Epitaxial formation of rotating lattice single crystals from amorphous complex oxides

Crystallization from an amorphous precursor via solid phase epitaxy (SPE) enables a wide range of opportunities in the formation of oxide electronic materials in new geometries. The large density changes induce stress at the amorphous/crystal interface and can lead to the formation of structural defects. The problem is particularly challenging in complex nanoscale geometries because of the inherent three-dimensional variation of the stress field. The crystallization of SrTiO₃ (STO) was studied by lithographically defining the initial sites of crystallization on a Si₃N₄ covered STO 001 single-crystal substrate. Amorphous STO was deposited on the patterned substrates at room temperature and crystallized by heating to 450 °C. The crystallization of STO proceeded by laterally propagating the amorphous/crystalline interface across the Si₃N₄ covered surface. Synchrotron x-ray nanobeam diffraction imaging revealed that the stress leads to a continuous lattice rotation of several degrees per micron of crystallization distance. The rotation is consistent with a mechanism in which defects form at the crystal/amorphous interface. The growth of a rotating lattice single crystal can in principle be controlled by varying the amorphous-crystalline density difference.