Transmission Electron Microscopy of Thin Glass Samples

Mechanical thinning and fracturing techniques for preparing thin glass samples for direct-transmission electron microscopy are discussed. A modification of the Doherty and Leombruno procedure for mechanically thinning ceramic materials is described. These techniques make possible more reliable electron microscope studies of fine-scale submicrostructure in glass systems. Electron microscope observations on fused silica, an alkali borosilicate glass, and some binary silicate glasses are reported and discussed in terms of present understanding of glass structure.     

Transmission Electron Microscopy of Hydrated Dicalcium Silicate Thin Films

A method of preparing calcium silicate hydration products for transmission electron microscopy is presented. Thin films of dicalcium silicate are evaporated onto substrates and hydrated in a vacuum chamber. Since the resulting hydration products are undisturbed, the interrelations of the species can be studied. The technique provides specimens suitable for high-resolution microscopy. This method produces hydration products like those reported when conventional specimen preparation techniques are used. Calcium silicate hydrate gel, two forms of C-S-H II (fans and fiber bundles), afwillite, and Ca(OH)₂ morphologies were observed. Coevaporated CaCl₂ additions improve the electron diffraction patterns obtained from the C-S-H II fan structures but increase shrinkage of these structures on drying.     

General Fracture Method for Preparation of Foils for Transmission Electron Microscopy

A mechanism for crack propagation is presented to explain the production of thin foils when a brittle material fractures. A general technique for continuing this process and collecting the foils for electron microscopy is described. This method has been successful with every material examined, although there was considerable variation in the number and sizes of foils produced. The materials studied include single-crystal MgO, LiF, twinned KAlSi₃O₈ (microcline), CaCO₃, Ge, Si, Zn, MgAl₂O₄, Al₂O₃, and glasses, and the polycrystalline materials SiC, talc, MgO, and Al₂O₃ all in order of relative success. A brief review of other electron transmission sample preparation methods is included with special reference to those most similar to the method described herein.     

Transmission Electron Microscopy and Microanalytical Studies of Ion-Beam-Thinned Sections of Tricalcium Silicate Paste

Mature tricalcium silicate cement pastes were examined in ion-beam-thinned sections. The microstructure consisted of very homogeneous amorphous hydrate gel surrounding residual unhydrated cores of tricalcium silicate, these regions being linked by a fibrillar outer hydration product. Carbonation had produced microcrystals of calcite within the outer product only. X-ray microanalysis gave Ca: Si ratios for the hydrate regions which showed considerable deviations but were-on average in fairly good agreement with indirectly determined Ca: Si ratios of pastes of the same material. There was no significant difference in composition between inner and outer hydration products.     

Thin Films in Electron Microscopy

Thin films play an important role in electron microscopy as they can be used to improve the contrast and stability of specimens, as well as to make specimens electrically conductive. In order to avoid overlapping of specimen and coating structures, it is necessary to understand how thin films are formed in the various coating technologies and how to create them reproducibly as part of the different preparation techniques for electron microscopy. In contrast, electron microscopy can be applied to learn more about the structural details of thin films used, for instance, in the optical coating industry. Heat shock fracturing and Pt-C surface replication of the cross sections resulted in reliable transmission electron micrographs (TEM) of the coating microstructure. These studies demonstrate that, under optimal conditions, it is possible to find a correlation between the measured optical properties and the microstructure of the coatings. TEM replica investigations reveal single events, so they can be useful if discrepancies in the (statistical) physical data have to be investigated.     

Transmission Electron Microscopy of Glass-Ceramics

A new technique has been developed by which thin sections of glass-ceramics can be prepared for direct observation by transmission electron microscopy. Techniques for identifying crystalline phases are discussed, and the degree of crystallinity in several glass-ceramics is presented.     

Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Characterization of Glass Phase in Sol-Gel-Derived Mullite

Sol-gel-derived mullite ceramics were processed by pressureless sintering at 1600°, 1650°, and 1700°C for 4 h. Microstructural and microchemical characterization of the mullite materials was performed using transmission electron microscopy, in conjunction with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy (EELS). Apart from mullite grain diameter and triplepocket size, no major microstructural changes were observed with increasing sintering temperature. Residual glass was present at triple pockets and along two-grain junctions. Not all grain boundaries revealed the presence of a continuous amorphous intergranular film. Clean interfaces were observed only at boundaries with one grain parallel to the [001] orientation (low-energy configuration). Quantitative EELS analysis of mullite grains and glass pockets revealed only small changes in composition with increasing sintering temperature; i.e., the alumina:silica ratio slightly increased for mullite and glass. The analysis implied that mullite with this relatively high aluminum content would not be stable adjacent to residual glass. However, a stable glass-mullite system has been proposed, because impurity cations were detected within glass pockets, which suggested a slight shift of the subsolidus line (glass-mullite/ mullite) to a higher amount of alumina. Energy-loss nearedge structure studies of the Si- L _2,3 edge revealed a similar near-edge structure for the mullite, residual glass, and quartz. Thus, SiO₄ tetrahedra were thought to be the main building units of the glass contained in sintered mullite.     

