Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA.
Nanoscale. 2018 Feb 15;10(7):3262-3271. doi: 10.1039/c7nr07203a.
The ferroelectric domain pattern within lithographically defined PbTiO/SrTiO ferroelectric/dielectric heteroepitaxial superlattice nanostructures is strongly influenced by the edges of the structures. Synchrotron X-ray nanobeam diffraction reveals that the spontaneously formed 180° ferroelectric stripe domains exhibited by such superlattices adopt a configuration in rectangular nanostructures in which domain walls are aligned with long patterned edges. The angular distribution of X-ray diffuse scattering intensity from nanodomains indicates that domains are aligned within an angular range of approximately 20° with respect to the edges. Computational studies based on a time-dependent Landau-Ginzburg-Devonshire model show that the preferred direction of the alignment results from lowering of the bulk and electrostrictive contributions to the free energy of the system due to the release of the lateral mechanical constraint. This unexpected alignment appears to be intrinsic and not a result of distortions or defects caused by the patterning process. Our work demonstrates how nanostructuring and patterning of heteroepitaxial superlattices allow for pathways to create and control ferroelectric structures that may appear counterintuitive.
在光刻定义的 PbTiO/SrTiO 铁电/介电异质外延超晶格纳米结构中，铁电畴模式受到结构边缘的强烈影响。同步加速器 X 射线纳米束衍射表明，此类超晶格表现出的自发形成的 180°铁电极化条纹畴采用了一种在矩形纳米结构中，畴壁与长图案化边缘对齐的配置。来自纳米畴的 X 射线漫散射强度的角分布表明，畴相对于边缘在大约 20°的角度范围内对齐。基于时变 Landau-Ginzburg-Devonshire 模型的计算研究表明，由于释放了侧向机械约束，系统自由能的体和电致伸缩贡献降低，导致了对齐的优选方向。这种出乎意料的对齐似乎是内在的，而不是由于图案化过程引起的变形或缺陷造成的。我们的工作表明，异质外延超晶格的纳米结构化和图案化如何为创建和控制铁电结构提供途径，这些结构可能看起来违反直觉。
