High Voltage Electron Microscope Study Research Articles

Evolution of dislocation loops and effect of annealing temperature on hydrogen-ion-implanted Fe-based binary alloys

Reduced activation ferritic/martensitic (RAFM) steels have been considered as a family of prime candidate structural materials for fusion reactors due to low radioactivity and good resistance to irradiation swelling. Various types of defects such as dislocation loops can form in these materials during irradiation. Effects of alloying elements in iron on the formation and migration of dislocation loops have been widely investigated. However, most studies dealt with interstitial-type dislocation loops in iron alloys, while very few focused on vacancy-type dislocation loops. Previous high voltage electron microscope (HVEM) studies from the authors' group have shown that interstitial loops are fully eliminated in hydrogen-ion-implanted α-Fe at 500 ℃, only vacancy loops remain and can achieve up to 100 nm in size. The addition of Ni in α-Fe can reduce the formation temperature of vacancy-type dislocation loops (<i>T</i><sub>c</sub>) to ~450 ℃, while the addition of Cr can increase the temperature to above 600 ℃. However, these experiments are usually difficult to perform due to the scarce resource of HVEM facilities. In this work, in-situ observations by conventional transmission electron microscope (CTEM, 200 kV) are systematically carried out on the hydrogen-ion-implanted α-Fe and Fe-based binary alloys (Fe-3wt.%Cr, Fe-1.4wt.%Ni and Fe-1.4wt.%Mn). The evolutions of morphology and average size of dislocation loops under different annealing temperatures are investigated. The formation temperatures of vacancy-type dislocation loops are determined from the change of average loop size with annealing temperature. The results are consistent with previous studies by HVEM. The effect of Mn atoms in α-Fe is similar to that of Cr atoms, which leads to <i>T</i><sub>c</sub> increase, and the addition of Ni in α-Fe can reduce <i>T</i><sub>c</sub>. Furthermore, the results of D thermal desorption spectrum analysis show that <i>T</i><sub>c</sub> is affected by the binding and release process of hydrogen isotopes to vacancies in α-Fe. Alloying element Ni promotes the binding and release of hydrogen isotopes to vacancies, which leads to<i> T</i><sub>c</sub> decrease. Cr and Mn inhibit the binding and release of hydrogen isotopes to vacancies, causing <i> T</i><sub>c</sub> to increase.

Enhancement of molecular-level ordering of isoindigo based organic materials through deprotecting of cleavable carbamate groups with long alkyl chains

A new highly soluble isoindigo based organic material with both cleavable carbamate protecting groups bearing long alkyl chains and thiophene groups was successfully synthesized. The carbamate protecting groups were easily removed by solvent-vapor thermal annealing using a mixture of trifluoroacetic acid and chloroform. Deprotection of the NH functional groups in the isoindigo backbone in situ facilitated H-bonding that dramatically improved the strength of the intermolecular interactions. X-ray diffraction and high-voltage electron microscopy studies of the resulting organic material showed long-range ordered crystalline structure. High crystallinity due to enhanced π-π stacking and hydrogen bonding significantly improved the charge carrier mobility. The hole mobilities of isoindigo based organic material measured by SCLC method improved from 3.46 x 10−6 cm2 V−1 s−1 to 1.13 x 10-3 cm2 V−1 s−1 upon deprotection of the NH functional groups.

Immunohistochemical and Electron Microscopic Study of the Meridian-like System on the Surface of Internal Organs of Rats

Threadlike structures on the surfaces of mammalian internal organs were recently observed, and they can be the anatomical basis of the meridian-like network of internal organs as detected by the Bi-Digital O-Ring test imaging method. Morphological and histological studies were performed to reveal their novel features by using confocal and electron microscopy, and there is evidence that reveals that they have a ductal structure in which some liquid flows. They form a part of the network of acupuncture meridians that is thought to be a circulatory system distributed throughout an animal body. In order to confirm further the circulatory function it was necessary to provide evidences for the existence of endothelial cells at the inner boundaries of the microchannels that form the threadlike ducts. In this work we performed immunohistochemical studies for the identification of endothelial cells. In addition, we identified the extracellular matrices between the microchannels in the threadlike structure by using antifibronectin, elastin, laminin, and collagen type IV. Since immunohistochemical data are not sufficient for definite proof we supplemented the analysis with ultra structural information by using transmission electron microscopy (TEM). Yet TEM images show only ultrathin sections (50 nm) of a specimen, we needed to take 3-dimentional images to provide a visual demonstration of the microchannels in the threadlike ducts. We conducted high voltage electron microscopic studies for this purpose and obtained corroborating tomograms that exhibit the microchannels. In conclusion, the meridian-like tissues are ducts with microchannels, which implies the circulatory function of the acupuncture meridian network.

