Functional perovskite oxides are recognized for their stunningly rich physics and for their potential as next-generation electronic materials. Their properties include high Tc superconductivity, colossal magnetoresistance, record-high dielectric/ferroelectric/piezoelectric performances, multiferroic behavior, resistive switching behavior, giant thermoelectric and magnetocaloric effects, giant ionic conduction, and catalytic behavior. Due to their intrinsic chemical and crystal similarities, functional oxides can be stacked in multilayer heterostructures exhibiting an astonishing degree of epitaxial perfection. Such artificial systems not only allow one to combine in a single device the functionalities of their individual layers, but often reveal an even wider range of emergent novel properties that can be surprisingly different from those of the single building blocks. The goal of this issue of MRS Bulletin is to present the state of the art of oxide interfaces in inscience and technology. Here we provide an introduction to their properties, serving as a base for the following topical articles.

Novel electronic and magnetic phases are being observed at interfaces between insulating, non-magnetic oxide compounds, with the most notable example being the interface between SrTiO3 and LaAlO3. The basic properties of these interfaces will be discussed, as well as prospects for applications and possible future developments.

Quantum wells created from nanostructured transition metal oxides offer unique possibilities for creating and manipulating quantum states of matter, including novel superconductors, high Curie temperature magnets, controllable metal-insulator transitions, and new topological states. This article explores what is known and conjectured about confined electronic states in oxide quantum wells. Theoretical challenges are reviewed, along with issues arising in the creation of oxide quantum wells. Examples from the current experimental state of the art are summarized, open questions are discussed, and prospects for the future are outlined. The key roles of epitaxial strain and proximity effects are emphasized.

Oxide thin films and interfaces exhibit a variety of novel magnetic phenomena, which are unknown in well-crystallized bulk material. The origin of these phenomena must be sought in the changes in electronic structure due to broken symmetry, strain, and electronic or atomic reconstruction, including oxygen and cation defects. These effects are first discussed in magnetically ordered 3d oxide thin films and heterostructures, wherein a metal-insulator transition up on changing film thickness may influence the magnetism. In heterojunctions, the interface magnetic order can be modified, and exchange bias may appear. A high-temperature ferromagnetic-like response in dilute and undoped oxide films appears to be associated with defects near the substrate interface. A two-dimensional electron gas emerges at interfaces of a polar oxide and SrTiO3, where electronic reconstruction brings electrons into the bottom of the Ti d band; ferromagnetism then emerges as a result of localized or delocalized d states in the presence of atomic defects.

Artificially layered superlattices of oxide materials have been intensely investigated for some time, but continue to reveal new potential as a route to advanced functional materials. As well as considering electrostatics and strain, a more complete picture of the interfaces in these systems also needs to incorporate the possibility of additional structural distortions, electronic redistributions, and complex polarization domain structures. Here we focus on superlattices composed of two perovskite oxide materials, where one is a ferroelectric, and discuss the important interactions between the component materials that determine the behavior of the new artificial material. We discuss interfaces both with and without electronic screening. The first class of interface contains technologically relevant ultrathin ferroelectric capacitors and the more recently studied ferroelectric-metal superlattices. In these systems, the influence of the ferroelectric polarization decreases rapidly with distance from the interface. By contrast, in systems where the materials adjacent to the ferroelectric layers are dielectrics, the polarization of the ferroelectric layer influences the properties of the adjacent layers over a much longer distance, setting the stage for fascinating competition between the properties of the combined materials.

The new field of nano-ionics is expected to yield large improvements in the performance of oxide-based energy generation and storage devices based on exploiting size effects in ion conducting materials. The search for novel materials with enhanced ionic conductivity for application in energy devices has uncovered an exciting new facet of oxide interfaces. With judicious choice of the constituent materials, oxide heterostructures can exhibit enhanced ion mobility compared to the bulk counterparts. Here we review recent experimental and theoretical progress on enhancement of oxide-ion conductivity arising in oxide ultrathin layers and at their interfaces, and describe the different scenarios, space-charge effects, epitaxial strain, and atomic reconstruction at the interface, proposed to account for the observed conductivity enhancement.

A review is presented of the development of in situ high-resolution transmission electron microscopy (HRTEM) and its application to directly study the atomic behavior in thermally activated material reactions. Not only are the atomic re-arrangements continuously recorded, but kinetic measurements can be made at controlled elevated temperatures. Examples include work on the atomic motion on CdTe surface ledges, solid phase epitaxial regrowth of silicon, crystallization of amorphous silicon and of amorphous tantalum oxide thin films, solid-state amorphization at metal-silicon interfaces, metal-induced crystallization of amorphous silicon, germanium and carbon, phase separation and crystallization in hafnium silicate thin films, and “spiking” across thin gate oxides separating nickel silicide from a monocrystalline silicon substrate. The future prospects of in situ HRTEM are discussed, and the increasing breadth of application of this approach is recognized, especially in light of the advances in HRTEM capabilities.