New epitaxy paradigm in epitaxial self-assembled oxide vertically aligned nanocomposite thin films

Self-assembled oxide-based vertically aligned nanocomposite (VAN) thin films have aroused tremendous research interest in the past decade. The interest arises from the range of unique nanostructured films which can form and the multifunctionality arising from these forms. Hence, a large number of oxide VAN systems have been demonstrated and explored for enhancing specific physical properties, such as strain-enhanced ferroelectricity, tunable magnetotransport, and novel electrical/ionic transport properties. The epitaxial growth of the nanocomposite thin films and the coupling at the heterogeneous interfaces are critical considerations for future device applications. In this review, the advantages of strain coupling along vertical interfaces and film-substrate interfaces in nanocomposite films over conventional single phase films are discussed. Specifically, a unique strain compensation model enabling the epitaxial growth of two-phase nanocomposites having large lattice mismatch with substrates is proposed. Out-of-plane strain coupling between the two phases is also discussed in terms of designing strain states for desired functionalities.