Atomically resolved structure of ligand-protected Au₉ clusters on TiO₂ nanosheets using aberration-corrected STEM

Triphenylphosphine ligand-protected Au₉ clusters deposited onto titania nanosheets show three different atomic configurations as observed by scanning transmission electron microscopy. The configurations observed are a 3-dimensional structure, corresponding to the previously proposed Au₉ core of the clusters, and two pseudo-2-dimensional (pseudo-2D) structures, newly found by this work. With the help of density functional theory (DFT) calculations, the observed pseudo-2D structures are attributed to the low energy, de-ligated structures formed through interaction with the substrate. The combination of scanning transmission electron microscopy with DFT calculations thus allows identifying whether or not the deposited Au₉ clusters have been de-ligated in the deposition process.