Toward Controlled Area Electrode Assemblies: Selective Blocking of Gold Electrode Defects with Polymethylene Nanocrystals

Using electrochemical and chemical probes, we demonstrate that thin films of crystalline polymethylene (PM), formed via solution decomposition of diazomethane on gold surfaces, exist in the form of a heterogeneous distribution with microscopically small pores at low average PM coverages. For evaporated gold substrates, as the PM loading increases above ∼0.8 μg·cm^-2, a mass density equivalent to an ∼7 nm thick, fully dense planar film, a transition from a micropore to a blocked electrode occurs. This microstructural picture is confirmed by the ability to backfill open areas with alkanethiolates and electropolymerized aniline. Parallel experiments on sputter-deposited gold films show that the blocking threshold occurs at much lower average PM coverages and alkanethiolate chemisorption data suggest that the open pores are approaching the sizes of individual molecules. These results can be rationalized by a more uniform nucleation of PM nanocrystals across sputter-deposited relative to evaporated surfaces. This ability to regulate the conformal deposition of an inert, low dielectric material at the nanometer scale on gold surfaces offers a new way to engineer electrodes with controlled, micropore dielectric barrier structures and "quasi-two-dimensional" nanocomposite films.