Complex metal oxides, which show a variety of functional properties such as ferromagnetism, ferroelectricity, multi-ferroelectricity, superconductivity, and ionic conduction, have attracted much attention in the past decades. These exotic physical properties arise from a complex hierarchy of competing interactions among spin, charge, orbital, and lattice degrees of freedom. The development of advanced characterization techniques such as electron microscopy, neutron scattering, synchrotron scattering and imaging, spectroscopy at high magnetic fields, and others has enabled us to study the interactions among these degrees of freedom coupled with strain, defect, and interface Vertically aligned nanocomposite thin films with ordered two phases, grown epitaxially on substrates, have attracted tremendous interest in the past decade. These unique nanostructured composite thin films with large vertical interfacial area, controllable vertical lattice strain, and defects provide an intriguing playground, allowing for the manipulation of a variety of functional properties of the materials via the interplay among strain, defect, and interface. This field has evolved from basic growth and characterization to functionality tuning as well as potential applications in energy conversion and information technology. Here, the remarkable progress achieved in vertically aligned nanocomposite thin films from a perspective of tuning functionalities through control of strain, defect, and interface is summarized. Thin FilmsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201803241. 12 11 12where c 11 and c 12 are elastic moduli of the film material. Epitaxial strain gradually changes with film thickness in perovskite manganites. Figure 3 shows reciprocal space mapping or RSM (103) of La 0.7 Ca 0.3 MnO 3 (LCMO) films on STO (001) substrates. It captures the gradual strain relaxation process with increasing film thickness in manganite thin films. When the film is very thin, the interface is coherent with

The tuning of functional properties in thick oxide films via nanoscaffolds induced large vertical lattice strain.

Black TiO2 nanoparticles with a crystalline core and amorphous-shell structure exhibit superior optoelectronic properties in comparison with pristine TiO2. The fundamental mechanisms underlying these enhancements, however, remain unclear, largely due to the inherent complexities and limitations of powder materials. Here, we fabricate TiO2 homojunction films consisting of an oxygen-deficient amorphous layer on top of a highly crystalline layer, to simulate the structural/functional configuration of black TiO2 nanoparticles. Metallic conduction is achieved at the crystalline-amorphous homointerface via electronic interface reconstruction, which we show to be the main reason for the enhanced electron transport of black TiO2. This work not only achieves an unprecedented understanding of black TiO2 but also provides a new perspective for investigating carrier generation and transport behavior at oxide interfaces, which are of tremendous fundamental and technological interest.