講座內容：Clusters and nanoparticles occupy special places in fundamental research and practical applications. To understand the properties of functional nano-structures, it is essential to gain full knowledge of their three-dimensional atomic structures. However, this is still a challenging task for clusters and nanoparticles. In this talk, the current status of cluster structure research will be briefly reviewed, together with what an aberration-corrected scanning transmission electron microscopy (STEM) can offer in this area. The STEM capabilities will be illustrated by examples from our recent research in nano-catalysis and nano-optics: (1) counting gold atom by atom; and (2) seeing below surfaces. In both cases, direct evidence of atomistic details at surface, subsurface and interfaces will be presented and the size-dependent effects and their mechanistic origins will be discussed with computer modeling results. The possibility of linking the atomic structures of nanoclusters with their enhanced catalytic properties or novel optical properties will be discussed.