Achieving Structurally Indexed Measures of Nanocrystal Surface Reactivity Toward Advanced Applications

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, and the Established Program to Stimulate Competitive Research (EPSCoR) at the National Science Foundation, Prof. Andrew Greytak of the University of South Carolina will investigate how molecules pack on the surface of nanometer-scale crystals of semiconducting and magnetic compounds.

Semiconductor nanocrystals are well-established as a system with unique and size-tunable electronic properties, as emphasized by the awarding of the 2023 Nobel Prize in chemistry for the formation of nanocrystal quantum dots (QDs). Although much effort has been devoted to understanding how organic molecules and inorganic complexes that adhere to the surfaces of nanocrystals in solutions can guide nanocrystal growth and the resulting shapes, there are relatively few examples of selective modification of different nanocrystal facets.

The ability to selectively modify nanocrystal surfaces according to crystal size and symmetry, leading to control over the type and spatial orientation of interparticle interactions, could ultimately enable new applications of fluorescent and/or magnetic nanocrystals ranging from efficient LEDs, to fluorescent voltage sensors, to quantum information technologies, to multiplexed detection of biomarkers. The project will support mentorship of student researchers including a first-year Undergraduate Research Initiative at USC.

The concepts of spectra, fluorescence, materials chemistry, and nanoscience will be communicated to the next generation via a new partnership with the South Carolina State Museum, as well as with local public schools via additions to the Department of Chemistry & Biochemistry’s Outreach Education program.

The project design centers on characteristic ligand exchanges on several classes of nanocrystals in which a high degree of structural control can be achieved, including (1) “magic size” nanocrystals sharing the zincblende crystal structure; (2) a series of nanorods of different lengths and nanoplatelets of different lateral dimensions with uniaxial hexagonal crystal structures; and (3) magnetite nanocrystal samples with narrow size distributions. This project will overcome previous limitations by using isothermal titration calorimetry (ITC) as a principal measurement by which to distinguish reactivity at different types of surface sites.

In this manner, the project aims to make it possible to reconcile effective parameters obtained from measurements with microscopic parameters returned by theoretical models, and evaluate circumstances in which selective functionalization of surface sites can be accomplished at room temperature.

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.