Spontaneous Ordering of Oxide-Oxide Epitaxial Vertically Aligned Nanocomposite Thin Films

The emerging field of self-assembled vertically aligned nanocomposite (VAN) thin films effectively enables strain, interface, and microstructure engineering as well as (multi)functional improvements in electric, magnetic, optical, and energy-related properties. Well-ordered or patterned microstructures not only empower VAN thin films with many new functionalities but also enable VAN thin films to be used in nanoscale devices. Comparative ordered devices formed via templating methods suffer from critical drawbacks of processing complexity and potential contamination. Therefore, VAN thin films with spontaneous ordering stand out and display many appealing features for next-generation technological devices, such as electronics, optoelectronics, ultrahigh-density memory systems, photonics, and 3D microbatteries. The spontaneous ordering described in this review contains ordered/patterned structures in both in-plane and out-of-plane directions. In particular, approaches to obtaining spontaneously ordered/patterned structures in-plane are systematically reviewed from both thermodynamic and kinetic perspectives. Out-of-plane ordering is also discussed in detail. In addition to reviewing the progress of VAN films with spontaneous ordering, this article also highlights some recent developments in spontaneous ordering approaches and proposes future directions.