High Angle Dark Field STEM for Advanced Materials

Incoherent imaging in the scanning transmission electron microscope (STEM) provides enhanced image resolution, strong Z-contrast, and the capability for direct inversion to the projected structure. It relies on the use of a high angle annular detector to average phase correlations between diffracted beams, while the coherent incident probe leads to columnar channelling in thick specimens. The Z-contrast image also provides a convenient, high intensity, reference image for atomic resolution electron energy loss spectroscopy, since incoherent imaging conditions may be established simultaneously for both signals. Recent results from a 300 kV STEM are reviewed, including the determination of dislocation core structures in compound semiconductors, distinguishing between oxygen and metal termination at a metal/ceramic interface, and resolving the atomic structure of supported catalyst clusters.