Tailoring of Functional Oxide Materials : Strategies, Growth, and Applications

Abstract

Metal oxides are non-stoichiometric compounds characterized by strong ionic and covalent bonds between positive metal ions and negative oxygen ions. Metal oxide-based electronic devices have garnered significant attention due to their desirable properties, including high electron mobility, chemical resistance, transparency, low cost, and ease of processing. However, without further modifications to the inherent characteristics of metal oxides, the performance of various metal oxide-based electronic devices has reached its limits. This dissertation presents strategies for tailoring functional metal oxides to overcome these challenges. In the first part of this dissertation (Chapter 2), Zr doped HfO2 thin films using pulsed laser deposition are studied. The HfO2 is attractive material because of its CMOS-compatible properties. It is being developed for a variety of next-generation storage devices. However, due to its extraordinary characteristics, the understanding of its mechanism is very slow. We have used in-situ XRD and various measurements to investigate the memristor behavior in Hf0.5Zr0.5O2. By providing insights into device degradation mechanisms beyond commonly reported properties, this dissertation offers valuable perspectives for performance improvements for next-generation memory devices. In the second part of this dissertation (Chapter 3), heterostructure with WSe2 and Bi2O2Se realized by pulsed laser deposition process for enhancement of optical property and photoresponse is discussed. The Bi2O2Se, which is a novel layered oxychalcogenide, is stacked onto WSe2 thin films to form type-II heterostructure. Notably, on/off ratio of heterostructure about photoresponse improved approximately 110% without requiring lithography process. Therefore, we corroborated the effect of heterostructure for enhancing optical property in Bi2O2Se using WSe2 layers. The third part of this dissertation (Chapter 4) focuses on sulfur-loaded WO3 microspheres synthesized through a two-step hydrothermal process as a cost-effective material for gas sensors. By employing sulfur as a catalyst, the WO3 microspheres exhibited an increased concentration of oxygen vacancies, which is enhancing their suitability for gas sensing applications. As a result, the sensing performance toward NO2 was extremely improved compared to the pristine WO3. Moreover, we provide the sensing mechanism in terms of the role of sulfur. This approach could offer an alternative to the widely used noble metal for effective gas sensing.