bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect studies in strained-layer quantum well heterostructures
Authors: Brown J.M. , Mochel M.E. , Holonyak N. , Camras M.D. , Ludowise M.J. , Dietze W.T. , Lewis C.R.
Published: June 2020

The epitaxial growth of mismatched or strained III-V layers was shown to be viable as early as 1960. Osbourn et al suggested that strained layer GaP-GaAs1-xPx superlattices grown by organo-metal1ic vapor phase epitaxy (OMVPE) could be used to fold the Brillouin zone and make indirect-crystal direct. More recently, it has been shown that a strained-layer superlattice can be grown free enough of defects at heterointerfaces to make possible stimulated emission. This has been demonstrated on OMVPE GaAs1-xPx-GaAs (x=0.25) and GaAs-InxGa1-xAs (x=0.2) strained layer superlattices which have been operatedas photopuraped continuous (cw) 300K lasers but which at high excitation levels (> 103Acm-2) prove to be unstable. This paper presents the results of an electron microscope study of the defects produced in a GaAs-InxGa1-xAs strained superlattice as a result of high excitation levels of operation.
Electron diffraction study of hydrogenated amorphous SiC
Authors: Sabatini R. L. , Kampas F. J. , Vanier P. E. , Taftø J.
Published: June 2020

Hydrogenated amorphous SiC (a-SiC:H) is a promising new solar cell material. In constrast to structural studies of amorphous Si and amorphous C, studies of amorphous SiC are rare. The main features of the diffraction patterns of amorphous Silicon and amorphous Carbon are two diffuse halos which for Si correspond to interatomic distances of about 2.35 Å and 3.85 Å and for C to 1.50 Å and 2.50 Å. These distances are close to the nearest interatomic distances present in the crystalline form of the same elements.

Using 120 KeV electrons, we observe two pronounced halos also for a-SiC:H, similar to what is observed for pure Si and pure C. Figure 1 shows diffraction patterns from a-SiC:H and for comparison from Si and C.
Some applications of electron beam microanalysis techniques in VLSI process evaluation
Authors: Thomas Simon
Published: June 2020

Trends in the technology development of very large scale integrated circuits (VLSI) have been in the direction of higher density of components with smaller dimensions. The scaling down of device dimensions has been not only laterally but also in depth. Such efforts in miniaturization bring with them new developments in materials and processing. Successful implementation of these efforts is, to a large extent, dependent on the proper understanding of the material properties, process technologies and reliability issues, through adequate analytical studies. The analytical instrumentation technology has, fortunately, kept pace with the basic requirements of devices with lateral dimensions in the micron/ submicron range and depths of the order of nonometers. Often, newer analytical techniques have emerged or the more conventional techniques have been adapted to meet the more stringent requirements. As such, a variety of analytical techniques are available today to aid an analyst in the efforts of VLSI process evaluation. Generally such analytical efforts are divided into the characterization of materials, evaluation of processing steps and the analysis of failures.
The growth of mica polytypes as studied by conventional and high-resolution TEM
Authors: Baronnet A. , Amouric M.
Published: June 2020

The origin of mica polytypes has long been a challenging problem for crystal- lographers, mineralogists and petrologists. From the petrological point of view, interest in this field arose from the potential use of layer stacking data to furnish further informations about equilibrium and/or kinetic conditions prevailing during the crystallization of the widespread mica-bearing rocks. From the compilation of previous experimental works dealing with the occurrence domains of the various mica "polymorphs" (1Mr, 1M, 2M1, 2M2 and 3T) within water-pressure vs temperature fields, it became clear that most of these modifications should be considered as metastable for a fixed mica species. Furthermore, the natural occurrence of long-period (or complex) polytypes could not be accounted for by phase considerations. This highlighted the need of a more detailed kinetic approach of the problem and, in particular, of the role growth mechanisms of basal faces could play in this crystallographic phenomenon.
A SEM/TEM/STEM investigation of the nature of ferrite/pearlite aggregates in hot-rolled low-alloy steels
Authors: Thompson S.W. , Burket M.-G. , Petrucci A.M. , Claus C. , Howell P.R.
Published: June 2020

As part of a broader investigation concerning the reaustenitization characteristics of a series of hot-rolled, low alloy steels, the structure of the hotrolled material has been examined using SEM, TEM and STEM. The results presented in this paper relate to an Fe - 1.5%Mn, - 0.3%Si - 0.15%C alloy. Specimens for examination by SEM were prepared using standard metallographic techniques, etched in 2% nital and examined in an ISI Super IIIA operating at 25kV. Specimens for examination by TEM and STEM were prepared in a twin-jet electropolisher using an electrolyte consisting of 5% perchloric acid and 95% glacial acetic acid at 273K and at a potential of 35V. TEM imaging was performed using either a Philips EM300 or a JEOL 200CX operating at 100kV and 200kV respectively and STEM imaging using a JEOL 100CX operating at 100kV.
Comparison of damage microstructures in neutron-irradiated vanadium and iron
Authors: Horton L. L. , Farrell K.
Published: June 2020

