六方氮化硼（hexagonal boron nitride, h-BN）具有寬能隙、化學穩定性與原子級平坦表面，常作為二維材料元件中的絕緣層與封裝材料。近年研究指出，當 h-BN 的層間堆疊對稱性被破壞時，層間相對滑移可誘發面外電偶極，使其展現滑動鐵電性。本研究以在SiC斜坡基板上磊晶成長之四層 h-BN 為研究對象，探討其局部鐵電響應、外加電場寫入行為，以及多重極化態與中間態切換特徵。
本研究利用雙頻共振追蹤壓電力顯微鏡（dual-frequency resonance tracking piezoresponse force microscopy, DFRT-PFM）與頻率調變克氏探針表面電位顯微鏡（frequency-modulated Kelvin probe force microscopy, FM-KPFM）量測樣品的 PFM 相位、PFM 振幅、PFM 響應訊號與表面電位分布。結果顯示，磊晶四層 h-BN 在原生狀態下即具有可分辨的局部相位與電位對比。進一步透過切換光譜壓電力顯微鏡（switching spectroscopy PFM, SS-PFM）觀察到接近 180° 的相位反轉與振幅遲滯行為，支持其具有外加電場可切換的局部鐵電響應。
在外加直流脈衝寫入實驗中，PFM 與 KPFM 顯示局部極化相關區域可被寫入，且極化疇尺寸隨脈衝時間增加而顯著變大。KPFM 時間演化量測顯示，向上飽和態與向下飽和態之間的表面電位差會隨時間下降並逐漸趨於平緩，說明外加電場寫入後的局部極化並非瞬時電荷效應，而具有穩定存在的極化特徵。
此外，本研究進一步分析磊晶四層 h-BN 的中間態特性。透過定義簡化界面偶極疊加模型（simplified interfacial dipole superposition model），我們在PFM/KPFM 量測可辨識出飽和態與中間態，並顯示相鄰狀態之間具有可分辨的表面電位差；SS-PFM 量測呈現多階極化切換行為；PUND 量測亦觀察到極化遲滯與中間極化訊號。綜合 PFM、KPFM、SS-PFM 與 PUND 結果，磊晶四層 h-BN 可展現可切換鐵電響應與多重極化態。然而，表面電位隨時間變化也顯示局部電荷注入或電荷重排可能參與訊號形成，因此其極化行為可理解為滑動鐵電極化、界面偶極與電荷效應共同作用的結果。本研究顯示，磊晶多層 h-BN 具有發展多態非揮發性元件與二維鐵電裝置的潛力。

Hexagonal boron nitride (h-BN) is a wide-bandgap two-dimensional insulating material commonly used in van der Waals heterostructures. Recent studies have shown that broken interlayer stacking symmetry in multilayer h-BN can induce out-of-plane electric dipoles through relative interlayer sliding, giving rise to sliding ferroelectricity. In this thesis, four-layer (4L) epitaxial h-BN grown on a stepped graphene/SiC substrate is investigated to clarify its local ferroelectric response, electric-field-induced writing behavior, and multistate polarization switching characteristics. Piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM) measurements reveal distinguishable local phase and surface potential contrasts in the pristine state. Switching spectroscopy piezoresponse force microscopy (SS-PFM) further shows a nearly 180° phase reversal and hysteretic amplitude response, switchable ferroelectric response. Direct-current (DC) pulse writing experiments demonstrate that local polarization-related domains can be written by an external electric field, with domain size increasing as the pulse duration increases. In addition, PFM/KPFM contrasts, multistep SS-PFM behavior, and electrical measurements indicate the presence of saturated and intermediate polarization states in 4L h-BN. These results suggest that four-layer epitaxial h-BN exhibits a switchable ferroelectric response and multistate polarization characteristics, while charge-related effects may also contribute to the measured signals. This study highlights the potential of epitaxial multilayer h-BN for multistate nonvolatile memory devices and two-dimensional ferroelectric electronic systems.

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