The recent revival of techniques for the imaging of crystal surfaces, using electrons forward-scattered in the RHEED mode and employing modern electron microscopes, has lead to the introduction of valuable new methods for the study of surface structure. Either fixed beam or scanning transmission electron microscopy (STEM) instruments may be used and in each case a lateral resolution of 10Å or better is possible. Simple theoretical treatments suggest that the contrast from surface steps may be attributed to a combination of phase-contrast, diffraction contrast and geometric effects. With a STEM instrument the image information can be combined with information on the local composition and crystal structure by use of microanalysis and microdiffraction techniques. Examples of applications include studies of the surface structure of metals, semiconductors and oxides, and the surface reactions.

A high resolution electron microscope investigation of the residual oxidized silver of a few monolayers thickness on the surface of (111) Au films has shown that a reconstructed (2×1) surface structure occurs for (110) oriented Ag2O and can be observed at atomic resolution levels. Image enhancement via a digital frame store processor has revealed improved images which have then been compared to computer simulated diffraction patterns and images of the Ag2O surface. Several iterations of surface structure models and image simulations reveal that the (2×1) reconstruction is consistent with a missing row model. The atomic arrangements of these rows often undergo a translation along the direction of the row to produce cusp like image features. It has also been possible to observe the effect of contraction of the underlying layer which can produce diagonal contrast lines in the images. These features often vary rapidly over lateral distances of a few tens of angstroms and give an indication of the surface topography and the degree ordering of the surface.

Amorphous silicide films can be formed by rapid quenching using techniques of vapor deposition and ion beam mixing and also by slow heating using solid state interdiffusion and reaction. For example, amorphous TaSi2 films can be formed by sputtering or dual electron guns co-deposition. Amorphous Pt2Si3 films have been produced by mixing PtSi and Si at room temperature with an ion beam at about 100 to 300keV. Recently, an amorphous Rh-Si alloy phase has been made by slowly heating to 300°C a very thin crystalline Rh films (∼50Å) on amorphous Si. The formation and crystallization behavior of these amorphous silicide alloys has been studied by transmission electron microscopy and electrical conductivity measurement.

Experimental observation of many interfaces in metals indicate the presence of a dislocation-like structure. The geometrical basis for such a structure to exist is discussed, and the suitability of the transmission electron microscope (TEM) to characterise it considered. It is shown by reference to examples of grain and phase boundary structures in metals that such geometrical models may be used as a first step to predicting interfacial structures, and that the dislocations observed may play a role in thermo-mechanical behaviour of polycrystals. The general applicability of the applicability of the approach to non-metallic systems, such as semiconductors and ceramics is also indicated.

Interface migration is the fundamental process in numerous phase transformations. For those which are thermally activated the basic event is addition of atoms to a defect in an interface. Interfacial defects can have a range of topographic and elastic characteristics which complicates investigations by transmission electron microscopy, it is difficult to make quantitative in-situstudies of interface migration because of problems of resolution and control of driving forces in specimens where surface effects dominate.

The crystalline structure of small gold particles in the size range between 50–200 Å is studied using STEM in microdiffraction.

It is found that some single-crystalline particles showed an anomalous diffraction pattern. In some cases these pattern be indexed as an hexagonal lattice with a ratio c/a= 2.46. A number of models to explain the hexagonal diffraction are discussed. In some other cases the patterns correspond to fcc structures but with a large splitting effect. The results reveal the strong dynamical character of the diffraction by small gold particles.

The growth of CU2-xS in the (0001) basal face of single crystal cadmium sulfide has been studied with high resolution transmission electron microscopy (HRTEM) and diffraction. Cross-sectional Cu2-xS/CdS specimens and plan-view Cu2-xS separated films were prepared from heterojunctions formed by the aqueous conversion of CdS to topotaxial Cu2-xS. Low chalcocite films were found to form in two principal stages; 1) coalescence of low chalcocite islands and 2) an accelerated reaction localized at pores in the Cu2-xS film. Several possible misfit accommodation mechanisms involving twinning, cracking, and a second copper sulfide phase were identified.

A variety of bcc and hexagonal metals have been deposited onto fcc(001) surfaces held at between 150 and 350°C. The epitaxial relationships developed between deposit and fcc substrate have been investigated , and the application of current theories of the energy of interphase boundaries to explaining these results is critically discussed.

The LPCVD of polysilicon on oxidized silicon wafers sometimes results in defective material having a “hazed” appearance. Examination of this material by SEM has revealed surface nodules which correlate on a one-to-one basis with anomalously large silicon grains, observed by transmission microscopy. Darkfield microscopy has shown that this abnormal grain growth initiated during deposition. X-ray EDS analysis of isolated poly-Si nodules revealed the presence of metallic impurities.

The formation of misfit dislocations in the interface between the metallic and insulating phases which occur in 1.2% Cr doped V203 near room temperature was confirmed by TEM. Orientations of Burgers vectors of misfit dislocations were determined by the weak beam technique. The Burger vectors were parallel to principal axes in the basal plane (<100>) and inclined somewhat to interfaces. The Burgers vectors of misfit dislocations are, however, close enough to the direction of the maximum misfit in the interface. Only one or two misfit dislocations appear in an interface regardless of the thickness of specimens, and these were always located near the surface.

