher Knute A.
Published: June 2020

Numerous scanned probe microscopes (SPM) have been developed over the past decade. Most are based on the precise positioning of sample and probe using piezoelectric transducers, and some have the capability of imaging flat surfaces with atomic resolution. The first atomic resolution SPM applied to biological samples was the scanning tunneling microscope (STM). The atomic force microscope (AFM) was subsequently developed and over the past few years has become the instrument of choice for biological applications.

Early investigators applied the STM to examinations of organic and biological systems ranging from small molecules to nucleic acids, globular and fibrillar proteins, and larger structures such as viruses, membranes, and even whole cells. Much of this work was done during the mid-80s using electricallyconductive highly-oriented pyrolytic graphite (HOPG) as a substrate. Images were often difficult to obtain and control experiments were lacking. Unfortunately, when careful experiments were undertaken, they revealed that HOPG itself was capable of generating images previously thought to be biological.
Distortion in lattice-resolution scanned-probe microscope images
Authors: Fei L.
Published: June 2020

Scanned probe microscopes (SPM) have been widely used for studying the structure of a variety material surfaces and thin films. Interpretation of SPM images, however, remains a debatable subject at best. Unlike electron microscopes (EMs) where diffraction patterns and images regularly provide data on lattice spacings and angles within 1-2% and ∽1° accuracy, our experience indicates that lattice distances and angles in raw SPM images can be off by as much as 10% and ∽6°, respectively. Because SPM images can be affected by processes like the coupling between fast and slow scan direction, hysteresis of piezoelectric scanner, thermal drift, anisotropic tip and sample interaction, etc., the causes for such a large discrepancy maybe complex even though manufacturers suggest that the correction can be done through only instrument calibration.

We show here that scanning repulsive force microscope (SFM or AFM) images of freshly cleaved mica, a substrate material used for thin film studies as well as for SFM instrument calibration, are distorted compared with the lattice structure expected for mica.
Image simulation in scanning electron microscopy
Authors: Radzimski Z. J.
Published: June 2020

The development of image acquisition and processing software has made microscopy, including scanning electron microscopy (SEM), a very precise tool. Various processing techniques for image quality enhancement and image quantification have been introduced. However, the theoretical bases for SEM analysis are not always fully understood. Using Monte-Carlo (MC) methods several important issues have been successfully addressed, for example, X-ray production and backscattered electron (BSE) simulation. MC methods provide insight into the physical basis of electron beam/solid interactions and offer a wide degree of freedom in setting the simulation conditions regarding sample geometry, the electron beam, and signal collection. The results can be extracted at any stage of electron-target interactions to determine energy, angular and/or spatial distributions. MC programs with a single scattering approach, Mott scattering cross section and corrected Bethe's formula for energy loss can be used for both low and high energy electrons. The simulation can be performed for complicated structures with multi-element phases of various shapes.
High-resolution SEM and STEM of adrenocortical endothelium: Molecular resolution of membrane complexes
Authors: Apkarian Robert P.
Published: June 2020

A multitude of complex ultrastructural features are involved in endothelial cell (EC) gating and sorting of lipid through capillaries and into steroidogenic cells of the adrenal cortex. Correlative microscopy is necessary to distinguish the structural identity of features involved in specific cellular pathways. In addition to diaphragmed fenestrae that frequently appear in clusters, other 60-80 nm openings; plasmalemma vesicles (PV), channels and pockets fitted with diaphragms of the same dimension, coexist on the thin EC surface. Non-diaphragmed coated pits (CP) (100-120 nm) involved in receptor mediated endocytosis were also present on the EC membrane. The present study employed HRSEM of cryofractured and chromium coated specimens and low voltage HRSTEM of 80 nm thick LX-112 embedded sections stained with 2.0% uranyl acetate. Both preparations were imaged at 25 kV with a Topcon DS-130 FESEM equipped with in-lens stage and STEM detector.