Microstructure of plastic zones around crack tips in silicon revealed by HVEM and AFM

Abstract In order to understand the dislocation process for the sharp brittle-to-ductile transition in silicon crystals, microstructures of plastic zones around crack tips have been investigated using high-voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into {1 1 0} silicon wafers at room temperature by Vickers indentation method. The temperature of specimens indented was raised to higher than 823 K to activate dislocation sources around a crack tip under the presence of residual stress due to the indentation. The crack observed was extending along the 〈1 1 0〉 direction from the edge of the indent. AFM study has revealed two types of fine slip bands around the crack tip: one type of slip bands is those parallel to 〈1 1 2〉, and another type is those parallel to the 〈1 1 0〉 direction. The former is corresponding to so-called hinge-type plastic zone, and the latter is 45° - shear-type. HVEM study has revealed the characteristics of dislocation structures corresponding to the both types of plastic zones. Detailed analyses of each dislocation, including the determination of the sign of Burgers vector, have been made to characterize those plastic zones.

Studies of cerebral endothelium by scanning and high-voltage electron microscopy.

This chapter reviews methods for the preparation of central nervous system (CNS) tissues for scanning (SEM) and high-voltage electron microscopic (HVEM) studies of the cerebral vasculature. The techniques described here have been used by the authors for the past two decades for investigations of pathologic alterations of the blood-brain barrier (BBB) after a variety of experimentally induced injuries in mammalian (, , , ) and non-mammalian species (, , ). The question of when to use one morphologic application over another becomes important for studies of cerebrovascular endothelial cells (ECs).

Three-Dimensional Analysis of Tranverse Tubules in Normal and Failing Heart: A Combined Confocal and High Voltage Electron Microscope Study

Early electron microscopic studies documented that significant changes in the membrane systems of cardiac cells occur in both ischemic and non-ischemic heart failure. These studies relied on analysis of two-dimensional sections and although quantitative changes were observed, the overall organization of the tranverse tubules (T-tubules) and the sarcoplasmic reticulum could not be assessed. In a 3-dimensional study using high voltage electron microscopy (EM) of the T-tubules in spontaneously hypertensive rats, Nakamura and Hama (1991) observed that concomitant with an increase in surface area, the T-tubule system becomes progressively more disorganized and exhibits structural irregularities such as increased numbers of longitudinal tubules, numerous short dead end branches and complex tubular aggregates. These authors suggested that this disorganization may interfere with synchronous contraction over the entire cell.In the present study, we examined the 3-dimensional organization of T-tubules in the left ventricle of explanted human hearts using confocal microscopy and EM tomography.

In-situ HVEM study of dislocation generation in patterned stress fields at silicon surfaces

Results are presented of an in-situ high voltage electron microscopy study of surface damage induced dislocation generation and propagation in silicon samples with a periodic mechanical stress field at the surface. The experimental observations are interpreted in the frame of a theoretical model describing dislocation nucleation as a function of substrate and stress field orientation. It is shown that in-situ studies of dislocation generation can elucidate basic mechanisms of defect formation in integrated circuit structures.

High Voltage Electron Microscope Study of Radiation-induced Precipitation of Gold-Nickel Alloys

Gold-nickel solid solution alloys were irradiated by high voltage electron microscopy with 2.0 MeV electrons. After irradiation, specimens were examined by energy dispersive X-ray microanalysis, quantitative stereo microscopy and high resolution electron microscopy. Defect clusters were formed by irradiation at high temperatures, at which dislocation loops were not formed. β-Ni precipitates were identified, which were octahedral and were surrounded by {111} planes. These precipitates were formed homogeneously and shrank when the irradiation was interrupted. This is radiation-induced homogeneous precipitation, which was observed for the first time in gold-nickel alloys

HVEM Study on the Non-Equilibrium Solid Phases Produced by MeV Electron Irradiation

