Oxide Thin Film Synthesis
Thin film synthesis serves as the foundation of the group’s research activities. We use molecular beam epitaxy to deposit films and superlattices with nominal unit cell precision. We are currently focused on ABO3 perovskite oxides with iron, manganese, and nickel on the B-site. In addition, we synthesize quadruple perovskites (AB’3B4O12) and brownmillerites (A2B2O5).
The ability to control the position, occupation and composition of the anion site has emerged within the last few years as one of the most promising means to engineer physical properties in epitaxial oxide heterostructures. We are working on developing scattering-based techniques to measure octahedral rotations, understand their dependence on strain and interfacial coupling, and engineer electronic, optical and ferroic properties through the control of the local octahedral bonding environment. We are exploring how reversible changes in oxygen content can be used to induce dramatic changes to electronic and optical properties. We are also working on synthetic routes to stabilize mixed-anion perovskite films via post-growth topotactic processes. For example, we have recently realized oxyfluoride ferrite and nickelate films through reactions with fluorine containing polymers.
Electronic Phase Transitions
Complex oxides have been identified as candidate materials for future electronic devices due to their ability to exhibit electronic and ferroic properties that are lacking in conventional semiconductors. An electronic phase transition, in which a material exhibits an abrupt and reversible change from a high to low resistance state, is an example of one such functionality. Our group is working to better understand and control electronic phase transitions in La1-xSrxFeO3and CaMn7O12 heterostructures and devices. These efforts include electronic transport measurements, synchrotron-based characterization of nominally charge ordered states, and device fabrication and testing.
Engineering Static and Dynamic Optical Properties in Oxides
Many perovskite oxides are semiconducting with gaps throughout the visible spectrum, enabling potential applications in optoelectronics, solar energy conversion, or sensing. Our group is working to contribute to the scientific foundation for future oxide optical applications by addressing fundamental issues such as engineering optical absorption and maximizing photoexcited carrier lifetimes. Examples of these efforts include band gap engineering through A– and B-site substitution, fundamental studies of the origin of optical transitions, and exploring photoexcited carrier dynamics in collaboration with Prof. Jason Baxter’s group.
Magnetic Oxide Heterostructures
We explore fundamental aspects of magnetism in oxide heterostructures, with particular interest in how structural coupling and charge transfer at junctions can give rise to novel interfacial magnetic ordering. Understanding and manipulating interfacial magnetism is central to the development of magnetic devices for potential use in data storage. In our work, we make extensive use of synchrotron- and neutron-based scattering to provide elemental- and depth-resolved magnetic information in addition to conventional magnetometry.
This work is funded by the National Science Foundation (NSF-DMR-1151649, NSF-ECCS 1201957), and the Army Research Office (ARO W911NF-15-1-0133). We are also grateful to the Office of Naval Research and Petroleum Research Fund for previous research support.