Analytical and High-Resolution Electron Microscopy Studies at Metal/Ceramic Interfaces

Both analytical electron microscopy and high-resolution electron microscopy are widely used to investigate the structure of and defects in materials. The spatial resolution of the analytical electron microscope (AEM) is < 5 nm and the point-to-point resolution of the high-resolution electron microscope (HREM) is small enough to image lattice planes in metals and ceramics directly. AEM and HREM are described in this paper with special emphasis on the study of interfaces between single crystal Nb-films grown by molecular beam epitaxy (MBE) on (0001) planes of sapphire (Al2O3)-substrates. From these specimens, cross-sectional specimens with thickness < 20 nm were prepared, so that the Nb/Al2O3-interface could be investigated by AEM and HREM. AEM studies revealed that Al2O3 was dissolved by the Nb so that Al could be detected in the Nb adjacent to the interface. The atomistic structure of the interface was identified by HREM. Defects at or close to the interface were analyzed and a model of the atomistic arrangements of the interface in the relaxed, "perfect" regions is described with a discussion of the results.