The ability to make nanocrystals of high quality (uniform size, no defects except the ones we want, designed surface, etc.) is key to this area of science, and also interesting in its own right. We grow nanocrystals with well controlled sizes and shapes by injecting molecular precursors into hot liquids that also contain molecular species that will coordinate to the growing nanoparticle surfaces. Some important questions of solid state chemistry can be addressed in the synthesis of nanocrystals. How does nucleation of a solid occur? What governs the rate of growth of each facet of a crystal? What is the stress and strain at the interface between a core and a shell of different materials?
We can think of a simple nanocrystal as a type of artificial atom. In that case, the next step in nanocrystal synthesis is to learn how to make artificial molecules, in which nanocrystals (atoms) of differing composition, size, and shape, and interconnected with each other in a designed arrangement. To accomplish this, we develop modular approaches to the chemical transformation of nanocrystals. Three such transformations we have developed and exploited are: Cation exchange, the nanoscale Kirkendall effect, and branching. With these we can make branched, striped, segmented, hollow, and nested nanoparticles. We are working to better understand the mechanisms of each of these transformations, as well as searching for new and general nanoparticle chemical transformations.
In addition to fundamental studies of nanocrystal synthesis, we are interested in developing automated, self-correcting nanocrystal syntheses, surface derivitization, and methods for nanocrystal characterization and assembly. A feature of our current work is the development of new methods to observe the growth trajectories and formation mechanisms of individual colloidal nanocrystals in liquid solutions.
Craftsmen were arguably the first nanoscientists. Artifacts from as early as the Bronze Age reveal that artisans harnessed nanoscale phenomena to produce a variety of effects: lustre in early Islamic ceramics, enhanced strength in 9th century Syrian swords, and rich colors in ancient Roman, Egyptian, Chinese, and medieval European glass. Historians of science tell us that early craftsmen's practices-gathering information through direct observation, measuring materials to promote reproducible results, and changing one variable at a time-did much to shape the methodology of science. Walk into a contemporary nanoscience lab, and you will find scientists using techniques that derive from ones developed by artists-for example, nanolithography and Lagmuir-Blodgett film-casting.
Thus, it is natural that an interdisciplinary lab such as ours would include an artist. Our artist-in-residence, Kate Nichols, was initially drawn to using nanomaterials because of her interest in structurally colored Morpho butteflies. (Morpho butterflies appear as brilliant blue despite their lack of blue pigmentation. Their blue color is structural rather than chemical, deriving from nanoscale features within their wings.) Once in our lab, Kate was inspired by medieval artisan's use of plasmonic nanoparticles in stained glass windows. She synthesizes similar plasmonic nanoparticles and uses them to create macroscale art whose structural colors arise from surface plasmon resonance. In her painting, photography, and writing, Kate continues to explore natural photonic structures. Her work can be seen at The Leonardo, a museum of art and science in Salt Lake City, on her website, and at TED.