It is known that bcc ferritic materials are more resistant to radiation- induced cavitational swelling than are other bcc materials. Furthermore, a recent study of neutron-irradiated iron reported several unusual features of the radiation-induced microstructures. One of these was the observation that the cavity morphology, a truncated octahedron with {111} faces and {100} truncations, was the shape commonly observed in fee materials. The morphologies commonly observed in bcc materials include truncated dodecahedrons with {110} faces and {100} truncations and cubes with {100} faces. Another interesting feature was that virtually all of the dislocation loops observed were near-edge, interstitial loops with = a<100>. While loops of this type are commonly found in irradiated iron and ferritic steels, interstitial loops found in many other bcc materials are oriented near-edge with = a/2. In the present study the cavity morphology and dislocation loop geometry in bcc vanadium are compared with the previously reported observations for neutron-irradiated iron.
Mismatch and misorientation at the precipitate/matrix interface in an Al-Zralloy
Authors: Porter Angus , Makin Louise , Ralph Brian
Published: June 2020

Much of the hardening of high strength aluminium alloys containing zirconium results from the precipitation of the metastable γ' (Al3Zr) phase (Ll2 structure, cube/cube related to the matrix). There exists some controversy in the literature as to the magnitude of the matrix (γ)-γ' misfit in Al-Zr alloys; the values reported range from 1% down to rather less than half this figure. In the present paper, the use of moire fringe imaging to study mismatch and misorientation between the γ and γ' lattice in a binary Al-Zr alloy will be considered. The advantages of this technique for the study of small second-phase particles are three-fold. The information obtained is specific to a single particle; the exact nature of the particle/matrix interface is unimportant, as long as the two lattices exhibit nearly coincident diffraction maxima; and mismatch and misorientation of particular sets of lattice planes can be determined from a single image.
AEM analysis of crystallization in Ti-based amorphous alloys
Authors: Pelton A.R. , Marshall A.F. , Lee Y.S.
Published: June 2020

Amorphous materials are of current interest due to their desirable mechanical, electrical and magnetic properties. Furthermore, crystallizing amorphous alloys provides an avenue for discerning sequential and competitive phases thus allowing access to otherwise inaccessible crystalline structures. Previous studies have shown the benefits of using AEM to determine crystal structures and compositions of partially crystallized alloys. The present paper will discuss the AEM characterization of crystallized Cu-Ti and Ni-Ti amorphous films.

Cu60Ti40: The amorphous alloy Cu60Ti40, when continuously heated, forms a simple intermediate, macrocrystalline phase which then transforms to the ordered, equilibrium Cu3Ti2phase. However, contrary to what one would expect from kinetic considerations, isothermal annealing below the isochronal crystallization temperature results in direct nucleation and growth of Cu3Ti2from the amorphous matrix.
Localization of immunolabels by electron microscopy and image averaging
Authors: Frank J. , Sizaret P.-Y. , Verschoor A. , Lamy J.
Published: June 2020

The accuracy with which the attachment site of immunolabels bound to macromolecules may be localized in electron microscopic images can be considerably improved by using single particle averaging. The example studied in this work showed that the accuracy may be better than the resolution limit imposed by negative staining (∽2nm).

The structure used for this demonstration was a halfmolecule of Limulus polyphemus (LP) hemocyanin, consisting of 24 subunits grouped into four hexamers. The top view of this structure was previously studied by image averaging and correspondence analysis. It was found to vary according to the flip or flop position of the molecule, and to the stain imbalance between diagonally opposed hexamers (“rocking effect”). These findings have recently been incorporated into a model of the full 8 × 6 molecule.

LP hemocyanin contains eight different polypeptides, and antibodies specific for one, LP II, were used. Uranyl acetate was used as stain. A total of 58 molecule images (29 unlabelled, 29 labelled with antl-LPII Fab) showing the top view were digitized in the microdensitometer with a sampling distance of 50μ corresponding to 6.25nm.
Specimen heating stage with in-situ evaporator in UHV-STEM for the observation and characterization of monolayered superstructures
Authors: Ohtsuki M. , Schuler J.J. , Crewe A.V. , Ichinokawa T.
Published: June 2020

In-situ evaporating experiments on solid surfaces become meaningful only when the evaporation takes place after the surface of the object is fully cleaned in ultra high vacuum (UHV). A specimen heating stage is usually used for the cleaning process.

For the observation of single heavy atom superstructures at atomic resolution in UHV, we have constructed a new specimen heating stage equipped with an insitu evaporator. The device is built into the specimen ante-chamber of the high-resolution UHV-STEM as shown in Figures 1 and 2. The vacuum of the chamber has been tested at 4 × 10-10 torr. with two 20 ℓ/ sec ion pumps attached close to the chamber. The vacuum of the STEM column is better than 1 × 10-10 torr. The heating stage is built into the specimen holder so that direct heating of the specimen is possible. In the detail shown in Figure 2, a thin specimen is mounted between two supporting grids which are then fastened together by two semi-circular tantalum clips. These clips are also used as contacts which carry the current to heat the specimen directly.
Design of objective lens for 200-kV high-resolution electron microscopes
Authors: Tsuno K. , Honda T. , Harada Y. , Naruse M.
Published: June 2020

Developement of computer technology provides much improvements on electron microscopy, such as simulation of images, reconstruction of images and automatic controll of microscopes (auto-focussing and auto-correction of astigmatism) and design of electron microscope lenses by using a finite element method (FEM). In this investigation, procedures for simulating the optical properties of objective lenses of HREM and the characteristics of the new lens for HREM at 200 kV are described.

