In-Situ STEM Studies of Ferroelectric Domains in Free-Standing Thin Films

Ferroelectrics are polar materials known for their spontaneous polarization, which can be reversibly switched by applying an external field. As these materials are cooled below their Curie temperature (T_C), the resulting domain structure and switching dynamics are driven by boundary their conditions, aiming to minimize electrostatic and elastic energy in the system.<br/>A particularly interesting aspect of ferroelectrics is the effect that surface chemical species have on the screening mechanism, and its resulting domain structure, and vice versa, how domains affect the surface chemistry. The latter could be exploited to tailor surface reactivity for electrochemical, catalytical,[1-6] and other energy harvesting applications.[2, 7-9]<br/><br/>This study focuses on investigating the thermally induced behavior of ferroelectric-ferroelastic domains in free-standing thin films under different chemical environments using in-situ scanning transmission electron microscopy (STEM) techniques. The similarities and differences between these environments are discussed, along with the associated challenges.<br/><br/>To the best of our knowledge, this is the first time in-situ heating under controlled gas environments has been employed to study ferroelectric-ferroelastic domains. Our findings provide valuable insights into the intricate relationship between important ferroelectric characteristics such as (T_C, domain size, etc) and the chemical environment. Furthermore, this work highlights the application of in-situ gas as a powerful technique for dynamically exploring the effects of other external variables such as pressure on polar materials.<br/><br/><br/><br/>[1] Y. Yun, E. I. Altman, <i>Journal of the American Chemical Society</i> <b>2007</b>, 129, 15684.<br/>[2] A. Kakekhani, S. Ismail-Beigi, <i>Journal of Materials Chemistry A</i> <b>2016</b>, 4, 5235.<br/>[3] T. L. Wan, L. Ge, Y. Pan, Q. Yuan, L. Liu, S. Sarina, L. Kou, <i>Nanoscale</i> <b>2021</b>, 13, 7096.<br/>[4] A. Kakekhani, S. Ismail-Beigi, <i>Physical Chemistry Chemical Physics</i> <b>2016</b>, 18, 19676.<br/>[5] Y. Li, J. Li, W. Yang, X. Wang, <i>Nanoscale Horizons</i> <b>2020</b>, 5, 1174.<br/>[6] A. Kakekhani, S. Ismail-Beigi, E. I. Altman, <i>Surface Science</i> <b>2016</b>, 650, 302.<br/>[7] H. Li, C. R. Bowen, Y. Yang, <i>Advanced Functional Materials</i> <b>2021</b>, 31, 2100905.<br/>[8] M. Xie, S. Dunn, E. L. Boulbar, C. R. Bowen, <i>International Journal of Hydrogen Energy</i> <b>2017</b>, 42, 23437.<br/>[9] S. Kim, N. T. Nguyen, C. W. Bark, <i>Applied Sciences</i> <b>2018</b>, 8, 1526.