Spatio-Temporal and Site-Specific Chemical Dynamics at Interfaces

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Chemical reactions at surfaces are everywhere, from the corrosion of metals to the fabrication of computer chips. However, compared with studying reactions in gases and solutions, chemical reactions at surfaces present unique challenges. The reactivity, for example, can depend on how fast reactant molecules collide with the surface, as well as the direction of approach. To complicate matters, surfaces are structurally imperfect at the atomic level and are littered with defects, including missing atoms, islands, and steps, each of which can react differently. Moreover, once the reaction occurs, it can shift nearby atoms around, changing the surface structure. With support from the Chemical Structure, Dynamics and Mechanism A program in the Division of Chemistry, Professor Steven J. Sibener at The University of Chicago is studying chemical reactions between highly reactive reagents such as oxygen and hydrogen atoms, as well as other energetic species, with metal and semiconductor surfaces. Working with his students, Professor Sibener directs atomic and molecular beams with known speed and direction at either bare surfaces, or surfaces decorated with molecules. The team then uses powerful microscopies capable of resolving individual atoms to monitor the reactivity at different sites, as well as how the surface structure changes in response to the reaction. Their discoveries could have broad implications for advanced materials fabrication, nanoscience, electronic materials, heterogeneous catalysis, combustion, and the design of protective coatings. The research team also participates in community outreach at local schools and museums to introduce the residents of Chicago's south-side to scientific issues that are essential for understanding our modern technological world. This program uses a combination of supersonic molecular beams, in situ scanning tunneling/atomic force microscopy, and surface spectroscopies to examine the site-specific chemical reactivity of clean and molecule decorated surfaces. Reactive scattering measurements are carried out with concurrent in situ atomic-level imaging. This program opens a direct path to understanding, with atomic resolution, spatio-temporal correlations in interfacial reactivity. It has focus on forefront issues in surface chemical dynamics that include adiabatic and non-adiabatic gas-surface interactions, atomically-resolved reactivity under non-equilibrium conditions, thin film growth and passivation, and geometry-constrained reaction studies with precise steric control over incident collision conditions. Such assessment of molecular reactivity as a function of known molecular orientation and local adsorption site is revealing remarkably detailed information on molecular reactivity and reaction potential energy surfaces suitable for quantitative comparison with theory and simulations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.