This review is concerned with high voltage electron microscopy (HVEM) studies on the non-equilibrium solid phases produced by MeV electron irradiation. In such studies, one can combine the strong points of electron irradiation that the primary defects are simple in their configuration and distribution, with the advantage of electron microscopy that in situ, direct observations make it possible to analyze both the morphology and structure of the phases produced. Making full use of this merit, HVEM studies to clarify the conditions in which non-equilibrium solid phases can successfully be produced under MeV electron irradiation have been carried out. Results on such subjects as electron-irradiation-induced crystalline-toamorphous transition in crystals, electron-irradiation-induced phase decomposition and electron-irradiation-induced foreign-atom implantation, are reviewed

HVEM study of the effects of alloying elements and impurities on radiation damage in Zr-alloys

The effect of alloying additions and impurities on radiation damage in Zr-alloys has been studied using a high voltage electron microscope (HVEM). The electron damage results have been compared with neutron damage results for the same materials. There is some qualtitative agreement between the two techniques in that the relative susceptibility to c-component loop formation is the same in both the neutron and electron case. Cavity formation, however, occurs more readily during electron irradiation. Because of the relationship between c-component loop formation and accelerated growth, these results show that electron irradiation using a HVEM can provide a preliminary indication of the susceptibility of Zr-alloys to accelerated growth prior to their use in nuclear reactors.

An High-voltage electron microscopic study of extracellular matrix-cell contacts in an attached collagen lattice

Fibroblasts can exert tension on a surrounding substratum. Collagen lattices provide a model system for studying extracellular matrix-cell interactions that may be important in tension generation by fibroblasts. Fibroblasts cultured in an attached collagen lattice will develop tension, which results in rapid lattice retraction upon mechanical release from the underlying substratum. Thus, the cells must generate contractile force and transmit it to the surrounding matrix. Actin microfilament bundles present in fibroblasts may generate the contractile force responsible for the generation of tension. The transmission of force to the surrounding matrix could occur through a specialized transmembrane association linking actin microfilaments and fibronectin fibrils, termed the fibronexus. In this study we used the high-voltage electron microscope to examine in three-dimensions the extracellular matrix-cell contacts present at the surfaces of fibroblasts exerting tension onto the collagen lattice.

High-voltage electron microscopic studies of the interrelationship between microglial cells and amyloid fibrils in scrapie-infected mouse brains

We have previously demonstrated the usefulness of high-voltage electron microscopy (HVEM) in the study of microvessels and inflammatory cell attachment in the central nervous system (CNS). In the present study, we used HVEM to further explore the interrelationship between microglial cells (MCs) and amyloid deposits in scrapie-infected mice. Scrapie infection in the mouse has been employed as an animal model to study the pathogenesis of amyloid fibril formation. The central question was whether three-dimensional (3-D) stereo-pair reconstruction would offer further insight into amyloid formation by MCs, which is currently the view of our group. Brains or cervical spinal cords from IM mice previously inoculated with 87V scrapie agent were used. One-half-micrometer thick plastic sections were stained with uranyl acetate and lead citrate. Light-microscopy views enabled us to target primary inoculation channels associated with amyloid deposits. Cells located at the periphery of the amyloid were identified as MCs (Fig. 1).

HVEM studies of the calcified bone interface with endosteal dental implants

Previous studies have suggested the prerequisite of bone interfacing successful endosteal dental implants. This is the concept of osseointegration of dental implants within the jaw. However, the ultrastructure of the actual bone interface is largely unknown. This current study is planned to elucidate with correlative high-voltage electron microscopy (HVEM) and conventional electron microscopy (TEM), the morphology of the interface of the support tissues to endosteal dental implants. All ultrastructural protocols involve undecalcified tissue sectioning.After 2 months healing following extraction of all premolars, 120 root form and blade-type endosteal dental implants were placed into the mandibles of 30 adult mongrel dogs. This report will be restricted to 12 implants retrieved from animals euthanized after 5 months of unloaded healing. Following perfusion with buffered 3% glutaraldehyde the implants were block resected with their encasement of mandibular tissues, fixed by immersion for 24 hr in glutaraldehyde and postfixed with 1% OsO4 for 2 hr.

