Probing the Vibrational and Electronic Properties of Atomically Precise Nanostructures: From Cadmium Selenide Quantum Dots to Graphene
Presented by Andrew Crowther, Barnard College
Hosted by Xiaoyang Zhu
The Crowther Group uses micro-Raman spectroscopy to investigate the vibrational and electronic properties of two nanostructure classes: semiconductor nanocrystals and carbon-based materials. Semiconductor nanocrystals occupy a size regime between the molecular and bulk limits. As a result, nanocrystal vibrational structure can be described using either a molecular "bottom-up" quantum chemical approach or a "top-down" phonon confinement model that truncates bulk phonon wavefunctions at the nanocrystal boundaries. We use temperature-dependent Raman spectroscopy to identify the size transition from molecular vibrations to confined phonons in a series of atomically precise cadmium selenide quantum dots of tetrahedral shape with edges that range from 1.7 nm to 2.6 nm in length. Surprisingly, the presence of only one unit cell in the nanocrystal is sufficient to successfully apply a phonon confinement model. In a second project, we use Raman spectroscopy to determine how solvation affects electron transfer from graphene to the model electron acceptor molecule iodine. Understanding these solvation effects is a necessary prerequisite for many graphene applications. Solution-phase isotherms demonstrate that solvent polarity, iodine concentration, and solvent-I2-graphene electronic interactions drive surface adsorption of I2 and subsequent electron transfer. We also identify a threshold I2 concentration for accessing the interface between graphene and the substrate for two-sided adsorption.
About Andrew Crowther: Andrew Crowther earned his B.A in Chemistry from Washington University in St. Louis in 2002 and his Ph.D. in Chemistry under the supervision of Professor F. Fleming Crim at the University of Wisconsin-Madison in 2008. He then completed a Christine Mirzayan Science and Technology Policy Fellowship at the Board on Chemical Sciences and Technology at the National Research Council, followed by postdoctoral research with Prof. Louis Brus at Columbia University. Professor Crowther has been an Assistant Professor of Chemistry at Barnard College in New York City since 2012, where his research group uses Raman spectroscopy to investigate the fundamental vibrational and electronic properties of nanostructures. His research has been supported by the American Chemical Society Petroleum Research Fund and the National Science Foundation.