隨著二維材料研究的快速發展，二維鐵電性成為重要的研究方向，而六方氮化硼（h-BN）作為二維材料中唯一的絕緣材料，因它的絕緣性和原子級平坦表面使其成為最常用的基板和閘極介電材料，在二維電子學中扮演重要角色。近年來，h-BN已經超越其在二維電子學中的傳統輔助角色，並在其中發現了許多奇異量子現象。在本研究中，我們利用導電式原子力顯微鏡（CAFM）辨別磊晶成長的多層h-BN結構，藉由不同電流值分佈清楚分辨不同層數的h-BN及其位置，並利用壓電力顯微鏡（PFM）發現其層狀堆疊h-BN具有多種層間極化堆疊結構，進一步地，我們也利用了Switching Spectroscopy PFM（SS-PFM）量測到鐵電經典滯回現象的發生，以及藉由施加正負電壓來回切化極化域，發現其具有鐵電材料的記憶特性和可逆切換的特性。另外，由於4°錯切的碳化矽（SiC）基板，表面會呈現鋸齒階梯狀的排列，我們將其分成凹、凸台階處和平坦處，藉由PFM外加電壓和時間控制發現極化域的形成和擴散速度與位置相關，並且部分區域的極化域擴散會受邊界影響。最後，我們利用SS-PFM在三層h-BN進行單點量測，其鐵電滯回現象在中間電壓區間出現了轉折，並且藉由PFM外加電壓與時間控制觀察極化域變化，發現具有不同的對比度呈現，這都揭示了中間狀態的存在可能性，而這種可操控的多態極化行為，為多態鐵電儲存裝置的開發提供了巨大的可能性。

With the rapid development of 2D material research, 2D ferroelectricity has become an important area of study. Hexagonal boron nitride (h-BN), as the only insulating 2D material, is crucial in 2D electronics due to its insulating properties and atomically flat surface. Recently, h-BN has surpassed its traditional role, revealing many exotic quantum phenomena. In this study, conductive atomic force microscopy (CAFM) was used to identify multilayer h-BN structures and their locations by analyzing current distributions. Piezoresponse force microscopy (PFM) revealed various interlayer polarization stacking structures while Switching Spectroscopy PFM (SS-PFM) demonstrated ferroelectric memory and reversible switching phenomena. The step-like arrangement of the 4° miscut SiC substrate influenced the formation and diffusion of polarization domains, showing position-dependent behavior. SS-PFM measurements on trilayer h-BN revealed intermediate states, and by controlling the applied voltage and time with PFM, these intermediate states were formed, indicating significant potential for the development of multi-state ferroelectric memory devices.

1. Novoselov, K.S., et al., Electric field effect in atomically thin carbon films. science, 2004. 306(5696): p. 666-669.
2. Novoselov, K.S., et al., Two-dimensional atomic crystals. Proceedings of the National Academy of Sciences, 2005. 102(30): p. 10451-10453.
3. Mak, K.F., et al., Atomically thin MoS 2: a new direct-gap semiconductor. Physical review letters, 2010. 105(13): p. 136805.
4. Cao, Y., et al., Unconventional superconductivity in magic-angle graphene superlattices. Nature, 2018. 556(7699): p. 43-50.
5. Yasuda, K., et al., Stacking-engineered ferroelectricity in bilayer boron nitride. Science, 2021. 372(6549): p. 1458-1462.
6. Yoo, H., et al., Atomic and electronic reconstruction at the van der Waals interface in twisted bilayer graphene. Nature materials, 2019. 18(5): p. 448-453.
7. Kerelsky, A., et al., Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature, 2019. 572(7767): p. 95-100.
8. McGilly, L.J., et al., Visualization of moiré superlattices. Nature Nanotechnology, 2020. 15(7): p. 580-584.
9. Lv, M., et al., Spatially resolved polarization manipulation of ferroelectricity in twisted hBN. Advanced Materials, 2022. 34(51): p. 2203990.
10. Kim, D.S., et al., Electrostatic moiré potential from twisted hexagonal boron nitride layers. Nature materials, 2024. 23(1): p. 65-70.
11. Woods, C., et al., Charge-polarized interfacial superlattices in marginally twisted hexagonal boron nitride. Nature communications, 2021. 12(1): p. 347.
12. Wu, M., et al., Hydroxyl-decorated graphene systems as candidates for organic metal-free ferroelectrics, multiferroics, and high-performance proton battery cathode materials. Physical Review B—Condensed Matter and Materials Physics, 2013. 87(8): p. 081406.
13. Shirodkar, S.N. and U.V. Waghmare, Emergence of ferroelectricity at a metal-semiconductor transition in a 1 T monolayer of MoS 2. Physical review letters, 2014. 112(15): p. 157601.
14. Chang, K., et al., Discovery of robust in-plane ferroelectricity in atomic-thick SnTe. Science, 2016. 353(6296): p. 274-278.
15. Liu, F., et al., Room-temperature ferroelectricity in CuInP2S6 ultrathin flakes. Nature communications, 2016. 7(1): p. 1-6.
16. Li, L. and M. Wu, Binary compound bilayer and multilayer with vertical polarizations: two-dimensional ferroelectrics, multiferroics, and nanogenerators. ACS nano, 2017. 11(6): p. 6382-6388.
17. Ahn, C., K. Rabe, and J.-M. Triscone, Ferroelectricity at the nanoscale: local polarization in oxide thin films and heterostructures. Science, 2004. 303(5657): p. 488-491.
18. Zheng, Z., et al., Unconventional ferroelectricity in moiré heterostructures. Nature, 2020. 588(7836): p. 71-76.
19. Vizner Stern, M., et al., Interfacial ferroelectricity by van der Waals sliding. Science, 2021. 372(6549): p. 1462-1466.
20. Lines, M.E. and A.M. Glass, Principles and applications of ferroelectrics and related materials. 2001: Oxford university press.
21. Deb, S., et al., Cumulative polarization in conductive interfacial ferroelectrics. Nature, 2022. 612(7940): p. 465-469.
22. Meng, P., et al., Sliding induced multiple polarization states in two-dimensional ferroelectrics. Nature Communications, 2022. 13(1): p. 7696.
23. Feng, S., et al., Strain Release in GaN Epitaxy on 4° Off‐Axis 4H‐SiC. Advanced Materials, 2022. 34(23): p. 2201169.
24. Wu, C.-L., et al., Epitaxially ferroelectric hexagonal boron nitride on graphene. 2023.
25. Rogée, L., et al., Ferroelectricity in untwisted heterobilayers of transition metal dichalcogenides. Science, 2022. 376(6596): p. 973-978.