The process for designing the objective lens is divided into three stages. Stage 1 is the process for estimating the optical properties of the lens. Firstly, calculation by FEM is made for simulating the axial magnetic field distributions Bzc of the lens. Secondly, electron ray trajectory is numerically calculated by using Bzc. And lastly, using Bzc and ray trajectory, spherical and chromatic aberration coefficients Cs and Cc are numerically calculated. Above calculations are repeated by changing the shape of lens until! to find an optimum aberration coefficients.
Surface structures of platinum crystal films grown epitaxially on silver
Authors: Hines R. L.
Published: June 2020

Ultrathin platinum crystals a few atom layers thick are expected to have a number of properties that might make them useful as test objects to characterize the structure of platinum surfaces of interest in catalysis. Previous experiments on surface structures of platinum crystal films have indicated a rough surface when platinum crystal films were prepared at growth rates of 0.1 nm/minute in an oil pumped vacuum system at a nominal pressure of 2 micro- Torr. For the experiments reported here the platinum crystal.s are grown at growth rates of 0.1 nm/minute in a vacuum of 0.05 microTorr in an ion pumped system. The ultrathin platinum crystals are grown by first depositing approximately 200 nm of silver on the surface of a freshly cleaved piece of mica held at 270 °C in a vacuum of 0.05 microTorr. Then the platinum is evaporated onto the clean silver surface with the silver substrate at a set temperature between 50 °C and 270 °C. Then a carbon layer approximately 10 nm thick is deposited on the platinum by carbon arc evaporation.
Radiation effects on minerals in the electron microscope
Authors: Veblen David R. , Buseck Peter R.
Published: June 2020

Radiation damage is commonly the most important limiting factor in transmission electron microscopic studies of minerals. This is especially true for high-resolution TEM (HRTEM) investigations, which typically utilize a relatively large electron dose. Conversely, because of this requirement, HRTEM studies provide a good opportunity for observing the effects of radiation in the electron microscope on different minerals. In this contribution, we attempt to impose some chemical and structural order on observations of beam damage in minerals, mostly silicates, based on HRTEM investigations of a wide range of specimens over the past decade.

Because reports of radiation damage rates in the TEM are typically anecdotal, with no fixed point of reference, we here limit our comparisons of rates to first-hand observations. These observations were made primarily at lOOkV in a JEOL JEM100B microscope, although some of the same systematics also have been noted in other instruments at voltages up to 200kV. In addition, experiments of others where part of a crystal structure damages selectively are discussed.
Electron-beam spreading in thin foils at 40keV
Authors: Stephenson T.A. , Loretto M.H. , Jones I.P. , Augustus P.
Published: June 2020

Experiments have been performed to determine the effects of thickness, and crystallinity on beam spreading in thin foils. The experimental technique consists of measuring an incident and exit electron probe size as shown in Fig. 1. Beam spreading is defined as the difference between these two quantities. Results were compared with Monte Carlo calculations.

Beam spreading experiments in single crystal silicon oriented positive of a 440 reflection have shown that the experimental measurements are adequately described by Monte Carlo calculations using Doyle and Turner elastic scattering cross-sections (Fig.2). The addition of an inelastic component via the Bethe continuous loss approximation produces an insignificant change. Adjustment for the generation and scattering of fast secondary electrons is reserved for future work.

Two experiments were performed to elucidate the effects of crystallinity. The first involved single crystal silicon in which exit grobe size measurgments were performed with diffracting conditions s=+0.0027Å-1 and s=-0.0034Å-1 from 220 (Table 1). Since beam spreading is dependent on high angle scattering, these results are qualitatively consistent with the orientation dependence of high angle diffuse scattering.
Energy loss spectra from silicon compounds: SiL edges
Authors: Carpenter R. W. , Skiff W. M. , Lin S. H.
Published: June 2020

Electron energy loss microanalysis is of great interest for analysis of second phases containing light elements in semiconductor materials. Small precipitates (minimum dimension ∼10nm) in heat treated CZ-Si wafers were identified in-situ earlier as amorphous SiOx particles, and it was also noted that there was a marked change in the shape of the Si-L edge in spectra from the precipitate relative to those from the surrounding matrix.

