Analytical electron microscopy studies of radiation damage

Analytical electron microscopy (AEM) has provided structural, crystallographic, and compositional characterization to aid in the understanding of radiation damage processes, especially in multiphase materials. The range of AEM techniques is based on the use of as many of the signals produced by the interaction of an electron beam with a specimen as possible. This paper briefly discusses the origins, capabilities, and current developments of AEM, including the spatial resolution of the various techniques. Several important applications of AEM in radiation damage studies, including radiation-induced segregation and phase instability in austenitic stainless steels, will be reviewed. From the comparison of phase equilibria under irradiation to that under thermal aging, principles for alloy development in non-nuclear applications will be discussed. This paper is based on a presentation made in the symposium “Irradiation-Enhanced Materials Science and Engineering” presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD.     

Structural organization of the intact bacterial cellulosome as revealed by electron microscopy

The architecture of the intact cellulosome of Clostridium thermocellum, a huge extracellular multi-polypetide bacterial enzyme complex engaged in degradation of cellulose, was investigated by electron microscopy. This was done because former electron microscopic studies aimed at elucidation of the structure of polycellulosomes and cellulosomes were restricted by the fact that data on macromolecular details could only be derived from deformed or disrupted enzyme complexes, or by application of cryo preparation and imaging techniques yielding insufficient resolution. The shape of well-preserved cellulosomes was more or less spherical, often similar to that of an olive fruit with a cavity. Therein, multiple fibrillar structures could be visualized, interpreted to be the proximal stretches of copies of the fibrillar protein Cip A ('scaffoldin'), the nonenzymatic scaffolding protein known to function as attachment site for the enzymatic subunits, as well as fibrillar parts of anchoring proteins. The enzymatic subunits were depicted to be attached, in a repetitive fashion, to the distal stretches of the Cip A proteins. The enzymatic subunits were seen, in the intact cellulosome, to form a shell-like complex substructure surrounding the cavity. Obviously, this kind of architecture makes sure that the catalytic domains of the enzymatic subunits are exposed to the environment, and, hence, to the substrate, the cellulose fibrils. Attempts were made to demonstrate the alternating occurrence of coiled domains and fibrillar stretches along the elongated protein Cip A previously characterized by sequencing, X-ray, and NMR studies. To this end, Cip A molecules, with adhering enzymatic subunits, were partially removed from their native location within the cellulosome, "stretched" by hydromechanical forces directly on the electron microscopic support film, negatively stained, and depicted by electron microscopy. The alternating occurrence of presumed coiled domains and fibrillar stretches along Cip A could be visualized, together with detached enzymatic subunits found on the support film.     

Recent studies of thin films and surfaces by high-Resolution electron microscopy

The technique of high-resolution electron microscopy represents a powerful method for characterizing the microstructure of thin films and surfaces. We demonstrate its usefulness by reference to some recent studies of metals, semiconductors, and oxides, in particular, showing that it can be used to follow physical and chemical changes inducedin situ by the electron beam orex situ as a result of annealing or chemical treatment. This invited critical overview paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Transmission electron microscopy studies of the ordering of nitrogen in tantalum

Tantalum containing 4at.% nitrogen was aged at 673 K. and 873 K respectively, for different aging times. The specimens were investigated by means of transmission electron microscopy (TEM). On the selected area diffraction pattern superlattice reflections could be observed. After aging at 673 K, a high density of ordered precipitates could be observed, the mean diameter is ~ 2 nm. After aging at 873 K, the density of the ordered precipitates decreased, while the mean diameter increased lying between 50 and 250 nm depending on the aging time. It could be shown that the ordered precipitates are distorted tetragonally. The tetragonal axis is parallel to a [100] direction. The axis ratio could be estimated to be c/a = 1.03 ± 0.02.     

Scanning electron microscopy studies of the human lens capsule after capsulorhexis

Choledochal cysts are malformations of the biliary ductal system, which rarely occur in infancy. In neonates and infants, choledochal cysts are congenital, may be associated with distal biliary atresia and typically presents with cholestatic jaundice and acholic stools characteristic of biliary obstruction. In older children and adults, it may be acquired in association with an anomalous pancreaticobiliary union and presents with any combination of intermittent jaundice, abdominal pain, and a palpable abdominal mass. Early detection of choledochal cysts is important in the prevention of the fatal complications of biliary obstruction. Here, we present two cases of congenital choledochal cyst in which the patients were 9 weeks old and 7 weeks old respectively. Both of them presented with jaundice, acholic stools, and hepatomegaly. Combined use of sonography, computed tomography and hepatobiliary scintigraphy demonstrated the presence of choledochal cysts. Thereafter, they underwent surgical excision of the cysts with Roux-en-Y reconstruction of the biliary tree; the results were successful.     

Studies of superplasticity by high voltage electron microscopy

Experiments and calculations are described that enable the validity of in situ high voltage electron microscopy studies of superplasticity to be estimated. It is shown that previous in situ studies of the Zn-Al eutectoid are open to question because the diffusivity in the aluminium-rich grains is calculated to be enhanced by a factor of 10⁵ by irradiation damage from the electron beam. Direct evidence of this damage has been observed in terms of irradiation induced dislocation loops, and enhanced precipitation and coarsening rates. The results from the in situ experiment were not typical of bulk material and their conflict with previous texture measurements performed on bulk material can be explained.     

