Cr2O3 layer inhibits agglomeration of phosphine-protected Au9 clusters on TiO2 films

Effect of TiO2 Film Thickness on the Stability of Au9 Clusters with a CrOx Layer

Radio frequency (RF) magnetron sputtering allows the fabrication of TiO₂ films with high purity, reliable control of film thickness, and uniform morphology. In the present study, the change in surface roughness upon heating two different thicknesses of RF sputter-deposited TiO₂ films was investigated. As a measure of the process of the change in surface morphology, chemically -synthesised phosphine-protected Au₉ clusters covered by a photodeposited CrO_x layer were used as a probe. Subsequent to the deposition of the Au₉ clusters and the CrO_x layer, samples were heated to 200 ℃ to remove the triphenylphosphine ligands from the Au₉ cluster. After heating, the thick TiO₂ film was found to be mobile, in contrast to the thin TiO₂ film. The influence of the mobility of the TiO₂ films on the Au₉ clusters was investigated with X-ray photoelectron spectroscopy. It was found that the high mobility of the thick TiO₂ film after heating leads to a significant agglomeration of the Au₉ clusters, even when protected by the CrO_x layer. The thin TiO₂ film has a much lower mobility when being heated, resulting in only minor agglomeration of the Au₉ clusters covered with the CrO_x layer.

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis

Atomically precise gold clusters are highly desirable due to their well-defined structure which allows the study of structure-property relationships. In addition, they have potential in technological applications such as nanoscale catalysis. The structural, chemical, electronic, and optical properties of ligated gold clusters are strongly defined by the metal-ligand interaction and type of ligands. This critical feature renders gold-phosphine clusters unique and distinct from other ligand-protected gold clusters. The use of multidentate phosphines enables preparation of varying core sizes and exotic structures beyond regular polyhedrons. Weak gold-phosphorous (Au-P) bonding is advantageous for ligand exchange and removal for specific applications, such as catalysis, without agglomeration. The aim of this review is to provide a unified view of gold-phosphine clusters and to present an in-depth discussion on recent advances and key developments for these clusters. This review features the unique chemistry, structural, electronic, and optical properties of gold-phosphine clusters. Advanced characterization techniques, including synchrotron-based spectroscopy, have unraveled substantial effects of Au-P interaction on the composition-, structure-, and size-dependent properties. State-of-the-art theoretical calculations that reveal insights into experimental findings are also discussed. Finally, a discussion of the application of gold-phosphine clusters in catalysis is presented.