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

非技术概述：铁电材料的特征是它们能够形成具有自发电极化(域)的局部区域，这些区域可以通过外部电场进行切换。这一特点使它们对存储器和晶体管等信息技术很有吸引力。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方面正变得越来越突出。这归功于它们出色的可扩展性和与互补的金属氧化物半导体工艺的兼容性，这是采用钙钛矿型结构的传统铁电材料所不具备的优势。然而，随着材料尺寸因高密度加工而缩小，以及器件集成不同的材料，理解和关联磁畴结构与合成工艺和铁电性能带来了挑战。该项目由材料研究部陶瓷项目支持，旨在通过基于先进的电子显微镜技术和现场偏置实验开发新的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的磁畴结构，产生结构特性与铁电开关特性的可靠关联。这反过来又为目标铁电性能的新材料设计原则提供了洞察力。与这项研究相一致的是，这个陶瓷职业奖支持为佛罗里达州北部代表性较低学校的中学生开办一所K-12显微镜学校。这项外展活动的目标是通过在高度协作的学习环境中的实践活动，增加STEM劳动力中任职人数不足的学生的参与。此外，这一职业奖通过整合视频教程和定制图像分析工具，促进了电子显微镜技术和图像处理方法在线学习模块的开发。这些教育材料计划在PI小组的网页和另一个开放的在线平台(NanHub.org)上出版和维护，以增加科学界的可及性和可用性。技术概述：利用热力学亚稳态相开辟了控制陶瓷材料性能的新机会，从而为现实世界的应用创造了新的功能。然而，由于很难表征基态和亚稳态相的结构并了解它们在使用条件下的演变，因此确定稳定目标亚稳态材料的材料设计路径带来了挑战。为了克服这一挑战并探索控制亚稳态陶瓷材料的科学，该职业奖旨在表征纳米级萤石结构铁电材料中亚稳态极性相的形成和演化机制。目标包括：(I)开发高精度的相指数方法来识别Hf_2O_3薄膜中的亚稳态多晶型，(Ii)建立相纯纳米铁电材料的微结构织构，(Iii)通过关联结构和电学性质来建立工艺-结构-性能关系，以及(Iv)利用原位偏置实验来阐明极化转换机制。该项目在陶瓷计划的支持下，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地识别铁电薄膜中的亚稳态相。所获得的见解有望指导具有可控微结构的铁电薄膜中理想亚稳态相的合成策略，扩大材料设计空间以提高性能。这项研究的更广泛影响包括开发具有技术上重要功能的陶瓷材料，这些功能源于相的亚稳性或相变。同时，这一职业奖项支持教育举措，包括一所K-12显微镜学校，为不同级别的学生提供电子显微镜在线学习模块，以及为代表性不足的本科生提供研究实习机会。全面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，并为不同的学生群体在STEM领域的职业生涯做好准备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.