Probing molecular-level organizational structure and electronic decoupling of tartaric acid domains supported on Ag(111)

Abstract

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 article we discuss the submonolayer ordering of a chiral molecule, tartaric acid (C4H6O6), weakly bound to an achiral metal surface, Ag(111), as studied with low temperature scanning tunneling microscopy (STM) and differential conductance imaging. Molecularly resolved images of enantiomerically pure (R,R)- and (S,S)-tartaric acid domains on Ag(111) are presented and the role of intermolecular hydrogen bonding in stereospecific domain and superlattice formation is addressed. Additionally, we consider films formed from the deposition of a racemic mixture of tartaric acid enantiomers. Lastly we present differential conductance mapping of tartaric acid molecular domains that highlights an intrinsic decoupling of molecular film electronic states with respect to the metallic lattice. While the chiral expression that drives the formation of enantiomeric domains does not induce stereospecific conductance, we demonstrate electronic differentiation of submonolayer organic domains from the Ag(111) surface.