Towards quantitative analysis of core-shell catalyst nano-particles by aberration corrected high angle annular dark field STEM and EDX

One of the most useful and apparently straightforward attributes of annular darkfield (ADF) STEM imaging is the ability to image heavy atoms on relatively light substrates using Z-contrast (High-Angle ADF) imaging. From multislice calculations, however, some isolated heavy atoms, e.g. Re, can go undetected in a thin Co matrix in standard aberrationcorrected HAADF-STEM imaging of catalyst nanoparticles oriented accurately on a zone-axis [2]. More recently simultaneous Medium-Angle and High-Angle ADF imaging of a few layers of BN has shown experimentally that some adatoms are invisible in MAADF whilst exhibiting very strong contrast in HAADF. Simulations confirm that this can occur for atoms such as sodium. In both situations HOLZ ring imaging can be used to extract additional information.