Understanding and Controlling the Reactivity of Metal Oxide Nanoparticles

This thesis describes the development and application of a gas aggregation cluster source for the production of metallic nanoparticles (NPs). This high vacuum technique can produce a beam of crystalline particles through magnetron sputtering which may then be manipulated in-flight to further modify the properties of the particles. The particles were then subject to a detailed study of their reactivity as oxidation, in particular, proceeds very differently at the nanoscale compared to the bulk. Creating an understanding of oxidation at the nanoscale is critical to a more widespread application of these particles in industry.

After an introduction, the theory of solid state diffusion and oxidation is discussed. Particular attention is paid to the shortfalls of the bulk theories of oxidation at the nanoscale as well as highlighting the work to bridge the gap between the two length scales. Chapter 3 focuses on the experimental techniques used throughout this project to investigate the oxidation of the metal NPs. Chapter 4 describes in detail the gas aggreggation cluster source, starting with the theory of particle growth and beam production, then providing a comparison to other popular methods of growing NPs, before finally describing the work that took place to develop the cluster source at York. Chapters 5, 6, and 7 then present the results of targeted studies into the oxidation of Fe NPs. Fe is particularly relevant due its magnetic properties and high reactivity. Chapter 5 shows the work of in-situ environmental transmission electron microscopy experiments that allowed the determination of the diffusion coefficient of Fe in Fe oxide for the first time. Chapter 6 shows the results of in-situ spectroscopic measurements investigating the different types of oxide that form, with Chapter 7 showing the work that was undertaken to attempt to control/inhibit the oxidation process through coating with a secondary material.