Colossal Terahertz Field Enhancement Using Split-Ring Resonators with a Sub-10 nm Gap

Terahertz (THz) nanogap structures have emerged as versatile platforms for THz science and applications by virtue of their strong in-gap field enhancements and accompanying high levels of sensitivity to gap environments. However, despite their potential, reliable fabrication methods by which to create THz structures with sub-10 nm gaps remain limited. In this work, we fabricated THz split-ring resonator (SRR) arrays featuring a sub-10 nm split gap. Our fabrication method, involving photolithography, argon ion milling, and atomic layer deposition, is a high-throughput technique that is also applicable to the fabrication of other THz structures with sub 10 nm gaps. Through THz-time domain spectroscopy and a numerical simulation, we identified the fundamental magnetic resonances of the nanogap SRRs, at which the electric field enhancement factor is experimentally estimated to be around 7000. This substantial field enhancement makes SRRs with a sub-10 nm gap suitable for the study of high-field phenomena and related applications.