PhD: Helena Rabelo Freitas

Directors:

ICREA Prof. Jordi Arbiol, Group Leader of the Advanced Electron Nanoscopy group at Institut Català de Nanociència i Nanotecnologia (ICN2)

Prof Maria Chiara Spadaro, Visiting Professor at ICN2

Short Abstract: This thesis investigates the nanoscale structural properties of semiconductor materials using advanced scanning transmission electron microscopy (STEM) to understand how strain, defects, interfaces, and compositional variations influence their functional performance in energy and photonic applications. High-resolution imaging, spectroscopy, and diffraction-based techniques are combined to correlate structural and chemical information across multiple length scales. Zn₃P₂ is studied through four complementary investigations, revealing localized surface oxidation during atmospheric degradation, polycrystalline growth on graphene driven by nucleation, defect control through selective area epitaxy, and temperature-dependent effects of post-growth annealing on defect evolution and optoelectronic properties. ZnO/ZnS heterostructures are examined to understand strain accommodation at graded interfaces, while GaAs nanostructures are analyzed to identify the structural origin of above-bandgap emission, excluding strain and polytypism as dominant mechanisms.

Overall, this work demonstrates that advanced STEM methodologies establish direct relationships between atomic-scale structure and material functionality, providing insights for optimizing future semiconductor materials.

REGISTER HERE