在本研究中，以壓電力顯微鏡(Piezoelectric Force Microscopy，PFM)與導電式原子力顯微鏡(conductive-Atomic Force Microscopy，c-AFM)探討磊晶鐵酸鉍(BiFeO3，BFO)薄膜的導電態切換特性與特殊向心狀鐵電域壁的導電特性。利用施加不同時間與強度的外加電場，調控薄膜與探針之間的載子濃度分布，以PFM和c-AFM同時觀察到了壓電訊號屏蔽與導電性增強現象，並由電流電壓曲線擬合發現Pt/BiFeO3/SrRuO3結構的傳導機制在低電場時為蕭特基發射，高電場狀態時則為福勒－諾德漢穿隧效應所主導。施加的外場吸引氧空缺累積於薄膜表面降低局部位障成為高導電狀態。
凝態物理中域壁作為拓樸缺陷，在近來的研究中受到很大的重視，尤其多鐵性材料的域壁有低維度電子傳輸及磁電耦合特性，擁有發展新式電子裝置的潛力。透過單點脈衝電壓的施加，可在鐵酸壁薄膜中形成向心狀電域結構，結構內部域壁相對於電域中心皆為高導電狀態。能夠由多次的脈衝電壓操控電域與域壁形貌，進而改變局部的導電狀態。

In this study, I present the conduction switching and central-type-domain conductivity in epitaxial BiFeO3 (100) films by the piezoresponse force microscopy (PFM) and conductive-atomic force microscopy (c-AFM). The local carrier density of the BFO film can be controlled by electric field with different time and magnitude through applying voltage pulses from the tip. The phenomenon of conductivity enhancement can be observed directly on the c-AFM image and also revealed in the PFM image by the shielding of piezoresponse signal. From the current-voltage curve fitting, the transmission mechanism in the domain of Pt/BiFeO3/SrRuO3 structure was confirmed as Schottky emission and Fowler-Nordheim tunneling under low and high bias voltages, respectively. The applied field attracted the oxygen vacancies which were accumulated at the film surface and reduced the barrier for electron transport.
Domain walls (DWs), as the topological defects in condense materials, had attracted a lot of interests recently. In multiferroics, DW is potential for application in novel functional electronic devices, given their low-dimensional confinement for electron transport as well as the particular magneto-electric coupling behaviors. Through applying pulse voltage through tip, we can create the central-type-domain. The domain walls have high conductivity in central-type-domain structure. We can control the domain wall by applied pulse voltage, and change the local conduction state.

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