Strong coupling of dielectrics with terahertz gap plasmons within metallic nano-slots

Abstract

In this work a real metal regime of metallic nanostructures in terahertz frequencies, where most noble metals are treated as perfect electric conductors, is discussed.With an aid from gap plasmon modes, that is, coupling of surface plasmons from the two metal sides forming a gap, large amount of terahertz electric field can enter the metal with electric permittivity of 106 when the gap is smaller than 100 nm. A method for highthroughput fabrication of such gaps is first presented, and then peculiar optical responses – anomalous resonance shifts and a large Ohmic absorption – are experimentally and theoretically realized. Also, wet etching of a gap spacer within a 5 nm gap is demonstrated, enabling aqueous nano-optic experiments below 10 nm scale. This comprehensive study on terahertz gap plasmon and nanogaps is expected to greatly benefit convergence of chemistry or bio-chemistry with nano-optics, especially in sub-10 nm regime.