Robust Hybrid Plasmon-Photon Modes in Colloidal Metasurfaces Probed by Angle-Resolved SERS

Area of Science:

• Plasmonics and photonics
• Metasurface engineering
• Spectroscopy

Background:

• Plasmonic-photonic metasurfaces offer spectrally selective field enhancement for surface-enhanced Raman scattering (SERS).
• Identifying low-loss hybrid plasmon-photon modes under typical excitation conditions is challenging.
• SERS performance requires modes tolerant to fabrication defects and structural variations.

Purpose of the Study:

• To investigate and identify low-loss hybrid plasmon-photon modes in colloidal metasurfaces.
• To quantify the robustness of these modes against structural imperfections.
• To establish design rules for tunable and robust SERS metasurfaces.

Main Methods:

• Fabrication of colloidal metasurfaces with varying nanoparticle concentrations and lattice periods using template-assisted self-assembly.
• Angle-resolved surface-enhanced Raman scattering (SERS) measurements under ultrahigh numerical aperture excitation.
• Analytical modeling to understand the nature of the observed hybrid modes.

Main Results:

• A direct correlation was found between nanoparticle concentration, structural order, and the emergence of hybrid modes.
• Optimized periodicity significantly maximized SERS intensity (up to 2.32x).
• Angle-resolved SERS under oblique incidence demonstrated up to 36x higher intensity when hybrid guided-mode resonance was tuned to the laser line.

Conclusions:

• Hybrid modes arise from phase-coupled waveguide coupling and collective plasmonic chain resonances.
• Practical design rules for robust, tunable colloidal plasmonic-photonic SERS metasurfaces were established.
• Dispersion engineering of hybrid modes is key for optimizing SERS performance.