Quantifying the Ultimate Limit of Plasmonic Near-field Enhancement

Abstract Quantitatively probing the ultimate limit of near-field enhancement around plasmonic nanostructures remains elusive, despite more than five decades since the discovery of surface-enhanced Raman scattering (SERS). Theoretical calculations have predicted an ultimate near-field enhancement exceeding 1000 using the best plasmonic material Ag, but experimental estimations disperse by orders of magnitude. Here, we design a high-quality Ag plasmonic nanocavity with atomic precision and precisely quantify the upper limit of near-field enhancement in ~ 1 nm junctions. A hot-spot averaged SERS enhancement of 4.29×1010 is recorded with a small fluctuation, corresponding to an averaged electric field enhancement larger than 1000 times. This result quantitatively delineates the ultimate limit of plasmonic field enhancement around plasmonic nanostructures, establishing a foundation for diverse plasmon-enhanced processes and strong light-matter interactions at the atomic scale.