We have developed the capability to elucidate interfacial reaction dynamics using an arguably unique combination of supersonic molecular beams combined with in situ STM and AFM visualization.  These capabilities have been implemented in order to reveal the complex spatio-temporal correlations that govern heterogeneous reactions at their most fundamental level spanning atomic, nano, and meso length-scales.  For example, time-lapse visualization of reacting interfaces is allowing us to probe the reactivity of specific sites at interfaces and how the presence of a reacted site or local region influences the subsequent reaction probability at proximal sites. Such correlations are important in chemisorption, catalysis, materials oxidation and erosion, and film processing. This capability also opens up a new view for interfacial reaction dynamics where incident beam kinetic energy and angle of incidence can be used for reaction control parameters with outcomes such as site-specific reactivity, changes for overall time-evolving mechanisms, and where the on-surface fate of chemisorbed species can be definitively ascertained. In this work the time-evolving interface can be probed either in real-time or, for reactions occurring under extreme thermal conditions, using time-lapse sequential imagery. This presentation will give illustrative examples from our recent work on the atomic and multiscale oxidative reactivity of HOPG graphite, the energetic oxidation of GaAs(100), H reactivity with SAMs, and the energy disposal and geometric endpoint for molecular nitrogen chemisorption on Ru.  The nitrogen experiment provides a new approach for assessing the importance of adiabatic vs. non-adiabatic interactions in dissociative chemisorption by examining the rate of energy disposal and ultimate atomic resting adsorption sites for the dissociatively adsorbed atoms from each individual molecular scattering event.  The results provide a direct and information-rich complement to traditional gas-surface scattering experiments which monitor volatile products, especially with respect to uncovering the important multiscale spatio-temporal correlations that influence interfacial reaction pathways.

Spatio-temporal correlations in interfacial reaction dynamics elucidated via the combination of energetic supersonic molecular beams with in situ STM/AFM visualization

ACS Spring 2022

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