Formation Mechanism of Monodisperse Colloidal Semiconductor Quantum Dots A Study of Nanoscale Nucleation and Growth Matthew William Greenberg Since the fortuitous discovery of the existence of quantum size effects on the band structure of colloidal semiconductor nanocrystals, the development of synthetic methods that can form nanoscale crystalline materials of controllable size, shape, and composition has blossomed as an empirical scientific achievement. The fact that the term "recipe" is
... m "recipe" is commonly used within the context of describing these synthetic methods is indicative of the experimentally driven nature of the field. In this respect, the highly attractive photophysical properties of semiconductor nanocrystals-as cheap wavelength tunable and high quantum yield absorbers and emitters of light for various applications in lighting, biological imaging, solar cells, and photocatalysis-has driven much of the interest in these materials. Nevertheless, a more rigorously predictive first-principlesgrounded understanding of how the basic processes of nanocrystal formation (nucleation and growth) lead to the formation of semiconductor nanocrystals of desired size and size dispersity remains an elusive practical and fundamental goal in materials chemistry. In this thesis, we describe efforts to directly study these dynamic nucleation and growth processes for lead chalcogenide nanoparticles, in many cases in-situ, using a mixture of X-ray scattering and UV-Vis/NIR spectroscopy. The lack of a rigorously predictive and verified mechanism for nanocrystal formation in solution for many material systems of practical interest is due both to the inherent kinetic 1.8. References 74 Reproduced in part from Abécassis, B.; Greenberg, M. W.; Bal, V.; Campos, M. P.; Hendricks, M. P.; DeRosha, D.; Bennett, E.; Saenz, N.; Peters, B. Owen, J. S. Monodisperse PbS Nanocrystals Following Persistent Nucleation and Size Dependent Growth. Manuscript in Preparation. Prof. Benjamin Abécassis and Dr. Michael Campos are recognized for valuable contributions in helping carry out X-ray scattering experiments and Prof. Abécassis for data model development and modeling as is Dr. Vivekanada Bal and Prof. Baron Peter for population balance modeling of particle formation parameters extracted from diffraction data.