UC Davis

Quantum dots (QDs) are novel building blocks that feature size-tunable and uniquephotophysical properties. The interactions (e.g., electronic, excitonic, magnonic) in self- assembled QD superlattices (SLs) can be tuned by changing particle size, size distribution, shape, inter-particle spacing, structural ordering, surface chemistry and defects, making QD solids an exciting playground for mesoscale science. To date, the properties of QD-made devices have been limited by the relatively high energetic and spatial disorder of the coupling pattern of QDs, inhibiting the emergence of new collective mesoscale behavior. However, rational improvements in film synthesis relies on comprehensive understanding of the 3D structure that current studies have yet been able to present with conventional 2D diffraction and imaging techniques. In this dissertation, I demonstrate the use of full-tilt Electron Tomography based on High Angular Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) images in generating quantitively interpretable digital reconstruction of the QD SLs. With sufficient spatial resolution of under 0.4 nm over a volume containing thousands of QDs, both superlattice and atomic lattice structural order and morphological information are obtained through real and reciprocal space calculations. This allows hierarchal analyses on the spatial variations of and correlations among different structural features. These new knowledges enable new understandings of the QD oriented-attachment mechanism and provide rational guidance to film quality refining.