Surface Chemical Effects On Localized Surface Plasmon Resonance In Metal Oxide Nanocrystals

With support from the Macromolecular, Supramolecular and Nanochemistry Program (MSN) in the Division of Chemistry, Professor Delia Milliron of the University of Texas at Austin is combining surface chemical reactions and advanced chemical analysis to study how the optical and electronic properties of metal oxide nanocrystals are influenced by their surface chemistry. In these tiny crystals, highly mobile electrons move under the influence of light, harnessing energy and concentrating otherwise diffuse infrared light into local regions the size of individual molecules. However, the very small size of the crystals means that their surfaces have a big impact on their mobile electrons and their interaction with light. Professor Milliron and her students are using chemical reactions to change the properties of the nanocrystal surfaces to understand and control the influence of surface chemistry. Their discoveries could lead to improved optoelectronic devices, like solar cells and displays, and to more sensitive chemical sensors to detect toxins or biochemical indicators of disease. The team is using virtual outreach strategies, especially targeting younger audiences, to broaden public awareness of science and to make science more accessible. This project involves the post-synthetic surface chemical modification of doped metal oxide nanocrystals. Aliovalent dopants are incorporated in the nanocrystals during colloidal synthesis, introducing a high concentration of free electrons and leading to localized surface plasmon resonance (LSPR) in the infrared spectral region. Their localized surface plasmon resonance (LSPR) absorption spectra and the near-field enhancement of electromagnetic field intensity are strongly influenced by the presence of surface electronic states that induce band bending. This project employs post-synthetic surface chemical reactions to modify the electronic structure of the nanocrystal surfaces. Dipolar organic molecules are attached to the surface to shift the energy levels and modify the depletion layer. During overgrowth of insulating metal oxide shells by colloidal atomic layer deposition, reactions with the chemical groups responsible for band banding shift the energy levels of the associated surface states. Optical analysis will be combined with photoemission spectroscopy to analyze the mechanisms by which surface chemistry influences LSPR, with the aim of establishing the foundational understanding needed to develop sensitive and chemically specific detectors, and to direct the flow of energy to tune and enhance catalytic processes. 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.