Plasmonic nanoparticles exhibit extraordinary optical properties due to their resonant interaction with light. Their unique optical properties can be tuned through their size, shape and composition. When coupled, they behave as optical antennas, focusing electromagnetic fields to enable surface enhanced spectroscopies. Properly engineered, these optical antennas are capable of enabling field enhanced spectroscopic detection that is orders of magnitudes more sensitive than the analogous conventional spectroscopies. This makes the plasmonic sensors an attractive option for trace analyte detection in security applications. Through self-assembly process, we have fabricated vertically aligned superlattice arrays for the detection of various analytes. In this presentation, we will present computational simulation study of such plasmonic superlattice arrays made of anisotropic nanoparticles (e.g. Au nanorods). We will present the field confinement effect in plasmonic superlattices through finite difference time domain simulation. The electric field confinement tends to located at the expected interparticle junction in the single layer nanoparticle array. In larger plasmonic superlattices, field enhancement can come from structural resonances in addition to the gap coupling modes between the immediately coupled plasmonic nanostructures. Surprisingly, field strength tends to diminish towards the centre of the superlattice, possibly due to the screening effect. We will discuss the implication of field enhancements from both modes and its uses as surface enhanced Raman spectroscopy (SERS) sensors for the detection of small molecules. We will also present experimental measurement obtained from plasmonic nanocluster assemblies and correlate their SERS characteristics with their structural morphology.

Electromagnetic field confinement in self-assembled anisotropic plasmonic nanoparticle superlattice

2019 Fall National Meeting

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