奇異的極性拓樸結構已在鐵電氧化物薄膜和異質結構中被研究發現，然而，如何多元誘導生成鐵電極性拓樸電疇域仍是一大議題，本研究主要探討給予鐵電材料應變條件看是否能夠誘發出奇異的極性渦漩拓樸鐵電疇域。值得注意的是，極性渦漩拓樸鐵電具有拓樸保護特性，可以透過計算拓樸數這一項指標參數得知，並且鐵電材料還具備記憶特性，意味著可以通過外加電場搭配上幾何應變的調控，創造出奇異的極性拓樸渦漩結構，在非揮發性的記憶體等元件上具有相當大之應用價值，然而，我們是利用了磊晶以及蝕刻還有獨立式自支撐的方式做到幾何應變調控，進而去控制鐵電材料的鐵電疇域。而透過蝕刻達到幾何應變調控來操縱鐵電材料特性的優勢在於，以往是單純透過基板與鐵電材料之間的晶格大小差異，有限度的造成應變效果，而在此透過蝕刻的方式，卻能以不同的需求而造成不同的幾何應變調控，在製程上有一定程度的方便性。
本實驗分為兩類，第一類是透過磊晶與濕式蝕刻做到精準操縱幾何結構大小，在磊晶生長在(001)取向的鈦酸鍶(STO)基板上的鑭鍶錳氧(LSMO)薄膜上建構出人工孔洞(Artificial Pinhole) ，隨後我們再次磊晶覆蓋了鐵酸鉍(BFO)薄膜其中蝕刻的形狀分別有圓形，方形以及菱形，其大小約為數微米到幾百奈米，並且進一步去研究這些在被規範的應變圖案下的人工域的特性。而第二類則是獨立式自支撐轉移技術，想透過因YBCO與BFO之間的表面晶格常數差異，在蝕刻過程造成天然的奈米島而形成極性渦漩，並朝向透過控制蝕刻YBCO的程度操縱奈米島大小，便能夠配合蝕刻技術以更靈活的手法去探究極性渦漩結構。而在實驗上主要是透過壓電力顯微鏡(Piezoresponse Force Microscopy，PFM)技術搭配表面電位顯微鏡(Kelvin Probe Force Microscopy，KPFM)以及導電力顯微鏡(Conductive Atomic Force Microscopy，CAFM)，來探測鐵電疇域的結構，結果顯示在BFO/LSMO/STO(001)系統在室溫下BFO薄膜受到幾何應變的調控後，當蝕刻尺寸縮小至幾百nm時，便會出現極性渦漩拓樸結構，這是因為蝕刻造就基板給於雙平面的應變梯度而造成彎電效應以及氧化物薄膜與底電極之間的蕭特基接觸造成的內建電場，使得上下層有電位差形成類似平行電容版的結構，最終形成極性拓樸渦漩結構，並最終透過電控實行操縱卷繞數。

Ferroelectric materials with controllable spontaneous polarization and strong correlated order parameters provide great potential for designing nonvolatile memory devices. To produce novel topological polar structures, the ferroelectric ordering can be tailored through strain induced by substrate vicinality. In our study, we designed two material systems.The first system consists of two samples, both using Pulsed Laser Deposition (PLD) and Wet Etching techniques to create artificial pinholes on La0.7Sr0.3MnO3 (LSMO) thin films epitaxially grown on (001)-oriented SrTiO3 (STO) substrates. Subsequently, we covered these pinholes with BiFeO3 (BFO) thin films, with etching shapes including circles, triangles, and squares. The first sample has sizes of approximately 4-6 micrometers, while the second sample ranges from around 1 micrometer to several hundred nanometers. We further employed Piezoresponse Force Microscopy (PFM), Kelvin Probe Force Microscopy (KPFM), and Conductive Atomic Force Microscopy (C-AFM) techniques to investigate the artificial domain characteristics under defined strain patterns. Our results showed that the polarization variants point along the (110)-axis and form a flux-closure domain structure, with the strain tending to result in non-leakage characteristics. We successfully demonstrated a method to control topological ferroelectric domains and enhance piezoelectric properties through epitaxial growth.The second system involves using Pulsed Laser Deposition (PLD) with a freestanding (FS) method to create heterostructure thin films from three different target materials: BFO, STO, and YBCO. The YBCO layer is etched away to obtain FS-BFO/STO bilayer epitaxial films, which are then transferred to a target substrate via the FS method. Due to the lattice constant differences on the YBCO surface, BFO forms island structures. We further employed Piezoresponse Force Microscopy (PFM) techniques to study the artificial domain characteristics under the BFO island structures. Our results indicated that the strain boundaries provided by the island structures form Head-to-Head centered vortex domain structures in order to minimize elastic energy.

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