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Author ORCID Identifier

https://orcid.org/0000-0002-9500-0876

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Kevin R. Kittilstved

Subject Categories

Chemistry | Inorganic Chemistry | Materials Chemistry

Abstract

Diluted magnetic semiconductor quantum dots (DMS-QDs) is a class of material prepared by introducing a small percentage of magnetic impurities to impart new magneto-optical properties to the host nanocrystal (NC). Such materials are regarded as promising candidates for their potential application in spintronic devices. The overall functionality of the DMS‑QD is highly dependent on the dopant position within the host structure. A thorough understanding of the doping mechanism is, therefore, critical to gain better control over the dopant speciation in nanocrystal lattice and material properties. In this work, we utilized II‑VI molecular clusters that are analogous to bulk semiconductors as model systems to obtain mechanistic insight into the doping process. More specifically, we developed new protocols for dopant speciation and to achieve precision doping in these clusters. These molecular clusters are often studied to gain a detailed understanding of the size‑property relationship in quantum‑confined semiconductor nanocrystals. However, studies of the doping of these structurally well‑defined materials and the effect on the host properties are rare. The work presented here focuses on elucidating the solution dynamic of clusters in order to develop controlled doping strategies. The work is primarily centered on Mn2+ and Co2+ as the dopants and CdS molecular cluster as the host. Monitoring the relative peak intensity of both doped and undoped fragments of Mn2+ or Co2+ substituted CdS cluster by electrospray ionization mass spectrometry (ESI‑MS) is demonstrated to be an effective method determining for dopant speciation. The cluster‑cluster equilibria unraveled from our investigations led us to establish a process that allows for precision doping of clusters. Synthetic methods were formulated based on our understanding of equilibria to yield a larger sized cluster. Furthermore, the presence of impurity ions was found to have a significant impact on the equilibria as well, demonstrating that dopants participate in both cation exchange reactions and the cluster evolution.

In addition, the solution dynamic of the isolated clusters was observed and shown to have higher sensitivity towards its surrounding environment. New equilibria were rapidly established once small traces of metal ions were introduced to a solution of pure clusters. The solvent and core chalcogenide ions were found to have a profound effect on the equilibrium as well as the disintegration and growth processes. The studies of solution dynamics presented in this work provide insights relevant to the development of synthetic routes for precise impurity ion doping at the molecular level and to the cluster growth mechanism.

Available for download on Sunday, May 10, 2020

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