CAREER: Geometric Control of Flexoelectricity in Patterned Dielectric Thin Films

非技术描述：电脉冲和机械脉冲之间的耦合是许多传感器和执行器基本行为的基础。经典的压电材料是基于电荷与外加应力（传感器应用）或在外加电场（执行器应用）下产生的应变之间的线性相关。随着微型和纳米机电系统（MEMS和NEMS）的小型化，压电材料受到了额外的关注，因为在纳米尺度上，压电驱动和传感可以用比静电和磁电方法高得多的驱动功率密度来进行。这一发现与传统的压电材料形成了对比，后者只能提供有限的应变范围，而致动装置结构只能提供有限的微米级以下的可扩展性。这项工作旨在利用纳米尺度上出现的新型物理现象，即柔性电（应变梯度和发展电荷之间的耦合），开发可扩展到纳米尺寸的新型机电材料系统，同时允许大应变。机电响应与柔性电复合材料（因此是小型化样品）的尺寸成反比，这与目前可用的大块单晶或陶瓷压电材料中观察到的趋势相反。柔性电复合材料的响应不能被热降解或电降解，无铅的组合物应该比现有的基于铅的压电材料提供更大的机电响应。因此，柔性电纳米复合材料可以实现更广泛的小型化应用，并且是当前大块传感器和执行器的环保替代品。技术细节：本研究的目的是实现对柔性电作为所有电介质机电响应的贡献者的基本理解，并将其作为微纳米系统的新转导方法加以利用。精确的纳米制造方法与严格的介电和（微观和宏观尺度）压电表征的结合，以及详尽的微观结构表征，将为柔性电复合材料的多尺度科学提供重要的见解。本研究旨在建立微纳米电介质中柔性电高机电响应的理论和实验限制，并关联介电（微结构）和柔性电（几何）缩放效应，以了解它们对柔性电介质中有效压电响应的共同调节。对柔性电的新理解有助于摆脱含铅晶体的要求，而含铅晶体仍然是陶瓷传感器和执行器的基石。一旦理解了应变梯度、纳米结构和相变之间的关系，柔性电耦合将为传统的固溶体工程方法提供潜在的变革伙伴。这个项目的一个组成部分是在科学和工程领域征聘和保留妇女。这一目标是通过针对5-12年级女生群体的实践研讨会（以智能材料为重点），以及针对前沿科技领域的研究生和本科生的指导、研究和教育活动来实现的。

NON-TECHNICAL DESCRIPTION: Coupling between electrical and mechanical impulses underlies the basic behavior of many sensors and actuators. Classical piezoelectric materials are based on a linear correlation between the developed charges and applied stress (sensor applications) or strain developed under an applied electric field (actuator applications). With the drive towards miniaturization for micro- and nano-electromechanical systems (MEMS and NEMS), piezoelectric materials have received additional interest because piezoelectric actuation and sensing at the nanoscale can be conducted with much higher actuation power densities than with electrostatic and magnetoelectric approaches. This finding is in contrast to classical piezoelectric materials that offer only a limited strain range, and actuating device structures offer only limited scalability below the micron level. This work aims to take advantage of novel physical phenomena, i.e. flexoelectricity (coupling between strain gradients and developed charge), emergent on the nanoscale, to develop novel electromechanical materials systems scalable to nanometer sizes, while allowing for large strains. The electromechanical response scales inversely with the dimensions of flexoelectric composites (and therefore miniaturized samples), a trend opposite to what is observed in currently-available bulk single-crystal or ceramic piezoelectrics. The response of flexoelectric composites cannot be thermally or electrically degraded, and Pb-free compositions should offer much larger electromechanical response than current Pb-based piezoelectric materials. Therefore, flexoelectric nano-composites may enable a wider range of miniaturized applications and an environmentally-safe alternative to current bulk sensors and actuators.TECHNICAL DETAILS: This research aims to achieve fundamental understanding of flexoelectricity as a contributor to the electromechanical response of all dielectrics, and to harness it as a new transduction approach for micro- and nano-systems. The combination of precise nano-manufacturing methods with rigorous dielectric and (micro- and macro-scale) piezoelectric characterization, in addition to exhaustive microstructural characterization will provide a major insight into the multiscale science of flexoelectric composites. This research aims to establish theoretical and experimental limits for high electromechanical response through flexoelectricity in micro- and nano-meter patterned dielectrics, and correlate dielectric (microstructural) and flexoelectric (geometric) scaling effects to understand their co-regulation of the effective piezoelectric response in flexoelectric patterned dielectrics. A new understanding of flexoelectricity facilitates the required departure from lead-containing crystals, which remain the cornerstone of ceramic sensors and actuators. Flexoelectric coupling provides a potentially transformative companion to the conventional approaches of solid-solution engineering once the relationships between strain gradients, nanostructure, and phase transitions are well understood. An integral part of this project is the recruitment and retention of women in science and engineering. This objective is achieved through hands-on workshops (focused on smart materials) targeted to groups of girls in grades 5-12, as well as mentorship, research and education activities targeted at graduate and undergraduate students in cutting-edge scientific and technological fields.