This work has been extended to include spectra from other Si compounds, to examine the shape change of the L edge when silicon is in different environments. All of the spectra shown here were taken at l00kV with fixed, convergent probe. The incident probe size on the specimens was ∼10nm. Many of the spectra was taken using a cryogenic stage with the specimen near -196°C, which made possible extended observations of a single area. All specimens were wedge shaped (crushed or ion-thinned), with spectra taken from thin edges.
A time-shared image-processing system for electron microscopy
Authors: Krakow William , Baron R.A.
Published: June 2020

A time shared television digital image processing system has been developed for on-line electron microscopy and uses a large mainframe computer (IBM 3033). The system consists of a TV frame store (Grinnell GMR275 full color processor) capable of storing five-512x512x8 bit deep monochrome pictures and four-5 12x512x1 bit graphic overlays. The frame store has many standard features such as: an an 8 bit video digitizer, zoom and pan controls, graphic cursors, image analyzers, arithmetic and boolean processors, alpha numeric generators, lookup tables and so on. A high speed interface has been developed to connect between the host computer and the frame store and can bidirectionally transmit data at 1 Mbit/sec rates over coaxial cable (see Fig. 1). The processor can be controlled from any terminal within the research center. At present a digital switch box has been constructed which will allow up to ten video inputs to be individually assessed from microscopes at remote sites. Also, up to ten full color video ouputs (RGB) from the processor are switchable under computer control.
Is full computer automation of H.R.E.M. feasible?
Authors: Krivanek O.L. , Stadelmann P. , Higgs A. , Chen C. , Disko M.M.
Published: June 2020

Recently it has become clear that a high resolution electron microscope (H.R.E.M.) can be controlled by a computer which "sees" the image via a TV camera connected to a digital framestore, and which "adjusts" the microscope imaging parameters via a D/A (Digital/Analog) control interface so as to optimize the image. The question therefore arises whether it will some day be possible to replace human microscope operators with inexpensive minicomputers capable of performing all the traditionally human tasks, but with much greater precision, repeatability, and speed.

Fig. 1 shows a schematic of the computer control system for a JEM 200CX HREM under development at ASU. The TV camera is coupled via a 2:1 reducing fibre- optics bundle to a P22 phosphor screen as described previously. The DeAnza framestore has enough memory for up to four 512x512x8 bit images, and can perform various simple operations such as adding or subtracting two images at TV rates (on-line).
Microprocessor control of a field-emission scanning electron microscope (Model S-800)
Authors: Saito S. , Nakaizumi Y. , Nagatani T. , Todokoro H.
Published: June 2020

We have developed an ultra high resolution scanning electron mícroscope utílízíng a fíeld emíssíon electron source (Fig.1). This instrument has a guaranteed resolution of 2 nm in the secondary electron image mode and it has incorporated a microprocessor control for optimized operating conditions and maximum ease of operation by various automated functions. The microprocessor control system includes field emission electron gun control, electron optical system control, and video signal control. The field emission electron gun control system includes flashing operation which is used to clean the tip surface by heating for a very short time, high voltage operation of accelerating voltage (V0) and tip voltage (V1), correction of emission current which changes with time, and correction of virtual source position which changes with a voltage ratio V0/V1. We have automated these series of operations by developing an auto FE gun control system. Fig. 2 shows details of this system.
Microtubules, sickle cell hemoglobin fibers, and various crystal structures
Authors: Edelstein Stuart J. , Crepeau Richard H. , Akey Christopher W. , Ceska Thomas A.
Published: June 2020

Structural studies involving electron microscopy and image reconstruction techniques are now approaching levels of resolution that had previously been the domain of x-ray crystallography. Studies on purple membrane are a prime example. Although few other systems have reached comparable levels of resolution, progress is being made on several fronts. Citing work from this laboratory, I will illustrate three ways we are using electron microscopy to approach the border with x-ray crystallography, in studies on: three-dimensional crystals (cytochrome oxidase from P. aeruginosa, catalase, and beef heart F1-ATPase); arrays of proteins which do not form three-dimensional crystals (tubulin sheets and microtubules); and the supra-molecular structure of a protein of known atomic structure (sickle cell hemoglobin).

A. Electron microscopy as an adjunct to X-ray crystallography for threedimensional crystals

Our applications in this area have primarily consisted of embedding and sectioning techniques with crystals that are too small or otherwise unsuitable for x-ray crystallography, such as occur for cytochrome oxidase from P. aeruginosa or beef heart F1-ATPase.
Electron microscopy of frozen hydrated suspensions
Authors: Lepault Jean
Published: June 2020

High resolution electron microscopy of biological objects requires minimizing of both preparation artefacts and beam damage. Taylor and Glaeser have shown that these two requirements can be fulfilled by observing frozen hydrated specimens. Routine use of frozen hydrated specimens has been limited by two factors: the lack of preparation methods and the technical difficulty in building high resolution low temperature stages compatible with cold transfer. This last limitation has been removed by the development of new gas cooled specimens holders, by the improvement of existing holders, and by creation of a super conducting lens system where the specimen is kept at 4.2 k. Finally, recent methods of preparing thin films of water (500 - 3000 Å) have allowed routine observation of frozen suspensions. Parameters influencing structural preservation during both preparation and observation can thus be analyzed.

HYDRATION AND VITRIFICATION: Maintenance of hydration of biological objects in the electron microscope high vacuum permits preservation of structural details to better than 3Å.
Differential staining of crystalline arrays of outer mitochondrial membrane channels
Authors: Mannella Carmen A. , Frank Joachim
Published: June 2020

The mitochondrial outer membrane contains pore-forming polypeptides (Mr⋍= 30,000) which are its main protein components in plants and fungi. Outer membranes (OM) isolated from Neurospora mitochondria often contain extended regular arrays of subunits with stain-accumulating centers 2-3 nm in diameter. That these subunits are the mitochondrial channels has been established immunologically. Antibodies against the predominant 31-kDa OM polypeptide of Neurospora (a) prevent in vitro insertion of OM channels into bilayers and (b) preferentially bind to the crystalline membranes in OM fractions.

