CAREER: Elucidating the Formation and Evolution of Metastable Phases in Fluorite-Structured Ferroelectrics using Advanced Electron Microscopy

University Of Florida, Gainesville FL

Investigators

Abstract

Non-Technical Summary: Ferroelectric materials are characterized by their ability to form local regions with spontaneous electric polarization (domains) that can be switched with an external electric field. This characteristic makes them attractive for information technologies such as memory and transistors. In particular, ferroelectric materials with a fluorite crystal structure are gaining prominence for next-generation memory and transistors. This is attributed to their superior scalability and compatibility with complementary metal-oxide-semiconductor processing, advantages not shared by conventional ferroelectric materials adopting a perovskite structure. However, as material dimensions shrink for high-density processing and devices integrate diverse materials, understanding and correlating domain structures with synthesis processes and ferroelectric performance pose challenges. This project, supported by the Ceramics Program in the Division of Materials Research, aims to address this challenge by developing novel characterization methods based on advanced electron microscopy techniques and in situ biasing experiments. This approach enables quantitative analysis of static and dynamic domain structures, producing reliable correlation of structural properties to ferroelectric switching characteristics. This, in turn, provides insights into new materials design principles for targeted ferroelectric performance. Aligned with the research, this Ceramics CAREER award supports the launch of a K-12 microscopy school for middle-school students from schools in northern Florida. The goal of this outreach activity is to increase the participation in the STEM workforce through hands-on activities in highly collaborative learning environments. In addition, this CAREER award facilitates the development of online learning modules on electron microscopy techniques and image processing methods by incorporating video tutorials and custom image analysis tools. These educational materials plan to be published and maintained on the PI group webpage and another open online platform (nanoHub.org), increasing accessibility and usability within the scientific community. Technical Summary: Harnessing thermodynamically metastable phases opens up new opportunities to control the properties of ceramic materials, thereby creating novel functionalities for real-world applications. However, identifying materials design pathways to stabilize targeted metastable materials poses challenges due to the difficulties in characterizing the structures of the ground-state and metastable phases and understanding their evolution under in-service conditions. To overcome this challenge and explore the science of controlling metastable ceramic materials, this CAREER award aims to characterize the mechanisms of the formation and evolution of metastable polar phases in nanoscale fluorite-structured ferroelectrics. Objectives include (i) developing high-precision phase indexing methods for identifying metastable polymorphs in hafnium oxide thin films, a model fluorite-structured ferroelectric material, (ii) establishing microstructure texturing for phase-pure nanoscale ferroelectric materials, (iii) building process-structure-property relationships by correlating structural and electrical properties, and (iv) elucidating polarization switching mechanisms using in situ biasing experiments. This project, supported by the Ceramics Program, employs scanning electron nanobeam diffraction and machine learning-aided image processing methods for unambiguous identification of metastable phases in ferroelectric thin films with quantitative structural information. Insights gained are expected to guide synthesis strategies for desirable metastable phases in ferroelectric thin films with controllable microstructure, expanding the materials design space for improved performance. The broader impact of this research includes the development of ceramic materials with technologically important functionalities arising from phase metastability or transition. Concurrently, this CAREER award supports education initiatives, including a K-12 microscopy school, online learning modules on electron microscopy for students at various levels, and research internship opportunities for undergraduate students. The comprehensive education and outreach activities aim to increase awareness of cutting-edge ceramic materials research and prepare students for careers in STEM fields. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.