Abstract
Metallic nanostructures with nanogap features can confine electromagnetic fields into extremely small volumes. In particular, as the gap size is scaled down to sub-nanometer regime, the quantum effects for localized field enhancement reveal the ultimate capability for light-matter interaction. Although the enhancement factor approaching the quantum upper limit has been reported, the grand challenge for surface-enhanced vibrational spectroscopic sensing remains in the inherent randomness, preventing uniformly distributed localized fields over large areas. Herein, a strategy to fabricate high-density random metallic nanopatterns with accurately controlled nanogaps, defined by atomic-layer-deposition and self-assembled-monolayer processes, is reported. As the gap size approaches the quantum regime of approximate to 0.78 nm, its potential for quantitative sensing, based on a record-high uniformity with the relative standard deviation of 4.3% over a large area of 22 mm x 60 mm, is demonstrated. This superior feature paves the way towards more affordable and quantitative sensing using quantum-limit-approaching nanogap structures.