Mechanisms of Surfactant-Mediated Crystallization of Colloidal Quantum Dots

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With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Professor Jonathan Owen at Columbia University is studying the fundamental processes that control the growth of nanometer scale crystals. With deeper understanding of crystal growth mechanisms, scientists can design and manufacture crystals with improved performance in solar cells, light emitting diodes, lasers, and infrared cameras capable of capturing images at night. In this project, crystal growth kinetics is monitored with X-rays generated at synchrotron light sources that allow the first moments of crystal formation to be visualized. Mathematical models are developed to describe the evolution of the growing crystals and predict the growth of new materials. Professor Owen develops an educational program that integrates the research with the education of high school, undergraduate and graduate student researchers, including students at New York City schools serving under-represented elementary, middle school, and high school students. The group communicates the value of research on nanoscale materials to the public.The concentration and temperature dependence of lead selenide and lead sulfide nucleation and growth is probed in this project using in situ optical spectroscopies and X-ray scattering. The solute concentration and the nanocrystal size and yield are monitored in real time. The atomic structure of intermediates formed during the nucleation phase is probed in situ using pair distribution function (PDF) analysis of X-ray scattering. These studies are complemented by ex situ studies of the precursor conversion reaction and the size dependence of the growth kinetics to arrive at a holistic understanding of each of the coupled phases of the reaction. Rate equation models and structure prediction methods are used to model the evolution of the solute and nanocrystals throughout nucleation and growth. Professor Owen is using a synergistic approach to help determine whether the nucleation mechanism follows a classical process involving a critical nucleus whose radius changes with the supersaturation, a rate limiting transition between specific “magic size” clusters, crystallization from an amorphous intermediate, or a molecular process. A deeper understanding of crystal nucleation growth can accelerate the design of a broad array of new materials for luminescent displays, solid state lighting, and photovoltaics. Professor Owen is also working with high school, undergraduate and graduate students closely on this project. He develops a laboratory module to teach high school students about luminescence and shares the teaching tools with local schools serving underrepresented minority students.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.