A combined theory-experiment study of electronic, magnetic and thermal properties of complex oxide nano-structures

非技术描述：过渡金属陶瓷表现出广泛的特性和功能，使其成为许多下一代电子设备和传感器的理想材料。然而，许多过渡金属陶瓷对外界刺激，如热或电磁场的响应尚不清楚。当器件结构的尺寸接近纳米级，并且材料的响应与整体观察到的响应不同时，情况尤其如此。在本项目中，探索了一种在纳米尺度上测量过渡金属陶瓷对温度或外加电场或磁场的响应的新方法。然后用实验/理论相结合的方法来量化和控制纳米级过渡金属陶瓷材料界面上的磁、电和热输运性质。该项目的研究活动围绕理工科本科生和研究生的教育和培训展开。招募和培训的重点是下一代研究人员，特别是通过国家姓名交换计划和与当地高中的伙伴关系，让代表人数不足的群体和少数族裔的学生参与进来。本科生参与积极的研究项目是通过伊利诺伊大学芝加哥分校的PI本科生研究杂志培养的。毕业生通常在学术界、国家实验室或行业找到工作，包括半导体公司。技术细节：本研究项目的目标是对控制过渡金属钙钛矿氧化物异质结构的电子、磁性和热学性质的原子尺度机制有一个基本的了解。研究了两个过渡陶瓷系统，一个在特定的薄膜厚度下表现出新颖的磁性和输运性质，另一个系统表现出铁电性质和潜在的二维电子气的存在。结合原位扫描电子显微镜和第一性原理密度泛函理论(DFT)的计算，结合薄膜和纳米粒子的合成。该项目包括两个任务：1)利用一种新的方法测量纳米分辨率的热膨胀系数，并探索该方法是否可以用于量化衬底/薄膜界面的热膨胀和传输。这种方法是基于测量作为温度函数的等离子体激元峰位移，并结合材料介电响应的从头算模拟。2)了解钙钛矿氧化物薄膜的磁性和电输运性质。研究了超薄氧化钴外延薄膜的输运反常现象，并与不同衬底上生长的薄膜进行了比较。研究了界面电荷对化合物半导体衬底上钛氧化物电子结构和铁电极化的影响。通过对本科生和研究生进行最先进的原位扫描、透射、电子显微镜和理论材料物理方面的培训，将研究和教育整合在一起，这是该项目的一个组成部分。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: Transition metal ceramics exhibit a wide range of properties and functionalities, making them the ideal materials for many next generation electronic devices and sensors. However, the response of many transition metal ceramics to external stimuli, such as heat or electro-magnetic fields remains unknown. This is especially true when the size of device structures is approaching the nanometer scale and the response of the material differs from that observed in the bulk. In this project, a novel approach is explored for measuring, at the nanometer scale, the response of transition metal ceramics to changes in temperature or applied electric or magnetic fields. The combined experimental/theoretical approach is then used to quantify and control the magnetic, electronic and thermal transport properties at interfaces in nanoscale transition metal ceramic materials. The project's research activities center around education and training of science and engineering undergraduate and graduate students. Recruitment and training focuses on the next generation of researchers, in particular involving students from underrepresented groups and minorities through the National Name Exchange program and partnership with local high schools. The participation of undergraduate students in active research projects is fostered through the PI's Journal of Undergraduate Research at the University of Illinois at Chicago. Graduates typically find employment in academia, National Laboratories or industry, including semiconductor companies. TECHNICAL DETAILS: The objectives of this research project are to develop a fundamental understanding of the atomic-scale mechanisms that govern the electronic, magnetic and thermal properties of transition metal perovskite oxide hetero-structures. Two transition ceramic systems are studied, one exhibiting novel magnetic and transport properties below a specific film thickness and the other showing ferroelectric properties and the potential existence of a 2-dimensional electron gas. A combination of in-situ scanning transmission electron microscopy and first-principles density functional theory (DFT) calculations is used together with thin-film and nano-particle synthesis. The project consists of two tasks: 1) Utilizing a novel approach towards measuring the thermal expansion coefficient with nanometer resolution and exploring whether this approach can be utilized to quantify the thermal expansion and transport across substrate/film interfaces. This approach is based on measuring the plasmon peak shift as a function of temperature combined with ab-initio modeling of the materials' dielectric response. 2) Understanding the magnetic and electric transport properties of perovskite oxide thin films. The transport anomalies in ultra-thin cobalt-oxide epitaxial films are examined and compared to films grown on different substrates. The effects of interfacial charges on the electronic structure and ferroelectric polarization of Ti-oxides on compound semiconductor substrates are examined. The integration of research and education through the training of undergraduate and graduate students in state-of-the-art in-situ scanning transmission electron microscopy and theoretical materials physics is an integral feature of this project.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.