The objective of the thesis was the fabrication of high-quality and purity Cu2O using Chemical Vapor Deposition (CVD) systems via the complete thermal oxidation of Cu to Cu2O. The produced Cu2O was then extensively investigated where its structural properties, surface morphology and crystallinity were examined using a variety of characterization methods including conventional transmission electron microscopy and high-resolution transmission electron microscopy (CTEM/HRTEM), X-ray diffraction (XRD), optical transmission microscopy and scanning electron microscopy (SEM). Extensive analysis was conducted regarding the surface morphology, crystal structure and local chemical composition near the surface and within the bulk of the Cu2O obtained via Chemical Vapor Deposition. The undesired complete oxidation of Cu into CuO is a focal point of this work, since this oxide disrupts the optoelectronic properties of Cu2O and therefore hinders the ability of this material to be used in optoelectronic devices, optical cavities and applications such as water-splitting, quantum computing, energy conversion and photocatalysis. Using high-resolution transmission electron microscopy (HRTEM), the surface and bulk of Cu2O were investigated for CuO where a distribution of nanoparticles with an average diameter of 11 nm was detected on the surface while practically no CuO was observed within the bulk of Cu2O. In addition, we observed that the Cu2O consists of large single-crystal grains that have a cubic crystal structure and extend down to an irregular layer of Kirkendall voids surrounded by Cu2O nanocrystals. These voids form near the middle due to the bifacial oxidation of Cu. The extent of the void layer is strongly dependent on the initial thickness of the Cu foil and is limited to secluded Kirkendall voids in the Cu2O samples derived from 30 μm and 60 μm Cu, as is demonstrated by cross-sectional scanning and transmission electron microscopy. In this case the Cu2O grains extend from top to bottom largely due to the fact that the time required to complete the oxidation is sufficiently short to prevent vacancy accumulation and their subsequent aggregation into voids. In addition, the oxidation mechanism and material kinetics that led to the formation of the Kirkendall void layer during thermal oxidation is described. Lastly, the importance of these findings is discussed for the integration of the Cu2O into devices in optoelectronics, solar cells and optical cavities, and in conclusion, certain methods of further processing in order to remove the CuO on the surface and the Kirkendall void layer, as suggested.
Κωνσταντίνος Β. Κουτσοκώστας (Wed,) studied this question.