HRSEM images of the capillary lumen coated with a lnm continuous fine grain Cr film, provided the ability to scan many openings and resolve (SE-I contrast) the fine structure of diaphragm spokes and central densities (Fig. 1).
Instrumental developments for electron microscopes: A STEM detector and correctors for a LVSEM and a 200 kV TEM
Authors: Haider Max
Published: June 2020

One advantage of scanning transmission electron microscopy (STEM) over conventional TEM which is often cited is the capability to simultaneously record the various scattered electrons with properly designed detectors. So far, this advantage has only been utilized to record bright-field or inelastic and dark-field (low and high angle) images in parallel. However, it has not been used to record all transmitted electrons separately according to their scattering angle. We developed a flexible multichannel detector system based on a silicon chip which has been fabricated to our specifications. This detector consists of 30 rings which are split into 4 quadrants (see Fig. 1), and is operated in an electron counting mode. The rings can be used to separate the electrons according to their scattering angle for low and high angle dark-field images, to obtain the various phase-contrast images and to normalize the signals by the sum of all detectors. The system records the signals of the 120 channels in parallel and the counts of each channel can be combined in an integer processing unit in order to form 8 different images.
Brightness measurements of nanometer-sized field-emission tips
Authors: Scheinfein M.R. , Qian W. , Spence J.C.H.
Published: June 2020

It has recently been suggested that the brightness of electron field-emitters of atomic dimensions may greatly exceed that of conventional field-emission sources. We have therefore measured the brightness of tungsten nanotip field emitters. Brightness is defined as the current density per unit solid angle at a point for limitingly small angles and areas. The axial brightness, B =∂2I/∂W∂A, when divided by the relativistically corrected acceleration potential V*, the reduced brightness, b=B/V*, is invariant at all points along the axis of a symmetric electron-optical system. For a given emission mechanism, the brightness at a point on a flat source is, by definition, independent of source size. Recently, there have been suggestions that new mechanisms come into play for cold field-emission sources of atomic dimensions, leading perhaps to higher brightness. These include reported departures from Fowler-Nordheim behaviour, and quantum-mechanical focussing effects. The attainment of the theoretical brightness limit is often prevented by space charge effects.
A linear-field scanning-force microscope: Application to x-ray gabor holography
Authors: Lindaas Steve , Jacobsen Chris , Howells Malcolm
Published: June 2020

We have built a linear field Scanning Force Microscope to readout x-ray Gabor holograms recorded in photoresist. A field linearity yielding one half or less pixel registration error (for 10-50nm pixel sizes) across the scanned hologram is needed so that the resulting reconstruction is not significantly degraded. The desire for a large (75μm)2and linear scanning field necessitated designing our own stage since these conditions could not be met commercially.

Gabor holography is well positioned to exploit flash x-ray sources, such as x-ray lasers and free electron lasers, as well as ultra-bright third generation synchrotron sources as a sub-50nm resolution imaging technique for biological samples. Gabor holography requires no optics (except for a monochromator with λ/Δλ ∽ 500) and no sample prefocusing since the image is focused in the reconstruction process. Furthermore, sample alignment is eased since the area of illumination can be quite large. In fact, Gabor holography can be used to image large fields with multimode sources with the resulting numerical aperture, and hence resolution, being limited by the size of a single mode.
Coherent soft x-ray single unit-cell diffraction
Authors: Chapman Henry N. , Balhorn Rod
Published: June 2020

Following the basic ideas of x-ray structure analysis of single unit-cell specimens by Sayre it should be possible to determine the structure of weakly-scattering non-crystalline material from the radiation scattered from it, at a maximum resolution equal to half the wavelength of the radiation. Therefore, in principle, it should be possible to determine structures to 1 nm resolution by soft x-ray diffraction at 2 nm wavelength. An imaging method based solely on diffraction should be an extremely powerful x-ray microscopy tool.

In order to determine the structure of the diffracting object however, the incident beam must be completely temporally and spatially coherent and the complex wave-field must be sampled across some surface at spatial frequency intervals of 1/(2 * Δ), where Δ is the resolution. Thus, a three-dimensional data set (a two-dimensional complex field) must be recorded to obtain the three-dimensional structure of the scatterer. In most cases, an area detector is used to determine the intensity of the wave-field, losing the phase information.
Chemical contrast in scanning transmission x-ray microscope
Authors: Zhang X. , Ade H. , Jacobsen C. , Kirz J. , Lindaas S. , Oehler V. , Williams S. , Wirick S.
Published: June 2020

The Scanning Transmission X-ray Microscope (STXM) on the X1A undulator beamline, at the National Synchrotron Light Source, BNL, has been used for imaging various wet, unstained biological samples at 55 nm Rayleigh resolution. The microscope's Modulation Transfer Function was measured and agrees well with theoretical calculations, confirming the performance of the microscope as designed. The microscope is operated mainly in direct imaging mode where x-rays of fixed energy are diffractively focused to a microprobe and the sample is scanned in two dimensions. By varying the x-ray energy while keeping the beam focused to one spot on the sample enables us to get localized chemical composition of the sample from the absorption spectra in an area smaller than 0.2 by 0.2 micron at present. The spatial distribution of the chemical compositions can be obtained with a spacial resolution of 55 nm by imaging at absorption maxima of specific chemical bonds.

