Associate Professor, Institute of Engineering Innovation, The University of Tokyo
Understanding the atomic-scale structures of surfaces and interfaces is essential to control the functional properties of many materials and devices. Recent advances in aberration-corrected scanning transmission electron microscopy (STEM) have made possible the direct characterization of localized atomic structures in materials, especially at interfaces.
In STEM, a finely focused electron probe is scanned across the specimen and the transmitted and/or scattered electrons from a localized volume of the material are detected by the post-specimen detector(s) as a function of raster position. By controlling the detector geometry, we gain flexibility in determining the contrast characteristics of the STEM images and the formation mechanisms involved. Thus, it may be possible to obtain further useful information by exploring new detector geometries in atomic-resolution STEM. From 2006, we have been developing a segmented-type STEM detector capable of atomic-resolution imaging and proposed new imaging possibilities by controlling detector geometries: annular bright-field (ABF) imaging and atomic-resolution differential phase contrast (DPC) imaging. ABF-STEM imaging enables us to directly visualize light element atomic columns of materials. DPC-STEM imaging can be used to detect local electric fields inside materials and devices. We applied DPC imaging to atomic resolution STEM and succeeded in directly observing electric field distribution inside atoms for the first time. This new imaging capability should assist our fundamental understanding of the origins of properties in materials and devices.
Fig.1) Experimental atomic electric field imaging of a BaTiO3 single crystal using atomic-resolution differential phase contrast STEM.