Probing Local Origins of Nonlinearity in Ferroelectric Films

非技术故障：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，多层电容器用于几乎所有手持设备和计算机，以及用于先进显微镜系统的高精度定位系统。 围绕着高交变电场下材料的性能，还有许多未解答的问题;随着我们继续对器件进行封装，这些问题变得越来越重要。 该计划试图通过调查缺陷在影响铁电畴壁的迁移率中所起的作用来解决与场依赖性的属性相关的开放性问题。 这里获得的见解将用于帮助设计下一代组件。教育推广计划将利用由主要研究人员及其研究生教授的针对小学生的讲习班。 这些将每年吸引约80名学生参加一系列旨在教授材料科学基础的实践实验活动。该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工作。技术优势：铁电材料是胎儿和心脏监测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。 铁电材料中的缺陷会导致畴壁钉扎，从而影响介电和压电响应。 随着器件尺寸的不断缩小，人们越来越需要了解畴壁迁移率和微结构之间的相互作用。 因此，这个程序是解决以下基本问题：什么是潜在的深度与任何钉扎中心？钉扎畴壁需要缺陷的浓度是多少？特定的缺陷类型如何影响参与畴壁级联的材料的体积？宏观非线性是如何从局部响应发展而来的？为了解决这些关键问题，模型铁电薄膜与控制缺陷浓度正在增长，包括外延铁电薄膜的双晶体基板上已知的扭曲和倾斜角。 大晶粒多晶薄膜允许更广泛的晶界分布进行探测。 点缺陷浓度通过在阳离子亚晶格上的异价掺杂来定制，或者通过受控的还原水平来在阴离子亚晶格上产生缺陷。 由此产生的膜被探测带激发压电力显微镜提供一个定量测量的畴壁迁移率在一个非常精细的空间尺度，使我们可以了解每种类型的缺陷在控制畴壁迁移率的相对重要性。

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.