Nanometer-Scale Aspects of Molecular Ordering in Nanocrystalline Domains at a Solid Interface: The Role of Liquid Crystal−Surface Interactions Studied by STM and Molecule Corrals

Chiral molecular monolayers deposited on a graphite surface in contact with a bulk liquid crystal (LC) droplet showed unexpected long-range morphological correlations between adjacent crystalline domains. These correlations included tendencies for nearby surface domains to exhibit similar chirality and to possess similar crystallographic orientation. Both correlations were found to decrease with increasing domain separation. Multiple nanocrystalline domains were grown in “molecule corrals”, which are flat-bottomed, nanometer-sized pits produced on the graphite surface by an oxidation reaction. Domain structure was investigated using scanning tunneling microscopy (STM). The observations are explained as arising from anchoring interactions between the adsorbed monolayer and the liquid crystal interfacial fluid. A model based on a modification of the Rapini−Popoular potential for the surface free energy of a nematic LC is developed that quantitatively describes the orientational component of the interaction. From a statistical analysis of the STM data, it was possible to elucidate molecular-scale details of the interfacial LC fluid structure, including the orientation of the local LC director, the anchoring energy, and the way anchoring changed over different surface regions.