Designing Plasmonic Sensors to Detect Refractive Index Changes in Palladium

Abstract

This thesis describes the design and self-assembly of Au nanoparticles to detect hydrogenation in palladium nanoparticles. These gold nanoparticles have a collective oscillation of conduction electrons at a resonant frequency known as a plasmon resonance. At this resonance, a large electric field enhancement occurs that induces a significant increase in scattering intensity. The plasmon resonance frequency is highly dependent on the refractive index of the surrounding medium. Therefore, any change in refractive index of the surrounding will result in a change in peak scattering wavelength. This sensitivity is utilized by dimerizing a palladium nanoparticle with a gold plasmonic nanoparticle. Upon hydrogenation of the palladium, the peak scattering intensity of the plasmonic nanoparticle will shift, effectively acting as a sensor. This thesis describes design considerations when creating a plasmonic sensor. We suggest that the largest change in peak scattering wavelength will likely occur at a wavelength that exhibits the largest refractive index difference between palladium and palladium hydride. Further, we demonstrate an electrostatic self-assembly technique using silicated Au nanorods with Pd nanocubes that showed moderate success. To experimentally investigate the plasmonic resonance location, preliminary dark-field spectroscopy measurements on single gold nanorods were taken. We also describe potential future work opportunities for improvement of self-assembly process and alternative characterization techniques for improved refractive index data.