Date: 03.02.2023, Time: 15:30h

Location: Kleiner Physik-Hörsaal N 020, Fakultät für Physik
The talk will also be streamed online.

Prof. Naomi Ginsberg
University of California, Berkeley

Hierarchical materials - materials that include a hierarchy of bonding interactions because their basic building block are more complex than those of individual atoms - present a wide array of underexplored phase behaviors and emergent properties. Examples include many current functional materials comprised of molecules or small particle building blocks, such as glasses and polymer-based plastics in which disorder is deliberately harnessed, and also next-generation semiconductors that can be formed with far more modest protocols than conventional ones, such as those being explored for display technology and solar cells. I will review the basic similarities among and differences between these hierarchical materials' structure and formation processes and also the emergent properties of various forms of energy transport. One current hallmark of the typical structures of hierarchical materials is that they are often trapped far from equilibrium, presenting heterogeneities that can affect their emergent properties. Studying these materials is therefore best done using a combination of reciprocal-space and direct-space approaches, and I will provide examples of resolving different types of material evolution with each.

First, I will describe our transient optical approaches to directly image the nanoscale transport dynamics of various types of quasiparticles in a wide range of hierarchical semiconducting and conducting materials. For example, by characterizing the mean squared expansion of initially localized charge carriers, bound electron-hole pairs, heat, and sound, we elucidate the impact of various material heterogeneities on electronic and thermal transport and also the interplay between heat and charge distributions. Next, many hierarchical materials we study are formed via self-assembly protocols, especially in the solution phase. I will also share recent observations of in situ X-ray scattering of self-assembly and annealing of strongly coupled nanoparticle superlattices. The strong coupling is borne out of the use of short, highly multivalent anionic chalcogenometallates used both as electrolyte anions and stabilizing ligands for the high dielectric nanoparticles, and I will describe our initial work to elucidate the specific mechanisms that drive the assembly and ordering, which could open many possibilities to create hierarchical materials with new functions deterministically from the bottom-up.