Compressing Light into Molecular Regime: Metal-Air-Metal Structure

Detection of antigens on self-assembled antibody monolayers have been a major application of Surface Plasmon Resonance. To detect the antigens on the antibodies, it is important to overlap electric field with the antigens. Size of an typical IgG type antibody is about 10~15 nm, and the antigens are bonded on tip of the antibody. Therefore concentrating light in the region exactly 10~15 nm distant from the surface is a key point to increase sensitivity. However, decay length in air region of a propagating surface plasmon polariton is about 200 nm and Localized surface plasmons are mostly confined within 10 nm range from the surface [1]. We suggest a horizontal MIM air-gap structure. The size of the air-gap can be controlled between 4 nm ~ 40 nm. The structure can be fabricated using photolithography only.

As a matter of fact, we fabricated plasmonic waveguide ring resonators with 4 nm ~ 40 nm air gap via the process consist of multilayer deposition, photolithography, dry etching, selective wet etching [2] and metal deposition. Every procedure can be achieved as mass-production. The calculated surface sensitivity was 1.6 THz/nm and the bulk sensitivity was 150 THz/RIU when operated at 200 THz frequency region (1500 nm in wavelength). The optical modes of the plasmonic air-slot ring resonators have been demonstrated using tapered fiber experiment [3]. Still, integrating a microfluidic channel and bulk measurement method is required to realize real-time detection. The results on these works will also be provided.

[1] “Localized Surface Plasmon Resonance Spectroscopy and Sensing” Annu. Rev. Phys. Chem. 2007. Katherine A. Willets and Richard P. Van Duyne

[2] “A silicon nitride microdisk resonator with a 40-nm-thin horizontal air slot” Opt. Exp. 2010. Shinyoung Lee, Seok Chan Eom, Jee Soo Chang, Chul Huh, Gun Yong Sung and Jung H. Shin

[3] “Plasmonic Waveguide Ring Resonators with 4 nm Air Gap and λ²/15000 Mode-Area Fabricated Using Photolithography” Nano Lett. 2014. Jaehak Lee, Juhee Song, Gun Yong Sung, and Jung H. Shin

jaehak@kaist.ac.kr