The combination of epitaxial strain and defect engineering facilitates the tuning of the transition temperature of BaTiO3 to >800 °C. Advances in thin-film deposition enable the utilization of both the electric and elastic dipoles of defects to extend the epitaxial strain to new levels, inducing unprecedented functionality and temperature stability in ferroelectrics.

We present the temperature-and thickness-dependent structural and morphological evolution of strain induced transformations in highly-strained epitaxial BiFeO 3 films deposited on LaAlO 3 (001) substrates. Using high-resolution X-ray diffraction and temperature-dependent scanningprobe-based studies we observe a complex temperature-and thickness-dependent evolution of phases in this system. A thickness-dependent transformation from a single monoclinically distorted tetragonal-like phase to a complex mixed-phase structure in films with thicknesses up to ~200 nm is the consequence of a strain-induced spinodal instability in the BiFeO 3 /LaAlO 3 system. Additionally, a breakdown of this strain-stabilized metastable mixed-phase structure to non-epitaxial microcrystals of the parent rhombohedral structure of BiFeO 3 is observed to occur at a critical thickness of ~300 nm. We further propose a mechanism for this abrupt breakdown that provides insight into the competing nature of the phases in this system.

Correlated electron oxides prove a diverse landscape of exotic materials' phenomena and properties. One example of such a correlated oxide material is strontium ruthenate (SrRuO3) which is known to be a metallic itinerant ferromagnet and for its widespread utility as a conducting electrode in oxide heterostructures. We observe that the complex electronic structure of SrRuO3 is also responsible for unexpected optical properties including high absorption across the visible spectrum (commensurate with a low band gap semiconductor) and remarkably low reflection compared to traditional metals. By coupling this material to a wide band gap semiconductor (TiO2) we demonstrate dramatically enhanced visible light absorption and large photocatalytic activities. The devices function by photo‐excited hot‐carrier injection from the SrRuO3 to the TiO2 and the effect is enhanced in thin films due to electronic structure changes. This observation provides an exciting new approach to the challenge of designing visible‐light photosensitive materials.

The ability to control nanostructure shape can strongly affect the overall properties of that system. Here we report the ability to deterministically control nanostructure shape, surface facet orientation, and surface potentials of the oxide semiconductor Cu(2)O. Epitaxial Cu(2)O nanostructures with different shapes and geometries-from boxes to pyramids to huts-have been grown via pulsed laser deposition. By varying the adatom energy and flux per laser pulse we can tune the nature of the nanostructure geometry, the total density of features, the relative surface area to volume ratio, and can create polar, nonequilibrium surfaces. In addition to detailed structural analysis of the nanostructures, high-resolution Kelvin probe force microscopy has been used to systematically analyze the surface potential and electronic structure of the (100), (110), and (111) surfaces of Cu(2)O. These studies suggest that each surface, possessing a unique atomic structure, gives rise to different surface energy levels of conduction and valence bands and the formation of electronic surface junctions. The implication of these findings in terms of a range of applications is discussed.

n-n Schottky, n-n ohmic, and p-n Schottky heterojunctions based on TiO2 /correlated "metallic" oxide couples exhibit strong solar-light absorption driven by the unique electronic structure of the "metallic" oxides. Photovoltaic and photocatalytic responses are driven by hot electron injection from the "metallic" oxide into the TiO2 , enabling new modalities of operation for energy systems.