Hierarchical Semiconductor, Metal and Hybrid Nanostructures and the Study of their Light-matter Interactions

The work presented in this thesis explores the optical properties of hierarchical structures composed of nanoscale building blocks ranging from metals to semiconductors and composites, organized through bottom-up design methods. 1) By following the dynamic generation of hot-spots in self-assembled chains of gold nanorods (NRs), we have established a direct correlation between ensemble-averaged surface-enhanced Raman scattering (SERS) and extinction properties of these nanoscale chains. Experimental results were supported by comprehensive finite-difference time-domain simulations (FDTD). The relationship established between the structure of nanorod ensembles and their optical properties provides a basis for producing dynamic, solution-based, plasmonic platforms for applications ranging from sensing to nanoelectronics. 2) We report theoretical and experimental analyses of the optical properties of side-by-side assembled gold NRs. Comprehensive FDTD simulations showed a blue shift of the surface plasmon resonance in the side-by-side assembled NR structures and a reduction of electric field intensity as the number of NRs per stack increased. These results were experimentally verified via extinction measurements and ensemble-averaged SERS spectroscopy. The experimental results and electrodynamic simulations were found to be in agreement. 3) The efficacy of hollow core photonic crystal fibers (HCPCF) as a platform for SERS spectroscopy was demonstrated. SERS measurements carried out using this platform showed the capability to monitor minute amounts of ligands on the surface of gold nanoparticles and SERS signals from HCPCF exhibited a 10-fold enhancement. Using the exchange of cetyltrimethylammonium bromide with α-methoxy-ω mercaptopolyethylene glycol on the surface of gold nanorods as an exemplary system, we showed the feasibility of using HCPCF SERS to monitor the change in surface chemistry of NRs. 4) Facile, solution-phase formation of ordered, lamellar quantum dot (QD) arrays exhibiting structural integrity and temporal stability, without the need for chemical crosslinking, was achieved. While micrometers in diameter, they are typically only two to three QD layers thick. These structures are capable of carrying a cargo of water-soluble ions, molecules, metal nanoparticles, or biomolecules. The photoluminescence of the host CdSe QDs were enhanced by the encapsulation of gold nanoparticles within the lamellae, demonstrating the ability to modulate their properties through the cargo they carry. 5) This chapter explores a bottom-up method to produce a metamaterial designed to function as an optical cloak in the visible range. A composite material consisting of an array of silver nanowires (NWs) in a dielectric host has been produced based on the theory of a non-magnetic optical cloak. The required radial array of silver NWs was achieved by electroless deposition of the metal into the channels of a porous alumina structure grown perpendicularly from the curved surface of a micrometer scale aluminum wire. The functionality of the cloak was demonstrated by partial cloaking in the visible range (540 nm).

Keywords: nanoscience
optical properties
hierarchical nanostructures
quatum dots
gold nanoparticles
metamaterials
Advisor: Kumacheva, Eugenia