Seizing the third dimension in correlated oxide thin films: cation-ordering strategies toward absolute atomic control

The scope of this work is a theoretical prediction of the effect of cation-ordering in the properties of correlated oxide thin films. The PI proposes to perform first-principles studies to achieve deterministic control of structural parameters in all 3 dimensions in such films. Engineering cation ordering – the atomic scale periodic arrangement of cations – in correlated oxide thin films (COTF) enables the design of new materials with superior functionalities. The goals of the proposed work are: (1) to demonstrate that cation ordering is a robust mechanism for controlling the out-of-plane c-lattice parameter and interatomic spacing in COTF with the Ruddlesden-Popper (RP) structure, and (2) to harness that mechanism to direct the electron-lattice interactions, creating new functional electronic materials with properties not present in compositionally identical bulk analogues. These goals will be accomplished computationally by using advanced density functional theory (DFT) techniques combined with group theoretical approaches. The plan is based on isolating the effects of A-site cation ordering and ionic size on the atomic displacement patterns and out-of-plane (z-direction) lattice relaxations of RP (A, A’) MnO4 thin films, where A and A’ are trivalent and divalent cations, respectively, under tensile and compressive biaxial (x y-plane) strain. 2.3 Interest The Space and Naval Warfare Systems Center Pacific in support of the Defense Advanced Research Projects Agency (DARPA) is involved with research and development of microelectronics, micro-electromechanical systems (MEMS), opto-electronics, photonics technology, and/or other areas which offer the potential for significant impact on the current technology and the national defense. We are jointly interested in developments resulting from leading edge experimental and/or theoretical research in the all of these areas and more. The public good anticipated from successful completion of this effort is the prediction of the properties of novel correlated oxide thin films wherein both in-plane and out-of-plane strain is controlled. This will have an impact in the development of new materials forming the basis for ultracompact devices with strong magneto-electric, magneto-optical and opto-electronic responses.