Importance of oxide layer in plasmonic structures for optical enhancement applications

This work studies the effect of varying the SiO₂ thickness on a Si substrate containing plasmonic nanostructures. The goal of this oxide layer optimization is to improve surface enhancement for optical plasmonic applications. Optimization of plasmonic structure geometry and materials for specific combinations of incident light wavelength and polarization is crucial to the fabrication of ideal devices for light enhancement applications. It is also critical to investigate the effects of the oxide thickness on these devices, as many plasmonic structures are fabricated on Si substrates containing an oxide layer. Often, the thickness of this layer is not optimized, but doing so has been found to provide a potential eight-fold increase in enhancement. Here, we apply previous computational electromagnetic design results to the fabrication of nanodevices for improved signal strength, utilizing surface-enhanced Raman spectroscopy (SERS) and cathodoluminescence. SERS results are obtained using a custom-built Raman system, and plasmon resonance excitability is studied via cathodoluminescence to validate computational models that optimize the substrate for plasmonic enhancement.