2pm on Monday 15th February 2016 in Room 361 Physical Sciences Building
Chractrization of Au9 –nanocluster deposited on titania surfcae by using spectroscopic and microscopic techniques
PhD Student, Flinders University
In this work chemically made clusters stabilised by organic ligands (Au9), Au9 (PPh3)8(NO3)3, deposited on titania surfaces are investigated by using various surface sciences techniques to study the structures of gold clusters and the influences of titania surfaces (Figure 1). Chemical reactivity of metal clusters is determined by three main factors: (a) the size of the clusters, (b) the geometric arrangement of the atoms forming the clusters and (c) the electronic structure. Supported size specific metallic nano-clusters have emerged as superior catalysts in a few cases but, up until now, fabrication and activation of catalysts using chemically synthesised atomically precise gold clusters supported on titania is not well understood compared with gas phase gold clusters.
XPS results were combined with a high resolution scanning probe microscopy (STM and AFM) and scanning transmission electron microscopy (STEM). Aberration corrected HAADF-STEM with lower electron-beam acceleration voltages have been successfully used to resolve directly the geometric structure of the ultrasmall protected Au9 clusters deposited on titania nanosheet at atomic resolution for the first time. We compare the structures found using the STEM with DFT calculations of clusters of 9 Au atoms in the gas phase. While the influence of the substrate on the Au9 structure is missing in the DFT calculations, it is possible to classify the structures of Au9 clusters deposited on titania as found experimentally using the STEM. XP spectra are presented and the interpretation compared to the Au cluster structure found with STEM. AFM and STM observations show all the nanoclusters are highly distributed and their average size has been measured as well.