Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Mark P. Stoykovich

Second Advisor

Charles B. Musgrave

Third Advisor

Aaron E. Saunders

Fourth Advisor

Daniel L. Feldheim

Fifth Advisor

Alan W. Weimer

Abstract

Colloidal nanocrystals have unique physical, optical, and transport properties compared to both molecular systems and bulk materials. Nanocrystals of noble metals such as copper, for example, exhibit a size- and shape-dependent optical response known as the localized surface plasmon resonance (LSPR). We have found that the plasmon response in solution-based copper nanocrystals is solvent-dependent, with solvents containing π-bond significantly damping the LSPR signal until a monolayer of copper oxide forms on the nanocrystal surface and causes the plasmon signal to return, due to electron donation from the solvent. In addition, the copper LSPR signal can be monitored in-situ and in real time using UV-vis absorbance spectroscopy to study the oxidation of copper to copper oxide. We have determined the oxidation kinetics for Cu as a function of temperature (50-300°C) and, through application of a reaction-diffusion model for oxidation, quantified temperature-dependent diffusion parameters in the Cu/Cu2O system. The Cu2O nanoparticles were also characterized structurally and were found to form hollow shells upon oxidation via a phenomenon known as the nanoscale Kirkendall effect. The hollow Cu2O nanoparticles were formed at temperatures from ~100 to 200°C, but were thermodynamically unstable and collapsed to solid nanoparticles at higher temperatures. Cadmium selenide (CdSe) and semiconductor nanocrystals also are of great interest because their absorption at UV-vis wavelengths is size- and shape-dependent making them well suited for photovoltaics. Most of the shape control demonstrated for the wurtzite crystal structure of CdSe has previously centered on high aspect ratio rods and tetrapods, due to the inherently elongated unit cell of wurtzite. We have synthesized new nanocrystal morphologies in wurtzite CdSe, including cubes and hexagonal platelets, by controlling reaction conditions such as temperature, precursor concentrations, and the nucleation process through the use of a seeded-growth mechanism. A new algorithm based on the Fourier descriptor method was developed to classify the nanocrystal shapes from transmission electron micrographs and provided high-throughput, quantitative information about shape for each synthetic condition.

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