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

Abstract

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.

Metal Clusters on Semiconductor Surfaces and Application in Catalysis with a Focus on Au and Ru

“…These images are shown in Figure . One structure was 3D and was attributed to clusters which were still ligand‐stabilized, while the other two were unique deligated pseudo‐2D structures demonstrating the fluxionality of the cluster . Larger clusters can exhibit fluxionality with a larger input of energy; this has been shown experimentally for Au 38 , where several structural changes were observed upon repeated measurements of the same cluster also using HAADF‐STEM.…”

“…Another commonly used ligand is thiolates (SR), which can be used to stabilize clusters of a large range of sizes . While we mostly focus on carbonyls and thiolates as common exemplars, there are many other types of ligands which can stabilize clusters including triphenylphosphine (PPh 3 ),20,25a,29 and glutathione (GSH),1i,30 which have been used to stabilize gold clusters among others.…”

“…In this case, even the internal surfaces of a porous support can be coated with clusters. For a crystal wafer support, this would be immersed in the solution for a prechosen time period 20,29c,e,f. A variant on this method is to drop cast the cluster solution onto the wafer and wait for the solvent to evaporate 18,29f.…”

“…Images I, III, and IV are DFT models for three matching isomers of Au 9 . Reproduced with permission . Copyright 2016, AIP Publishing.…”

“…The latter is limiting in photocatalytical processes. TiO 2 comes in a variety of different forms which can affect the end properties of the system 20,24,29a,d,e,g. Single crystal TiO 2 is well characterized for all the crystal phases of titania; rutile, anatase, and brookite, and is therefore used when uniform and well‐characterized supports are required 4d,29b,c,116.…”