Toward controlled area electrode assemblies: Selective blocking of gold electrode defects with polymethylene nanocrystals

Using electrochemical and chemical probes, we demonstrate that thin films o f crystalline polymethylene (PM), formed via solution decomposition of diaz omethane on gold surfaces, exist in the form of a heterogeneous distributio n with microscopically small pores at low average PM coverages. For evapora ted gold substrates, as the PM loading increases above similar to 0.8 mu g. cm(-2), a mass density equivalent to an similar to 7 nm thick, fully dense planar film, a transition from a micropore to a blocked electrode occurs. T his microstructural picture is confirmed by the ability to backfill open ar eas with alkanethiolates and electropolymerized aniline. Parallel experimen ts on sputter-deposited gold films show that the blocking threshold occurs at much lower average PM coverages and alkanethiolate chemisorption data su ggest that the open pores are approaching the sizes of individual molecules . These results can be rationalized by a more uniform nucleation of PM nano crystals across sputter-deposited relative to evaporated surfaces. This abi lity to regulate the conformal deposition of an inert, low dielectric mater ial at the nanometer scale on gold surfaces offers a new way to engineer el ectro des with controlled, micropore dielectric barrier structures and "qua si-two-dimensional" nanocomposite films.