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Germanium is a small-gap semiconductor that efficiently absorbs visible light, resulting in photoexcited electrons predicted to be sufficiently energetic to reduce H 2 O for H 2 gas evolution. In order to protect the surface from corrosion and prevent surface charge recombination in contact with aqueous pH 7 electrolyte, we grew epitaxial SrTiO 3 layers of different thicknesses on p-Ge (001) surfaces. Four-nanometer SrTiO 3 allows photogenerated electrons to reach the surface and evolve H 2 gas, while 13 nm SrTiO 3 blocks these electrons. Ambient pressure x-ray photoelectron spectroscopy indicates that the surface readily dissociates H 2 O to form OH species, which may impact surface band bending.

Current piezoelectric sensors and actuators are limited to operating temperatures less than ~200 °C due to the low Curie temperature of the piezoelectric material. Strengthening the piezoelectric coupling of high-temperature piezoelectric materials, such as La2Ti2O7 (LTO), would allow sensors to operate across a broad temperature range. The crystalline orientation and piezoelectric coupling direction of LTO thin films can be controlled by epitaxial matching to SrTiO3(001), SrTiO3(110), and rutile TiO2(110) substrates via pulsed laser deposition. The structure and phase purity of the films are investigated by x-ray diffraction and scanning transmission electron microscopy. Piezoresponse force microscopy is used to measure the in-plane and out-of-plane piezoelectric coupling in the films. The strength of the out-of-plane piezoelectric coupling can be increased when the piezoelectric direction is rotated partially out-of-plane via epitaxy. The strongest out-of-plane coupling is observed for LTO/STO(001). Deposition on TiO2(110) results in epitaxial La2/3TiO3, an orthorhombic perovskite of interest as a microwave dielectric material and an ion conductor. La2/3TiO3 can be difficult to stabilize in bulk form, and epitaxial stabilization on TiO2(110) is a promising route to realize La2/3TiO3 for both fundamental studies and device applications. Overall, these results confirm that control of the crystalline orientation of epitaxial LTO-based materials can govern the resulting functional properties.

Thin-film oxide heterostructures show great potential for use in spintronic memories, where electronic charge and spin are coupled to transport information. Here we use a La0.7Sr0.3MnO3 (LSMO)/PbZr0.2Ti0.8O3 (PZT) model system to explore how local variations in electronic and magnetic phases mediate this coupling. We present direct, local measurements of valence, ferroelectric polarization and magnetization, from which we map the phases at the LSMO/PZT interface. We combine these experimental results with electronic structure calculations to elucidate the microscopic interactions governing the interfacial response of this system. We observe a magnetic asymmetry at the LSMO/PZT interface that depends on the local PZT polarization and gives rise to gradients in local magnetic moments; this is associated with a metal-insulator transition at the interface, which results in significantly different charge-transfer screening lengths. This study establishes a framework to understand the fundamental asymmetries of magnetoelectric coupling in oxide heterostructures.