Domain Wall-Defect Interactions in Ferroelectric Films

铁电材料在商业上广泛应用于电容器、精密定位装置、燃油喷射器、非易失性存储元件和医疗超声换能器等领域。铁电材料的测量特性是晶体对外加电场的本征响应和在外加电场和应力作用下畴壁运动引起的本征响应的函数。畴壁运动在优化体压电材料外在性能中的作用已经得到了广泛的研究，但在薄膜中，很少有相关的研究试图了解畴壁如何与缺陷相互作用。为了使基于压电薄膜的微机电系统（即纳米电机和致动器）得到广泛应用，需要优化其性能并提高其可靠性。可靠性的一个方面是在设备的使用寿命内保持相同的压电响应的能力。目前，由于薄膜内的晶界、点和平面缺陷等缺陷在循环过程中逐渐钉住畴壁，限制了这一点。本提案旨在通过应用先进的透射电子显微镜、压电显微镜和经典FEstack测量相结合的方法来研究一系列定制的铁电薄膜，从而建立对钉住畴壁缺陷作用的基本理解，其中特定类型的缺陷已经被设计出来。英国的努力专注于TEM，并直接与宾夕法尼亚州立大学（Trolier-McKinstry，薄膜沉积和FEStack）和橡树岭国家实验室（Kalinin，压电显微镜）之间已经资助的项目联系起来。

Ferroelectric materials are in widespread commercial use as capacitors, precision positioning devices, fuel injectors, non-volatile memory elements, and as medical ultrasound transducers, among other applications. The measured properties of ferroelectric materials are a function of both the intrinsic response of the crystal to applied fields and the extrinsic response due to motion of domain walls under applied electric fields and stresses. The role of domain wall motion in optimising the extrinsic properties of bulk piezoelectrics has been extensively investigated but in thin films there have been few coherent studies that have attempted to understand how domain walls interact with defects.For piezoelectric thin film based micro electromechanical systems (i.e. nano-motors and actuators) to gain widespread usage, their properties need to be optimised and their reliability improved. One aspect of reliability is the ability to maintain the same piezoelectric response over the lifetime of the device. This is currently limited by progressive pinning of domain walls during cycling by defects such as grain boundaries, point and planar defects within the film. This proposal aims to establish a fundamental understanding of the role of defects in pinning domain walls by applying a combination of advanced transmission electron microscopy, piezo-force microscopy and classic FEstack measurements to the study of a bespoke series of ferroelectric films in which specific types of defects have been engineered. The UK effort concentrates exclusively on TEM and links directly to an already funded programme between Pennsylvania State University (Trolier-McKinstry, film deposition and FEStack) and Oak Ridge National Laboratory (Kalinin, piezo-force microscopy).