Planar projections of individual OM channel layers have been reconstructed from electron micrographs of negatively stained crystalline vesicles by Fourier filtration. In the usual array (Fig. 1a) the unit cell is a parallelogram which can hold six stain centers (putative pore openings) arranged in a hexagon with p2 symmetry. There are large pore-free areas in these arrays (* in Fig. 1a) which are likely composed of phospholipid, since they disappear when the membranes are treated with phospholipase A2(Fig. 1b).
Toward an alignment of the actin molecule within the actin filament
Authors: Smith P.R. , Fowler W.E. , Aebi U.
Published: June 2020

An understanding of the specific interactions of actin with regulatory proteins has been limited by the lack of information about the structure of the actin filament. Molecular actin has been studied in actin-DNase I complexes by single crystal X-ray analysis, to a resolution of about 0.6nm, and in the electron microscope where two dimensional actin sheets have been reconstructed to a maximum resolution of 1.5nm. While these studies have shown something of the structure of individual actin molecules, essential information about the orientation of actin in the filament is still unavailable.

The work of Egelman & DeRosier has, however, suggested a method which could be used to provide an initial quantitative estimate of the orientation of actin within the filament. This method involves the quantitative comparison of computed diffraction data from single actin filaments with diffraction data derived from synthetic filaments constructed using the molecular model of actin as a building block. Their preliminary work was conducted using a model consisting of two juxtaposed spheres of equal size.
Membrane-bound vesicles associated with the microvilli in the midgut of the freshwater microcrustacean, Daphnia magna
Authors: Jansma Patricia L.
Published: June 2020

The presence of the membrane bound vesicles or blebs on the intestinal epithelial cells has been demonstrated in a variety of vertebrates such as chicks, piglets, hamsters, and humans. The only invertebrates shown to have these microvillar blebs are two species of f1ies. While investigating the digestive processes of the freshwater microcrustacean, Daphnia magna, the presence of these microvillar blebs was noticed.

Daphnia magna fed in a suspension of axenically grown green alga, Chlamydomonas reinhardii for one hour were narcotized with CO2 saturated water. The intestinal tracts were excised in 2% glutaraldehyde in 0.2 M cacodyl ate buffer and then placed in fresh 2% glutaraldehyde for one hour. After rinsing in 0.1 M cacodylate buffer, the sample was postfixed in 2% OsO4, dehydrated with a graded ethanol series, infiltrated and embedded with Epon-Araldite. Thin sections were stained with uranyl acetate and Reynolds lead citrate before viewing with the Philips EM 200.
Low-voltage scanning electron microscopy
Authors: Pawley J. B. , Winters M. P.
Published: June 2020

There are two reasons for the renewed interest in using the SEM at beam voltages, Vb, around 1kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage. The second reason postulates that the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in topographic spatial resolution if only a sufficiently small probe diameter can be obtained. We shall treat these two areas separately and then mention some of the strategies that have been adopted to make LVSEM work.

Surfaces are very important in the manufacture of modern semiconductor devices and the ability of the electron probe to induce current flow (EBIC), to detect variations in surface voltage, Vs, and to excite characteristic x rays in addition to its ability to image topography in an easily understandable way guaranteed the SEM a major role in programs of semiconductor development and failure analysis. There were two problems, however, charging and beam-induced damage to the specimen.
Low-temperature scanning electron microscopy
Authors: Echlin Patrick
Published: June 2020

More than thirteen years have passed since the first micrographs were taken of specimens maintained in a frozen state on the cold stage of a scanning electron microscope (SEM).O) The pictures which were taken showed little we did not already know about the particular cells and tissues but it did demonstrate that this was potentially a powerful technique for examining and analysing hydrated material in as near a natural state as possible. Cryofixation is, for all intents and purposes, a physical process, and as such can avoid the use of wet-chemical preparative methods. Low temperatures immobilize the liquid state, arrest physiological processes, and diminish the movement of dissolved substances. Where specimens are examined and analysed at low temperatures inside the microscope the presence of large areas of cold surfaces results in a significant reduction in contamination and in the damage to the specimen. It is therefore appropriate to examine the progress that has been made in the intervening years and for convenience this will be discussed under three separate headings: 1) Instrumentation, 2) Morphological studies, and 3) Analytical studies.
Qualitative and quantitative SEM of gastrointestinal tract
Authors: Carr K.E. , Hayes T.L. , Hume S.P. , Kamel H.M.H.
Published: June 2020

Introduction:

The natural mucosal surfaces of the digestive tract provide an interface with the environment which undergoes structural changes in response to experimental procedures and naturally occurring disease. This paper describes the application of modern scanning electron microscopy (SEM) techniques to gastrointestinal research. Initially based on qualitative studies of mucosal responses to insult such as irradiation or hyperthermia, the interpretation of recent results has come to rely increasingly on the semi-quantitative assessment of surface damage and on the use of frozen hydrated specimens to eliminate processing artefact and to permit quantitative elemental analysis.

