TUM: Lechner
UofA: Meldrum, Hegmann
Students: Matthias Krinninger

Abstract:

Understanding the behaviour of metal clusters on various oxides surfaces on the atomic scale is of utmost importance for a wide range of applications reaching from heterogeneous catalysis and sensing to energy storage and conversion. In this project, we will use near-ambient pressure scanning tunnelling microscopy (NAP-STM) with video-rate scan speed to observe the dynamic structural fluxionality of clusters and support roughening / morphology as a function of various parameters including the ambience composition and pressure as well as temperature. For cluster generation, an established laser-ablation as well as a new magnetron-sputtering cluster source will be used.

We will focus on Pt clusters supported by thin silica films which are grown on different substrates. Monitoring the cluster shape by NAP-STM will allow us to study the influence of cluster charge state on its stability and activity during a catalytic reaction. It is well-known that the catalytic activity of a cluster changes with its charge state, but the effect is difficult to explore experimentally without changing the particle-support interface. We propose to tackle this challenge by growing chemically identical amorphous silica films on differently doped substrates. Preliminary NAP-XPS experiments have shown that Pt clusters on the native oxide of n-type Si are oxidized in O₂, while the same clusters on the native oxide on p-type Si are unaffected under the same conditions, implying that they exhibit a different charge state on the two supports. We will investigate the effect of cluster charge state on oxidation reactions, e.g. the NH₃ oxidation. By comparing different size clusters, we will study whether certain sizes accommodate more charge and how this influences their fluxionality and consequently catalytic activity.