Self-Assembly in Supercritical Fluids—Connecting Top-Down and Bottom-Up Approaches to Nanoengineering

The development of devices based on single-molecule junctions requires not only robust control over molecular self-assembly but integration into structures that can interface with the macroscopic world. Accomplishing this task requires a manufacturing technique that simultaneously offers the reproducibility and accuracy of photolithography as well as the nanoscale control offered by solution phase self-assembly. In order to unify top-down and bottom-up approaches to nanoengineering, we are developing physical supercritical fluid deposition. This technique leverages the unique solubility properties of supercritical fluids to deposit molecules without the need for in-situ chemical reactions. The process relies on a peak in the isobaric saturation solubility with respect to temperature allowing thin films to be formed via precipitation onto heated substrates. The location of material deposition can be accomplished by controlling the local temperature on the substrate via simple joule heating. The resistive traces used for joule heating can be created via photolithography, allowing us to direct the solution phase self assembly with the accuracy of photolithography. Progress towards improving the resolution limit of the technique will be discussed as will the mechanisms of self-assembly and their effect on the nanoscale morphology of polymeric materials.