Asymmetric self-organization from a symmetric film by phase separation

Self-organization realizes various nanostructures to control material properties such as superconducting vortex pinning and thermal conductivity. However, the self-organization of nucleation and growth is constrained by the growth geometric symmetry. To realize highly controlled three-dimensional nanostructures by self-organization, nanostructure formation that breaks the growth geometric symmetry thermodynamically and kinetically, such as tilted or in-plane aligned nanostructures, is a challenging issue. A vertically aligned nano-checkerboard is typically formed from ZnMnGaO₄ with the twin domain vertically aligned by the stress from the MgO substrate. The change in the template structure is promising to form a different type of nanostructure. The cubic ZnMnGaO₄/MgO films were annealed to form nanoscale tetragonal domains in the tilted direction from the surface, which is determined by lattice mismatch, lattice symmetry, and atomic bonding. On the other hand, as a result of free deformation, in-plane aligned twin domains were formed on the SrTiO₃ substrate with a thin MgO buffer layer, which does not induce stress in the ZnMnGaO₄ film. By annealing the ZnMnGaO₄/MgO/SrTiO₃ film, the nano-checkerboard with a size of ∼10 nm and a length of ∼200 nm is elongated to the in-plane [100] or [001] direction. This study demonstrates the possibility of fabricating a nanostructure that breaks the growth geometric symmetry, which is not achieved by the previous self-organization. The phase separation with controlled template opens more complicated three-dimensional structures by self-organization.