"Probing Molecular-level Organizational Structure and Electronic Decoupling of  Weakly Surface Bound Metallic Nanoparticles, Chiral Domains, and Biomolecular Species"

Mechanisms of adsorption and organization of organic molecules on metallic surfaces play a significant role in the growth of chemically and electronically tuned, monolayer thin films.  Intercommunication between functional groups for individual adsorbates can serve as the primary driving force for monolayer crystallinity as well as electronic structure especially in the limit of weak interaction between the adsorbate and substrate.  In this talk I will present a series of examples involving weakly bound surface species probed with high spatial resolution scanning tunneling microscopy and spectroscopy.  As a first example, data will be discussed regarding spectral diffusion features for ligand encapsulated Au11 nanoparticles supported and isolated on alkanethiolate monolayers.  The bulk of the work presented will involve submonolayer ordering of a chiral molecule, tartaric acid (C4H6O6), weakly bound to an achiral metal surface, Ag(111), as studied with low temperature STM and density functional theory (DFT).  Molecularly resolved images of enantiomerically pure (R, R)- and (S, S)-tartaric acid domains on Ag(111) will be presented and the role of intermolecular hydrogen bonding in stereospecific domain and superlattice formation will be addressed.  Additionally, we will consider chiral domain formation and phase separation from a racemic mixture of tartaric acid enantiomers.  Lastly we will present differential conductance mapping of tartaric acid molecular domains that highlight an intrinsic decoupling of molecular film electronic states with respect to the metallic lattice.  While the chiral expression which drives the formation of enantiomeric domains does not induce stereospecific conductance, we demonstrate electronic differentiation of submonolayer organic domains from the Ag(111) surface.  Density functional theory calculations will be discussed as they relate to both the molecular organization as well as the deconvolution of electronic structure between the molecular film and the metallic substrate.  Finally, I will also highlight recent work in our group involving the study of functionalized, single and double stranded DNA molecules anchored to both metallic and ferroelectric surfaces.