Silicon Nanocrystals: High-Temperature Reactions of Silicon and Silicon Oxides

• Author / Creator

  O'Connor, Kevin

• Hydrogen silsesquioxane (HSQ) is a versatile material with a lengthy history in the synthesis of silicon nanocrystals (SiNCs). Although SiNCs are an exciting material for many optical, electronic, and biological applications, the focal point of this thesis challenges many of the preconceived notions regarding SiNC synthesis from HSQ disproportionation. The reliability of HSQ as a precursor material for silicon nanoparticles is examined and our understanding of its behavior under previously unexplored reaction conditions is expanded. Chapter 1 introduces materials at the nanoscale with a particular focus on silicon nanocrystals. Promising applications featuring SiNCs are highlighted and the major synthesis routes to SiNCs are discussed. The introduction closes with a section on the history of HSQ and its use as a precursor material for SiNC preparation. Chapter 2 pushes the boundaries of silicon nanoparticle (SiNP) synthesis by subjecting HSQ to previously unexplored high-temperature environments. In the course of investigating the HSQ disproportionation reaction under various temperatures and dwell times, a perplexing set of observations for a specific range of reaction conditions was discovered, resulting in the complete absence of elemental silicon. Although it has previously been assumed that the resulting Si–SiO2 interface is unreactive, sufficiently high temperatures can promote the reduction of SiO2 by Si to produce SiO gas. Under appropriate conditions, this somewhat unexpected reaction can complicate solid state nanomaterial syntheses by etching away the desired products. In both mixed Si/SiO2 powders and HSQ, the crystallization of silica into cristobalite facilitated the transport of silicon atoms through silicon monoxide formation. Elevating the reaction temperature to 1700°C effectively mitigated this undesired reaction in HSQ by softening the surrounding silica and inhibiting matrix crystallization. Chapter 3 presents the synthesis of SiNCs in ambient air from hydrogen silsesquioxane. SiNCs were produced in lower yield in air than in inert atmosphere; SiNCs prepared in argon showed no significant improvement in photoluminescence than those prepared in forming gas (5% H2 in Ar). The reducing atmosphere did impact particle size at 1700°C, indicating an onset of increased Si particle growth in the presence of hydrogen at high temperatures. Many insights gained from this research have implications for other group 14 nanocrystal syntheses employing solid-state disproportionation reactions. The demonstration of photoluminescent SiNCs grown in non-inert environments offers a promising synthesis route for other air-sensitive nanomaterials. Experimental work is summarized and future projects are presented in the final chapter.

• Subjects / Keywords

  • Silicon Nanocrystal
  • Silicon Nanoparticle

• Graduation date

  Spring 2024

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-qban-3t11

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.