Transmission electron microscopy studies of (111) twinned silver halide microcrystals

Minimal information is available on the autonomic response to exercise under adverse environmental conditions. Traditionally, pharmacological blockade has been used to study autonomic responsiveness but, owing to its invasive nature, such studies have been limited in their scope. Recent advances in electrocardiographic tape recording, telemetry and associated computing systems have provided investigators with noninvasive methods for assessing the autonomic response to various physiological stressors. This article describes methods for the analysis of heart rate variability (HRV) and discusses the reports of those who have used HRV analysis to evaluate autonomic regulation during exercise, heat exposure and the combination of these 2 stressors. Spectral analysis of HRV reduces variations in the R-R interval into component sine waves of differing amplitude and frequency. Amplitude (variance) is displayed as a function of frequency, and power (cumulative variance) is calculated for specified frequency ranges (< 0.03 Hz, 0.03 to 0.15 Hz and 0.15 to 0.5 Hz). Parasympathetic nervous system activity can be inferred from the several indices of high frequency power; however, the estimation of sympathetic nervous system activity from low frequency power is more problematic. Data on HRV have shown that sympathovagal regulation during exercise is dependent on the intensity of the activity and the environmental conditions. At the onset of exercise, heart rate is increased by a reduction in vagal tone and a temporary increase in sympathetic tone. A continuation of physical activity is associated with a continued withdrawal of vagal activity and an attenuation of sympathetic nervous system tone. However, with the additional stimulus of a heated environment, sympathetic activity remains increased throughout exercise.     

High resolution transmission electron microscopy studies of the Ag/MgO interface

Ag layers with a thickness of 100 nm were deposited on {100} MgO substrates by molecular beam epitaxy (MBE). The substrates were produced by cleaving MgO single crystals and subsequent annealing in ultra high vacuum. X-ray texture measurements indicate a preferential orientation of Ag {100} planes parallel to the {100} surface of the MgO substrate. The atomistic structure of the Ag/MgO interface was imaged by high resolution transmission electron microscopy (HRTEM). Lattice images of Ag and MgO in parallel orientation show structural defects and lattice strain at the Ag/MgO interface, which are introduced by the lattice mismatch of 3% between Ag and MgO. The atomic resolution images are compared with the computer-simulated lattice image of a model structure. Finally our atomistic model of the Ag/MgO interface, which includes a misfit dislocation network is discussed in connection with theoretically calculated interfacial energies.     

Molybdenum work function determined by electron emission microscopy

A polycrystalline molybdenum sample was recrystallized and thermally stabilized. Quantitative measurements of the emission from each individual grain were obtained with an electron emission microscope. The effective work function for each grain was then calculated. The crystallographic orientation of each grain was determined by Laue back-reflection techniques. A polar plot of effective work function vs crystallographic orientation for the sample was constructed to provide a correlation between effective work function and crystallographic orientation. DEAB L. JACOBSON, formerly Section Manager Electro-Optical Systems, Division of Xerox Corp., Pasadena, Calif.     

Three-dimensional model of membrane-bound ribosomes obtained by electron microscopy

A low-resolution three-dimensional man has been obtained from crystalline arrays of membrane-bound eukaryotic ribosomes. It shows both ribosomal subunits to be adjacent to the membrane surface, attached to it by a part protruding from the large subunit.     

The classification of short range order by electron microscopy

After discussion of the various modelling concepts, a broad classification of short range order (sro) is suggested, differentiating between uniform and bounded ‘micro-domains’ and unbounded ‘static concentration wave packets’. It is explained why this classification is physically useful, and how transmission electron microscopy (TEM) imaging provides a direct means of differentiating between these two models. The analogy between this model classification and the microcrystallite-amorphous problem in the classification of ‘glassy’ structures is discussed.Criticisms [1] of our earlier work [2] on electron diffraction information obtained for Ni₄Mo have been carefully analysed. We could find no reason to change our view of the nature of s.r.o. in this particular material. Our essential conclusion is that it is unrealistic to describe sro in quenched Ni₄Mo as of microdomain type.     

The role of ledges in vapor/solid phase transformations observed by low-energy electron microscopy and photoemission electron microscopy

Adsorption at monatomic ledges was observedin situ, in real time, during the epitaxial growth of Cu deposited from the vapor phase onto Mo{110}. Migration of monatomic ledges of Cu was followed during both growth and sublimation near equilibrium conditions and was independent of crystallographic direction in accord with fundamental theories of crystal growth. Evidence is presented showing that the two-dimensional (2-D) vapor pressure of Cu Actatoms on the terraces near curved ledges differs from that near straight ledges. Formerly with the Technical University of Clausthal.This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.     

Diagnostic electron microscopy of neoplasms

OBJECTIVE: We describe a patient with a prolonged and severe hypercapnia occurring during an episode of status asthmaticus induced by ophthalmic instillation of carteolol. SETTING: Prehospital Emergency Medical Service and Pulmonary Intensive Care Unit in a university hospital. PATIENT: A 35-year-old female developed an acute asthma attack while at home, which required advanced life support. INTERVENTION: On hospital admission, arterial blood gases revealed a PaCO2 of 208 mmHg. Hypercapnia persisted with a PaCO2 of more than 190 mmHg for 10 h, with pH always less than 7.00. The patient was finally discharged after 26 days without sequelae. CONCLUSION: This case illustrates the cerebral and cardiovascular tolerance of severe and prolonged hypercapnia associated with major acidosis.