BiFeO3多铁薄膜表面、界面能带结构的光电子谱研究

Currently BiFeO3 is the only emerged single-phased multiferroic material with simutaneous ferroelectric and magnetic orderings at room temperature. It has been extensively studied due to its potential application of new generation memory and spintronic devices, and also its interesting physics related to the stongly correlated electronic system. While the interface, e.g. the electorde material, the Schottky barrier and the band alignment, play a crucial role in stablizing the ferroelectric domain and establishing highly reliable performance of the devices. Based on the previous studies on PZT interface, this project will concern on the surface and interface of multiferroic BiFeO3 thin films by means of photoelectron spectroscopy, and try to give a systematical, direct and quantitive determination results especially on the band structures and chemical reactions at the interface with different electrodes, furthermore, we will explore the modulation of the barrier heights at the multiferroic interfaces by electric and magnetic field, and the absolute variation values are expected. The relationship between the band structure and the lattice strain，lattice orientation, polarization and even the magnetic field at the multiferroic interface will be deduced. This study is important for clrifying the mechanism of the band alignment and explaining the variation of the barrier height at the multiferroic interface.The results definitely will be helpful for the experimental and theoretical research on multiferroic tunnel junctions and other novel devices as well, also the photoelectron spectroscopy route will provid another possibility to investigate the polar interfaces among oxide heterojunctions.

BiFeO3室温多铁材料兼具铁电性和磁性，磁、电之间的耦合赋予了电子器件许多新颖的功能和特点，同时丰富了强关联电子的物理图像，引起了人们极大的研究兴趣。由于薄膜物性和器件性能都强烈依赖于界面的性质，本项目将利用光电子谱这一直接有效的实验手段，研究BiFeO3薄膜的表面、界面能带结构。我们将在前期研究Pb(Zr,Ti)O3铁电薄膜界面的基础上，选择不同的单晶衬底制备外延BiFeO3多铁薄膜，研究晶格应力引起的薄膜表面费米能级的变化；结合原位电极生长方式，研究晶格取向和电极类型引起的界面能带结构的变化以及界面形成中的化学反应；同时探索电场和磁场调制下多铁材料界面势垒的演变规律，以了解多铁极化界面的能带结构与极化电荷及磁场的关系。这些工作将为高质量多铁隧道结和新型多铁器件的研制提供必要的实验基础。

BiFeO3室温多铁材料兼具铁电性和磁性，磁、电之间的耦合丰富了强关联电子的物理图像，赋予电子器件许多新颖的功能和特点，引起了人们极大的研究兴趣。其薄膜物性和器件性能都依赖于界面的性质，本项目将在前期Pb(Zr,Ti)O3的研究基础上，使用光电子谱方法研究了BiFeO3多铁薄膜的与金属电极以及氧化物电极的界面形成，作为对比同时研究同样具有钙钛矿结构的KNN薄膜的界面，发现：（1）BFO薄膜与金属电极之间有明显的化学反应，氧化Bi可以被还原成金属Bi，而BFO与氧化物ITO的界面之间则没有此一反应。BFO的这一性质与PZT类似，而且两者都具有明显的疲劳效应；（2）KNN与金属和氧化物之间的界面都未观测到明显的元素价态变化，而且KNN具有非常难得抗疲劳特性。这一研究结果表明铁电材料的疲劳行为与其界面有着非常直接的关联。本项目对阐明多铁界面能带排列的形成机制，揭示铁电材料的疲劳行为形成机制提供了实验结果，为多铁隧道结及新型多铁器件的实验与理论研究奠定基础，也为氧化物极性界面的研究提供了新的思路和方法