Symmetry Making and Breaking in the Synthesis and Assembly of Stellated and Bimetallic Nanocrystals

Indiana University, Bloomington IN

Investigators

Abstract

Nature demonstrates symmetry in the beauty of a flower, the precision of a honeycomb, and the elaborate patterns of snowflakes. Beyond the appeal of symmetric forms, symmetry can also impart function. For example, orb spiders weave in a spiral pattern to maximize the strength of their webs and bees construct honeycombs with close packed hexagons to maximize honey storage. This correlation between structure and function is also captured in modern nanomaterial design, where changing the symmetry of a nanocrystal or the internal order of a superstructure built from nanocrystals can give novel function. However, the synthesis and assembly of nanomaterials have been limited to simple compositions and structures until recently. In this research, the principal investigator, Sara Skrabalak, is developing new synthetic methods to make metal nanostructures with multiple metals and defined shapes. These nanostructures are also being used as building blocks to form larger structures, where the symmetries of the building blocks direct the shapes of the larger superstructures. The principal investigator and her students also study how the compositions and structures impart functionality. In particular, studies into the new light-matter interactions that arise as a function of symmetry are underway in an effort to achieve multi-functional platforms for chemical sensing applications. Ultimately, this research has broader impacts in the field by forging links between multiple disciplines, including nano/inorganic/solid-state chemistry, condensed matter physics, surface science, and material science. This project also incorporates outreach and educational efforts that introduce nanoscale concepts to non-scientists. The project also involves undergraduates in research activities in ways that emphasize their connection to the surrounding community. The Skrabalak group at Indiana University is developing seed-mediated co-reduction as a new synthetic strategy to multimetallic nanostructures, where multiple metals are simultaneously deposited onto shape-controlled nanocrystals. The symmetry of the nanocrystal seeds is transferred to the final nanostructures. This research includes studying how lattice mismatch and deposition kinetics contribute to bimetallic distribution. This work is coupled with a study of how symmetry can be reduced along specific crystallographic directions during seed-mediated co-reduction in order to achieve new stellated nanocrystal symmetries and in turn functional diversification. Finally, the Skrabalak group is using the stellated metal nanocrystals to assemble close-packed and low-density lattices to expand crystallization capabilities to new structural classes. They also characterize the collective optical properties that emerge. These three aims are coupled with outreach and educational efforts in which undergraduate researchers are Science Ambassadors to their former high schools, introducing nanoscale concepts to students and serving as role models to those interested in science, technology, engineering and mathematics fields. Advancement in the research expands the classes of nanocrystals and superstructures possible and identifies the roles of seed and building block symmetry in the synthesis and assembly of metal nanocrystals for broader impact in the science.