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.     

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.     

叶腊石干法研磨过程中偏叶腊石相的HRTEM研究

采用高分辨透射电镜(HRTEM)对叶腊石研磨的中间产物偏叶腊石相进行晶体结构的研究,并就研磨与热处理对叶腊石晶体结构的影响首次进行了傅里叶变换红外(FTIR)光谱的对比.结果表明:(1)干法研磨过程中,叶腊石研磨的中间相为偏叶腊石,且研磨使得叶腊石的晶体结构出现明显的晶格膨胀,其中研磨作用对叶腊石沿其c轴方向的晶体结构的影响较大.(2)研磨或者热处理条件下,叶腊石的FTIR光谱中3673 cm-1处峰形尖锐的羟基伸缩振动峰的强度随着研磨时间或煅烧温度的增大而逐渐降低,并最终消失.该结论表明热与机械力研磨处理对叶腊石晶体结构的破坏具有相似性.     

Application of Transmission Electron Microscopy to Radiation Damage in Ceramics

Ceramics are becoming increasingly important in many radiation environments. In addition to refractory fissionable fuels, electrical insulators will be needed for instrumentation in breeder reactor systems and will be widely applied in all fusion reactor concepts, including first-wall coatings, blanket gaps, injectors, divertors, magnet insulation, and windows. These applications require mechanically stable (and in some cases transparent) dielectric solids which must maintain electrical as well as mechanical integrity under severe radiation fields. Refractory ceramic materials of low atomic number will be increasingly useful in structural applications as well because they resist activation and contribute less objectionable sputter contaminants. Ceramic solids are also likely to be increasingly utilized as repository media for active nuclear wastes. The irradiation behavior of these nonmetallic materials is critical and at present poorly understood, but transmission electron microscopy is beginning to reveal significant similarities, as well as substantial differences, in their behavior as compared to that of better-characterized metallic solids.     

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.     

Applications of Dedicated Scanning Transmission Electron Microscopy to Nonmetallic Materials

The operating characteristics of a scanning transmission electron microscope are described and discussed with particular emphasis on those operating modes where scientific advantages and/or advantages of convenience can be realized in microstructural analysis. Several examples demonstrating these operating modes are presented.     

Application of Transmission Electron Microscopy to Engineering Practice in Ceramics: Introduction, Fundamentals, and Application to Precipitation Phenomena

This paper, the first of eight in this issue of the Journal devoted to transmission electron microscopy (TEM) of ceramics, provides a brief introduction to the physics of electron optics as it relates to the study of microstructural defects in crystalline solids. The particular application of TEM discussed in this paper, the study of subsolidus precipitation in star sapphire (Ti-doped AI₂O₃) and in magnesia-partially stabilized zirconia (Mg-PSZ), illustrates the usefulness of this technique in providing detailed crystallographic and microstructural information on precipitation reactions. In star sapphire, TEM was used to identify unambiguously the needle-like precipitate phase responsible for the asterism in gem-quality crystals as rutile, the stable tetragonal form of TO₂. The observed orientation relation between precipitate and matrix allows good lattice matching between the two phases. The work on PSZ described in the present paper consists of "deciphering" the precipitation history of a commercial, sintered, polycrystalline ceramic showing, in particular, that precipitation occurred in three distinguishable stages. Although tetragonal ZrO₂ is the precipitate phase in all three stages, a polymorphic transformation to monoclinic symmetry occurs in two of the three types of precipitates; the tetragonal symmetry is retained metastably in the third. Furthermore, the internal structure of the precipitates and the precipitate/cubic zirconia host microstructural relations are different in each case; these differences can profoundly affect mechanical properties.     

Application of Transmission Electron Microscopy to the Study of Deformation in Ceramic Oxides

Slip systems, dislocation reactions, and dislocation dissociations are reviewed in relation to the crystal structures of ceramic oxides. Techniques of deformation and transmission electron microscopy (TEM) are described. The impact of TEM on the understanding of deformation in oxides is discussed by relating the observed dislocation substructures to the mechanical properties in several oxide systems. Important information can be obtained on dislocation glide and climb processes in relation to work hardening, recovery, and creep. Yielding and the brittle-to-ductile transition temperature are discussed in terms of the magnitude of the Burgers vector in various crystal structures and the influence of dissociation reactions and diffusion. Examples include oxides with close-packed anions such as MgO, MgAl₂O₄ BeO, A1₂O₃, TiO₂, and Mg₂SiO₄, and other oxides such as Cu₂O, UO₂, and SiO₂.     

Oxide Reduction in NiO-Containing Solid-Solution Systems During Transmission Electron Microscopy

The effects of electron irradiation on NiO-containing solid solution systems are described. Partially hydrated NiO solid solutions, e.g., NiO-MgO, undergo surface reduction to Ni metal after examination by TEM. This surface layer results in the formation of moire interference patterns.     

Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Study of Nonstoichiometric Silicon-Carbon-Oxygen Glasses

Crystallization behavior of Si-C-O glasses in the temperature range of 1000°–1400°C was investigated using transmission electron microscopy (TEM) in conjunction with electron energy-loss spectroscopy (EELS). Si-C-O glasses were prepared by pyrolysis of polysiloxane networks obtained from homogeneous mixtures of triethoxysilane, T^H, and methyldiethoxysilane, D^H. Si-C-O glass composition depended on the molar ratio of the precursors utilized. At a ratio of T^H/D^H= 1, the formation of a carbon-rich glass was observed, whereas a ratio of T^H/D^H= 9 yielded a Si-C-O glass with excess free silicon. Both materials were amorphous at 1000°C, but showed a distinct difference in crystallization behavior on annealing at high temperature. Although T^H/D^H= 1 revealed a small volume fraction of SiC precipitates in addition to a very small amount of residual free carbon at 1400°C, T^H/D^H= 9 showed, in addition to SiC crystallites, numerous larger silicon precipitates (20–50 nm), even at 1200°C. Both materials underwent a phase separation process, SiC _x O_2(1-x)→ x SiC + (1 - x )SiO₂, when annealed at temperatures exceeding 1200°C.     

High-Resolution Transmission Electron Microscopy of Transformed Magnesia-Partially-Stabilized Zirconia Precipitates

Transformed Mg-PSZ precipitates consist of monoclinic bands that are twin-related across either (100)_m or (001)_mplanes in an arrangement that leads to accommodation of the shear component of the transformation shape strain. High-resolution images of these variants reveal these twin relationships quite clearly. It is shown that complete compensation of shear does not always occur. This paper also shows observations of monoclinic variants related by a rotation of 90° around the normal to (001)_m, in addition to those related by a 180° rotation for the twin-related variants. These findings conform to the predictions of martensite theory and their implications are discussed in terms of shear compensation and reduction in overall strain energy.     

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.     

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.     

Scanning Electron Microscopy and Transmission Electron Microscopy Study of Ferroelectric Domains in Doped BaTiO3

This paper describes the results of detailed studies carried out on Ca-doped and Nb-doped BaTiO₃ using scanning electron microscopy and transmission electron microscopy. The techniques used were topographical contrast, selected-area diffraction, and microdiffraction Kikuchi pattern analysis. By these methods it was possible to unambiguously identify the different types of domain boundaries. Also, evidence was obtained for the existence of an unconventional 90% domain boundary which has not previously been reported.     

Surface Defects in Polished Silicon Studied by Cross-Sectional Transmission Electron Microscopy

The cross-sectional TEM technique is applied to Si(100) surfaces, which are exposed to mild polishing with diamond paste in the 0.25- to 6-μm-size range as well as with the commercial polishing medium Syton HT 50. Syton polishing is also used to prepare electron-transparent foils for TEM studies, and this preparation technique shows several advantages over ion thinning. Mild diamond polishing results in small-scale abrasive grooving and production of superficial dislocation loops of 1/2〈110〉{111} type. Debris of amorphous material tends to aggregate in surface cavities. These aggregates are formed during polishing, not by ion milling. Syton polishing results in very smooth surfaces, with no signs of abrasive grooving or dislocation density. Two major mechanisms of mass removal are suggested: (1) "smearing" of very superficial material at a nearly atomic level, resulting in amorphous aggregates and (2) strongly localized plastic cutting or shearing. In mild polishing, both mechanisms are suggested to be active, localized plastic cuttinglshearing becoming progressively more dominant for increasing particle size.     

Contact Damage in Single-Crystalline Silicon Investigated by Cross-Sectional Transmission Electron Microscopy

Cross-sectional transmission electron microscopy (TEM) is demonstrated as a powerful tool for investigating subsurface damage in the micrometer and submicrometer ranges in brittle materials, and applications to a wide variety of contact damage in silicon are discussed and illustrated with TEM images. Regions of plasticity and different types of cracking are identified and characterized for various contact situations: indentation, scribing, solid-particle impacts, and polishing/grinding. Most single-point contact situations result in similar types of damage in silicon, although transitions between different damage mechanisms occur between different load levels. Normally, the crack geometry is governed by the principal stress directions and is only weakly influenced by the lattice orientation. Grinding with metal-bonded abrasives results in fairly deep subsurface damage zones, but the main mode of material removal is superficial lateral cracking. Polishing with small-size free abrasives results in very superficial damage zones and mirror-like surface finish.     

Transmission Electron Microscopy and X-Ray Diffraction of Doped Tricalcium Silicate

Member of oxides, including MgO, ZnO, La₂O₃, Al₂O₃, TiO₂, and F were reacted with C₃S, either individually or in combination, in order to stabilize a variety of polymorphic forms. The resultant phases were examined by both XRD and TEM. It was found that the results obtained by the conventional means of observing groups of reflections in powder X-ray diffraction patterns were not in agreement with the structure types identified by electron diffraction. In particular, the rhombohedral form of alite, synthesized by the addition of either ZnO or Al₂ O₃+ F to C₃S, was not observed by TEM although the corresponding X-ray patterns all displayed single peaks characteristic of the rhombohedral cell. Electron diffraction of C,S doped with 2.02 and 4.43% ZnO gave mono-clinic patterns, whereas C₃S doped with Al + F gave several forms, all of them different from the form produced by ZnO-doped C₃S. The addition of La₂0₃ produced a new hexagonal lattice with cell dimensions of a = 2.575 and c = 2.50 nm. When Al + F was incorporated in C₃S, the modifications found included the triclinic lattice characteristic of pure C₃S, the hexagonal lattice characteristic of La-doped C₃S, and a complex lattice distinguished by the presence of incommensurate doublet reflections and sometimes extra weak spots. A similar incommensurate superlattice was found in alites containing Mg, Al, and a large amount of Ti (0.13 mole). The Jeffery cell for the Mm modification of C₃S doped with 1.63% MgO was confirmed.