In this project funded by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Andrew J. Gellman (Carnegie Mellon University), E. Charles H. Sykes (Tufts University) and David S. Sholl (Georgia Institute of Technology) will collaborate to develop and apply methods for high throughput study of structure sensitive surface chemistry. The core of the experimental program is the preparation, characterization and study of curved single crystal metal surfaces that expose continuous distributions of surface orientations; i.e. regions of the surface that expose different step and kink densities. Spatially resolved experimental tools such as STM, XPS, and LEIS will be used to characterize the local structures of these surfaces and to measure surface reaction kinetics at each point. This effort will resolve the role of step and kink density in several surface reactions. Complementary computational modeling tools will be used to understand the role of surface orientation in surface reaction kinetics. These methods will greatly accelerate the study of structure sensitive surface chemistry. The impact of this work will be development of a fundamental understanding of several catalytically important surface reactions. The broader impact will include outreach to high school students, exposure of undergraduates to research and the development of short videos on surface science and nanoscience for public viewing.
In many instances, when a chemical reaction occurs on a surface the reaction mechanism depends on the specific arrangement of atoms on and in the surface. Previous results in the field on these effects, which lead to the 2007 Nobel Prize in Chemistry, were only determined systematically after sequential preparation and data collection on numerous different surfaces. To improve upon this time-intensive process, we have developed a new type of substrate termed a Surface Structure Spread Single Crystal (S4C). This system allows us to study the interaction of molecules with a large distribution of atomic arrangements simultaneously in a high-throughput manner experimentally and to compare to theory. On these surfaces we have shown the rate of oxygen uptake changes depending on the arrangement of atoms. We also used these results to determine that oxygen uptake affected reactions involving methanol which is an important chemical because it can be used to make hydrogen for energy demands as well as specialty chemicals. We have also investigated the adsorption of chiral molecules (non-super imposable mirror images or "enantiomers") on surfaces. When pharmaceuticals are chiral they often need to be sold and taken in an enantiomerically pure form (one mirror image). Purity is required because enantiomers of different mirror handedness will react differently in the body even though they are physically identical. One chiral molecule, tartaric acid, undergoes a unique decomposition event that is similar to a chain reaction. We were able to follow this event on the single-molecule level and show that as the decomposition happens the molecules re-arrange the underlying surface and pull up atoms from the surface. These results have implications in: (i) general reactivity because the molecules physically remove atoms from the surface creating a more reactive complex, and (ii) in chiral chemistry, because the removed atoms are arranged in a chiral manner and offer a new opportunity to chirally template metal surfaces for chiral separations and reactions. The projects incorporating this work have led to three PhD students gaining expertise in their respective fields while allowing several MS and undergraduate students to acquire experience conducting research. The PhD students also developed writing and presentation skills as they have presented this work at various technical conferences and written several peer-reviewed journal articles. This research has also provided a platform for urban high school students to get exposure to science and nanotechnology. This was accomplished by visiting local high schools to give science presentations and do on-site demonstrations for the students. The students also visited the universities to tour the labs to see how research is conducted and to see what college life is like to ease the transition from high school to college. Our work is also available to larger audiences through YoutubeTM videos that are made by students in the lab focusing on our research. To date these videos have received > 68,000 views.
