Abstract

"Colloidal gels from plasmonic metal oxide nanocrystals"

Controlling the arrangement of inorganic nanocrystals in assemblies allows realization of materials whose properties depend both on the distinctive characteristics of their nanoscale building blocks and on their organization. We assemble superlattices and gel networks from colloidal nanocrystals that absorb infrared light due to their composition-tunable plasmonic resonance. Control and modulation of infrared optical signals is important for applications ranging from telecommunications to molecular sensing or thermal control – our work touches on each of these by establishing fundamental principles that govern light-matter interactions in doped metal oxide nanocrystal assemblies. To control the structure and dynamic optical properties of porous gel networks of nanocrystals, we synthetically tune their dynamic covalent bonding ligands. Small angle X-ray scattering provides a quantitative measure of the interactions between nanocrystals that govern these assemblies. Not only can these studies help us design responsive optical materials, they can also inform our understanding of the forces at work in directing the phase behavior and assembly of less ideal nanoscale components, like proteins.

Abstract

"How tiny, transparent crystals with a sprinkle of impurities hold the key to controlling infrared light"

As optical materials, metal oxides usually fulfill basic functions, like transparent window glass or particles that scatter light in bright white paint. Going beyond these simple, static properties, we make materials with highly tunable and even dynamic spectral response by doping metal oxides with deliberate impurities and by shrinking their dimensions to the nanoscale. Replacing a few percent of the metal ions in an insulator like indium oxide with charged dopants like tin results in the unusual combination of optical transparency with metallic conductivity in indium tin oxide (ITO). When chemically synthesized in nanocrystal form, ITO maintains its visible transparency, while the spatial confinement of free electrons results in the strong absorption of infrared light. I will discuss emerging applications of these nanocrystals that take advantage of their solution processibility and spectrally selective optical properties, including transparent conductors for optoelectronics, smart windows that dynamically control solar heating, and coatings that can keep solar cells cool to boost their efficiency.