Mechanical control of the electronic properties of 2D ferroelectrics

铁电材料的特征在于负电荷与正电荷的分离和排列，所述负电荷与正电荷可以通过施加电场而瞬时翻转。这些相反排列或极化的状态可以作为二进制数据的1和0存储和读取，即使在电源被切断时，这些状态也保持稳定。这为这些材料在非易失性存储器应用以及许多其他先进电子器件中的使用提供了基础。通常，这种性质存在于大块晶体、陶瓷和薄膜中。最近，理论模型预测，由弱力键合的原子平面组成的二维（2D）层状材料也可以表现出极化状态。然而，这些材料中的电荷的电翻转是极其困难的，因为电偏压的应用引起简单地燃烧样品的高电流。该项目探索机械应力作为一种新的方法来调制电子电荷和相关的电阻变化。一个微小的导电探针被用来向样品施加局部压力，并检测由此产生的极化以及样品电导率在纳米级的变化。该项目通过将所有种族、性别和背景的学生带入科学、技术和工程领域，加强了内布拉斯加大学的研究、教育和推广任务。技术描述实现基于二维（2D）铁电体的先进电子器件取决于确定性控制其极化状态的能力。这些材料的高电导率排除了使用常规的电学方法来测试和操纵极化响应。本研究的首要目标是通过确定性的无电压极化控制来研究二维铁电体的电子性质的可调谐性。该研究主要集中在三个密切相关的部分：（1）实验研究二维铁电体的挠曲电行为;（2）通过机械手段研究二维材料中的极化反转;（3）评估应变和应变梯度在调制其极化耦合电子特性中的作用。扫描探针显微镜技术将被用来探索本地传输性能和flexoelectrically-enabled纳米级域工程之间的相互作用。利用挠曲电效应代表了用于控制极化耦合电子行为的新范例，其适用于任何2D铁电材料，而不管其电子性质如何。这项研究的最重要成果是开发概念新颖的电子设备，其中动态机械刺激允许调制与极化耦合的各种功能特性，例如机电响应，两个-该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

Nontechnical description Ferroelectric materials are characterized by a separation and arrangement of negative vs positive charges that can be instantaneously flipped by applying of an electric field. Those oppositely aligned, or polarized, states can be stored and read as the 1s and 0s of binary data, with the states remaining stable even when a power source has been cut. This provides a basis for use of these materials in nonvolatile memory applications as well as in a number of other advanced electronic devices. Typically, this property is found in the bulk crystals, ceramics and thin films. Recently, theoretical modeling predicted that two-dimensional (2D) layered materials consisting of the atomic planes bonded by weak forces could also exhibit polarized states. However, electrical flipping of the electrical charges in these materials is extremely difficult as application of the electrical bias gives rise to a high current that simply burns the sample. This project explores mechanical stress as a novel method to modulate the electronic charges and the associated changes in electrical resistance. A tiny conducting probe is used to apply local pressure to the sample and to detect the resulting polarization as well as the change in the sample conductance at the nanoscale level. The project enhances the research, education, and outreach missions of the University of Nebraska by bringing students of all races, genders and backgrounds into science, technology and engineering.Technical description Realizing advanced electronic devices based on two-dimensional (2D) ferroelectrics depends on the ability to deterministically control their polarization state. High electrical conductance of these materials precludes using conventional electric methods for testing and manipulating the polarization response. The overarching objective of this research is to investigate the tunability of the electronic properties of 2D ferroelectrics via deterministic voltage-free control of polarization. The proposed research focuses on three closely related components: (1) experimentally investigating the flexoelectric behavior of 2D ferroelectrics; (2) investigating the polarization reversal in 2D materials by mechanical means; (3) evaluating the role of strain and strain gradient in modulation of their polarization-coupled electronic properties. Scanning probe microscopy techniques will be used to explore an interplay between the local transport properties and flexoelectrically-enabled nanoscale domain engineering. Utilizing the flexoelectric effect represents a new paradigm for controlling the polarization-coupled electronic behavior, which is applicable to any 2D ferroelectric material irrespective of its electronic properties. The most important outcome of this research is to develop conceptually novel electronic devices where dynamic mechanical stimulation allows modulation of a variety of the functional properties coupled to polarization, such as electromechanical response, two-dimensional conductivity and photovoltaic effect.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.