The chemical sensitivity of the X-ray Absorption Near Edge Structure (XANES) provides a new contrast mechanism for organic system imaging.
Structure and properties of organic liquid crystals
Authors: Voigt-Martin I.G.
Published: June 2020

Organic liquid crystals (LCs), both in the monomeric and polymeric state, are capable of self organisation because of the anisotropic shape of their molecules. By suitable molecular engineering it is thus possible to induce interesting physical properties like ferroelectricity, second harmonic generation (SHG) and photoconductivity. For a deeper understanding it is necessary to gain insight into the relationship between molecular characteristics (electronic charge distribution, dipole moments, hyperpolarisabilities, molecular conformation), structural relations (symmetry relations, space groups, defects) and the above physical properties

For structure analysis electron diffraction patterns from different crystallographic zones with many higher orders of diffraction are required. Unfortunately a characteristic feature of LCs is their loss of all higher order reflections and a change in symmetry. Furthermore, LCs give rise to specific defects, which give important information about the elastic energy density of the system. These can only be characterised by a phase contrast imaging method in which the small angle spatial frequencies are transferred by the electron microscope phase transfer function.
On the experimental determination of low-order structure factors in TiAl by energy-filtered convergent-beam electron diffraction
Authors: Swaminathan S. , Jones I. P. , Zaluzec N. J. , Maher D. M. , Fraser H. L.
Published: June 2020

It has been claimed that the effective Peierls stresses and mobilities of certain dislocations in TiAl are influenced by the anisotropy of bonding charge densities. This claim is based on the angular variation of electron charge density calculated by theory. It is important to verify the results of these calculations experimentally, and the present paper describes a series of such experiments. A description of the bonding charge density distribution in materials can be obtained by utilizing the charge deformation density (Δρ (r)) defined by(1)

where V is the volume of the unit cell, Fobs is the experimentally determined low order structure factor and Fcalc is the structure factor calculated using the Hartree-Fock neutral atom model. To determine the experimental low order structure factors, a technique involving a combination of convergent beam electron diffraction (CBED) and electron energy loss spectroscopy (EELS) has been used.
Are HOLZ lines kinematic in off-zone-axis orientation?
Authors: Zuo J. M. , Weickenmeier A. L. , Holmestad R. , Spence J. C. H.
Published: June 2020

The application of high order reflections in a weak diffraction condition off the zone axis center, including those in high order laue zones (HOLZ), holds great promise for structure determination using convergent beam electron diffraction (CBED). It is believed that in this case the intensities of high order reflections are kinematic or two-beam like. Hence, the measured intensity can be related to the structure factor amplitude. Then the standard procedure of structure determination in crystallography may be used for solving unknown structures. The dynamic effect on HOLZ line position and intensity in a strongly diffracting zone axis is well known. In a weak diffraction condition, the HOLZ line position may be approximated by the kinematic position, however, it is not clear whether this is also true for HOLZ intensities. The HOLZ lines, as they appear in CBED patterns, do show strong intensity variations along the line especially near the crossing of two lines, rather than constant intensity along the Bragg condition as predicted by kinematic or two beam theory.
Application of energy-filtered imaging to the characterization of heterogeneous catalysts
Authors: Crozier P.A. , McCartney M. R.
Published: June 2020

Heterogeneous metal catalysts often consist of one or more metal species distributed over a highly porous oxide support. In many cases, there is not a clear understanding of the relationship between the microstructure of such systems and their catalytic properties. Indeed, the systems often possess complex morphologies with domains containing many different phases. To build up a clear picture of the microstructure of these materials it is essential to have an accurate representation of the distribution of elements over reasonably large areas of the sample. Here we employed a Zeiss EM 912 fitted with an omega filter to determine elemental distributions over large areas in amination catalysts.

The microscope, which operates at 120 kV, is interfaced to a Gatan slow-scan CCD camera (10242pixels) which can be used to acquire images, diffraction patterns and energy-loss spectra from regions of the sample. At present our machine is fitted with a W filament as an electron source which gives high beam current but limits the usable energy resolution to about 2 eV.
Growth behavior and structures of carbon nanotubes
Authors: Liu Mingqi , Cowley John M.
Published: June 2020

Recent discovery of the novel hollow graphitic tubules of nanometer dimensions, so called carbon nanotubes, has greatly stimulated the studies in the field of carbon fiber growth. Their potential applications in electronic and materials industries have been suggested. In the present study, carbon nanotubes were fabricated by an arc-discharge method. The microstructures of nanotubes thus obtained were examined with a JEM-2000FX high-resolution transmission electron microscopy (HRTEM) and with an electron nanodiffraction technique in a VG HB-5 scanning transmission electron microscopy (STEM).