Mechanisms of inflammatory cell attachment in chronic relapsing experimental allergic encephalomyelitis: A scanning and high-voltage electron microscopic study of the injured mouse blood-brain barrier

Brain and spinal cord blood vessels from mice subjected to chronic relapsing experimental allergic encephalomyelitis were examined by scanning (SEM) and high-voltage electron microscopy (HVEM). SEM analysis of veins and venules from affected tissue regions demonstrated inflammatory cells (ICs), primarily lymphocytes or monocytes, attached to the luminal endothelial cell (EC) surface adjacent to the junctional complexes. In transverse section these cells were shown by HVEM to extend and to insert filopodia (lymphocytes) or flap-like lamellapodia (monocytes) into the luminal EC surfaces. Affected ECs often expressed increased microvillar projection as well as parajunctional crater-like structures on their luminal surfaces. Based on scanning and high-voltage electron microscopy, we present morphological evidence that some populations of sensitized ICs do not penetrate the EC junctions initially during EC attachment but instead insert pseudopodial projections into specialized openings in the ECs that are formed in response to chronic inflammation.

Influence of plastic deformation on Barkhausen power spectra in steels : Journal of Physics D, Vol. 22, No. 8, pp. 1240–1242 (Aug. 1989)

Barkhausen power spectra and hysteresis curves have been measured for a pearlitic constructional steel over a range of plastic deformations up to 20%. The intercept of the power spectrum is seen to decrease with increasing deformation while the coercivity increases and both the permeability and remanence decrease. The results are discussed in the context of earlier reports and high-voltage electron microscopy studies.

Three-dimensional spatial relationship between the collagen fibrils and the inorganic calcium phosphate crystals of pickerel ( Americanus americanus) and herring ( Clupea harengus) bone

High-voltage (1.0 MV) electron microscopy and stereomicroscopy, electron probe micro-analysis, electron diffraction and three-dimensional computer reconstruction, have been used to examine the spatial relationship between the inorganic crystals of calcium phosphate and the collagen fibrils of pickerel and herring bone. High-voltage stereo electron-micrographs were obtained of cross-sections of the cylinder-shaped intramuscular bones in uncalcified regions, in regions where only one or only several crystals had been deposited in some of the fibrils, and in successive sections containing progressively more mineral crystals until the stage of full mineralization was reached. High-resolution electron probe microanalysis confirmed that the electron-dense particles contained calcium and phosphorus. In the earliest stages of mineralization and progressing throughout the mineralization process, the crystals are located only within the collagen fibrils; crystals are not observed free in the extracellular spaces between collagen fibrils. The progressive increase in the mass of mineral deposited in the bone tissue with time occurs, essentially, completely within the collagen fibrils including the stage of full mineralization. At this stage, cross-sectional profiles of collagen fibrils are completely obliterated by mineral. A small number of crystals that are located on or close to the surface of the fibrils appear to extend a very short distance into the spaces between the fibrils. These ultrastructural observations of the very onset of calcification in which nucleation of the calcium phosphate crystals is clearly shown to begin within specific volumes of collagen fibrils, and of the subsequent temporal and spatial sequences of this phenomenon, which shows that calcification continues wholly within the collagen fibrils until maximum calcification is achieved, add important information on the basic physical chemical mechanism of the calcification and the structural elements that are involved. The spatial and temporal independence of the sites where mineralization is initiated establishes that such ultrastructural locations within individual collagen fibrils represent independent, physical chemical nucleation loci. The findings are totally inconsistent with the proposal that crystals must first be deposited in matrix vesicles, or other components such as mitochondria, and subsequently released and propagated in the interfibrillar space, until they eventually reach and impregnate the hole zone regions of the collagen fibrils. Three-dimensional computer reconstruction of serial transverse and longitudinal sections demonstrates periodic swellings along the collagen fibrils, corresponding to the hole zone region of their axial period as mineralization proceeds. Bulging of fibrils was observed only in the more heavily mineralized regions of the tissues, a result suggesting that structural changes of the collagen fibrils may occur to accommodate additional mineral mass during the progressive increase in the deposition of a solid phase of calcium phosphate within the fibrils. We have also examined the same fish bones used for high-voltage electron optical studies using neutron diffraction techniques, from which the volume of space within collagen fibrils potentially available for the deposition of a solid mineral phase of calcium phosphate can putatively be calculated. Contrary to the direct visual observations of the location of the calcium phosphate crystals by high-voltage electron microscopy, calculations based on the data obtained from neutron diffraction techniques reveal that there is not a sufficient volume of space within the collagen fibrils of fish bone to accommodate all of the mineral phase present in the fully mineralized tissue. This discrepancy between direct observation by high-voltage electron microscopy and quantitative calculations of the three-dimensional space within collagen fibrils based on neutron diffraction and theoretical models of the packing of collagen molecules in collagen fibrils, raises serious questions about the validity of the particular neutron diffraction methods employed, and the assumptions used to calculate the intrafibrillar volume of the collagen fibrils. The correctness of the high-voltage electron microscopy studies is confirmed in other experiments in which the extracellular, interfibrillar volume of space in the tissue was measured directly by high-voltage electron microscopy of cross-sections of the tissue. The interfibrillar volume was found to be very much less than that required to house the large proportion of the mineral phase in the tissue calculated to be present in the interfibrillar space of fully mineralized bone from the neutron diffraction data using the methods and assumptions of Bonar and co-workers.

