鐵酸鉍-鈷鐵氧自組裝奈米結構之管狀介面區域導電現象

Abstract

強關聯氧化物介面上晶格、電荷、軌道及自旋等自由度間的交互作用產生獨特的電子行為並導致許多新穎現象，如LaAlO3-SrTiO3異質介面的二維電子氣以及鐵係氧化物疇域壁的導電現象。因此，複雜氧化物介面提供一新的管道以發掘新穎現象。但，除了人為操作的雙層異質介面以及材料為降低能量而產生之同質介面，是否還存在另一種氧化物介面？為尋找新的複雜性氧化物介面，我們檢視了目前存在的氧化物異質結構，發現了自組裝奈米結構中的管狀氧化物介面仍未被仔細研究。自組裝奈米結構常被用於研究兩相材料性質之結合，如鐵電性BiFeO3 (BFO)與亞鐵磁CoFe2O4 (CFO)系統的磁電耦合效應或是光伸縮SrRuO3與磁伸縮CFO系統的光磁耦合現象等。實驗中我們選用BFO- CFO自組裝奈米薄膜並透過導電原子力顯微鏡(C-AFM)以及掃描穿隧顯微鏡(STM)於微觀尺度下觀察及研究管狀介面局部導電現象。從I-V曲線分析可知其介面區域導電現象受兩種導電機制主導而導電成因可能為氧空缺於管狀介面累積所致。研究中所獲得之結果可以作為協助未來於整合奈米複合材料至功能性微電子元件的基礎。

The interplay among degrees of freedom - lattice, charge, orbital and spin – at the interfaces of strongly correlated oxides generate unique electronic phases and cause many intriguing phenomena, such as 2 dimensional electron gas at the LaAlO3 -SrTiO3 hetero-interface and the electrical conduction at the domain walls (homo-interface) in ferroics. Therefore, complex oxides provide a new arena to explore novel phenomenon. However, is there another oxide interface existing beside the artificial manipulated bi-layer heterointerfaces and homointerfaces due to the reduction of free energy? In order to search for new types of complex oxide interfaces, we examined the existing oxide heterostructures and found that the tubular oxide interfaces in self-assembled hetero-epitaxial nanostructures, which form spontaneously during the growth process due to competition of the surface energies, have not been explored yet. Self-assembled nanostructures are used to study the properties of the combination by two materials, such as the magnetoelectric coupling in the system of ferroelectric BiFeO3 (BFO)-ferrimagnetic CoFe2O4 (CFO) or the photomagnetic coupling in the photostrictive SrRuO3 – magnetostrictive CFO system. In this study, we adapted the BFO- CFO as a model system to carry out the systematic research on the BFO-CFO tubular interface and the phenomenon of local conduction at the tubular interface was observed and studied at the nano scale through conducting atomic force microscope (C-AFM) as well as scanning tunneling microscope (STM). Form the analysis of I-V curves, two transport models are found to be the dominant conduction mechanism and the nature of the interfacial band structure is also resolved. Knowledge extracted from our results could serve as a guide for future works on integration of nano-composites into functional nanoelectronic devices.