Nanocrystal Solids: A Modular Approach to Materials Design
Prof. Dmitri V. Talapin
Department of Chemistry, The University of Chicago
Tuesday, March 23, 11am
Chemistry Division Auditorium, TA-46, Bld. 535, Rm. 103
Nanoparticles of different metals, semiconductors and magnetic materials can self-assemble from colloidal solutions into long range ordered periodic structures (superlattices). Combining two types of nanoparticles yields binary nanoparticle superlattices (BNSLs) exhibiting very rich phase diagrams with a multitude of close-packed and non-close-packed phases, including quasicrystalline arrangements. Through a series of systematic studies of self-assembly phenomena in single- and multicomponent nanoparticle assemblies we demonstrate that observed structural diversity is a result of the intricate interplay of entropy-driven crystallization with isotropic and anisotropic interparticle interactions, such as van der Waals, Coulombic and dipolar forces. Colloidal nanocrystals are considered promising building blocks for electronic and optoelectronic devices. Potentially, they can combine the advantages of crystalline inorganic semiconductors with size-tunable electronic structure and inexpensive solution-based device fabrication. However, the insulating nature of the surface ligands used for nanocrystal synthesis typically results in the poor electronic coupling between individual nanocrystals. In an attempt to address this fundamental problem, we demonstrated that molecular metal chalcogenide complexes can serve as versatile ligands for a broad range of inorganic nanomaterials. This new class of nanocrystal colloids provides a set of advantages such as all-inorganic design and diverse compositional tunability for both nanocrystal and ligand constituents. We observed electron mobility of ~10 cm2/Vs in arrays of CdSe nanocrystals and ~200 S/cm conductivity in arrays of 5 nm gold nanocrystals capped with metal chalcogenide Zintl ions. We demonstrate the power of this approach on several examples of prospective thermoelectric and photovoltaic materials.