近年來，二維材料由於其卓越的物理和化學特性，引起了極大的關注。最近的研究表明，通過特定的堆疊方法，有可能打破反演對稱並誘導自發極化的產生，從而開發出二維鐵電材料，如3R-MoS2和AB & BA堆疊的h-BN，而這一發現為二維材料的新功能性提供了巨大潛力。我們的研究專注於一種更為特別的二硫化鉬 (MoS2)―― ST-3R MoS2，比起一般情況下以CVD製成的3R-MoS，我們更能穩定地在ST-3R MoS2中觀察到多領域的存在，而這正是能使我們更容易在二維鐵電材料中觀察到滯迴現象的條件。
我們使用基於SPM的技術，包括壓電響應力顯微鏡（PFM）和頻率調制開爾文探針力顯微鏡（FM-KPFM），來研究其鐵電域，並通過施加外部電場來調查其鐵電開關機制。這項研究從奈米尺度的角度提供了對二維鐵電材料中域和電壓驅動機制的見解。

Two-dimensional materials have garnered significant attention in recent years due to their exceptional physical and chemical properties. Recent research indicates that through specific stacking methods, there is an opportunity to break the inversion symmetry and induce spontaneous polarizations, leading to the development of two-dimensional ferroelectric materials, such as 3R-MoS2 and AB & BA stacking h-BN. This holds great potential for the novel functionality of two-dimensional materials. Our research focuses on a more special type of MoS2--ST 3R-MoS2, which exhibits more significant hysteresis behavior compared to the 3R-MoS2 typically produced by CVD.
We used SPM based techniques, including piezoresponse force microscopy (PFM) and frequency-modulated Kelvin probe force microscopy (FM-KPFM), to study its ferroelectric domains and investigate its ferroelectric switching mechanisms by applying external electric fields. This study provides the nanoscale point of view of the domains and voltage-driven mechanisms in 2D ferroelectric materials.

1. Meng, P., Wu, Y., Bian, R. et al. Sliding induced multiple polarization states in two-dimensional ferroelectrics. Nat Commun 13, 7696 (2022).
2. Jing Liang, Dongyang Yang, Jingda Wu, Jerry I. et al. Phys. Rev. X 12, 041005 – Published 14 October 2022
3. Vizner Stern et al. Interfacial ferroelectricity by van der Waals sliding, Science 372, 1462–1466 (2021)
4. Weston, A., Castanon, E.G., Enaldiev, V. et al. Interfacial ferroelectricity in marginally twisted 2D semiconductors. Nat. Nanotechnol. 17, 390–395 (2022)
5. Yang, T.H., Liang, BW., Hu, HC. et al. Ferroelectric transistors based on shear-transformation-mediated rhombohedral-stacked molybdenum disulfide. Nat Electron 7, 29–38 (2024).
6. Yasakau, K. Application of AFM-Based Techniques in Studies of Corrosion and Corrosion Inhibition of Metallic Alloys. Corros. Mater. Degrad. 2020, 1, 345-372.
7. Cappella, Brunero, and Giovanni Dietler. "Force-distance curves by atomic force microscopy." Surface science reports 34.1-3 (1999): 1-104.
8. Nina Balke, Petro Maksymovych, Stephen Jesse. et al. Kalinin Differentiating Ferroelectric and Nonferroelectric Electromechanical Effects with Scanning Probe Microscopy. ACS Nano 2015 9 (6), 6484-6492
9. Nina Balke, Petro Maksymovych, Stephen Jesse, et al. Exploring Local Electrostatic Effects with Scanning Probe Microscopy: Implications for Piezoresponse Force Microscopy and Triboelectricity. ACS Nano 2014 8 (10), 10229-10236
10. Horiuchi, S., Tokura, Y. Organic ferroelectrics. Nature Mater 7, 357–366 (2008).
11. M. Wu and J. Li, Sliding ferroelectricity in 2D van der Waals materials: Related physics and future opportunities, Proc. Natl. Acad. Sci. USA 118, e2115703118 (2021).
12. Wu, M. Two-Dimensional van der Waals Ferroelectrics: Scientific and Technological Opportunities. ACS Nano 2021, 15, 9229−9237.
13. Yang, D., Liang, J., Wu, J. et al. Non-volatile electrical polarization switching via domain wall release in 3R-MoS2 bilayer. Nat Commun 15, 1389 (2024).
14. Wu M, Burton JD, Tsymbal EY, Zeng XC, Jena P. Hydroxyl-decorated graphene systems as candidates for organic metal-free ferroelectrics, multiferroics, and high-performance proton battery cathode materials. Phys Rev B. 2013; 87(8):081406.
15. Wu M. 100 years of ferroelectricity. Nat Rev Phys. 2021; 3(11): 726.
16. Tu, Z.; Wu, M.; Zeng, X. C. Two-Dimensional Metal-Free Organic Multiferroic Material for Design of Multifunctional Integrated Circuits. J. Phys. Chem. Lett. 2017, 8 (9), 1973– 1978
17. Cao, T., Wang, G., Han, W. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nat Commun 3, 887 (2012).
18. Wang, X., Yasuda, K., Zhang, Y. et al. Interfacial ferroelectricity in rhombohedral-stacked bilayer transition metal dichalcogenides. Nat. Nanotechnol. 17, 367–371 (2022).
19. Deb, S., Cao, W., Raab, N. et al. Cumulative polarization in conductive interfacial ferroelectrics. Nature 612, 465–469 (2022).
20. 簡赫伸,“以進階壓電力顯微技術結合機器學習探究鋯酸鉛薄膜的反鐵電性, 成功大學, 碩士論文, (2023)
21. 洪湘評,”以應變誘發低維與獨立式薄膜中的非尋常電域結構”, 成功大學, 碩士論文, (2022)