Materials and Methods:

Tissue has been collected from several sources. Irradiated mouse intestine has been compared with similar tissue exposed to hyperthermia or drug treatment. Biopsies of gastrointestinal tissue have been collected prospectively or retrospectively, the latter by dewaxing blocks of interest from hospital files. Routine scanning electron microscopy has often been followed by post-embedding the specimen for resin light microscopy and transmission electron microscopy (TEM). Alternatively, resin sections 1 μm thick mounted on coverslip fragments were surface etched by oxygen plasma, shadowed with platinum/palladium and gold coated prior to examination in the SEM. Etched surfaces of mouse duodenum and stomach have also been examined in the frozen hydrated state to record cell and tissue structure as well as data on ion concentrations through x-ray microanalysis.

Results and Discussion:

Qualitative studies of mucosal responses using secondary electron imaging, in use since the 1960s, are enhanced by the ability of the SEM to record extensive surface areas, if necessary through montage techniques. in this way, the problems of individual variation in an experimental series can be minimised. Mucosal responses to irradiation in small bowel have been documented. The collapse of the villous pattern from erect finger-like processes to irregular conical projections follows a time scale of several days after a single dose of irradiation, whereas equivalent structural changes are completed within 24 hours of an episode of heat injury. Correlative light microscopy and TEM studies show that the changes in shape of the villi after irradiation may be linked to alterations at the interface between surface epithelium and underlying connective tissue: focal irregularities of the basal lamina and detachment of epithelial cells may represent the earliest manifestation of subsequent damage to surface contours.
Photoemissive markers for cell surface labeling in photoelectron microscopy
Authors: Griffith O. Hayes , Bruce Birrell G.
Published: June 2020

Developing markers or labels to correlate the observed structure with biological function is important in any microscopic technique. Photoelectron microscopy (photoemission electron microscopy or PEM) has developed to the point where good images of cell surfaces, cell organelles and viruses have been obtained. Therefore it is now appropriate to begin a study of markers that can be used to locate specific sites on cell surfaces in the photoelectron images. The experimental approach is illustrated in Fig. 1. The specimen is placed on the substrate, evacuated, and subjected to ultraviolet light. Unlike TEM or SEM there is no electron gun; the specimen itself is the source of electrons. The ultraviolet light induces some photoionization of electrons from all cell surface components but generally with a low quantum yield. Ideally, the marker (M in Fig. 1) has a very much higher electron quantum yield resulting in bright objects easily seen against the background of the cell surface. The ideal PEM marker would be 1) very photoemissive, 2) small in size, 3) stable and 4) readily coupled to a sitespecific ligand by covalent bonding or high affinity adsorption. Among the possibilities being considered as PEM markers are fluorescent dyes, derivatives of porphyrins and phthalocyanines, viruses, metal colloids, peroxidase/diaminobenzidine reaction deposits and cesium.
The stapedius muscle of the squirrel monkey
Authors: Fermin C.D. , Igarashi M. , Thompson G.
Published: June 2020

Contraction of the stapedius muscle (the acoustic reflex) is useful in the clinical diagnosis of various auditory disorders. In an effort to better understand the basic innervation of the acoustic reflex we are presently studying its neuroanatomy in the squirrel monkey (Saimiri sciureus). Since the morphology of the squirrel monkey stapedius muscle (SMSM) has not been previously described, we will present here our own findings from eleven muscles observed under light (LM) and transmission electron microscopy (TEM). Squirrel monkeys were perfused intracardially with either 10% neutral buffered formalin or 3% buffered glutaraldehyde. The stapedius muscles were dissected out under the operating microscope. For LM, the muscles were embedded in JB-4 plastic and cut serially at 5 micra and for TEM, the muscles were processed as previously described (2).

The topography of the SMSM in the middle ear is similar to the human (3). The muscle attaches to the posterior side of the stapes' head by a thin collagenous tendon that extends almost midway into the muscle in a postero- ventral direction.
Filamentous arrays reminiscent of tropomyosin crystals in Hirano bodies of Alzheimer's disease
Authors: Metuzals J. , Montpetit V. , Clapin D.F. , Nelson R.F.
Published: June 2020

Distinctive acidophilic rods, Hirano bodies, have been observed in brains of patients under a variety of pathological conditions, including Alzheimer's disease, and also in normal, aged individuals. Data on the three-dimensional conformation and on the chemical composition of these structures are presently controversial. The presence of actin in Hirano bodies has been indicated immunocy tochemically. Other authors have proposed that Hirano bodies are crystalline arrays of ribosomes attached to membranes. We report here the results of an investigation of Hirano bodies in the brains of Alzheimer's patients. Applying the techniques of three-dimensional electron microscopy, we have demonstrated as a major component of the Hirano bodies, characteristic arrays of filamentous proteins reminiscent of tropomyosin crystals produced in vitro.

