Atomic-Resolution Scanning Transmission Electron Microscopy with Segmented Annular All Field Detector

Aberration-corrected scanning transmission electron microscopy (STEM) has become an indispensable tool for characterizing atomic-scale structure in materials and devices. In STEM, a finely focused electron probe is scanned across the specimen and transmitted and/or scattered electrons from a localized material volume are detected by the post specimen detector(s) as a function of raster position. By controlling the detector geometry, we have a lot of flexibility in determining the contrast characteristics of STEM images and the formation mechanisms involved. We have developed an area detector which we refer to as the “Segmented Annular All Field (SAAF)” detector and which is capable of atomic-resolution STEM imaging [1]. This area detector can obtain 16 simultaneous atomicresolution STEM images which are sensitive to the spatial distribution of scattered electrons on the detector plane [1]. The angle range can be easily controlled by changing camera length settings. In addition, we have a rotation capability for this detector, and thus we can precisely align the orientation of the detector relative to the crystallographic orientation of the specimen. The detector is easy to operate, and we have shown that the signals from individual segments can readily be combined to synthesize the signal corresponding to standard annular detectors, such as annular dark field. After this initial success, the second generation SAAF detector for the state-of-the art STEM is now being developed.