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

非技术总结：铁电材料的特征在于它们形成具有自发电极化（畴）的局部区域的能力，所述自发电极化（畴）可以用外部电场切换。这一特性使它们对存储器和晶体管等信息技术具有吸引力。特别是，具有萤石晶体结构的铁电材料在下一代存储器和晶体管中越来越突出。这归因于它们的上级可扩展性和与互补金属氧化物半导体处理的兼容性，这些优点是采用钙钛矿结构的常规铁电材料所不具有的。然而，随着高密度加工的材料尺寸缩小和器件集成不同的材料，理解和关联域结构与合成工艺和铁电性能提出了挑战。该项目由材料研究部陶瓷项目支持，旨在通过开发基于先进电子显微镜技术和原位偏置实验的新型表征方法来应对这一挑战。这种方法能够定量分析静态和动态畴结构，产生可靠的相关性的结构特性铁电开关特性。这反过来又为针对铁电性能的新材料设计原理提供了见解。与这项研究相一致，这个陶瓷职业奖支持在佛罗里达北方代表性不足的学校为中学生推出K-12显微镜学校。这项推广活动的目标是通过在高度协作的学习环境中开展实践活动，增加代表性不足的学生在STEM劳动力中的参与。此外，该职业奖通过结合视频教程和自定义图像分析工具，促进了电子显微镜技术和图像处理方法的在线学习模块的开发。这些教育材料计划在PI小组网页和另一个开放的在线平台（nanoHub.org）上发布和维护，以提高科学界的可访问性和可用性。技术总结：利用介稳相为控制陶瓷材料的性能开辟了新的机会，从而为现实世界的应用创造了新的功能。然而，由于难以表征基态和亚稳相的结构并理解其在使用条件下的演变，确定材料设计途径以稳定目标亚稳材料带来了挑战。为了克服这一挑战并探索控制亚稳陶瓷材料的科学，该CAREER奖旨在表征纳米级萤石结构铁电体中亚稳极性相的形成和演变机制。目标包括（i）开发用于识别氧化铪薄膜（一种模型萤石结构铁电材料）中的亚稳多晶型物的高精度相位索引方法，（ii）建立用于相位纯纳米级铁电材料的微结构纹理，（iii）通过关联结构和电性能来建立工艺-结构-性能关系，以及（iv）使用原位偏置实验阐明偏振转换机制。该项目由陶瓷计划支持，采用扫描电子纳米束衍射和机器学习辅助图像处理方法，通过定量结构信息明确识别铁电薄膜中的亚稳相。所获得的见解，预计将指导合成策略的理想的亚稳相的铁电薄膜具有可控的微观结构，扩大材料的设计空间，以提高性能。这项研究的更广泛的影响包括陶瓷材料的发展与技术上的重要功能所产生的相亚稳态或过渡。同时，该职业奖支持教育计划，包括K-12显微镜学校，电子显微镜在线学习模块，为各级学生提供电子显微镜，并为代表性不足的本科生提供研究实习机会。这一综合性的教育和推广活动旨在提高人们对尖端陶瓷材料研究的认识，并为STEM领域的职业生涯培养多样化的学生群体。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

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 underrepresented schools in northern Florida. The goal of this outreach activity is to increase the participation of underrepresented students 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 underrepresented undergraduate students. The comprehensive education and outreach activities aim to increase awareness of cutting-edge ceramic materials research and prepare a diverse group of 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.