Limits of high-density, low-force pressure contacts

Using a custom-built apparatus we have been characterizing extremely small pressure contacts with applied forces down to a few nN and corresponding contact areas down to 10^-13 cm². At these forces, which are many orders of magnitude smaller than those currently employed in electrical contacts, nominally clean gold-gold and iridium-gold contacts in air exhibit resistivities higher than that predicted from a simple model based on the plastic deformation of the gold. A film of the insulating polymer PMMA three monolayers (2.7 mm) thick deposited on a gold surface affects its conductance significantly, and a film of seven monolayers insulates it completely