Reduced and Oxidized Colloid Quantum Dots: Photophysics and Transport

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Semiconductor Nanocrystals with controlled composition, size and shape are novel materials with the unique potential for specifically engineered electronic and optical properties. This project addresses the possibilities afforded by dynamically tuning the charges. One single electron has large consequences even at room temperature, such as dramatically switching the "color" of a nanocrystal both in the visible and in the infrared. This project will first address the challenges to controllably inject and retain a well-defined charge in a small colloid quantum dot. This is an interfacial redox chemistry problem, which requires a coupled synthetic and characterization approach. Second, charges strongly interact with one another and they should greatly influence the carrier dynamics. Internal carrier dynamics is a basic and poorly understood subject in quantum dot physics and in this project, time-resolved spectroscopy will shed light on the influence of charges. Third, colloidal quantum dots are "artificial atoms", which can be assembled into crystalline solids with controlled spacers between dots. This project will investigate the transport properties of such nanocrystal arrays as a function of the charging of each nanocrystals. The project integrates research and education in a highly interdisciplinary fashion. It trains students in an area of nanoscience with potential applications in sensors, lighting a communications.There are only about 100 common elements in Nature but the variety of their chemistry is greatly enhanced by their various degrees of ionization. For example, the Chlorine ion Cl- is an unreactive but essential element for life, while the Chlorine molecule, C12, was the very poisonous gas used in World War I. Over the past twenty years material scientists have achieved a great degree of control of the synthesis and assemblies of very small crystals of semiconductors that mimic in many ways the electronic structure of atoms. By designing size, shape and composition of the "nanocrystals", one has now the possibility of designing supra "artificial atoms", from which countless benefits in electronic, optical and biological technologies are expected while several are already starting to be realized. The project will provide the basic research to dramatically expand the realm of these new "artificial atoms" by controlling their various degrees of ionization. The project integrates research and education in a highly interdisciplinary fashion. It trains students in an area of nanoscience with potential applications in sensors, lighting and communications.