Colloquium
Spatially resolved organizational structure and electronic properties of weakly surface bound nanostructures
Dr. Thomas Pearl
Department of Physics
North Carolina State University
Thursday, September 25,
2008, 12:15
p.m.,
SCIC 126
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.
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