Doctoral Dissertations

Date of Award

8-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Philip Rack

Committee Members

Jason Fowlkes, Gerd Duscher, Gong Gu

Abstract

This dissertation fully interrogates two bimetallic material systems for plasmonic applications and also evaluates the ability of a new optical delivery system mounted on a (S)TEM for stimulated near field imaging of plasmonic modes.Plasmonics involves the collective oscillation of free electrons which are weakly bound to lattice ions. Despite the term ‘plasmonics’ being coined as the name for the field of study only in 2001, plasmonics has played a role in history dating back to the famous Lycurgus cup in the 4th century AD which displays a red color in transmission and a green color in reflection due to the presence of metal nanoparticles. Current plasmonics research is driven by developments in optical antennas, photothermal therapy for cancer, sensing, photovoltaics, and metamaterials. Silver and gold have been at the forefront of plasmonic materials due to strong local field enhancement, low losses, and biocompatibility (gold). Recently, however, significant research is devoted to finding novel plasmonic materials which overcome the limitations the traditional materials. Additionally, advancement in characterization methods is beneficial for increased understanding of plasmonic materials.In Chapter 1, the fundamentals of plasmonics and discusses the dielectric function and characterization methods with a focus on electron energy loss and gain spectroscopy. Additionally, examples of popular plasmonic materials are presented for monatomic materials and bimetallic materials. Chapters 2 and 3 explore two binary metallic systems, Au-Al (Chapter 2) and Au-Ni (Chapter 3), as potential plasmonic materials. Mixed metallic alloys are an important exploratory pathway to tune the plasmon resonance or combine or combine plasmonic properties with other functionalities. These studies explore the full compositional space of the two mixed systems by correlating the optical properties with composition and crystallographic phases. Chapter 4 explores optically stimulated near field imaging of plasmonic nanostructures. A (S)TEM mounted optical delivery system developed by Waviks Inc is used to optically stimulate Au nanorods. We demonstrate the ability to image the near field of the m = 1, 2, and 3 longitudinal localized surface plasmon modes using cw excitation.

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