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The surface of SrTiO3 (001) is considered to be weakly polar, and in this work, we study the validity of this notion. It exhibits a surface structural distortion, quantified here using low energy electron diffraction at room temperature. Structural analysis shows the presence of strong surface rumpling in the TiO2 terminated surface with the oxygen atoms moving outward and Ti atoms moving inward. Density functional calculations confirm the measured rumpling, and experimental data show the distortion is localized at the surface. Angle-dependent core-level X-ray photoemission spectroscopy (XPS) shows that the surface rumpling strongly impacts the electronic structure of the surface. This observation is reinforced by density functional theory, which demonstrates that the valence state of Ti at the surface is reduced while O is enhanced, where we found the Ti–O bonds are more covalent near the surface. Our results show that surface rumpling is accompanied by a change in the bond hybridization of Ti–O at the surface. Changes in the XPS satellite structures at the surface are consistent with this picture of the change in bonding, indicating that the (001) surface of SrTiO3 is not polar and charge rearrangement is a consequence of surface rumpling.

Lattice structure can dictate electronic and magnetic properties of a material. Especially, reconstruction at a surface or heterointerface can create properties that are fundamentally different from those of the corresponding bulk material. We have investigated the lattice structure on the surface and in the thin films of epitaxial SrRuO3 with the film thickness up to 22 pseudo-cubic unit cells (u.c.), using the combination of surface sensitive low energy electron diffraction and bulk sensitive scanning transmission electron microscopy. Our analysis indicates that, in contrast to many perovskite oxides, the RuO6 tilt and rotational distortions appear even in single unit cell SrRuO3 thin films on cubic SrTiO3, while the full relaxation to the bulk-like orthorhombic structure takes 3-4 u.c. from the interface for thicker films. Yet the TiO6 octahedra of the substrate near the interface with SrRuO3 films show no sign of distortion, unlike those near the interface with CaRuO3 films. Two orthogonal in-plane rotated structural domains are identified. These structural distortions are essential for the nature of the thickness dependent transport and magnetism in ultrathin films.

One major challenge for engineering functional nanocomposites is how to tune the geometry structure and control the chemical composition. We demonstrate here that columnar nanocomposite films can be grown by using alternate deposition of La2/3Sr1/3MnO3 and V2O3 on LaAlO3 (111). A solid state reaction, rather than simple spinodal decomposition, dictates the nanocomposite structure, chemical composition, and functionality. By controlling the deposition time ratio of the two compounds, the physical properties of the composite films can be tuned, thus providing a flexible way to tailor nanocomposites for advanced functionality.

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