Dependence of the Kirkendall Void Layer on the Thickness of Cu2O Obtained via the Thermal Oxidation of Cu under Ar and O2 at High Temperatures

Cu₂O has been obtained via the thermal oxidation of 5, 30, 60, and 120 μm thick Cu foil under Ar and O₂ at 1020 °C after annealing the Cu under H₂ for up to 180 min at 1000 °C. 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. We suggest that 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 not observed in the Cu₂O derived from 30 and 60 μm Cu as shown by cross-sectional scanning and transmission electron microscopy. In this case, we only observe isolated voids in the single-crystal Cu₂O grains that extend from the 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 aggregation into voids. We discuss the importance of these findings for the integration of Cu₂O into devices and cavities.

Cu₂O has been obtained via the thermal oxidation of Cu with different thicknesses under Ar and O₂ at 1020 °C. The Cu₂O obtained from 120 μm-thick Cu consists of large single-crystal grains that have a cubic crystal structure and extend down to a layer of voids due to the bifacial oxidation of Cu. However, the void layer is not observed in the Cu₂O derived from 30 and 60 μm Cu. In this case, we only observed isolated voids in the single-crystal Cu₂O grains that extend from the top to bottom. We discuss the importance of these findings for the use of this novel p-type metal oxide semiconductor as an archetype for the observation of Rydberg excitons.