Tuning the Fano resonance between localized and propagating surface plasmon resonances for refractive index sensing applications

TL;DR

This study investigates the Fano interference between localized and propagating surface plasmon resonances in nanostructures, demonstrating how tuning these interactions enhances refractive index sensing performance.

Contribution

It introduces a phase-sensitive spectroscopic ellipsometry method to analyze Fano interference in plasmonic nanostructures, revealing how anti-crossing improves sensor sensitivity and figure-of-merit.

Findings

Pronounced anti-crossing and asymmetric line shapes observed.

Anti-crossing significantly increases refractive index sensitivity.

Figure-of-Merit reaches values between 24 and 58.

Abstract

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here we study the fano interference that occurs between localized (LSPR) and propagating (SPP) modes by means of phase sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each others vicinity, accompagnied of largely increased phase differences between the respective plasmon resonances. Moreover we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the Figure-Of-Merit which reaches values between 24 and 58 for the respective plasmon modes.