Insights from Scanning Transmission Electron Microscopy and X-Ray Diffraction Into the Structure and Composition of Non Crystalline Thin Solid Films
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Non-crystalline thin solid films are seeing increasing interest for a wide variety of applications. However, understanding structure and compositional variations in these films is an immense challenge. Conventional bulk structural or compositional characterization techniques such as X-ray diffraction often do not provide an adequate amount of information on their own. Electron microscopy is an incredibly powerful technique for structural and compositional film characterization, but is limited to inspection of only a small volume of any given sample. Rather than using one technique alone to gain information about a specimen, the greatest success is realized when these techniques are used in concert. This dissertation illustrates the idea that statistical analysis of electron microscopy data can provide information invaluable to interpreting bulk structural and compositional data from non-crystalline films. The first set of examples include demonstration of a statistical analysis method that can be applied to electron microscopy data to determine the presence of inhomogeneity along one film axis. This analysis method is applied to understanding compositional inhomogeneity that develops during formation of amorphous oxide films from aqueous solutions. Key insights are revealed that aid interpretation of bulk film X-ray characterization and possible processing conditions that lead to the compositional inhomogeneity. The second and third sets of examples describe the importance of electron microscopy analysis for structure determination in rotationally-disordered, non-epitaxial 2D heterostructures prepared from modulated elemental reactants. The second set of examples investigates the effects of nanoarchitecture on interlayer interactions and layer structure in heterostructures with interleaved BiSe and NbSe2 layers. The BiSe layers in these compounds display an interesting structural variation that impacts the overall compound properties. The structural variation is not visible using typical X-ray diffraction experiments, but analysis of electron microscopy images provides key insight into its existence. Finally, the third set of examples investigate several SnSe-containing heterostructures that provide insight into the unusual consequences of their non-epitaxial structure and film formation from modulated elemental reactants. Electron microscopy analysis, in conjunction with other characterization techniques, was invaluable for uncovering structural and compositional details within these compounds. This work contains previously published and unpublished co-authored material.