Probing Local Origins of Nonlinearity in Ferroelectric Films

非技术细节：铁电材料(具有可切换自发极化的材料)是用于胎儿和心脏监测的超声成像系统的核心，用于几乎所有手持设备和计算机的多层电容器，以及用于先进显微镜系统的高精度定位系统。围绕着材料在高交变电场下的性能有许多悬而未决的问题；随着我们不断地将设备微型化，这些问题变得越来越重要。本程序试图通过研究缺陷在影响铁电畴壁迁移率中所起的作用来解决与特性的场相关性相关的未解决的问题。这里获得的见解将被用来帮助设计下一代组件。教育推广方案将利用由主要调查人员及其研究生讲授的针对小学生的讲习班。这些课程每年将吸引约80名学生参加一系列旨在教授材料科学基础的动手实验活动。这位研究生将在宾夕法尼亚州立大学和橡树岭国家实验室的纳米材料科学中心度过一段时间。技术细节：铁电材料是用于胎儿和心脏监测的超声成像系统的核心，几乎所有手持设备和计算机以及高精度定位系统都使用多层电容器。众所周知，缺陷会引起铁电材料中的磁化壁钉扎，从而影响铁电材料的介电和压电响应。随着器件尺寸的不断缩小，人们越来越需要了解磁化壁迁移率和微观结构之间的相互作用。因此，这个程序正在解决以下基本问题：与任何钉扎中心相关的潜在深度是多少？需要什么浓度的缺陷才能钉住磁区壁？特定的缺陷类型如何影响参与磁区壁级联的材料的体积？宏观非线性如何从局部响应中发展？为了解决这些关键问题，正在生长缺陷浓度受控的模型铁电薄膜，包括在已知扭角和倾角的双晶衬底上生长的外延铁电薄膜。大颗粒多晶薄膜允许探测更广泛的晶界分布。点缺陷浓度是通过在阳离子亚晶格上进行等价掺杂来定制的，或者通过控制还原水平来在阴离子亚晶格上产生缺陷。用带激励压电力显微镜对得到的薄膜进行了探测，以便在非常精细的空间尺度上定量测量磁畴壁的迁移率，这样我们就可以了解每种类型的缺陷在控制磁畴壁迁移率方面的相对重要性。

NON-TECHNICAL DETAILS: Ferroelectric materials (materials that have a switchable spontaneous polarization) are at the heart of ultrasonic imaging systems for fetal and cardiac monitoring, the multilayer capacitors used in virtually every handheld device and computer, as well as in high precision positioning systems for advanced microscope systems. There are a number of unanswered questions surrounding the properties of the materials under high alternating electric fields; these are becoming increasingly more important as we continue to miniaturize devices. This program attempts to address open questions associated with the field dependence of the properties by investigating the role that defects play in influencing the mobility of ferroelectric domain walls. The insights gained here will be utilized to help design next generation components. The educational outreach program will utilize workshops directed at elementary school students taught by the principal investigators and their graduate students. These will engage ~ 80 students per year in a series of hands-on experimental activities designed to teach fundamentals of materials science. The graduate student will spend time both at Penn State University and at the Center for Nanoscale Materials Science at Oak Ridge National Laboratories.TECHNICAL DETAILS: Ferroelectric materials are at the heart of ultrasonic imaging systems for fetal and cardiac monitoring, the multilayer capacitors used in virtually every handheld device and computer, as well as in high precision positioning systems. It is known that defects contribute to domain wall pinning in ferroelectric materials, and so influence the dielectric and piezoelectric response. There is a growing need to understand the interplay between domain wall mobility and microstructure as devices continue to scale down in dimensions. Thus, this program is addressing the following fundamental questions:What is the potential depth associated with any pinning center?What concentration of defects is required to pin a domain wall?How do particular defect types influence the volume of material participating in a domain wall cascade?How do macroscopic nonlinearities develop from local responses?To address these critical questions, model ferroelectric films with controlled defect concentrations are being grown, including epitaxial ferroelectric films on bicrystal substrates with known twist and tilt angles. Large-grained polycrystalline films allow a wider distribution of grain boundaries to be probed. Point defect concentrations are tailored through aliovalent doping on cation sublattices, or through controlled levels of reduction to create defects on the anion sublattice. The resulting films are being probed by band excitation piezoelectric force microscopy to provide a quantitative measurement of the domain wall mobility at a very fine spatial scale, so that we can understand the relative importance of each type of defect in controlling domain wall mobility.