Formation of nanoparticles by thin film dewetting

The synthesis and assembly of nanostructures has been extensively researched because of the potential for developing new device arrays and the myriad applications they might entail. Fundamental physical laws, however, dictate the combinations of materials/substrates that provide the requisite conditions, especially in physical vapor deposition. To circumvent these limitations, a common approach is to use solution---based techniques to form nanostructures that are then dispersed and dried on substrates of choice. While solution---based techniques produce structures with closely controlled compositions and sizes, the impurities associated with the process and interactions between capping agents (to prevent clumping) and particles affect the electronic properties of the final nanostructures.;A robust way of circumventing the growth restrictions of vapor deposition onto a substrate is buffer-layer-assisted growth (BLAG). In BLAG, a thin film (buffer) is grown on the substrate prior to deposition of the nanostructure material. The properties of the resulting structures are dependent on the interaction of the deposited species with the buffer rather than with the substrate, making possible a wide range of nanostructures---on---support systems. The sizes and number densities of the structures can be controlled by varying the amount of material deposited and the thickness of the buffer layer. As the buffer material is removed, the formed nanostructures are soft landed on the substrate.;Nanostructure aggregation in BLAG takes place due to instabilities in the buffer that cause it to dewet. Typical buffers are thin films of rare gases, notably xenon, condensed on substrates held at 20--50 K, though the aggregation process also occurs for CO2 and H2O layers and can be extended to metal thin films. Despite the differences in the buffer material and the consequent change in dewetting and sublimation or evaporation temperatures, the underlying processes remain the same. With increasing complexity of the buffer material and nanostructure combination, new insights into particle formation and their interaction with the buffer can be obtained.;Chapter 1 of this thesis describes the BLAG process, and the structural properties of the nanostructures produced by BLAG. Chapters 2 and 3 discuss specific applications of BLAG. Chapter 2 focuses on compound and elemental semiconductor nanostructures and quantum confinement effects in them. Chapter 3 discusses embedded non-magnetic nanoparticles in a magnetic matrix and the measurement of induced magnetism using polarized x-ray absorption spectroscopy. Chapters 4 and 5 extend the BLAG process to particles formed on metal films. Chapter 4 is devoted to the study of growth and embedding of nanoparticles in metal films. The embedding process is driven by differences in free energies between the two materials, and we show how competition between growth and embedding affects the size distributions, both experimentally and by kinetic Monte Carlo simulations. Chapter 5 discusses the interaction between the embedded particles and the thin film during annealing. This interaction is important to understand the formation of nanostructures during dewetting and the effect of particles on dewetting.