Phase Transitions in Strongly Correlated Oxides Modulated Through Electrochemical Gating

非技术描述：该项目研究了在被称为金属-绝缘体相变的某些金属氧化物中观察到的一种不寻常的性质，其中绝缘氧化物的电导率可以通过在液体电解质存在下施加电场在超快时间尺度内显着增加。显示出这种性质的氧化物在许多下一代电子、光学和能量收集设备中至关重要，例如可充电金属空气电池、太阳能电池、场效应晶体管以及用于通信、检测和隐形技术的设备。尽管它们的重要性，绝缘体到金属相变的基本机制还没有得到很好的理解，是提高器件性能和进一步扩大这些氧化物基器件的范围的瓶颈。该项目研究电解质中的离子与金属氧化物纳米结构中的结构缺陷相互作用的基本方面，以及它们在通过最先进的电学和光学光谱技术诱导金属-绝缘体转变中的作用。研究工作包括纳米材料制造，先进的光谱表征和设备制造。该研究团队由从研究生到K-12的各个层次的学生组成，他们将接受这项多学科研究的培训，该研究通过课程工作，能源研讨会，夏令营和互动式动手演示模块与材料科学，电化学，先进光谱学和固态物理学进行交互。通过参加科学博览会、国际会议和领导力讲习班，使广大公众了解当前工作的影响。技术说明：电化学门控是一种强大的技术，用于调制强相关氧化物的许多不寻常的性质，如高温超导性，巨磁阻和金属-绝缘体相变，在各种光电器件中有应用。然而，这种门控过程的基本机制还没有得到很好的理解，特别是空位缺陷在诱导相变中的作用。本研究计画主要研究钒、镍、锰等强相关氧化物的金属-绝缘体转变。这项研究的动机是最近观察PI和同事的一种新的类型的相变在非化学计量的氧化镍，涉及电化学门诱导的半导体到绝缘体到金属的过渡。这个项目的总体目标是通过探测空位缺陷和氧化还原物种之间的相互作用的性质来阐明门控过程中各种类型的相变的起源。该研究采用了三重实验方法，使用先进的光谱技术：（1）通过操作中的电学和电化学测量确定电化学门控期间电子相变的性质，（2）通过原位光致发光监测空位-离子相互作用，和（3）通过非原位X射线光电子能谱监测金属离子氧化态的变化并鉴定吸附物种的化学性质。这些测量的集体结果将作为发展缺陷-性能-功能相关性的基础。这项工作的主要成果将是更好地理解电子结构，缺陷平衡，氧化还原物质的化学性质和器件特性之间的相互关系，这可能对不同领域的性能和功能氧化物基器件产生变革性影响，如电催化，光电子，电池，燃料电池和传感器。

Non-technical Description: The project investigates an unusual property seen in certain class of metal oxides known as metal-insulator phase transition, wherein the electrical conductivity of an insulating oxide can be dramatically increased in ultrafast timescale through application of electric field in the presence of a liquid electrolyte. Oxides that show this property are of utmost importance in number of next-generation electronic, optical, and energy harvesting devices, such as rechargeable metal-air batteries, solar cells, field effect transistors, and devices employed in communications, detection, and stealth technologies. Despite their importance, the underlying mechanism of insulator-to-metal phase transition is not well understood, and is a bottleneck for improving the devices performances and further expanding the scope of these oxide-based devices. This project studies the fundamental aspects of interaction of ions in the electrolyte with structural defects in nanostructure of metal oxide and their roles in inducing metal-insulator transition through state-of-the-art electrical and optical spectroscopic techniques. Research efforts encompass nanomaterial materials fabrication, advanced spectroscopic characterization and device fabrication. The research team comprises of students from all levels from graduate to K-12, who will be trained in this multidisciplinary study that interfaces with material science, electrochemistry, advance spectroscopy, and solid-state physics through course work, energy workshops, summer camps, and interactive hands-on demo modules. The impacts of current work are brought to the awareness of the broader public through participation in science fairs, international conferences, and leadership workshops. Technical Description: Electrochemical gating is a powerful technique for modulating number of unusual properties of strongly-correlated oxides, such as high-temperature superconductivity, colossal magnetoresistance, and metal-insulator phase transitions that have applications in diverse optoelectronic devices. However, the fundamental mechanism of this gating process is not well understood, especially the role of vacancy defects in inducing phase transitions. This research project studies metal-insulator transitions in strongly correlated oxides of vanadium, nickel and manganese. The study is motivated by the recent observation by PI and coworkers of a new type of phase transition in nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition induced by electrochemical gating. The overall goal of this project is to elucidate the origin of various types of phase transitions during gating by probing the nature of interactions between vacancy defects and redox species. The research employs a threefold experimental approach using advanced spectroscopic techniques to: (1) determine the nature of electronic phase transitions during electrochemical gating via in-operando electrical and electrochemical measurements, (2) monitor vacancy-ion interactions by in-situ photoluminescence, and (3) monitor the changes in the oxidation state of metal ions and identify the chemical nature of adsorbed species by ex-situ X-ray photoelectron spectroscopy. Collective results from these measurements will serve as the basis for developing defect-property-function correlation. The main outcome of this work would be a better understanding of the interrelationships between the electronic structures, defect equilibria, chemical nature of redox species, and device properties, which can have a transformative impact on the performance and functionality oxide-based devices in diverse fields such as electrocatalysis, optoelectronics, batteries, fuel cells and sensors.