Core-Shell Nanoparticle Resonances in Near-Field Microscopy Revealed by Fourier-Demodulated Full-Wave Simulations

Area of Science:

• Nanophotonics
• Optical Microscopy
• Computational Physics

Background:

• Established contrast mechanisms in infrared scattering-type scanning near-field optical microscopy (s-SNOM) are crucial for nanoscale imaging.
• Core-shell nanoparticles offer tunable optical properties but their near-field response is complex.

Purpose of the Study:

• To investigate the near-field optical response of core-shell nanoparticles using advanced simulations.
• To understand how geometrical and optical resonances influence s-SNOM contrast in these structures.
• To develop a predictive framework for the optical signatures of heterogeneous nanostructures.

Main Methods:

• Fourier-demodulated full-wave simulations were employed.
• Finite Element Method (FEM) simulations were utilized, closely mirroring s-SNOM measurement conditions.
• The interplay between core and shell properties was systematically examined.

Main Results:

• Significant modifications to established s-SNOM contrast mechanisms were observed.
• Unexpected resonance shifts and massively enhanced scattering were identified in core-shell nanoparticles.
• Both core and shell components were found to drive these distinct optical phenomena.

Conclusions:

• Core-shell nanoparticles exhibit unique near-field optical responses not predicted by simpler models.
• The study provides a refined theoretical framework for predicting optical signatures of complex nanostructures.
• This work advances the understanding of near-field interactions in heterogeneous nanosystems.