微纳尺度下铁电畴壁钉扎与蠕动现象的实验研究

Very recently, many new phenomena and effects are found in the ferroelectric domain walls. This leads to a new developing research topic named ‘domain wall nanoelectronics’. It is essential for the ferroelectric domain wall (DW) nanoelectronics to understand the dynamics of DW at the scales from micron to nanometer. In veiw of that the direct observation of DW motion is crucial to.understand the DW dynamics, such as roughening and nonlinearity, we proposed a method to manual generate a nearly-straight DW in ferroelectric thin film capacitors. With the accessibility of the initial nearly-straight DW, it is not only easy to record DW motion experimentally by snapshot-type piezoresponse force microscopy (PFM), but also possible to analyze DW dynamics theoretically by the models of disordered medias. Based on this method, we will focus on exploring the pinning and creep phenomena (such as roughening, evolution history, and velocity-field relationship) in the ferroelectric thin film capacitors at micro-to-nano-scale. Specially, we will utilize PFM to snapshot the profiles of DW during pinning-creep process, and apply theoretical models of the disordered elastic system to extract the characteristic parameters of DW dynamics. In order to get insight into the nature of defects in DW pinning and creep, we will prepare ferroelectric samples with typical dominant defects, like oxygen vacancy and grain boundaries, and compare the differences of DW dynamics in these samples. This project will provide experimental supports for understanding DW dynamics, and unveil the physical nature of defects governing the DW pinning and creep behaviors. This project will also pave the way to further exploring of the new phenomena in ferroelectric DW and future development of ferroelectric domain wall nanoelectronics.

最近，铁电薄膜畴壁中陆续发现了多种新现象和新效应，由此形成了“畴壁纳米电子学”这一前沿研究领域，其发展迫切需要深入认识微纳尺度下的铁电畴壁动力学行为。鉴于从实验上观察畴壁运动有助于直观认识畴壁的运动特征，如畴壁的粗化与自相似、非线性运动等。本项目提出了一种在铁电薄膜平板电容结构中人工形成准直线畴壁的方法。以此为基础，采用快照式压电响应力显微镜为主要实验手段，结合弹性弦和微观格点模型的理论分析方法，系统研究铁电薄膜畴壁的钉扎与蠕动现象（包括畴壁粗化与演变历史、畴壁速度与外场关系等）。针对畴壁钉扎与薄膜典型缺陷（氧空位、晶界等）之间的密切关系，制备具有不同缺陷特征的铁电薄膜，对比研究其中的畴壁运动差异性，掌握典型缺陷对畴壁钉扎与蠕动行为的影响规律。通过本项目的研究，可以深入认识铁电薄膜畴壁的动力学行为，掌握薄膜缺陷影响畴壁运动及材料性能的机制，对于探索的畴壁新现象、新效应具有重要的科学意义。

针对“畴壁纳米电子学”这一前沿研究领域迫切需要深入认识微纳尺度下的铁电畴壁动力学行为的基础研究背景，本项目研究了一种在铁电薄膜平板电容结构中人工形成准直线畴壁的方法，以快照式压电响应力显微镜为主要实验手段，研究了三种典型铁电薄膜（外延PbZrTiO3和BiFeO3薄膜、单晶LiNbO3薄膜）的畴壁运动行为，实验观测了畴壁蠕变与钉扎过程中的粗化现象。在PZT 薄膜中，直接观察到了畴壁运动与反转电场强度的依赖性：随着电场的增加，畴壁运动出现了从新畴成核占主导向畴壁横向扩张移动占主导的转变；在低温4K和室温290K的条件下，测量了BiFeO3薄膜畴壁运动速度与外场关系，通过分析畴壁的粗糙度指数，确定了畴壁蠕动主要归因于随机场型钉扎中心。还通过实验发现了畴壁蠕动激活能与温度呈1/T变化规律；在LiNbO3单晶薄膜上，观察到畴壁蠕动粗化的过程不仅Ar离子轰击缺陷的钉扎作用有关，还与畴壁前方的新畴成核有关。本项目建立的测试技术为进一步研究畴壁纳米电子学提供的新的表征和分析方法，进一步揭示了铁电薄膜畴壁的动力学行为复杂性，具有重要的科学意义。