Investigation of Magnetic Materials and Semiconductor Nanostructures by Electron Holography (English shop)

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Changlin Zheng’s dissertation “Investigation of Magnetic Materials and Semiconductor Nanostructures by Electron Holography” investigates the structural and physical properties of magnetic materials and semiconductor nanostructures using advanced electron holography techniques. The research focuses on correlations between microstructure and magnetic properties in nanocrystalline FeCo-based and Fe-based soft magnetic alloys, as well as the three-dimensional reconstruction of silicon-germanium nanostructures. Transmission electron microscopy, Lorentz microscopy, and off-axis electron holography are employed to analyze crystallite sizes, magnetic domain configurations, and domain wall widths. The findings demonstrate that annealing temperature significantly influences grain growth and magnetic behavior. Smaller crystallites promote favorable soft magnetic properties, whereas larger grains increase domain wall pinning and disrupt magnetic flux distributions. Quantitative magnetic flux density measurements and observations of dynamic magnetization processes provide further insights into the relationship between nanoscale structure and magnetic performance. The dissertation also investigates epitaxially grown silicon-germanium islands, reconstructing their three-dimensional morphology from two-dimensional electron phase maps. By evaluating electron phase shifts and calculating mean inner potentials, the study establishes methods for determining nanostructure dimensions. The results demonstrate the capabilities of electron holography for quantitative nanoscale characterization of magnetic and semiconductor materials.