Measurement and Control of Nanoscale Interactions and Assemblies
Detailed understanding and control of the intermolecular forces that govern molecular assembly are necessary to engineer structure and function at the nanoscale. Liquid crystal (LC) assembly is exceptionally sensitive to surface properties, capable of transducing nanoscale intermolecular interactions into a macroscopic optical readout. Self-assembled monolayers (SAMs) modify surface interactions and are known to influence LC alignment. Here, we exploit the different dipole magnitudes and orientations of carboranethiol and dithiol positional isomers to deconvolve the influence of SAM-LC dipolar coupling from variations in molecular geometry, tilt, and order. Director orientations and anchoring energies are measured for LC cells employing various carboranethiol and dithiol isomer alignment layers. Using LC alignment as a probe of interaction strength, we elucidate the role of dipolar coupling of molecular monolayers to their environment in determining molecular orientations.
Determining the three-dimensional, atomic-scale structures of complex or buried structures will transform our understanding of chemical and biological processes at the nanoscale. We outline the development of a technique to elucidate single-molecule structure using a scanning tunneling microscope to detect, to localize, and to resolve nuclear spin signals. Inhomogeneous magnetic field will add another dimension to the spin resolution, enabling three-dimensional mapping of spin species. Targeted systems include: cobalt nanoparticles, organic molecules possessing a nuclear spin center, and linear, ‘chain-like’ molecules containing biologically relevant nuclei.
We address the importance of the dynamic molecular ink concentration at a polymer stamp/substrate interface during microcontact displacement or insertion printing. We demonstrate that by controlling molecular flux, we can influence both the molecular-scale order and the rate of molecular exchange of SAMs on gold surfaces. Surface depletion of molecular ink at a polymer stamp/substrate interface is driven predominantly by diffusion into the stamp interior, which we model numerically. Controlling interfacial concentration improves printed film reproducibility and the fractional coverage of multicomponent films can be controlled to within a few percent. We describe two experiments that illustrate control over ink transfer during experiments: the role of contact time on monolayer reproducibility and molecular order, and the fine control of fractional monolayer coverage in SAMs modified using displacement printing.