HVEM studies of the effects of hydrogen on the deformation and fracture of AISI type 316 austenitic stainless steel

The mechanisms of hydrogen embrittlement in AISI type 316 austenitic stainless steel have been investigated by in situ straining in a high-voltage electron microscope (HVEM) equipped with an environmental cell. Hydrogen effects on strain-induced phase transformations, the generation rate and velocity of dislocation, and crack propagation rates were studied. The salient features of the fracture were similar for cracks propagating in vacuum and in hydrogen gas. In each case, ε and α′ martensite formed at the crack; the ε phase extended ahead of the crack while the α′ phase was restricted to high stress regions near the crack tip. The principal effect of hydrogen was to decrease the stress required for dislocation motion, for phase transformation of the austenite, and for crack propagation.

High-voltage electron microscopic studies of inflammatory cell attachment during blood-brain barrier inflammation

Previous studies have suggested the usefulness of high-voltage electron microscopy (HVEM) for investigating blood-bram barrier (BBB) injury and the mechanism of inflammatory-cell (IC) attachment. These studies indicated that, in evaluating standard conventional thin sections, one might miss cellular attachment sites of ICs in their process of attaching to the luminal endothelial cell (EC) surface of cerebral blood vessels. Our current studies in animals subjected to autoimmune disease suggest that HVEM may be useful in localizing precise receptor sites involved in early IC attachment.Experimental autoimmune encephalomyelitis (EAE) was induced in mice and rats according to standard procedures. Tissue samples from cerebellum, thalamus or spinal cords were embedded in plastic following vascular perfusion with buffered aldehyde. Thick (0.5-0.7 μm) sections were cut on glass knives and collected on Formvar-coated slot grids stained with uranylacetate and lead citrate and examined with the AEI EM7 1.2 MV HVEM in Albany, NY at 1000 kV.

High voltage electron microscopy studies of grain boundary effects on hydrogen embrittlement of stainless steel

The effects of the grain boundary on hydrogen embrittlement of AISI type 316 stainless steel were studied by means of in situ environmental cell straining techniques in a high voltage electron microscope. During hydrogen embrittlement the grain boundaries effectively blocked dislocations and dislocation pile-ups were developed. The grain boundary relieved the accumulated stress by activating grain boundary dislocation or stacking fault sources, and the ϵ martensitic phase nucleated and grew. The propagation of crack across a grain boundary was observed. A crack nucleated in a second grain close to the intersection of the pile-ups with the grain boundary and propagated along the second grain.

A HVEM study on the deformation microstructures of quartz in the fault rocks from a seismic fault zone in west china

Our work has been aimed at the exploratory observation and study on the intracrystalline submicron deformation structures of quartz in a series of deformed rocks occurred along the Fuyun fault zone in Xinjian, West China, which is a typical seismic one with strong activities since Cenozoic period, in connection with the corresponding works on seismology and structural petrology, using the ultra high voltage electron microscope (HVEM).With the successful method of sample preparation by select area stripping from a petrographic microscopy section and ion thinning, and with the advantages of stronger penetration power and lower radiation damage of HVEM, our observation on the intracrystalline deformation microstructure has been made more reliable and productive.In the light of dislocation theory and the experimental results of quartz deformation, up to hundred of HVEM micrographs have been analysed and summarized with reference to the current conceptual model of fault.