Crystallographic Rotation during Solid-Phase Epitaxy of SrTiO3 from Nanoscale Seed Crystals

The crystallization of amorphous complex oxide layers from isolated seed crystals presents an opportunity to remove geometric constraints posed by thin-film epitaxial growth methods employing single-crystal substrates. The crystallization processes initiated by a distribution of isolated nanoscale seeds occur in a state of mechanical stress that is different from planar thin-film epitaxy. The effects of this stress were probed in the crystallization of the model perovskite oxide SrTiO3 nucleated by isolated nanoscale SrTiO3 seeds. Synchrotron nanobeam scattering and diffraction were used to probe the spatial distribution of crystalline and amorphous SrTiO3. Contributions to the diffraction patterns from these components were identified using non-negative matrix factorization. Individual SrTiO3 crystallites exhibit a lattice rotation resulting from the density difference between amorphous and crystalline SrTiO3. Stress at the crystal-amorphous interface advancing from the seeds produces a rotation of the crystal lattice at a rate of tens of degrees per micron of crystallization in the plane of the film. The rate of the lattice rotation provides insight into the crystallization mechanism. The lattice rotation indicates that nanoscale morphological control during solid-phase epitaxial crystallization from nanocrystal seeds can be achieved by manipulating the interface stress between the amorphous and crystalline phases to control dislocation dynamics.