Electronic Structure Analysis Through Ligation and DFT Calculations of Ultrasmall CdSe Quantum Dots
Discipline: Nanoscience
Subcategory: Nanoscience
Kristi Pepa - City College of the City University of New York
Co-Author(s): Megan Webster, Department of Chemical Engineering, City College of the City University of New York ; Ilona Kretzschmar, Department of Chemical Engineering, City College of the City University of New York; Gustavo Lopez, Department of Chemistry, Lehman College of the City University of New York ; Anthony Cruz, Department of Chemistry, Lehman College of the City University of New York
The electronic structure of quantum dots can be manipulated by taking advantage of the size dependence of quantum confinement and through modifications of the quantum dot surface, e.g. ligation. As such, quantum dots have been considered for a wide variety of applications. Cadmium Selenide (CdSe) quantum dots, for example, show promise as an innovative photovoltaic material due to their size dependent electronic band structure. As their size decreases, these nanostructures emit light at shorter wavelengths. However, at radii of less than 2 nm, CdSe quantum dots have been observed to emit white light. A possible mechanism for this phenomenon is fluxionality, in which, due to the high degree of disorder stemming from the large surface area to volume ratio of these CdSe quantum dots, the surface is constantly reconfiguring, resulting in a fluctuating band gap. Through a combination of surface modifications and density functional theory (DFT) simulations, the mechanism behind this white light emission and the effects of ligands on the electronic structure of ultrasmall CdSe quantum dots is explored. The CdSe quantum dots are capped with various aliphatic thiol chains and compared to models using the PBE and PBE0 functional. The electronic properties of the quantum dots are investigated using photoluminescence spectroscopy and ultraviolet-visible spectroscopy. Transmission electron microscopy is used to understand the crystal structure of the quantum dots. Thiol chains were found to both quench and red shift the photoluminescence of the CdSe quantum dots. Future research involves analyzing the effects of different functional groups on the band gap of the quantum dots.
Not SubmittedFunder Acknowledgement(s): I thank the NSF CREST program for funding this project.
Faculty Advisor: Ilona Kretzschmar, ikretzschmar@ccny.cuny.edu
Role: I've done work on synthesizing and capping the ultrasmall CdSe quantum dots and ultraviolet-visible and photoluminescence spectroscopy. I've also done first principle molecular dynamics on small CdSe clusters.