The Versatile Imaging Capabilities of Aberration-Corrected STEM

Abstract

The recent advancement in aberration-corrected electron microscopy, especially aberration-corrected STEM (AC-STEM), makes it possible to routinely extract atomic scale information of a variety of solid materials. With the availability of sub-angstrom size electron probes and the appropriate selection of detectors one can extract useful information on the atomic structure, chemical composition, oxidation state, and strain field of the sample of interest. The common choice of selecting high-angle scattered electrons for atomic number contrast (HAADF imaging mode) and the directly transmitted electrons for phase contrast (BF-STEM imaging mode) may pose challenges when non-ideal samples are encountered. Fortunately, many other imaging modes are available in STEM and can be utilized to provide unique, although selective, information. For example, the large-angle bright-field (LABF) imaging mode provides information complementary to those of the HAADF imaging mode, and configured detectors were proposed to manipulate the scattered signals for desired information [1-2]. The thin annular detector BF (TADBF), thin annular detector DF (TADDF), and the marginal DF-BF detector configurations all provide unique information of the sample by judiciously utilizing the variations in the electron scattering profiles of different materials [3-5]. For example, light-element materials supported on heavy-element materials, such as carbon on platinum, have been imaged [4-5]. The flexibility of incorporating different types of detectors in the STEM makes it a versatile tool.