Nanocluster Deposition Dynamics and Model Catalyst Preparation.

The experiments described on this page take advantage of our phase-space-compressed ion beam deposition instrument. Phase-space compression is critical to these experiments because it allows us to focus the low intensity cluster ion beam to a small spot even at low deposition energies. The instrument design is shown below.

The problems: We are interested in two related problems, but we have to understand the first in order to address the second.
1. Cluster-surface impact dynamics: Ion impacts on surfaces are important in a variety of physical deposition techniques used to grow films and coatings, and in plasma etching and other materials processing methods. Impacts at energies below 1 keV are not very well understood, and cluster ion impacts are an even less understood subset of low energy ion impacts. Such low energy cluster impacts are important in sputter coating, cluster beam deposition methods, and possibly for novel nano-materials preparation schemes. The issues of interest are characterizing behavior such as sticking, fragmenation, penetration (implantation), and impact-driven reactions, and how these behaviors depend on cluster size, energy, mass ratios, etc. It is reasonable to expect that by controlling impact properties, novel surface structures can be prepared, expected to have applications in nanoscale materials, films, and catalysis.
2. Mono-disperse, size- and energy-selected catalysts: Most catalysts are composed of small metal clusters, dispersed on a support material. With traditional catalyst preparation tools, a distribution of cluster sizes is produced, and shifting this size distribution is one of the tools used to optimize catalyst performance. Many studies have shown that the size of the clusters can have a dramatic effect on catalytic chemistry. Note, however, that studying size effecs is complicated by the size distribution, and by the fact that controlling cluster size usually involves varying catalyst parameters such as metal loading, preparation conditions, etc. that may independently affect activity. With size-selected cluster deposition, we can vary cluster size, metal loading, impact energy, support preparation, etc. independently, to unravel the interelated effects.

Techniques: Deposition of size-, composition-, and energy-selected nanocluster ions on well characterized surfaces in ultra-high vacuum. The instrument is equipped with in situ X-ray photoelectron spectroscopy (XPS) to measure oxidation states, Auger electron spectroscopy (AES) to characterize the surface, Ion scattering spectroscopy (ISS) to probe cluster/support morphology, and temperature-programmed desorption/reaction (TPD/R) to characterize chemical properties of the surface, and the usual surface cleaning/annealing/preparation tools. We recently added a fourier transform IR reflection-absorption spectroscopy (IRAS) setup