A Thin Film Approach to Engineering Functionality into Oxides

Abstract

The broad spectrum of electronic and optical properties exhibited by oxides offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired. Here we describe the use of reactive molecular‐beam epitaxy and pulsed‐laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time. Owing to the dependence of properties on direction, it is often optimal to grow functional oxides in particular directions to maximize their properties for a specific application. But these thin film techniques offer more than orientation control; customization of the film structure down to the atomic‐layer level is possible. Numerous examples of the controlled epitaxial growth of oxides with perovskite and perovskite‐related structures, including superlattices and metastable phases, are shown. In addition to integrating functional oxides with conventional semiconductors, standard semiconductor practices involving epitaxial strain, confined thickness, and modulation doping can also be applied to oxide thin films. Results of fundamental scientific importance as well as results revealing the tremendous potential of utilizing functional oxide thin films to create devices with enhanced performance are described.

Massive band gap variation in layered oxides through cation ordering

“…To realize our theoretical predictions, we suggest thin film growth methods like oxide molecular beam epitaxy (MBE) to be well-suited for experimentally achieving the proposed cation ordering variants [37][38][39] . Recently, A-site cation ordered LaSrNiO 4 and LaSrMnO 4 RP oxides were experimentally grown with precise atomic control using oxide-MBE techniques 40,41 .…”

Film size-dependent voltage-modulated magnetism in multiferroic heterostructures

“…Such isotropic strain ε 0 can be obtained either from the intrinsic lattice and/or thermal mismatch between a film and a substrate [84] or from external piezoelectric actuation [85]. As seen, the CFO film displays a uniform single-domain structure at such a small lateral size (see the inset of figure 4a).…”

Competing interactions in ferromagnetic/antiferromagnetic perovskite superlattices

“…[1] Specifically, the class of perovskite oxides (ABO3) has garnered much attention due to the possibility of creating epitaxial superlattices composed of stacks of alternating sublayers, each with their own order parameter, formed with atomic-scale control, and designed to exploit interactions at interfaces. [2][3][4][5] A few remarkable examples have shown the appearance of an additional order parameter (i.e. superconductivity or ferromagnetism) at interfaces despite the fact that it does not exist in the constituent materials.…”