Part I. The exact composition, size and morphology of semiconductor nanocrystals precisely determine their opto-electronic properties (band gap, exciton lifetime and decay pathways, carrier mobility). While researching the synthesis of binary CdE nanocrystals and their ternary CdE-CdE' alloys (E, E' = S, Se), we found that the relative ease of formation of different nanocrystalline phases is a direct consequence of the reactivity of their molecular precursors. Using a series of closely related molecular precursors, we are building a working scale of chemical reactivities for chalcogenide, pnictide and cationic precursors. This could obviate the need for time-consuming testing of several different reaction conditions or unrelated precursors as is currently practiced in the field of solution phase nanocrystal synthesis.            Part II. Controlling the degree of functionalization or valence per nanocrystal remains an unsolved challenge in colloidal semiconductors. Surface modification is routinely performed by exchanging the nanocrystal's native ligands with excess carboxylate- or amine-terminated thiols. This ligand exchange approach fails to control the extent of surface modification. We are investigating fundamentally new surface ligand doping strategies that enable to control the degree of functionalization or valence per nanocrystal while retaining its original colloidal and photo stability. As part of this goal we also investigate changes in ligand organization, surface chemistry and nanocrystal properties that result from surface modification. The extent of surface coverage by a particular functional group has a large impact on a nanocrystal's surface affinity and permeability, and thus on its ability to localize, penetrate, and be transported across specific biological tissues, cellular and subcellular structures.

Molecular control of nanoscale composition, morphology and function: From compositionally graded nanorods to surface doped quantum dots

247th National Meeting (2014)

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