Study of atomic-scale mechanisms for deposition of nanostructured films from nanoparticles
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The LAMA process (Laser Ablation of Microparticle Aerosols) is a manufacturing process for producing thin to thick films by supersonically impacting nanoparticles (NPs) onto a target substrate. The goal of this work is to study the mechanisms occurring at the atomic scale during LAMA within the impacting NPs and in the nearby substrate, and ultimately to use this knowledge to control the microstructure and properties of the resulting films. For example, dense, polycrystalline films or single-crystal (epitaxial) films would produce films with high conductivity and would make the LAMA process a good candidate for manufacturing films with properties that cannot be achieved at room temperatures by other film deposition techniques. Conversely, films with high porosity and surface area are desirable for catalysis and other applications. Thus, the ability to systematically tune the film microstructure through control of the process parameters would broaden the applicability of LAMA for film production. In this dissertation, the impaction of silver nanoparticles is studied in detail through a combination of experimental techniques. Scanning electron microscopy, transmission electron microscopy, and x-ray diffraction techniques are utilized to study the final microstructure of the films. The experimental results are compared with molecular dynamics (MD) simulations that allow both the evolution of the microstructure during impaction as well as the final microstructure after impaction to be studied. The influence of increasing the speed of impacting NPs on the morphology of Ag films is studied, and evidence is shown that film density can be increased using this route. Epitaxial deposition of NPs at a local level is observed using electron microscopy observations and the mechanisms for the occurrences of epitaxial deposition is presented. The challenges for obtaining fully epitaxial deposition of films are discussed.