Materials World Network: Nanoscale Structure and Shaping of Ferroelectric Domains

铁电材料在没有外场的情况下具有内置的电偶极矩，正以无数种方式进入我们的日常生活。我们在杂货店收银台的条形码阅读器、高速电光调制器和其他为我们的信息高速公路提供动力的有源元件中发现了它们。这类材料最吸引人的特点之一是，材料性能可以通过适当安排铁电畴轴来定制。例如，非线性光学器件通过周期性改变（周期性极化）铁电轴来调制非线性光学特性，从而有效地、有选择地将光从一个波长转换为另一个波长。到目前为止，这类现有器件的域模式的特征尺寸和周期都是有限的，至少只有几微米。为了开发更紧凑、功能更新颖的纳米光子学器件，需要在亚微米和纳米尺度上对铁电畴取向进行更高水平的控制。这项工作通过汇集多方面的方法来解决这一重大挑战，包括解决有关纳米尺度畴壁结构和动力学的基础科学问题，开发使用光学和扫描探针显微镜进行畴图像化的新技术，以及演示具有后向非线性耦合的光学参量振荡器、电光布拉格反射器和非线性光子晶体器件等设备。这个国际项目是由美国的三个小组（利哈伊大学、宾夕法尼亚州立大学和佛罗里达大学）、德国帕德博恩大学的应用物理小组（Sohler教授）和德国波恩大学的应用光学小组（Buse教授）合作进行的。该团队最近的发现表明，实现更小特征尺寸的关键在于详细了解畴壁区域的结构和动力学，以及它们如何依赖于原子尺寸缺陷。该项目将结合理论和新的实验工具来探索这些问题，以进行畴壁成像和实时表征。最近在激光辅助域写入方面的突破表明，基于对潜在过程的良好理解，对这些缺陷的精细操作可以成为精确控制域生长和纳米尺度图案的强大新工具。教育和外联是这一合作的关键部分。在pi小组工作的本科生、研究生和博士后学者将通过所有参与组织的旅行交流和研讨会，获得全球互动的独特视角。该团队将通过WISER和BEST计划以及利哈伊科学推广计划为K-12举办先进材料及其尖端技术的年度研讨会。该项目由国际科学与工程办公室共同资助。

Ferroelectric materials, which have a built-in electrical dipole moment in the absence of an external field, are making their way into our daily lives in countless ways. We find them in barcode readers in grocery checkouts, in high-speed electro-optic modulators and in other active elements that power our information superhighway. One of the most attractive features of this class of materials is that the material properties can be tailored by properly arranging the ferroelectric domain axis. Examples are non-linear optical devices that efficiently and selectively convert light from one wavelength to another by modulating the nonlinear optical properties by periodically changing (periodically poling) the ferroelectric axis. The feature sizes and periods of domain patterns in existing devices of this kind are limited, so far, to a minimum of a few microns. To develop nano-photonics devices that are more compact and offer both novel and higher functionalities, a new level of control of the ferroelectric domain orientation on the submicron and nanometer scale is required. This work addresses this major challenge by bringing together a multifaceted approach that includes solving basic science questions about the nano-scale domain wall structure and dynamics, developing new techniques for domain patterning using light and scanning probe microscopies, and demonstration of devices such as an optical parametric oscillator with backward nonlinear coupling, electro-optical Bragg reflector, and nonlinear photonic crystal devices. This international project is being carried out in collaboration among three groups in the US (Lehigh University, Pennsylvania State University State, and the University of Florida), the Applied Physics group (Prof. Sohler) at the University of Paderborn, Germany, and the Applied Optics Group (Prof. Buse) at the University of Bonn, Germany. Recent discoveries by this team have shown that the key to achieve smaller feature sizes lies in a detailed understanding of the structure and dynamics of the domain wall region and how they depend on atomic size defects. The project will explore these issues using a combination of theory and novel experimental tools for domain wall imaging and real-time characterization. Recent breakthroughs in laser-aided domain writing have shown that a delicate manipulation of these defects based on a sound understanding of the underlying processes can become a powerful novel tool for precise control of domain growth and nano-scale patterning. Education and outreach is a critical part of this collaboration. The undergraduate, graduate and post-doctoral scholars working in the PIs groups will acquire a unique perspective in interacting globally through travel exchanges and workshops involving all participating organizations. The team will hold annual workshops on advanced materials and their cutting edge technologies for K-12 through WISER and BEST programs as well as through the Lehigh Science Outreach program. This NSF project is co-funded by the Office of International Science and Engineering.