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

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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.