Temperature-controlled defect engineering in ceria nanostructures using thin film VO2-CeOx bilayers

CeO2 nanostructures (CNs) have found applications in many fields due to their unique oxidative regenerative properties. Unique properties of ceria have been linked to the defect structure of CNs which allows it to switch between two different oxidation states Ce3+ ↔Ce4+. As the defect structure of CNs is crucial therefore various methods were developed to engineer defects in CNs. However, precise, and reversible control over defect structure characters remains a persistent challenge. Herein, we report a method of temperature-controlled, reversible defect control in CeO2 nanostructures through the fabrication of VO2-CeO2 hetero-nano bilayers using atomic layer deposition (ALD). Reversible defect engineering in CeO2 films has been demonstrated using X-ray photoelectron spectroscopy (XPS) studies with in situ heating and cooling. Defect levels were identified as variance in the Ce3+/Ce4+ oxidation states. A remarkable Ce3+/Ce4+ ratio of 5.97 (Ce3+ ∼ 85%) was obtained and modulated over a temperature range from room temperature to 90 °C. Raman studies with in situ heating and cooling were done to understand the mechanism behind the phenomenon further. In situ Ellipsometry, AFM, TEM, and STEM/EDS techniques were utilized to characterize the sample. Our temperature-controlled defect engineering platform for CeO2 nanostructures can enable the precise designing of systems specific to various applications.