Title

Synthesis and Processing of Core/Alloy Nanoparticles: Optical Properties and Morphological Evolutions

Author

Wenjie Wu

Date of Award

8-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Mathew M. Maye

Second Advisor

Eric A. Schiff

Keywords

Core/Alloy, Morphological Evolutions, Nanoparticles, Optical Properties, Processing

Subject Categories

Chemistry

Abstract

In this thesis, I describe the synthesis and processing of core/alloy nanoparticles (NPs) from the two major perspectives: optical properties and morphological evolutions. In Chapter 2, I take advantage of atomic interdiffusion at nanoparticle interfaces to fabricate Au/AuxAg1-x core/alloy and Au/AuxAg1-x/Ag core/alloy/shell nanoparticles. The alloy formation and subsequent interdiffusion allowed us to tailor nanoparticle composition and ultrastructure, as well as surface plasmon response (SPR). The resulting surface plasmon resonance signatures were modeled as a function of alloy or monometallic shell thickness, as well as alloy composition, using the discrete dipole approximation (DDA) method.

In Chapter 3, I discusse the synthesis of Au/AuxAg1-x/Ag nanoparticles (NPs) further in terms of the effects of temperatures and reducing agents. Temperature range from TH = 90 - 215 oC and the reducing agents--ascorbic acid and sodium borohydride were examined.

In Chapter 4, I investigate the internal composition and microstructure of plasmonic core/alloy nanoparticles (NPs) by comparing changes in SPR signature in depth with DDA simulations. Depending on the processing temperature, alloying occurs at the core/shell interface. The extent of alloying was related to changes in the SPR. Using DDA in conjunction with TEM determined morphology, we are able to determine alloy shell composition (x) and thickness (tS). Through a series of core/alloy models with x = 0.2 - 0.8, and shell thickness to core radius ratios (tS/rC) of 0.05 - 1.0. Using this approach we are able to produce a variety of SPR rich features, which can reproduce the experimental results.

In Chapter 5, I describe the sulfidation of Au/Ag core/shell and Au/AuxAg1-x core/alloy nanoparticles (NPs), where interesting diffusion process and morphological changes upon sulfidation are shown. The sulfidation leads to the formation Au/Ag2S asymmetric heterodimers with a Janus-like geometry.

In Chapter 6, I explore the oxidation properties of Fe/FexCr1-x core/alloy NPs with stainless steel like interfaces. These particles show a unique morphological transformation that is induced by surface oxidation, oxide passivation, and vacancy coalescence. In Chapter 7, I describe the preliminary results that are based on the further processing of core-void-shell morphologies described in Chapter 6.

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