For twenty years now scanning probe microscopy has been used to manipulate atoms and molecules to assemble structures on surfaces.  When the manipulations are performed using non-contact atomic force microscopy (AFM), the forces and energy barriers encountered as the structures are assembled can be obtained.  In principle, such measurements yield the potential energy surfaces adsorbed molecules see as they diffuse across the surface and encounter other molecules including potential reaction partners.  Thus it becomes possible to quantify key steps in catalysis based on direct measurements on individual molecules.  We have been studying benzene on Cu(100) and  iodobenzene and benzyl radicals on Pt(111) as initial steps in this direction.   Experimental results for bezene on Cu(100) indicate that the the molecules were either pushed, pulled, jumped to the tip, or did not move depending on the chemical surroundings of the molecules and the chemical identity of the tip.  For the case of weakly interacting benzene with Cu(100), tip-molecule interaction forces acting perpendicular to the surface dominate resulting in an under-estimate of the molecular diffusion barrier on the surface.  Computational results obtained using a Bayesian Optimization Structure Search protocol also reveals that the measured diffusion barrier evolves with the chemical identity of the tip as well as the environment surrounding the molecule.  The theory suggests approaches to minimizing the impact of the tip on the measurements.  To gain insight into systems where catalytic reactions come into play, results for interactions of iodobenzene and benzyl radicals with Pt(111) and one another on teh Pt surface will also be presented.

Using atomic force microscopy to trace the potential energy surfaces of adsorbed molecules and reaction intermediates

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.