HRTEM images show that nanotubes, consisting of 3 to 30 carbon sheets, have a length up to 1 μm and a diameter of 6 to 26 nm. Some nanotubes have a symmetric uniform sheet spacing of 0.34 nm. Others show non-symmetric uneven fringes (Fig. 1), indicating that they may have a polyhedral cross section. Most nanotubes are closed by cone-like or polyhedral shaped caps (Figs. 2 and 3). The closure angle varies from 17 to 40° and the internal sheets have a tendency to be closed in pairs. Fig. 4 shows the image of a growing tubes.
The bright future of digital imaging in scanning electron microscopy
Authors: Postek M. T. , Vladar A. E.
Published: June 2020

One of the major advancements applied to scanning electron microscopy (SEM) during the past 10 years has been the development and application of digital imaging technology. Advancements in technology, notably the availability of less expensive, high-density memory chips and the development of high speed analog-to-digital converters, mass storage and high performance central processing units have fostered this revolution. Today, most modern SEM instruments have digital electronics as a standard feature. These instruments, generally have 8 bit or 256 gray levels with, at least, 512 × 512 pixel density operating at TV rate. In addition, current slow-scan commercial frame-grabber cards, directly applicable to the SEM, can have upwards of 12-14 bit lateral resolution permitting image acquisition at 4096 × 4096 resolution or greater. The two major categories of SEM systems to which digital technology have been applied are:

In the analog SEM system the scan generator is normally operated in an analog manner and the image is displayed in an analog or "slow scan" mode.
Imaging peristome movement in the environmental SEM
Authors: Long J.C. , Mueller D.M.J.
Published: June 2020

The ElectroScan Environmental Scanning Electron Microscope is a powerful new tool in the study of spore dispersal mechanisms in bryophytes. The ESEM is similar in many ways to a conventional SEM, but with a few important differences. While the ESEM column remains at high vacuum (10−7torr), the specimen chamber typically operates in a water vapor environment at low vacuum (1 to 20 torr). The secondary electron signal is generated by gaseous signal amplification and is collected by the Environmental Secondary Detector.

This new technology has significant implications regarding sample preparation and specimen requirements. First, there is no need to dry the sample, thus observations in the natural state are possible. Second, the water vapor dissipates charge build up, therefore a conductive coating is not necessary.

The ESEM lends itself directly to the understanding of spore dispersal in mosses, which involves the sensitivity of the peristome to changes in ambient moisture (hygroscopicity).
Z-contrast imaging of an ordered interface structure in the Si/CoSi2/Si system
Authors: Chisholm M. F. , Jesson D. E. , Pennycook S. J. , Mantl S.
Published: June 2020

We show the atomic structure of buried CoSi2/Si(001) boundaries involves a 2×1 ordering of the interfacial Co atoms. The ability to directly image and interpret this unforeseen structure is possible through the Z-contrast technique, and presents a new level of insight into the important and controversial relationship between the atomic structure and electronic properties, such as the energy barrier for electron transport across metal-semiconductor interfaces.

The buried CoSi2 layer was produced by implanting Co+ ions (200 keV, 2 × 1017 ions/cm2) in a Si(001) substrate heated to 350°C. The substrate was capped with 200 nm of SiO2 and then given a two-step anneal in high purity argon (750°C for 30 s + 1150°C for 10 s). This treatment results in a continuous buried CoSi2 layer ~70 nm thick, ~90 nm below the substrate surface. The layer and the substrate are oriented such that the cubic CaF2 unit cell of CoSi2 is aligned parallel to the cubic unit cell of Si.
Ultramicrotomy for study of interfaces and coatings
Authors: Williams G. , Malis T.
Published: June 2020

While grain and phase boundaries in conventional alloys are examined quite readily by classic TEM specimen preparation methods such as electropolishing and ion thinning, the plethora of metal, ceramic and/or polymer combinations in many advanced materials have proven to be a much stiffer challenge. Whether in the form of composites, coatings, multilayers or thin films, such material systems have given rise to newer methods such as low angle ion thinning, mechanical (tripod) polishing to electron transparency and diamond knife sectioning. The damage incurred during the latter method may be offset by the advantages of a controlled thickness which is fairly insensitive to the type of material.

