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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

Year Degree Awarded

2016

Month Degree Awarded

May

First Advisor

Kevin R. Kittilstved

Subject Categories

Chemistry | Inorganic Chemistry | Materials Chemistry

Abstract

Spin-based electronics use the spins of electrons in addition to their charges and have potential applications to create a next generation of quantum computers, capable of storing vast amounts of data in an energy-efficient way. Diluted magnetic semiconductor quantum dots (DMS-QDs) have shown great promise as ideal materials for application in spin-based electronics. However, doping impurities into quantum confined colloidal nanocrystals (NCs) has been a great challenge due to the lack of control over the dopant reactivity during the specific stages of nucleation and growth. The mechanism of dopant incorporation into nanocrystals is complex and well-defined and atomically precise molecular clusters can provide detailed knowledge and novel insights into the doping process. This work focuses on the synthesis of Co2+ substituted CdS and ZnS based molecular clusters and understanding doping mechanism at the molecular level and use these clusters as precursors to make doped nanocrystals. The cation exchange rates and thermodynamic stability of dopants in the smallest tetrameric clusters is found to depend mainly on the identity of the host cation in the cluster. The surface ligand dynamics of clusters directly control the rate of dopant ion exchange into molecular clusters. As the size of molecular clusters increases the ligand dynamics decreases and dopant exchange into these larger clusters becomes less feasible.

We developed a method to synthesize doped NCs using these pre-doped magnetic molecular chalcogenide clusters, as single-source precursors. We obtained very high concentration of cobalt impurities into CdS nanocrystals without undergoing spinodal decomposition. This high doping level is attributed to the growth mechanism that involves formation of dopant substituted metastable magic-sized nuclei (CdS)34 before the critical nuclei during the synthesis. Furthermore, the particular growth mechanism of doped nanocrystals can be controlled by the size of diluted magnetic molecular precursors. The synthetic strategy demonstrated here utilizes magnetic inorganic clusters as true single-source precursors and provides an effective and tunable route to synthesize doped nanocrystals with high dopant concentrations.

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