ORCID

http://orcid.org/0000-0001-9979-7061

Date of Award

Spring 5-15-2020

Author's School

Graduate School of Arts and Sciences

Author's Department

Chemistry

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

This dissertation presents various surface-ligand exchange reactions on cadmium selenide quantum belts (QBs), specifically between L-type, Z-type and bound-ion-pair AX salt type ligation. The surface ligation of nanocrystals determines their optical and transport properties, and thus purposeful control of nanocrystal surface chemistry is under active investigation. Colloidal 2D II-VI (specifically CdSe) QBs provide an ideal system for the study of rapid, complete, and reversible surface exchange at room temperature. Interchange of different types of ligands is observed. The surface exchanges are characterized by a variety of means, and the absorption and emission spectra of the QBs are extremely sensitive to surface ligation. We demonstrate that L-type ligands are rapidly, reversibly, and completely exchanged by Z-type metal halide ligands. Amine-ligated {CdSe[n-octylamine]0. 53±0. 06} QBs undergo instantaneous, reversible exchange of the L-type amine ligation for Z-type ligation provided by the neutral metal halides MX2 (M= Cd, Zn; X= Cl, Br, I). Exchange from L-type to Z-type MX2 ligation results in large shifts of the quantum-belt absorption features to lower energy, which are 252, 151, and 157 meV for CdCl2, CdBr2, and CdI2 ligation, respectively. These reversible exchanges demonstrate the strong influence of surface ligation on the electronic properties of the 2D nanocrystals. We also demonstrate that Z-type ligation of CdSe QBs is exchangeable by bound-ion-pair X-type ligation. Simple salts AX (A= NR4+ or Na+) displace Z-type ligation to give bound-ion-pair X-type ligation. These exchange reactions are also rapid, complete, and fully reversible. The approach used here may shed light on a broad technological adaption of solution-processed metals, dielectrics, and semiconductors. Finally, we differentiate thiol and thiolate ligands on CdSe QBs. We identify various bonding modes and conclude that thiol and thiolate ligands are readily exchangeable on CdSe QBs.

Language

English (en)

Chair and Committee

William E. Buhro

Committee Members

Sophia Hayes, Loomis A. Richard, Bryce Sadtler, Li Yang,

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