High resolution electron microscopy of partial dislocations in the Laves phase structure

A Mg-base Laves phase was investigated by high resolution electron microscopy (HREM). Linear defects found at terminations of stacking faults were classified into three groups. The first is a partial dislocation at a termination of a stacking fault, the second is a superposed partial dislocation which is defined as a defect produced by a superposition of terminations of two or more stacking faults lying on neighbouring layers, and the third is a combined linear defect which consists of a characteristic combination of terminations of stacking faults. In the last case the total stacking fault vector becomes equal to the translation vector in the basal plane, so that the defect needs no relaxation of the lattice. The Burgers vectors of the partial dislocations were estimated with the aid of modified Burgers circuits.     

An electron microscopy study of worn ceramic surfaces

An electron microscopy investigation of worn surfaces of monolithic alumina, whisker-reinforced alumina, monolithic silicon carbide and silicon-silicon carbide has been performed. The emphasis has been to explore the mechanisms of wear debris generation and tribofilm formation and their influence on the tribological behaviour in closed contacts of the flat-on-flat category.     

Scanning electron microscopy and transmission electron microscopy study of hot-deformed γ-TiAl-based alloy microstructure

The aim of this work was to assess the changes in the microstructure of hot‐deformed specimens made of alloys containing 46–50 at.% Al, 2 at.% Cr and 2 at.% Nb (and alloying additions such as carbon and boron) with the aid of scanning electron microscopy and transmission electron microscopy techniques. After homogenization and heat treatment performed in order to make diverse lamellae thickness, the specimens were compressed at 1000 °C. Transmission electron microscopy examinations of specimens after the compression test revealed the presence of heavily deformed areas with a high density of dislocation. Deformation twins were also observed. Dynamically recrystallized grains were revealed. For alloys no. 2 and no. 3, the recovery and recrystallization processes were more extensive than for alloy no. 1.     

An environmental scanning electron microscopy study of aqueous gibbsite suspensions

Synthetic gibbsite has been used as a model system for study in the environmental scanning electron microscopy (ESEM), to probe its utility as a tool to study clay dispersions under different conditions of aggregation. We have been able to show that we can study the nature of the platelet interactions as the pH is altered, by imaging the dispersions after water evaporation from the surface to permit the surface of the platelets to be clearly seen. It has been possible to show that at alkaline pH there are very few face-edge contacts between the platelets, consistent with what is known about the charges at high pH on the faces and edges of the gibbsite. In contrast, at lower pHs, when faces and edges have opposite sign charges, there are significantly more platelets touching with edge and faces in contact. Finally, when the salt lithium chloride is added to a dispersion at approximately neutral pH, the plates appear to stack suggesting face-face interactions in the dispersion. Thus, ESEM has been able to demonstrate the variability of packing in gibbsite dispersions and to correlate the structures observed with the known charge distribution on the gibbsite platelets.     

High-resolution cryo-scanning electron microscopy study of the macromolecular structure of fibronectin fibrils

High-resolution cryo-scanning electron microscopy was used to examine fibronectin fibrils formed in culture by human skin fibroblasts and in a cell-free system by denaturing soluble plasma fibronectin with guanidine. These studies indicate that the conformation of fibrils formed in culture and in a cell-free system appeared to be similar and that fibronectin fibrils have at least two distinct structural conformations. Fibronectin fibrils can be very straight structures with smooth surfaces or highly nodular structures. The average diameter of the nodules in these fibrils is 12 nm. Both conformations can be seen within an individual fibril indicating that they are not different types of fibronectin fibrils but rather different conformational states. Immunolabeling studies with a monoclonal antibody, IST-2, to the heparin II binding domain of fibronectin revealed that the epitope was buried in highly smooth fibrils, but it was readily exposed in nodular fibrils. We propose, therefore, that fibronectin fibrils are highly flexible structures and, depending on the conformation of the fibril, certain epitopes on the surface may be buried or exposed.     

