The 2D-scale study of relevant biomolecules, like amino acids, is pertinent for a variety of applications from the origin of biological homochirality and the amplification of surface chirality to the examination of noncovalent supramolecular interactions. The need for pristine molecular resolution of these systems requires the use of ultra-high vacuum scanning tunneling microscopy (UHV STM) in the initial characterization of the systems. Importantly, it is also possible to study the assembly of these molecules with liquid or in situ STM in an attempt to bridge the temperature and pressure gap of ultra-high vacuum studies. In this way, these amino acid systems can be studied at more relevant conditions, and solvent choices can be made to mimic biological environments. Through the examination of the self-assembly behavior of five amino acid molecules on a Cu(111) single crystal in UHV, an unexpected phenomenon was discovered. All of the amino acids assisted in the immobilization of copper atoms on the surface. The energetic landscape of the surface as mediated by temperature and molecular coverage facilitated the growth of copper islands and clusters. The growth and size fluctuation of the islands offered an interesting snapshot of metal nanocluster diffusion that often occurs at time scales beyond the resolution of a given surface science technique. The presence of ~1 ML of molecules on the surface effectively trapped the metal atoms into localized islands. Elevated temperature were used to promote further diffusion, coalescence, and extinction of the islands. In conclusion, while these systems provide insights into the chiral assembly of amino acids as studied in both UHV and in liquid, they also provide a unique glimpse into metal surface diffusion and offer the ability to study the mass transport of metal atoms, which is important for the understanding of thin film growth and its morphological evolution.

Amino acids on metals: Chiral assembly and dynamic restructuring of copper surface

247th National Meeting (2014)

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