Fabrication of Size-Controlled Metallic Nanogaps down to the Sub 3-Nm Level

Metallic nanogaps are fundamental components of nanoscale photonic and electronic devices. However, the lack of reproducible high-yield fabrication methods with nanometric control over the gap-size has hindered practical applications. Here, we report a patterning technique based on molecular self-assembly and physical peeling that allows the gap-width to be tuned over the range 3 – 30 nm and enables the fabrication of massively parallel nanogap arrays containing hundreds of millions of ring-shaped nanogaps (RSNs). The method is used here to prepare molecular diodes across sub-3-nm metallic nanogaps and to fabricate visible-light-active plasmonic substrates based on large-area, gold-based RSN arrays. The substrates are applicable to a broad range of optical applications, and are used here as substrates for surface-enhanced Raman spectroscopy (SERS), providing high enhancement factors of up to 3e8 relative to similar, gap-free thin gold films.