Dinosaur eggshell study using scanning electron microscopy

Visualization and analysis of structural features in fossil dinosaur eggs by scanning electron microscopy augment information from traditional petrographic light microscopy. Comparison of characteristics in fossil and modern eggshells allows inferences to be made regarding dinosaur reproductive biology, physiology, and evolutionary relationships. Assessment of diagenetic alteration of primary eggshell calcite structure that occurs during fossilization provides important information necessary for taxonomic identification and paleoenvironmental interpretations.     

A replica technique for extracting precipitates from zirconium alloys for transmission electron microscopy analysis

A reliable two-stage carbon replica technique has been developed to extract precipitates from zirconium alloys. Using this technique, all precipitating phases can be extracted from Zircaloy-2, Zr-Cr-Fe, and Zr-Nb-Fe alloys. Precipitate identification using EDS X-ray analysis and convergent beam electron diffraction was greatly facilitated in comparison to thin foils. In addition, the sensitivity for the detection of trace elements in particles was increased using extraction replicas. The chemical compositions of the precipitates as determined from both replica and thin foils were in excellent agreement.     

Analytical transmission electron microscopy and electron diffraction for characterization of multiphase Ni-P-Ti surface layer on Ti-6Al-4V alloy

The microstructure, chemical and phase composition of the hard Ni‐P‐Ti layer formed on the Ti‐6Al‐4V alloy after duplex surface treatment were investigated by light microscopy, X‐ray diffraction, scanning electron microscopy and analytical/high‐resolution transmission electron microscopy. These investigations showed that the improved mechanical and tribological properties of the surface‐treated alloy were related to the presence of a multilayered microstructure containing several phases from the Ni‐Ti‐P‐Al system.     

Characterization of an oil-degrading Microcoleus consortium by means of confocal scanning microscopy, scanning electron microscopy and transmission electron microscopy

A consortium of microorganisms with the capacity to degrade crude oil has been characterized by means of confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The analysis using CLSM shows that Microcoleus chthonoplastes is the dominant organism in the consortium. This cyanobacterium forms long filaments that group together in bundles inside a mucopolysaccharide sheath. Scanning electron microscopy and transmission electron microscopy have allowed us to demonstrate that this cyanobacterium forms a consortium primarily with three morphotypes of the heterotrophic microorganisms found in the Microcoleus chthonoplastes sheath. The optimal growth of Microcoleus consortium was obtained in presence of light and crude oil, and under anaerobic conditions. When grown in agar plate, only one type of colony (green and filamentous) was observed.     

Reflection electron microscopy methods for the study of surface structure

The techniques of reflection electron microscopy (REM) using TEM instruments and scanning reflection electron microscopy (SREM) using STEM instruments have been explored as means for the observation of surface structure with high spatial resolution, better than 1 nm in each case. Under the ordinary environment of a commercial TEM instrument, we have studied the contrast in REM images of atomic steps and made comparison with the calculated results from the multi-slice dynamical diffraction theory. Comparison has also been made between the REM images of defects and the calculated images based on the column approximation. The influence of surface resonances on the contrast has been investigated. By SREM performed in a modified HB5 STEM with attached high vacuum preparation chamber, we have observed the formation of periodically distributed Pd particles on the surface of cleaved MgO.     

TEM and HREM study of Al3Zr precipitates in an Al-Mg-Si-Zr alloy

The structure of Al₃Zr precipitates in Al‐1.0Mg‐0.6Si‐0.5Zr (in wt.%) alloy was investigated using conventional transmission electron microscopy (TEM) and high‐resolution TEM (HREM). After annealing of the alloy in the temperature range 450–540 °C, spherical precipitates of metastable L1₂‐Al₃Zr phase appeared nearly homogeneously within the matrix, and elongated particles were found at grain boundaries. L1₂‐structured Al₃Zr were about 20–30 nm in diameter and coherent with the matrix. Inside some of them, planar faults parallel to {100} planes were revealed by use of HREM. Most probably, these faults are an indication of the transition stage of transformation to the stable D0₂₃‐type Al₃Zr phase. The elongated precipitates (about 100 nm) were identified as D0₂₂‐type Al₃Zr. Energy‐dispersive X‐ray analysis showed that they contain, apart from Al, mainly Zr with small amounts of Si. The substitution of Al by Si increased the stability of the D0₂₂‐Al₃Zr as compared with D0₂₃‐Al₃Zr.     

