Atomistic phase transition dynamics of In₂Se₃ semiconductor
image: Atomistic phase transition dynamics of In₂Se₃ semiconductor triggered by electron beam illumination or heat is controlled and captured by in-situ STEM. The newly formed non-layered phase exhibits 6H SiC-type atomic configuration, where the anionic sites are occupied by Se ions and cation sites are occupied by In ions and vacancies.
Credit: Nano Research, Tsinghua University Press
To overcome the bottleneck of the von Neumann computing architecture, developing high-density, low-power in-memory computing devices has become a core research direction in the post-Moore era. The van der Waals (vdW) layered ferroelectric semiconductor, α-In₂Se₃, shows great promise for novel non-volatile memory and neuromorphic computing due to its ability to maintain stable out-of-plane ferroelectricity even down to monolayer. However, thermal budgets during device fabrication or operational cycling are inevitable. These thermal stimuli can induce complex phase transitions, affecting device performance and reliability. Due to the existence of multiple polymorphs and low phase transition barriers in α-In₂Se₃, unveiling its phase transition dynamics at atomic scale is of critical importance for precisely controlling its phases and improving device stability, yet remains a significant challenge.
Recently, a team from the East China Normal University (ECNU), led by Professor Junhao Chu of the Key Laboratory of Polar Materials and Devices (Ministry of Education), addressed this key scientific issue. Using advanced in-situ spherical aberration-corrected electron microscopy, the team systematically investigated the thermally induced phase transition process in ferroelectric 2H-α In₂Se₃. They successfully tracked its unique phase transition pathway in real-time at atomic scale. The findings were published in Nano Research under the title "Atomistic phase transition dynamics of In₂Se₃ semiconductor."
The study reports the first direct observation of a unique, atomic-level in-plane directional phase transition in 2H-α In₂Se₃. This transition originates from the In-Se octahedral framework and is driven by the migration of both indium (In) ions within the octahedra and vacancies in the vdW gap, revealing a novel rearrangement pathway for intralayer and interlayer In atoms and vacancies. The research demonstrates that the initial layered In-Se octahedral configuration evolves into two non-layered In-Se tetrahedral frameworks, which ultimately merge to form a novel, non-layered 6H-type In₂Se₃ phase. In this new phase, the cation sites are potentially occupied by one-third vacancies and two-thirds In atoms.
This study provides detailed microscopic insights into the phase transition dynamics of ferroelectric 2H-α In₂Se₃ under thermal stimulus. It not only deepens the understanding of the phase transition mechanisms in 2D ferroelectric materials but also offers important experimental guidance and evidence for the precise control of specific In₂Se₃ phases and for improving the reliability and performance stability of In₂Se₃-based nanodevices.
East China Normal University (ECNU) is the first affiliation for this paper. Yufan Zheng and Beituo Liu are the (co-)first authors. Professor Fangyu Yue and Senior Engineer Ruijuan Qi are the co-corresponding authors. This research was supported by the National Natural Science Foundation of China (NSFC), the Key Project from China Space Station, based on the Key Laboratory of Polar Materials and Devices (Ministry of Education) at ECNU and the Electron Microscopy Center of the Public Service Platform at ECNU.
Other contributors include Fengrui Sui, Rui Ge, Yilun Yu, Rong Jin, Jiawen Dai, Shujing Jia from the Key Laboratory of Polar Materials and Devices (MOE) of ECNU, and Junhao Chu from the Key Laboratory of Polar Materials and Devices (MOE) of ECNU and the Shanghai Institute of Technical Physics of Chinese Academy of Sciences.
This work was partially supported from the National Natural Science Foundation of China (grants 62274061, 12134003), the National Key Research Project of China (grant 2022YFA1402902), the Natural Science Foundation of Chongqing, China (CSTB2023NSCQ-MSX0975), the East China Normal University Multifunctional Platform for Innovation (004), the Innovation Foundation of Central University, Natural Science Foundation of Shanghai (25ZR1403003), the Foundational Research Funds for the Central Universities grant YBNLTS2024-022, the Postdoctoral Fellowship Program of CPSF grant GZB20250144, and the Open Fund of State Key Laboratory of Infrared Physics grant SITP-NLIST-ZD-2024-06.
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.