Meta-to-Insulator Transition at Correlated Electron Interfaces: In-Situ Growth and Characterization of Thin Oxide Films

*非技术摘要*该奖项支持凝聚态物理实验研究，研究复杂氧化物化合物薄膜和多层膜界面附近的不寻常物理性质。这些人工结构材料展示了奇异的功能，与未来先进的电子设备和能源应用相关。特别是，这些材料的界面通常表现出与相应的块体化合物不同的新性质。另一方面，几乎所有的电子设备都是从理解界面势垒的形成、电磁结构和控制开始的：界面就是设备。要将复杂氧化物的各种物理性质融入设备中，需要从基本的理解开始。非常令人兴奋的是，现代氧化物薄膜生长和探测技术提供了必要的原子尺度的精度来构建界面结构，并显示其电子性质，如金属到绝缘体的转变，这正是本项目的研究内容。这项研究的目标是了解并最终学习如何操纵氧化物材料界面的传输特性，从而为下一代电子设备设计新的功能。此外，这一努力的一个重要成果将是将材料制造、表征、分析和设计整合到一个独特的研究和教育计划中，以基本了解复杂的氧化物界面和培训未来的科学技术(S&T；T)劳动力。研究生和本科生都将参与材料制造和表征工作，他们将发展基本的“化学”和“物理”思维能力。*技术摘要*这项研究项目旨在研究如何利用表面或界面的对称性破缺和空间限制来操纵过渡金属氧化物(TMO)材料，特别是金属-绝缘体转变(MIT)薄膜的跃迁性质。这一目标将通过利用一套全面的原位材料生长和原子分辨表征能力来实现。越来越清楚的是，TMO的表面、界面和薄膜显示出丰富多样的迷人特性，这些特性与块体现象有关，但并不完全相同。麻省理工学院就是这些新兴资产之一。然而，这些现象的机制仍然存在激烈的争议。对这些现象的可能解释包括电子和氧空位掺杂、互扩散和晶格扭曲。该项目将利用原子表征和原位生长能力相结合的方法，探索应变、缺陷和氧空位、化学成分和界面结构扭曲在界面和薄膜中出现的MIT中的作用。具体地说，它将专注于(Sr，Ca)RuO_3和(Sr，Ca)VO_3的薄膜，这两种著名的伪立方金属钙钛矿，但处于麻省理工学院的边缘。通过改变衬底、薄膜厚度、阳离子位置组成引起的应变，该项目旨在深入了解推动麻省理工学院的Jahn-Teller失真和电子-电子关联之间的相互作用。

****NONTECHNICAL ABSTRACT****This award supports experimental condensed-matter physics research on the unusual physical properties near the interface of films and multilayers of complex oxide compounds. These artificially structured materials, which exhibit exotic functionalities, are relevant to future advanced electronic devices and energy applications. Especially, the interfaces of these materials generally show new properties different from the corresponding bulk compounds. On the other hand, almost all electronic devices began with an understanding of interface barrier formation, electronic/magnetic structure, and control: the interface is the device. Incorporating the diversity of physical properties of complex oxides into devices needs to begin with a basic understanding. What is very exciting is that modern oxide thin-film growth and probe techniques give the requisite atomic-scale precision to construct interface structure and manifest its electronic properties such as metal to insulator transition, which is exactly the research in this project. The goal of this research is to understand and ultimately learn how to manipulate the transport properties at the interfaces of oxide materials and thus to design new functionalities for next generation of electronic devices. Moreover, a significant product of this endeavor will be to integrate materials fabrication, characterization, analysis and design into a unique research and educational program for the basic understanding of complex oxide interfaces and the training of the future science and technology (S&T) workforce. Both graduate and undergraduate students will be involved in both material fabrication and characterization efforts and they will develop the essential ability to think "chemically" and "physically". ****TECHNICAL ABSTRACT****This research project is designed to study how the broken symmetry at a surface or interface and spatial confinements can be used to manipulate the emergent properties in a thin film of transition metal oxide (TMO) materials, especially the metal-insulator transition (MIT). The objective will be achieved by utilizing a comprehensive set of in-situ materials growth and atomically-resolved characterization capabilities. It is becoming increasingly clear that surfaces, interfaces, and thin films of TMOs display a rich diversity of fascinating properties that are related to, but not identical to, the bulk phenomena. MIT is one of these emerging properties. While the mechanisms for these phenomena are still hotly contested. Possible explanations for these phenomena include doping with electrons and oxygen vacancies, interdiffusion and lattice distortion. This project is going to take advantage of atomic characterization combined with in-situ growth capability to explore the role of strain, defects and oxygen vacancies, chemical composition and interface structural distortion in MIT emerging at interfaces and thin films. Specifically, it will focus on thin films of (Sr,Ca)RuO3 and (Sr,Ca)VO3, two well-known pseudo-cubic metallic perovskites, but at the verge of MIT. By varying strain induced by substrate, film thickness, cation-site composition, the project aims to gain insight into the interplay of Jahn-Teller distortion and electron-electron correlation driving the MIT.