Discerning single atoms on TiO₂ nanoplatelets using STEM-based atomically-resolved secondary electron techniques

Single-atom catalysts (SACs) play a crucial role in heterogeneous catalysis due to their efficient atomic utilization and unique catalytic properties. Despite significant progress in SAC synthesis and application, accurately identifying SACs surface features at the atomic scale remains challenging. This study employs a state-of-the-art approach combining atom-resolved secondary electron (SE) and annular dark-field (ADF) imaging using a probe-corrected scanning transmission electron microscope (STEM) to investigate single vanadium (V) and tungsten (W) atoms immobilized on TiO₂ nanoplatelets. Our results demonstrate that both V and W atoms are clearly visible in SE images, while only W atoms are detectable in ADF images. These findings demonstrate that SE imaging offers distinct Å-scale height contrast and atomic mass contrast for supported single atoms, greatly complementing current STEM imaging techniques in identifying surface features of nanomaterials. The combined use of ADF and SE imaging techniques enables precise identification and differentiation of supported heteroatoms, providing valuable insights into their surface topography and elemental contrast. This research highlights the utility of advanced imaging techniques in studying single-atom catalysts, thereby supporting innovations in catalyst design and application.