Geometry, Topology and Defects in the Programmable Assembly of Nanoparticles
Materials whose fundamental units are nanocrystals (NC)s, instead of atoms or molecules, are emerging as major candidates to solve many of the technological challenges of our century. Those materials display unique structural, dynamical and thermodynamical properties, often reflecting deep underlying geometric, packing and topological constraints. In this talk, I will briefly introduce different NC systems studied in our group, such as those whose assembly is driven by DNA, electrostatic phase separation of neutral polymers, attachment of irreversible dithiol linkers, interpolymer complexation, Nanocomposite Tectons and also, via solvent evaporation. I will elaborate on this latter strategy and present the Orbifold Topological Model (OTM), which accurately describes the structure of crystal or quasicrystal arrangements of NCs (superlattices). The OTM represents capping ligands as Skyrmion textures, with “atomic orbitals” consisting of vortices, which enable the generation of a spontaneous valence and reveal the universal tendency of these systems towards icosahedral order. I will elaborate on the success of the OTM in describing existing experimental structural data on single component and binary superlattices with spherical NCs. Finally, I will present the diverse phase diagram of mixed Perovskite (cubic) and spherical NCs and emphasize the optoelectronic properties of these superlattices, thus demonstrating how a precise control of the structure determines the function.
Alex Travesset got his PhD from the Universitat de Barcelona in 1997. After Postdoc positions in Syracuse University and University of Illinois at Urbana Champaign, he joined the faculty at the Department of Physics and Astronomy at Iowa State University, where he is now full professor. He also holds an appointment in Materials Science and Engineering and is an associated scientist at the Ames lab.