Design, synthesis, and properties of colloidal multi-dot nanorod heterostructures

The Shim research group is dedicated to synthesizing novel anisotropic nanocrystals and incorporating them into solution-processed optoelectronic devices. My research is focused on colloidal II-VI nanorod heterostructures: how to synthesize them with precision, and how particle geometry affects electronic band structure and optical properties. In the closely related field of spherical and isotropic core-shell quantum dots, there are only a few geometric parameters to consider in particle design: the radius of each component, of which there are often just two. By contrast, a dot-in-rod has the radius of the core, the length of one side of the rod, the radius of that side, the length of the other side, and the radius of that side. If we grow just one more segment on each tip, that’s another four parameters. Each of these factors influences the optical properties, and the design space is very large! This is to say nothing so far of how one might synthesize such particles. The situation is considerably complicated by several factors: One, the substrate is three-dimensional and has many facets of different chemical termination. Two, the substrate is polar, and is suspended in nonpolar solvent by means of amphiphilic ligands which bind differently to different facets. Three, we must create about 10^17 of the substrates in a typical reaction, and we must make them as identical as possible to one another so that we can utilize them in macroscopic applications and characterize them with macroscopic instruments. After decades of theories, experiments, observations, and simulations, these issues are (mostly) resolved for core-shell quantum dots, and one can readily find such optimized products for sale. While we can extensively utilize this scientific foundation in the pursuit of more complex geometries, often there are very new problems which appear. What used to be a terminating surface must now be used to grow another component, and suddenly its shape becomes much more important. Precursors might react differently or not at all on different regions of a multi-composition substrate. Chemicals rarely do ”just” one thing - one which promotes epitaxy in a certain direction might also affect nucleation kinetics. Once we understand these synthetic challenges and how to address them, we can return to the realization of new and optimized particle designs, and lay the foundation for applications beyond efficient conversion of current to light (though they should still do that, too). What should be the shape of a particle which converts light to current just as efficiently? One that converts low energy photons to those of higher energy using thermoelectricity? One whose color and brightness depends on the color and intensity of excitation, or which is sensitive to the chemical and electronic environment? Can we create a particle which localizes charges when they’re balanced, and delocalizes them when they’re not? With anisotropic heterostructures, we can achieve these properties and more - to some extent. Some of the geometries have been optimized for their desired purpose, while others presented here are but prototypes which exemplify certain processes. The following chapters describe this process of band structure design and synthesis optimization, and the properties which arise from the emergent complexity of the geometric parameter space.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Drake, Gryphon

Contributors dc:contributor

• Shim, Moonsub
• Zuo, Jian-Min
• Smith, Andrew M
• Schleife, Andre

• Quantum Dot
• Colloidal Synthesis
• Nanorod Heterostructure
• Electron Microscopy
• Photoluminescence
• Photochemical Doping

Statement dc:rights

• © 2023 Gryphon Drake

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/120503

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F120503