Frontal lobe biopsies from 3 patients with pre-senile dementia diagnosed as Alzheimer's disease were investigated by three-dimensional electron microscopy. Fig. 1 is a survey of a Hirano body occupying the main portion of a neurite. It is comprised of sheets of filaments forming characteristic network patterns.
Probing the ultrastructure of the mitotic and meiotic spindle in eggs: An expeditious approach based on semi-thin (0.25 μm) serial sections
Authors: Rieder Conly L. , Bowser S. , Nowogrodzki R. , Ross K. , Sluder G.
Published: June 2020

Eggs have long been a favorite material for studying the mechanism of karyokinesis in-vivo and in-vitro. They can be obtained in great numbers and, when fertilized, divide synchronously over many cell cycles. However, they are not considered to be a practical system for ultrastructural studies on the mitotic apparatus (MA) for several reasons, the most obvious of which is that sectioning them is a formidable task: over 1000 ultra-thin sections need to be cut from a single 80-100 μm diameter egg and of these sections only a small percentage will contain the area or structure of interest. Thus it is difficult and time consuming to obtain reliable ultrastructural data concerning the MA of eggs; and when it is obtained it is necessarily based on a small sample size.

We have recently developed a procedure which will facilitate many studies concerned with the ultrastructure of the MA in eggs. It is based on the availability of biological HVEM's and on the observation that 0.25 μm thick serial sections can be screened at high resolution for content (after mounting on slot grids and staining with uranyl and lead) by phase contrast light microscopy (LM; Figs 1-2).
Dark field EM of the RNA of the small subunit of the E. coli ribosome
Authors: Korn A. P. , Elson D. , Spitnik-Elson P. , Ottensmeyer F. P.
Published: June 2020

We have embarked on a series of EM experiments using the dark field mode in an attempt to ascertain how much of a role the ribonucleic acid (RNA) component of the ribosome has in determining the structure of the protein-nucleic acid complex. We have observed that treatment of specimens of the smaller subunit enhances the visibility of band-like structures on the "back" of the subunit. In total, though not necessarily all appearing at once on a single individual, three parallel bands of 20 Å diameter are seen (Fig. 2). We have speculated that these are double stranded sections of the RNA that emerge on the surface. This does not preclude external single stranded sections that are not as prominent, however. The identification of the bands with double stranded external RNA is still subject to further testing. In a very recent experiment we have examined a heated RNAase digestion product that has been shown to lack a section of its RNA.
Supporting freeze-etch specimens with “Lexan” while dissolving biological remains in acids
Authors: Steere Russell L. , Erbe Eric F.
Published: June 2020

In studies of cold hardiness in plants it became important to have freezeetch specimens of woody poplar stems (populus sp.) and to fracture them at −75°C. The most satisfactory approach involved the use of two pairs of precooled pliars to break off small, 1 to 2 mm thick, pieces of the frozen stems. Glycerol (40%) was frozen at −75°C onto the upper grooved surface of a modified specimen cap. A small pool of the glycerol was melted with a metal probe and a fractured piece of specimen was placed on the pool which refroze very rapidly with no glycerol contacting the upper fracture surface. The specimen cap was transferred to the cold stage of a Denton Freeze-etch module. Excess frost was removed by holding specimen temperature at −100°C for the 10 min required to obtain a vacuum of 2 × 10−7 Torr and to cool the shroud to −196°C. The specimens were then held at −90°C for an additional 10 min for further etching.
Quantitative electron microscopic study of the hepatic endoplasmic reticulum in Reye’s syndrome
Authors: Sturgess J. M. , de la Iglesia F. A.
Published: June 2020

Reye’s syndrome represents a serious clinical condition in children with symptoms of liver involvement, acute encephalopathy and biochemical alterations. This condition, for which the etiology is not yet known, has been linked to mycotoxin poisoning, viral infection, or simulated by drug toxicity, particularly salicylates. However, basic cellular mechanisms and early ultrastructural changes have not been well defined. The liver endoplasmic reticulum (ER) plays a fundamental role in detoxification. Our understanding of ER changes in this syndrome would clarify the processes leading to liver damage.

Quantitative electron microscopic aspects of hepatocytes were evaluated to characterize numerically the tissue changes in liver biopsies from patients with Reye's syndrome and compared with data available from age-matched controls. Liver biopsies were evaluated from three patients, 1.5, 6.5 and 13.5 years of age, having clinical and pathological evidence of Reye's syndrome. All biopsies were obtained within 24 hours of clinical onset. Preservation of architecture of hepatocytes was adequate for critical evaluation of ultrastructure.
Effects of O3 on submucosal gland of bonnet monkey trachea
Authors: Yamashiro S. , Wilson D. , St. George J. , Hyde D. , Plopper C. , Dungworth D.
Published: June 2020

In the past, ozone inhalation studies have focused on the lower airways and lung parenchyma. The purpose of this study was to evaluate the effects of ozone on submucosal glands of upper airways. Six adult male bonnet monkeys were exposed to 0.64 ppm ozone continuously for 7 days, and three were exposed to chamber conditions without ozone. The animals were exsanguinated under barbiturate anesthesia. The trachea and lung were fixed by airway infusion of Karnovsky's fixative, which was adjusted to pH 7.4 and 440 milliOsmols. Sagittal sections of ventral trachea were embedded in glycol methacrylate and Araldite 502 for light and electron microscopy. One micrometer methacrylate sections were stained with Alcian blue-periodic acid Schiff (AB/PAS). Selected areas of Araldite-embedded tissue were sectioned for transmission electron microscopy, stained with uranyl acetate and lead citrate and examined with a Zeiss EM 10. Volume percentages of the lumen, granular and nongranular regions of fhe gland and the duct wall, respectively, were estimated by stereologic methods on AB/PAS stained sections.
Cytochemical localization of nitrate reductase in Chlorella
Authors: Michaels A. , Wolosowick J. , Kriho V. , Solomonson L.
Published: June 2020

