Spontaneous orientation-tuning driven by the strain variation in self-assembled ZnO-SrRuO₃ heteroepitaxy

Heteroepitaxial ZnO and SrRuO₃ were grown on SrTiO₃ (111) substrates and formed a self-assembled wurtzite-perovskite nanostructure. Spontaneous orientation-tuning of the SrRuO₃ pillars was observed, with the growth direction changing from [111]_SRO to [011]_SRO as the film thickness increased, which is attributed to a misfit strain transition from the biaxial strain imposed by the SrTiO₃ substrate to the vertical strain provided by the ZnO matrix. The [011]-SrRuO₃ and [0001]-ZnO combination presents a favorable matching in the nanocomposite films, resulting in higher charge carrier mobility. This vertically integrated configuration and regulation on the crystallographic orientations are expected to be employed in designing multi-functional nanocomposite systems for applications in electronic devices.