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Computer-Aided Analysis of Oriented Crystallites by Diffraction Pattern Simulation and Tilt-Stage Control in a TEM

Electron diffraction patterns taken in the transmission electron microscope (TEM) provide information about crystal structures and orientations in small sample areas. Extracting this information and manipulating local crystal orientations has become a great deal easier with the availability of desktop computer programs that allow simulation matching of experimental patterns and crystallographic control of sample tilting in the TEM. This presentation will illustrate an application of computer-aided crystallography for analyzing oriented crystallites in an experimentally complex material. The surface corrosion films that form on reactive metals such as hafnium or zirconium in hot water provided our example. Cross-sectional examinations of the corrosion films revealed a columnar microstructure of monoclinic HfO2/ZrO2 grains extending normal to the metal/corrosion-film interface.The columnar grains were only about 50 nm in width, and thus were too small to analyze individually by selected-area diffraction. Local strains in the films smeared the diffraction fine structure so there was little hope for analysis by convergent-beam diffraction methods.