Sectionable microcarrier beads: An improved method for the preparation of cell monolayers for electron microscopy

Cross-linked dextran beads provide an excellent surface for tissue-cultured cell monolayers, and can be processed for transmission (TEM) and scanning (SEM) electron microscopy, as well as light microscopy (LM). Cells are grown to confluency on the surface of the microcarriers, where at any point aliquots can be removed and experimentally treated as desired (e.g. immunocytochemistry) providing a representative sample. Sample preparation for TEM follows standard procedures for any cell monolayer, but infiltration times must be at least doubled to allow penetration of the beads. The polymerized blocks can then be sectioned for TEM or LM with no additional steps required. SEM sample preparation involves attaching the fixed bead/cell suspension to a glass coverslip with poly-1-lysine, dehydration, critical point drying, and coating for conductivity. The fixed and dried sample can also be attached directly to the SEM stub as free beads and subsequently gold coated. These beads provide (1) an increased surface area of cells visible per area of thin section, (2) eliminates the careful orientation required for flat substrate methods of embedding, (3) decreases the amount of sample manipulation in the forms of re-embedding and gluing, and (4) decreases the amount of drying artifact seen as cracking in SEM monolayer preparations.     

New system for secondary electron detection in variable-pressure scanning electron microscopy

A novel secondary electron detection system combining a two‐stage detector head and a differential pumping system is presented. The detector head consisted of a scintillation Everhart‐Thornley detector and a microsphere plate, separating it from the lower vacuum in the intermediate chamber (below 0.1 mbar). The system was arranged asymmetrically, which should contribute to a lower gas leakage through the plate and a longer life span of the plate. The system offered all the advantages of the scintillator detector in a wide range of gas pressures, from high vacuum to those of the order of 10 mbar, typical of high‐pressure scanning electron microscopy.     

3-D morphological characterization of the liver parenchyma by atomic force microscopy and by scanning electron microscopy

A comparative study of atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging of the healthy human liver parenchyma was carried out to determine the similarities and the differences. In this study, we compared the fine hepatic structures as observed by SEM and AFM. Although AFM revealed such typical hepatic structures as bile canaliculi and hepatocytes, it also showed the location of the nucleus and chromatin granules in rough relief structure, which was not visible by SEM. By contrast, SEM visualized other structures, such as microvilli, the central vein, and collagenous fibers, none of which was visualized by AFM. For better orientation and confirmation of most of the structures imaged by SEM and AFM, Congo Red-stained specimens were also examined. Amyloid deposits in the Disse's spaces were shown especially clearly in these images. The differences between the SEM and AFM images reflected the characteristics of the detection systems and methods used for sample preparation. Our results reveal that more detailed information on hepatic morphology is obtained by exploiting the advantages of both SEM and AFM.     

