挠曲电效应下极性畴结构演化及极性信息力学载荷可擦写研究

In recent years development of electronic devices undergoes the rapid trend towards complex and deformable structures. Functional devices with complex and deformable structures inevitably generate stress and strain gradients, thereby leading to the coupling between stress/strain gradients and polarization, namely flexoelectric effect. Numerous studies show that low-dimensional ferroelectric materials exhibit significant flexoelectric effect, which can largely affect the basic characteristics (such as phase transition, dielectric, polarization) and other related properties of low-dimensional ferroelectric materials. It is critical to reveal the flexoelectric effect and its regulation on relevant performance of low-dimensional ferroelectric materials. However, currently there is a serious shortage of both theoretical and experimental research on ferroelectric flexoelectric effect. Research on flexoelectric coefficient and the mechanism of flexoelectric effect on basic material characteristics and on the evolution of ferroelectric domain structure is still in its infancy. This project intends to consider flexoelectric effect and its coupling with multiple factors including mechanical loads, structure, size, temperature, surface and interface, etc., to make an in-depth study on the formation, stability and evolution of polar domain structure and the mechanical erasing of polar domain information. We will establish multiscale simulation methods for the flexoelectric effect of low-dimensional ferroelectric materials and systematically explore experimental method of processing low dimensional ferroelectric materials and characterizing their flexoelectric effect. Our study will lay the foundation of mechanic research for the design, application and development of polar domain storage, information sensing devices and other functional devices based on flexoelectric effect.

近年来电子器件结构朝着可复杂变形的趋势迅速发展。可复杂变形功能器件不可避免产生应力应变梯度，从而形成应力应变梯度与极性耦合的挠曲电效应。大量研究表明低维铁电材料存在明显的挠曲电效应，能够显著影响低维铁电材料相变、介电、极化等基本特性及相关特性。揭示低维铁电材料的挠曲电效应及其对相关性能的调控性十分关键。然而当前针对铁电挠曲电效应的理论及实验研究依然严重不足，材料的挠曲电系数、挠曲电效应对铁电基本特性及畴结构演化影响机理的研究还处于起步阶段。本项目拟综合考虑挠曲电效应与力学加载、结构、尺寸、温度、表面、界面等多重因素作用，针对极性畴结构形成、演化、演化以及极性信息力学载荷可擦写特性进行深入研究，建立低维铁电材料挠曲电效应多尺度模拟方法，系统研究低维铁电材料制备工艺和挠曲电效应测试表征方法，为挠曲电效应在极性存储、信息传感等器件及其它功能器件的设计、应用与发展奠定力学研究基础。

项目围绕“挠曲电效应下极性畴结构演化及极性信息力学载荷可擦写研究”展开相关理论及实验工作。理论方面，我们基于自主开发的铁电畴壁相场模拟方法，结合密度泛函理论计算、基于有效哈密顿量的分子动力学模拟等方法，深入、系统研究了含复杂表界面及剪切效应下极性畴结构翻转机理、极性涡旋态手性的力电翻转机制、针尖载荷下极性信息写入及相互作用机制、挠曲电效应下极性翻转的动力学行为等。实验方面，我们运用物理激光沉积PLD、Langmuir-Blodgett技术等工艺对纳尺度铁电材料的制备进行了大量的探索，成功制备出铁电超薄膜、铁电纳米点等结构；搭建了针对铁电超薄膜畴壁分析和测试的实验平台，对铁电超薄膜、铁电纳米点极性畴结构演化及极性信息力学载荷可擦写特性进行了表征测试，重点揭示其中的挠曲电效应和表界面效应。基于大量的理论和实验结果，总结了一系列挠曲电效应下极性畴结构演化调控规律及极性信息力学擦写方案。相关成果在力学、材料和物理领域国际期刊发表论文34篇，包括固体力学权威期刊J. Mech. Phys. Solids、材料顶级期刊Acta Materialia、ACS Appl. Mater. Interface、物理权威期刊Phys. Rev. B、Phys. Rev. Mater.、Phys. Rev. Appl.等，学术章节1篇，申请国家专利1项。本项目研究为发展铁电畴结构力学和挠曲电效应相关理论、实验方法和器件概念设计奠定了基础。