Endorsing a Hidden Plasmonic Mode for Enhancement of LSPR Sensing Performance in Evolved Metal-insulator Geometry...

Area of Science:

• Plasmonics
• Nanomaterials Science
• Biosensing

Background:

• Nanoplasmonic structures, specifically nanomushrooms (NM), comprise a spherical plasmonic cap (e.g., gold) on a silicon dioxide stem.
• NM geometry evolves from nanoislands (NI) via etching and is known for enhanced localized surface plasmon resonance (LSPR) sensitivity in biosensing.
• The precise optical mechanism behind NM's enhanced LSPR sensitivity, often attributed to inter-pillar electric fields, remains largely uncharacterized.

Purpose of the Study:

• To elucidate the optical phenomenon responsible for the enhanced LSPR sensitivity in nanomushroom (NM) geometries.
• To investigate the relationship between LSPR modes, light polarization, and refractive index sensitivity in NM and NI structures.
• To explore the potential of advanced analytical techniques for understanding complex plasmonic properties.

Main Methods:

• Magneto-optics measurements were performed on NM and NI geometries.
• Absorbance spectra were deconvoluted during local refractive index changes.
• Principal component analysis (PCA), an unsupervised machine learning technique, was employed to analyze spectral data.

Main Results:

• A hidden plasmonic mode associated with LSPR enhancement in NM was identified.
• An explicit relationship was observed between deconvoluted LSPR modes, differential absorption of circularly polarized light, and refractive index sensitivity.
• PCA effectively correlated spectral features with the sensing performance of NM and NI.

Conclusions:

• The enhanced LSPR sensitivity of nanomushrooms is linked to a specific, previously unidentified plasmonic mode.
• Magneto-optics and machine learning provide powerful tools for dissecting complex plasmonic behaviors.
• Findings pave the way for novel methods to characterize plasmonic materials and understand their photonic properties.