SURFACE PROPERTIES AND ELECTRONIC STRUCTURE OF SEMICONDUCTOR NANOCRYSTALS

Semiconductor nanomaterials, including quantum dots and nanoplatelets, are poised to address pressing global energy challenges due to their unique optical and electronic properties. These optoelectronic properties arise due to quantum confinement of charge carriers below the Bohr radius. Due to the nanoscale nature of these materials, they exhibit a high surface-to-volume ratio, and nearly all desirable and undesirable properties are influenced by the surface. Notably, the QD surface is highly susceptible to defectivity that can hinder the utility of the material for targeted applications. For example, undercoordinated surface ions can localize excited state charge carriers thereby quenching the photoluminescence of the material — a key property of semiconductor nanomaterials for display technologies. Alternatively, the same surface defects can impact charge transfer reactions necessary for photocatalytic reactions.Material optimization by defect mitigation requires a holistic understanding of their origin, impact, and methods to eliminate defects. This compendium of research on quantum dots and nanoplatelets leverages complementary spectroscopic techniques to deliver molecular-level insight to the surface properties of the material and demonstrates a unique application of nanomaterials for polariton-mediated chemical reactivity. Defect elimination by post-synthetic treatment of defect-rich QDs is monitored by photoluminescence spectroscopy and 1H NMR spectroscopy which allows for quantitative characterization of the QD surface. These techniques are used to establish an effective method of defect remediation by controlled chemical reactions. These concepts are expanded to applications of QDs including photocatalysis. Precisely tuned defects are controllably introduced to the QD surface and their impact on interfacial charge transfer is monitored by cyclic voltammetry. Complementary work to advance NMR spectroscopy and diffusiometry methods for surface characterization are presented to guide highly controlled ligand exchange reactions. In an alternative area of research, semiconductor nanoplatelets are integrated in a surface lattice resonance cavity to generate exciton polaritons and in-situ control of exciton polaritons is achieved by an applied electrochemical potential. Ultimately, a foundational understanding of QD surface properties is crucial to realizing the full potential of QD-based devices.