Fano-resonance boosted cascaded field enhancement in a plasmonic nanoparticle-in-cavity nanoantenna array and its SERS application

TL;DR

This paper introduces a plasmonic nanoparticle-in-cavity array leveraging Fano resonance to significantly boost cascaded field enhancement, enabling highly sensitive SERS detection with a cost-effective fabrication method.

Contribution

It presents a novel high-quality PIC nanoantenna array design with Fano resonance for enhanced field amplification and demonstrates a reliable room-temperature nanoimprinting fabrication process.

Findings

Field enhancement factor up to 5×10^2 in PIC array

SERS enhancement factor up to 2×10^7

Effective detection of 4-aminothiophenol molecules

Abstract

Cascaded optical field enhancement (CFE) can be realized in some specially designed multiscale plasmonic nanostructures, where the generation of extremely strong field at nanoscale volume is crucial for many applications, for example, surface enhanced Raman spectroscopy (SERS). Here, we propose a strategy of realizing a high-quality plasmonic nanoparticle-in-cavity (PIC) nanoantenna array, where strong coupling between a nanoparticle dark mode with a high order nanocavity bright mode can produce Fano resonance at a target wavelength. The Fano resonance can effectively boost the CFE in the PIC, with a field enhancement factor up to 5X10^2. A cost-effective and reliable nanofabrication method is developed with room temperature nanoimprinting lithography to manufacture high-quality PIC arrays. This technique guarantees the generation of only one gold nanoparticle at the bottom of each nanocavity, which is crucial for the generation of the expected CFE. As a demonstration of the performance and application of the PIC array, it is used as active SERS substrate for detecting 4-aminothiophenol molecules. The SERS enhancement factor up to 2X10^7 is obtained experimentally, verifying the field enhancement and potential of this device.