Plasmon-enhanced Infrared Spectroscopy Based on Metasurface Absorber with Vertical Nanogap

Abstract

In this study, we introduce a sensing platform based on a plasmonic metasurface absorber (MA) with a vertical nanogap for the ultra- sensitive detection of monolayer molecules. The vertical nanogap of the MA, where the extremely high near-field is uniformly dis- tributed and exposed to the external environment, is formed by an under-cut structure between a metallic cross nanoantenna and themirror layer. The accessible sensing area and the enhanced near-field of the MA further enhance the sensitivity of surface-enhancedinfrared absorption for the target molecule of 1-octadecanethiol. To provide strong coupling between the molecular vibrations and plas- monic resonance, the design parameters of the MA with a vertical nanogap are numerically designed.