Single Particle Spectroscopy and Microscopy of Doped Colloidal Semiconductor Nanocrystals

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Semiconductor nanocrystals are small, crystalline particles that contain only hundreds to thousands of atoms. At these small sizes, new optical and electronic properties emerge, which can be adjusted by changing the particle's size and shape. These properties can also be manipulated by swapping just a few atoms in the crystal lattice with atoms of another element, or dopant. The precise control over the number and placement of these dopant atoms within a nanocrystal is challenging. With support from the Macromolecular, Supramolecular and Nanochemistry program in the Chemistry Division, Professor Todd Krauss and his students at the University of Rochester are using sophisticated microscopy methods to correlate the number and position of dopants in a single nanocrystal with their luminescent and electronic properties. Their discoveries could have important implications for designing nanocrystals used in emerging technologies that range from solar energy conversion to quantum information systems. The project is also training the next generation of scientists in the development and application of advanced experimental physical chemistry methods. The team is introducing the project research to the public and fostering an enthusiasm for scientific discovery through outreach efforts at the Rochester Museum and Science Center and other public venues. The project is developing the detailed understanding of nanocrystal doping and doping mechanisms needed to synthesize nanocrystals and nanocrystal assemblies with improved chemical and photophysical properties. Studies of silver cation (Ag+)-doped cadmium selenide (CdSe) nanocrystals and nanoplatelets are uncovering the specific chemical mechanisms occurring during the doping process. State-of-the-art electrostatic force microscopy measurements in combination with simultaneous measurements of photoluminescence from a single nanocrystal reveal how impurity atoms change the electronic and optical properties of the intrinsic nanoparticle. The project is also investigating the optical properties of tin telluride (SnTe) nanocrystals. This emerging direct-bandgap material could be used as an environmentally friendly alternative to current materials in infrared-based technologies. However, the basic properties of the SnTe excited state (e.g. electronic, excitonic, or plasmonic) remain unknown. Steady-state and time-resolved spectroscopies are used in conjunction with high-resolution electron microscopies to correlate photophysical observations with material composition to develop a detailed picture of the SnTe excited state.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.