In Situ Tensile Measurements of Single Fibers by Scanning Electron Microscopy

A newly developed tensile module allows tensile experiments of single fibers to be carried out under visual observation in the scanning electron microscope. This allows correlation of measured data with observed changes in the microstructure, such as surface irregularities and crack formation. With point heating, the thermal behavior of the fibers may be studied up to 2500°C. The results are presented with tensile elongation recordings and micrograph sequences of the structural changes. Carbon fibers with and without an aluminum coating were selected as testing specimens.     

Study of the Ion‐Irradiation Behavior of Advanced SiC Fibers by Raman Spectroscopy and Transmission Electron Microscopy

6H–SiC single crystals and two types of SiC fibers, Hi‐Nicalon type S and Tyranno SA3, have been irradiated with 4‐MeV Au³⁺ up to 2 × 10¹⁵ cm^?2 (4 dpa) at room temperature, 100°C and 200°C. These fibers are composed of highly faulted 3C–SiC grains and free intergranular C. Stacking fault linear density and grain size estimations yield, respectively, 0.29 nm^?1 and 26–36 nm for the Hi‐Nicalon type S fibers and 0.18 nm^?1 and 141–210 nm for the Tyranno SA3 fibers. Both transmission electron microscopy and surface micro‐Raman spectroscopy reveal the complete amorphization of all the samples when irradiated at room temperature and 100°C and a remaining crystallinity when irradiated at 200°C. The latter observations reveal a multi‐band irradiated layer consisting in a partially amorphized band near the surface and an in‐depth amorphous band. Also, nanocrystalline SiC grains with high stacking fault densities can be found embedded in amorphous SiC at the maximum damage zone of the Hi‐Nicalon type S fibers irradiated at 200°C.     

Cathodoluminescence and Cross-sectional Transmission Electron Microscopy Studies for Deformation Behaviors of GaN Thin Films Under Berkovich Nanoindentation

In this study, details of Berkovich nanoindentation-induced mechanical deformation mechanisms of metal-organic chemical-vapor deposition-derived GaN thin films have been systematic investigated with the aid of the cathodoluminescence (CL) and the cross-sectional transmission electron microscopy (XTEM) techniques. The multiple “pop-in” events were observed in the load-displacement (P–h) curve and appeared to occur randomly by increasing the indentation load. These instabilities are attributed to the dislocation nucleation and propagation. The CL images of nanoindentation show very well-defined rosette structures with the hexagonal system and, clearly display the distribution of deformation-induced extended defects/dislocations which affect CL emission. By using focused ion beam milling to accurately position the cross-section of an indented area, XTEM results demonstrate that the major plastic deformation is taking place through the propagation of dislocations. The present observations are in support to the massive dislocations activities occurring underneath the indenter during the loading cycle. No evidence of either phase transformation or formation of micro-cracking was observed by means of scanning electron microscopy and XTEM observations. We also discuss how these features correlate with Berkovich nanoindentation produced defects/dislocations structures.     

An Introduction to Energy-Filtered Transmission Electron Microscopy

This article introduces the topic of energy-filtered transmission electron microscopy (EFTEM). It reviews the technique combining theory with a number of applications from materials science to highlight the progress made in the subject. Examples of EFTEM of catalysts are also reviewed with a discussion of how the technique could be used to study many more catalyst structures in the future.     

In–Situ Transmission Electron Microscopy Crystallization Studies of Sol–Gel-Derived Barium Titanate Thin Films

Barium titanate (BaTiO₃) thin films that were derived from methoxypropoxide precursors were deposited onto (100) Si, Pt/Ti/SiO₂/(100) Si, and molecular-beam-epitaxy-grown (MBE-grown) (100) BaTiO₃ on (100) Si substrates by spin coating. The crystallization behavior of the amorphous-gel films was characterized using in-situ transmission electron microscopy heating experiments, glancing-angle X-ray diffraction, and differential thermal analysis/thermogravimetric analysis. Amorphous-gel films crystallized at a temperature of ∼600°C to an intermediate nanoscale (5–10 nm) barium titanium carbonate phase, presumably BaTiO₂CO₃, that subsequently transformed to nanocrystalline (20–60 nm) BaTiO₃. Random nucleation in the bulk of the gel film was observed on all substrates. In addition, oriented growth of BaTiO₃ was concurrently observed on MBE-grown BaTiO₃ on (100) Si. High-temperature decomposition of the intermediate carbonate phase contributed to nanometer-scale residual porosity in the films. High concentrations of water of hydrolysis inhibited the formation of the intermediate carbonate phase; however, these sols precipitated and were not suitable for spin coating.