Size Selected Nanoclusters

The ability to generate stoichiometrically controlled metal oxide clusters allows for fundamental studies of their properties. Size selected clusters of a particular mass are generated using a magnetron sputtering source. Using a combination 2 photon photoemission and surface science techniques it becomes possible to study the both the catalytic activity of small nanoclusters as well as their electronic properties. 

Specifically, particle–support interactions in catalysts can greatly affect the catalytic performance. In this project, we conduct studies on supported size-selected nanoclusters as model catalysts to understand the relationship between interfacial charge transfer and reactivity. In particular, we are interested in metal oxide clusters deposited on a metal or an ultrathin metal oxide film formed on a metal. Size selection allows us to control the stoichiometry of the clusters so that we can study the effects of the metal oxidation states in the clusters. We use two-photon photoemission (2PPE) spectroscopy to probe the work function shift arising from interfacial charge transfer, and conduct temperature-programmed desorption or reaction studies to investigate the reactivity.

  Figure 1: Schematic of the 2PPE process

Figure 1: Schematic of the 2PPE process

 We also carry out density functional theory (DFT) calculations to assist with the interpretation of our experimental results. The theory provides insight into the adsorption geometry of the cluster–support systems as well as the energetics of the reactions that occur on them. Currently, we are focused on easily reducible metal oxide clusters (e.g., NbxOy, TixOy, CexOy) deposited on Cu(111) or a thin film of Cu2O on Cu(111) and their activity toward water dissociation, which is the rate-limiting step in the industrially important water gas shift reaction.

 

    Figure 2: DFT-calculated structure of a H2O molecule adsorbed on Nb3O7 on Cu(111)

 

Figure 2: DFT-calculated structure of a H2O molecule adsorbed on Nb3O7 on Cu(111)