First Advisor

Andrea Goforth

Term of Graduation

Fall 2024

Date of Publication

12-16-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Chemistry

Department

Chemistry

Language

English

Subjects

DOE, Material Science, Nanoscience, Silicon

Physical Description

1 online resource (xvi, 159 pages)

Abstract

Silicon nanocrystals (SiNCs) show promising physiochemical properties that could be used in industrial applications. The production of SiNCs through solid-state synthesis is ideal due to relatively low cost of equipment and chemical reagents, as well as the ability to scale-up production. A widely known and commonly used precursor previously used in solid-state synthesis for SiNCs, hydrogen silsesquioxane (HSiO1.5), was discontinued in chemical manufacturing, which has led to researching alternative precursors (or starting materials). We have identified that there is a gap of knowledge related to producing these precursors, as well as the mechanistic understanding of the chemical reactions that occur in solid-state synthesis that favor the production of SiNCs.

This dissertation addresses several key steps in the complete synthesis of SiNCs. The first step was producing a precursor that was similar to HSiO1.5, which is a hydrogen-rich silicon suboxide (HSiOx) polymer. Using a design of experiment (DOE), the produced were analyzed for the elemental and structural compositions and linked to experimental variables that impacted these characteristics (Chapter 2). We identified both single and combined experimental variables that had the greatest influence on the HSiOx chemical and structural properties; namely the molar ratio of solvent used as well as the solvent addition rate. All polymers produced shared similar elemental composition but had structural variety, differing in the calculated percentages of cage-like structural features.

The next step was producing SiNCs through solid-state annealing (Chapter 3), using HSiOx polymers produced in Chapter 2. A second DOE was conducted where examined experimental variables in the annealing process were quantitively correlated with characteristics of composite powders produced. These experimental variables were the ramp rate to the maximum hold temperature, the dwell time at the maximum hold temperature, and the type of HSiOx polymer used (regarding cage-like composition). Composite powders produced from annealing HSiOx polymers were examined through multiple methods such as visible light imaging, fluorescence, Fourier transform infrared (FTIR), and Raman spectroscopy. Experimental variables correlated with the production of SiNCs were identified and the SiNCs were characterized in relation to their composition (crystallinity) and photochemical properties (fluorescence). A brief investigation into etching the SiNCs from the composite powders and suspending them in a solvent was done in Chapter 4. Physical properties (size) and photochemical properties (fluorescence) were analyzed with notable effects from oxidation impacting both properties. Composite powders containing unexpected by-products were characterized for silica polymorphs (Chapter 5).

Overall experimental trends of synthesizing both HSiOx polymers, as well as SiNCs from these polymers, are summarized in Chapter 6. Ideal physical and chemical traits of HSiOx polymers are described, as well as synthesis conditions that are suitable for producing brightly fluorescent SiNCs in either composite powders or etched into a solution.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/42913

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