Resonator arrays with non-uniform unit cell design for surface-enhanced infrared absorption spectroscopy

Abstract

Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful analytical tool for identifying the composition of biochemical molecules by resolving their characteristic absorption fingerprints. Plasmonic nanostructures can localize light within nanoscale “hot spots”, thereby enhancing SEIRA signals, with the achievable enhancement primarily determined by the structure design. In this work, a non-uniform resonator design strategy is proposed for significantly increasing the field enhancement factor. Numerical simulations and experimental studies demonstrate the superior performance of non-uniform designs over their conventional uniform counterparts, using uniform cross nanorods and split-ring resonators (SRRs) as reference structures. To experimentally assess the SEIRA performance, PEO polymers with multiple absorption bands from 1100 cm⁻¹ to 1400 cm⁻¹ were deposited on the fabricated resonator arrays as analytes. For non-uniform cross nanorods, the SEIRA signal improvement is 64% compared with uniform cross nanorods. For non-uniform SRRs, the SEIRA signal improvement is 210% compared with uniform SRRs. The presented non-uniform design focuses on the structure optimization of “cold part” of resonators, and is beneficial for not only SEIRA applications but also other infrared photonic devices.