Optical and Structural Studies of Shape-Controlled Semiconductor Nanocrystals and Their Self-Assembled Solids

Colloidal nanocrystals are prominent candidates to displace current electronic active layers in solid-state device technologies and offer a body of physics which diverges from those of bulk materials and discreet molecules. Realizing the potential of colloidal nanocrystals may transform the costs and performance of common technologies, but understanding of the relationship between particle size, shape, uniformity, and composition and outputs like physical properties or device performance is often incomplete. This work uses the controlled synthesis of anisotropic colloidal nanocrystals to implement characterization techniques including X-ray diffraction and simulation, which allows an ensemble-level description of particle structure, as well as polarized and time-resolved spectroscopy, which demonstrates subtle synthetic control over the properties of quantum-mechanical wavefunctions. Time- and temperature-resolved optical spectroscopy is employed to analyze the behavior of nanocrystal samples under more realistic device operating conditions and to determine the structure/property relationships that underpin improved performance. Highly-uniform samples of colloidal nanocrystals are self-assembled into large-area thin films. Discussion of self-assembly is placed within the context the fundamentals of self-assembly processes and the roadmap to high-performance devices based upon colloidal nanocrystals. X-ray diffraction and microscopic analysis are performed to analyze and qualify the structure of self-assembled films. These measurement techniques provide figures of merit for nanocrystal assemblies including the sample crystallinity and purity, surface coverage, homogeneity. Diffraction analysis is further used to measure alignment of nanocrystal assemblies with respect to a substrate and the orientation of individual particles within assemblies. Monodisperse anisotropic building blocks encode the unique optoelectronic properties of isolated nanocrystals into solid state materials with long-range structural orientation.