Defect/surface interactions in heat-treated ceramic thin films
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The use of transmission electron microscopy to study the interaction of lattice defects with surfaces of heat-treated ceramic materials is discussed. The approach used throughout the work described has been to prepare a thinned sample in a form suitable for imaging in the electron microscope and then to remove all preparation-induced damage by heat-treating the thinned sample. Applications of the technique to the movement and pinning of individual surface steps in alumina and the grooving of antiphase boundaries in silicon carbide are illustrated. I. INTRODUCTION Surface structures and surface properties can affect the usefulness of a range of ceramic materials including bulk, sintered compacts and thin ceramic films. Considerations that are particularly important are (a) surface diffusion, mass transport, and the sintering process; (b) catalysis; (c) bonding and adhesion; (d) corrosion and chemical reactions at surfaces; (e) crystal growth and evaporation; (f) interface structures and epitaxy; (g) crystallographic anisotropy of surface properties; (h) thermal grooving, etc. Although the need for monitoring surface structures and other surface phenomena is recognized, information recorded from ceramic surfaces is very limited.1 A large fraction of the surface data now available to the ceramist has been recorded from structures that were prepared in ultra-high vacuum (UHV) and which are therefore considered intrinsic surface structures. For example, low-energy electron diffraction (LEED) studies, which are necessarily conducted on planar specimens in UHV, have reported that the (\/31 x V^I) R9° periodicity for the (0001) CK-AI2O3 surface may be considered an intrinsic surface structure above —1500 °C. 2 However, most presentday applications of ceramics do not require that the material be processed in a UHV environment. Surface information obtained under experimental conditions that more closely resemble those encountered during typical ceramics processing treatments is particularly lacking. This latter category of ceramic surfaces would be considered "dirty" in the strict surface-science sense.3 In addition to an uncertain degree of surface cleanliness, real ceramic surfaces are not simply planar terraces but, rather, are stepped.4 Furthermore, steps are sites for active catalysis and defects at which nucleation may occur. The intersections of dislocations with surfaces are growth sites for synthetic ceramic materials. Thus, the ^Present address: Analytical Sciences Laboratory, The Dow Chemical Company, Midland, Michigan 48667. b>Address correspondence to this author, Dept. Chem. E. & Mat. S., University of Minnesota, Minneapolis, Minnesota 55455-0132. J. Mater. Res., Vol. 6, No. 11, Nov 1991 http://journals.cambridge.org
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interactions between surface defects are of interest in the field of crystal growth. The need for an experimental technique tailored to examine the detailed structure of real ceramic surfaces is therefore apparent. Thin ceramic films can now be produced with crystalline su
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