Surface Chemistry Studies with Cluster Ion Beams

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Nicholas Winograd and his group at Pennsylvania State University focus on elucidating the fundamental aspects of the interaction of energetic particles with solids, with the goal of advancing the utility of secondary ion mass spectrometry (SIMS) experiments. Results from this research should find materials characterization applications in such diverse fields as polymer science, astrophysics, drug discovery, organic electronics, organic photovoltaics and molecule-specific imaging. The emergence of cluster ion sources such as C60 has opened unique opportunities in molecular depth profiling. In this situation, the layers of a molecular solid are removed by the cluster source without significant accumulation of chemical damage and with a depth resolution of less than 10 nm. This modality offers the possibility of interrogating buried interfaces with unprecedented spatial resolution. Molecule-specific imaging is another unique feature of SIMS, and when combined with molecular depth profiling, yields a 3-dimensional rendering of the chemistry. Protocols for optimizing these experiments will be developed from predictions of computer simulations of the cluster bombardment event, and by performing experiments on model systems where a number of parameters, such as projectile energy and angle, can be systematically examined. A special emphasis is placed upon characterizing gas cluster ion beams that now produce argon clusters with more than 2000 atoms, and on searching for new H-containing species that may enhance ionization through dynamically created pre-formed ions. The ultimate goal, then, is to acquire a fundamental understanding of cluster-solid interactions and to provide a new mass spectrometry-based 3-dimensional imaging protocol that operates on the nanoscale. This new methodology should find valuable applications to a wide range of biologists and material scientists for characterization purposes. The project will include participation of three graduate students who will develop novel instrumentation for imaging and for cluster ion beams. They will acquire skills that are designed to be valuable assets in their post-graduate careers. Throughout this effort, dual emphasis is placed upon acquiring a fundamental understanding of ion-solid interactions, and of utilizing this information to advance the applications. This philosophy lends a synergism to the program and provides a unique learning experience for those involved. International collaboration and outreaching to high school students through the SEECoS program are also proposed.