Both plasmonic and photonic materials manipulate light by structurally-defined optical properties. While photonic crystals prevent the transmission of light at their defined bandgap, plasmonic materials, which are defined by the oscillation of a metal’s free electron density, have resonances which confine light at the nanoscale. By matching the frequency of the photonic bandgap and external source used to excite the plasmon resonance, the two processes could couple to produce a larger optical response. Recent advances have found that integrating plasmonic materials into a photonic architecture enhances light absorption in thin film solar cells and improves visible light photocatalysis. However, the enhancements and effects created within a dual plasmonic-photonic system have yet to be defined. Because plasmonic enhancement can be observed with surface-enhanced Raman spectroscopy (SERS), this coupling of light can be analyzed quantitatively. Our study strategically incorporates a photonic system by using butterfly wings which are colored due to the existence of photonic crystals. To better understand the wavelength dependence of plasmon resonances coupled to photonic crystals, we have fabricated SERS substrates of silver nanoparticles embedded within the unique architecture of five different types of butterfly wings. Comparing the SERS response of each wing color revealed that the excitation wavelengths most closely matching the photonic bandgap produced the most intense Raman signal. Results found approximately four times larger Raman signal for butterfly substrates with a photonic bandgap matching the plasmon excitation frequency. Therefore, naturally abundant photonic structures have potential for use as cheaper, wavelength-selective SERS substrates. Applying these results may advance visible light plasmonic photocatalysis, molecular sensing, and thin film solar cell efficiencies.<br/>

Analyzing plasmonic and photonic coupling in butterfly wings using surface-enhanced Raman spectroscopy

2019 Spring National Meeting

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