Identification of bacteria by studying one section under light microscopy,scanning, and transmission electron microscopy

A method for bacterial identification has been developed by means of studying the same histological sections through several types of microscopy. With this method, one section was processed and analyzed respectively for light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Sections of gingival biopsies were Gram stained and bacteria tentatively identified by LM. Photographs of the sections were taken and presketched transparent acetate sheets (PTAS) were made from the photos. The same section was later prepared for SEM, areas previously thought to contain bacteria were localized by placing the PTAS onto the SEM monitoring screen. The SEM specimens were subsequently processed for TEM, bacteria were located, and micrographs obtained. The results showed that out of ten diseased gingival biopsies observed under the LM, bacteria were found to be present in all the specimens and were identified as both Gram positive and Gram negative. By transferring the section from LM to SEM, the bacteria could be relocated and their morphotype (cocci, rods, etc.) clearly identified in most of the cases. Since cocci may resemble other biological granular structures under SEM, they require further analysis under TEM for additional positive identification. This study demonstrated that the method described here is a useful tool for assessing the presence and identifying bacteria within the gingival tissues.     

Imaging of semiconducting polymer blend systems using environmental scanning electron microscopy and environmental scanning transmission electron microscopy

This study has investigated the potential of environmental electron microscopy techniques for studying the structure of polymer‐based electronic devices. Polymer blend systems composed of F8BT and PFB were examined. Excellent contrast, both topographical and compositional, can be achieved using both conventional environmental scanning electron microscopy (ESEM) and a transmission detector giving an environmental scanning transmission electron microscope (ESTEM) configuration. Controllable charging effects present in the ESEM were observed, giving rise to a novel voltage contrast. This shows the potential of such contrast to provide excellent images of phase structure and charge distributions.     

The observation of large magnetite (Fe3O4) crystals from magnetotactic bacteria by electron and atomic force microscopy

Magnetite crystals inside coccoid magnetotactic bacteria found in lagoons near Rio de Janeiro city were examined by electron microscopy (EM) and atomic force microscopy (AFM). For AFM, ultrathin sections of bacteria embedded in Epon resin were etched with an ethanolic NaOH solution and observed both in the height and in the force modes. Comparative electron microscope images were useful for identifying crystalline reliefs in the etched sections. Different situations representing particular arrangements of crystal chains were observed by AFM. The majority of the bacteria examined presented unusually large magnetite crystals which remained strongly attached in linear chains even after the laboratory procedures for their isolation. This behaviour is different from all other biogenic magnetite crystals isolated so far. It is suggested that this attachment is due to the strong field between individual crystals as well as to the contact areas, which are the largest observed until now. The correct identification of a particular topography by AFM as a crystal relief may be critical when crystals are not aligned in chains; in these cases the linear dimensions and the presence of well-defined edges and faces are important features to be taken into account. Characterization of the crystal faces is important for the study of magnetotactic micro-organisms since the crystalline habits seem to be species-specific. Observation of etched sections proved to be a helpful approach for crystal relief observation, especially when small amounts of bacteria were available.     

Preparation of fish tissues for electron microscopy

Many of the techniques applied to study the morphology of lower vertebrates were originally developed for analysis of mammalian tissues. However, not all of these methods, especially those involving tissue perfusion, can be directly applied to piscine tissues because of the considerable physiological differences between fish and mammals. The present paper examines these physiological variables in fish and describes how they might affect morphological studies that employ tissue perfusion. A method for perfusion of fish tissues is described in detail. This procedure can be used for administration of fixatives, chemical markers, and vascular replicating resins.     

An improved specimen loader for cryo-scanning electron microscopy

Cryo-electron microscopy of cryofixed samples is a well-established and accepted technique for imaging liquid-containing specimens without removing water and other volatile components. There are many steps between cryofixation and cryo-observation in the microscope, during which the sample and sample holder need to be handled. One such major step is the loading of the specimen onto the sample holder and the fixing of the sample holder onto the transfer mechanism. During this handling, the specimen is often exposed (mostly inadvertently) to moisture in the atmosphere, which results in frost deposition. The new specimen loader described here is designed to overcome the traditional tedious handling and to achieve ease in specimen loading. The modifications made are mainly towards allowing movement of the liquid freon cup, eliminating the need for a lock-screw and improving the shape of the stage holder, which makes the mounting of the specimen holder easy, thereby permitting smooth specimen loading without too much handling and with consequent reduced frost deposition.