Film-coupled nanoparticle systems have proven a reliable platform for exploring the field enhancement associated with sub-nanometer sized gaps between plasmonic nanostructures. In this Letter, we present a side-by-side comparison of the spectral properties of film-coupled plasmon-resonant, gold nanoparticles, with dielectric spacer layers fabricated either using atomic layer deposition or using organic layers (polyelectrolytes or self-assembled monolayers of molecules). In either case, large area, uniform spacer layers with sub-nanometer thicknesses can be accurately deposited, allowing extreme coupling regimes to be probed. The observed spectral shifts of the nanoparticles as a function of spacer layer thickness are similar for the organic and inorganic films and are consistent with numerical calculations taking into account the nonlocal response of the metal. © 2014 AIP Publishing LLC.