Date of Award
Doctor of Philosophy (PhD)
Apparao M Rao
Jeffrey N Anker
During the past twenty years, plasmonic nanostructures have evolved as one of the most promising candidates for applications in miniaturized optical and electronic devices, bio-sensors and photonic circuits, etc. Silver nanoparticles can interact with light more strongly than any known materials with similar dimensions, and support tunable optical properties based on their size, shape and sounding medium, which are more stable than optical properties of traditional pigments and dyes.
Thanks to the recent progress in the synthesis of various silver nanoparticles with different shape and sizes, which has opened doors to the exciting research field of plasmonics. However, silver nanoparticles tend to aggregate when cast on substrates from its aqueous suspension, which compromises their plasmonic properties. In Chapter 2, we describe a simple and reliable method to immobilize silver nanoparticles on polymer coated substrates to mitigate aggregation and allow further chemical modification of silver nanoparticles, if needed. In this project, interesting nanostructured craters were discovered, which were extensively studied using atomic force microscopy (AFM).
Fluorescence is widely used in many biosensing applications such as the quantification of disease markers, protein activity, cytokine and small molecule signals. Metallic nanoparticles alter fluorescence emission by influencing either the incident excitation field, or the radiative and non-radiative decay rates of dye molecules. In Chapter 3, we describe a simple method for tuning the shape of silver nanoparticles to synergistically achieve high fluorescence enhancements in an ensemble of dye molecules. Specifically, we show that the fluorescence emission from Rhodamine B (RhB) is enhanced by >30 folds (with respect to RhB on bare glass) in the presence of Ag nanodisks due to a simultaneous increase in the excitation intensity and photon mode density. Moreover, our detailed finite-element simulations, which account for incident, scattered, and dipole radiated electric fields, evidenced that the enhancement is strongly dependent on the orientation of RhB dipole relative to Ag NPs and nanodisks.
While aggregation of silver nanoparticles is not desirable, it facilitates creation of fascinating nanostructures that exhibit new properties due to the mystical coupling between plasmonic resonances of particles within the aggregate. Prior research has shown that such coupling leads to Fano resonances, greatly enhanced local electromagnetic fields, unidirectional scattering of light, etc. In Chapter 4, we describe a method for assembling silver nanoparticles into specific configurations, such as a linear chain or a nanoring by manipulating individual silver nanoparticles into such configurations with the help of the AFM tip. We discovered novel far field focusing properties of light by nonorings, which is a result of coupled plasmonic resonances of nanoparticles present within the nanoring.
Hu, Longyu, "Modulation of Photonic Mode Density in Silver Nanodisks and Far Field Focusing of Light by Coupled Plasmonic Nanorings" (2017). All Dissertations. 2549.