Growth-induced non-stoichiometry in complex oxide systems

Oxides;Pulsed Laser Deposition;Thin Films;Interfacial Phenomena

Breckenfeld, Eric

关键词: Oxides;    Pulsed Laser Deposition;    Thin Films;    Interfacial Phenomena;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/49584/Eric_Breckenfeld.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Complex perovskite oxides have been studied extensively over the past few decades due to their wide range of functional properties and relative ease of epitaxial synthesis. These two factors have allowed such oxide systems to see a multitude of applications including sensors, memory, thermal management, and energy harvesting. The ability to access so many different functionalities is owed largely to the chemical diversity available to the perovskite unit cell, opening the door for metal-insulator-transitions, ferroelectricity, and superconductivity, to name a few. However, the same chemical diversity that enables so many potential applications also opens the door for a myriad of chemistry-related defects. Separating out the relative contributions of such extrinsic (or defect-driven) effects from the intrinsic material properties is crucial to enabling the use of these materials in high-performance, next-generation devices. In this work, we examine several model systems in order to explore the relationship between the pulsed laser deposition growth process, the film chemistry, and the subsequent effects on the defect landscape and film properties. We show that small changes to the laser fluence can have a marked impact on the chemical composition of the film, leading to cation stoichiometry deviations as large as 10% in SrTiO3, LaAlO3, and NdNiO3 systems. We demonstrate that such chemical deviations can lead to significant changes in the bulk thermal and dielectric properties of SrTiO3 and LaAlO3 films. We have also investigated the interface between SrTiO3 and LaAlO3, which has been studied extensively over the past 8 years due to the supposed presence of a 2-dimensional electron gas (2DEG). Our results indicate that the presence of cation defects in the LaAlO3 has a profound impact on the electronic properties of the 2DEG interface. Finally, we have similarly shown that cation non-stoichiometry can cause the metal-insulator-transition material NdNiO3 to behave more like a degenerately doped semiconductor, suppressing both the high-temperature metallic and low-temperature insulating states.