We have investigated the subcellular location of nitrate reductase in Chlorella. Chlorella is a unicellular green algae. The algae can be readily cultured under defined conditions. When cultures of Chlorella are grown in media containing ammonia, as a nitrogen source, there is a very low activity of nitrate reductase. If cultures are are grown in the absence of ammonia, but with nitrate substituted as a nitrogen source, the activity of the enzyme increases about ten-fold. This increase is dependent on protein synthesis and is inhibited by cycloheximide.

Nitrate reductase was purified to homogeneity and injected into rabbits. Antinitrate reductase IGg was prepared and used to localize the enzyme in the light microscope with FITC conjugated goat anti-rabbit IGg and electron microscope with goat anti-rabbit IGg coupled to colloidal gold.

Samples of ammonia and nitrate grown cultures were fixed in gluteral- dehyde and embedded in polyethylene glycol. Thick and thin sections were cut for light and electron microscope localization according to Wolosowick and May.
Atomic orientation effects in proton stopping at low velocity
Authors: Lam Kin
Published: June 2020

The energy of moving ions in solid is dependent on the electronic density as well as the atomic structural properties of the target material. These factors contribute to the observable effects in polycrystalline material using the scanning ion microscope. Here we outline a method to investigate the dependence of low velocity proton stopping on interatomic distances and orientations.

The interaction of charged particles with atoms in the frame work of the Fermi gas model was proposed by Lindhard. For a system of atoms, the electronic Lindhard stopping power can be generalized to the form

where the stopping power function is defined as
Ultrastructural morphometric analysis of lymphocyte nuclear structure
Authors: Dardick I. , Bladon T. , Sinnott N. , Dardick A. , Hall R. , Jeans D. , Setterfield G.
Published: June 2020

Despite the important -role of nuclear morphology in tissue recognition and tumor diagnosis, the variation of this organelle in terms of size, shape and condensed chromatin organization, and the mechanisms involved, are poorly understood. Since antigenic and mitogenic activation of the normal lymphocyte leads to considerable alteration in the nucleus in terms of size and condensed chromatin distribution, this cell type affords an opportunity to study this phenomenon in detail. Previous studies have shown that a sizeable amount of nuclear protein is made during lymphocyte transformation.

This ultrastructural morphometric image analysis was undertaken in an attempt to quantitate modifications in nuclear components during T-lymphocyte (human peripheral) and B-lymphocyte (mouse spleen) transformation induced with concanavalin A (Con A) and bacterial lipopolysaccharide (LPS) respectively. Cell suspensions and tissue samples were obtained at varying intervals after mitogen stimulation. Random nuclei, both unstimulated (Type 1), partially transformed (Type 2), and fully transformed (Type 3) were photographed (Figs 1 to 3).
Structural analysis of the photosynthetic membrane from Ectothiorhodospira halochloris
Authors: Engelhardt H. , Guckenberger R. , Baumeister W.
Published: June 2020

Bacterial photosynthetic membranes contain, apart from lipids and electron transport components, reaction centre (RC) and light harvesting (LH) polypeptides as the main components. The RC-LH complexes in Rhodopseudomonas viridis membranes are known since quite seme time to form a hexagonal lattice structure in vivo; hence this membrane attracted the particular attention of electron microscopists. Contrary to previous claims in the literature we found, however, that 2-D periodically organized photosynthetic membranes are not a unique feature of Rhodopseudomonas viridis. At least five bacterial species, all bacteriophyll b - containing, possess membranes with the RC-LH complexes regularly arrayed. All these membranes appear to have a similar lattice structure and fine-morphology. The lattice spacings of the Ectothiorhodospira haloohloris, Ectothiorhodospira abdelmalekii and Rhodopseudomonas viridis membranes are close to 13 nm, those of Thiocapsa pfennigii and Rhodopseudomonas sulfoviridis are slightly smaller (∼12.5 nm).
Epitaxial crystallization of lipids containing alkane chains
Authors: Dorset Douglas L.
Published: June 2020

As shown in an accompanying paper, the quantitative use of electron diffration data from slightly bent, thin microcrystals for structure analysis is impeded when a long unit cell axis is parallel to the incident beam. A total crystallographic analysis is allowed, on the other hand, if a shorter cell edge parallels this direction so that the largest Patterson components along this vector are not severely spread out by slight crystal bending.

Because of favored van der Waals interactions, typical solution crystal growth of molecular organic compounds causes the longest unit cell axis to lie approximately perpendicular to the best developed crystal face. A crystal growth forcing the longest unit cell axis to lie in this direction, on the other hand, can be realized by epitaxy, the earliest demonstration for polymethylene chain materials given by Willems. Although the use of cleaved salt crystal faces has long been popular for nucleation of epitaxial growth, organic substrates, such as naphthalene, present certain advantages.