The structure of different grain boundaries and phase boundaries are discussed by reference to a series of specific examples. The chosen examples of grain boundaries include the <l10>{l10} tilt boundary, the (001) twist boundary and the first-order twin boundary in spinel and the basal twin and the (1123) twin in Al2O3 . The phase boundaries discussed are the β'''-alumina/spinel interface, the wustite/spinel interface and the spinel/alumina interface. It is shown that these interfaces do have properties which result specifically from the ionic nature of the material and the large unit cells involved in each case.

High resolution microscopy of ceramics has its specific problems due to the difficulties in preparing thin foils. Most of these Problems however can be overcome and recent years a lot of effort has been concentrated on electron microscopy of ceramics because of their high technological importance. Some results on important ceramics such as SiC, Mg-Si-O, ZrO2 -ZrN and Si-Al-O-N obtained by high resolution microscopy will be briefly discussed here.

The defect structures of Fe9S10 have been studied by high-resolution transmission electron microscopy. Lattice images of the 3C and 4C superstructures and at least one other phase, which has not been previously reported, were observed. It has been found that the 4C superstructure transforms into the 3C superstructure rather than the MC phase as previously suggested. Intrinsic stacking faults in the sulfur sublattice and two different types of vacancy-ordering antiphase domains were also observed. Evidence from optical diffratograms of areas containing these defects suggests that complex features in the electron diffraction pattern may be artifactual.

Dissociation of both basal and prism plane dislocations in sapphire,α−Al2O3,is common and the partial dislocations can be imaged using conventional transmission electron microscopy and weak beam dark field imaging techniques. At elevated temperatures the dissociation takes place by conservative self-climb, a process involving short range diffusion, whereas at low temperatures the dissociation can occur by glide. Dissociation of a dislocation can in some situations give rise to very strong contrast when using g vectors for which g→.b→=0 for the undissociated dislocation. Those contrast conditions can be used to obtain information about the dislocation morphology and the stacking fault energy of the fault plane through determination of the separation distance.

Grain boundaries in ZrO2-containing alumina, ZrO2, and in Ni1−yO (containing different impurities) were investigated by TEM including analytical studies. Quite frequently, interphases exist at the boundaries. The interphases are composed mainly by impurities present in the materials. The “width” of boundaries in Ni1-yO depends on intrinsic defects as well as on impurities; the dependency will be discussed. The observations are related to properties of the different ceramics.

Fault structures occurring in crystalline CVD silicon nitride deposits have been examined using transmission electron microscopy. A variety of mixed rotation and displacement faults are observed. The faults have extensive basal plane facets but also extend onto other planes within the grains. Possible structures for the faults are discussed with reference fo the structures of the a and P silicon nitride polymorphs.

High resolution transmission electron microscopy (HRTEM) has been used to study structures found in secondphase particles in commercial alumina compacts. Analytical electron microscopy has been used to identify elements present in the particles. Computer image simulation has been used for both the structural interpretation of high resolution images and predicting the effect which the presence of other elements would have on the observed structures.

The primary objective of this research was to deduce the mechanisms of the γ to α transformation of Al2O3. The specimens studied were from spherical powder precipitated from sulfate solutions and thin films prepared by low temperature oxidation of Al. The primary experimental technique employed was the transmission electron microscope. Since alumina is so important commercially, there is a body of literature on both the mechanism and kinetics of the transformation. A brief review of the most relevant publications is thus essential.

Measurements of the equilibrium electrical conductivity of Ca-doped BaTiO3 indicate a highly acceptor-doped behavior when y > 1 in the general formula (Ba1−xCaxO)yTiO2. It has been suggested that when there is an excess of alkaline earth oxides, some Ca++ occupies Ti-sites, where it acts as a doubly charged acceptor, CaTi''. This possibility has been checked with a recently developed technique for determining the crystallographic site occupancy of impurity atoms. Known as ALCHEMI (Atom Location Using Channeling-Enhanced Microanalysis), the technique relies on the dependence of the characteristic X-ray emission on the incident electron beam direction. A significant channeling effect was observed for slightly positive and negative excitations of the [100] reflection. The results indicate that for the composition (Ba0, 85Ca0.15O)1.02TiO2.00, a substantial fraction of the total calcium (> 20%) occupies Ti sites.

In the past the application of electron microscopy to cement hydration has been limited largely to the study of fracture surfaces in SEM, of ground cement in TEM and of polished sections in EMPA. Consequently the microstructure of bulk cement pastes is, as yet, ambiguous.

The present work shows how techniques not previously used in the study of cement, an environmental cell on HVEM, preparation of ion beam thinned foils for STEM and BEI of polished surfaces in SEM, can give a more detailed view of the development of morphology in hydrating cement. Using a combination of electron optical techniques together with other methods a detailed characterisation of cement hydration can be made.