Near-field coupling between molecular vibrations and plasmonic metal oxide nanocrystals

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Chemists can grow extremely small crystals. The smallest crystals can be only a few nanometers in size, or about 100,000 times smaller than a sheet of paper. These small crystals contain just a few thousand atoms. Some nanocrystals can concentrate light and the focused energy can be used in applications ranging from solar energy conversion to sensing. However, a single type of nanocrystal can only concentrate a few colors of light. By changing its chemical composition, one can adjust this color for specific applications. With support from the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professor Delia Milliron at the University of Texas at Austin is growing nanocrystals that concentrate infrared light. While we cannot see infrared light, we feel it as heat from sunlight or a hot fire. Working with her students, Professor Milliron is studying how the size, shape, and composition of a nanocrystal influences its ability to concentrate infrared light. Their discoveries could lead to better ways of detecting specific chemicals and improved catalytic methods, which would have important benefits to society. An interactive educational module regarding nanoscience and light-matter interactions is being adapted to reach diverse audiences, including high school students at Texas School for the Deaf and younger students who visit UT's campus for Girl Day and Explore UT, both are community-oriented outreach events.This project targets the synthetic development of colloidal metal oxide nanocrystals (NCs) containing aliovalent dopants that induce a high concentration of free electrons, leading to localized surface plasmon resonance (LSPR) in the mid-infrared spectral region. Coupling between LSPR modes and the vibrational modes of proximal organic molecules is studied quantitatively. Most research on LSPR has focused on noble metals, which must be patterned into larger, micron-scale metal structures to reach mid-infrared frequencies. The limitations of that approach motivate the investigation of plasmonic metal oxide NCs. This is quantitatively establishing how NC physiochemical properties control the nature and strength of coupling between LSPR and vibrational modes, ultimately leading to the foundational understanding needed to develop sensitive and chemically specific detectors, and to direct the flow of energy to tune and enhance catalytic processes. The team is creating interactive educational activities that illustrate how the interaction of light and matter is used in modern applications, such as electronic displays and solar cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.