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Abstract

I begin this dissertation with an overview of the colloidal nanomaterials field and highlight the versatility of colloidal methods for producing nanoscale soluble precursors to useful optoelectronic materials. The subsequent content is divided broadly between two aspects of colloidal nanomaterials science. In the first portion, Chapters 2 and 3, I discuss an in-depth study of the properties of InP quantum dot emitters with an emphasis on elucidating the barriers to achieving better performance and providing a path forward for future optimization. Chapter 2 covers an investigation into carrier dynamics in these materials by a range of spectroscopic techniques and presents evidence of defect coupled emission in passivated InP quantum dots. Chapter 3 continues to explore InP quantum dot emitters by following up on the hypothesis of defect coupled emission presented at the end of Chapter 2, and makes use of Raman spectroscopy, x-ray absorption fine structure spectroscopy and density functional theory calculations. Here, I aim to observe and account for classes of structural disorder in InP quantum dot emitters that can lead to defect coupled emission and persistently broad ensemble emission linewidths. In the latter portion of the document, Chapters 4 and 5, I turn the focus away from the properties of isolated colloidal particles and toward studying assembly of extended solids composed of colloidal nanomaterials. In particular, I examine the relation between surface chemistry and interparticle forces. I study the effect of this relationship on the morphology of aggregates grown from colloids that are electrostatically stabilized by compact inorganic ligands. In Chapter 4, I present a new method for growing ordered and maximally dense supercrystals of metal nanoparticles capped with inorganic ligands. Characterization of structural, optical, and electronic properties of these assemblies verifies strong electronic coupling and macroscopically metallic behavior. In Chapter 5, I investigate the mechanism of densification and ordering in these assemblies and find that an interaction between the high polarizability of the individual nanocrystal units and asymmetric electrolyte species in solution produces a crucial short-range repulsive potential. It is this repulsion that prevents particles from jamming and allows for the system to settle into the thermodynamically favored, ordered, and dense supercrystalline phase.

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