Fig. 1 demonstrates that the high degree of deformation generated in ductile materials by no means prohibits conventional grain boundary imaging due to the substantial degree of dislocation self-recovery which generally occurs in thin sections. Alloy phase boundaries also are amenable to examination after sectioning, although the particle/matrix interface may debond somewhat as the hardness difference increases.
Recent developments in low-voltage SEM of polymers
Authors: Krause S.J. , Adams W.W.
Published: June 2020

Over the past decade low voltage scanning electron microscopy (LVSEM) of polymers has evolved from an interesting curiosity to a powerful analytical technique. This development has been driven by improved instrumentation and in particular, reliable field emission gun (FEG) SEMs. The usefulness of LVSEM has also grown because of an improved theoretical and experimental understanding of sample-beam interactions and by advances in sample preparation and operating techniques. This paper will review progress in polymer LVSEM and present recent results and developments in the field.

In the early 1980s a new generation of SEMs produced beam currents that were sufficient to allow imaging at low voltages from 5keV to 0.5 keV. Thus, for the first time, it became possible to routinely image uncoated polymers at voltages below their negative charging threshold, the "second crossover", E2 (Fig. 1). LVSEM also improved contrast and reduced beam damage in sputter metal coated polymers. Unfortunately, resolution was limited to a few tenths of a micron due to the low brightness and chromatic aberration of thermal electron emission sources.
Electron tomography of microstructural elements in strongly segregated block copolymers
Authors: Spontak Richard J. , Smith Steven D. , Agard David A.
Published: June 2020

Block copolymers are composed of long contiguous sequences (blocks) of chemically dissimilar monomer species. By themselves or in microphase-separated blends, these materials readily undergo self-organization into either disordered micelles or ordered morphologies, much in the same way as do small-molecule amphiphiles. In the strong-segregation regime, wherein only repulsive monomer interactions and periodic morphologies prevail, a copolymer can assemble into spherical or cylindrical dispersions of one block in a continuous matrix of the other or alternating lamellae. Recent efforts have also shown that an ordered bicontinuous double-diamond morphology (OBDD) exists between the cylindrical and lamellar morphologies. Ongoing studies continue to reveal the existence of other non-classical morphologies, such as the lamellar catenoid, in both pure copolymers and in blends. Attempts to elucidate the 3-D structure of these materials have relied upon computer simulation of idealized periodic surfaces and comparison between “slices” of simulated structures with projections from transmission electron microscopy (TEM).
Dynamic low-dose electron diffraction and imaging of phase transitions in polymers
Authors: Martin David C. , Liao Jun
Published: June 2020

By careful control of the electron beam it is possible to simultaneously induce and observe the phase transformation from monomer to polymer in certain solid-state polymcrizable diacetylenes. The continuous change in the crystal structure from DCHD diacetylene monomer (a=1.76 nm, b=1.36 nm, c=0.455 nm, γ=94 degrees, P2l/c) to polymer (a=1.74 nm, b=1.29 nm, c=0.49 nm, γ=108 degrees, P2l/c) occurs at a characteristic dose (10−4C/cm2) which is five orders of magnitude smaller than the critical end point dose (20 C/cm2). Previously we discussed the progress of this phase transition primarily as observed down the [001] zone (the chain axis direction). Here we report on the associated changes of the dark field (DF) images and selected area electron diffraction (SAED) patterns of the crystals as observed from the side (i.e., in the [hk0] zones).

High resolution electron micrographs (HREM), DF images, and SAED patterns were obtained on a JEOL 4000 EX HREM operating at 400 kV.
Microscopy of ceramics: Through the looking glass and out the other side
Authors: Hobbs Linn W.
Published: June 2020

Because this exposition will be followed by nine distinguished symposium contributions detailing better than could any single individual the modern approaches to microscopical analysis of surfaces and interior microstructures of ceramic solids, I have thought it the wiser course to adopt an historical approach and identify those significant points of departure where substantial leaps were made in our understanding of ceramic materials through the application of microscopical techniques. Developments in two techniques are outlined here.

The light microscope was developed in the Netherlands by Hans Jensen and his son Zacharias between 1590 and 1610. This was a compound microscope, consisting of two lenses, but it was the single lens microscope, extensively exploited by Anthony van Leeuwenhoek and Robert Hooke in the 17th century, that provided the first significant microscopical advances, notably in biology. In 1733 an English barrister, Chester More Hall, discovered that a compound lens comprising glass elements of different dispersion could correct the chromatic aberration which limited the resolution of the compound microscope, although the principle was not applied to microscopy until 1791; and not until 1830 that another barrister, Joseph Lister, set forth the principles underlying correction of spherical aberration.