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Dynamics and Interactions of Organic Molecules Bound to the Cu(111) Surface


The progress of modern technology is dominated by shrinking component size (with a goal of reaching angstrom scale resolution), particularly with respect to electronics and optimization of common industrial processes such as heterogeneous catalysis. Understanding of such systems lies at the upper end of applicability for first-principles calculations and existing theoretical models, and a scientific framework is needed to understand, predict, and control these systems at the molecular level. My research has focused on organic molecules adsorbed on a Cu(111) surface as model systems, studied experimentally by means of scanning tunneling microscopy (STM) as well as theoretically by density functional theory (DFT) and development of simplified explanatory models. Results of this investigation show that: 1) on Cu (111) full mono-layer coverages of acetylene undergo long-range ordering which at short-range is driven by a need to minimize localized stress induced in the upper substrate layers by adsorption while at longer ranges DFT finds an oscillatory interaction that correlates well with the surface state, 2) long-range ordered networks of anthraquinone (AQ) are found to mold the surface state into optimized quantum dots - this need for optimization under the constraint that neighbors must form H-bonds drives formation of the network at the precise size and shape observed in STM, 3) CO molecules co-adsorbed into the AQ network's pores titrate the surface state quantum dots and experience increased mobility, 4) the adsorption of anthracene modified with chalcogen linkers onto Cu (111) when viewed within a molecular orbital theory framework yields a chemical explanation for the diffusion behavior observed in STM. In combination, these observations and derived explanatory models help to characterize and quantify the fundamental physics underlying the interactions of adsorbates with one another and with the Cu (111) substrate, in a broader context acting as a model for other confined surface systems where the same kinds of interactions play a dominant role.

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