Research Update: Fast and tunable nanoionics in vertically aligned nanostructured films

Abstract

This review provides the design principles to develop new nanoionic applications using vertically aligned nanostructured (VAN) thin films, incorporating two phases which self-assemble in one film. Tunable nanoionics has attracted great attention for energy and device applications, such as ion batteries, solid oxide fuel cells, catalysts, memories, and neuromorphic devices. Among many proposed device architectures, VAN films have strong potential for nanoionic applications since they show enhanced ionic conductivity and tunability. Here, we will review the recent progress on state-of-the-art nanoionic applications, which have been realized by using VAN films. In many VAN systems made by the inclusion of an oxygen ionic insulator, it is found that ions flow through the vertical heterointerfaces. The observation is consistent with structural incompatibility at the vertical heteroepitaxial interfaces resulting in oxygen deficiency in one of the phases and hence to oxygen ion conducting pathways. In other VAN systems where one of the phases is an ionic conductor, ions flow much faster within the ionic conducting phase than within the corresponding plain film. The improved ionic conduction coincides with much improved crystallinity in the ionically conducting nanocolumnar phase, induced by use of the VAN structure. Furthermore, for both cases Joule heating effects induced by localized ionic current flow also play a role for enhanced ionic conductivity. Nanocolumn stoichiometry and strain are other important parameters for tuning ionic conductivity in VAN films. Finally, double-layered VAN film architectures are discussed from the perspective of stabilizing VAN structures which would be less stable and hence less perfect when grown on standard substrates.

Metal Oxide Nanocomposites: A Perspective from Strain, Defect, and Interface

“…In a recent review article, Lee et al discussed recent ionotronic progress using a device structure based on VANs . Similar to YSZ:GDC system, the enhancement in vertical ionic conductivity has been also demonstrated in other VAN systems .…”

Atomic‐Scale Study of Metal–Oxide Interfaces and Magnetoelastic Coupling in Self‐Assembled Epitaxial Vertically Aligned Magnetic Nanocomposites

“…Vertically aligned nanocomposites (VANs) form a class of hybrid thin films, that has attracted significant interest since the discovery of self‐assembled vertical nanopillar microstructures in the La 0.67 Ca 0.33 MnO 3 :MgO system . Possible applications for these heterostructured materials have been proposed in the fields of nanomagnetism, spintronics, multiferroics, catalysis, and ionic conductors . The versatility of VANs results from their peculiar nanoarchitecture: they are composed of an array of nanopillars vertically embedded and epitaxially coupled to a surrounding single crystal matrix, which is depicted schematically in Figure for the case of the particular combination of materials studied in this work.…”

Role of Interlayer in 3D Vertically Aligned Nanocomposite Frameworks with Tunable Magnetotransport Properties

“…[ 6–12 ] Among all the two‐phase nanocomposite designs, vertically aligned nanocomposites (VANs) offer high‐density vertically aligned interfaces, strain coupling, and strong anisotropic physical properties and have thus attracted great attention. [ 3,13–20 ]…”